obtención, caracterización y aplicaciones de dispositivos ópticos basados en nanoestructuras de...

Obtención, caracterización y aplicaciones de dispositivos ópticos

basados en nanoestructuras de silicio.

PhD Thesis Defense

Daniel Navarro Urrios

Realisation, characterisation and applications of optical devices based on silicon nanostructures.

Dpto. de Física Básica, Universidad de La LagunaDpto. de Física Básica, Universidad de La Laguna

PhD thesis defense, La Laguna, 5-12-2006 Daniel Navarro Urrios 2/60

Outline

• General Introduction

• Amplification studies in planar waveguides based on oxidised porous silicon

• Form birefringence in Si-Nc planar waveguides

• Er coupled to Si-Nc optical amplifiers

• General conclusions


Outline







General introduction

• Silicon is the leading material for microelectronics. Huge processing technology (CMOS) infrastructure, process learning and capacity.

• In photonics it can do also well (waveguides, fast modulators, power splitters and combiners, tuneable optical filters, detectors…)

• It is the ideal plattform for integrating optical and electrical devices.


General introduction

• However Silicon is NOT an efficient light emitter, internal quantum efficiencies int~10-6

Indirect band-gap

Need for an optical amplifier and a signal

generator (laser)

based on Silicon


Different strategies to amplify light based on Silicon materials

• Dye-doped planar waveguides based on oxidised porous silicon

• Si-Nc in SiO2 planar waveguides

• Er coupled to Si-Nc planar amplifiers


Outline







Porous silicon formation

I

HF

Si

time

I

Pore dimension

2 ... 50 nm

It is luminiscent (quantum confinement)But hard to realise population

inversion

Effective refractive index (air + silicon)High absorption in the visible


Effect of thermal oxidationEffect of thermal oxidation

PartialoxidationT > 400ºC

Naturaloxidation

Silicon

SiO2

CompleteoxidationT > 800ºC

Porous silica

DensificationT > 1000ºC

(many hours)

Bulk silica

Consequences:

• It becomes transparent for the visible

• It becomes a passive material

• Porous structure maintained good for impregnation

• We have still control of the refractive index (1.15<n<1.40)

•Low refractive indices (n1.15), close to air good cladding material for building waveguides


Planar waveguides

Silicon (n=3.5)

Core (Porous silicon, less porous, n1.8)

Cladding (Porous silicon, more porous, n1.35)

Core (Porous silica, less porous, n1.3)

Cladding (Porous silica, more porous, n1.15)

Silicon (n=3.5)

After oxidation (900ºC, 3h)

Cut this way:

Cladding (Porous silicon, n1.35)

Silicon (n=3.5)

Cladding (Porous silica, n1.15)

Silicon (n=3.5)

After oxidation (900ºC, 3h)

Core (PMMA-polymethylmethacrylate-,n1.49)

1) Oxidised porous silicon waveguides 2) Polymeric waveguides with oxidized porous silicon cladding

Two types

PSW PMW

core

cladding

Si substrate


1.12 1.16 1.20 1.24 1.28 1.32 1.36 1.403

4

5

Inte

nsity

in t

he d

etec

tor

(a.u

.)

effective refractive index

Detector

nm

m-line characterisation

We can excite each of the modes supported by the

planar waveguide

Knowledge of the effective refractive indices of the supported modes


0 2000 4000 6000 8000 10000 12000

1.0

1.2

1.4

drift=1.3%

n mat

thickness (nm)

no

ne

1.2391.255

1.15

0.5

1.0

TM exp TM sim

Nor

mal

ised

inte

nsity

1.15 1.20 1.25 1.30

0.3

0.6

0.9

1.2

TEexp TE sim

neff

Nice agreement between experiments and simulations

Modelling the waveguides parametersModelling the waveguides parameters


Single-mode waveguides (Single-mode waveguides (==633nm))

1.15 1.20 1.25 1.30 1.35 1.40 1.45 1.50

2

3

TE TM

Ref

lect

ance

(a

.u.)

Effective refractive index

Core (500nm)

Cladding (5-10m)

Silicon substrate

1) PSW

1.15 1.20 1.25 1.30 1.35 1.40 1.45 1.500.6

0.8

1.0

1.2

Effective refractive index

Ref

lect

ance

(a.u

) TE TMCore (400nm)

Cladding (5-10m)

Silicon substrate

2) PMW

TE 50%

TE 70%


Dye impregnation (Nile Blue-LC 6900)

Chosen because it is quite robust when dried.Impregnation:PSW: 5 min inmersion of the waveguides in ethanol+dye solutionPLW: Precursor PMMA solution

mixed with the dye

500 550 600 650 700 750 800

0.0

0.4

0.8

1.2

Absorption from literature Normal PL

Inte

nsi

ty (

a.u

.)

Wavelength (nm)

500 550 600 650 700 750 800

0.0

0.4

0.8

1.2


Inte

nsi

ty (

a.u

.)

Wavelength (nm)

Pulsed pump at 532nm


Experimental setupExperimental setup

DoubledNd:YAG

(532 nm, 5ns pulses)

Cylindrical lens

To monochromator and PMT

Sample

Guided PL setup

if there is gain, the PL shape should narrow and grow superlinearly with power

Spot size:~3cm 300m

10 cm

lens


Guided PL vs Pump Power

620 640 660 680 700 720 740 760 780 800

10-8

10-7

10-6

10-5

10-4

10-3

10-2

2700 J

30 J

Gui

ded

PL

Wavelength (nm)

10 100 100010-7

10-5

10-3

10-1

694nm 676nm

Gui

ded

PL

Pulse Energy (J)

b=9.2

b=1

10 100 100010-7

10-5

10-3

10-1

676nm

Gui

ded

PL

Pulse Energy (J)

10 100 1000

10-6

10-5

10-4

10-3

10-2

Gui

ded

PL

Pulse energy (J)

700 nm 650 nm

b=1.06

b=6.6

b=2.1

10 100 1000

10-6

10-5

10-4

10-3

10-2

Gui

ded

PL

Pulse energy (J)

650 nm

1) PSW

620 640 660 680 700 720 740 760 780 800

10-7

10-6

10-5

10-4

10-3

10-2

10-1

Gui

ded

PL

Wavelength (nm)

2250J

56J

2) PMW

bI a


Variable Stripe Length (VSL)Variable Stripe Length (VSL)

L

1exp1

)( gLg

LI ASE

Amplified SpontaneousEmission (ASE)

g depends on power!And passes from negative to positive values

by increasing the pump flux


Guided PL vs Pump Power

0 1 2 3 4 510-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

VS

L in

tens

ity (

arb.

uni

ts)

Illumination length (mm)

2700J 20J g=8.7 cm-1

g= -10 cm-1

At 700 nm

1) PSW 2) PMW

0 1 2 3 4 510-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

Illumination length (mm)V

SL

inte

nsity

(ar

b. u

nits

)

3000J50J

g= +13cm-1

g= -25cm-1

At 694nm

Net optical gain has been observed in both cases


Further studies on the impregnation of PSW

550 600 650 700 750

0

500

1000

1500

2000

2500

Inte

nsity

(a.

u)

Wavelength (nm)

Guided PL

550 600 650 700 750

0

500

1000

1500

2000

2500

Inte

nsity

(a.

u)

Wavelength (nm)

Guided PL Air TE Air TM

Optical Fiber

This signal is not travelling through the waveguide because putting a screen it disappears.

Interferences

N.A.<0.025

550 600 650 700 750

0.0

0.4

0.8

1.2


Inte

nsi

ty (

a.u

.)

Wavelength (nm)

Observation of narrow and linearly polarised spectral peaks

2

1

0

z1

z2

Incoherent emitters. Each emitter point can interfere only with itself.

Collecting the light at 90º


0 2 4 6 8 10 12 14

1.0

1.1

1.2

1.3

n mat

thickness (m)

no

ne

0.20.40.60.81.0

TM exp TM sim

Nor

mal

ised

inte

nsity

1.10 1.15 1.20 1.25

0.20.40.60.81.0

TEexp TE sim

neff

600 650 700 750 800

0.0

0.2

0.4

0.6

0.8

1.0

Experimental Simulation

Wavelength (nm)

Nor

mal

ised

Inte

nsity

600 650 700 750 800

0.0

0.2

0.4

0.6

0.8

1.0

No

rma

lise

d In

ten

sity

(a

.u.)

Wavelength (nm)

Simulation Measurement

0 2 4 6 8 10 12 14 16

0

4

8

12

16

n

z

m

z (m)

sample thickness

600 650 700 750 800

0.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ised

Inte

nsity

(a.

u.)

Wavelength (nm)

Simulation Measurement

z

Silicon

The first 200-300 nanometers are emitting much stronger


550 600 650 700 750

103

104

105

Inte

nsity

(co

unts

)

Wavelength (nm)

1E-4M 1E-5M 1E-6M

Possible explanations Could it be that the pump is being strongly attenuated

through the structure? The contrast of the interferences is independent of the pumping

wavelength.

Also losses would be more than 105cm-1

The concentration of dye in the first hundreds of nanometers is orders of magnitude higher than

in the rest of the sample

NO

Decreasingconcentration

No dramatic reduction of the contrast


In this kind of samples we have observed In this kind of samples we have observed net gainnet gain in in the guided configuration. the guided configuration.

We believe that the main contribution to the gain is We believe that the main contribution to the gain is due due to these first hundreds of nanometersto these first hundreds of nanometers, because , because we have built micro and macro-cavities and no we have built micro and macro-cavities and no amplification behaviors with pump power were observed amplification behaviors with pump power were observed when detecting normal to the sample.when detecting normal to the sample.


Outline







Introduction

2

Courtesy of J. Linnros

Si nanocrystals usual fabrication techniques


Introduction

Usual growing techniques :

• Large size dispersion:

• Inhomogeneous broadening of the emission band

• Reduction of the stimulated emission efficiency (not all nanocrystals show optical gain).

Courtesy of B. Garrido


The studied samplesSiO2 substrate, alternating layers of SiO

and SiO2 are grown by evaporation.

After the annealing in N2 at 1100ºC for 1h monodispersed Si-nanocrystals are

formed in a waveguide configuration.

Investigation of the waveguiding properties of these samples

dSiO(nm) dSiO2(nm) dSiO/(dSiO+dSiO2)

Sample D 5 5 0.50

Sample C 4 5 0.44

Sample B 3 5 0.38

Sample A 2 5 0.29

1.2 1.4 1.6 1.8 2.0

0.0

0.2

0.4

0.6

0.8

1.0

1000 900 800 700 600

N

orm

aliz

ed P

L

sample D sample C sample B sample A

Energy (eV)

Energy width=0.22eV

Decreasing SiOsingle layer thickness

Wavelength (nm)

Optical gain under pulsed pumping has been demonstrated in these

samplesM. Cazzanelli, D. Navarro-Urrios, et al.

Journal of Applied Physics, 96, 3164 (2004).


M-line measurements (543nm-633nm)

We are able to know the effective index of each mode for each

wavelength measured

DetectorPrism

Sample

0.9

1.0

Inte

nsi

ty (

a. u

.)

nTE

=1.476

TE

nTM

=1.471

Sample C

TM

neff

1.45 1.50

0.9

1.0

nTE

=1.497

TE

1.45 1.50

nTM

=1.458

TM

543nm

633nm


Information extracted from m-line, TEM images and mode solver simulations

-Thicknesses and number of periods of the SL (TEM images)

-Dimension of each period (TEM images)

-Effective modal indices (m-line) Material refractive indices (simulations)


Information extracted from m-line, TEM images and mode solver simulations

It is impossible to fit the extracted effective indices unless we assume a negative

birrefringent structure.

The origin of the observed birrefringence is found on the particular structure of the core, i.e., a multilayer periodic structure made of two different kind of layers of

different refractive indexes.

SiOx

SiO2

Isotropic SL

Air

“Form Birefringence”

Material birefringence= (%) 100 e o

o

n n

n

no>ne


Modellization of the structureTheoretical model for a

superlattice

2 22 22 1w SiO SiO w NS NS

ot

N n d N n dn

d

22

2 22

11

t

w SiOe w NS

SiO NS

dN dn N d

n n

dSiO2+dNS=SL period

no and ne:ordinary and extraordinary refractive indices of the equivalent layer

Nw:number of Si-NC layers in the SL

dSiO2 (nSiO2) and dNS (nNS):thicknesses (refractive indexes) of the SiO2 and nanocrystal single layers of the SL

dt: total thickness of the SL

n1,d1

n2,d2

.

.

.

.

.

.

TE

TMk

no

ne

SiOx

SiO2

SL

Air

dNS, nNS ?


Results

2 22 22 1w SiO SiO w NS NS

ot

N n d N n dn

d

2

22 2

2

11

t

w SiOe w NS

SiO NS

dN dn N d

n n

0.0 0.2 0.4 0.6 0.8 1.0

1.50

1.55

1.60

1.65

1.70

1.75

1.80

1.85

no(simulated)

ne(simulated)

ne (from m-line) 1.6

nNS

1.8

Ma

teri

al r

efr

act

ive

ind

exe

s

Relative thickness (dNS

/dSiO2

+dNS

)

1.705n

o (from m-line)

Unique solution!!

0.63


ResultsWaveguide B Waveguide C Waveguide D

633 nm 543 nm 633 nm 543 nm 633 nm 543 nm

nTE 1.462±0.001 1.473±0.001 1.476±0.001 1.497±0.001 1.519±0.001 1.553±0.001

nTM 1.456±0.002 1.463±0.001 1.458±0.001 1.471±0.001 1.486±0.001 1.518±0.001

B 0.006±0.003 0.010±0.002 0.018±0.002 0.026±0.002 0.033±0.002 0.035±0.002

TE(%) 27 42 44 59 72 81

TM(%) 3 23 10 35 56 73

nSiOx 1.4755 1.4790 1.4755 1.4790 1.4755 1.4790

no 1.564±0.003 1.568±0.002 1.600±0.002 1.611±0.002 1.621±0.001 1.643±0.001

ne - 1.567±0.005 1.581±0.004 1.596±0.002 1.603±0.001 1.624±0.001

(%) - -0.5±0.5 -1.1±0.3 -1.0±0.3 -1.1±0.1 -1.1±0.1

dNS - 2.2±0.3nm 3.1±0.2 nm 3.3±0.1nm 4.4±0.1 nm 4.4±0.1 nm

Independent calculations…but the same dNS (independent of )

nNS(633nm)= 1.705 nNS(543nm)= 1.735


50nm

Ion implanted samples with random distributed nanocrystals gave

isotropic behaviorno=ne

Other studied samples

20 nm

Similar samples growed by sputtering technique

showed similar results

N. Daldosso et al., Journal of Luminescence, 121, 2, 2006


Other studied samplesAnother type of material birefringence have been also studied

Combination of m-line + transmission (linearly polarised light) measurements

Reactive Si deposition method + annealing 1100ºC for 1h

Vertical structures

x

y

z

no

ne

The Si-NC shape would be similar to the ellipsoid of indices

0 2000 4000

1.01.21.41.61.82.0

n mat

thickness (nm)

no

ne

0.5

1.0

TM exp TM sim

Nor

mal

ised

inte

nsity

1.4 1.5 1.6 1.7 1.8

0.5

1.0

TEexp TE sim

neff


Other studied samplesReactive Si deposition method + annealing 1100ºC for 1h

Non-perpendicular geometry between the Si beam axis

and the substrate

Si NC

nx

nz

ny

z

y

x

ne

no

x

y

z

We need TEM images for confirmation

10000 12500 15000 17500 200005060708090

Tra

nsm

issi

on (

%)

Energy (cm-1)

0 20 40 60 80 100

1275

1280

1285

1290

Polarization angle (º)

Sp

aci

ng

(cm

-1)

Transmissionmeasurements

0 2000 4000

1.2

1.6

2.0

n mat

thickness (nm)

no

ne

0.5

1.0

TM exp TM sim

Nor

mal

ised

inte

nsity

1.50 1.65 1.80 1.95

0.5

1.0

TEexp TE sim

neff

M-linemeasurements


Outline







We want to improve

Erbium (Er3+)

Usual EDFAsUsual EDFAs (Erbium doped Fiber Amplifier)(Erbium doped Fiber Amplifier)

absabs1010-21-21 cm cm22

Expensive pumping source Expensive pumping source

(resonant, intense and coupled)(resonant, intense and coupled)

by using

Si substrate

buffer S

iO 2

EDWA EDWA (Erbium doped Waveguide Amplifier)(Erbium doped Waveguide Amplifier)

By taking advantage of the couplingBy taking advantage of the coupling

between Si-Nc and Erbetween Si-Nc and Er3+ 3+ ionsions

Introduction

x x

x x

x

x

x

x

x

x

x x

x

x

x x

x x

x

x

x

x

x

x

x x

x

x

x x

x x

x

x

x

x

x

x

x x

x

x


Why Si-Nc?

Broad band absorption (UV-VIS)

Increment of excitation for Er3+ : exc from ~10-21 (in SiO2) to 10-16-10-18 cm2 (with Si-Nc)

Fast (~ 1s) and efficient (~55%) energy transfer from Si-nc to Er3+

Possibility of electrical pumping

Higher index contrast for light confinement

CMOS compatibility


( )exc excNC NC exc t exc ind Er

dN NN N k N C N

dt

Excitons:

NC NCexc

NC t ind Er

NN

k C N

Steady state:

Nexc

4I15/2

4I13/2

4I11/2, 4I9/2

Er3+

Introduction

Nexc : density of excitonsNNC: total density of Si-Nc NC: absorption cross section : intrinsic lifetime of the exciton kt: average coupling rate Cind: percentage of Er3+ coupled to Si-Nc

Exciton generation and strong Auger

Intrinsic recombination

Transfer to Er3+


22 21 d 1 up 2 1 2

d

NN + N - -C Nexc p abs s em s

dNKN N N

dt

221 up 2 1 2

d

NN - -C Nexc p abs s em sN N

Absorption and stimulated emission term

Important for pump and probe measurements

Nexc

N1

N2

Er3+

Excitation term De-excitation mechanisms

Introduction

abs, em, exc, d, Cup ?


The samplesThe samplesEr:Si-nc produced by Reactive Magnetron co-Sputtering and successive annealing to get phase separation and reduction of non

radiative defects

Dep. conditions

Annealing T

F. Gourbilleau et al., JAP, 94, 3869 (2003)JAP 95, 3717 (2004).

Si-substrate

Si-nc doped Er3+(1m)

SiO2

(2÷6 m)

SiO2 (m)

800 nm

Annealing time

Waveguide sample

Annealing

time (min)

Si excess

(at. %)

Er content(x1020

cm-3)

n

B 60 7 4±0.1 1.545 0.51

C 30 6-7 5.4±0.2 1.516 0.48

D 10 6-7 5.4±0.2 1.48 0.28 n increases with annealing time

Optical litography andReactive ion etching


Determination of abs and em

h

kTem abs e

Mc Cumber relation:

From transmission measurements

abs and em

abs and em similar to that of Er3+ in SiO2

1400 1450 1500 1550 1600

30

35

40

450

2

4

6

0

2x10-21

4x10-21

6x10-21

ab

s (cm

2 )

ab

s (

dB

/cm

)

Real measurement Background losses

In

s. lo

sse

s(d

B)

Wavelength (nm)

abs

L

Absorption losses


2.1 2.2 2.3 2.4 2.5 2.6

4

8

12

16

0.4

0.2

0.1

n2

n SiO2

(m

s-1)

rad (from equation)

PL

(measured)

Life

time (

ms)

n2

rad, SiO2

2.1 2.2 2.3 2.4 2.5 2.6

0

5

10

n SiO2

abs(1

0-21 cm

2 )

SiO2

Radiative lifetime determination

2

22

0

81e

rad

nd

c

Also, from Mc Cumber analysis:

Local fieldeffects prevail

Medium fieldeffects prevail


Total lifetime and cooperative up-conversion

22 2up 2

d

( ) N ( )-C N ( )

dN t tt

dt

Quantitative measurements of the photon flux emitted from the samples. It is so possible to correlate

the number of emitted photons with N2


Total lifetime and cooperative up-conversion

0 2 4 6

1017

1018

1019

N2(c

m-3)

time (ms)

sample B-60' sample C-30' sample D-10'

1x1020 (ph/cm2s)

Sample D

Sample C

Sample B

1.98.0E-175.60E+18

3.25.5E-171.06E+19

3.82.0E-179.00E+18

21(ms)Cup (cm3 s-1)N2(t=0) (cm-3)

Sample D

Sample C

Sample B

1.98.0E-175.60E+18

3.25.5E-171.06E+19

3.82.0E-179.00E+18

21(ms)Cup (cm3 s-1)N2(t=0) (cm-3)

d and Cup


Excitation cross section at low pump power1 1

excr d

0

10

20

30

40

1/ r -

1/ d(s

-1)

1017 ph/s cm2

=2x10-17cm2

=1x10-16cm2

Sample C

0

10

20

30

40

=2x10-17cm2

488 nm 476 nm

Sample B=8x10-17cm2exc

…but seems to be flux dependent, the slope is changing with increasing pump flux

exc is orders of magnitude higher than that of Er3+ in pure silica (~10-21 cm2),

for samples B and C, resonant (488 nm) and non-resonant (476 nm) result in the same exc


Excited Er3+ vs pump flux

1017 1018 1019 1020 10211017

1018

1019

N2

(cm

-3)

Photon flux (ph/cm2s)

experimental data

pump

=488nm

Sample B, 60'

1E16 1E17 1E18 1E19 1E20 1E21 1E22 1E23 1E24 1E25 1E26 1E271E14

1E15

1E16

1E17

1E18

1E19

1E20

1E21

1E22

N2 p

opul

atio

n (c

m-3)


through Si-Nc directly excited totalexperimental data

ind

=2E-17 cm-2

d=5E-21cm-2

k=2%

0 1 2 3 4 5 6 7 8 9 10

x 1017

0

5

10

15

20

25

30

photon flux(ph/cm2 s)

1/ta

uris

e-1/

tauf

all(s

-1)

simulationexperimental (Fabrice)

11

1(

)r

d

s


…but

SimulationExperimental


( )nc

o

R R

Rexc o dR e

ModellingModelling

Model for exc

Er3+ ions near the Si-NC are efficiently coupled to them, whereas Er3+ ions far away behave more and more as Er3+ in SiO2 that can be excited only directly.

We consider that the first Er to be excited and therefore the strongest coupled would be the closest to the Si-Nc

The coupling diminishes with the distance

is then solved for each R Thus, by integrating over all the shells, we get the temporal dependence of the total excited state population.

22 21 up 2

d

NN - -C Nexc

dN

dt

We have divided discretely the region around the Si-Nc into shells of different probability. The rate equation:


Simulations

1016101710181019102010211022102310241025102610271014

1015

1016

1017

1018

1019

1020

1021

1022

N2 (

cm-3)


through Si-Nc directly excited totalexperimental data

pump

=488nm

Sample B

0 2 4 6 8 10

0

10

20

30

40

1017 ph/s cm21/ r -

1/ d

(s-1)

experimental simulation

d=3.8 ms, Cup=2x10-17cm3s-1, o=3x10-16cm2, d=5x10-21cm2,

Rnc=4nm , Ro=0.5nm, NNC=1x1017cm-3.

And this means that only 2-3% of the whole erbium population can be excited trough transfer from Si-Nc.

In any case it is about 10-100 excitable Er3+ per Si-Nc

Doing this for each flux we obtain….

Short range interaction


• Around 96% of the total volume of the sample is occupied by Er3+ that are only excitable through direct photon excitation, because simply they are too far from a Si-Nc.


INPUT OUTPUT

PROBE

PUMP

Signal enhancement (Pump&Probe experimental setup)


Signal enhancement

&2

2exp(2 ) exp

1( )

pump probe excem em Er

probeexc

d

ISE N L N L

I

probe

Signal from sa

mple

To detector

Si substrate buffer S

iO 2

Pump

Probe

SE>1SE1

0 50 100 1500.015

0.020

0.025

0.030

0.035

Inte

nsity

(V

)

pump onpump off

time (sec)

pump off

0.5 1 5 100.9

1.0

1.1

1.2

1.3

1.4

100 1000

B at 1535 nm C at 1535 nm D at 1535 nm

Power density (W/cm2)

Sig

na

l En

ha

nce

me

nt

(1020phot/cm2s)

0 10 20 30 40 50 60 70 80

1.00

1.05

1.10

pump on

Sig

nal e

nhan

cem

ent

time (sec)

pump off probe

1510nm Sample D


Signal enhancement

Sample Max SE

(dB/cm)

Propagation

Losses

(dB/cm)

Absorption

Losses (dB/cm)

Max internal gain

(CA corrected)

(dB/cm)

needed

(ph/cm2 s)

B-60’ 0.12 1.2 5.4 0.6 1x1022 (488nm)

C-30’ 0.65 1.6 8.5 0.76 5x1020 (488nm)

D-10’ 0.45 2.0 7.5 0.56 1x1021 (532nm)


Signal enhancement

• From maximum gain value:

2 2em

abs Er Er

N Ng

N N

Sample Max N2/NEr

B-60’ 11%

C-30’ 9%

D-10’ 7%

…but only 1-3% is being excited thorugh transfer from the Si-Nc


Conclusions (about oxidised porous silicon waveguides)

• We have succeed in building two types of dye doped planar waveguides based on oxidised porous silicon (PSW and PMW)

• We have measured net optical gain around 700nm of about 9cm-1 (PSW) and 13 cm-1 (PMW)

• With these measurements we have demonstrated the feasibility of using an oxidised porous silicon material both as an embedding medium for other active substances and as an optimum cladding material for growing compact optical amplifiers

• We have characterised the dye infiltration goodness in the PSW by simulations of the oscillating signal detected travelling parallel to the sample surface. We have concluded that the upper part of the core (~200-300nm) has a much higher dye concentration, and it is indeed providing the measured optical gain.


Conclusions (about birefringence in Si-Nc planar waveguides)

•We have reported for the first time form birefringence phenomena in Si-Nc planar waveguides.

•In the case of the multilayer structures, we were able to simulate the experimental data with a theoretical model of parallel layers of different refractive indices.

•With this model, we have been able to evaluate different parameters (no, ne, nNS) and to make an upper limit estimation of the nanocrystals diameter (dNS), which is in good agreement with nominal growing parameters and PL spectra.


Conclusions (about Er coupled to Si-Nc optical amplifiers)

• We have measured and quantified reliable values for:

Absorption and emission cross sectionsTotal lifetimes and cooperative up-conversion coefficientsEffective excitation cross sections at low pump powerIndirectly excitable Er3+ population through Si-Nc energy

transfer (2-3% of the Er3+ concentration)

• Using a pump and probe technique we have demonstrated values of internal gains of around 0.6dB/cm

We still have to optimize the Si-Nc:Er3+ ratio and the characteristics of the Si-Nc in order to excite the whole Er population through indirect energy transfer


PublicationsIn scientific journals: 1. D. Navarro-Urrios, M. Melchiorri, N. Daldosso, L. Pavesi, C. García, P. Pellegrino, B.

Garrido, G. Pucker, F. Gourbilleau and R.Rizk, “Optical losses and gain in silicon-rich Silica waveguides containing Er ions”, Journal of Luminescence, 121 249–255 (2006).

2. B. Garrido, C. García, P. Pellegrino, D. Navarro-Urrios, N. Daldosso, L. Pavesi, F. Gourbilleau, R. Rizk, “Distance dependent interaction as the limiting factor for Si nanocluster to Er energy transfer in silica”, Applied Physics Letters, 89, 163103 (2006).

3. C. J. Oton, D. Navarro-Urrios, N. E. Capuj, M. Ghulinyan, L. Pavesi, S. González-Pérez, F. Lahoz, and I. R. Martín, “Optical gain in dye-impregnated oxidized porous silicon waveguides”, Applied Physics Letters, 89, 011107 (2006).

4. N. Daldosso, D. Navarro-Urrios, M. Melchiorri, L. Pavesi, C. Sada, F. Gourbilleau and R. Rizk, “Refractive index dependence of the absorption and emission cross sections at 1.54 m m of Er 3+ coupled to Si nanoclusters”, Applied Physics Letters, 88, 161901 (2006).

5. K. Luterová , M. Cazzanelli, J.-P. Likforman , D. Navarro-Urrios, J. Valenta, T. Ostatnický, K. Dohnalová, S. Cheylan, P. Gilliot, B. Hönerlage, L. Pavesi, I. Pelant, “Optical gain in nanocrystalline silicon: comparison of planar waveguide geometry with a non-waveguiding ensemble of nanocrystals”, Optical Materials 27, 750–755 (2005).

6. K. Luterová, D. Navarro-Urrios, M. Cazzanelli, T. Ostatnický, J. Valenta, S. Cheylan, I. Pelant, and L. Pavesi, “Stimulated emission in the active planar optical waveguide made of silicon nanocrystals”, phys. stat. solidi (c), 2, No. 9, 3429-3434 (2005).

7. D. Navarro-Urrios, C. Pérez-Padrón, E. Lorenzo, N. E. Capuj, Z. Gaburro, C. J. Oton and L. Pavesi, “Structural and light-emission modification in chemically post-etched porous silicon”, phys. stat. sol. (a) 202, No. 8, 1518–1523 (2005).

8. E. Lorenzo-Cabrera, C. J. Oton, N. E. Capuj, M. Ghulinyan, D. Navarro-Urrios, Z. Gaburro, L. Pavesi, “Fabrication and optimization of rugate filters based on porous silicon”, phys. stat. sol. (c) 2, No. 9, 3227–3231 (2005).

9. V. Venkatramu, D. Navarro-Urrios, P. Babu, C.K. Jayasankar , V. Lavín, “Fluorescence line narrowing spectral studies of Eu 3+-doped lead borate glass”, Journal of Non-Crystalline Solids 351, 929–935 (2005).

10.E. Lorenzo, C. J. Oton, N. E. Capuj, M. Ghulinyan, D. Navarro-Urrios, Z. Gaburro, L. Pavesi “Porous silicon-based rugate filters”, Applied Optics, 44, 26 (2005).

11.D. Navarro-Urrios, F. Riboli, M. Cazzanelli, A. Chiasera, N. Daldosso, L. Pavesi, C. J. Oton, J. Heitmann, L. X. Yi, R. Scholz and M. Zacharias, “Birefingence characterization of mono-dispersed silicon nanocrystals planar waveguides”Optical Materials 27 (5) pp. 763-768 (2005).

12.N. Daldosso, D. Navarro-Urrios, M. Melchiorri, and L. Pavesi, F. Gourbilleau, M. Carrada, R. Rizk, C. García, P. Pellegrino, B. Garrido, and L. Cognolato, “Absorption cross section and signal enhancement in Er-doped Si-nanocluster rib-loaded waveguides”, Applied Physics Letters, 86, 261103 (2005).

13.M. Cazzanelli, D. Navarro-Urrios, F. Riboli, N. Daldosso, L. Pavesi, J. Heitmann, L.X. Yi, R. Scholz, M. Zacharias, and U. Gösele, “Optical gain in mono-dispersed silicon nanocrystals”, Journal of Applied Physics, 96, 3164 (2004).

14.F. Riboli, D. Navarro-Urrios, A. Chiasera, N. Daldosso, L. Pavesi, C. J. Oton, J. Heitmann, L.X. Yi, R. Scholz and M. Zacharias, “Birefringence in optical waveguides made by silicon nanocrystal superlattices” Applied Physics Letters 85 (7) pp. 1268-1270 (2004).

15.D. Navarro-Urrios, N. Daldosso, L. Pavesi, C. García, P. Pellegrino, B. Garrido, F. Gourbilleau and R. Rizk, “Signal enhancement and limiting factors in waveguides containing Si Nanoclusters and Er 3+ ions”, submitted to Journal of Lightwave Technology.

16. N. Daldosso, D. Navarro-Urrios, M. Melchiorri, C. García, P. Pellegrino, B. Garrido, C. Sada, G. Battaglin, F. Gourbilleau, R. Rizk, L. Pavesi, “Er Coupled Si Nanocluster Waveguide”, to be published in IEEE- Journal of Selected Topics in Quantum Electronics.

17. C. J. Oton, D. Navarro Urrios, M. Ghulinyan, N. E. Capuj, S. González Pérez, F. Lahoz, I. R. Martín and L. Pavesi, “Optical gain in oxidized porous silicon waveguides impregnated with a laser dye”, accepted in Physica Status Solidi.

18. D. Navarro-Urrios, M. Ghulinyan, N. E. Capuj, C. J. Oton, F. Riboli, I. R. Martín and L. Pavesi, “Waveguiding, absorption and emission properties of dye-impregnated oxidized porous silicon”, submitted to Physica Status Solidi.

19. L. Khriachtchev, D. Navarro-Urrios, L. Pavesi, C. J. Oton, N. Capuj and S. Novikov, “Cut-off and m-line spectroscopy of silica layers containing Si nanocrystals: Experimental evidence of optical birefringence”, to be published in Journal of Applied Physics.

20. F. Lahoz, N. E. Capuj, D. Navarro-Urrios, and S. E. Hernández, "Optical amplification in Ho3+ - doped transparent oxyfluoride glass-ceramics at 750nm", submitted to Applied Physics Letters.

21. D. Navarro-Urrios, M. Ghulinyan, P. Bettotti, C. J. Oton, N. E. Capuj, F. Lahoz, I. R. Martin, and L. Pavesi, "Optical gain in dye-doped polymeric slab waveguides on silicon", submitted to Applied Physics Letters.

Conference proceedings: 22. C. J. Oton, E. Lorenzo, N. Capuj, F. Lahoz, I. R. Martín, D. Navarro-Urrios, M. Ghulinyan,

F. Sbrana, Z. Gaburro, L. Pavesi, “Porous silicon-based Notch filters and waveguides”Proceedings of SPIE, 5840, 434 (2005).

23. Pump-probe experiments on low loss silica waveguides containing Si nanocrystals, D. Navarro-Urrios, N. Daldosso, M. Melchiorri, F. Sbrana, L. Pavesi, C. García, B. Garrido, P. Pellegrino, J.R. Morante, E.Scheid and G. Sarrabayrouse, Mater. Res. Soc. Symp. Proc. Vol. 832, F10.11.1 (2005).

24. Pump-probe experiments on Er coupled Si-nanocrystals rib-loaded waveguides, N. Daldosso, D. Navarro-Urrios, M. Melchiorri, L. Pavesi, F. Gourbilleau, M. Carrada, R. Rizk, C. García, P. Pellegrino, B. Garrido, and L. Cognolato, Mater. Res. Soc. Symp. Proc. Vol. 832, F11.3.1 (2005).

25. D. Navarro-Urrios, C. Pérez-Padrón, E. Lorenzo, N. E. Capuj, Z. Gaburro, C. J. Oton and L. Pavesi, “Chemical etching effects in porous silicon layers”Proceedings of SPIE, 5118 pp. 109-115 (2003).

Contributions to books: 26. “Nanostructured Silicon for Photonics - from Materials to Devices –“ , Z. Gaburro, P.

Bettotti, N. Daldosso, M. Ghulinyan, D. Navarro-Urrios, M. Melchiorri, F. Riboli, M. Saiani, F. Sbrana and L. Pavesi, Materials Science Foundations, Volume 27 until 28 (2006), ISBN 0-87849-488-x


AcknowledgementsFinantial Support:• European projects SINERGIA and LANCER.• Dipartimento di Fisica della Università di Trento• Istituto Nazionale per la Fisica della Materia, INFM • Integrated Action Spain-Italy, 2004-2006

Special acknoledgements to C. J. Otón, L. Pavesi and N. Daldosso for some slides used in this presentation and to everybody that have collaborated in this research work.

Thank you!Thank you!


Silicon vs. III-V

Direct band gap: efficiency• –VCSEL 50%• –LED 37%, potentially 50%

– •Tunability400nm -10 μm you choose! – •Material and processing expensive– •Integration with CMOS devices: costly, low

yield, still difficult


Oxidised porous silicon waveguides (extra slides)


Amplification studies in planar waveguides based on oxidised porous silicon

• Dye doped oxidized porous silicon waveguides (PSW)

• Dye doped polymeric waveguides with oxidized porous silicon cladding (PMW)


Oxidized porous silicon planar waveguides.

•1) Two layers of porous silicon. Core less porous than cladding to achieve light confinement. Different core thicknesses from 500nm to several m and cladding of several m.

•2) Thermal annealing at 900ºC for 3 hours to completely oxidize the samples and avoid visible light absorption.

•3) Impregnation with laser dye dissolved in ethanol.

0 4 8 12 16 (m)0

4

8

12

16

(m)

Core Cladding Silicon substrate


1.20 1.28 1.36

3

4

5In

tens

ity (

a.u.

)

effective index

CDNM01_TE CDNM01_blue_TE

1.20 1.28 1.36

3

4

5In

tens

ity (

a.u.

)

effective index

CDNM01_TE CDNM01_blue_TE

Detector

nm

m-line characterisation

After impregnation of the dye


600 650 700 750 800

0.0

0.2

0.4

0.6

0.8

1.0

TE TM

Inte

nsity

(a.

u)

Wavelength (nm)

600 650 700 750 800

0.0

0.2

0.4

0.6

0.8

1.0

TE TM

Inte

nsity

(a.

u)

Wavelength (nm)

core

cladding

Observation of narrow and linearly polarised spectral peaks

N.A.=0.65


600 640 680 720 760 800

0.0

0.2

0.4

0.6

0.8

1.0

Experimental Simulation

Nor

mal

ised

Inte

nsity

Wavelength (nm)0 5 10 15 20 25 30 35

1.0

1.1

1.2

1.3

n mat

thickness (m)

no

ne

0.0

0.5

1.0

TM exp TM sim

Nor

mal

ised

inte

nsity

1.12 1.14 1.16 1.18 1.20 1.22 1.24

0.5

1.0

TEexp TE sim

neff

Also first 300-400nm main emitting region

Thicker cladding


550 600 650 700 750

100

1000

10000

0.8W 0.5W 0.3W 0.2W 0.1W

Inte

nsity

(co

unts

)

Wavelenght (nm)

Decreasing from low to very low pump density powers

0.1 1103

104

105

slope=1.40366

Sig

nal I

nten

sity

(co

unts

)

Pump Power (W)

intensity at 653nm fit

At low pump power the dye is mainly in the fundamental state. The absorption is maximum and the ray emitted towards thebottom attenuates.

No oscillationsOscillations


Could it be in the surface?

• We fit very well the data.

• Why optical gain. If it is in the surface the overlapping with the confined mode will be very low.


Future work

SNOMSNOM characterizationcharacterization of the profile of dye concentration is of the profile of dye concentration is in progress.in progress.

1D vertical photonic crystals.1D vertical photonic crystals. We have to achieve several We have to achieve several microns with high dye concentration if we want to arrive microns with high dye concentration if we want to arrive to an eventual microcavity or impregnate a random to an eventual microcavity or impregnate a random photonic crystal. We will decrease the porosity of the photonic crystal. We will decrease the porosity of the high index layer although we will loose index contrast. high index layer although we will loose index contrast.


Birefringence extra slides


Sample D: The thicknesses of the uncrystallized layers are sufficiently small to neglect its effect on the effective index determination.

Procedure (1)

The extraordinary and ordinary refractive indexes are univocally extracted from the waveguide simulator software.

Using these two values (no and ne) and applying the theoretical formulas we extracted the mean thickness (nanocrystal diameter) and refractive index of the nanocrystal layers (1.705 for the red line, 1.735 forthe green one).

In order to fit the other samples we will assume that the refractive index of the nanocrystal layers is independent of the sample.


Procedure (2)

Samples C and B: We worked paralelly with a waveguide simulation software and the theoretical model to extract a unique solution for the parameters of the superlattice compatible with the m-line measurements

Sample A: No guided modes were observed

Ion implanted samples: No birrefringent behavior was observed, i.e. We can fit the m-line dataassuming an isotropic model where no = ne

Check of the model


Gain measurements

-0.04 0.00 0.04 0.08 0.12 0.16 0.201

10

(b)

0.432 J cm-2

AS

E in

ten

sity

(a

. u.)

Stripe length (cm)

Sample A

0.036 J cm-2

0.1

1

10

100

1000

Waveguide B

0.357 J cm-2

g= -33±10 cm-1

g= -26±3 cm-1

g= - 10±5 cm-1

g=27.2±0.2 cm-1(a)

0.014 J cm-2

Sample A Waveguide B Waveguide C Waveguide D

g(cm-1) -26±3 27±0.2 22±3 -2±0.5

TR-VSL (time resolved variable strip length) measurements

High positive optical gain under high pumping energy is observed in waveguides B and C

A birefringent structure is not detrimental for the observation of optical gain.

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