Nonvolatile and broadband silicon photonic tunable coupler with phase change material

We propose a nonvolatile and broadband 2 × 2 silicon photonic tunable coupler with phase change material (PCM). By arranging broadband 3-dB couplers point-symmetrically, the tunable coupler achieves broadband characteristics at any splitting ratio. We consider two types of broadband 3-dB couplers for the point-symmetric tunable coupler: one based on asymmetric waveguide widths and the other based on asymmetric PCM states. Both have high fabrication tolerance, but the latter additionally allows for fabrication error compensation. The proposed tunable coupler with a device length of 109.8 µm provides less than 1.6% deviation from the ideal power-splitting ratio and less than 0.032 dB excess loss within the wavelength range of 1.53-1.57 µm. This device contributes to the realization of low-power programmable photonic circuits.