Cyclic silicon waveguide four-mode converter for mode division multiplexing transmission.

In this paper, a novel cyclic mode converter (CMC) is proposed and fabricated to implement cyclic mode permutation (CMP) on-chip for differential mode delay and mode-dependent loss elimination in the mode division multiplexing (MDM) transmission system. Cascaded by three optimally designed mode converters that do not affect the non-target modes, the proposed CMC can realize the conversion of any input mode among the TE/TE/TM/TM modes. The three-dimensional finite-difference time-domain (3D-FDTD) simulation results show that the insertion loss of our device is less than 0.59 dB, and the crosstalk of each mode is lower than -15 dB under the range of 1500-1600 nm. The flat spectral response of this CMC is maintained even in the presence of fabrication errors up to±10 nm, showing great robustness. The experimental results also prove that at the center wavelength of 1550 nm the measured insertion loss of each mode is below 2.22 dB, and the crosstalk of each mode is lower than -15 dB. The proposed CMC provides a new idea for effectively reducing link damage in the MDM transmission system.