Compact and fabrication tolerant polarization insensitive mode-order converter for MDM systems

Abstract

With the increasing capacity demands of data communications, mode division multiplexing in on-chip optical interconnect systems is becoming an attractive solution. Compact, broadband, and fabrication-tolerant mode-order converters unaffected by polarizations are considered crucial for the progress of on-chip systems utilizing mode division multiplexing. A proposal for a design scheme for an on-chip mode-order converter that is insensitive to polarization is presented, utilizing a combination of 3D finite-difference time-domain (FDTD) and particle swarm optimization (PSO). The conversion of TE₀/TM₀-to-TE₁/TM₁ mode is achieved through phase matching between a subwavelength grating and an input–output tapered waveguide. Theoretical studies indicate that the TE₀-to-TE₁ and TM₀-to-TM₁ insertion losses are below 0.46 dB and 0.78 dB at a wavelength of 1550 nm. The TE₀-to-TE₁ and TM₀-to-TM₁ insertion loss is under 1.0 dB, with crosstalk below −15 dB within the 190 nm (1432∼1622 nm) and 81 nm (1515∼1596 nm) operating ranges. Experimental data indicates that the device measuring 7 × 1.58 μm² can successfully convert mode orders regardless of polarization within an 81 nm bandwidth (1515∼1596 nm), effectively doubling the data transmission capacity of the MDM system. In addition, the devices fabricated by a standard CMOS process demonstrate the potential for mass production.