High-efficiency suspended three-tip edge coupler for Mid-infrared photonics

Abstract

A high-efficiency suspended three-tip edge coupler based on a silicon-on-insulator (SOI) platform for fiber-to-chip coupling in Mid-infrared (MIR) region is designed. The device is composed of a three-tip edge coupler and subwavelength grating (SWG) waveguides. The edge coupler is suspended in order to avoid the high absorption loss from the Silicon dioxide (SiO2) in the SOI substrate in MIR. The three tips of the suspended edge coupler increase the coupling between the optical field in the waveguide and the mode field in the single mode fiber and reduce the reflection loss. A low overall coupling loss of 0.19 dB at 4.3μm for transverse-electric (TE) mode polarization can be achieved with the designed 60-μm-long three-tip edge coupler. The device can operate over a broad spectral range of 4.02μm – 4.59μm with extra loss of less than 0.3 dB. Because of its low-loss and ultra-broad optical bandwidth and the simple fabrication process, the proposed device is promising for fiber-to-chip edge coupling in MIR application.