Composite superprism photonic crystal demultiplexer: analysis and design.

We present the analysis and design of a superprism-based demultiplexer that employs both group and phase velocity dispersion of the photonic crystal (PhC). Simultaneous diffraction compensation and spatio-angular wavelength channel separation is realized in a slab region that divides the PhC. This avoids the excessive broadening of the beams inside the PhC and enhances the achievable angular dispersion of the conventional superprism topology. As a result, a compact demultiplexer with a relaxed requirement for low divergence input beams is attained. The dynamics of the beams envelops are considered based on the curvature of the band structure. Analysis shows at least 36-fold reduction of the PhC area and much smaller propagation length in slab compared to the preconditioned superprism, based on the same design model. PhC area scales as Δω(-2.5) with Δω being the channel spacing.