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

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

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
Carefully Design 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

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
Try not to spend too much time on this slide
*Beck Mason, Erik Skogen, Larry Coldren

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

7. 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

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

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

10. Thermal Consideration – Interferometer Design
Is Zhaoyang speaking to this point on thermal? If yes, can you push this slide to him? It also needs some bullets.

11. Epitaxial Heterostructure

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

13. Critical Steps - Verification
Active Regions Removal
PL Line Scan
Gratings Etch
AFM Scan  
Active Regions
Actual Device Layout (Active and Ridge Layer Shown)
This slide is somewhat busy and confusing. Is there any way to simplify and clean up?

14. First Generation Tunable Wavelength Converter
5 um
What are you trying to show here? There is a lot going on and cluttered.

15. Gain Bandwidth and Tuning Range
Gain Peak – 1560nm
Tuning Range – 22nm

16. Tuning Efficiency
This needs a clearer statement of what you are showing here.

17. Mirror Design
Why new design is better?
Current Design
New Design

18. Electrical/Optical Control
Maybe don’t need this slide
Optical Control
Electrical Control

19. DC Extinction Map
This is good
Higher Extinction
For low bias currents

20. Power-Extinction Analysis
Difference in SOA Output Power Strongly Affects Extinction
Keep Powers Equal in Both Branches and Change Phase Independently

21. Phase-Extinction Relation
SOA Phase Change of Pi Required
Extend the SOA Length

22. Test Setup EOM Data Gen. λin EDFA BPF Device Pin PD BER Error Rate
λout
Back-to-back
Attenuator PC

23. 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
1555nm
1585nm

24. 2.5GB/s Conversion – Fixed Input Wavelength
Input Eye
Diagram
PRBS 231-1
1557nm
1566nm
Converted
Data
1577nm
1570nm

25. 2.5GB/s Bit Error Rate Testing
Fixed SGDBR
Output Wavelength
PRBS Input
L-band (due
to filter/receiver)
Indicate power penalties on graph
~2dB Power Penalty

26. First Generation WC Performance Limits
5GB/s Eye
λin=1590nm
+4mW (SGDBR Power
Difference

27. Summary of Issues to be Resolved
Mirror Design
Low MZI Input Power (<0.8mW)
Improve conversion efficiency (input to output)
Measure and understand analog characteristics
Speed up Carrier Dynamics
Non Optimum Electrical and Optical Extinction

28. 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 !

29. Second Generation WC with TIR Mirror
This is cool!

30. Carrier Recovery Time Slide (QWI)

31. Summary Fabricate Second Generation Devices
Finish Analog Characterization for Gen I Devices
Compare Performance (Digital/Analog)
Can you give Zhaoyang your submount pictures to include in the packaging talk?