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1550 nm Tunable Lasers and VCSEL Arraysfor WDM applications
L. A. ColdrenUC-Santa Barbara
• Increase bandwidth without increasing data rate/electronics' performance
• Parallel protection channels in one medium (cost/size/weight/robustness)
• Wavelength selective routing (very fast, efficient, and remote routing)
• Outstanding leverage in commercial marketplace (but it isn't addressing important issues)
• Need small, fast, efficient, chip-scale O/E components
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1. REPORT DATE 18 APR 2000
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4. TITLE AND SUBTITLE 1550 nm Tunable Lasers and VCSEL Arrays for WDM Applications
5a. CONTRACT NUMBER
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6. AUTHOR(S) 5d. PROJECT NUMBER
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7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) University of California, Santa Barbara
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12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release, distribution unlimited
13. SUPPLEMENTARY NOTES DARPA/MTO, WDM for Military Platforms Workshop held in McLean, VA on April 18-19, 2000, Theoriginal document contains color images.
14. ABSTRACT
15. SUBJECT TERMS
16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT
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Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18
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Outline(1550 nm InP-based hardware)
• SGDBR Widely-tunable Lasers/Laser-Modulators/Laser-Amplifiers
-- Needed: Compact/efficient wavelength converter/SGDBR Compact/efficient wavelength router
Integration/packaging
• 1550nm VCSELs
-- Needed: Higher performance/better manufacturability WDM arrays/coupling optics Amplifiers/wavelength converters
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Improved Sampled Grating DBRWidely-Tunable 1.55µm Lasers
Larry A. Coldren, University of California Santa Barbara
Objective•Improved widely tunable SGDBR laser•Increase tuning range to greater than60nm•Develop integrated wavelength monitorfor tuning control•Develop integrated modulator &lifier designs
Approach•Dry etch gratings through windows in SiNxmask for improved regrowth•Employ a thick low bandgap waveguide toincrease index tuning efficiency•Taper the active passive junctions toeliminate spurious reflections•Employ a buried heterostructure design forimproved carrier confinement
Accomplishments•Demonstrated continuous tuning range of 72 nm forburied device•Developed integrated wavelength monitor•Integrated the tunable laser with an electro-absorption modulator capable of 22dB extinctionover a 47nm tuning range•Integrated a SOA with a gain of 8.5dB and a 6mWsaturation power together with the SGDBR•Transferred technology to Agility Communications
Gain
Phase
FrontMirror
SGDBR Laser BackMirror
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Introduction SGDBR Lasers
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Inte
nsity
(dB
m)
Wavelength (nm)
0
0.2
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0.6
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Ref
lect
ion
Coe
ffici
ent
• Periodically sampling the gratings inthe mirrors yields multiple reflectionpeaks.
• The laser wavelength is controlled byaligning reflection peaks in the frontand back mirrors.
Front Mirror GainPhaseControl Back Mirror
n - InP
p - InP
Offset Quantum W ells
Stop Etch Layer
1.4Q W aveguide
Sam pling Period
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72 nm Quasi-Continuous Tuning Range
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Lase
r Wav
elen
gth(
nm)
Front Mirror Tuning Current (mA)
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Lase
r Wav
elen
gth(
nm)
Front Mirror Tuning Current (mA)
72 72 nmnm
• 180 50 GHz channels, > 35 dB SMSR, 2 mW peak power• Tuning range limited by available gain from MQW.
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Integrated SGDBR and SOA Device Structure
Curved PassiveOutput Guide(R~10-4)
GainPhase
Front Mirror
Amplifier
Back Mirror
Grating Bursts
n-InP Implanted Region
p-InP
SiNx
Waveguide
Quantum Wells
InGaAs Contact Layer Ti/Pt/Au Contact
Buried Ridge Stripe (Buried Ridge Stripe (BRSBRS))
•• WaveguideWaveguide: 1.4 : 1.4 µµmm InGaAsP InGaAsP•• Active Region: Six 1% Active Region: Six 1% CompressivelyCompressively Strained Strained QWsQWs
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Integrated Amplifier Characteristics
• 6 mW peak output power (1 mW min) , 8.5 dB gain.• <10 GHz wavelength shift with 45 dB power variation.
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ativ
e In
tens
ity (d
Bm
)Wavelength (nm)
+/- 0.04 nm (5 GHz)
45 dB
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25 mA, 3.8 dB50 mA, 7.1 dB150 mA, 8.7 dBTransparency
Out
put P
ower
(mW
)
Input Power (mW)
1 dB Gain Compression Point
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SGDBR Lasers With IntegratedElectro-Absorption Modulators
• Extinction Ratio is Greater Than 22dB over the entire 40 nm tuningrange of the laser for a 250 µm longmodulator.
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1525.11541.91548.31565.5
Extinction (dB)
Voltage (V)
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Extin
ctio
n (d
B)
Wavelength (nm)
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0.0 V
EAM
Gain Back Mirror
Implanted Section
Front Mirror
Phase
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Wavelength Converter types
All-optical λλλλ-converter: -Uses interferometric branches - Signal remains optical - Design more complex - Physically large device
Jennifer DolanJennifer Dolan 4/11/004/11/00
Opto-Electronic λλλλ-converter: - Optical signal is converted to an electrical signal, then retransmitted - Large tunability and conversion range - Much smaller device - very flexible
InputOpticalsignal
OutputOptical Signal
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Curre nt C ond it io ni ng El em en t
S. I.
pn •φ
Pha se
• •
SG DB RTu ne -2SG DB R Tu n e-1
Gai n SOA -1•
SOA Bi as -1
SOA -2•
EA M•
Acti veBi as
SOA Ab so rb e r
H+
• • •
Tu ne -1 Tu ne -2Pre-Amp lif ierBi as
H +
Bi as
•
SOA Bi as -2
D B R D B R
(Much simpler versions are possible by eliminating optional elementssuch as gratings and preamp in receiver section or an SOA in thetransmitter section.)
Perspective view of O/E/O wavelength converter.
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Wavelength Routing Element(possibly remote)
Integration of processing elements and packet switchingsystem on a chip using wavelength routing techniques.
Headerextraction/insertion
Wavelength converters
Optical Switching/Routing
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1-D O/E/O widely-tunable wavelength converter array with a compact AWG. A32 x 32 switch should fit on a 1 cm2 chip, assuming 250 µm input & outputwaveguide spacings.
D ETSGDBR
>
•••
•••
λ fD ET
SGDBR>
D ETSGDBR
λ k
A 1
A 5
A n
> > > > > > > BnB 1
λq
Slab- Waveguide
Beam-Expansion/ Interference
Section
InP Substrate
Integrated optical crossbar switch
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n-InG aA lA s
A ctive
A ctive
A ctive
n-T op DBR
n -Bottom DBR
pn
pn
pn
D etector
V inpu t
output
n-InG aA lA s
n-InP-sub strate
p-InG aA sn-InG aA lA s
Surface-normal wavelength converter.
• InP-based VCSEL with multiple-active-regions and seriesphotodetector => PNA
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MAR VCSEL
n-InP substrate
35 period n-typeAlGaInAs/AlInAs
DBRR=98.4%
45 period n-typeAlGaInAs/AlInAs
DBRR=99.8%
2-λ cavityEsaki-junctions
QW activeregions
Good quality DBRsTotal thickness of epitaxial layers ~ 20 µµµµm
Fully-epitaxial,lattice-matched
to InP
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MAR VCSEL Results
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01234567
0 10 20 30 40 50 60 70 80Current (mA)
Volta
ge (V
)
• Jth as low as 570 A/cm2
• ηd > 60 % (d = 50µm)• Pout > 15 mW• Vth ~ 3 V (3hν = 2.4eV)• Rd ≈ 100 Ω (d = 25µm)• λ ≈ 1.55 µm
I = 2Ith
I = 1.1Ith
0
2
4
6
8
0 10 20 30 40 50 60Current (mA)
Pow
er (m
W)
D=100µµµµm
D=50µµµµmD=25µµµµm
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0
0.2
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1
0 10 20 30 40
Ligh
t Out
put [
mW
]
Current [mA]
Pulsed: 300ns, 1kHz15oC
Sb-Based DBR VCL with Underetched Active Region
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Out
put P
ower
[mW
]
Current [mA]
25µµµµm Etched Pillar
15µµµµm Etched Pillar
15µµµµm Underetched:Jth=1.6kA/cm2
ηηηηD=8.0%
Pulsed: 300ns, 1kHz15oC
Etched Pillar VCL VCL with Underetched Active Region
InAlGaAs QW
AlGaAsSb DBR
AlGaAsSb DBR
SiO2 + SiN
Ti/Pt/Au
AuGe/Ni/Au
50µµµµm:Jth=1.3kA/cm2
ηηηηD=8.2%
25µµµµm:Jth=1.2kA/cm2
ηηηηD=7.6%
15µµµµm:Jth=3.1kA/cm2
ηηηηD=4.4%
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New VCSEL Results
• ηd ~ 7%, Jth ~ 800A/cm2
• Voltage reduced by 50% ! !• CW lasing being tested
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1
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8
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Volta
ge [V
]
Current [mA]
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0C5C10C13C17C20C25C30C35C40C45C50C55CLi
ght [
mW
]
Current [mA]
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n-InP
n -InP
InP Substrate
AlInGaAs QWsOxide aperture
Tunnel diode
AlAsSb/AlGaAsSb DBR
Au contacts
Intracavity-contacted all-epitaxial device with no mirror doping and InP heat spreaders
Thermally Managed Long Wavelength VCSEL
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Tapered Oxide Apertures in AlInAs on InP
AlInAs (λ/4)AlInGaAs (λ/4)
?????????????????????????????
AlInGaAs (λ/4)
TaperedOxide Oxidant
Supply Layer
OxidationLayer30 minutes at 500 °C
1 hour at 500 °C
The presence of the oxidant supply layer acceleratedthe lateral oxidation rate of the neighboring ??????layer by a factor of 4 relative to identical AlInAslayers elsewhere in the structure.
Vertical oxidation of ?????? (oxidation downwardfrom the oxidant supply layer) resulted in a taper.
??????
Layer thicknessnot to scale.
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Ligh
t Int
ensi
ty (d
Bm)
Wavelength (nm)
81 2 3 4 5 6
7
8
BOTTOM-EMITTING PIE-VCSEL
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Fiber
VCSEL Chip
λ1
λ2
λ3
λn
•••
Coupling of several VCSELs to the same point by offset integrated microlenses.Nearly lossless coupling possible for multimode fiber for angles within its NA.
Coupling of WDM VCSEL Array to Fiber
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•••
• • •
2-D WDMVCSEL Array with µlenses
Driver Circuit
Fiber
CGH
Use of computer generated hologram (or simple grating in one dimension)to provide spectral separation for matching to single mode fiber
Coupling of WDM VCSEL Array to Fiber
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Outline(1550 nm InP-based hardware)
• SGDBR Widely-tunable Lasers/Laser-Modulators/Laser-Amplifiers
-- Needed: Compact/efficient wavelength converter/SGDBR Compact/efficient wavelength router
Integration/packaging
• 1550nm VCSELs
-- Needed: Higher performance/better manufacturability WDM arrays/coupling optics Amplifiers/wavelength converters
APPROVED FOR PUBLIC RELEASE, DISTRIBUTION UNLIMITED
1550 nm Tunable Lasers and VCSEL Arraysfor WDM applications
L. A. ColdrenUC-Santa Barbara
• Increase bandwidth without increasing data rate/electronics' performance
• Parallel protection channels in one medium (cost/size/weight/robustness)
• Wavelength selective routing (very fast, efficient, and remote routing)
• Outstanding leverage in commercial marketplace (but it isn't addressing important issues)
• Need small, fast, efficient, chip-scale O/E components