Light source approach for silicon photonics transceivers September 2014 Fiber to the Chip
Silicon Photonics Silicon Photonics Technology: Silicon material system & processing techniques to manufacture integrated optical circuits and devices Passive optics + optical modulation + optical detection (+ electronic circuits) Goal of Silicon Photonics: Leverage from the IC industry: o Design infrastructure and methodologies o Wafer manufacturing and methodologies o Packaging & Test infrastructure and methodologies Enable a high level of integration: o Increased functionality and density o Simplification of optical/electrical packaging & test Where Silicon Photonics makes little sense: Low volume applications (not interesting for fab) Manufacturing process requires too many changes (no leverage) Page 2
Silicon Photonics Transceiver Architecture Serial Interface Digital Control 1:4 Optical Splitter To Other Channels Single-Mode Waveguide SFP In TX Control HSPM Cal. ADC PIN Distributed MZI Driver and Calibration Circuit Monitor PD Tap SPGC Optical Outputs Laser Driver SFP Out SFP Driver Receiver PD PSGC Optical Inputs Laser Page 3
Optical Transceiver Optical Requirements Transmitter Optimize Optical Modulation Amplitude: Modulator o Low passive insertion loss o High phase modulation efficiency ( > ER) Light Source: o Increase optical output power (limited by eye safety requirements) Power dissipation: Modulator: o Low HSPM parasitic capacitance o High modulation efficiency Light Source: o High slope efficiency (also at high T) Receiver Optimize receiver sensitivity: High responsivity photodiode High bandwidth photodiode Low dark current photodiode Low capacitance photodiode Trade off BW/noise in TIA design High Performance Silicon Photonics Device Library Low loss coupling Low loss waveguides High efficiency modulators High responsivity, high bandwidth photodiodes High performance, efficient and stable CW light source Maximize coupled power Increase laser diode efficiency Advanced modulation (e.g. PAM) may add additional requirements such as RIN, line width, Some devices (e.g. rings) may add additional requirements Page 4
Searching a Suitable Light Source for Si Photonics Many types of light sources were explored: Lessons learned: Use mature InP laser diode technology Include an optical isolator Use efficient coupling scheme into die Wafer level assembly, packaging and test Use established burn in methods We settled on a standard InP laser diode in a silicon micropackage Page 5
Light Source: Laser Micro Package LIGHT SOURCE APPROACH: Standard BH MQW DFB Laser diode packaged in hermetic silicon housing Magnifying optics for low loss coupling Build in optical isolation using latched garnet SILICON MICRO MACHINED LASER DIODE HOUSING: Base wafer: silicon micro bench Lid wafer: cavity with mirror Hermeticity obtained by solder seal Reflector Polarization rotator AR Coating Laser diode Pads Reflector Membrane Laser diode Wave plate Ball Lens Pads Magnified Beam Waist Solder Seal Wave plate Page 6
Light Source: Wafer Level Manufacturing 6 base wafer (~3000 LaMPs/wafer) All components passively placed with commercial semiconductor pick & place tools Automated wafer level optical test More than 3/4 million LaMPs in the field Page 7
Light Source: Wafer Level Test WAFER LEVEL OPTICAL TEST: Test of assembled LaMPs on wafer scale Optical tests performed: Coupled power into SMF, LIV Parameters (Ith, slope efficiency), Spectral: Wavelength/SMSR and beam profile Hermeticity test by membrane deflection Automated wafer tester Electrical and optical probing Fiber LaMP Wafer Electrical Probes Page 8
Light Source: Thermal Considerations Temperature sensitivity of device performance The temperature dependence of performance parameters is included in the behavioral models in the design kit T sensitivity in resonant silicon photonic devices can be compensated with control systems Laser diode is temperature sensitive: Lasing wavelength, output power Effect of temperature on reliability: For electronic circuits and laser diode the junction temperature should not exceed a certain level to ensure reliability Heat sinking of those devices is therefore often mandatory Thermal modeling/measurements in combination with performance and reliability requirements define: Maximum case temperature, or Combination of power dissipation, air temperature and airflow Page 9
Light Source: Reliability Light Source: DFB laser diode packaged with magnifying optics in a miniature hermetic silicon housing Laser Diode Reliability: Off the shelf, InP based, MQW BH DFB laser diode InPlaser diode reliability: o Mitsuo Fukuda Reliability and Degradation of Semiconductor Lasers and LEDs, Artech House, 1991 o Osamu Ueda Reliability and Degradation of III V Optical Devices, Artech House, 1996 Laser diode suppliers provide: o Burn in conditions and pass fail criteria o Random failure rate estimate, e.g. based on > 90 billion field hours: < 0.05 FIT o Wear out reliability model Described by output power degradation rate at constant current (in %/khr) Quarterly monitoring of wear out reliability behavior to confirm model Laser aging model used to establish transceiver total failure rate of <10 FIT at 5 years @ 70 C case temperature Page 10
Summary Silicon Photonics requires: High volume Process technology close to processes available in standard CMOS fabs Optimize optical modulation amplitude (OMA) of optical transmitters: Output power (CW light source) High modulation extinction ratio (ER) Micro packaged laser diode: High volume manufacturing on wafer scale (assembly & test) High intrinsic light source efficiency and high efficiency coupling Built in optical isolator for stable operation High performance: optical power, efficiency, spectral, reliability Proven manufacturing and reliability by hundreds of thousands of devices in the field Page 11
Acknowledgements This presentation shows the work of the entire Luxtera team, their contributions are greatly acknowledged. Thank you for your interest. Page 12