Photodetectors and Photoemitters laboratory work Photonics Laboratory

Master in Photonics

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PHOTOEMITTERS AND PHOTODETCTORS

Profs: Crina Cojocaru, Josep Trull

Departament de Fsica i Eng. Nuclear Universitat Politcnica de Catalunya

e-mails: crina.maria.cojocaru@upc.edu

jose.francisco.trull@upc.edu 1. General objective It is well known that photoemitters and photodetectors are among the most basic components or devices in photonics. They are involved directly or indirectly in any photonic system or experimental set-up in this field, since light needs first to be generated, and then needs to be detected. These components usually work independently one from each other, but they can also be combined to built simple compact devices (like for instance, combining one photoemitter with one photodetector) which can be useful for specific functions or applications. An overview over the most important characteristics of the main types of phottoemitters and photodetectors is given in the core course Introduction to Photonicsgiven by Prof. R. Vilaseca. We recommend reading and/or refreshing the chapters related with the photoemitters and photodetectors before the laboratory session. We include also the corresponding slides of this course as annex in this guideline.

The aim of this laboratory work is to experimentally study the main characteristics of different types of phottoemitters (first session) and photodetectors (second session) in order to evidence their physical characteristics and to gain practice in their use. In the second session, the student will also operate several simple photonic devices that combine photoemitters and photodetectors and their applications as sensors.

The students forming each working group will have at their disposal different photoemitters, photodetectors as well as all the additional material necessary for their characterization. In what follows, we list some of the studies and measurements that have to be done, but the students team has some degrees of freedom to select the manipulations and observations that they will prefer or need for a particular application. This degree of freedom applies also to the report that you have to make at the end of the session. This report has to reflect in a free format all the aspects of the work developed in the lab. At the end we will appreciate if you give your opinion on the experiments and improvement suggestions for the next year.

Photodetectors and Photoemitters laboratory work Photonics Laboratory

Master in Photonics

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Part 1: PHOTOEMITTERS

1. Equipment

The student will dispose of simple components of the main classes of photoemitters. Going from broadband emission to progressively more monochromatic emission, these classes are:

Thermal radiators: traditional tungsten light bulbs and a halogen lamp with variable intensity.

Fluorescent lamps: electrical-discharge lamps with fluorescent painting and different compact fluorescent lamps.

LEDs: with emission in infrared (IR), visible (red, yellow, green and blue), white, and multicolour.

Electrical-discharge lamps: mercury, neon, helium, water vapour, etc. Lasers: Low-power diode laser, He-Ne laser.

Complementary equipment: Fiber optic spectrometer system (AvaSpec Avantes) optical bench and related optical and mechanical elements, stabilized-voltage power supply optical filters.

3.- Observations and experiments to perform.

We list below the main classes of experiments and observations that can be performed with the available equipment. The students team should try to compare their observations within each class of photoemitters with the expected behaviour known from the working principle. Nevertheless, if the students team prefers to focus more deeply in a few classes, they could do it. The main observations regard the spectral features of different class of photoemitters. The optical fiber spectrometer (AVASPEC 2048) and the corresponding software allow recording the optical spectra between 200 and 1100nm (UV/VIS/IR). The spectra and the relative intensities as a function of wavelength can be analyzed on the computer screen. The user manual of the spectrometer and of the software will be available in the lab. You can find the main features and information about how to record a spectrum in annex 1. The irradiance set-up is very simple and it is schematically shown below:

Photodetectors and Photoemitters laboratory work Photonics Laboratory

Master in Photonics

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The different light sources have to be placed in front of the collector of the optical fiber and the spectra are recorded on the computer screen. Special attention has to be paid to the saturation of the detector. A kit of neutral density optical filters is available for the intensity adjustment.

The students have to make the following observation and measurements:

Incandescent bulb: o analysis of the spectra

Halogen lamp: o analysis of the spectra; o study of the displacement of the maximum intensity wavelength and of the

broadening of the emission band when the temperature increases. Electrical-discharge lamps:

o Spectra analysis and comparison of different type of fluorescent lamps (with and without fluorescent painting) and different compact fluorescent lamps.

o Are there similitudes with the spectra of the mercury lamp? LEDs:

o measurement of the central wavelength and the spectral width of different LED (violet, blue, green, yellow, red, infrared). Are they monochromatic?

o Analysis of the spectra of the white led. Possible explanation? Lasers:

o Measurement of the central wavelength and of the spectral width of laser diodes, He-Ne laser and a green pointer. Discussion about the monocromacity. Comparison with LEDs.

Photodetectors and Photoemitters laboratory work Photonics Laboratory

Master in Photonics

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After all these measurements, general comments may be done:

Qualitative (or semi-quantitative) comparison between the dominant wavelengths and measurement of the widths of the corresponding spectral domains.

Comparison of the experimental observations and theory for each type of photoemitter. Comments!

Observation of the reduction and displacement in the emission band when going from broadband emitters such as filament lamps (working at different colour temperatures) to monochromatic emitters such as lasers. The measurements of the wavelength may be done with very good precision using the spectrometer.

Study of colour and interferential filters. Place different filters (neutral density, coloured filters, interferential filters) in front of the halogen lamp and observe the spectra of the light that pass trough it. Discuss different types of applications when these kinds of filters may be required.

4.- Bibliography.

The students can make use of the bibliography and class notes they used for courses on Photonics Technology, Photonics Devices, Introduction to Photonics, etc. For instance: - Fundamentals of Photonics, B. E.A. Saleh and M.C. Teich (Wiley, 2nd ed. 2007).

- Optoelectronics, E. Uiga (Prentice Hall, 1995).

Photodetectors and Photoemitters laboratory work Photonics Laboratory

Master in Photonics

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ANNEX 1: AVASPEC SPECTROMETER

Photodetectors and Photoemitters laboratory work Photonics Laboratory

Master in Photonics

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ANNEX 2: EMMITERS CHARACTERISTICS