Research On Optical Phase-locked Loop

Optical Phase-Locked Loop(OPLL) is an electrical feedback technique to synchronize one optical carrier to another. Using this method, the phases of one or more optical wave are locked to a reference optical phase. For its small size, low power consumption and the ability to actively reduce laser phase noise, optical phase-locked loop has attracted much attention in the field of coherent optical communication, coherent optical measurement, microwave photonics and coherent optical power combining. In these applications, OPLL plays as an essential element in the system.This thesis gives a detailed introduction of OPLL technique, which includes its applications, classification and principles, etc. Then it focuses on the design of OPLL in two applications. In the application of Optical Frequency Domain Reflectometry(OFDR), a wide-range frequency-sweeping narrow-linewidth laser source based on heterodyne OPLL is studied. In the application of inter-satellite optical communication, a high sensitivity optical homodyne receiver using Costas Loop is studied. Both these two works include theoretical modeling and analysis, system design consideration, loop parameter optimization and experimental results analysis.In this thesis, the theoretical analysis of OPLL technique can be separated into three sections, which are Optical Voltage-Controlled Oscillator(OVCO), Optical Phase Detector(OPD) and loop filter. In OVCO section, the frequency modulation response and optical phase noise of different types of OVCO are studied. In OPD section, we compared the homodyne and heterodyne, digital and analog, linear and nonlinear optical phase detection technique. We studied the features and typical applications for each kind of OPD. In the discussion of loop filter, we modeled the loop transfer function using normal phase-locked loop(PLL) theory. We investigated and simulated the loop performance including loop bandwidth, lock-in time, static error, residual phase noise and loop stability. Finally, we studied some other important issues in OPLL, including propagation delay of signal in the loop, composite loop technique and measurement of optical phase noise.Based on theoretical analysis, a heterodyne OPLL for wide-range frequency-sweeping narrow-linewidth laser source is implemented, which is used in OFDR. In this thesis, key components are well selected, an OPLL circuit is designed and the loop parameters are optimized. With this OPLL subsystem, the OFDR achieved 1mm spatial resolution over measuring range of 500 meters.In this thesis, we also implemented a high-sensitivity homodyne receiver using Costas Loop technique. This nonlinear OPLL scheme is used in the inter-satellite optical communication. By using this technique, we designed and optimized a 5 Gbps Binary Phase Shift Keying(BPSK) receiver. In this system, the phase tracking between signal laser and local oscillator laser is realized. The residual phase noise below 3.5 degree and sensitivity of-41.4 dBm for the BER of 10-9 is achieved.