Broadband Spin-Dependent Directional Coupler via Single Optimized Metallic Catenary Antenna.

With the rapid development of on-chip optics, integrated optical devices with better performance are desirable. Waveguide couplers are the typical integrated optical devices, allowing for the fast transmission and conversion of optical signals in a broad working band. However, traditional waveguide couplers are limited by the narrow operation band to couple the spatial light into the chip and the fixed unidirectional transmission of light flow. Furthermore, most of the couplers only realize unidirectional transmission under the illumination of the linear polarized light. In this work, a broadband polarization directional coupler based on a metallic catenary antenna integrated on a silicon-on-insulator (SOI) waveguide has been designed and demonstrated under the illumination of the circularly polarized light. By applying the genetic algorithm to optimize the multiple widths of the metallic catenary antenna, the numerical simulation results show that the extinction ratio of the coupler can be maintained larger than 18 dB in a wide operation band of 300 nm (from 1400 to 1700 nm). Moreover, the coupler can couple the spatial beam into the plane and transmit in the opposite direction by modulating the rotation direction of the incident light. The broadband polarization directional coupler might have great potential in integrated optoelectronic devices and on-chip optical devices.