In this work we discuss liquid-crystal (LC) anisotropic axicons for the dynamic control of the Bessel beam polarization variation along propagation. We first present a technique that employs a LC spatial light modulator (LC-SLM) to display two diffractive axicons, each one affecting one of the two orthogonal linear polarization components. If the two axicons have a slightly different period, a periodic variation in the polarization state of the Bessel beam occurs over propagation. Second, we present a more compact alternative consisting in a combination of a refractive axicon and a LC element of linear phase profile along the radial coordinate. This combination creates a compound compact and tunable anisotropic axicon that produces Bessel beams with tunable polarization modulation. The capability of changing the polarization state of the Bessel beam along its propagation opens new venues in axial polarimetry, optical trapping in multiple planes or axial-dependent laser microfabrication.
In this work, we designed a fused silica lab-on-chip that combines optical techniques such as absorption, Raman scattering and fluorescence to quantify phytoplankton type and concentration in water. In the absorption stage of the chip, a Fabry-Perot resonator significantly enhances the spectral response. Scattering and fluorescence spectroscopy are considered with light focusing on sample channel. The design process, and more specifically the integrated in-chip aspheric lenses, is carried out by ray-tracing simulations.
All-dielectric metasurfaces have attracted increasing attention due to their negligible losses and sharper resonances compared to their metallic counterparts. In this work, we numerically studied the optical performance of a novel alldielectric metasurface based on complementary split-ring resonators (CSRRs), in which ultrathin slots were periodically etched in a thin silicon layer. The proposed CSRR metasurface exhibits two multipolar resonances in the near-infrared (NIR) window. Moreover, a quasi-bound state in the continuum (quasi-BIC) with an ultra-high quality factor can be excited by breaking the symmetry of the structure. Taking advantage of the high-quality factor quasi-BIC mode and its sensitivity to the superstrate medium refractive index (S = Δλres/Δn), we design an ultra-high figure of merit (FoM = S/FWHM) refractive index sensor for biomedical applications. By three-dimensional finite element method (3D-FEM), we evaluate the sensitivity of the sensing device to the variation of the superstrate refractive index in the range 1.31-1.33, which is typical for aqueous solutions. Our simulations reveal that a sensitivity of S ~ 155 nm RIU-1 and an extraordinary FoM ~ 387500 RIU-1 can be achieved using the ultra-narrow quasi-BIC resonance in the CSRR metasurface structure. The proposed approach opens new paths to develop flat biochemical sensors with high accuracy and real-time performance.
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