Design and simulation of 4-mode (de)multiplexers implemented in conventional and subwavelength grating Si/SiO2 platforms

Abstract

This work presents two 4-mode, broadband, low loss, compact, and fabrication tolerant (de)multiplexers comprised of a 1 × 4 mode converter-splitter, multimode interferometer MMI, and phase shifter devices. The first device is designed using conventional waveguides. The second one is built utilizing subwavelength grating technology introduced in the multimode section of the MMI coupler. To the best of our knowledge, this is the first demonstration of a 4 × 4 (de)multiplexer based on a SWG-MMI coupler. Both devices are built in a silicon-on-insulator (SOI) platform. In the operation of the designed devices, four input modes TE0, TE1, TE2, and TE3 are split and converted into a fundamental TE0 mode at the output end. 80 nm (1510–1590 nm) operating bandwidth, losses > −0.5 dB, and crosstalk < −15 dB are achieved from the conventional version of the (de)multiplexer, while 140 nm (1480–1620 nm), losses > −0.5 dB, and crosstalk < −15 dB, are achieved from the subwavelength grating assisted device. The overall size of the designed devices is 4.5 × 173 µm2 and 4.5 × 123 µm2, for the conventional and subwavelength grating devices, respectively. Subwavelength grating technology offers flexibility in refractive index engineering for extra bandwidth (75% additional bandwidth) and compactness (30% size reduction) compared to the conventional counterpart.