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

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

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

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

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

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

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

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

Facet Reflections Depending on the SOA Gain, Maximum Tolerable Reflection R=0.251.25 10-4 Optimized Output Waveguide Required Multilayer (3) AR Coating Width Taper 5 µm 7° Angle 04/25/03

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

Epitaxial Heterostructure 04/25/03

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

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

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

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

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

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

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

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

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

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

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

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

2.5GB/s Bit Error Rate Testing Fixed SGDBR Output Wavelength PRBS 231-1 Input Indicate power penalties on graph ~2dB Power Penalty 2dB 04/25/03

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

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

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

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

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

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

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