“区域光纤通信网与新型光通信系统”国家重点实验室

New Opportunities for Optical Phase-locked Loops in

Coherent PhotonicsLarry A. Coldren , Mingzhi Lu, Hyun-chul

ParkECE UCSB

“区域光纤通信网与新型光通信系统”国家重点实验室

Outline

Background• Coherent Optical Communication• Optical Frequency Synthesizer/Sweeper

Architecture of OPLL

Experiments and Results

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“区域光纤通信网与新型光通信系统”国家重点实验室

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

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“区域光纤通信网与新型光通信系统”国家重点实验室

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

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“区域光纤通信网与新型光通信系统”国家重点实验室

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

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“区域光纤通信网与新型光通信系统”国家重点实验室

Optical Phase-Locked Loop

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OPLL Concept Optical: Laser Output Phase-Locked: Phase error (Phase noise)

Reduction / Synchronization Loop: Feedback

OPLL Structure

“区域光纤通信网与新型光通信系统”国家重点实验室

OPLL: Optical Phase Detector

Phase Detector Types• Homodyne / Heterodyne• Linear / Nonlinear

Linear Homodyne Detection Balanced loop

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“区域光纤通信网与新型光通信系统”国家重点实验室

OPLL: Optical Phase Detector

Other Detection Types Costas/Decision-driven loop SyncBit loop

Dither loop

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“区域光纤通信网与新型光通信系统”国家重点实验室

OPLL: Optical Voltage Controlled Oscillator

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OVCO techniques:

• Resonator mirrors tuning (by PZT)• Laser driving current

• Phase modulation• Acousto-optic modulation• SSB modulation

LaserPZT/Current control

V c

f LO

OVCO

Laser

V c

+

OVCO

ElectricalVCO

PM/AOM/MZM

f LO

f VCO

“区域光纤通信网与新型光通信系统”国家重点实验室

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

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“区域光纤通信网与新型光通信系统”国家重点实验室

Architecture of OPLL

Costas LoopHomodyne / HeterodyneLoop bandwidth: 1.1GHzPhase error variance: <0.03

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“区域光纤通信网与新型光通信系统”国家重点实验室

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

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EIC: • LIA• SSB Mixer• XOR and a delay line• 1.30 × 1.20 • 50 ps propagation delay

“区域光纤通信网与新型光通信系统”国家重点实验室

Architecture of OPFD

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SSB Mixer • Heterodyne• Frequency sweep (Range:1~20GHz)

SSB Mixer

PFD• Quadricorrelator Type• Pull-in range ： 46GHz

“区域光纤通信网与新型光通信系统”国家重点实验室

Hybrid Loop Filter

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Type II 2nd Order Loop Filter

• High DC gain• OPA delay of 200ps

Feedforward capacitor• Phase compensation

Phase Margin =

“区域光纤通信网与新型光通信系统”国家重点实验室

Experiment and Result

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Locking 10MHz linewidth laser to 100KHz

“区域光纤通信网与新型光通信系统”国家重点实验室

Experiment and Result

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40Gbit/s coherent receiver using costas loop

“区域光纤通信网与新型光通信系统”国家重点实验室

Conclusion

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High bandwidth Small size and low powerLarge optical frequency synthesis rangeFor multiple applications

• Frequency-Modulated Continuous-Wave (FMCW) Light Detection and Ranging (LIDAR) systems

• Widely-and-fast-tunable ultra-narrow-linewidth lasers• Ultra-accurate optical spectrum analyzers

“区域光纤通信网与新型光通信系统”国家重点实验室

谢 谢！