Reconfigurable high-order mode pass filter for mode-division multiplexing

In mode division multiplexing (MDM) optical system, the mode filter has become an inseparable part to reduce modal crosstalk and transmit the desired modes unabatedly. As filtering out lower-order mode is difficult, here we propose a reconfigurable structure of a higher-order mode pass filter consisting of two tunable mode converters and a directional coupler (DC) in a three-mode planar waveguide platform. By switching the working states of the mode converters, the structure can also be used as a fundamental mode (TE(0)) pass filter and hence dynamic output signals can be achieved. For the second-order mode (TE(2)) transmission, the simulated excess loss is ∼0.61 dB at 1.550 μm and the extinction ratio remains ≥24 dB (power ratio of TE(0) & TE(2) Launch) and ≥25 dB (power ratio of TE(1) & TE(2) Launch) at the entire C-band (1.530–1.565 μm). The device has negligible polarization dependence and hence the TM polarization exhibits similar results.