Phase noise analysis of clock recovery based on an optoelectronic phase-locked loop

A detailed theoretical analysis of a clock-recovery (CR) scheme based on an optoelectronic phase-locked loop is presented. The analysis emphasizes the phase noise performance, taking into account the noise of the input data signal, the local voltage-controlled oscillator (VCO), and the laser employed in the loop. The effects of loop time delay and the laser transfer function are included in the stochastic differential equations describing the system, and a detailed timing jitter analysis of this type of optoelectronic CR for high-speed optical-time-division-multiplexing systems is performed. It is shown that a large loop length results in a higher timing jitter of the recovered clock signal. The impact of the loop length on the clock signal jitter can be reduced by using a low-noise VCO and a low loop filter bandwidth. Using the model, the timing jitter of the recovered optical and electrical clock signal can be evaluated. We numerically investigate the timing jitter requirements for combined electrical/optical local oscillators, in order for the recovered clock signal to have less jitter than that of the input signal. The timing jitter requirements for the free-running laser and the VCO are more relaxed for the extracted optical clock (lasers's output) signal.