1. External Modulation OEIC Wavelength Converters
Task Area: [1,3] Jon Barton, Matt Sysak, Jeff Henness,
John Hutchinson (Intel), Larry Coldren, Dan Blumenthal
University of California
Santa Barbara, CA
Tel: (805) ;

2. Outline Objective/Scope: Approach: Major Accomplishments: Issues:
To pursue alternative wavelength converter designs to achieve higher speed, chirp tailorability and wavelength monitoring capabilities
Approach:
Integrated external modulators
Major Accomplishments:
1st Generation OEIC-WC mask fabricated – using laser-EA modulator devices currently in process
Issues:
Drive voltage - MQW design
Bandwidth – traveling wave to reach > 10 GHz

3. Wavelength Converter Designs
Direct Modulated SGDBR
Integrated External Modulator
SGDBR
SGDBR
Post Amp SOA
Front Mirror
Gain
Phase
Back Mirror
EAM
Front Mirror
Gain
Phase
Back Mirror
Preamplifier SOA
Photodetector
Preamplifier SOA
Photodetector

4. External modulators for OEICs WC
Electro-Absorption (EA) Modulators (Franz-Keldysh and MQW types with lumped and Traveling wave electrodes)
Tandem EA modulators for chirp compensation
Mach-Zehnder modulators for high speed, low drive voltage, low photocurrent generation and chirp tailorability EA EA

5. OEIC-MOD Equivalent Circuit & Operation
Detector
Mod
Pindet
Pout R Vm
-Vb
Pinmod
Detector
For EAM, Pindet >> Pinmod to avoid saturation (or kill DC photocurrent in EAM)
For MZ reduced photocurrent issue
(permits higher laser power – modulator gain)
Mod.
Combined EAM-detector and EAM shown by Hsu-feng Chou

6. Reduction in Photocurrent Study
Goal:
Reduce effective carrier lifetime significantly below the device transit time.
Propose use of thermally stable Ion Implantation to produce regions of high resistivity through introduction of mid-gap energy levels.
EA Modulator h+
p - InP hv
implant
n - InP e-

7. OEIC-Mod ac Equivalent Circuit
CEAM
 0.3pF
CPhotoDetector
 0.2pF
50Ω
Best case lumped element devices limited to approximately 6 GHz
Model verified using P-Spice Equivalent Circuit Model for OEIC

8. Lumped EAM modulator performance
Typical bandwidth measurement for a lumped 250m long device

9. Traveling-wave EAM Initial work funded by RFLICS PMGI bridge Waveguide
n-contact
p-contact
CPW feedline G S Au
PMGI
N-contact
P-contact
Initial work funded by RFLICS

10. Traveling-wave rf response
Frequency (GHz)
-50
-45
-40
-35
-30
-25 10 20 30 40 50
Relative EO- frequency response
open
50 ohm
35 ohm
Dot curve : experiment (35 Ohm)
The bandwidth :
> 30GHz
-3dB
50 termination : -6 dB 40GHz from D.C.
Velocity mismatch & microwave loss : -2.0dB
Initial work funded by RFLICS

11. Waveguide Photodetector Performance
Franz-Keldysh
waveguide detectors
Very linear response
High saturation current
OEIC detector requires mW input power (to get mA of current) to drive modulator or gain section 10 20 30 40 50 60 70 80 5 15
EAM photocurrent (mA)
Input optical power (au)
SOA
Mod

12. First Generation OEIC-EAM Devices
Pre Amp SOA
Pre Amp SOA
Photodetector
Photodetector
Pre Amp SOA
First Generation Devices Designed and in Process

13. Alternative OEIC Solutions
Integrated Mach Zehnder
SGDBR
MZ Modulator
Front Mirror
Gain
Phase
Back Mirror
Preamplifier SOA
Photodetector

14. Mach-Zehnder Based Devices
Mach Zehnder Device Based Wavelength Converters
Better Power handling capability than EA Modulators – low photocurrent generation
Chirp tailorability – increased reach
Low Drive Voltage Vp < 3V
High Bandwidth > 10 GHz
Wide Tuning Range

15. Integrated MZ Layout SOA SGDBR Mach-Zehnder 1x2 MMI splitter
Lumped electrode Mach-Zehnder
Mach-Zehnder
10 µm
1x2 MMI splitter
2x2 combiner
Phase shifter
Tunable MMI
Lumped MZ Pads

16. Integrated Mach-Zehnder Results
Initial work funded by RFLICS

17. Traveling-Wave Mach-Zehnder
Distributed contacts )) ( )
1.4
optical n
electrical (n L c B
group - = p
Initial work funded by RFLICS

18. Summary/Future Work Preliminary Circuit Modeling completed for devices
Design completed and Processing started on 1st Generation OEIC using tandem external EA-modulators
Consideration of Mach-Zehnder based OE Wavelength converters and traveling-wave devices

19. Integration Platforms

20. Wavelength Converter Enhancements Using QWI
Task Area: Integration Platforms
Wavelength Converter Enhancements Using QWI
James Raring, Erik Skogen, Jon Barton, Larry Coldren

21. Overview Accomplishments Main issues Objective Approach
Develop a novel QWI process for the fabrication of CQW wavelength-agile PICs to allow for the monolithic integration of high power SGDBRs with other optimized components
Approach
Impurity-free vacancy-enhanced QWI
Accomplishments
Achieved 3 band edges in single PIC
Monolithically integrated optimized SGDBRs with EAMs
Main issues
OEIC: Improve EAM design for better absorption and bandwidth
AOWC: Optimize SOA design for low saturation power

22. Quantum Well Intermixing Theory
Impurity-free vacancy-enhanced quantum-well-intermixing
Theory
Create vacancies
Thermal process to diffuse vacancies
Vacancies allow atoms to exchange positions
Smears the well/barrier interface, increasing the quantized energy level
λg1
λg2

23. Quantum Well Intermixing Process
Novel QWI process
Ability to achieve multiple band edges with a single implant

24. Offset Vs CQW
- 50% larger confinement factor in CQW → 50% more modal gain

25. Advantages for Wavelength Converters
Low Threshold High Power SGDBR Lasers
50% more modal gain with centered quantum wells
Higher overall efficiency
AOWC
OEIC
Efficient EA Modulator
- Higher Δα/ΔV with shallow MQWs
-Reduced length and higher speed
Low saturation power SOAs
-Enhanced cross-gain modulation

26. Initial SGDBR/EAM Results: PL
Achieved three desired band edges across wafer
Monolithically integrated widely-tunable laser with EAM

27. SGDBR CQW BRS Cross Section
1.7um ridge
7 x 65Å wells
8 x 80Å barriers
Proton Implant
10um mask in gain
4um mask in EAM

28. SGDBR Results Ith = 8.2 mA ηi = 85% Slope Efficiency = 25%mA
αia = /cm
αip = 2.8 1/cm

29. EAM Frequency Response
• Capacitance due to homojunction can be reduced with tighter implant
• Implanted EAM appears to be limited by pad capacitance
- No pad capacitance on wavelength converter design

30. EAM DC Absorption Add quantum wells for increased absorption
Results in ~ 1V/10dB with 200um length in 10 QW

31. Future Work Improve modulator bandwidth for OEIC
Minimize EAM parasitics
Low k dielectric under interconnect for reduced capacitance
Tighter implant profiles for reduced homojunction capacitance
Explore traveling wave designs
EA and Mach-Zehender modulators
Improve EAM efficiency for OEIC
Redesign active region for increased absorption
Develop technology for higher-efficiency AOWC
Design SOAs with low saturation power
Fabricate OEIC wavelength converters using QWI
Fabricate AOWC wavelength converters using QWI