Abstract

We consider all-optical switching in the device shown in Figure la, which consists of two channel waveguides coupled by microresonators, all of which are Kerr nonlinear. We present numerical simulations that show that it is possible to use the channels as input ports, hence creating an optical AND gate based on a scheme similar to coupled gap soliton formation, even in the presence of linear and nonlinear loss mechanisms. The advantage of our AND gate scheme over earlier proposed schemes based on Bragg gaps is twofold^1,2: First, our gate is much shorter than those based on Bragg gaps; second, the threshold energy required for operation is much smaller than in a Bragg gap system. The basic operation of the gate is as follows. Forward travelling light in the bottom (top) channel guide can couple, via the resonators, to backward travelling light in the top (bottom) guide^3,4. For simplicity we assume that light propagation is governed by the effective index _neff, common to both channel guides and the resonator. We define the resonant frequency, ω_r = c/(n_effR)-the frequency at which one round-tri through the resonator corresponds to the accumulatio of 2π of phase. Light with frequency at or near an integer multiple of ω_r is highly reflected, because th coupling of light from one channel guide to the othe is resonantly enhanced. In the presence of nonlinearity, light of high intensity will experience nonlinear phase accumulation through self phase modulation (SPM) and cross phase modulation (CPM). We consider the situation where one pulse of high intensity injected into either the top or bottom channel is reflected, despite its SPM. However, whe accumulation due to CPM will be sufficient to switch off the resonance, so that the structure becomes highly transmitting. For our system, the coefficient describing CPM is twice as large as that describing SPM, whereas in schemes based on orthogonal polarization the CPM coefficient is only two-thirds of the SPM coefficient¹; this makes our scheme more efficient than one based on polarization.

© 2002 Optical Society of America