A 20 GHz optoelectronic phase-locked loop

The paper describes operation and design of an optoelectronic phase-locked loop. The optoelectronic phase-locked loop consists of a fast optoelectronic phase detector operating in the optical domain. The rest of the optoelectronic phase locked loop is made of conventional electronic devices. The task of the optoelectronic phase detector is to detect the phase difference between the modulation of an optical input signal into the phase detector and frequency multiple of a voltage controlled oscillator signal. The optoelectronic phase detector should in principle operate faster than the conventional electronic phase detectors. The optoelectronic phase-locked loop is mainly used as a clock recovery device in optical time division multiplexed (OTDM) systems. The bit rates of OTDM data signals reach 160 Gb/s. At these bit rates it is difficult to construct conventional electronic phase detectors. As a clock recovery device the optoelectronic phase-locked loop locks itself on the discrete spectral line at the clock frequency in the OTDM data signal. The output signal of the phase-locked loop is synchronized with the clock of the input data signal and prescaled to the lower frequency. The extracted prescaled clock is used for demultiplexing the OTDM signal.