Mode division (de)multiplexer based on transverse mode conversion in photonic crystal using asymmetric directional couplers

Abstract

Mode division multiplexing technology has the potential to increase the channel capacity of a single wavelength carrier. Attaining cost-effective high-bandwidth-density devices with small footprints is a concern, and photonic crystal based devices are promising for ultra-small on-chip communications. This paper presents a 2D photonic crystal based mode division (de)multiplexer on a silicon on insulator platform. The device comprises two coupling regions of asymmetric directional couplers that perform mode conversion operations between the fundamental mode and higher-order modes. Each coupling section is dedicated to converting a specific mode. Mode conversion is achieved by designing a multimode waveguide to satisfy the phase-matching condition of the desired mode with the single mode waveguide. Two linear adiabatic tapers are introduced for the smooth transition of modes between waveguide sections. The device is designed and simulated for three-channel modes at 1550 nm using the finite-difference time-domain technique. The obtained insertion loss and cross talk are <0.41dB and <−20.14dB, respectively. The overall size of the proposed mode division (de)multiplexer is 328.5µm2. A fabrication tolerance study for the proposed device is performed by varying the rod radius and position in the device structure’s taper and bus waveguide regions. The proposed 2D photonic crystal based mode division (de)multiplexer has the potential to be used in large-capacity optical communication systems.