Signal enhancement and limiting factors in waveguides containing Si nanoclusters and Er 3+ ions D....

Signal enhancement and limiting factors in waveguides containing Si nanoclusters and Er3+ ions

D. Navarro Urrios, N. Daldosso, L. Ferraioli, F. Gourbilleau, R. Rizk, P. Pellegrino, B. Garrido and L. Pavesi

D. Navarro-Urrios, Microtechnologies for the New

Millenium 2007, 2-4 May, Maspalomas

2/20

Introduction to the system under study.Characterisation and modelling of the

studied samples.Signal enhancement setup and

measurements.Conclusions

Outline



3/20

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

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x

x

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x



4/20

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



5/20

( )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+



6/20

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 ?



7/20

Dep. conditions

Annealing T

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

radiative defects

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

A 240 7 3±0.1 1.61 0.62

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

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

NSi-nc1x1017cm-3



8/20

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

abs (

cm2)

abs (

dB

/cm

)

Real measurement Background losses

In

s. lo

sses

(dB

)

Wavelength (nm)

abs

L

Absorption losses

5dB/cm

Decreasing with annealing time



9/20

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



10/20

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

Decreases with annealing time

Increases with annealing time



11/20

Excitation cross section at low pump power

1 1exc

r 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



12/20

Excited erbium population vs photon flux

1016 1017 1018 1019 1020 1021 1022 10231017

1018

1019

1020

1021

1022

measurement simulations

N

2 (cm

-3)

Photon flux (ph/cm2s)

pump

=488nm

Sample B

Population

inversion



13/20

( )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

Rnc

Ro



14/20

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.Doing this for each flux we obtain….

Short range interaction

And this means that only 2-3% of the whole erbium population can be excited trough transfer from Si-nc. The rest can only be excited directly because

simply it is too farIn any case it is about 10-100 excitable Er3+ per Si-nc



15/20

INPUT OUTPUT

PROBE

PUMP

Signal enhancement (Pump&Probe experimental setup)



16/20

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

Internal gain = g



17/20

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)



18/20

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 2-3% is being excited thorugh transfer from the Si-nc



19/20

Conclusions

• 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 0.7dB/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



20/20

THANK YOU!



21/20



22/20



23/20

As much Er3+ as possible (avoiding up-conversion phenomena, NEr4-5x1020cm-3)

Enough Si-nc to excite all the Er3+ ions Good modal confinement Low waveguide losses (not that due to absorption of Er3+)

Gain favouring

Gain limiting Up-conversion (shifts the pump threshold for population inversion

towards higher pump energies) Excited state absorption Non radiative de-excitation (Auger de-excitation with a nearby

exciton) Carrier absorption in Si-nc (decreases the signal and blocks the

transfer to Er ions)



24/20

Propagation losses at 1600nmPropagation losses at 1600nm

Losses at 1600 nm are essentially propagation losses of the rib loaded waveguide



25/20

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



26/20

Excited Er3+ vs pump flux

1017 1018 1019 1020 10211017

1018

1019

N2

(cm

-3)


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

)Photon flux (ph/cm2s)

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



27/20

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.

Signal enhancement and limiting factors in waveguides containing Si nanoclusters and Er 3+ ions D....

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