Compact InGaAsP/InP nonblocking 4 × 4 trench-coupler-based Mach-Zehnder photonic switch fabric.

The existing photonic switch matrices usually show the drawbacks of either a large footprint or high cross talk. Here, we propose a compact InGaAsP/InP rearrangeable nonblocking 4×4 photonic switch fabric based on 2×2 Mach-Zehnder interferometer (MZI) switch elements in a Benes architecture. Each switch element consists of two frustrated total internal reflection (TIR) couplers and TIR mirrors serving as 90° waveguide bends, forming the square layout configuration of the 2×2 MZI switches. We investigate the design parameters of the switch element and 4×4 photonic switch matrix by using FDTD and transfer matrix methods, respectively. Our analysis results show that the proposed device exhibits an ultracompact chip size of ∼340  μm×120  μm, the minimum cross talk of -23  dB in the 1.5∼1.6  μm wavelength range, the total insertion loss of ∼3.9  dB, the low electrical energy of ∼0.4  pJ/bit, and an operation speed up to 50 GHz. Experimentally, we can demonstrate the feasibility of fabricating 2×2 MZI switches and an operational low-loss trench-coupler. The enabling component of the 2×2 MZI switch can scale its pattern in the 2D directions. This as-formed compact 4×4 switch fabric can be potentially applied in large-scale InP-based photonic integrated circuits.