Reconfigurable and low-loss three-mode optical switch based on Ψ-junctions and multimode interferometers

A scheme for <i>N-</i>channel mode-division multiplexing (MDM) signal switching is proposed on a silica planar lightwave circuit. Specifically, we demonstrate a three-mode optical switch that adopts cascaded symmetric Ψ-junctions, Mach-Zehnder interferometer (MZI) waveguides, and electrode phase shifters for thermo-optic modulation. The symmetric Ψ-junctions split the E₁₁, E₂₁, and E₃₁ modes into the E₁₁ mode and couple them back to their original modes. The MZIs act as the modulation arms of this three-mode optical switch. Fabricated via CMOS-compatible silica-on-silicon processing, the device enables low-loss switching of the three modes. At 1550 nm, when E₁₁, E₂₁, and E₃₁ modes are input individually, the fabricated switch exhibits an insertion loss (IL) of 3.7 ± 0.1 dB, an extinction ratio (ER) of 10.3 ± 0.5 dB, and a response time of <1.36 ms. For E₁₁ and E₂₁ modes, the operational bandwidth extends over 100 nm (1500-1600 nm), with IL <5 dB and ER ≥8 dB. Reconfigurable to route all propagating modes simultaneously or individually, this switch meets diverse application requirements. Moreover, the device holds broad application prospects in optical interconnects of MDM system modules.