Design of Deeply Etched Antireflective Waveguide Terminators

An alternative solution to achieve an antireflective waveguide terminator is proposed by adopting a deeply etched waveguide structure to replace the conventional facet interference coatings. The performance is evaluated by different numerical approaches and optimum designs can be achieved based on the combination of the finite-difference time-domain method and the transfer matrix method. Perfectly matched layer absorbing boundary conditions are employed and pre-optimized in order to eliminate any nonphysical reflections due to the computation window introduced artificially. Results show that a power reflectivity of less than $5.0 \times 10^{-3}$ over almost the entire C-band with a minimum value as low as $1 \times 10^{-5}$ can be achieved. The effects on etching with a tilted angle and etching with finite depth are also studied.