Compact and broadband mode demultiplexer using a subwavelength grating engineered MMI coupler

A compact and broadband mode demultiplexer (DEMUX) using a subwavelength grating (SWG) engineered multimode interference (MMI) coupler is proposed and analyzed in detail. To effectively separate the input TE0 and TE1 modes, the input port is formed by cascading two tapers, connected by a silicon wire, in a single SWG MMI coupler. Moreover, by partially tailoring the grating duty cycle of the SWGs, an extra phase shifter is directly integrated in the MMI coupler, parallel to the input port for adjusting the phase in mode conversion. The input TE0 mode can pass through the first taper and the silicon wire while being cut off and evolve into SWGs in the second taper, so that it is hardly affected by the extra phase shifter and directly mapped into the output port via MMI. On the contrary, the input TE1 mode is cut off in the first taper and evolves through the sidewall of the first taper into two TE0-like components in the SWG region. Then an extra pi/2 phase shift between them is generated by the phase shifter. Finally, they are combined into the output TE0 mode via MMI. By carefully choosing the structural parameters, the proposed TE0/TE1 mode DEMUX shows a broad bandwidth of 350 nm from 1520 to 1870 nm for insertion loss <1.0 dB and cross talk < -10 dB and achieves a low insertion loss of 0.37 dB/0.40 dB and cross talk of -18.50 dB/-17.00 dB for TE0/TE1 input at 1550 nm, within a short device length of only 18.6 mu m. In addition, the device also shows a good fabrication tolerance to the deviations of structure parameters. (C) 2021 Optical Society of America

Automated summary

A compact and broadband mode demultiplexer using a subwavelength grating engineered multimode interference coupler is proposed, achieving low insertion loss and cross talk over a wide bandwidth by carefully choosing structural parameters. The device shows good fabrication tolerance and performance for TE0/TE1 input at 1550 nm within a short device length.