Ultra-compact reflective mode converter based on a silicon subwavelength structure.

Mode converters play an essential role in mode-division multiplexing systems. A reflective mode converter (RMC), which is utilized to accomplish the mode conversion in the contra-propagation process, can fold the optical path and realize the mode exchange in an optical network. In this paper, we propose and experimentally demonstrate an RMC based on a silicon subwavelength structure. It can convert the input fundamental mode (TE0) into the first-order mode (TE1) in a 2.0 mu m x 2.0 mu m footprint. The simulated insertion loss and cross talk are lower than 0.6 dB and -20.3 dB in 1525-1565 nm. Experimental results verify the functionality of the device. The measured insertion loss and cross talk are lower than 2.2 dB and -16.2 dB. To further prove the generality of the methodology, we design another two RMCs realizing the mode conversion functions of TE0 to TE2 and TE0 to TE3 modes. The simulated insertion losses are lower than 1.1 dB and 1.8 dB. (C) 2020 Optical Society of America