The reflection sidelobes of a corrugated optical waveguide filter are shown to be suppressed when the corrugation depth is tapered with a function that has low, Fourier-transform sidelobes. Several specific taper functions are considered, and sidelobe levels lower than -70 dB are shown to be feasible. A simple rule for estimating the 3-dB reflection bandwidth of a tapered corrugation is also presented.
P. S. Cross and H. Kogelnik, "Sidelobe suppression in corrugated-waveguide filters," Opt. Lett. 1, 43-45 (1977)