Directly Modulated OEIC-WC (1st Generation – Task Area 3) Jeff Henness, John Hutchinson (Intel), Leif Johansson, Jon Barton, Matt Sysak, Jon Getty, Larry Coldren, Dan Blumenthal University of California Santa Barbara, CA, 93106 Tel: (805)893-8465; Email: henness@engineering.ucsb.edu 4/25/2003 - 1

Overview Objective/Scope Approach Major Accomplishment Demonstrate a modulated OEIC-WC with monitoring capability Approach Photodiode directly connected to SGDBR gain Major Accomplishment Designed and fabricated 1st run of 1st gen OEIC-WC Begun initial testing/characterization Main Issues/Problems/Limitations Contacts, parasitics in test setup limit RF performance Improve monitor design Improve preamp-SOA design, SGDBR tuning, power output Extinction ratio and chirp 4/25/2003 - 2

OEIC Approach In-situ signal monitoring provided No carrier lifetime limitations Reduce pattern dependence Increase linearity Increase bandwidth No filter to remove input wavelength Separate optimization of detection and modulation Net signal gain and programmable 2R regeneration possible High integration density – no branching waveguides required 4/25/2003 - 3

Direct vs External Modulation Directly Modulated SGDBR Integrated External Modulator PostAmp SOA Front Mirror Gain Phase Back Mirror EAM Front Mirror Gain Phase Back Mirror Preamplifier SOA Photodetector Preamplifier SOA Photodetector 4/25/2003 - 4

Concept for Direct Mod Device Layout 1 2 3 5 6 4 PD SGDBR PD Bias Pre Amp SOA SOA Bias Laser Bias Post Amp Input Output 50Ω Signal Monitor 4/25/2003 - 5

SGDBR Direct Modulation Small signal bandwidth = 8GHz 10dB extinction demonstrated at 5GHz with no mode hops 4/25/2003 - 6

Laser Efficiency Enhancements Gain-lever Cascaded Multiple Active Region (MAR) 4/25/2003 - 7

Directly Modulated WC Design Gain-Lever w/ Meander Post-Amp SOA Front Mirror Gain Section Phase Back Mirror Absorber Output Input (optional) Input Pre-Amp SOA PhotoDetector Signal Interconnect PhotoDetector Pre-Amp SOA (for discrete component testing) 500m PreAmp SOA into 50m active photodetector Metal trace to carry photocurrent (data signal) to drive gain section Meander line to provide AC block SGDBR with 300m PostAmp SOA Gain-lever designs included in mask 4/25/2003 - 8

Gain Lever CW Spectra and PD Response Gain Lever SGDBR exhibits low current turn-on PD exhibits linear I-L response Photocurrent enough to provide significant modulation 4/25/2003 - 9

OEIC-WC CW Conversion Spectra in = 1540nm, out = 1546nm Pin of 4dB gives Pout of 17dB – high differential gain 4/25/2003 - 10

Contacts – Error in Fabrication Run Issue: Large number of open circuit N-metal contacts Cause: Nitride not removed under metal – processing error Solution: Oxygen FIB to open area to underlying metal Effect: High resistivity & capacitance ground contact P-metal: Ti/Pt/Au SiN InP FIB 8kV Oxygen opening (80mx80m) N-metal: Ni/AuGe/Ni/Au Long term solution: Change mask and process flow 4/25/2003 - 11

Frequency Response 3dB down at >2.5GHz Clean waveform at 2.5GHz 3dB 4/25/2003 - 12

Signal Monitoring Signal via bias-tee to 50Ω scope input 310A/mW monitor signal -15.6dB conversion fiber-to-fiber 4/25/2003 - 13

Segmented Ridge Laser (Cascaded Multiple Active Region) N series connected diodes in one laser cavity Differential efficiency multiplied by N Signal/noise multiplied by N Threshold current divided by N Stages isolated by ion implants Compatible with SGDBR technology SI InP substrate NV o I /N H + , He Implantation Initially Funded via RFLICS 4/25/2003 - 14

CW Results for MAR Facets: uncoated Stage Temp: 20ºC Stages & Length CW Diff. Efficiency CW Thresh. Current CW Thresh. Voltage DC Input Impedance 12x50mm 390% 2.8 mA 11.3 V 470 W 6x100mm 218% 4.8 mA 5.8 V 110 W 3x200mm 119% 9.9 mA 3.1 V 48 W 1x600mm 37% 29 mA 1.04 V 5.8 W Facets: uncoated Stage Temp: 20ºC Internal Loss: 12.2 cm-1 Internal Efficiency: 69.4% Heatsink: soldered to AlN Initially Funded via RFLICS 4/25/2003 - 15

Segmented Laser Performance Linearity improved by segmentation 3-stage SFDR = 120.3 dB/Hz2/3 Control SFDR = 114.5 dB/Hz2/3 High speed operation possible 5 GHz small-signal bandwidth Resonance-limited Initially Funded via RFLICS 4/25/2003 - 16

Current Status and Future Directions Devices to mounted on carrier, RF probing improved High speed measurements possible Possibly satisfy Phase I milestones Second mask spin will address several aspects Improved monitor/bias connection Improved SOA/detector design Improved SGDBR design Inclusion of multiple-active region embodiment Investigation of saturable absorbers for improved extinction in digital applications 4/25/2003 - 17