Ultra-compact, ultra-low-loss and broadband 2 × 2 nonvolatile optical switch based on Sb₂Se₃ phase change material

We propose an ultra-compact broadband 2 × 2 nonvolatile optical switch based on two adjacent silicon waveguides embedded with a low-loss phase change material (Sb₂Se₃). In the crystalline state of Sb₂Se₃, the two waveguides in the middle section are not coupled, and meanwhile they have a π phase difference. Consequently, the structure functions as a Mach-Zehnder interferometer, and the optical switch operates in the bar state, achieving insertion loss of 0.068 dB and crosstalk of -31.97 dB at wavelength 1550 nm. In the amorphous state, this structure serves as a three-stage directional coupler, and the optical switch operates in the cross state, achieving insertion loss of 0.034 dB and crosstalk of -29.27 dB at 1550 nm. The footprint of the optical switch is as small as ∼3.6 × 27.6 µm², and the length of Sb₂Se₃ is only 1.63 µm, resulting in ultra-low loss over a large wavelength range. It is found that the insertion loss of optical switch is less than 0.17 dB, while the crosstalk is less than -15 dB, within a bandwidth broader than 64 nm. Furthermore, the simulations reveal that the device exhibits high tolerance to fabrication errors. Owning to the compactness, ultra-low loss and broadband, our nonvolatile optical switch has bright application prospects in advanced photonic integrated circuits.