NKNU phys. Master Thesis

高師大物理系超快光電實驗室Ultrafast OptoElectronics LaboratoryDepartment of Physics, National Kaohsiung Normal University, Kaohsiung, Taiwan, R.O.C.Tel: 886-7-7172930 Ext. 3273 Fax: 886-7-7111681 WWW: http://www.nknu.edu.tw/~oelab/

UOEL 王尊信撰王尊信撰

NKNU phys. Master Thesis

The measurement and study of

femto-second gain dynamics of

GaAs single quantum well

semiconductor laser amplifiers 國立彰化師大物理系博士班入學口試



Contents

•Chap.1 Introduction

•Chap.2 GaAs SLA

•Chap.3 Theory

•Chap.4 Laser system

•Chap.5 Gain dynamics

•Chap.6 Summary

•Appendix

3



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

4



Chap.1 Introduction 1.1 Background 1.2 Study focus

5



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

6



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

7



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

8



2.1 Introduction

Tx

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

9



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

10



2.2 SLD830 GaAs

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

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

830 <GaAs band-gap wavelength=870nm

11



Manufactory LI & Spectrum

12



Structure

substrate

p-metal

p-GaAs

p-confiningactive

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

θ

n-confining

p-cap

n-Al 0.4Ga0.6As(1.5μm)

p-GaAs(0.5μm)SiO2(0.01μm)

n-metal

Zinc diffusion

13



Photos ~bird’s eye & side

14



2.3 Mounting system &circuit box

(a)

(b)

21.5°

15



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

16



(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。

17



18



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

19



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(v

olt)

20



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(μ

W)

GaAs SQW SLA L-I curve

0

20

40

60

80

100

120

0 20 40 60 80 100 120

I(mA)

L(μ

W)

TMTE

21



Spectrum ~TE & TM=1:10

22



Bandwidth=2nm

23



Transparent current

Lockin

CW Ti:saphhire

chopper

SLA

24



SLD-830 transparent current

-100

-50

0

50

100

150

0 20 40 60 80 100 120

I(mA)

Vol

tage

(μV

)

25mA

25



Gain curve

Lockin

CW Ti:saphhire

chopper

SLA

powerdetector

26



SLD-830 Gain curve

-10

0

10

20

30

0 20 40 60 80 100 120

I (mA)

Gai

n (d

B)

27



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

28



3.1 Introduction

cm

kcEE

2

22

vm

kvEE

2

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

29



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

30



R: index ， I: gain

phph

phphvphc

Eg

phR dT

ffM

22

2 /1)()()()(

ph

ph

phvphc

Eg

phI dT

TffM

22

2

22

/1)(

/1)()()(

31



32



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

33



3.3 Semi-phenomenological model

1989 AT&T G.P. Agrawal

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

ANgit

A

vz

A

g

)()1(2

11

34



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

35



4.1 Introduction Ultra fast Mode-locking fs pulse laser

36



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

37



Coherent Verdi

38



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

39



Coherent Mira

40



4.4 Pulse-width and bandwidth

41



Auto-correlator

Femto-chrome FR-103XL

42



Pulse-width=110fs un-chirped

43



Line-width=10nm transform limited

OSA:HP 71451B

44



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

45



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

46



5.2 Pump probe system System

requirements Experiment

sketch

47



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

48



Experiment sketch

49



Data acquisition &instrument control

Detector

stepper

chopper

λ/2λ/2

ND Filter30/70 BS

70/30 BS

SLA

Ti:SA Laser

probe

pump Dataacquisition

PC

50



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

51



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

52



(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)

Norm

. pro

be tra

ns.

(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)

Norm

. pro

be t

rans.

(au)

(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)

No

rm.

pro

be t

ran

s.(a

u)

Pump: probe=10:1,50.60.70mA

53



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

54



(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)

Norm

. pro

be t

rans.(

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)

No

rm.

pro

be

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)

Norm

. pro

be t

rans.

(au)


55



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

56




(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)

Norm

. pro

be t

rans.

(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)

Norm

. pro

be t

rans.

(au)

(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)

Norm

. pro

be t

rans.(

au)

No CH?

57



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

58



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.(a

u) 10:1

20:1

30:1

59



60mA overlapping

60mA

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)

10:1

20:1

30:1

60



70mA overlapping

70mA

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)

10:1

20:1

30:1

61



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 cohere

nt artifacts? Norm. probe: dip Relaxation time <1ps =>fit well with other theses

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

62



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!

63



Curve fitting graph

Gain 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 12

Time delay(ps)

Norm

. pro

be tr

ans.(

au)

Experiment

curve fitting

64



Chap.6 Conclusion 6.1 Summary 6.2 Future works

65



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

66



Summary-2 Gain dynamics measurement:

femto-second resolving ability tunable power 、 time delay and polarization of pump beam and pr

obe 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

67



6.2 Future works Pulse

above and below band-gap chirped or compressed

Gain dynamics more evidence coherent artifacts

Index dynamics Simulation

68



Appendix A. Data acquisition and instrument

control B. Theory deducing C. Conference poster: PSROC

69



A. Data acquisition and instrument control

70



B. Theory deducing

),(])(22

[2

222

22 tzAAibt

iz p

),()}(]1)[(2

1]

)(

1)[(

2

1{ tzAtOitgi

tftg gTTNN

71



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 )

72





Hyper-links

•Mounting system

•System requirements

•Experiment setup

•Experiment results

Documents

NKNU phys. Master Thesis