A Compact and Broadband 2×2 3-dB Adiabatic Coupler Based on Trapezoidal Subwavelength Gratings

We propose a compact, broadband 2×2 3-dB adiabatic coupler using trapezoidal subwavelength gratings on silicon-on-insulator platform. The proposed device is constructed by two tapered waveguides, which are composed of trapezoidal subwavelength gratings. Broadband 3-dB optical power splitting with a coupling length of 24 μm is achieved by the adiabatic mode evolution of the two lowest order transverse electric modes. By using the finite time difference method, the power splitting ratio better than 3±0.21 dB and the insertion loss less than 0.19 dB are obtained in the wavelength range of 1450 nm to 1650 nm.