Master Thesis

彰化師大物理系藍光實驗室博士生王尊信 Tsun-Hsin Wang / Phd Student / Blue-ray Laser Laboratory /Department of Physics / National Changhua University of Education http://ykuo.ncue.edu.tw/~wthwth mailto:[email protected]

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Master Thesis

The measurement and study of femto-second gain dynamics of GaAs single quantum well semiconductor laser amplifiers

http://ykuo.ncue.edu.tw/~wthwth


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Contents

•Chap.1 Introduction•Chap.2 GaAs SLA •Chap.3 Theory•Chap.4 Laser system•Chap.5 Gain dynamics•Chap.6 Summary •Appendix


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Advantages & support SLA advantages

Small volume<500 micro-meter Short response time<200ps High gain>30dB Broad band>5T Hz

Support: NSC87-2112-M-017-001 NSC87-2112-M-017-002 Follow up:NSC87-2112-M-017-003


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Chap.1 Introduction 1.1 Background 1.2 Study focus


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1.1 Background Experiment

~1980:linear gain 1980~fs laser

Nonlinear gain MIT: ps pump probe technique & TDI UC Davis: fs

Nonlinear index ~MIT Theory

1989:AT&T 1992:UC Davis 1992:TFL(Sweden)

Domestic researches


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1.2 Study focus

雷射性質量測

激發偵測實驗組裝

自製載台設計與製作

SLA基本性質量測

增益機制量測

結果分析

半導體雷射放大器飛秒增益機制研究


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Chap.2 GaAs SLA 2.1 Introduction 2.2 SLD830 2.3 Mounting system and circuit box 2.4 SLD830 measurement


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2.1 IntroductionTx

Tx

Tx

Tx

Rx

Rx

Rx

Rx

(a)In line amplifiers

AA

(b)Power amplifiers

A

(c)Pre-amplifiers

(d) LAN amplifiers

A

A

fiber

fiber

fiberfiber


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放大器

電放大器雷射放大器聲放大器

半導體雷射放大器 (SLA)

摻鉺光纖雷射放大器(EDFA)

能量守恆放大訊號

是否抗反射

是

行波式(TWSLA)

否

FP 式(FPSLA)

結構

塊材(bulk)

量子井(quantum well)

量子線(quantum wire)

量子點(quantum dot)

應用波段

長波長 1300~1500nm

短波長800nm


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2.2 SLD830 GaAs

Direct band-gap Gain: LD,LED & SLA Absorption: optical detector: Photo Diode

SLD USA Sarnoff Inc. Single Quantum Well (SQW) Double Hetero-junction Structure (DHS) Peak wavelength: 825nm Striped angle:5 deg. Active layer:0.08 micro-meter P-side down

830 <GaAs band-gap wavelength=870nm


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Manufactory LI & spectrum


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Structure

substrate

p-metal

p-GaAs

p-confiningactive

p-Al 0.4Ga0.6As(1.5μm)Al 0.04Ga0.96As(0.08μm)θ

n-confiningp-cap

n-Al 0.4Ga0.6As(1.5μm)p-GaAs(0.5μm)SiO2(0.01μm)

n-metal

Zinc diffusion


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Photos ~bird’s eye & side


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2.3 Mounting system &circuit box

(a)

(b)

21.5°


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自製載台流程

量測樣品長寬高

考慮載台符合各種需求

繪製載台設計圖

實際製作載台

載台是否合乎需求

載台製作是否合乎需求

完成自製載台

是

否

是

否

修改


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(a)

(b)

(c)

(d)(e)

(f)

(g)

(h)

(a) 樣品裝載；(b) 頂住的螺絲(c)SMA 接頭；(d) 基座；(e) 基座裝載；(f) 絕緣夾層；(g) 載台支撐棒；(h) 圓形壓版。


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2.4 SLD830 measurement

電壓對電流曲線(V-I)

發光對電流曲線(L-I)

頻譜(Spectrum)

穿透電流(transparent

current)

增益曲線(gain curve)

半導體雷射放大器性質量測


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VI

SLAPowerDetector V

SpectralAnalyzer

GaAs SQW SLA V-I curve

0

0.5

1

1.5

2

0 10 20 30 40 50 60 70 80 90 100 110

I(mA)V(

volt)


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LIGaAs SQW SLA L-I curve

0

20

40

60

80

100

120

140

160

0 10 20 30 40 50 60 70 80 90 100 110

I(mA)

L(μW

)

GaAs SQW SLA L-I curve

0

20

40

60

80

100

120

0 20 40 60 80 100 120I(mA)

L(μW

)

TMTE


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Spectrum ~TE & TM=1:10


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Bandwidth=2nm


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Transparent current

Lockin

CW Ti:saphhire

chopper

SLA


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SLD-830 transparent current

-100

-50

0

50

100

150

0 20 40 60 80 100 120

I(mA)

Volta

ge (μ V

)

25mA


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Gain curve

Lockin

CW Ti:saphhire

chopper

SLA

powerdetector


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SLD-830 Gain curve

-10

0

10

20

30

0 20 40 60 80 100 120

I (mA)

Gain

(dB)


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Chap.3 Theory Models 3.1 Introduction 3.2 Pump probe technique 3.3 Semi-phenomenological model


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3.1 Introduction

cmk

cEE2

22

vmk

vEE2

22

Where:mc: electron effective mass in conduction bandmv: hole effective mass in valance bandEc: bottom energy of conduction bandEv: top energy of valance bandEg( energy gap)=Ec-Ev

In semiconductors: two level energy model+ energy conservation law + momentum conservation law+ boundary conditions


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Well known equations Optical joint density of states Fermi Golden Rule Lorentzian line-shape function


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R: index ， I: gain ph

ph

phphvphc

EgphR d

TffM

2

22 /1)(

)()()(

phph

phvphcEg

phI dT

TffM

2

22

22

/1)(/1

)()()(


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3.2 Pump probe technique

where: h(t): resonance function G(2)(t):convolution of h(t) S(τ): auto-correlation function of G(2)(t)

)()(*)()()(*)( )2(111 tGthdtttItIdtthdtS


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3.3 Semi-phenomenological model

1989 AT&T G.P. Agrawal

where: Vg: group velocity g(N): gain α: Line-width Enhancement Factor

ANgitA

vzA

g

)()1(211


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Chap.4 Laser System 4.1 Introduction 4.2 Pumping source:NdYVO4 Laser 4.3 Ultra-short mode-locking Ti:

sapphire Laser 4.4 Pulse-width and bandwidth


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4.1 Introduction Ultra fast Mode-locking fs pulse laser


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4.2 Pumping source:NdYVO4

laser Power>5W Wavelength: 532nm Quasi single frequency:<1nm Spot size:2.25mm Beam waist:1/e^2 ， beam divergence<0.5mrad Polarization: vertical: parallel>100:1


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Coherent Verdi


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4.3 Ultra-short mode-locking Ti: sapphire laser

Wavelength tunable:730~850nm Repetition rate:76MHz CW power:800mW Mode-locking power:600mW Peak power:50KW Spot size:0.8mm Full angle divergence:1.5mrad Polarization:TEM00,p polarization


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Coherent Mira


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4.4 Pulse-width and bandwidth


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Auto-correlator

Femto-chrome FR-103XL


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Pulse-width=110fs un-chirped


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Line-width=10nm transform limited

OSA:HP 71451B


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Chap.5 Gain Dynamics 5.1 Introduction 5.2 Pump probe system 5.3 Gain dynamics 5.4 Experiment result


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5.1 Introduction Pump probe 3 factors =pump beam + probe beam +time

delay Two beams pump probe/three beams Parallel polarization/orthogonal

polarization Refraction /reflection


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5.2 Pump probe system System

requirements Experiment

sketch


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System requirements Pump & probe power tunable Pump & probe polarization tunable Wavelength tunable SLA driving current tunable Time delay tunable Alignment requirement Fine tuning and double check


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Experiment sketch


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Data acquisition &instrument control

Detector

stepper

chopper

λ/2 λ/2

ND Filter30/70 BS

70/30 BSSLA

Ti:SA Laser

probepump Data

acquisition

PC


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5.3 Gain dynamicsPUMP PROBE CALIBRATION

probe [email protected]

probe [email protected]

pump:probe=1:1

pump [email protected]

pump [email protected]

attenuatedprobe [email protected]

fixed

alternative


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5.4 Experiment result Carrier Depletion (CD): linear, ps scale Carrier Heating (CH) Free Carrier Absorption (FCA) * Two Photon Absorption (TPA )* Spectral Hole Burning (SHB )* *:can’t be resolved in my experiment


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(a)

0

0.2

0.4

0.6

0.8

1

1.2

-10 -8 -6 -4 -2 0 2 4 6 8 10 12Time delay(ps)

Nor

m. p

robe

tran

s.(au

).

(b)

0

0.2

0.4

0.6

0.8

1

1.2

-10 -8 -6 -4 -2 0 2 4 6 8 10 12

Time delay(ps)

Nor

m. p

robe

tran

s.(a

u)

(c)

0

0.2

0.4

0.6

0.8

1

1.2

-10 -8 -6 -4 -2 0 2 4 6 8 10 12

Time delay(ps)

Nor

m. p

robe

tran

s.(a

u)

Pump: probe=10:1,50.60.70mA


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Results analysis~10:1 50mA:

-10ps~-1ps:norm. probe=1 ， probe fall behind pump: no gain -1ps~0ps:norm. probe=0.6~0.7:CD recover time>10ps 0ps~2ps:dip~1ps ， CH

60mA:like 50mA 70mA:like 50mA


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(a)

0

0.2

0.4

0.6

0.8

1

1.2

-10 -8 -6 -4 -2 0 2 4 6 8 10 12

Time delay(ps)

Nor

m. p

robe

tran

s.(a

u) (b)

0

0.2

0.4

0.6

0.8

1

1.2

-10 -8 -6 -4 -2 0 2 4 6 8 10 12

Time delay(ps)

Nor

m. p

robe

tran

s.(a

u)

(c)

0

0.2

0.4

0.6

0.8

1

1.2

-10 -8 -6 -4 -2 0 2 4 6 8 10 12

Time delay(ps)

Nor

m. p

robe

tran

s.(a

u)



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Results analysis~20:1 50mA:like 10:1 60mA:like 10:1 70mA:like 10:1


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(a)

0

0.2

0.4

0.6

0.8

1

1.2

-10 -8 -6 -4 -2 0 2 4 6 8 10 12

Time delay(ps)

Nor

m. p

robe

tran

s.(a

u) (b)

0

0.2

0.4

0.6

0.8

1

1.2

-10 -8 -6 -4 -2 0 2 4 6 8 10 12

Time delay(ps)

Nor

m. p

robe

tran

s.(a

u)

(c)

0

0.2

0.4

0.6

0.8

1

1.2

-10 -8 -6 -4 -2 0 2 4 6 8 10 12

Time delay(ps)

Nor

m. p

robe

tran

s.(a

u)

No CH?


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Results analysis~30:1 50mA:no CH? Saturated? 60mA:like 10:1 70mA:like 10:1


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50mA overlapping50mA

0.5

0.6

0.7

0.8

0.9

1

1.1

-10 -8 -6 -4 -2 0 2 4 6 8 10 12

Time delay(ps)

Nor

m. p

robe

tran

s.(au

) 10:120:130:1


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0.5

0.6

0.7

0.8

0.9

1

1.1

-10 -8 -6 -4 -2 0 2 4 6 8 10 12Time delay(ps)

Nor

m. p

robe

tran

s.(au

) 10:120:130:1


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0.5

0.6

0.7

0.8

0.9

1

1.1

-10 -8 -6 -4 -2 0 2 4 6 8 10 12

Time delay(ps)

Nor

m. p

robe

tran

s.(a

u)

10:120:130:1


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Conclusion CD:50mA 、 60mA&70mA:10:1 、 20:1&30:1 ，

linear norm. probe from 1 to 0.5~0.8 recover time>10ps =>fit well with other theses

CH:50mA 、 60mA&70mA: 10:1 、 20:1 nonlinear increasing ， 30:1 saturated? or coherent artifacts? Norm. probe: dip Relaxation time <1ps =>fit well with other theses

<110 fs nonlinearity can’t be resolved (TPA,FCA,SHB)


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Curve fitting function 1987 MIT Ippen. et al h(t)=a0+a1*exp(-t/τ1)+a2*exp(-t/τ2) a0=0.5 、 a1=-1 、 a2=0.5 、 τ1=0.65ps 、 τ2=0.2ps constraints: 1>a0>0 、 a1<0 、 a2>0 where a0:long lasting term ,a1 、 a2:short lasting term =>CH:650 fs Mine:a0=0.7 、 a1=-2.65 、 a2=3 、 τ1=0.68ps 、 τ2=0.56ps =>CH:680 fs fit quite well!


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Curve fitting graphGain dynamics curve fitting

0.5

0.6

0.7

0.8

0.9

1

1.1

-10 -8 -6 -4 -2 0 2 4 6 8 10 12Time delay(ps)

Norm

. probe

trans.

(au)

Experimentcurve fitting


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Chap.6 Conclusion 6.1 Summary 6.2 Future works


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6.1 Summary I have successfully built up the

measurement system of gain dynamics. Light source (Verdi+ Mira) measurement:

Pulse-width:110fs :un-chirped Line-width:10nm :transform limited

Sample (SLD830)measurement: highly polarization dependent transparent current is about 25mA gain:25dB at 100mA


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Summary-2 Gain dynamics measurement:

femto-second resolving ability tunable power 、 time delay and polarization of pump beam and probe beam expandability of different samples ability to co-operate with the computerized instrument control and data acquisition system.

Experiment data slow recovering term :time constant is much bigger than 10ps fast recovering term :time constant is about 580fs

Possible corresponding explanation slow recovering term: CD fast recovering term :dominated by CH


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6.2 Future works Pulse

above and below band-gap chirped or compressed

Gain dynamics more evidence coherent artifacts

Index dynamics Simulation


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Appendix A. Data acquisition and instrument

control B. Theory deducing C. Conference poster: PSROC


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A. Data acquisition and instrument control


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B. Theory deducing

),(])(22

[ 2222

22 tzAAib

ti

z p

),()}(]1)[(21]

)(1)[(

21{ tzAtOitgi

tftg gTTNN


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C. Conference poster: PSROC-1999

Femto-second Pump Probe Measurement of GaAs Single Quantum Well Semiconductor Laser Amplifiers T.H. Wang ( 王尊信 ), Y.H. Chang( 張玉衡 ), and Y.H. Chen( 陳雅惠 ) Pump-probe Data Acquisition Control System for Semiconductor Laser Amplifiers Y.H. Chen( 陳雅惠 ),Y.H. Chang( 張玉衡 ),T.H. Wang( 王尊信 )


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Master Thesis

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