Efficient silicon-based higher-order mode converters based on subwavelength grating slots

Higher-order mode conversion plays a vital role in on-chip multimode applications. Here, we propose an efficient silicon-based higher-order mode conversion scheme that can achieve the mode-order conversion from T E 0 to T E 1 ( T E 0 − T E 1 ) mode and from T E 0 to T E 2 ( T E 0 − T E 2 ) mode, respectively. These mode conversion functions are realized by etching subwavelength grating (SWG) slots on a silicon waveguide, where the design of the SWG slot pattern matches with the required T E 1 ( T E 2 ) higher-order mode. According to the calculations, the mode conversion length is only 3.3 µm (4.32 µm) with the mode conversion efficiency (CE) 92.1% (95.6%), mode crosstalk (CT) − 17.5 d B ( − 16.7 d B ), and insertion loss 0.65 dB (0.5 dB) for the T E 0 − T E 1 ( T E 0 − T E 2 ) mode converter at λ = 1.55 µ m . Moreover, device bandwidths over 110 nm ( C E > 90 % and C T < − 15 d B ) and other higher-order mode conversions can also be achieved using the proposed scheme (e.g., T E 0 − T E 3 and T E 0 − T E 4 mode converters). We believe such a device scheme would help increase the transmission capacity of on-chip multimode multiplexing transmissions by leveraging more mode channels.