New Opportunities for Optical Phase-locked Loops in Coherent Photonics

1. New Opportunities for Optical Phase-locked Loops in Coherent Photonics Larry A. Coldren , Mingzhi Lu, Hyun-chul Park ECE UCSB

2. Outline • Background • Coherent Optical Communication • Optical Frequency Synthesizer/Sweeper • Architecture of OPLL • Experiments and Results

3. Coherent Optical Communication • Spring up in 1980s • Coherent receiver vs. IMDD • Improve sensitivity • Longer reach between repeaters • Optical homodyne: Best power penalty performance • OPLL prototypes • Phase error reduction/Synchronization • LIMIT • Laser linewidth • Loop bandwidth • Stability: temperature, vibration, environment fluctuations • Refrigerated in 1990s • EDFA • WDM

4. Coherent Optical Communication • 2000s, Digitalization • Spectral efficiency • Full vector optical field • Linear, nonlinear effects introduced by long-distance propagation • Intradyne: • High-speed ADCs • Sophisticated DSPs • Complicated algorithms • Costly to design/fabricate/operate, Power consumption • 2010s, revival • Enhanced sensitivity • Small size, low power • Sensor applications

5. Optical Frequency Synthesizer/Sweeper • Optical signal processing • Microwave photonics: • Microwave signal generation • Microwave Phase Detector/Shifter • Military: • Beam-forming • LO distribution • Up/Down Conversion • Coherent Optical Measurement and Sensing Systems • FMCW LIDAR • OFDR • Ultra-accurate optical spectrum analyzers

6. Optical Phase-Locked Loop • OPLL Concept Optical: Laser Output Phase-Locked: Phase error (Phase noise) Reduction / Synchronization Loop: Feedback • OPLL Structure

7. OPLL: Optical Phase Detector • Phase Detector Types • Homodyne / Heterodyne • Linear / Nonlinear • Linear Homodyne Detection Balanced loop

8. OPLL: Optical Phase Detector • Other Detection Types Costas/Decision-driven loopSyncBit loop Dither loop

9. OPLL: Optical Voltage Controlled Oscillator • OVCOtechniques: • Resonator mirrors tuning (by PZT) • Laser driving current • Phase modulation • Acousto-optic modulation • SSB modulation + Laser Laser PZT/ Current control PM/AOM/MZM Electrical VCO

10. Optical Phase-Locked Loop • Requirement • Large loop bandwidth • Bandwidth of OPD、OVCO • Short loop delay for stable operation • Narrow laser linewidth • Insensitive to environment fluctuation • Small size • Low power • No crosstalk between phase-locking signal and data • Transparent link • No residual carrier transmission required

11. Architecture of OPLL • Costas Loop • Homodyne / Heterodyne • Loop bandwidth: 1.1GHz • Phase error variance: <0.03

12. Architecture of OPLL • PIC: • SG-DBR laser • Optical Hybrid • four uni-traveling carrier PDs • 4.3 × 0.56 • 40 ps propagation delay • Size: 10 × 10 • Loop delay: 120 ps • EIC: • LIA • SSB Mixer • XOR and a delay line • 1.30 × 1.20 • 50 ps propagation delay

13. Architecture of OPFD • SSB Mixer • Heterodyne • Frequency sweep (Range:1~20GHz) • PFD • Quadricorrelator Type • Pull-in range：46GHz SSB Mixer

14. Hybrid Loop Filter • Type II 2nd Order Loop Filter • High DC gain • OPA delay of 200ps • Feedforward capacitor • Phase compensation • Phase Margin =

15. Experiment and Result • Locking 10MHz linewidth laser to 100KHz

16. Experiment and Result • 40Gbit/s coherent receiver using costas loop

17. Conclusion • High bandwidth • Small size and low power • Large optical frequency synthesis range • For multiple applications • Frequency-Modulated Continuous-Wave (FMCW) Light Detection and Ranging (LIDAR) systems • Widely-and-fast-tunable ultra-narrow-linewidthlasers • Ultra-accurate optical spectrum analyzers

18. 谢 谢！