Reduction of pattern effect for clock recovery based on semiconductor optical amplifier using cw assist light

Abstract

cw assist light in the gain region or at transparency wavelength of a semiconductor optical amplifier (SOA) is introduced into an SOA-based clock recovery circuit to overcome the pattern effect. A numerical model considering intraband effects in the SOA, such as carrier heating and spectrum hole burning, is constructed to study the pattern effect on clock recovery. The pattern effect reductions for different injection powers and wavelengths of cw assist light and different bias currents of the SOA are simulated to optimize this system. In an experiment, high-quality clock pulses were recovered from a (231–1)-pseudorandom-bit sequence (PRBS) at 20 and 40 Gbit/s by using cw assist light. Simulation and experimental results show that a lower pattern effect can be effectively obtained by using a cw assist light with highest power near the highest-gain wavelength when the SOA works at a high current level. In this respect, cw assist light in the gain region is superior to light at the transparency wavelength. This scheme can be applied to SOA-based all-optical clock recovery and other all-optical signal processing for pattern effect reduction.