annual report 2000 · koskenvuori, mika, student research assistant 451 2184...

Helsinki University of Technology Department of Electrical and

Communications Engineering

Metrology Research Institute Report 18/2001

Espoo 2001

ANNUAL REPORT 2000

Helsinki University of Technology

Metrology Research Institute Report 18/2001

Espoo 2001

ANNUAL REPORT 2000Editor Petri Kärhä

Helsinki University of TechnologyDepartment of Electrical and Communications EngineeringMetrology Research Institute

Teknillinen korkeakouluSähkö- ja tietoliikennetekniikan osastoMittaustekniikan laboratorio

Distribution:

Helsinki University of Technology

Metrology Research Institute

P.O. Box 3000

FIN-02015 HUT

Finland

Tel. +358-9-451 1

Fax. +358-9-451 2222

E-mail: [email protected]

© Metrology Research Institute

ISSN 1237-3281

Picaset Oy

Helsinki 2001

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CONTENTS

1 INTRODUCTION............................................................................... 32 PERSONNEL ...................................................................................... 53 TEACHING ....................................................................................... 10

3.1 Courses ................................................................................................103.2 Degrees ................................................................................................11

3.2.1 Doctor of Science (Technology), D.Sc. (Tech.) 113.2.2 Master of Science (Technology), M.Sc. (Tech.) 11

4 NATIONAL STANDARDS LABORATORY................................ 124.1 Radiometry ..........................................................................................124.2 Photometry...........................................................................................144.3 Spectrophotometry...............................................................................144.4 Wavelength..........................................................................................15

5 RESEARCH PROJECTS................................................................. 165.1 Optical Radiation Measurements ........................................................16

5.1.1 Improving the accuracy of UV radiation measurement 165.1.2 A portable field calibrator for solar UV measurements 175.1.3 Comparison measurements of spectral irradiance 185.1.4 Absolute measurement method for luminous flux 195.1.5 Relative scale of spectral diffuse reflectance 215.1.6 Development of a national standard for fibre optic power 225.1.7 UV-laser for radiometric characterisations of detectors 24

5.2 Length Metrology................................................................................265.2.1 Iodine-stabilised He-Ne lasers 265.2.2 Iodine-stabilised diode lasers 265.2.3 Iodine-stabilised Nd:YAG lasers 27

5.3 Fibre-Optic Measurements ..................................................................295.3.1 Characterisation of group-delay ripple in chirped fibre

Bragg gratings 295.3.2 Fibre laser 305.3.3 Effect of optical filtering on pulses generated with a

gain-switched DFB-laser 315.3.4 Nonlinear crosstalk in a WDM network transmitting

digital television channels 325.3.5 Wavelength monitoring of DWDM systems using a

temperature-controlled Fabry-Perot filter 335.4 Microtechnologies ...............................................................................35

5.4.1 Micromechanical resonators for RF-applications 355.4.2 Finite element modelling of microsystems 365.4.3 High-Q micromechanical silicon oscillators 37

5.5 Applied Quantum Optics .....................................................................395.5.1 Installation of the Ti:Sapphire laser system 39

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5.5.2 Microtrap for neutral atoms 405.5.3 Coupling of coherent fields in second harmonic generation 415.5.4 Digital laser frequency stabilisation 425.5.5 Coherent population trapping in 85Rb 435.5.6 All-optical 3-GHz frequency standard based on dark

states of 85Rb 446 INTERNATIONAL CO-OPERATION.......................................... 46

6.1 International Comparison Measurements............................................466.2 Thematic Networks .............................................................................47

6.2.1 Thematic network for ultraviolet measurements 476.2.2 Fibre Optics Technology Network 48

6.3 Conferences and Meetings ..................................................................496.4 Visits by the Laboratory Personnel......................................................516.5 Research Work Abroad .......................................................................516.6 Guest Researchers ...............................................................................526.7 Visits to the Laboratory .......................................................................52

7 PUBLICATIONS .............................................................................. 537.1 Articles in International Journals.........................................................537.2 International Conference Proceedings.................................................547.3 National Conference Proceedings .......................................................577.4 Other Publications ...............................................................................57

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1 INTRODUCTION

The research activities in the Metrology Research Institute cover a broad rangefrom microsystems to fibre optics or from quantum optics to applied metrology.Year 2000 was very successful for the Institute and the number of personnel in-creased rapidly. Two major scientific positions were established in the Institute:Hanne Ludvigsen received the position of the Academy Research Fellow inAugust 2000 and Ilkka Tittonen was appointed as Professor in December 2000.

A considerable teaching task of the Metrology Research Institute is involved inthe course Fundamentals of Measurements, which is offered to all second yearstudents of the Department. The Institute is active also in post-graduate educa-tion and is partner in several National Graduate Schools. Eight master’s degreesand one doctoral degree were completed in 2000.

An exceptionally large number of international comparison measurements, alto-gether eleven, were carried out last year by the Metrology Research Institute.One of the main research efforts of the Institute during the recent years has beendevelopment of characterised filter radiometers for absolute measurement ofoptical radiation quantities. The comparison measurements have clearly indi-cated that the developed methods are very competitive and meet the high de-mands for the measurement uncertainty of spectral irradiance in the visible andultraviolet wavelength region.

For optical communication systems, a tunable micro-filter was developed to im-prove and monitor the transmitter performance. This work was presented in theOptical Fiber Communications Conference (OFC 2000). It is remarkable thatthe presentation is the first Finnish oral contribution in this demanding series ofconferences.

A new Ti:Sapphire laser system was installed in 2000. With its high outputpower and wavelength tunability, this laser facility will offer the possibility forexciting applications in quantum optics and basic metrology.

The Metrology Research Institute is an active participant within EU ResearchProgrammes. We co-ordinate the Thematic Network for Ultraviolet Measure-ments with about fifty participants from all over the Europe. The EU fundedpart of this project was successfully completed in November 2000. Other EUprojects where the Institute plays a significant role are Fibre Optic Thematic

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Network (FOToN) and an R&D project on ultraviolet radiation measurements.We take part in international activities within the framework of EUROMET,CCPR and COST. It should be noted that during the past year collaborationwith National Metrology Institutes outside Europe has also developed consid-erably.

Erkki Ikonen

Personnel of the Institute visiting Kungliga Tekniska Högskolan in Sweden.

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2 PERSONNEL

Helsinki University of TechnologyDepartment of Electrical and Communications EngineeringMetrology Research Institute (Mittaustekniikan laboratorio)P.O.Box 3000, FIN-02015 HUT, Finland

Visiting address: Otakaari 5 A, Espoo (Otaniemi) Finland

Switchboard +358 9 451 1Telefax +358 9 451 2222http://www.hut.fi/HUT/Measurement/

In 2000, the total number of employees working at the Metrology Research In-stitute was 43.

Telephone E-mail

Wallin, PekkaProfessor, Head of Department,Laboratory Director

451 22800400-445 699

[email protected]

Ikonen, Erkki, Dr.Tech.Professor, Head of the NationalStandards Laboratory

451 2283050-550 2283

[email protected]

Tittonen, Ilkka, Dr.Tech.Professor

451 2287040-543 7564

[email protected]

Ludvigsen, Hanne, DocentAcademy Research fellow

451 2282 [email protected]

Hänninen, JaanaAdministrative secretary

451 2288050-308 8403

[email protected]

Metsälä, SeppoLaboratory technician

451 2220

Ahola, Tero, studentResearch assistant


http://www.hut.fi/HUT/Measurement/

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Envall, Jouni, studentResearch assistant


Genty, Goëry, M.Sc.Research scientist


Hahtela, Ossi, studentResearch assistant


Heiliö, Miika, studentResearch assistant


Hovila, Jari, studentResearch assistant


Kasvi, Aki, studentResearch assistant(till June 19)


Kimmelma, Ossi, studentResearch assistant


Kokkonen, Pauli, studentResearch assistant(till May 31)


Koskenvuori, Mika, studentResearch assistant


Kujala, Markku, M.Sc.Research scientist(till August 31)


Kübarsepp, Toomas, Dr.Tech.Research scientist(till November 30)


Kärhä, Petri, Dr.Tech.Senior research scientist, Qual-ity manager

451 2289050-511 0307

[email protected]

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Lahti, Kristian, M.Sc.Project manager


Lamminmäki, Tuomas, M.Sc.Project manager


Laukkanen, Samuli, studentResearch assistant(till May 31)


Laukkanen, Tommi, M.Sc.Research scientist


Lindvall, Thomas, M.Sc.Research scientist


Manoocheri, Farshid, Dr.Tech.Research scientist, Head ofcalibration services


Marno, Sami, studentResearch assistant(till February 29)


Merimaa, Mikko, M.Sc.Research scientist


Nera, Kaisa, M.Sc.Research scientist


Nevas, Saulius, M.Sc.Research scientist


Niemi, Tapio, M.Sc.Research scientist, Student ad-visor


Noorma, Mart, studentResearch assistant


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Nyholm, Kaj, Dr.Tech.Senior research scientistCentre for Metrology and Ac-creditation


Rantakari, Pekka, studentResearch assistant


Ruokonen, Kaius, studentResearch assistant


Siivola, Markus, studentResearch assistant(till July 31)


Simonen, Tarmo, studentNetwork and PC Administrator


Toivanen, Pasi, Dr.Tech.Research scientist


Tuominen, Jesse, studentResearch assistant


Uusimaa, Maria, M.Sc.Research Scientist(till May 31)


Vahala, Eero, studentResearch assistant


Vainio, Markku, studentResearch assistant


Väänänen, Ossi, studentResearch assistant


Ylönen, Mari, studentResearch assistant


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Docents and lecturers:

Jokela Kari STUK, Radiation and NuclearSafety Authority

+358 9 759 881

Kalliomäki Kalevi University of Oulu +358 8 553 1011

Kaivola Matti Helsinki University of Technology +358 9 451 3151

Kauppinen Jyrki University of Turku +358 2 333 5670

Ludvigsen Hanne Helsinki University of Technology +358 9 451 2282

Ståhlberg Birger University of Helsinki +358 9 191 1

Franssila Sami Helsinki University of Technology +358 9 451 2332

Häkkinen Esa Helsinki Institute of Technology +358 9 310 8311

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3 TEACHING

3.1 Courses

The following courses were offered by the Metrology Research Institute (Mit-taustekniikan laboratorio) in 2000. Those marked by * are given biennially.

S-108.180 Electronic Measurements and Electromagnetic Compatibility2 credits (Petri Kärhä, Esa Häkkinen, Kristian Lahti)

S-108.181 Optics2 credits (Erkki Ikonen)

S-108.186 Microsystems technology4 credits (Ilkka Tittonen and Sami Franssila)

S-108.184 Computer-based Measurements2 credits (Kristian Lahti)

S-108.189 Project Work in Measurement Technology2-5 credits (Pekka Wallin)

S-108.191 Fundamentals of Measurements Y2 credits (Mikko Merimaa)

S-108.194 Electronic Instrumentation3 credits (Pekka Wallin)

S-108.195 Fundamentals of Measurements A2.5 credits (Mikko Merimaa)

S-108.198 Biological Effects and Measurements of Electromagnetic Fieldsand Optical Radiation2 credits (Kari Jokela)

S-108.199 Optical Communications and Optical Instruments5 credits (Erkki Ikonen)

S-108.901 Electrical Engineering Project1-5 credits (Pekka Wallin)

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S-108.903 Fourier Transforms in Measurements*4 credits (Jyrki Kauppinen)

S-108.911 Postgraduate Course in Measurement Technology7.5 credits (Ilkka Tittonen)

S-108.913 Postgraduate Course in Physics of Measurement*3 credits (Birger Ståhlberg)

S-108.914 Research Seminar on Measurement Science1 credit (Erkki Ikonen)

3.2 Degrees

3.2.1 Doctor of Science (Technology), D.Sc. (Tech.)

Pasi Toivanen: Detector based realisation of units of photometric and radiomet-ric quantities. Opponent: Dr. Yoshi Ohno, National Institute of Standards andTechnology (NIST)

3.2.2 Master of Science (Technology), M.Sc. (Tech.)

Ari Karjalainen: Micro-pattern detectors and readout electronics

Tiina-Liisa Forssell: Mode field diameter and cut-off wavelength in optical fi-bers with OTDR measurements

Maria Uusimaa: Temperature-tunable micro-filter for improving and monitor-ing transmitter performance in optical communications systems

Saulius Nevas: Facility for measurements of spectral diffuse reflectance

Thomas Lindvall: All-optical 3-GHz frequency standard based on rubidiumtransitions

Kaisa Nera: Fabrication and characterisation of a high-Q micromechanical sili-con oscillator

Tuukka Hytönen: Challenges in the implementation of the long haul wavelengthdivision multiplexing network

Tommi Laukkanen: Erbium-doped fiber-ring laser for telecommunication re-search

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4 NATIONAL STANDARDS LABORATORY

Metrology Research Institute is the Finnish national standards laboratory for themeasurements of optical quantities. The institute was appointed by the Centrefor Metrology and Accreditation (MIKES) in April 1996.

The institute gives official calibration certificates on the optical quantities listedin the following tables. During 2000, 41 calibration certificates were issued.The calibration services are mainly used by the Finnish industry and various re-search organisations. There are three accredited calibration laboratories in thefield of optical quantities.

The institute offers also other measurement services and consultation in thefield of measurement technology. Various memberships in international organi-sations ensure that the laboratory can also influence e.g. international standardi-sation so that it takes into account the national needs.

The Metrology Research Institute performs its calibration measurements undera quality system approved by MIKES. The quality system is based on standardsEN45001 and ISO Guide 25. Work is underway to update the system to meetnew requirements of ISO/IEC 17025.

4.1 Radiometry

Optical power meters and coherent radiation sources can be calibrated withvarious reference detectors and light sources of the laboratory. For the mostprecise optical power measurements, the cryogenic absolute radiometer is used.This device forms the basis for the traceability for most optical quantities. Theuse of the highest accuracy is rather limited in wavelength and signal level. Apractical transfer standard for optical power is a trap detector, which is directlytraceable to the cryogenic absolute radiometer. For higher power levels and ex-tended wavelength range, a pyroelectric detector is used. In addition to the cali-bration of meters, spatial responsivity and linearity of the detectors can be char-acterised.

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Quantity Range Wavelength range Uncertainty (k=2)

Optical power 0,1 – 0,5 mW 458,1, 465,9, 472,8,476,6, 488,1, 496,6,501,9, 514,7, 543,5,

633,0 nm

0,05 %

10 nW – 1 mW 250 – 380 nm 0,3 % – 0,8 %

10 nW – 1 mW 380 – 920 nm 0,1 % – 0,3 %

10 µW – 10 W 250 nm – 16 µm 2 % – 10 %

Spectroradiometric calibrations are based on a filter radiometer very similar tothe reference photometer used in photometric calibrations. This unique filter ra-diometer utilises 13 interference filters that cover a wide spectral range fromnear-UV to the near-IR. By measuring a lamp using all the filters, the spectralirradiance of the lamp may be obtained. Such characterised lamps can be usedas standards of spectral irradiance when calibrating spectroradiometers. Thespectrum may also be used to calculate the colour temperature and the colourco-ordinates of the lamp with high accuracy. When used in combination withthe integrating sphere source used in luminance measurements, spectral radi-ance may be calibrated.

Quantity Range Wavelengthrange

Uncertainty(k = 2)

290 – 380 nm 1,1 % – 2,8 %Spectral irradi-ance

10 pW mm-2 nm-1 –500 µW mm-2 nm-1

380 – 900 nm 0,6 % – 1,1 %

Spectral radi-ance

5 µW m-2 sr-1 nm-1 –6 W m-2 sr-1 nm-1

290 – 900 nm 1,0 %

Colour co-ordinates (x, y)

0 – 1 – 0,1 %

Colour tem-perature

1 000 – 3 500 K – 0,15 %

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4.2 Photometry

Photometric calibrations are based on a reference photometer, the calibration ofwhich is traceable to the cryogenic radiometer. Using the reference photometer,units for illuminance, luminous intensity, luminance and luminous flux may berealised. Most photometric calibrations are performed on a 4,5-m long opticalbench enclosed in a light-tight enclosure. Stable photometric lamps and an inte-grating sphere source are used as light sources. Luminous flux measurementsare done with a 1,65-m integrating sphere.

Quantity Range Uncertainty (k = 2)

Luminous intensity 10 – 10 000 cd 0,3 %

Illuminance 10 – 200 lx 0,2 %

200 – 2 000 lx 0,3 % – 0,5 %

Luminance 5 – 40 000 cd m-2 0,8 %

Luminous flux 10 – 10 000 lm 1,0 %

4.3 Spectrophotometry

Spectrophotometric calibrations are carried out using a reference spectrometerfacility that is based on a single grating monochromator. By changing the grat-ing of the monochromator, a wide wavelength region from ultraviolet (250 nm)to near infrared (1700 nm) is covered. Spectral transmittance of filters up to10 cm in diameter can be measured. By using special accessories, measurementsof regular reflectance, diffuse reflectance, and spectral responsivity of photo-detectors can be carried out.

A commercial spectrophotometer (Perkin Elmer Lambda 900) is also being usedas a transfer standard instrument for the measurements of regular spectraltransmittance. The instrument provides transmittance calibrations of a range ofoptical components traceable to the reference spectrometer. The performance ofthe instrument has been tested by internal quality control and comparison meas-urements for the visible spectral range.

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Quantity Range Wavelength range Uncertainty (k = 2)

Transmittance 0,0005 – 1 250 – 380 nm 0,1 % – 1 %

0,0001 – 1 380 – 920 nm 0,05 % – 0,5 %

0,0005 – 1 920 – 1700 nm 0,1 % – 1 %

> 0,01 A/W 250 – 380 nm 1 %

380 – 920 nm 0,5 %

Spectral re-sponsivity

920 – 1700 nm 4 %

0,05 – 1 250 – 380 nm 0,5 % – 5 %Reflectance(5° – 85°)

0,01 – 1 380 – 1000 nm 0,3 % – 3 %

Diffuse reflec-tance

0,05 – 1 360 – 830 nm 0,4 % – 1 %

4.4 Wavelength

Optical wavelength calibrations are carried out with a commercial spectrumanalyser. The analyser is calibrated using the known wavelengths of gas lasersstabilised to transitions in iodine and acetylene.

Quantity Range Uncertainty (k = 2)

Optical wavelength 400 nm – 1,55 µm 0,01 nm

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5 RESEARCH PROJECTS

5.1 Optical Radiation Measurements

5.1.1 Improving the accuracy of UV radiation measurement

Petri Kärhä, Neil Harrison*, Saulius Nevas, Bill Hartree*,Issam Abu-Kassem†, and Toomas Kübarsepp‡

* National Physical Laboratory (NPL), UK† Bureau National de Métrologie (BNM), France

‡ HUT, now with Tartu Observatory, Estonia

One of the main objectives of theEuropean Commission funded project‘Improving the Accuracy of Ultravio-let Radiation Measurement’ was todevelop filter radiometers to measurethe radiation emitted from UV sourcesin the spectral range from 248 nm upto 365 nm with a target accuracy be-tween 0,1 % and 1 %. Two types offilter radiometers were developed forthe purpose. The first type built byNPL was based on wide band-gap so-lar blind photodiodes. The second typeof filter radiometer built by HUT util-ised trap detectors based on siliconphotodiodes.

All filter radiometers were character-ised by three institutes; HUT, NPLand BNM. The only exception was the248 nm filter radiometers that weremeasured by NPL and BNM only.The measurement results provide in-tercomparisons between the spectralresponsivity scales, spectral irradiancescales, wavelength scales, and facili-

ties for filter radiometer characterisa-tion between the three institutes. HUTand BNM characterised the radiome-ters using conventional mono-chromator-based spectrophotometerswhereas NPL utilised their laser-basedcharacterisation facilities.

Spectral responsivity of 313W10GPC

0,00

0,01

0,02

0,03

0,04

300 305 310 315 320 325Wavelength [nm]

Res

pons

ivity

[A/W

]

NPLBNMHUT 2000HUT 1999

Figure 5.1.1-1. Typical UV filter ra-diometer calibrations by HUT, NPLand BNM-INM.

This part of the project ended in year2000, and the final report has beenwritten. Figure 5.1.1-1 shows an ex-ample of the results.

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Most of the results were in agreementwithin their uncertainties. The agree-ment between the participating labo-ratories in the spectral irradiance andspectral responsivity measurementswas roughly on the level of 2 %.

The study pointed out various thingsto improve. The wavelength scales ofthe participating laboratories differmore than the stated uncertaintieswould imply. This appears to be apoint that has not earlier been properlytested, as intercomparisons are usuallyperformed using spectrally flat arte-facts.

The study did not show that one of thefilter radiometer types would be better

than the other. The angular propertiesof trap detectors are complicated, butsolar blind photodiodes have highernon-uniformity. These things may ex-plain some of the discrepancies, be-cause the beam geometries of the par-ticipating laboratories were not com-mon.

The stability of the interference filtersused was worse than anticipated.Changes up to 1,7 % in the transmit-tance within one year were noticed.

The work has been financially supported bythe Standards, Measurements and Testingprogramme of the European Union andTEKES.

5.1.2 A portable field calibrator for solar UV measurements

Petri Kärhä, Lasse Ylianttila*, and Toomas Kübarsepp†

* STUK, Radiation and Nuclear Safety Authority† HUT, now with Tartu Observatory, Estonia

Work package 4 of the EuropeanCommission funded project ‘Improv-ing the Accuracy of Ultraviolet Ra-diation Measurement’ develops aportable detector-stabilised calibrationsystem for solar UV spectroradio-meters. This work is collaborationbetween STUK, HUT, and NPL.

Calibration of e.g. Brewer spectro-radiometers is problematic, becausetheir transportation to calibration labo-ratories may affect their calibration,and calibration outside in the meas-

urement sites is influenced by envi-ronmental conditions.

During year 2000, the first prototypeof the calibrator was finished just be-fore summer. The construction of thefirst prototype calibrator can be seenin Figure 5.1.2-1. The calibrator util-ises a 1 kW DXW lamp as the lightsource. The output of the light sourceis continuously monitored with twotemperature-controlled filter radio-meters at 313 nm and 368 nm wave-lengths. The measurement distance of50 cm can easily be adjusted by using

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unique interchangeable adapter platesfor each spectroradiometer to be cali-brated.

Figure 5.1.2-1. A photograph of thefirst prototype calibrator with theassociated electronics for lampcontrol and the monitoring filter ra-diometers.

A significant part of the work has beenassigned for measuring the ageingproperties of DXW and FEL lamps. 12specimens of each type where burnedfor 80 hours and monitored for variousparameters. Based on the measurementresults, DXW lamps where chosen.The lamp is operated in current-stabilised mode. When the ageingcharacteristics of the lamp are known,the signals of the monitoring filter ra-diometers can be used to calculate cor-rections for the spectrum as the lampages.

The preliminary measurements are en-couraging. The device works satis-factorily in both laboratory and infield. Based on the experience gained,a second improved prototype calibra-tor will be built by summer 2001.

The work has been financially supported bythe Standards Measurements and Testingprogramme of the European Union andTEKES.

5.1.3 Comparison measurements of spectral irradiance

T. Kübarsepp*, H. Yoon†, S. Nevas, P. Kärhä, and E. Ikonen

* HUT, now with Tartu Observatory, Estonia† National Institute of Standards and Technology (NIST), USA

Comparison measurements of spectralirradiance between NIST and HUTwere conducted in June 2000. Thepurpose of the measurements was todirectly compare the spectral irradi-

ance scales in the wavelength rangefrom 290 nm to 900 nm.

In the comparison two sets of threeFEL-type 1 kW lamps were measuredat HUT. One set had the calibration

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from NIST source-based facility andthe other from HUT detector-based re-alisation of the scale.

300 400 500 600 700 800 900

-3

-2

-1

0

1

2

3

Wavelength [nm]

(a) HUT filter radiometer measurements: F305 F431 F432

NIST-HUT combined uncertainty (k=2)

(EH

UT-E

NIS

T)/E N

IST x

100

300 350 400 450 500 550 600

-2

-1

0

1

2

3 NIST filter radiometer measurements: HUT264 HUT266

NIST-HUT combined uncertainty (k=2)

Wavelength [nm]

(b)

(i mea

s-ica

lc)/i

calc x

100

Figure 5.1.3-1. Comparison of themeasurement results obtained witha) NIST calibrated lamps F305,F431, and F432, and b) HUT cali-brated lamps HUT264 and HUT266.

The NIST-calibrated lamps weremeasured against the primary standardfor spectral irradiance of HUT. Basedon the measurement results of HUT,

the spectral irradiance values of NISTlamps were derived and compared tothose given by NIST. The results ofthe comparison are depicted in Figure5.1.3-1 a).

The HUT-calibrated lamps weremeasured with three NIST filter radi-ometers. Based on the spectral irradi-ance values of HUT lamps and thespectral irradiance responsivity valuesof NIST filter radiometers, the ex-pected photocurrent values were cal-culated. The calculated photocurrentvalues were compared to those ob-tained in the measurements by NIST.The comparison results are shown inFigure 5.1.3-1 b).

The combined uncertainty of NIST-HUT comparison measurements variesbetween 3,1 % and 1,1 % (k = 2) in thewavelength range from 290 nm to900 nm.

The results of the comparison meas-urements between NIST and HUTshow that the spectral irradiancescales are in good agreement down tothe wavelength of 350 nm.

The work has been financially supported bythe Centre for Metrology and Accreditationand the Academy of Finland.

5.1.4 Absolute measurement method for luminous flux

J. Hovila, P. Toivanen, K. Lahti, I. Tittonen, and E. Ikonen

Luminous flux (unit lm) is a photo-metric quantity, which describes thetotal power of a light source as seen

by a human eye (lighting ability). Forthis reason, high accuracy calibrationsof luminous flux standard lamps are

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widely needed in the lighting indus-try. So far these standard lamps havebeen calibrated elsewhere, leading tolonger traceability chain and higheruncertainties.

The HUT luminous flux measure-ment set-up using the absolute inte-grating sphere method [1] was com-pleted in 2000 after a three-yearproject (see Figure 5.1.4-1). The lu-minous flux of the external source(1000 W Osram FEL T6) is obtainedby measuring the illuminance withinthe calibrated precision aperture byilluminance standard photometer.This ensures the traceability to theHUT illuminance unit. The signal ofthe sphere photometer is measuredfor both the external and the internalsource. The luminous flux of the in-ternal source is calculated from thesignal ratio. The result is fine-tunedby using a correction factor obtainedfrom the system characterisation.The correction factor of the HUTset-up is 1,0032.

Some modifications were madeduring the year 2000 to improve theset-up and the characterisation pro-cedures. For example, the aperturearray (made of black-anodised alu-minium) was completely re-designedand its inner walls are now coatedwith a high-absorbance material toreduce the stray light in the illumi-nance measurement. Also the LEDscanner used for measuring the re-flectance non-uniformity of thesphere coating was modified to im-

prove the LED mounting and beam col-limation.

The luminous flux standard lamp cali-bration range is 10 – 10 000 lm. Therelative expanded uncertainty of the re-alisation of the HUT luminous flux unitis 0,72 % (k = 2). The uncertainty maystill decrease after a better lamp holderfor the internal source is installed.

F1

F2

A

B1

B2

aperture array external source

internal source

Figure 5.1.4-1. The luminous fluxmeasurement set-up consisting of lightsources, baffles B1 and B2, precisionaperture A, illuminance standardphotometer F1 and sphere photometerF2.

The accuracy of the HUT luminous fluxunit was tested in summer 2000 by in-ternational comparison. Four NIST (Na-tional Institute of Standards and Tech-nology, USA) luminous flux standardlamps (180 W Osram Wi41/GLOBE)were measured using the HUT sphereset-up. On the average, the measuredvalues deviated less than 0,1 % from thevalues measured at NIST. This deviationis much smaller than the standard un-certainty of the measurements.

The work has been financially supported by theCentre for Metrology and Accreditation.

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[1] K. Lahti, J. Hovila, P. Toivanen, E.Vahala, I. Tittonen, and E. Ikonen,“Realisation of the luminous flux

unit using a LED scanner for the absoluteintegrating sphere method,” Metrologia37, 595-598 (2000).

5.1.5 Relative scale of spectral diffuse reflectance

S. Nevas and F. Manoocheri

Spectral diffuse reflectance measure-ments are widely used for determina-tion of optical properties of materialssuch as the colour and appearance.Paper industry needs calibration ofdiffuse reflectance standards, mainlyused as reference in measurements ofwhiteness of paper. To meet suchneeds, a facility for the measurementsof spectral diffuse reflectance has beenestablished at the Metrology ResearchInstitute of Helsinki University ofTechnology.

8oSpectrometerbeam

Sample

Referencestandard

Specular reflection port

Rotationstage

D

Adjustable iris

16o

Detector porton top Screens

Figure 5.1.5-1. Schematic view ofthe integrating sphere in the setupfor the measurements of spectraldiffuse reflectance.

The facility is based on a high-accuracy spectrometer and an inte-grating sphere detection system.Schematic view of the measurementsetup is shown in Figure 5.1.5-1. Thesingle grating monochromator-based

spectrometer provides a well-collimated beam. The 150-mm-diameter integrating sphere is posi-tioned on a high-accuracy rotary stage.The sphere features five 25-mm di-ameter ports designed for 8° geometry.The 0°/d geometry can be obtained byusing 8° sample and reference holders.Two internal screens prevent the firstreflection components from the sam-ple and the standard from reaching thedetector. A computer controls thespectrometer, the rotary stage, andreads the signal from the detector via adigital voltmeter.

The measurements are made relativeto reference standards traceable to anabsolute scale. At present, the relativescale at HUT takes its traceabilityfrom the absolute scales of PTB(Physikalisch-Technische Bundes-anstalt, Germany) and NRC (NationalResearch Council, Canada). Spectra-lon and white opal glass samples areused as reference materials. The dif-fuse reflectance of a sample is deter-mined by the ratio of the detector sig-nals obtained during the irradiation ofthe sample and the standard. This isachieved by rotating the sphere to ir-radiate the reference and the samplealternately. The measurement geome-

22

try of irradiation/view of the facilitycan be either 8°/diffuse (with specularcomponent included and excluded) or0°/diffuse.

0.9990

0.9992

0.9994

0.9996

0.9998

1.0000

1.0002

1.0004

1.0006

1.0008

1.0010

350 400 450 500 550 600 650 700 750 800 850Wavelength (nm)

ρ ρρρ H

UTD

R-W

1 /

ρ ρρρ H

UTD

R-W

2

Figure 5.1.5-2. Spectral diffuse re-flectance ratio measured for twoidentical samples.

With our facility we can measure opti-cal quality samples for spectral diffusereflectance in the range of 0,05 − 1,00and within 360 − 830-nm wave-lengths. The measurements can be per-formed with an expanded uncertaintyof 0,4 % − 1,0 %. The uncertaintyanalysis includes components related

to the reference standards, beam pa-rameters, and detection system.

Accuracy of the measurements hasbeen verified by a series of test meas-urements on a set of diffuse reflec-tance standards. Results of the com-parison measurements are in agree-ment well within the uncertainty of themeasurements. Figure 5.1.5-2 showstest measurement results for two iden-tical samples, HUTDR-W1 andHUTDR-W2.

As an extension of the project, the de-velopment of the absolute scale ofspectral diffuse reflectance was startedin the year 2000. The facility underdevelopment will provide spectral dif-fuse reflectance, transmittance and bi-directional radiance and transmittancefactors of a range of standards in ab-solute units.

The work has been financially supported bythe Centre for Metrology and Accreditation.

5.1.6 Development of a national standard for fibre optic power

J. Envall and P. Kärhä

Fibre optic power measurement is oneof the fundamental measurements intelecommunications. These measure-ments are needed for example to de-termine the losses in telecommunica-tion cables, in the maintenance of tele-communication networks and in thedevelopment of several fibre optic de-vices. Our goal is to achieve an un-certainty of 1,5 % (k = 2) or less for

the calibrations, which are traceable toour cryogenic radiometer.

Our calibration equipment consists ofthree photodiodes. Two of these pho-todiodes are mounted into black ano-dised aluminium cases. Adapters withstandard FC connectors are fitted intothe cases to allow an easy connectionfor optical fibre. The third photodiode

23

is fitted into an integrating sphere. Thesphere has two input ports, oneequipped with a similar adapter as thetwo detectors mentioned earlier, andone with no extra mountings. Thisstructure makes it possible to measurethe response of the sphere by eitherconnecting the fibre straight to thesphere or by aligning a collimatedbeam into the sphere. Using the inte-grating sphere makes it possible tomeasure the power from the optical fi-bre over the whole solid angle. This isa convenient feature because typicallythe optical power spreads to a widesolid angle from the end of the fibre.On the other hand, the response of theplain photodiode is greater than that ofthe integrating sphere by at least afactor of five. This means that by us-ing the plain diodes it is possible to dothe calibrations with lower power lev-els.

The equipment is to be calibrated us-ing the existing standards for opticalpower. The calibrations are done forthe two most common wavelengthsused in telecommunications, that is1550 nm and 1310 nm, and probablyfor 850 nm in the future. The calibra-tion of the integrating sphere is yet tobe done, but the characterisation of thetwo plain diodes has been completed.The following characteristics weremeasured: response for optical power,

linearity of the response, angular re-sponse and spatial response.

-2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0 2,5-3,0

-2,5

-2,0

-1,5

-1,0

-0,5

0,0

0,5

1,0

1,5

X [mm]

Y [mm]

0,0-0,2

-0,2-0,0

-0,4--0,2

-0,6--0,4

-0,8--0,6

-1,0--0,8

Change / %

Figure 5.1.6-1. The spatial responseof one of the two plain photodiodesat 1310 nm wavelength given asrelative change from the average re-sponse at the centre.

Figure 5.1.6-1 shows the spatial re-sponse of one of the photodiodes. Al-though we have the option of usingthe integrating sphere to improve uni-formity, it was very encouraging tonotice that both the angular responseand the spatial response of the diodeswere considerably flat. This increasesthe accuracy of the measurements inwhich the plain diodes are used, andno correction factors are needed. Infact, a flat spatial response was one ofthe key issues in choosing the photo-diodes for this project.

The work has been financially supported bythe Centre for Metrology and Accreditationand the Academy of Finland.

24

5.1.7 UV-laser for radiometric characterisations of detectors

M. Vainio, M. Merimaa, T. Kübarsepp, and E. Ikonen

Compact and reliable continuous-wave ultraviolet (UV) lasers areneeded for radiometric characterisa-tion of detectors in the biologicallyinteresting solar UV band around320 nm. Also, UV lasers are needed inspectroscopic applications, wherewavelength tunability is required. Di-ode lasers would be almost ideal forthese applications, but so far theiravailable wavelength range coversonly the red and infrared section of thespectrum. However, shorter wave-lengths can be obtained by secondharmonic generation (SHG) in a non-linear crystal. We have developed acontinuous-wave UV laser at 317 nmbased on diode laser and SHG.

Spectral properties of solitary diodelasers are not sufficient for efficientSHG, but these properties can be im-proved by operating diode laser in anexternal cavity. To improve the spec-trum a compact transmission-gratinglaser is used in this work. In additionto forcing the laser to operate in a sin-gle mode, the external-cavity configu-ration improves the wavelength tu-nability. The transmission geometry isused to remove the problem of direc-tional variation of the output beamwhile tuning the laser. The external-cavity laser is based on a commercial,AR-coated 30-mW diode laser oper-ating at 635-nm band.

634 nm

TransmissionGratin g Lase r

LAPP

LD TGR

λ/2

Opticalisolator

λ/2

Mode matchinglenses

λ/2

Planemirror

Curved mirrors (R=25 mm)

Crystal(BBO) 317 nm

Planemirror

L

Figure 5.1.7-1. Experimental setup of UV-laser realised with optical secondharmonic generation.

The experimental setup is schemati-cally shown in Figure 5.1.7-1. UVlight is generated from red 634-nm la-ser radiation using a nonlinear BBO(β-Barium-Borate) –crystal. To in-crease SHG efficiency, the crystal isplaced inside a resonator that builds

up the incoming red power with afactor of approximately 49. The reso-nator is formed by four mirrors in abow-tie ring configuration, which hasunidirectional operation. Mode-matching lenses are used to couple amaximum amount of the fundamental

25

power into the resonator and to opti-mise the beam focusing inside thecrystal. Electronic feedback, based onlock-in technique, is used to lock thelaser frequency to a cavity resonance.

The maximum UV power measured sofar is 36 µW.

The work has been financially supported bythe Academy of Finland.

26

5.2 Length Metrology

5.2.1 Iodine-stabilised He-Ne lasers

K. Nyholm

Three iodine-stabilised red He-Ne la-sers and two multi-colour He-Ne la-sers constructed jointly by MIKES(Centre for Metrology and Accredita-tion) and HUT (Helsinki University ofTechnology) have been maintained inthe qualified conditions. Measure-ments on the frequency stability andrepeatability of the two multi-colourHe-Ne lasers (MGI1 and MGI2) werecarried out at the metrologically im-portant wavelength of 543 nm. The

dependence of the laser frequency onsuch parameters as pressure of the io-dine cell and modulation amplitudewas studied, also. The results of theseexperiments together with the resultsof a bilateral comparison with DFM(Danish Institute of Fundamental Me-trology) showed that the MGI1 andMGI2 lasers are reliable enough to en-able the start of calibration services inMIKES at the wavelength 543 nm.

5.2.2 Iodine-stabilised diode lasers

M. Merimaa, P. Kokkonen, K. Nyholm, and E. Ikonen

Frequency-stabilised He-Ne gas lasersat 633 nm form the current basis foraccurate length measurements and aregenerally used for the realisation ofthe definition of the metre. However,there has been growing interest in fre-quency stabilisation of diode lasers at633 nm during last few years since theoutput power of a He-Ne laser is smalland He-Ne lasers are large in size andmechanically vulnerable.

We have constructed a portable(32 cm × 13 cm × 6 cm) laser fre-quency standard by frequency stabi-lising an external-cavity diode laser tothe Doppler-free spectrum of iodine.Compact structure is achieved using a

novel transmission grating in aminiaturised external-cavity laser. Thelaser has excellent noise properties,which leads to high S/N-ratio of de-tection and allows direct observationof the inverse Lamb-dips as shown inFigure 5.2.2-1.The optical set-up of the iodine-stabilised external-cavity laser isschematically shown in Figure 5.2.2-2.Frequency stabilisation of the laser isbased on Doppler-free saturationspectroscopy using collinear geometryin an external iodine cell.

27

-450 -400 -350 -300 -250

0.937

0.938

0.939

0.940

0.941

b12

Tra

nsm

issi

on

Frequency relative to the line b21 / MHz

Figure 5.2.2-1. The high S/N-ratioallows detection of inverse Lamb-dips even without a lock-in-amplifier.

The valuation of the performance ofthe laser system as an optical fre-quency standard proves that an iodine-stabilised external-cavity diode lasercan reach similar or better stabilitythan typically achieved with iodine-stabilised He-Ne-lasers. The relativefrequency stability (square root of theAllan variance) follows a slope of

7,9 × 10-12 τ-1/2 (10 s < τ < 4000 s) andthe best stability of 1 × 10-13 (47 Hz) isreached at an integration time of τ =4000 s. A good (4 × 10-12) day-to-dayrepeatability (1 σ) and good agree-ment with the CIPM values was alsoreached.

λ/2

L

PBS

λ/4L LM

M

M

M

I2-cell(10 cm)

APPLDTGR

λ/2

Double isolator

Output

PD(intensity stabilization)

Laser cavity

T=15 ºC ± 0.1ºC

PD(Signal)

BS

Figure 5.2.2-2. Experimental set-up.

The work is a collaboration project betweenHUT and the Centre for Metrology and Ac-creditation.

5.2.3 Iodine-stabilised Nd:YAG lasers

T. Ahola, K. Nyholm, M. Merimaa, and E. Ikonen

High-precision spectroscopy, opticalcommunications, and modern lengthmetrology rely on reference wave-lengths generated by lasers frequency-stabilised to atomic or molecular tran-sitions. Currently, practical lengthmetrology is mainly carried out usingiodine-stabilised He-Ne lasers at thewavelength 633 nm. Also, among thetwelve reference wavelengths (fre-quencies) recommended by theComité Internationales des Poids etMesures for the practical realisation of

the definition of the metre is thewavelength 532 nm realised by an io-dine-stabilised Nd:YAG laser.

Recently, diode-pumped iodine-stabilised Nd:YAG lasers at 532 nmhave demonstrated better stability thanHe-Ne lasers. These lasers have manyattractive metrological features, e.g.,they are compact in size, have low in-trinsic frequency and intensity noise,and they offer high power levels, si-multaneous output of two wave-

28

lengths, and long lifetime. Moreover,the absorption lines of iodine are verystrong and narrow near 532 nm and,therefore, form an almost ideal fre-quency reference. Hence, the intereston Nd:YAG lasers is steadily increas-ing within metrology community.A commercial diode-pumped Nd:YAGlaser was frequency-stabilised to Dop-pler-free spectrum of iodine at532 nm. The resonator of the laser is amonolithic non-planar ring. Becauseof this non-reciprocal ring, the cavityeliminates spatial hole-burning, oper-ates in a single longitudinal mode, andis insensitive to optical feedback.Moreover, the monolithic cavity con-struction offers excellent passive fre-quency and intensity stability. Thesecond harmonic output at 532 nm isgenerated in a periodically poled KTPcrystal. The power of the laser is

1,1 W at 1064 nm and 20 mW at532 nm. In order to use third-harmoniclocking technique for the stabilisation,two piezo-crystals were attached at thelaser crystal. One of the piezos is usedfor the frequency modulation and theother for frequency tuning. Coarsetuning is realised by temperature con-trol of the laser crystal.

In preliminary measurements, severalabsorption lines of iodine were de-tected and identified and the frequencyof the laser was successfully locked onthe hyperfine components. The short-term relative frequency stability of thelaser was estimated to be 1,7×10-12 τ-½

from the signal-to-noise ratio of themeasured hyperfine structure spectra.

The work is a collaboration project betweenHUT and the Centre for Metrology and Ac-creditation.

29

5.3 Fibre-Optic Measurements

5.3.1 Characterisation of group-delay ripple in chirped fibre Bragggratings

T. Niemi, M. Uusimaa, G. Genty, and H. Ludvigsen

Characterisation of group delay andamplitude properties of various com-ponents is important in designing ad-vanced optical networks. The phase-shift method is an established tech-nique for performing high-accuracymeasurements of these parameters.The accuracy in resolving the finestructure of the group delay, however,depends critically on the modulationfrequency used in the measurements.The choice of the modulation fre-quency is, in general, a trade off be-tween the desired accuracy of themethod and the resolution of the elec-trical phase measurement.

1554.00 1554.02 1554.04 1554.06 1554.08

-200

-150

-100

-50

0

50

100 1 GHz

500 MHz

250 MHz

Gro

up d

elay

rip

ple

[ps]

Wavelength [nm]

Figure 5.3.1-1. Measured (solidlines) and simulated (dashed lines)group delay for three differentmodulation frequencies.

We have built an experimental setupbased on the phase-shift method forcharacterisation of various filters such

as fibre Bragg gratings (FBG) andmultiplexers/demultiplexers. In par-ticular, we have studied the accuracyof the method in resolving densegroup-delay ripple that is present inchirped FBGs [1].

An example of the measured groupdelay for different modulation fre-quencies of a 20-cm long chirped FBGwith a bandwidth of 2 nm and a nomi-nal dispersion –660 ps/nm is given inFigure 5.3.1-1. To confirm the meas-ured group-delay values at 500 MHzand 1 GHz we used the 250 MHzgroup delay curve for simulation ofthe operation of the measurementsystem at higher frequencies. Theagreement between the simulated andmeasured group delays is good.

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0-40-20

020406080

100120140160180

Measurements

Simulations

Analytical model

Rip

ple

ampl

itude

[ps]

Modulation frequency fm [GHz]

Figure 5.3.1-2. Comparison of themeasured ripple amplitude with theanalytical model.

30

A comparison between the measuredamplitude of the ripple and the am-plitude calculated using an analyticalmodel with sinusoidal variation of theripple amplitude is given in Figure5.3.1-2. According to the model themeasured amplitude of sinusoidal rip-ple follows a sinc-function. It isclearly seen from both of the figuresthat the ripple is effectively averagedout when the modulation frequencyapproaches a multiple of half a periodof the ripple. The model gives a meansfor estimating the accuracy of the

group-delay ripple measurements forthe selected modulation frequency. Itfinds applications in the developmentof standardised measurement proce-dures of fibre Bragg gratings.

The work has been financially supported bythe Academy of Finland and TEKES.

[1] T. Niemi, M. Uusimaa, and H. Ludvig-sen, “Measurements of dense groupdelay ripple using the phase shiftmethod: Effect of modulation fre-quency,” in Proceedings of Symposiumon Optical Fiber Measurements, Sep-tember 26-28, 2000, pp. 165-167.

5.3.2 Fibre laser

T. Laukkanen, G. Genty, and H. Ludvigsen

Current optical communication sys-tems make use of the dense wave-length division multiplexing (DWDM)technique in the wavelength windowof 1530 – 1565 nm (C-band). To in-crease the transmission capacity ofoptical fibres in the future, the wave-length window will be extended to thewavelength range from 1565 nm to1625 nm (L-band). Erbium-doped fi-bre lasers have the potential to be usedin the L-band as optical transmittersand in the characterisation of varioustypes of fibre-optic components.

We have constructed an Erbium-dopedfibre-ring laser, which operates in theC-band in both continuous wave andpulsed mode. It will in the near futurebe redesigned to operate in the L-band. An outline of the laser setup for

pulsed operation is presented in Figure5.3.2-1. The laser design is based on afibre-ring cavity where the Erbium-doped fibre (EDF) is pumped by a di-ode laser at 980 nm. The pump light iscoupled into the cavity by a wave-length division multiplexer. An opticalisolator (I) determines the propagationdirection of the laser field. The bire-fringence of the fibre is compensatedfor with a polarisation controller (PC).Pulsed operation is achieved by intro-ducing a Mach-Zehnder modulator(MZ) into the cavity. The MZ isdriven with a wide bandwidth signalgenerator (S.G.). Ten percent of theoptical field power is coupled to thelaser output with a fibre coupler (FC).

31

MZPC

IEDF

WDM

Pump Laser

FC

Output

S.G.

Figure 5.3.2-1. Setup of the fibre la-ser for mode-locked operation.

We have obtained repetition rates of3 – 18 GHz and pulse widths down to5 ps for laser operation in the C-band.Autocorrelation traces of the opticalpulses for different average powers areshown in Figure 5.3.2-2.

48

12

16

20 -40-20

020

40

0

1

Am

plitu

de [a

.u.]

Time Delay [ps]

Laser Field Power [mW]

Figure 5.3.2-2. Autocorrelationtraces of the optical pulse train fordifferent intra-cavity powers.

The work has been financially supported bythe Academy of Finland

5.3.3 Effect of optical filtering on pulses generated with a gain-switched DFB-laser

T. Niemi, J.-G. Zhang*, and H. Ludvigsen

* HUT, Communications Laboratory

Short optical pulses have found manyapplications in optical fibre measure-ments, optical soliton transmission,and high-speed optical time-divisionmultiplexing (OTDM) communicationsystems. Several techniques to gener-ate short optical pulses have been pro-posed.

One commonly used method to pro-duce short pulses is gain switching ofa semiconductor laser. To achieve gainswitching, the laser is biased below itsthreshold current and, subsequently,

modulated with a reasonably high-voltage signal. By appropriately se-lecting the magnitudes of the DC-biasand the RF-signal, the laser can gener-ate optical pulses with the duration ofa few tens of picoseconds.

Usually, the gain-switched pulses arestrongly chirped, indicating that thefrequency of the light varies over theduration of the pulse. This feature canbe used for pulse compression by us-ing either a normally dispersive fibreor an optical filter. In general, an opti-

32

cal filter can be applied to remove thehighly chirped pulse components,which leads to the generation of nearlytransform-limited pulses. The use ofoptical filtering permits compact opti-cal transmitter implementation.

DFB-LASER

RF- SIGNALGENERATOR

BIASCURRENT

FASTDETECTOR

SAMPLINGOSCILLOSCOPE

TEMPERATURECONTROLLER

OPTICAL SPECTRUMANALYZER

TRIGGER

F-P ETALONEDFA

Figure 5.3.3-1. Experimental setupfor generating gain-switched pulseswith a DFB laser and for detectingthese pulses.

We have studied the effects of opticalfiltering on the shape of short opticalpulses generated with a gain-switcheddistributed feedback (DFB) laser di-ode applying the setup depicted inFigure 5.3.3-1. We found that tuningof an optical bandpass filter over theoptical spectrum of such a laser ex-hibits a strong effect on the temporalshape of the resulting gain-switchedpulses (see Figure 5.3.3-2).

We observed the generation of a seriesof secondary oscillations when thecentre frequency of the optical filterwas tuned to the short-wavelengthside of the spectrum. An investigationof this phenomenon was carried out bymeans of experimental observations.Furthermore, an analytical modelbased on filtering of linearly chirpedGaussian pulses with a Fabry-Perotfilter was developed to reveal the ori-gin of the generation of the secondaryoscillations.

200 225 250 275 300 325 3500.00

0.02

0.04

0.06

0.08

0.10

Without filter

ν 0=-12 GHz

ν 0=0 GHz

ν 0=12 GHz

ν 0=18 GHz

Sig

nal [

a.u.

]

Time [ps]

Figure 5.3.3-2. Measured pulsewaveforms of the gain-switched la-ser for several positions of the cen-tre frequency of an optical passbandfilter.


5.3.4 Nonlinear crosstalk in a WDM network transmitting digitaltelevision channels

T. Niemi and H. Ludvigsen

Broadband distribution, such asCATV, can conveniently be carriedout by using fibre-optic links. CATV

networks currently offer broadcastservices indicating that each customer,such as a single household, receives

33

the same information. In the near fu-ture, the information carried in aCATV network is directed to narrow-cast services, which offer a means todeliver customised services to a se-lected group of customers. The serv-ices provided in these networks mayinclude e.g. digital television, fastinternet and video-on-demand. Oneway to upgrade the fibre-optic CATV-network is to make use of the wave-length-division multiplexing (WDM)technique in which each wavelengthcan be used to allocate a selectedservice. The implementation of WDMin CATV transmission systems, how-ever, requires a deeper understandingof the interplay of the nonlinearities ofthe optical fibre.

We have constructed a test bed incollaboration with Teleste Ltd. formeasuring the effect of nonlinearcrosstalk in a digital television WDMapplication having eight wavelengths.The modulation format used in digitaltelevision transmission is QAM

(Quadrature Amplitude Modulation),which is less sensitive to distortionand noise compared to the purelyanalogue modulation format. The goalof the study was to determine thepractical limits for the optical powerthat can be launched into the fibrewithout degradation of the signalquality due to nonlinear crosstalk.

At high level of optical power nonlin-ear crosstalk is mainly induced bystimulated Raman scattering (SRS)and cross-phase modulation (XPM).These effects cause interference be-tween the electrical subcarriers thatare modulated at different wave-lengths. The contribution of SRSdominates for low subcarrier frequen-cies and XPM increases for high sub-carrier frequencies. We have built amodel for estimating nonlinearcrosstalk in a multi-wavelengthCATV-links.


5.3.5 Wavelength monitoring of DWDM systems using a tempera-ture-controlled Fabry-Perot filter

T. Niemi, T. Laukkanen, J. Tuominen, S. Tammela*, and H. Ludvigsen

* VTT, Microelectronics

As the channel spacing is decreasingin optical DWDM-systems the needfor accurate wavelength monitoring oflaser transmitters and the calibrationof DWDM measurement equipmentincreases. We have developed a de-

vice concept for monitoring and cali-bration purposes of a multi-channelDWDM-system.

The device makes use of a single tem-perature-tunable Fabry-Perot etalon

34

filter. The filter has been fabricated bydepositing two dielectric mirrors onboth sides of a double-side polishedsilicon wafer. The transmission of thefilter can be tuned by controlling thetemperature of the chip. The filter canbe used as a calibrated wavelengthreference by locking one of its fringesto a stable reference, such as a mo-lecular absorption line. When the filtertransmission as a function of wave-length is known, the close-by-lyingtransmission fringes can be applied formonitoring and referencing with anaccuracy adequate for practical appli-cations.

TEMPERATURECONTROLLER

F-P FILTER

DAQ

DM

UX

MU

X

Reference channel

WDM channels +Reference laser

200 GHz

Figure 5.3.5-1. Setup for wavelengthmonitoring of WDM channels usinga temperature-stabilised Fabry-Perot filter.

To demonstrate the concept we havelocked a transmission fringe of thefilter to a laser stabilised in frequencyto an absorption line of acetylene(13C2H2, Line P(22) at 1546,174 nm).The setup for applying the filter tomonitor the wavelengths of a WDMsystem is shown in Figure 5.3.5-1 [1].

When the wavelength of the laser inthe monitored channel shifts the

changes in its transmission can be di-rectly used to estimate the shift bycomparing it to the transmission spec-trum of the filter. The transmissionspectrum of the filter while it is lockedto the reference laser was measured byusing a broadband source and an opti-cal spectrum analyser (see Figure5.3.5-2). To improve the accuracy ofthe device concept both the wave-length and temperature dependence ofthe refractive index of silicon will bemodelled.

1544 1546 1548 1550 1552 1554 1556 1558 1560

-14

-12

-10

-8

-6

-4

-2

0

2 13C2H2 Stabilised reference laser at 1546.174T

rans

mis

sion

[dB

]

Wavelength [nm]

Figure 5.3.5-2. Measured transmis-sion spectrum of the filter which isreferenced to an acetylene stabilisedlaser line.


[1] T. Niemi, T. Laukkanen, S. Tammela,and H. Ludvigsen, “Wavelengthmonitoring of multi-channel DWDM-systems using a single temperature-tunable Fabry-Perot filter,” in Pro-ceedings of Conference on Lasers andElectro-Optics Europe, September 10-15, 2000, CTuP4, p. 164.

35

5.4 Microtechnologies

5.4.1 Micromechanical resonators for RF-applications

T. Lamminmäki, P. Rantakari, K. Ruokonen,M. Koskenvuori, and I. Tittonen

Bulk silicon offers both unique elec-trical and mechanical properties. Me-chanical silicon resonators have intrin-sically very low-loss resonances,which can be even further improvedby appropriate design. By using thestate-of-the-art SOI (silicon-on-insulator) processing technology alsosmall enough constructions can beobtained that can possess mechanicalresonances that are capacitively read-out and excited even in the MHzrange.

L = 44 µm

w = 4 µm

d = 0.5 µm

h = 8 µm

Figure 5.4.1-1. 14 MHz micro-mechanical bridge resonator.

Detailed analysis and understanding ofminiature size oscillators requires nu-merical methods. Capacitively actu-ated mechanical systems can success-fully be analysed using FEM (finiteelement method) simulation tech-niques by simultaneously taking into

account mechanical, thermal andelectromagnetic dynamic interactions.FEM can also be used to estimatethose parameters that are then later fedinto the circuit-simulation program re-vealing how the mechanical design ineffect works as a part of an RF elec-tronics circuit.

Rm Lm Cm

Cp

Figure 5.4.1-2. An RLC equivalentcircuit of a micromechanical reso-nator.

The processed constructions weremeasured using the network analyserin transmission (Figure 5.4.1-1). Thecomponent is coupled to electronicsvia capacitance trying to minimiseparasitic contributions. Vacuum en-capsulation was required to enhancesignal levels and to avoid air- dampingeffects. From the measured data a de-tailed transfer function was deduced.This data was even further processedand also fitted using the APLAC cir-cuit simulator and equivalent RLC cir-

36

cuit parameter values were obtained(Figure 5.4.1-2). At this point, wehave also obtained information aboutthe damping values (∝ 1/Q) whichcannot be obtained as an output fromthe FEM analysis. We also addedvarious nonidealities (e.g. parasitic

capacitances) to optimise and evaluatethe over-all performance of the novelRF circuit.

The work has been financially supported byNokia Research Center, VTI Hamlin, andTEKES.

5.4.2 Finite element modelling of microsystems

K. Ruokonen, O. Väänänen, M. Ylönen, T. Lamminmäki, and I. Tittonen

Accurate modelling of the resonatorstructures is required to allow the de-sign of components with the desiredproperties. Analytic modelling of mi-cromechanical capacitively actuatedresonators is complex, since the reso-nators are described by dynamic, non-linear equations coupling electric andmechanical energy domains.

Figure 5.4.2-1 Finite element modelof a clamped-clamped beam reso-nator.

Finite element method (FEM) simula-tions are first used to calculate the me-chanical properties of the resonatorstructures. Scaling behaviour of the

relevant physical parameters (f, Q) arederived by calculating modal frequen-cies and estimating mechanical radi-ated losses. Using a static displace-ment analysis the effective spring con-stant k* is calculated, and the effectivemass m* is obtained from the equation

*

*

21

mkfr π

= .

Nonlinear behaviour of effectivespring constant is analysed and used inoptimisation of the resonator design.Several resonator geometric shapesare investigated in order to obtain adesign fulfilling the RF and high-Qrequirements.

Figure 5.4.2-2 Simulated displace-ment of the beam under the action ofan external force.

37

Next an electrical equivalent circuitmodel is introduced for the resonatorto allow simulation of its electrome-chanical behaviour. The FEM-calculated mechanical parameters areincorporated into the model by using aseries RLC-circuit with frequency re-sponse equal to the mechanical reso-nator. We use a standard circuit simu-lation software (APLAC) for numeri-cal calculations. The effect of non-idealities (e.g. parasitic capacitances)is carefully analysed.

Finally the FEM and circuit analysisresults are used to explain the meas-urement data on resonator structuresfabricated using silicon-on-insulator(SOI) technique. As an example thedetailed analysis of simple clamped-

clamped beam lateral resonators oper-ating at a few MHz frequencies isshown in Figure 5.4.2-3. Q-values ofthe order of 104 are obtained.

F = 293x + 22x3

0

100

200

300

400

500

600

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8

Displacement [um]

Forc

e [u

N]

Figure 5.4.2-3 Nonlinear effectivespring constant calculated by the fi-nite element method (FEM).

The work has been financially supported byVTI Hamlin, Vaisala, Aplac Solutions, NokiaResearch Center, and TEKES.

5.4.3 High-Q micromechanical silicon oscillators

K. Nera, O. Hahtela, K. Lahti, T. Lamminmäki, K. Ruokonen,V. Voipio, and I. Tittonen

In sensor technology, high-Q siliconmicro-oscillators can elegantly beused in measurements of very smallchanges for instance in temperatureand pressure. It is evident that the re-sponse of a resonant system is propor-tional to inverse of the resonancelinewidth, thus motivating the pursuitfor very narrow resonances.

Some typical results of the processedsilicon oscillators have shown Q-values exceeding even one million(Figure 5.4.3-1 and Figure 5.4.3-2).

1E-4 1E-3 0,01 0,1 1 10 100 1000

0

200000

400000

600000

800000

1000000

1200000

Q

pressure (mbar)

Figure 5.4.3-1. Micromechanicalresonator Q-value as a function ofpressure, measured using thequadrature detection method.

38

Mechanical susceptibility can usuallybe measured either capacitively or op-tically. The standard optical tech-niques used are based on quadrature-and Doppler- detection schemes. Moresensitive methods are needed for ex-ample, in the detailed analysis of theoscillator phase noise.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

67670 67700 67730 67760 67790 67820Frequency (Hz)

Am

plitu

de [a

.u.]

-100

-50

0

50

100

150Ph

ase Amplitude

Phase

Figure 5.4.3-2. Typical amplitudeand phase response of a resonatoras a function of frequency.

In our configuration, the resonator sur-face is high-reflection coated and usedas a planar mirror in a Fabry-Pérot in-terferometer (Figure 5.4.3-3). The es-sence of the method lies in monitoringthe changes in the interferometer re-sponse driven by the physical oscilla-

tions of the mechanical oscillator.From the changes of the response themechanical susceptibility of the oscil-lator can be determined. At very lowtemperatures we expect to observeeven quantum effects in optomechan-ics.

Figure 5.4.3-3. Micromechanicaloscillator is used as a planar mirrorin a Fabry-Perot interferometer. Anoptical measurement should also re-veal interesting phase changescaused by thermal and other noisesources.


39

5.5 Applied Quantum Optics

5.5.1 Installation of the Ti:Sapphire laser system

K. Lahti and I. Tittonen

During the year 2000 a new state-of-the-art laser system was acquired andinstalled. The idea was to create pos-sibilities for various kinds of forth-coming research projects by havingsingle frequency laser light with ratherhigh output power in a broad tuningrange.

Figure 5.5.1-1. Ti:Sapphire laserwith the cover opened.

Lasers having high tunability are usu-ally dye lasers or solid stateTi:Sapphire lasers. The laser systemthat was bought contained a diodepumped frequency doubled Nd:YVO4

Verdi pump laser producing 10 W at532 nm and a monolithic block reso-nator (MBR-110) Ti:Sapphire laser.The average output power is 2W in therange of approximately 700 –1000 nm. This range can be coveredwith three separate optics sets thatneed to be changed manually.

Figure 5.5.1-2. 10.5W 532 nm Verdipump and the Ti:Sapphire laser.

The system contains also a thin etalonand a servo-locking system for elimi-nating mode hops. Locking to thebuilt-in reference cavity should givethe linewidth of 10 kHz. An automaticscanning range is approximately40 GHz based on the two Brewsterplates. In addition an external fre-quency doubling unit (MBD-200)was bought with what one can reacheven upper UV range. So the overallsystem can create simultaneouslygreen, red and even blue laser light.

The system, when ready, will havevarious applications. In radiometry, itwill be used to characterise spectral ir-radiance responsivities of filter radi-ometers. These filter radiometers willthen be used for high-accuracy meas-urements of spectral irradiance and ra-diation temperature.

40

5.5.2 Microtrap for neutral atoms

T. Lindvall, I. Tittonen, S. Franssila*, A. Huttunen†, M. Rodriguez†,P. Törmä†, A. Shevchenko‡, and M. Kaivola‡

* Microelectronics Centre, HUT† Laboratory of Computational Engineering, HUT

‡ Optics and Molecular Materials, HUT

A new 3-year project for trapping andguiding of neutral atoms and evenmolecules was initiated as a collabo-ration between three HUT laborato-ries. The progress in laser cooling andtrapping of neutral atoms during thepast decade has produced a variety oftechniques based on the use of lightforces and electromagnetic fields toreach extremely low temperatures inatomic vapours and to control thetranslational motion of atoms. Usingmodern microfabrication techniques itis possible to construct micron-sizedmagnetic microtraps on the surface ofa substrate. These traps can be loadedwith cold atoms from, for example,magneto-optical traps (MOT). Thiscould allow the integration of severalatom traps and other atom-opticalcomponents onto a so called atomchip. The miniaturisation can alsomake it possible to construct atomtraps with only a few populated energylevels, if the physical dimensions ofthe trap are of the same order of mag-nitude as the de Broglie wavelength ofthe atoms.

MOT laser beams

reflectionMOT

MOT quadrupolecoilatom chip and holder

UHV chamber

Figure 5.4.2-1: Schematic picture ofthe atom chip inside the UHVchamber. The atoms are firsttrapped in a magneto-optical trap,then transferred to the magnetictraps on the chip.

The goal of the project is to developnew chip fabrication techniques and toconstruct an ultrahigh-vacuum (UHV)setup, where the chips can be testedand used for experiments, as well as totheoretically study these concepts, inparticular the influence of heating andnoise on the trapped atoms. The atomchips will be fabricated at the HUTMicroelectronics Centre.


41

5.5.3 Coupling of coherent fields in second harmonic generation

K. Lahti and I. Tittonen

Nonlinear properties of a medium actas the basis for evaluation of the po-tentiality of the medium for secondharmonic generation (SHG) purposes.The next step is the maximum exploi-tation of the nonlinear properties, i.e.coupling of the coherent fields partici-pating in the process. There are twomajor phase matching schemes used toensure the maximal coupling, that isbirefringent- and quasi-phase-matching schemes.

0 2 4 6 8 10 12 14 16 18 200,0

0,2

0,4

0,6

0,8

1,0

2

Cross Coupling not Included Cross Coupling Included

Har

mon

ic In

tens

ity /

Λ [a

.u]

Λ [µm]

Figure 5.5.3-1: Generated secondharmonic intensity as a function ofpoling period in type II quasi-phase-matching for KTP. The effect ofcross coupling away from the majorcoherence length peak is clearlyseen.

The strongest coupling scheme is thedirect coupling, where the oscillatingdipole moments pumped by a certain

polarisation interfere. However, alsothe dipoles pumped by different po-larisations are able to interfere leadingto cross coupling of the fields. Due tothe weakness of this effect, the re-ported experimental results are gener-ally in good accordance with numeri-cal calculations where the cross cou-pling is neglected.

We have numerically analysed the ef-fect of cross coupling in two of thecurrently most common SHG proc-esses, that is the lithium triborate(KTP) and potassium titanyl phos-phate (LBO) pumped with a Nd:YAGlaser. The maximal effect of crosscoupling was calculated to exists withtype II quasi-phase-matched KTPcrystal. There the maximum poling pe-riod was shifted by tens of nanometers(See Figure 5.5.3-1). Additionally,when considering the regions awayfrom the major coherence length peak,the response and hence the possibleother local optimisations are strongeraffected (See Figure 5.5.3-1). In fu-ture, the theoretical and numericalcoupling analysis should be extendedto the optical parametric oscillator(OPO) systems, since the optimisationof operation at multiple wavelengthsis a more complex task than that of asingle frequency process.

42

5.5.4 Digital laser frequency stabilisation

M. Heiliö, E. Vahala, O. Kimmelma, K. Lahti, and I. Tittonen

Frequency stable coherent lightsources have a great significance inareas of optical spectroscopy, metrol-ogy and communications. Very highstabilities have been achieved usingthe Pound-Drever-Hall method [1],where the laser frequency is locked toa high-Q optical resonator using aphase modulation scheme. We use thistechnique to lock a Nd:YAG laser toan optical resonator with finessearound 14 000 [2].

Nd:YAGFI

PBS

PM

λ / 2

λ / 2

λ / 4

Digitalcontrol

Thermally stabilized environment Electrical signal

Laser

Modematchingoptics

FI = Faraday IsolatorPM = Phase modulatorPBS = Porarizing beam splitter

Slow

Fast

Figure 5.5.4-1. Nd:YAG laser islocked to a high-Q optical resonatorusing a phase modulation scheme.

One of the crucial elements of the sta-bilisation system is the laser servocontrol which tunes the laser fre-quency electromechanically and elec-trothermally based on the frequencyfluctuation information given by theresonator (Figure 5.5.4-1). The servocontrol must be able to operate at afrequency bandwidth covering totallythe laser technical frequency noise.The frequency noise of our laser be-comes quantum-limited approximatelyat frequencies higher than 100 kHz.Servo controls operating at this high

frequencies have traditionally beenconstructed using analogue electron-ics. In our experiment we have beenusing a high-speed digital signal proc-essor together with high-resolutionA/D & D/A converters incorporatingefficient digital filtering. The 150MHz processor clock frequency en-sures operation far beyond lasers tech-nical noise bandwidth and enables theuse of a rather complex algorithmcombining the advantages of tradi-tional fringe side locking and PDHmethod. Locking methods based ontransmission suffer from delay in-duced by cavity response time. How-ever, transmission provides the lock-ing algorithm with explicit informa-tion concerning triggering andachieving the lock in general.

Figure 5.5.4-2. The standing opticalmode inside the interferometercaptured on CCD.

[1] R. W. P. Drever et al, Appl. Phys. B.31, 97-105 (1983).

[2] T. J. Kane et al, Appl. Opt. 10, 65-67(1985).

43

5.5.5 Coherent population trapping in 85Rb

T. Lindvall, M. Merimaa, and I. Tittonen

Coherent population trapping (CPT)[1] was first discovered by studyingthe fluorescence of sodium (Na) atomspumped by a multimode laser [2]. Incombination with an excited level thetwo hyperfine ground levels of Naform a three-level system (Λ configu-ration, Figure 5.5.5-1 a). A reductionin fluorescence was detected when onelaser mode ωL1,2 was resonant with

each of the Λ transitions. This darkresonance, a two-photon Raman reso-nance, could classically be explainedby saying that each absorption of aphoton from one laser mode is fol-lowed by a stimulated emission of aphoton into the other mode. Thus theexcited state remains practically un-populated and no fluorescence can beobserved.

|0�

|2�|1�

�L2�L1

-4 -2 0 2 40

0.01

0.02

0.03

0.04

�0 0

� �L1/3034.5 3035.0 3035.5 3036.0 3036.5 3037.0

Frequency (MHz)

(a) (b) (c)

Figure 5.5.5-1. (a) Λ configuration, (b) excited state population ρ00 as a functionof detuning δL1, and (c) spectrum measured using 85Rb (1st derivative) with fiveZeeman resonances.

CPT can be analysed semiclassicallyby solving the optical Bloch equationsincluding relaxation mechanisms. Thisshows how the atomic populations andcoherences depend on the laser de-tunings and intensities (Figure 5.5.5-1b), but does not explain why. One can,however, introduce a new basis con-sisting of the excited state and twoorthogonal superpositions of the twoground states. These superpositionstates are excited by both fields andthe corresponding transition ampli-

tudes are correlated by the groundstate coherence. The transition prob-abilities will add up destructively forthe uncoupled superposition state andconstructively for the coupled state.Thus the atoms are optically pumpedinto the non-absorbing uncoupledstate. Practical implementation of thistheory includes taking into account theatomic velocity distribution, colli-sions, and other broadening mecha-nisms.

44

CPT has several applications. Thelinewidth of the resonance is deter-mined by the ground state coherenceand can therefore be very narrow,which makes it suitable as a frequencystandard. One can also use it as amagnetometer by measuring the fre-quency difference between resonances

corresponding to different Zeemansublevels (Figure 5.5.5-1 c).

[1] E. Arimondo, Prog. Opt. 35, 257(1996).

[2] G. Alzetta, A. Gozzini, L. Moi, and G.Orriols, Nuovo Cimento 36 B, 5 (1976).

5.5.6 All-optical 3-GHz frequency standard based on darkstates of 85Rb

M. Merimaa, T. Lindvall, I. Tittonen, and E. Ikonen

Atomic clocks form the basis for accu-rate time and frequency measure-ments. Cesium atomic clocks, havinga relative frequency reproducibility ofapproximately 1×10-13, are generallyused for the realisation of the defini-tion of the second. However, the ce-sium atomic clock is a complex devicewith limited lifetime and thus crystaloscillators are used in practical appli-cations.

3.036 GHz

~780 nm

Figure 5.5.6-1. The Λ-system of85Rb.

The frequency of crystal oscillators isdetermined by mechanical propertiesof the crystal and regular calibrationsare needed to maintain their accuracy.To provide an intermediate step be-tween the cesium atomic clock and acrystal oscillator in the calibrationchain, a secondary frequency standardwith better stability than what can beobtained with a crystal oscillator isneeded.

A relatively simple way to realise anall-optical secondary atomic clock iscoherent population trapping (CPT).In CPT, two laser fields interactingwith an atomic three-level Λ-system(see Figure 5.5.6-1) are coupled by theground state coherence and interferedestructively at two-photon resonance.The classical explanation to this so-called dark resonance is that each ab-sorption of a photon from one laserfield is followed by a simultaneousemission to the other, if the fields arein phase and the frequency differenceis exactly the same as the ground-level

45

splitting. Since the transition con-necting the ground states has a longlifetime, >1010 s, the natural linewidthof this resonance is very small and itforms an almost ideal frequency refer-ence.

In practice, the experimental parame-ters determine the linewidth, which iswidened due to pressure, power, tran-sit-time and wall collision broadening.The frequency noise of the RF-oscillator and lock-in detection furtherincrease the observed linewidth. Theabsolute frequency of the transition isalso slightly affected by pressure, lightand Zeeman-shifts.

In this work, we use a diode laserequipped with an integrated microlensas a laser source. Optical feedbackfrom the closely mounted microlenscan be used to improve the spectrumwithout hampering the modulationproperties of the laser and the secondlaser field can be generated directly bymodulating the laser frequency viainjection current. The Λ-system of85Rb is used in this work because laser

diodes operating at the frequency ofthe Rb 52S1/2-52P3/2 transition(780,24 nm) are easily available andthe modulation bandwidth of an edge-emitting diode laser covers the3,0357 GHz ground level splitting.

Rb-cell + buffer gas

PD

λ/4

Coil

Figure 5.5.6-2. Experimental setup.

The principle of the experimental set-up is shown in Figure 5.5.6-2. Inpractice, it is, however, necessary tolock the laser frequency to the hyper-fine structure of rubidium. An ex-panded beam and buffer gas are usedin the set-up to reduce transit-time andwall-collision broadening and a cur-rent coil is applied to lift the Zeeman-degeneracy. The RF-oscillator fre-quency has been successfully lockedto a 6 kHz wide CPT resonance usingthe magnetic sublevels mF = 0.Evaluation of the frequency stabilityof the system is being carried out.

46

6 INTERNATIONAL CO-OPERATION

6.1 International Comparison Measurements

CCPR-K1.a International comparison of spectral irradiance

The comparison is on spectral irradiance measurements of tungsten lamps in thewavelength region from 250 nm to 2500 nm. HUT participates in the wave-length region 290 – 900 nm. The first part of the measurements for this com-parison were carried out by HUT in 2000.

CCPR-K2.b International comparison of spectral responsivity in the visibleregion

The comparison is on spectral responsivity measurements of trap detectors andphotodiodes in the wavelength region from 300 nm to 1000 nm. The measure-ments for this comparison were carried out by HUT in 2000.

CCPR-K6 International comparison of regular spectral transmittance

The comparison is on spectral regular transmittance measurements in thewavelength region from 380 nm to 1000 nm. The measurements for this com-parison were carried out by HUT in 2000.

CCPR-S2 International comparison of aperture area measurements

The measurements for this comparison were carried out by HUT in 2000.

Bilateral comparison of spectral irradiance with NIST, USA

The spectral irradiance scales of NIST and HUT were compared in the 290 –900 nm region. The comparison indicates an agreement within the uncertaintiesof about 1 %, except below 350 nm wavelength, where the discrepancies (3 – 2%) are slightly higher than the uncertainty of the comparison.

Bilateral comparison of illuminance responsivity with NIST, USA

The illuminance scales of NIST and HUT were compared. The comparison in-dicates an excellent agreement [0,08 % ± 0,5 % (k = 2)] within the uncertaintyof the realisations of the units.

47

Bilateral comparison of luminous flux with NIST, USA

The new luminous flux scale of HUT was compared with the scale of NIST.The comparison indicates an excellent agreement [0,06 % ± 0,9 % (k = 2)]within the uncertainty of the realisations of the units.

Bilateral comparison of spectral responsivity with IFA-CSIC, Spain

The spectral responsivity scales of IFA-CSIC and HUT were compared in thewavelength region from 260 nm to 400 nm. The comparison indicates anagreement within the uncertainty of the comparison.

Bilateral comparison of optical frequencies of diode lasers with ISI Brno,Czech Republic

Optical frequencies of diode lasers were compared at the HUT in 2000. Due toinstability of one of the lasers, the results were inconclusive.

Improving the accuracy of ultraviolet radiation measurement

In this project funded by the SMT-programme of the EU, novel filter radiometertechniques developed by HUT are used to compare various ultraviolet calibra-tion facilities in France (BNM), Finland and UK (NPL). HUT acts as the pilotlaboratory in the comparison and measured during 1999 – 2000 all filter radi-ometers twice, before and after the measurements by other participants. Ac-cording to the preliminary results, measurements of HUT are in agreement withNPL and BNM.

International comparison of fibre Bragg grating group delay (COST-project)

A comparison was carried out for measurements of group delay, bandwidth andrelative transmittance for a fibre Bragg grating with several European partici-pants. The results are not yet available.

6.2 Thematic Networks

6.2.1 Thematic network for ultraviolet measurements

The Thematic Network for Ultraviolet Measurements is a three-year project(SMT4-CT97-7510) funded by the Standards, Measurements and Testing

48

(SMT) programme of the European Union (EU). The network is co-ordinated bythe Helsinki University of Technology (HUT). It started its operation on No-vember 15, 1997, and the official Commission-funded part ended on November14, 2000.

The Thematic Network is aimed to enhance exchange of results and ideas be-tween research laboratories and industry and also to obtain a better understand-ing of the problems associated with the calibration and testing work. The net-work has 51 participants from 13 European countries. In addition, there are nu-merous additional members also outside the Europe. The participants includee.g. small industrial companies, national standards laboratories, and researchorganisations working with ozone research and measurements related with oc-cupational health.

During its three years of operation, the network arranged a series of four work-shops. In year 2000, the fourth workshop was arranged at the Swedish NationalTesting and Research Institute (SP) in Sweden, and the second training coursewas arranged in Austria.

The network publishes a newsletter, UVNews, which is edited by the HUT. UV-News contains mainly information about the past and forthcoming events of thenetwork. In year 2000, three issues were printed in March, October and Novem-ber. The extra issue of November contains final reports of the working groupswithin the network. All issues of UVNews and reports to Commission are avail-able in the web-pages (http://metrology.hut.fi/uvnet/) of the Network.

6.2.2 Fibre Optics Technology Network

HUT is a member in the Fibre Optics Technology Network -(FOToN)- (SMT4-CT98-7523) co-ordinated by the National Physical Laboratory (NPL) in UnitedKingdom. FOToN is an interactive information network for the optical fibre us-ers community. It is sponsored by the European Commission under the Stan-dards Measurement and Testing Programme.

The three-year project was launched in November 1998 and it co-ordinates thework of thirteen Regional Groups. Hanne Ludvigsen acts as the regional co-ordinator of the Finnish participants in the network. The Regional Groups areresponsible for identifying common issues and concerns relating to fibre indus-try and for co-ordinating collaborative research. They also provide a nationalforum for the transfer of technology relating to standardisation issues.

49

The FOToN network is preparing web pages for the promotion of regionalgroup activities and to provide an interactive source of information on fibre op-tics.

In year 2000, two regional FOToN meetings were arranged in Finland. The firstmeeting was held in the spring at HUT and the second meeting in the autumn atNK Cables in Vantaa. The 4th regional meeting will be held in connection withthe Optics Days 2001 in Tampere. On national level the activity has been or-ganised within an Optical Fibre Measurement Club (OFMeC) which currentlyhas 39 members.

6.3 Conferences and Meetings

The personnel participated in the following conferences and meetings:

Euromet Consultative Committee/Rapporteur Meeting, Bern, Switzerland,January 12 – 13, 2000; Erkki Ikonen

Optical Fiber Communication Conference (OFC’2000), Baltimore, Maryland,USA, March 5 – 10, 2000; Tapio Niemi

XXXIIII Annual Conference of the Finnish Physical Society, Espoo, Finland,March 9 – 11, 2000; Miika Heiliö, Erkki Ikonen, Aki Kasvi, Petri Kärhä, Kris-tian Lahti, Thomas Lindvall, Ilkka Tittonen, Maria Uusimaa, Eero Vahala, andPekka Wallin

FOToN – 2nd Regional Meeting, Otaniemi, Finland, March 22, 2000; HanneLudvigsen and Tapio Niemi

Third International Conference on Modeling and Simulation of Microsystems,San Diego, USA, March 27 – 29, 2000; Tuomas Lamminmäki and KaiusRuokonen

POLAR kick off meeting, Tampere, Finland, March 30, 2000; Hanne Ludvigsen

EUROMET Contact Persons Meeting, Istanbul, Turkey, April 1 – 5, 2000;Erkki Ikonen and Petri Kärhä

Optics Expert Seminar, Helsinki, Finland, April 28, 2000; Hanne Ludvigsen

The Second Training Course on Ultraviolet Measurement, Innsbruck, Austria,May 4 – 5, 2000; Saulius Nevas

50

COST Action 265 – 3rd MC meeting, Gothenburg, Sweden, May 8 – 9, 2000;Hanne Ludvigsen

FOToN – 2nd MC meeting, Gothenburg, Sweden, May 10, 2000; Hanne Ludvig-sen

EU-project working group meeting, Berlin, Germany, May 13 – 17, 2000;Toomas Kübarsepp and Petri Kärhä

Conference on Precision Electromagnetic Measurements CPEM’00, Sydney,Australia, May 14 – 19, 2000; Mikko Merimaa and Goëry Genty

CCPR KC WG/RMO Meeting, London, United Kingdom, June 4 – 6, 2000;Erkki Ikonen

Northern Optics 2000, Uppsala, Sweden, June 6 – 8, 2000; Ilkka Tittonen, MiikaHeiliö, Jari Hovila, Aki Kasvi, Ossi Kimmelma, Kristian Lahti, Mikko Merimaa,Saulius Nevas, Tapio Niemi, Eero Vahala, and Maria Uusimaa

POLAR meeting, Tampere, Finland, June 12, 2000; Hanne Ludvigsen

EUROMET Committee Meeting, Istanbul, Turkey, June 13 – 16, 2000; ErkkiIkonen

Tag der Physik und Zehn Jahre Quantenoptik an der Universität Konstanz, July6 – 12, 2000; Ilkka Tittonen

EU-project working group meeting, Borås, Sweden, September 5, 2000;Toomas Kübarsepp and Petri Kärhä

3rd international workshop on detector-based UV radiometry (EUROMET proj-ect 437), Borås, Sweden, September 6, 2000; Erkki Ikonen, Toomas Kübarsepp,and Petri Kärhä

Fourth Workshop of the Thematic Network for UV Measurements, Borås, Swe-den, September 6 – 8, 2000; Erkki Ikonen, Toomas Kübarsepp, and Petri Kärhä

2000 Conference on Lasers and Electro-optics Europe, CLEO, Nice, France,September 10 – 15, 2000; Tapio Niemi, Thomas Lindvall, and Ilkka Tittonen

Symposium of Fiber Optic Measurements (SFOM’2000), Boulder, Colorado,USA, September 26 – 29, 2000; Tapio Niemi

51

Second Annual Seminar on Finnish Silicon Sampo, Helsinki, Finland, October2 – 3, 2000; Kaisa Nera and Ilkka Tittonen

FOToN – 3rd Regional Meeting, Vantaa, Finland, October 4, 2000; Hanne Lud-vigsen, Tapio Niemi, Goëry Genty, Petri Kärhä, and Erkki Ikonen

Baltic Electronics Conference BEC 2000, Tallinn, Estonia, October 8 – 11,2000; Toomas Kübarsepp

Conference on Quantum Optics, Mallorca, Spain, October 14 – 19, 2000; IlkkaTittonen

POLAR meeting, Tampere, Finland, October 20, 2000; Tapio Niemi

COST Action 265 - 4th MC Meeting, Bratislava, Slovac, October 23 – 24,2000; Hanne Ludvigsen

6.4 Visits by the Laboratory Personnel

Kaisa Nera to CNET, France Telecom, Paris, France, February 18, 2000

Personnel of the laboratory to Tallinn Technical University and KuberneetikaAS Ltd, Tallinn, Estonia, June 19 – 20, 2000

Petri Kärhä to NPL, London, United Kingdom, August 15, 2000

Toomas Kübarsepp to Nederlands Meetinsituut, Delft, The Netherlands, No-vember 20 – 22, 2000

Hanne Ludvigsen to COM, Lyngby, Denmark, November 20 – 22, 2000

6.5 Research Work Abroad

Farshid Manoocheri, National Institute of Standards and Technology (NIST),USA, August 1 – December 31, 2000

Goëry Genty, COM/Technical University of Denmark, Lyngby, Denmark, Oc-tober 24 – December 31, 2000

52

6.6 Guest Researchers

Sandrine Sigonneau, Ecole Supérieure d’Optique, Paris, France, June 1 –August 31, 2000

Mr. Ondrej Cip and Dr. Josef Lazar, Institute of Scientific Instruments, Brno,Czech, September 25 – October 7, 2000

6.7 Visits to the Laboratory

Mr. Malcolm White, National Physical Laboratory NPL, London, United King-dom, January 29 – February 1, 2000

Dr. Ulf Leonhardt, KTH Stockholm, Sweden, March 20 – 21, 2000

Mr. Otto Glatz, Coherent, Germany, May 2 – 5, 2000

Mr. Lars Holm, Gamma Optronik Ab, Uppsala, Sweden, May 2 – 5, 2000

Prof. David J. Richardson, Optoelectronics Research Centre, University ofSouthampton, United Kingdom, June 14, 2000

Dr. Peter Blattner, EAM, Switzerland, June 14 – 16, 2000

Dr. Howard Yoon, National Institute of Standards and Technology (NIST),Gaithersburg, USA, June 25 – July 1, 2000

Dr. Yoshi Ohno, National Institute of Standards and Technology (NIST), Opti-cal Technology Division, Gaithersburg, USA, June 29 – July 5, 2000

Dr. Angus Bell, (MicroLase) Coherent, Scotland, July 24 – 28, 2000 and Sep-tember 14 – 17, 2000

Mr. Mart Noorma, University of Tartu, Department of Physics, August 17, 2000

Dr. Olev Saks, Dr. Ivo Leito, and M.Sc. Viljar Pihl, University of Tartu, De-partment of Physics and Chemistry, August 24, 2000

Dr. Xu Gan, Singapore Productivity and Standards Board, Singapore, Septem-ber 8 – 11, 2000

53

7 PUBLICATIONS

7.1 Articles in International Journals

P. Kärhä, T. Kübarsepp, F. Manoocheri, P. Toivanen, E. Ikonen, R. Visuri, L.Ylianttila, and K. Jokela, “Portable detector-based primary scale of spectral ir-radiance,” J. Geophys. Res. 105, 4803-4807 (2000).

K. Jokela, L. Ylianttila, R. Visuri, P. Kärhä, and E. Ikonen, “Intercomparison oflamp and detector-based UV-irradiance scales for solar UV radiometry,” J.Geophys. Res. 105, 4821-4827 (2000).

T. Kübarsepp, P. Kärhä, and E. Ikonen, “Interpolation of the spectral responsiv-ity of silicon photodetectors in the near ultraviolet,” Appl. Opt. 39, 9-15 (2000).

M. Merimaa, H. Talvitie, P. Laakkonen, M. Kuittinen, I. Tittonen, and E.Ikonen, “Compact external-cavity diode laser with a novel transmission geome-try,” Opt. Comm. 174, 175-180 (2000).

M. Merimaa, H. Talvitie, I. Tittonen, P. Laakkonen, M. Kuittinen, and E.Ikonen, “Compact external-cavity diode laser at 633 nm with a transmissiongrating,” Trends in Optics and Photonics Series (TOPS), reprinted from pro-ceedings of Topical Meeting on Advanced Semiconductor Lasers and Their Ap-plications '99 31, 56-57 (2000).

A. Zarka, A. Abou-Zeid, D. Chagniot, J.-M. Chartier, J.-F. Cliché, O. Cip, C.Edwards, F. Imkenberg, P. Jedlicka, B. Kabel, A. Lassila, J. Lazar, Y. Milleri-oux, M. Merimaa, H. Simonsen, M. Tetu, and J.-P. Wallerand, “Internationalcomparison of eight semiconductor lasers stabilized on 127I2 at λ=633nm,” Me-trologia 37, 329-339 (2000).

G. Genty, A. Gröhn, H. Talvitie, M. Kaivola, and H. Ludvigsen, “Analysis ofthe linewidth of a grating-feedback GaAlAs laser,” IEEE Journal of QuantumElectronics 36, 1193-1198 (2000).

P. Toivanen, P. Kärhä, F. Manoocheri, and E. Ikonen, “Realization of the unit ofluminous intensity at HUT,” Metrologia 37, 131-140 (2000).

P. Toivanen, J. Hovila, P. Kärhä, and E. Ikonen, “Realizations of the units ofluminance and spectral radiance at HUT,” Metrologia 37, 527-530 (2000).

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K. Lahti, J. Hovila, P. Toivanen, E. Vahala, I. Tittonen, and E. Ikonen, “Reali-zation of the luminous flux unit using a LED scanner for the absolute integrat-ing sphere method,” Metrologia 37, 595-598 (2000).

K. D. Stock, K.-H. Raatz, P. Sperfeld, J. Metzdorf, T. Kübarsepp, P. Kärhä, E.Ikonen, and L. Liedquist, “Detector-stabilized FEL lamps as transfer standardsin an international comparison of spectral irradiance,” Metrologia 37, 441-444(2000).

T. Kübarsepp, P. Kärhä, F. Manoocheri, S. Nevas, L. Ylianttila, and E. Ikonen,“Spectral irradiance measurements of tungsten lamps with filter radiometers inthe spectral range 290 nm to 900 nm,” Metrologia 37, 305-312 (2000).

A. Lassila, K. Riski, J. Hu, T. Ahola, S. Naicheng, L. Chengyang, P. Balling, J.Blabla, L. Abramova, Yu.G. Zakharenko, V.L. Fedorin, A. Chartier, and J.-M.Chartier, “International comparison of He-Ne lasers stabilized with 127I2 atλ=633 nm,” Metrologia 37, 701-707 (2000).

M. Merimaa, P. Kokkonen, K. Nyholm, and E. Ikonen, “A portable laser fre-quency standard at 633 nm with a compact external-cavity diode laser,” Me-trologia (in press).

T. Niemi, M. Uusimaa, S. Tammela, P. Heimala, T. Kajava, M. Kaivola, and H.Ludvigsen, “Tunable silicon etalon for simultaneous spectral filtering andwavelength monitoring of a DWDM transmitter,” Photon. Technol. Lett. (inpress).

7.2 International Conference Proceedings

T. Niemi, M. Uusimaa, S. Tammela, P. Heimala, T. Kajava, M. Kaivola, and H.Ludvigsen, “Simultaneous spectral filtering and wavelength monitoring of aDWDM transmitter using a tunable Fabry-Perot filter,” Optical Fiber Commu-nication Conference, OSA Technical Digest, Baltimore, Maryland, USA, March5 – 10, 2000, pp. 28-30 (talk).

T. Lamminmäki, K. Ruokonen, I. Tittonen, T. Mattila, O. Jaakkola, A. Oja, H.Seppä, P. Seppälä, and J. Kiihamäki, “Electromechanical analysis of microme-chanical SOI-fabricated RF resonators,” in Technical Proceedings of the ThirdInternational Conference on Modeling and Simulation of Microsystems, SanDiego, USA, March 27 – 29, 2000, pp. 217-220 (poster).

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K. Ruokonen, T. Lamminmäki, and I. Tittonen, “Solving of electromechanicalcoupled field problem with FEM,” in Third International Conference on Mod-eling and Simulation of Microsystems, San Diego, USA, March 27 – 29, 2000,Presentation T44.05 (poster).

M. Merimaa, P. Kokkonen, K. Nyholm, and E. Ikonen, “A compact iodine sta-bilized external-cavity diode laser at 633 nm with a novel transmission grating,”in Conference Digest, Conference on Precision Electromagnetic MeasurementsCPEM'00, Sydney, Australia, May 14 – 19, 2000, pp. 679-680 (talk).

G. Genty, M. Kaivola and, H. Ludvigsen, “Measurement of linewidth variationwithin one external cavity mode of a grating-cavity laser,” in Conference Di-gest, Conference on Precision Electromagnetic Measurements CPEM'00, Syd-ney, Australia, May 14 – 19, 2000, pp. 570-571 (poster).

T. Kübarsepp, “Physical basis for interpolation of the spectral responsivity ofSchottky barrier-based PtSi-nSi photodiodes,” EU-project working groupmeeting, Berlin, Germany, May 13 – 17, 2000 (talk).

M. Merimaa, H. Talvitie, P. Laakkonen, M. Kuittinen, I. Tittonen, and E.Ikonen, “Compact external-cavity diode laser at 633 nm with a transmissiongrating,” in Proceedings of the Northern Optics 2000, Uppsala, Sweden, June6 – 8, 2000, p. 50, OR8 (talk).

J. Hovila, K. Lahti, P. Toivanen, E. Vahala, I. Tittonen, and E. Ikonen, “Abso-lute measurement of luminous flux,” in Proceedings of the Northern Optics2000, Uppsala, Sweden, June 6 – 8, 2000, p. 116, PO48 (poster).

T. Kübarsepp, P. Kärhä, F. Manoocheri, S. Nevas, P. Toivanen, and E. Ikonen,“Compact facility for High-accuracy measurements of spectral irradiance in theUV-VIS-NIR region,” in Proceedings of the Northern Optics 2000, Uppsala,Sweden, June 6 – 8, 2000, p. 141, PO73 (poster).

K. Lahti, M. Heiliö, E. Vahala, A. Kasvi, and I. Tittonen, “Laser frequency sta-bilization using a phase modulation scheme,” in Proceedings of the NorthernOptics 2000, Uppsala, Sweden, June 6 – 8, 2000, p. 143, PO75 (poster).

K. Lahti, E. Vahala, and I. Tittonen, “Matrix based method for determination ofgaussian beam parameters,” in Proceedings of the Northern Optics 2000,Uppsala, Sweden, June 6 – 8, 2000, p. 144, PO76 (poster).

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S. Nevas, F. Manoocheri, and E. Ikonen, “Measurement of spectral diffuse re-flectance based on an integrating sphere and a high-accuracy spectrometer,” inProceedings of the Northern Optics 2000, Uppsala, Sweden, June 6 – 8, 2000,p. 162, PO94 (poster).

T. Niemi, M. Uusimaa, G. Genty, and H. Ludvigsen, “Characterization of densegroup delay ripple using phase shift method: effect of modulation frequency,”in Proceedings of the Northern Optics 2000, Uppsala, Sweden, June 6 – 8,2000, p. 163, PO95 (poster).

M. Uusimaa, T. Niemi, S. Tammela, and H. Ludvigsen, “A tunable micro-filterfor simultaneous wavelength monitoring and spectral filtering of a DWDMtransmitter,” in Proceedings of the Northern Optics 2000, Uppsala, Sweden,June 6 – 8, 2000, p. 199, PO131 (poster).

T. Veijola, T. Mattila, O. Jaakkola, J. Kiihamäki, T. Lamminmäki, A. Oja, K.Ruokonen, H. Seppä, P. Seppälä, and I. Tittonen, “Large-displacement model-ling and simulation of micromechanical electrostatically driven resonators usingthe harmonic balance method,” in Proceedings of IMS 2000, Boston, USA, June11 – 16, 2000, pp. 99-102 (talk).

K. Ylä-Jarkko, S. Tammela, T. Niemi, and A. Tervonen, “Scalability of a met-ropolitan multifiber bidirectional WDM-ring network,” in 26th European Con-ference on Optical Communication (ECOC 00), Munich, Germany, September4 – 7, 2000, pp. 81-82 (talk).

T. Niemi, T. Laukkanen, S. Tammela, and H. Ludvigsen, “Wavelength moni-toring of multi-channel DWDM-systems using a single temperature-tunable Fa-bry-Perot filter,” in Proceedings of Conference on Lasers and Electro-OpticsEurope, Nice, France, September 10 – 15, 2000, paper CTuP4, p. 164 (talk).

T. Niemi, M. Uusimaa, and H. Ludvigsen, “Measurements of dense group de-lay ripple using the phase shift method: Effect of modulation frequency,” inTechnical Digest of Symposium of Optical Fiber Measurements 2000, Boulder,Colorado, USA, September 26 – 29, 2000, pp. 165-167 (talk).

T. Kübarsepp and U. Veismann, “Stability monitoring of radiometric standardlamp using solar blind phototube,” in Proceedings of Baltic Electronics Confer-ence BEC 2000, Tallinn, Estonia, October 8 – 11, 2000, pp. 281-284 (poster).

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7.3 National Conference Proceedings

M. Uusimaa, T. Niemi, S. Tammela, and H. Ludvigsen, “Temperature-tunablemicro-filter for spectral filtering of a DWDM transmitter,” in Proceedings of theXXXIV Annual Conference of the Finnish Physical Society, Report TKK-F-A797, Espoo 2000, paper 2.3 (talk).

K. Lahti, E. Vahala, M. Heiliö, A. Kasvi, and I. Tittonen, “Digital laser fre-quency stabilisation using a High-Q optical resonator as a reference,” in Pro-ceedings of the XXXIV Annual Conference of the Finnish Physical Society, Re-port TKK-F-A797, Espoo 2000, paper 2.4 (talk).

K. Nyholm, T. Ahola, J. Hu, and E. Ikonen, “Stabilization and frequency meas-urements of green He-Ne lasers,” in Proceedings of the XXXIV Annual Confer-ence of the Finnish Physical Society, Report TKK-F-A797, Espoo 2000, paper2.14 (poster).

P. Seppälä, O. Jaakkola, J. Karttunen, J. Kiihamäki, T. Lamminmäki, T. Mattila,A. Oja, K. Ruokonen, and H. Seppä, “Micromechanical resonators: Fabricationand characterization,” in Proceedings of the XXXIV Annual Conference of theFinnish Physical Society, Report TKK-F-A797, Espoo 2000, paper 5.20(poster).

7.4 Other Publications

I. Tittonen (editor), Annual report 1999, Metrology Research Institute, HelsinkiUniversity of Technology, Espoo 2000, Metrology Research Institute Report16/2000, 65 p.

P. Kärhä (editor in chief), UVNews, The official newsletter of the ThematicNetwork for Ultraviolet Measurements, Issue 4, Espoo 2000, 43 p.

P. Toivanen, Detector based realisation of units of photometric and radiometricquantities, Metrology Research Institute, Helsinki University of Technology,Espoo 2000, Metrology Research Institute Report 17/2000, 100 p.

A. Pietiläinen and M. Merimaa, Mittaustekniikan perusteiden laboratoriotyöt,7th edition, Espoo 2000, 108 p. (in Finnish).


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T. Niemi, M. Söderlund, and K. Ylä-Jarkko, “Uusien optisten WDM-verkkojenmittaukset,” Prosessori 2/2000, pp. 53-56. (in Finnish).

HELSINKI UNIVERSITY OF TECHNOLOGY METROLOGY RESEARCH

INSTITUTE REPORT SERIES

HUT-MRI-R8/1996 A. Pietiläinen, H. Ludvigsen, H. Talvitie and E. Ikonen,

Observation of coherent transient effects in a magneto-optical trap.

HUT-MRI-R9/1997 H. Nyberg and H. Ludvigsen (editors),

Annual report 1996.

HUT-MRI-R10/1997 A. Pietiläinen, M. Kujala, and E. Ikonen,

Investigation of trapped rubidium atoms through frequency-modulation-

induced coherent transient effects.

HUT-MRI-R11/1998 I. Tittonen (editor),

Annual report 1997.

HUT-MRI-R12/1998 P. Toivanen, A. Lassila, F. Manoocheri, P. Kärhä and E. Ikonen,

A new method for characterization of filter radiometers. 1998


Annual report 1998.

HUT-MRI-R14/1999 T. Kübarsepp, P. Kärhä, F. Manoocheri, S. Nevas, L. Ylianttila and E. Ikonen,

Absolute spectral irradiance measurements of quartz-halogen tungsten lamps

in the spectral range 290-900 nm.

HUT-MRI-R15/1999 T. Kübarsepp,

Optical radiometry using silicon photodetectors.


Annual report 1999.

HUT-MRI-R17/2000 P. Toivanen,

Detector based realisation of units of photometric and radiometric quantities.

ISSN 1237-3281

Picaset Oy, Helsinki 2001

annual report 2000 · koskenvuori, mika, student research assistant 451 2184...

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