Broadband optical directional full couplers based on Blackman function

A mismatched optical coupler with waveguide weighted by the Blackman function is numerically investigated in the demand of short-length, C+L-band, low crosstalk, and process tolerance. Utilizing the full factorial design, the structure parameters of coupling waveguide are obtained by beam propagation method. In the condition of crosstalk of -33.5 dB, the mismatched optical coupler with proper selected waveguide structure parameters is found to have a coupling length of 2.80 mm in the transmission wavelength ranges of C+L-band (1.53-1.61 μm). Obviously, the selection and design of waveguide structure are very important to satisfy the qualities of a mismatched optical coupler for the demand of short-length, bandwidth, and low-crosstalk.