Design of long-period waveguide grating filter by control of waveguide cladding profile

A simple and convenient method of designing long-period waveguide grating filters to generate sophisticated transmission characteristics is described. The method is based on controlling the index or thickness profile of the waveguide cladding along a uniform grating and thus avoids the use of specially designed grating masks. The flexibility of the method with the design of phase-shifted gratings, chirped gratings, and broadband filters is demonstrated. It was found that the index and thickness changes required for a significant change in the transmission characteristics of a grating are within the ranges that can be achieved easily with ultraviolet irradiation on photosensitive films. The method described in this paper provides a powerful approach of realizing various kinds of grating filters