semiconductor laser laboratory

Semiconductor Laser Laboratory

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Novel Integrable Semiconductor Laser Diodes

J.J. Coleman

University of Illinois

Urbana

1997-1998 Distinguished Lecturer Series IEEE Lasers and Electro-Optics Society


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Definition of the Problem

1. Epitaxial structure optimization Lasers and other optical devices generally have very

different optimum layer structures

2. Cleaved facet resonators Difficult (impossible) processing Poor optical coupling to other elements

Why aren’t conventional semiconductor diode lasers particularly suitable for integration?


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Outline

• Engineering in the optical path - selective area epitaxy

• Integrable laser resonators

• Examples of lasers integrated with other optical devices

• Summary


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Approaches to Wafer Engineering

• Universal substrate

Compromise epitaxial layer design

• Regrowth/overgrowth/multiple growth

Coupling and plane-of-propagation issues

• Selective area epitaxy

Multiple regrowths

T.L. Koch and U. Koren, OFC’92 Tutorial


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Single Stripe Pattern

• SiO SiO2 field • single open stripe • stripe width 25-150 µm


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Selective Epitaxy Boundary Conditions

ŽNŽx

= 0

Žy= 0ŽN = g(x)

ŽyŽN

ŽNŽx

= 0

Žy= 0ŽN


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Simulation Mesh


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Simulation Results

a) concentration profiles b) thickness profile


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Modeled and Experimental Data

• two stripe widths 50 and 125 µm

• modeled (dashed) • experiment (solid)

0

500

1000

1500

2000

2500

3000

-20 0 20 40 60 80 100 120 140Distance (µm)


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Wide Stripe Impracticalities

1. Growth rate enhancement is too large Poorer quality materials

Less control over thickness, especially for thin layers

2. Deep bowing Makes subsequent processing difficult Yields non-uniform quantumwell thicknesses

But, the basic parameters determined from these structures can be used to model more complex structures


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Dual Stripe Pattern

• open field • dual stripe • stripe separation 2-5 µm • stripe width 2-25 µm • dimensions small with

respect to a dif fusion length


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0

1

2

3

-60 -40 -20 0 20 40 60

Re

lativ

e T

hic

kne

ss

Distance (µm)

25 µm6 µm

E

E

EE

EEE

E

0

1

2

3

0 5 10 15 20 25

En

ha

nce

me

nt F

act

or

Oxide Stripe Width (µm)

w w

Dual Stripe Growth Enhancement


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Buried Heterostructure Growth Process

a) buffer layer and lower confining layer

b) selectively grown active layer

c) upper confining layer and cap layer


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Buried Heterostructure SEM Cross Section


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0

20

40

60

80

100

120

140

160

180

0 200 400 600 800 1000

Opt

ical

Pow

er (

mW

)

Current (mA)

0

1

2

3

0 5 10 15

P (

mW

)

I (mA)

Ith = 2.65 mA

Buried Heterostructure L-I Curves


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980 nm Wavelength Control

Ñ

Ñ

ÑÑ

ÑÑ

9600

9800

10000

10200

10400

10600

10800

0 5 10 15 20 25

Wav

elen

gth

(Å)

Oxide Stripe Width (µm)

E

EE

EE

EE

EE

EE E

9400

9500

9600

9700

9800

0 2 4 6 8 10 12Element Number

S = 5.5-10.5 µm


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1.55 µm Wavelength Control

• 110 nm wavelength range • uniform PL intensity • uniform PL halfwidth

Masahiro Aoki et al. IEEE J. Quantum Electron. 29, 2088 (1993)


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Basic Buried Heterostructure Building Block

• Engineered transition energy

• Automatic lateral optical waveguide

• Many relatively lossless coupling schemes are possible

abrupt, simple taper, more complex designs


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Integrable Resonator Geometries

• Etched Fabry-Perot facets

Scattering losses, verticality, flatness, coupling

• Corner reflectors/ring geometries

Mode selection

• Distributed feedback (DFB) resonators

Processing, sensitivity to reflections

• Distributed Bragg reflectors (DBR)

Processing, coupling


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Tunable DBR Reflectors

• Thin p-cladding structure • Single step post-growth

processing • Separate gain and tuning

electrodes


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J

0

5

10

15

20

25

30

35

40

0 25 50 75 100 125 150 175 200

-60

-40

-20

0

1000 1010 1020Wavelength (nm)

Current (mA)

20° C


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J

JJJJJ

J

J

0

20

40

60

80

100

120

140

160

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

20° C

Inverse Power (mW-1)

J J J JJ J J J J

J JJ J

J JJJ

J

J

1006

1008

1010

1012

1014

1016

0 20 40 60 80 100DBR Current (mA)


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First-order Gratings

0

2

4

6

8

10

Current (mA)0 10 0 10 0 10 0 10 0 10 0 10 20

a b c d e f

0.460.430.410.470.42

a b c d e f

68.5779

Device

Ith (mA)

(W/A) 0.43

8

Period (nm)

Peak (µm)

155.5 157.5 159.5 161 163 165

1.004 1.016 1.027 1.036 1.047 1.058

-70

-60

-50

-40

-30

-20

-10

0

0.99 1 1.01 1.02 1.03 1.04 1.05 1.06 1.07Wavelength (µm)

b c d e fa


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Selection of Integrated Photonic Devices

• Several laser-modulator structures

• A four-terminal flip chip laser-photodiode

• A dual (or redundant) source with a fiber coupler

• An 8-channel transmitter


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Example: Integrated Laser-Modulator

M. Aoki et al. IEEE J. Quantum Electron. 29, 2088 (1993)


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Integrated Laser/Modulator

• Laser with tunable DBR reflector and EA modulator

• Blue-shifted modulator and reflector sections


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Integrated Laser/Modulator

0

1

2

3

4

5

6

7

0 10 20 30 40 50 60 70Current (mA)

-60

-40

-20

0

1.015 1.025 1.035Wavelength (µm)

-18

-15

-12

-9

-6

-3

0

3

6

0 0.2 0.4 0.6 0.8 1 1.2 1.4Modulator Bias (V)

AR/HR CoatedUncoated


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• fixed lateral waveguide width • separately optimized transition energies

T. Kato et al. Electron. Lett. 28, 154 (1992)


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T. Tanbun-Ek et al. J. Crystal Growth 145, 902 (1994)


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Integrated Laser - Photodiode

• RIE etched laser facet • PD redshifted by 150Å • PD input facet angled

by • four-up contacts for

flip chip bonding


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0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 2 4 6 8 10 12LD Output Power (mW)

q = 3Þ

14Þ

45Þ

0

2

4

6

8

10

12

14

16

18

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60 70 80 90 100LD Current (mA)

0.219 mW/mA

8.9 µA/mA

L-I and Photodiode Response


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Dual (Redundant) Source

0

1

2

3

4

5

0 10 20 30 40 50 60 70 80 90Current (mA)

0.99 1.01 1.03 1.05 1.07Wavelength (µm)

Channel 2Channel 1

V2=-2

V1=0V2=0

V1=-2V2=0

V1=0


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Example: 8-Channel Transmitter

C.H. Joyner et al. IEEE Photonics Technol. Lett. 7, 1013 (1995)


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Summary

• Precise control of emission wavelengths can be obtained by selective area epitaxy

• The DBR reflector is a good candidate for an integrable resonator

• High performance novel integrated photonic devices are possible


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I would like to thank

M. Aoki (Hitachi)

J.A. Dantzig (Illinois)

P.D. Dapkus (USC)

J.G. Eden (Illinois)

C. Jagadish (ANU)

A.M. Jones (Illinois)

C.H. Joyner (Lucent)

S.M. Kang (Illinois)

R.M. Lammert (Ortel)

P.V. Mena (Illinois)

M.L. Osowski (Illinois)

S.D. Roh (Illinois)

G.M. Smith (ATMI)

T. Tanbun-Ek (Lucent)

W.T. Tsang (Lucent)

G.S. Walters (LEOS)

semiconductor laser laboratory

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