Four-Mode Thermo-Optic Switch Based on Y-Junctions Integrated With Multimode Interferometers

Mode-insensitive optical switch is becoming more and more important as one of the key elements for mode-division multiplexing (MDM) optical communication systems. However, the different structural relationships between the waveguides and the different modes make it challenging to control more spatial modes simultaneously. Here, we put forward a four-mode thermo-optic (TO) switch based on two Y-junctions integrated with two multimode interferometers (MMIs), where the symmetric Y-junction is used to split E₁₁, E₂₁, E₁₂ and E₂₂ modes into E₁₁ or E₁₂ mode, and the MMIs are designed to be insensitive for E₁₁ and E₁₂ modes by optimizing the waveguide geometries and electrode heater location. The proposed device can realize the switching functions for the guided four modes insensitively. Our fabricated device based on polymer waveguide platform shows an extinction ratio of larger than 6.2 dB with a power-consumption of 42.0 mW, over the wavelength range of 1500 nm to 1600 nm. The proposed four-mode TO switch is suitable for MDM systems.