Analog Optical Implementation of Spatial High Pass Filtering Using Evanescent Waves

TL;DR

This paper presents a novel optical high pass filter design using evanescent waves for edge detection, offering high resolution and compactness without Fourier lenses, verified through simulations.

Contribution

It introduces polarization-insensitive high pass filters based on total internal reflection and multilayer Bragg stacks, optimized for improved edge detection in optical systems.

Findings

Enhanced edge detection resolution demonstrated

Filters operate in transmission mode without Fourier lenses

Optimization of multilayer thickness improves filter approximation

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 no Fourier lens is required, since the operator is directly implemented in the spatial Fourier domain.