First-Band S-Vector Photonic-Crystal Superprism Demultiplexer Design and Optimization

In this paper, we present a complete approach to the design of a wavelength demultiplexer based on the S-vector superprism photonic-crystal phenomenon. We make use of a full 3-D modeling approach based on plane-wave-expansion method, which allows the full dynamics of beam propagation to be considered. This reveals significant nonuniformities in beam divergence and dispersion as a function of wavelength, which has been neglected in previous 2-D models and which reduces the scalability of these devices. We examine 1-D and 2-D photonic-crystal lattices and show that the 1-D lattice results in the smallest superprism area as a function of channel count. This is due to its lower band curvature relative to 2-D square and hexagonal lattices, even though it has much lower angular dispersion. We also modify the previous S-vector superprism design so that, for each channel, the prism region extends only as far as necessary for channel resolution at a specified crosstalk level. Based on silicon-on-insulator (SOI) technology, with a top silicon layer of 260 nm and minimum feature size of 75 nm, we present the design of a four-channel coarse-wavelength-division-multiplexing demultiplexer with theoretical crosstalk of 20 dB, which has a superprism area of 1367 mum²