Optical spatial differentiation with suspended subwavelength gratings

TL;DR

This paper demonstrates the use of suspended subwavelength gratings for first- and second-order spatial differentiation of optical beams, offering a simple, ultrathin, and loss-free component for beam shaping and optical processing.

Contribution

It introduces a novel application of suspended subwavelength gratings for spatial differentiation, validated by experiments and theoretical models.

Findings

High-quality spatial differentiation achieved in transmission

Excellent agreement between experiments and models

Potential for integration into optical information processing

Abstract

We demonstrate first- and second-order spatial differentiation of an optical beam transverse profile using thin suspended subwavelength gratings. Highly reflective one-dimensional gratings are patterned on suspended 200 nm-thick silicon nitride membranes using Electron Beam Lithography and plasma etching. The optical transmission of these gratings, designed for illumination with either TM or TE polarized light, are experimentally measured under normal and oblique incidence and found to be in excellent agreement with the predictions of an analytical coupled-mode model as well as Rigorous Coupled Wave Analysis numerical simulations. High quality first- and second-order spatial differentiation of a Gaussian beam are observed in transmission at oblique and normal incidence, respectively. Such easy-to-fabricate, ultrathin and loss-free optical components may be attractive for beam shaping and optical information processing and computing.