1550 nm Tunable Lasers and VCSEL Arrays for WDM applications · 1550 nm Tunable Lasers and VCSEL Arrays ... 1550 nm Tunable Lasers and VCSEL Arrays for WDM Applications 5a. ... 1548.6

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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

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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

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Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18


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


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 &amplifier 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


Introduction SGDBR Lasers

-70

-60

-50

-40

-30

-20

-10

0

1525 1530 1535 1540 1545 1550 1555 1560

Inte

nsity

(dB

m)

Wavelength (nm)

0

0.2

0.4

0.6

0.8

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


72 nm Quasi-Continuous Tuning Range

1500

1510

1520

1530

1540

1550

1560

1570

1580

0 5 10 15 20 25 30 35 40

Lase

r Wav

elen

gth(

nm)

Front Mirror Tuning Current (mA)

1500

1510

1520

1530

1540

1550

1560

1570

1580

0 5 10 15 20 25 30 35 40

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.


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


Integrated Amplifier Characteristics

• 6 mW peak output power (1 mW min) , 8.5 dB gain.• <10 GHz wavelength shift with 45 dB power variation.

-70

-60

-50

-40

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-20

-10

0

1548.6 1548.8 1549 1549.2 1549.4 1549.6

Rel

ativ

e In

tens

ity (d

Bm

)Wavelength (nm)

+/- 0.04 nm (5 GHz)

45 dB

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0 0.2 0.4 0.6 0.8 1 1.2

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


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.

-50

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-10

0

10

-4.0-3.5-3.0-2.5-2.0-1.5-1.0-0.50.0

1525.11541.91548.31565.5

Extinction (dB)

Voltage (V)

-40

-30

-20

-10

0

152015301540155015601570

Extin

ctio

n (d

B)

Wavelength (nm)

-4.0 V

-1.0 V-2.0 V

-3.0 V

0.0 V

EAM

Gain Back Mirror

Implanted Section

Front Mirror

Phase


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


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.


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


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


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


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


MAR VCSEL Results

1530 1535 1540 1545 1550λλλλ

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


0

0.2

0.4

0.6

0.8

1

0 10 20 30 40

Ligh

t Out

put [

mW

]

Current [mA]

Pulsed: 300ns, 1kHz15oC

Sb-Based DBR VCL with Underetched Active Region

0

0.2

0.4

0.6

0 2 4 6 8 10 12 14 16

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%


ηηηηD=7.6%


ηηηηD=4.4%


New VCSEL Results

• ηd ~ 7%, Jth ~ 800A/cm2

• Voltage reduced by 50% ! !• CW lasing being tested

0

1

2

3

4

5

6

7

8

0 5 10 15 20 25

Volta

ge [V

]

Current [mA]

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 5 10 15 20 25

0C5C10C13C17C20C25C30C35C40C45C50C55CLi

ght [

mW

]

Current [mA]


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


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.


-80

-70

-60

-50-40

-30

-20

-10

950 960 970 980 990 1000

Ligh

t Int

ensi

ty (d

Bm)

Wavelength (nm)

81 2 3 4 5 6

7

8

BOTTOM-EMITTING PIE-VCSEL


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


•••

• • •

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


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


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

Documents

1550 nm Tunable Lasers and VCSEL Arrays for WDM applications · 1550 nm Tunable Lasers and VCSEL Arrays ... 1550 nm Tunable Lasers and VCSEL Arrays for WDM Applications 5a. ... 1548.6