Design of Ultra-Compact Adiabatic Mode Circulator based on Adiabatic Mode Evolutions

Abstract

In this study, an adiabatic mode circulator based on the adiabatic mode evolution mechanism with thickness of 220 nm for the cyclic transfer of TE₁ modes is presented, which has two adiabatic mode converters suitable for mode conversion between TE₁ and TM₀ modes, and four adiabatic taper waveguides suitable for the transfer of either TE₁ or TM₀ modes. Due to the symmetry of the structure, only the first half needs to be considered: the first adiabatic taper waveguide evolves the TE₁ mode at width W₁ = 1.5 μm to the TE₁ mode at width W₂ = 0.7 μm. The first adiabatic mode converter evolves the TE₁ mode at width W₂ = 0.7 μm to the TM₀ mode at width W₃ = 0.62 μm. The second adiabatic taper waveguide evolves the TM₀ mode at width W₃ = 0.7 μm to the TM₀ mode at width W₄ = 0.4 μm. The design results show that the adiabatic mode circulator designed in this study can achieve the same power transfer efficiency with an ultra-compact device size compared with other design methods (such as the design approach in Ref. (Dai et al. Opt Exp 20(12):13425-13439, 2012). The device length of the proposed adiabatic mode circulator has been reduced by a factor of 80 compared to the design approach in Ref. (Dai et al. Opt Exp 20(12):13425-13439, 2012). As a result, the device size of the proposed adiabatic mode circulator is drastically reduced, enabling the design of ultra-compact adiabatic mode circulators.