Silicon Subwavelength Gratings Assisted Ultra-Broadband Dual-Polarization Mode-Order Converter

Hybrid multiplexing technology is an attractive solution to improve communication capacity by combining multi-wavelengths, multi-modes, as well as dual-polarizations. Although various positive solutions have been proven, there is still a lack of dual-polarization mode converters with a large bandwidth for hybrid multiplexing. In this article, we propose a novel ultra-broadband dual-polarization mode-order converter, which exploits the anisotropy and mode-manipulating ability of subwavelength material waveguides. The three-dimensional finite-difference time-domain simulation results show that the mode-order conversion can be achieved for any input mode among the TE
₀
/TE
₁
/TM
₀
/TM
₁
modes. The insertion loss of the device is less than 0.88 dB, and the total crosstalk is lower than −14.7 dB under the unprecedented 380 nm operating bandwidth. The device structure based on Mach–Zehnder interferometer and assisted with subwavelength grating shows high resistance to fabrication errors. The experimental results prove that the insertion loss of each mode in the C+L band is below 1.59 dB, and the crosstalk of each input mode is lower than −15.6 dB. As far as we know, our device is the dual-polarization mode-order converter with the largest bandwidth that has been reported currently. The proposed subwavelength engineering mode-order converter can be used in the deployment of new hybrid multiplexing transmission systems to effectively enhance communication capacity.