1×4 Optical Demultiplexer for TM Modes in a Hole-Type Silicon Photonic Crystal

Abstract

Based on the self-collimation (SC) effect of photonic crystals (PC), a two-dimensional photonic crystal $1\times 4$ optical demultiplexer (OD) with a second energy band in TM polarization mode is designed. The $1\times 4$ OD consists of two cascaded MachZehnder interferometers (MZIs) and an independent mirror. The theoretical formula of the output ports transmission spectrum is derived from the principle of optical interference, and the output ports are numerically simulated by the finite difference time domain (FDTD) method. The simulated transmission spectrum results are consistent with the theory. Choosing the correct cavity length ratio of MZIs can realize the function of a $1\times 4$ OD. The structural size of the $1\times 4$ OD is very small, about $57\mu \mathrm{m}\times 50\mu \mathrm{m}$. When the central working wavelength is 1550nm, the free spectral region (FSR) of the $1\times 4$ OD is about 23nm, almost covering the entire C-band window of optical communication, which has potential application value in the future optical communication field.