Analog optical edge detection by spatial high-pass filtering using lithography-free structures

Abstract

We introduce optical polarization-insensitive high-pass filters based on total internal reflection of light at the interface of two dielectric media (1D) and Bragg reflection of a multilayer stack (2D) in transmission mode. The wavevectors in the stopband become coupled to evanescent waves in our design, rather than the zero of a narrow-band resonant mode. This provides remarkable resolution enhancement for edge detection applications. Rigorous analysis based on plane wave expansion is carried out and the results are verified by full-wave numerical simulation. Also for the case of multilayer structure, the thickness of layers is tuned using an optimization algorithm to represent a better approximation of an ideal high-pass filter. The application of the designed high-pass filters for edge detection of input field profiles is demonstrated for both 1D and 2D operations. The proposed devices are compact and lithography-free and no Fourier lens is required, since the operator is directly implemented in the spatial Fourier domain.