We investigate spatial differentiation of optical beams using guided mode resonances in suspended dielectric one-dimensional photonic crystals. Various SiN grating structures are characterized under various incidence, polarization and beam size illuminations. We first observe first- and second-order spatial differentiation in transmission of Gaussian beams impinging at oblique and normal incidence, respectively, on gratings designed to be resonant for either TE- or TM-polarized incident light. Polarization-independent first-order spatial differentiation is then demonstrated with a specifically designed, doubly-resonant, one-dimensional and symmetric grating structure. Such ultrathin and essentially lossfree nanostructured dielectric films are promising for various optical processing, optomechanics and sensing applications.
Owing to their high optical and mechanical quality suspended silicon nitride thin films are widely used for photonics and sensing applications. We discuss the fabrication and characterization of highly reflective one- dimensional subwavelength gratings patterned on commercial high-tensile stress Si3N4 membranes. Their non- invasive structural characterization using Atomic Force Microscopy provides detailed information on both the grating transverse profile and the deflection of the films after etching, which are compared with optical measurements and mechanical simulations, respectively. We then apply these ultrathin, low-loss optical components to optical spatial differentiation and demonstrate high quality first- and second-order spatial differentiation of the transverse profile of a Gaussian beam.
The electromechanical actuation of two silicon nitride membranes forming a monolithic MOEMS is investigated. By controlling the tensile stress of the high quality membranes via a piezoelectrically controlled compressive force applied to the chip we demonstrate tuning of their mechanical spectrum, as well as strong intermode electromechanical coupling. Piezoelectric actuation is shown to enhance the nonlinear response of the membranes, which is evidenced by parametric amplification of the thermal fluctuations. Such a MOEMS array represents an attractive tunable and versatile platform for optomechanics and sensing applications.
Microcavities using high mechanical quality suspended thin films as flexible mirrors can be exquisitely sensitive to gas or radiation pressure changes. We demonstrate how to directly pattern thin (200 nm), suspended silicon nitride membranes with subwavelength gratings in order to enhance their reflectivity. We discuss how using such nanostructured trampolines to form ultrashort microcavities may lead to a combination of small modevolume and remarkably narrow linewidth which is interesting for improving the sensitivity of optical sensors or for cavity optomechanics. Using high mechanical quality nanotrampolines to form few-micron long sandwiches we realize squeeze film pressure sensors in which the modifications of their vibrations due to the compression of the gas between them are measured optically and whose state-of-the-art responsitivity and sensitivity are promising for absolute pressure measurements in the free molecular flow regime.