Broadband mode switch based on a three-dimensional waveguide Mach–Zehnder interferometer

We propose a mode switch that operates on modulating the optical phases of a three-dimensional balanced four-arm waveguide Mach–Zehnder interferometer. We design and fabricate the device with polymer material to achieve thermo-optic switching between any two of the E₁₁, E₂₁, E₁₂, and E₂₂ modes of the waveguide. Our experimental device shows an extinction ratio higher than 14 dB and a switching time shorter than 3.7 ms, measured with the E₁₁ mode switched to any of the other modes at 1550 nm. This mode switch can operate over a wide range of wavelengths with weak polarization dependence and could be used in reconfigurable fiber-based mode-division-multiplexing systems where mode routing is required.