Many technologies, including dot projectors and lidar systems, benefit greatly from using polarized illumination. However, conventional polarizers and polarizing beam splitters have a fundamental limit of 50% efficiency when converting unpolarized light into one specific polarization. Here, we overcome this restriction and achieve near-complete conversion of unpolarized light to a spatially uniform polarization state over several output directions with our topology-optimized metasurfaces. Our results provide a path toward greatly improving the efficiency of common unpolarized light sources, such as LEDs, for a variety of applications requiring uniformly polarized illumination. Our fabricated metasurface realizes a 70% conversion efficiency, surpassing the aforementioned limit, and achieves a polarization extinction ratio exceeding 20, when characterized with laboratory measurements. We further demonstrate that arbitrary power splitting can be achieved between three or more polarized outputs, offering flexibility in target illumination.
We develop an ultrathin source of two-photon polarization Bell states based on an InGaP nonlinear metasurface. The metasurface facilitates a local optical resonance with a tailored angular dispersion, enabling the generation of polarization-entangled photon pairs through spontaneous parametric down conversion. This opens new possibilities for practical applications of integrated metasurfaces in advanced quantum technologies.
In recent years, interest in infrared (IR) imaging has grown, motivated by applications in surveillance, quality control and healthcare. However, conventional IR imaging devices are limited by their low temperature operations and high-noise levels. Nonlinear metasurfaces offer a promising platform for up-conversion IR imaging, potentially allowing multi-color IR imaging in compact devices, at room temperature. Here, we demonstrate up-conversion IR imaging by employing a nonlocal lithium niobate metasurface supporting guided mode resonances. Driven by the resonant enhancement of the incident field, we demonstrate up-conversion of short-wave IR images at 1530 nm to visible images at 550 nm. Our study has important applications in the future development of compact night vision instruments and sensor devices.
Sum frequency generation is the process in which two incoming photons are converted into an outgoing photon of higher energy. This process is highly inefficient, and therefore requires either large interaction distances in bulky crystals, or large field concentrations in the non-linear materials. Metasurfaces are one such platform to generate extreme field enhancements with resonant processes. In this work, we use topology optimisation to design metasurfaces that exhibit increase high efficiency sum frequency generation, as well as the ability to tailor the generated polarisation.
We develop and experimentally realise a single-layer metasurface that converts unpolarised light into fully polarised light surpassing the efficiency limit of 50% for conventional polarisers. We achieve this by using an inverse-designed metasurface that splits incoming light into multiple outputs with the same polarisation. We predict a greater than 80% conversion efficiency when combining the powers of two or three outputs. We fabricate the freeform silicon metasurface and experimentally measure a combined efficiency of over 60% in converting unpolarised light to polarised light at 1550 nm with an overall extinction ratio 20.
We propose and experimentally demonstrate a dielectric metasurface that allows monitoring of polarization deviations from an arbitrary elliptical input anchor state simply by tracking in real-time the output ratio between the powers of horizontal and vertical components after the metasurface. Importantly, this ratio can be enhanced corresponding to increased responsivity. Such nontrivial functionality is achieved by designing binary metasurfaces that realize tailored nonunitary and chiral polarization transformation. We experimentally demonstrate the operation at telecommunication wavelengths with enhanced responsivity up to 25 for various anchor states, including the strongly elliptical and circular. We also achieve the uncertainty of deviation measurement that is significantly better than the fundamental limit for nonchiral metasurfaces.
Multi-photon split states, where each photon is in a different input mode, represent an essential resource for various quantum applications. Accordingly, characterisation of such states is important from the fundamental and practical perspectives. We propose a segmented coupled waveguide array as a new form of compact low-loss quantum circuit and apply it for the scalable multi-photon split state tomography with optimized performance and no need of reconfigurability. We develop an optimization algorithm to design the array with minimally necessary number of waveguides and smallest sensitivity to noise in the tomography. Such a novel platform can enable fast, scalable, and fully integrated quantum systems.
Transmissive-type metasurfaces represent an ultrathin alternative to traditional optical elements, e.g., lenses and waveplates. However, transmissive-type plasmonic metasurfaces (PMs) have significantly low efficiency compared to dielectric metasurfaces and reflective type PMs particularly in the visible range. For example, the state-of-the-art geometric PMs transmission efficiency is ≤10% with extinction ratios ~ 0 dB. The low transmission efficiency is mainly due to three loss channels (i) absorption losses in metals, (ii) diffraction to undesired high-orders, and most importantly (iii) symmetric forward-backward scattering which puts a 25% theoretical limit on cross-polarization conversion for ultrathin metasurfaces. We use tunable, multipole-interference-based meta-atoms to address all loss channels simultaneously. The experimentally demonstrated transmission efficiency and extinction ratio of our geometric PM are 42.3% and 7.8dB, respectively. As for dielectric metasurfaces, we demonstrate a new class of metasurfaces where the meta-atoms consist of a simple anti-reflective coating (ARC). ARCs enable the control over the entire 2 pi phase range by varying the dielectric films thicknesses while realizing ~ 99% transmission efficiency even in the visible range. The metasurface consists of patches of ARC meta-atoms with dielectric optical thicknesses much lower than that required in Fresnel optics to control the entire phase range.
An efficient phase-matched second harmonic generation (SHG) process induced in a silicon-organic hybrid plasmonic waveguide
with a thin nonlinear polymer layer deposited on top of a silicon slab and covered by a metal cap is theoretically
proposed. Owing to the hybridization property of the waveguide modes, the SHG from mid-infrared (~ 3.1 μm) to near-infrared
wavelength (~ 1.55 μm) is achieved with small fabrication-error sensitivity and large bandwidth. The SHG efficiency
is predicted up to 8.8% for a low pumping power of 100 mW.
We come up with a model of subwavelength-diameter fiber taper-based Bragg gratings (SWDFT-BGs) and numerically
investigated the chirp characteristics of Bragg gratings written in local single-mode fiber tapers based on coupled-mode
theory and transfer matrix method. The effective modal refractive index varies along adiabatic subwavelength-diameter
fiber tapers (SWDFTs), which results in an effective chirp in grating period. Additionally, SWDFT-BGs with full width
at half maximum (FWHM) up to 4.9 nm and time-delay slope over 25 ps/nm were achieved in simulations. This offers
an idea for fabricating single-mode chirped fiber Bragg gratings using uniform phase-mask and paves ways for
waveguide dispersion engineering and wide-bandwidth optical filters.
Allergic rhinitis is a common disease. Although it is already treated well clinically by widely using a new technology laser that is very popular with patients, but it is still not found home and aboard the detail research report about the pathological changes of nasoturbinal tissues before and after laser treatment. Recently, in order to further study the histopathological changes of the oedematous nasoturbinal mucosa irradiated by Nd:YAG laser. We have made pathological observation of the biopsy.
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