1. Monolithically Integrated Mach-Zehnder Interferometer Wavelength Converter and Widely-Tunable Laser in InP
Milan L. Mašanović, Vikrant Lal, Jonathon S. Barton, Erik J. Skogen, Daniel J. Blumenthal, Larry A. Coldren

2. Summary of Work Objective/scope Approach Major accomplishments Issues
Demonstrate InP monolithic integration of a widely tunable laser and all-optical wavelength converter for digital and analog wavelength conversion.
Approach
Utilize a common offset quantum well integration platform and a combination of passive, active and filter waveguides to implement on a single chip a Mach-Zehnder SOA Interferometer and widely tunable SGDBR laser.
Major accomplishments
Demonstration and testing of world’s first monolithically integrated tunable laser and AO wavelength converter
Wide conversion range: 50+nm in, 22nm (L-Band)
2.5GB/s error free operation
Issues
SGDBR on-chip output power and mirrors
Passive waveguide losses, chip insertion losses
SOA speed (gain recovery)
C-Band operation
04/25/03

3. Monolithically Integrated InP AOTWC
Sampled Grating DBR Laser
Mach-Zehnder Interferometer
Input Amplifier
04/25/03

4. Integration Challenges
Enable a Common Fabrication Platform
Offset Quantum Wells
Tradeoffs Between Laser and MZI Performance
Optical Isolation
Lasers Highly Sensitive to Coherent Reflections
Active/Passive Interfaces
Amplified Reflections
Facet Reflections Need to be Suppressed Effectively (10-5 or better)
Processing Issues
Material Quality - Uniformity
Processing Uniformity - Very Long Devices
04/25/03

5. SGDBR Laser Background
4 Section Device
Wide Tunability, High Power
Suitable for Integration
Passive – Active Waveguide Combination
Does not Require Facet Reflection to Lase
Realized in Several Integration Platforms(*)
Offset Quantum Wells
Burried Ridge Stripe (OQW, QWI)
Front Mirror
Gain
Phase
Rear Mirror
Offset QW Device
*Beck Mason, Erik Skogen, Larry Coldren
04/25/03

6. Interferometer - Cross Phase Modulation
π phase shift
CW in
No CW
light out
Converted
Signal Out
Data in
Cross-Phase Modulation Principle
Semiconductor optical
amplifiers used to achieve
 phase shift
Incoming data disturbs
phase balance
 data conversion
Transfer Function
SOA Current
Optical Power
Inverting Operation
Non Inverting Operation
04/25/03

7. Generation I Interferometer Designs
Two different interferometer realizations
MMI/S Bend Design
2 Stage MMI Design
1 - 1x2 MMI Splitter/Combiner
2 - S Bend
3 - MQW SOA 1 2 3
1 - 1x2 MMI Splitter/Combiner
2 - 2x2 MMI Coupler
3 - MQW SOA 3 1 2
04/25/03

8. MMI Components Function Properties N*N power splitting/coupling
Most common components:
1x2, 2x1 splitter/combiner
2x2 (3dB) coupler
Properties
Simple Structure and Fabrication
Low Inherent Loss
Large Bandwidth
Low Polarization Dependence
1515 nm
1545 nm
1575 nm
04/25/03

9. Facet Reflections
Depending on the SOA Gain, Maximum Tolerable Reflection
R=0.25
Optimized Output Waveguide Required
Multilayer (3) AR Coating
Width Taper
5 µm
7° Angle
04/25/03

10. Thermal Consideration – Interferometer Design
Thermal Crosstalk
Affects power/gain/dynamics
80 μm SOA Spacing
Tradeoff between device length and temperature effects 3
04/25/03

11. Epitaxial Heterostructure
04/25/03

12. Offset Quantum Well Process
Active – Passive Removal
Most Mature SGDBR Fabrication Technology
Requires Single MOCVD Regrowth
Grating Formation
InP/InGaAs Regrowth
Metalization/Anneal
Passivation/Implant
Ridge Etch
04/25/03

13. Critical Steps - Verification
Active Regions Removal
PL Line Scan
Gratings Etch
AFM Scan  
Active Regions
Actual Device Layout (Active and Ridge Layer Shown)
04/25/03

14. First Generation Tunable Wavelength Converter
5 um
04/25/03

15. Gain Bandwidth and Tuning Range
Gain Peak – 1560nm
Tuning Range – 22nm
04/25/03

16. Mirror Design Mirror Carrier Injection Cause for Index Change (7nm)
Gen 1 Mirror
Patchy Band Coverage
Irregular Supermode Tuning
Grating pitch – L-band lasers
Gen 2 Mirror
Problem Fixed
04/25/03

17. Electrical/Optical Control
Maybe don’t need this slide
Optical Control
Electrical Control
04/25/03

18. DC Extinction Map Higher Extinction For low bias currents 04/25/03
This is good
Higher Extinction
For low bias currents
04/25/03

19. Power-Extinction Analysis
Difference in SOA Output Power Strongly Affects Extinction
Keep Powers Equal in Both Branches and Change Phase Independently
04/25/03

20. Phase-Extinction Relation
SOA Phase Change of Pi Required
High Speed Operation – Lower Index Change
Extend the SOA Length
04/25/03

21. Test Setup EOM Data Gen. λin EDFA BPF Device Pin PD BER Error Rate
λout
Back-to-back
Attenuator PC
04/25/03

22. 2.5GB/s Conversion – Fixed SGDBR Wavelength
1535nm
1565nm
Input Eye
Diagram
PRBS 231-1
Maybe need to make this more readable.
1545nm
1575nm
Converted
Data
04/25/03
1555nm
1585nm

23. 2.5GB/s Conversion – Fixed Input Wavelength
Input Eye
Diagram
PRBS 231-1
1557nm
1566nm
Converted
Data
1578nm
1570nm
04/25/03

24. 2.5GB/s Bit Error Rate Testing
Fixed SGDBR
Output Wavelength
PRBS Input
Indicate power penalties on graph
~2dB Power Penalty
2dB
04/25/03

25. First Generation WC Performance Limits
5GB/s Eye
λin=1590nm
2.5GB/s
+4mW SGDBR
Power
Difference
1mW
04/25/03

26. Summary of Issues to be Resolved
Mirror Design
Tuning Range
Low MZI Input Power (<0.8mW)
Improve Electrical and Optical Extinction
Improve conversion efficiency (input to output)
Speed up Carrier Dynamics
04/25/03

27. Second Generation WC Design
Improvements
Redesigned Mirrors
Wider tuning range
Better ‘behavior’
Output Coupler
Light Evacuation
Phase Control
Improved Extinction
Input SOAs
Boost Input Power
Reduce Lifetime
1.4Q Waveguide
Higher Output Power
Fixed !
04/25/03

28. Second Generation WC with TIR Mirror
Insertion Loss
~200μm propagation
Distortion
No SOA at the input
SNR
Eliminated extra ASE
04/25/03

29. Second Generation WC with TIR Mirror
This is cool!
04/25/03

30. Requirements for High Speed Wavelength Conversion
Small Optical Area
Large Confinement
High Differential Gain
Long Length
High Bias Current
Buried Ridge Stripe using QWI
Improved Confinement
Reduced Losses/Reflections
Reduced Heating
04/25/03

31. Summary Major accomplishments Future Work
Demonstration and testing of world’s first monolithically integrated tunable laser and AO wavelength converter
Wide conversion range: 50+nm in, 22nm (L-Band)
2.5GB/s error free operation
Future Work
Fabricate Second Generation Devices
Analog Characterization for Gen I Devices
Compare Performance (Digital/Analog)
Can you give Zhaoyang your submount pictures to include in the packaging talk?
04/25/03