All-optical switch with low threshold over a wide wavelength range by use of a Mach-Zehnder racetrack resonator

This paper presents a theoretical investigation of an all-optical switch by using a Mach-Zehnder racetrack resonator. The switch can realize nonlinear optical switching between steady ON/OFF states at about200 microwatt low threshold over a wide wavelength range. The finesse of the racetrack resonator is adjustable by controlling the coupling ratio of the Mach-Zehnder coupler. Some undesirable effects are discussed. Attenuation, group delay and partial coherence result in a switching power increase and an extinction ratio reduction. Optical bistability and instability do not limit the practical applications of the device in optical switching. A desired tradeoff between bandwidth/response time and switching power can be obtained by adjusting the finesse. Picosecond ultrafast optical switching is predicted.