Development of an Optical Phase-Locked Loop for 1-THz Optical Beat Signal Generation

To support larger telecommunications capacities, the speed of optical transmission is increasing apace, and coming transmission rates in excess of 160 Gbit/s raise hopes for all-optical signal processing technologies that make possible high- speed signal processing. Accordingly, as the clock signal source that is indispensable for signal processing, we have developed an optical phase-locked loop (OPLL) that can generate a high- speed optical beat signal of 1 THz. The OPLL consists of an optical beat signal source and an all-optical phase detector, and to realize a simple construction has a pair of 3-electrode distributed feedback (DFB) laser diodes for the optical beat signal source and an all-optical phase detector based on two-photon absorption in a silicon avalanche photodiode. As a result of measurement of the synchronization characteristics with respect to a pulse train of 40-GHz repetition rate, it has been confirmed that this OPLL can synchronize 160-GHz and 1-THz beat signals with low timing jitter of 126 fs (0.016 rad 2) and 28 fs (0.03 rad 2) respectively.