Broadband and low crosstalk silicon on-chip mode converter and demultiplexer for mode division multiplexing.

In this paper, a compact and broadband mode converter and demultiplexer based on multimode interference (MMI) is designed and experimentally demonstrated on silicon-on-insulator. We have designed a mode converter using cascaded MMI to convert the fundamental mode into a higher-order (first-order mode) and vice versa. Subsequently, we have demonstrated an on-chip two-mode demultiplexer with a compact footprint and low loss. The proposed mode demultiplexer shows low insertion loss (0.22 dB for ${{\rm TE}_0}$TE and 0.36 dB for ${{\rm TE}_1}$TE mode) and crosstalk (${-}{25.2};{\rm dB}$-25.2dB for ${{\rm TE}_0}$TE and ${-}{24.4};{\rm dB}$-24.4dB for ${{\rm TE}_1}$TE mode) at wavelength 1550 nm using the eigenmode expansion method. Moreover, the device supports a broad bandwidth having crosstalk ${ \lt } {-} {20};{\rm dB}$<-20dB over a wavelength range of 1520-1580 nm. The proposed device can be used in mode division multiplexing for photonic network-on-chip.