[PPT] - Novel Integrable Semiconductor Laser Diodes J.J. Coleman PowerPoint Presentation

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Semiconductor Laser Laboratory

Novel Integrable Semiconductor Laser Diodes

J.J. Coleman University of Illinois 1998-1999 Distinguished Lecturer Series IEEE Lasers and Electro-Optics Society

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Semiconductor Laser Laboratory

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

Outline

Engineering in the optical path - selective

area epitaxy

Integrable laser resonators
Examples of lasers integrated with other
ptical devices
Summary

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Semiconductor Laser Laboratory

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

Single Stripe Pattern

SiO2 field
single open stripe
stripe width 25-150 µm

SiO2

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Semiconductor Laser Laboratory

Selective Epitaxy Boundary Conditions

boundary layer N = constant

= g(x) ∂N ∂y = 0 ∂N ∂y = 0 ∂N ∂x = 0 ∂N ∂x = 0 ∂N ∂y

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Semiconductor Laser Laboratory

Selective Epitaxy Boundary Conditions

boundary layer N = constant

= g(x) ∂N ∂y = 0 ∂N ∂y = 0 ∂N ∂x = 0 ∂N ∂x = 0 ∂N ∂y

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Semiconductor Laser Laboratory

Simulation Results

isoconcentration profiles thickness profile

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Semiconductor Laser Laboratory

Modeled and Experimental Data

two stripe widths (50

and 125 µm)

modeled (dashed)
experimental (solid)

500 1000 1500 2000 2500 3000

20

20 40 60 80 100 120 140 Distance (µm)

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Semiconductor Laser Laboratory

Wide Stripe Impracticalities

Growth rate enhancement is too large

– Poorer quality materials – Less control over thickness, especially for thin layers

Deep bowing

– Makes subsequent processing difficult – Yields non-uniform quantum well thicknesses

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

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Semiconductor Laser Laboratory

Dual Stripe Pattern

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

respect to a diffusion length

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Semiconductor Laser Laboratory

Dual Stripe Growth Enhancement

1 2 3

60
40
20

20 40 60 Relative Thickness Distance (µm) 25 µm 6 µm

1

2 3 5 10 15 20 25 Enhancement Factor Oxide Stripe Width (µm)

w w

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Semiconductor Laser Laboratory

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

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Semiconductor Laser Laboratory

Buried Heterostructure SEM Cross Section

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Semiconductor Laser Laboratory

Buried Heterostructure L-I Curves

20 40 60 80 100 120 140 160 180 200 400 600 800 1000 Current (mA) length = 760 µm

1 2 3 5 10 15 I (mA) Ith = 2.65 mA

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Semiconductor Laser Laboratory

980 nm Wavelength Control

9400

9600 9800 10000 10200 10400 10600 10800 5 10 15 20 25 Dual oxide stripe width (µm)

9400

9500 9600 9700 9800 2 4 6 8 10 12 Element Number S = 5.5-10.5 µm

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Semiconductor Laser Laboratory

1.55 µm Wavelength Control

110 nm wavelength range
uniform PL intensity
uniform PL half-width

Masahiro Aoki et al. IEEE J. Quantum

Electron. 29, 2088 (1993)

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Semiconductor Laser Laboratory

Basic Buried Heterostructure Building Block

Engineered transition energy
Automatic lateral optical waveguide
Many relatively lossless coupling schemes are possible

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Semiconductor Laser Laboratory

Integrable Resonator Geometries

Etched Fabry-Perot facets

– Scattering losses, verticality, flatness, coupling

Corner reflectors and 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

Tunable DBR Reflectors

Asymmetric (thin p-layer) cladding structure
Conventional ridge waveguide or selective-area epitaxy buried

heterostructure

Deep surface-etched DBR grating (1st, 2nd, or 3rd order)
Separate grating electrode for tuning purposes

Igain IDBR AlGaAs:p AlGaAs:n InGaAs-GaAs active layer GaAs:n

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Semiconductor Laser Laboratory

First-Order DBR Grating Lasers

First-order gratings formed with

RIE

Six grating periods studied
Threshold currents below 10 mA

and as low as 6 mA

Slope efficiencies greater than 0.4

W/A

Minimum emission linewidth about

the same as the measurement resolution ~ 40 kHz

20

40 60 80 100 120 140 160 0.02 0.04 0.06 0.08 0.1 0.12 0.14 Linewidth (kHz) 20° C Inverse Power (mW-1) 5 10 15 20 25 10 20 30 40 50 60 70 80 90 100 Power (mW) Current (mA)

75
50
25

1.048 1.058 1.068 Intensity (dB) Wavelength(µm)

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Semiconductor Laser Laboratory

Spectra versus DBR Tuning Current

T = 20C and drive current fixed at 40 mA
Single mode spectrum preserved over 100 mA tuning

current range

SMSR greater than 35 dB over an 8 nm tuning range
Current injection heating dominant tuning mechanism

GGG G G G G G G G G G G G G G G G G

1006 1008 1010 1012 1014 1016 20 40 60 80 100 Wavelength (nm) DBR Current (mA)

70
60
50
40
30
20
10

1000 1005 1010 1015 1020 1025 Relative Intensity (dB) Wavelength (nm) I DBR = 0 mA 50 mA 100 mA 20° C I gain = 40 mA

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Semiconductor Laser Laboratory

1.3 µm InGaAsP Ridge Waveguide DBR Lasers

First-order gratings formed by

chemically-assisted ion beam etching (CAIBE)

Compressively-strained MQW active

region

SMSR of ~ 40dB
InP:n

InGaAsP MQW active region 0.5 µm Gain Section First-Order DBR Grating 0.2 µm InGaAsP etch stop layer InP:u/p InP:p

5 10 15 20 25 30 35 40 Power (mW/facet) Current (mA) 0 20 0 20 0 20 0 20 0 20 0 20 0 20 0 20 40 80 120 Ith = 26.5 ± 0.26 mA

η = 0.290 ± 0.0047 W/A

60
50
40
30
20
10

1.355 1.36 1.365 1.37 1.375 Intensity (dB) Wavelength (µm)

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Semiconductor Laser Laboratory

Selection of Integrated Photonic Devices

Laser - external modulator
Laser - photodiode
Lasers for remote sensing applications
Multiple wavelength sources
An eight-channel transmitter

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Semiconductor Laser Laboratory

Example: Integrated Laser-Modulator

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

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Semiconductor Laser Laboratory

Integrated Laser/External Modulator

Buried heterostructure laser

grown by selective-area epitaxy

Tunable DBR grating as part of

the resonant cavity

Blue-shifted electro-absorption

modulator

MQW EA

Modulator 0.4 µm Al0.60Ga0.40As:p Al0.60Ga0.40As:n GaAs substrate MQW DBR Laser 1 µm DBR Gratings SiO2 SiO2 (a) (b) λLD λM 150 µm

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Semiconductor Laser Laboratory

Integrated Laser/External Modulator

Thresholds around 10 mA, single longitudinal mode operation
18 dB extinction ratio at 1 V bias
40 dB extinction ratio at 1.25 V bias with single mode fiber

1 2 3 4 5 6 7 10 20 30 40 50 60 70 Power (mW) Current (mA)

60
40
20

1.015 1.025 1.035 Power (dB) Wavelength (µm)

18
15
12
9
6
3

3 6 0.2 0.4 0.6 0.8 1 1.2 1.4 Optical Power (dBm) Modulator Bias (V) AR/HR Coated Uncoated

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Semiconductor Laser Laboratory

Integrated Laser-Photodiode

RIE etched laser facet
PD redshifted by 150Å
PD input facet angled by θ
four-up contacts for flip chip bonding

LD p-contact LD n-contact PD n-contact PD p-contact semi-insulating GaAs substrate GaAs:n + buffer AlGaAs-GaAs-InGaAs selective area epitaxy laser structure θ d 2 4 6 8 10 12 14 16 18 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 10 20 30 40 50 60 70 80 90 100 LD Current (mA) 0.219 mW/mA 8.9 µA/mA

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Semiconductor Laser Laboratory

DBR Lasers at 915-930 nm Wavelengths

Modified active region for shorter

strained-layer emission wavelength

Second-order gratings with three

different periods

Three emission wavelengths (915, 925,

935 nm)

Al In 0.3 µm 1.0 µm 700 Å 20 Å 0.1 µm 0.2 0.4 0.6 0.13 80 Å

50
40
30
20
10

0.91 0.915 0.92 0.925 0.93 0.935 0.94 Relative Intensity (dB) Wavelength (µm) (a) (b) (c) 2 4 6 8 10 12 14 16 18 20 10 20 30 40 50 60 70 80 90 100 Output Power (mW) 20C Igain (mA) λ = 916 nm λ = 934 nm λ = 924 nm

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Semiconductor Laser Laboratory

Application to Remote Sensing

White cell filled with

humid air

Path length 85 m
Coarse tuning with

temperature, fine tuning with DBR current

Lorentzian fit to the

data within 6% of HITRAN values for halfwidth

Balanced Receiver ADC White Cell TE Cooler DBR Current Source Gain Current Source Mounted Laser Variable Attenuator center wavelength = 1009.274 nm

0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1

9907 9907.2 9907.4 9907.6 9907.8 9908

Absorption (%) Wavenumber (1/cm)

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Semiconductor Laser Laboratory

Dual (Redundant) Source

1 2 3 4 5 10 20 30 40 50 60 70 80 90 Current (mA) 0.99 1.01 1.03 1.05 1.07 Wavelength (µm) Channel 2 Channel 1

V2=-2 V1=0 V2=0 V1=-2 V2=0 V1=0

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Semiconductor Laser Laboratory

Multiple Wavelength Laser

A. Talneau et. al. Photon. Technol. Lett. 11, 12 (1999)
Conventional growth for strain-

compensated MQW active region

Selectively-grown passive regions
Grating pitches adjusted for 4 nm spacing

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Semiconductor Laser Laboratory

Dual Wavelength DBR Laser

Single ridge waveguide output

aperture

Separate grating elements
Three grating period combinations

1 µm

Λ2 Λ1

Sample Λ 1 Λ 2 1 161.1 161.9 2 161.1 162.7 3 161.1 164.2

Λ1 Λ2 Gain Section

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Semiconductor Laser Laboratory

Dual Wavelength DBR Laser

Single mode operation (~30 db SMSR)
Dual operation over 10-12 mA range

1.042 1.047 1.052 1.057 1.062 Intensity (Log scale) Wavelength (µm) 32 mA 30 mA 35 mA 37 mA. 42 mA I = 45 mA CW, 15°C

Sample ∆λ 1 4.1 2 8.4 3 16.9

1.045 1.050 1.055 1.060 1.065 1.070 1.075 Intensity (10 dB/Div) Wavelength (µm) (a) (b) (c) CW, 15°C

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Semiconductor Laser Laboratory

Example: 8-Channel Transmitter

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

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Semiconductor Laser Laboratory

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

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)