Monolithically Integrated Mach Zehnder Interferometer Wavelength Converter and

Monolithically Integrated Mach. Zehnder Interferometer Wavelength Converter and Widely-Tunable Laser in In. P • Milan L. Mašanović, Vikrant Lal, Jonathon S. Barton, Erik J. Skogen, Daniel J. Blumenthal, Larry A. Coldren 04/25/03 Chip-Scale WDM Program

Summary of Work • Objective/scope – Demonstrate In. P 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, 22 nm (L-Band) – 2. 5 GB/s error free operation • Issues – – 04/25/03 SGDBR on-chip output power and mirrors Passive waveguide losses, chip insertion losses SOA speed (gain recovery) Chip-Scale WDM C-Band operation Program 2

Monolithically Integrated In. P AOTWC Sampled Grating DBR Laser Mach-Zehnder Interferometer Input Amplifier Chip-Scale WDM Program 04/25/03 3

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 Chip-Scale WDM Program 04/25/03 4

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

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

Generation I Interferometer Designs • Two different interferometer realizations – MMI/S Bend Design – 2 Stage MMI Design 1 - 1 x 2 MMI Splitter/Combiner 2 - S Bend 2 - 2 x 2 MMI Coupler 3 - MQW SOA 3 2 1 1 2 2 1 3 2 3 Chip-Scale WDM Program 04/25/03 1 7

MMI Components • Function – N*N power splitting/coupling – Most common components: • 1 x 2, 2 x 1 splitter/combiner • 2 x 2 (3 d. B) coupler • Properties – Simple Structure and Fabrication – Low Inherent Loss – Large Bandwidth – Low Polarization Dependence 1515 nm 1545 nm 1575 nm Chip-Scale WDM Program 04/25/03 8

Facet Reflections • Depending on the SOA Gain, Maximum Tolerable Reflection R=0. 25 10 -4 • Optimized Output Waveguide Required • Multilayer (3) AR Coating Width Taper 7° Angle 5 µm Chip-Scale WDM Program 04/25/03 9

Thermal Consideration – Interferometer Design è Thermal Crosstalk ðAffects power/gain/dynamics è 80 μm SOA Spacing ðTradeoff between device length and temperature effects Chip-Scale WDM Program 04/25/03 10

Epitaxial Heterostructure Chip-Scale WDM Program 04/25/03 11

Offset Quantum Well Process Active – Passive Removal Grating Formation In. P/In. Ga. As Regrowth • Most Mature SGDBR Fabrication Technology • Requires Single MOCVD Regrowth Metalization/Anneal Passivation/Implant Ridge Etch Chip-Scale WDM Program 04/25/03 12

Critical Steps - Verification • Active Regions Removal PL Line Scan • Gratings Etch AFM Scan Actual Device Layout (Active and Ridge Layer Shown) Active Regions Chip-Scale WDM Program 04/25/03 13

First Generation Tunable Wavelength Converter 5 um Chip-Scale WDM Program 04/25/03 14

Gain Bandwidth and Tuning Range Gain Peak – 1560 nm Tuning Range – 22 nm Chip-Scale WDM Program 04/25/03 15

Mirror Design • Mirror è Carrier Injection Cause for Index Change (7 nm) è Gen 1 Mirror ðPatchy Band Coverage ðIrregular Supermode Tuning ðGrating pitch – L-band lasers è Gen 2 Mirror ðProblem Fixed Chip-Scale WDM Program 04/25/03 16

Electrical/Optical Control Electrical Control Optical Control Chip-Scale WDM Program 04/25/03 17

DC Extinction Map • Higher Extinction For low bias currents Chip-Scale WDM Program 04/25/03 18

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

Phase-Extinction Relation • SOA Phase Change of Pi Required • High Speed Operation – Lower Index Change • Extend the SOA Length Chip-Scale WDM Program 04/25/03 20

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

2. 5 GB/s Conversion – Fixed SGDBR Wavelength Input Eye Diagram PRBS 231 -1 1535 nm 1545 nm 1565 nm 1575 nm Converted Data 04/25/03 1555 nm Chip-Scale WDM Program 1585 nm 22

2. 5 GB/s Conversion – Fixed Input Wavelength Input Eye Diagram PRBS 231 -1 Converted Data 04/25/03 1557 nm 1566 nm 1570 nm 1578 nm Chip-Scale WDM Program 23

2. 5 GB/s Bit Error Rate Testing Fixed SGDBR Output Wavelength PRBS 231 -1 Input ~2 d. B Power Penalty 2 d. B Chip-Scale WDM Program 04/25/03 24

First Generation WC Performance Limits 5 GB/s Eye λin=1590 nm 2. 5 GB/s 1 m. W 04/25/03 +4 m. W SGDBR Power Difference Chip-Scale WDM Program 25

Summary of Issues to be Resolved • Mirror Design • Tuning Range • Low MZI Input Power (<0. 8 m. W) • Improve Electrical and Optical Extinction • Improve conversion efficiency (input to output) • Speed up Carrier Dynamics Chip-Scale WDM Program 04/25/03 26

Second Generation WC Design • Improvements è Redesigned Mirrors ðWider tuning range ðBetter ‘behavior’ è Output Coupler ðLight Evacuation è Phase Control ðImproved Extinction è Input SOAs ðBoost Input Power ðReduce Lifetime è 1. 4 Q Waveguide ðHigher Output Power Chip-Scale WDM Program 04/25/03 27

Second Generation WC with TIR Mirror • TIR Mirror è Insertion Loss ð~200μm propagation èDistortion ðNo SOA at the input è SNR ðEliminated extra ASE Chip-Scale WDM Program 04/25/03 28

Second Generation WC with TIR Mirror Chip-Scale WDM Program 04/25/03 29

Requirements for High Speed Wavelength Conversion • Requirements – – – 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 Chip-Scale WDM Program 04/25/03 30

Summary • Major accomplishments – Demonstration and testing of world’s first monolithically integrated tunable laser and AO wavelength converter – Wide conversion range: 50+nm in, 22 nm (L-Band) – 2. 5 GB/s error free operation • Future Work – Fabricate Second Generation Devices – Analog Characterization for Gen I Devices – Compare Performance (Digital/Analog) Chip-Scale WDM Program 04/25/03 31