Master Thesis

transcript

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:wthwth@mail.cgjh.tcc.edu.tw

Master Thesis

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

Contents

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

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

Chap.1 Introduction 1.1 Background 1.2 Study focus

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

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

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

2.1 IntroductionTx

(a)In line amplifiers

(b)Power amplifiers

(c)Pre-amplifiers

(d) LAN amplifiers

fiberfiber

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

行波式(TWSLA)

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

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

Manufactory LI & spectrum

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

Photos ~bird’s eye & side

2.3 Mounting system &circuit box

21.5°

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

修改

(d)(e)

(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。

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

SLAPowerDetector V

SpectralAnalyzer

GaAs SQW SLA V-I curve

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

I(mA)V(

LIGaAs SQW SLA L-I curve

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

GaAs SQW SLA L-I curve

0 20 40 60 80 100 120I(mA)

Spectrum ~TE & TM=1:10

Bandwidth=2nm

Transparent current

Lockin

CW Ti:saphhire

chopper

SLD-830 transparent current

0 20 40 60 80 100 120

ge (μ V

Gain curve

Lockin

CW Ti:saphhire

chopper

powerdetector

SLD-830 Gain curve

0 20 40 60 80 100 120

I (mA)

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

3.1 Introduction

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

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

R: index ， I: gain ph

phphvphc

EgphR d

22 /1)(

)()()(

phvphcEg

phI dT

/1)(/1

)()()(

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

3.3 Semi-phenomenological model

1989 AT&T G.P. Agrawal

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

ANgitA

)()1(211

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

4.1 Introduction Ultra fast Mode-locking fs pulse laser

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

Coherent Verdi

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

Coherent Mira

4.4 Pulse-width and bandwidth

Auto-correlator

Femto-chrome FR-103XL

Pulse-width=110fs un-chirped

Line-width=10nm transform limited

OSA:HP 71451B

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

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

5.2 Pump probe system System

requirements Experiment

sketch

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

Experiment sketch

Data acquisition &instrument control

Detector

stepper

chopper

λ/2 λ/2

ND Filter30/70 BS

70/30 BSSLA

Ti:SA Laser

probepump Data

acquisition

5.3 Gain dynamicsPUMP PROBE CALIBRATION

probe voltage1mV@40mA.20mW

probe signal400nV@40mA.20mW

pump:probe=1:1

pump voltage1mV@40mA.20mW

pump signal400nV@40mA.20mW

attenuatedprobe signal20nV@40mA.1mW

alternative

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

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

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

Time delay(ps)

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

Time delay(ps)

Pump: probe=10:1,50.60.70mA

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

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

Time delay(ps)

u) (b)

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

Time delay(ps)

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

Time delay(ps)

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

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

Time delay(ps)

u) (b)

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

Time delay(ps)

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

Time delay(ps)

No CH?

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

50mA overlapping50mA

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

Time delay(ps)

) 10:120:130:1

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

) 10:120:130:1

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

Time delay(ps)

10:120:130:1

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)

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!

Curve fitting graphGain dynamics curve fitting

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

. probe

trans.

Experimentcurve fitting

Chap.6 Conclusion 6.1 Summary 6.2 Future works

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

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

6.2 Future works Pulse

above and below band-gap chirped or compressed

Gain dynamics more evidence coherent artifacts

Index dynamics Simulation

Appendix A. Data acquisition and instrument

control B. Theory deducing C. Conference poster: PSROC

A. Data acquisition and instrument control

B. Theory deducing

),(])(22

[ 2222

22 tzAAib

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

)(1)[(

21{ tzAtOitgi

tftg gTTNN

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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