Semiconductor Laser Laboratory
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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
Single Stripe Pattern
• SiO SiO2 field • single open stripe • stripe width 25-150 µm
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Semiconductor Laser Laboratory
ILLINOIS
Selective Epitaxy Boundary Conditions
ŽNŽx
= 0
Žy= 0ŽN = g(x)
ŽyŽN
ŽNŽx
= 0
Žy= 0ŽN
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Semiconductor Laser Laboratory
ILLINOIS
Simulation Mesh
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Semiconductor Laser Laboratory
ILLINOIS
Simulation Results
a) concentration profiles b) thickness profile
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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
Buried Heterostructure SEM Cross Section
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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
Tunable DBR Reflectors
• Thin p-cladding structure • Single step post-growth
processing • Separate gain and tuning
electrodes
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Semiconductor Laser Laboratory
ILLINOIS
Tunable DBR Reflectors
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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Semiconductor Laser Laboratory
ILLINOIS
Tunable DBR Reflectors
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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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
Example: Integrated Laser-Modulator
M. Aoki et al. IEEE J. Quantum Electron. 29, 2088 (1993)
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Semiconductor Laser Laboratory
ILLINOIS
Integrated Laser/Modulator
• Laser with tunable DBR reflector and EA modulator
• Blue-shifted modulator and reflector sections
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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
Example: Integrated Laser-Modulator
• fixed lateral waveguide width • separately optimized transition energies
T. Kato et al. Electron. Lett. 28, 154 (1992)
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Semiconductor Laser Laboratory
ILLINOIS
Example: Integrated Laser-Modulator
T. Tanbun-Ek et al. J. Crystal Growth 145, 902 (1994)
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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
Example: 8-Channel Transmitter
C.H. Joyner et al. IEEE Photonics Technol. Lett. 7, 1013 (1995)
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Semiconductor Laser Laboratory
ILLINOIS
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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Semiconductor Laser Laboratory
ILLINOIS
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)