A Design Study on Polarized Beam Splitter for Visible Light

Optimize the shape of curved-Fresnel lens to maximize its transmittance

The phenomenon of surface plasmon resonance in composite films consisting of gold nanoclusters in matrices of organic molecular materials calix[4]arene and poly(N-vinylcarbazole) has been investigated. The internal reflection coefficients Rs2 and Rp2 of s- and p-polarized light and their physical difference ρ = Rs2 − Rp2 have been measured according to the Kretschmann scheme as a function of the angle of light incidence θ at different wavelengths λ in the range 400–1000 nm. The angular characteristics reflect the cluster structure of the films, which is confirmed by electron microscopy. A topological size effect has been revealed. This effect is associated with the dependence of the excitation energy efficiency of surface plasmons on the azimuth of the linearly polarized light, the shape, and the distribution of nanoclusters in the coordinate space. The dependences ρ(λ) demonstrate that the local plasmon resonance is excited by both s- and p-polarized light, whereas the polariton resonance is excited by s-polarized light. The sign of the curvature of the dependence ρ(θ) determines the predominance of the excitation energy efficiency of electromagnetic modes with one of the two states of polarization of the excitation radiation.

The refractive indices along arbitrary wave vector are analyzed in a uniaxial crystal with buried optical axis. According to the Brewster angle law, the relations between the Brewster angles of the incident p-polarized light and the two principal refractive indices are obtained for the case that the optical axis is in the incident plane. Further, for the case of unknown optical axis, the two principal refractive indices and the direction of optical axis can be calculated by inserting the experimental Brewster angles into the specially derived equations. On the other hand, the functions for the reflectivity fitting corresponding to two cases, i.e. , s-polarized light and p-polarized light, are presented. Finally, the CaCO₃ crystal has been measured both in s-polarized light and p-polarized light with a view to carefully study the effect of incident angle on reflectivity. The accuracy of our measurement is able to reach 0.0001 without the need of any machining process on the sample.

Acousto-optic signal processors, such as convolvers and correlators, are usually designed to have increased bandwidth and high dynamic range. We will show how, by simply choosing the proper polarization of interacting light, diffraction efficiencies, bandwidth, and dy-namic range can be enhanced. This will be demonstrated bv examining the case of acousto-optic interactions between an unguided, linearly polarized optical beam and a surface acoustic wave. Using the side-entry technique, the optical beam is launched at grazing incidence onto a YZ-LiNb0₃ substrate, propagating laterally beneath the surface. A conventional coupled-mode analysis is performed, assuming plane wave optical beams. We show how the coupling parameter depends on the polarization and thickness of incident beam and on the acoustic power. Experimental results will also be presented, showing that for p-polarized incident light, diffraction efficiency bandwidths can be larger by a factor of two, when compared to the s-polarized case. Plots of diffraction efficiency versus both deviation from Bragg angle and transducer frequency will be shown. The coupled-mode analysis also gives conditions such that s-polarized light can have a larger bandwidth than p-polarized light, a fact which has not yet been demonstrated experimentally.

Robust retrieval of soil moisture at field scale across wide-ranging SAR incidence angles for soybean, wheat, forage, oat and grass

In modern optical applications, it has become an important need to flow light unidirectionally. An optical diode realizes this task as an electrical counterpart manipulates the flow of electrons in semiconductor materials. In this study, we show a broadband and polarization-independent optical diode-like mechanism in a metasurface configuration in the visible spectrum. The approach is passive such that the operating principle does not depend on any type of external biasing scheme. The constituted metasurface composed of a periodic type three-dimensional nanoarray of trapezoidal-shaped aluminum metal on a sapphire substrate is designed to produce the desired optical response for opposite directions of illumination. The optical transmission properties were systematically investigated using finite-difference time-domain computations. The asymmetric transmission frequency interval of the designed metasurface is associated with the Wood–Rayleigh anomaly, and the physical principle lies in the generation of the different number of higher order modes upon oppositely incident light. Our design has forward transmission of greater than 50%, backward transmission of less than 28%, and contrast ratio of greater than 3 dB in the entire visible spectrum. Specifically, a maximum forward transmission of 88% at 550 nm wavelength and a very high contrast ratio (∼23 dB) at a wavelength of 461 nm were obtained. It is numerically shown that the asymmetric transmission has been directly related to the appearance of high-order diffractions for only one direction excitation case. This study provides a path toward the realization of optical diodes for applications, such as optical communications and laser systems.

Substrate material selection model for dual-band multilayer diffractive optical elements with wide angle of incidence

Diffraction efficiency model for diffractive optical element with antireflection coatings at different incident angles

Polarizing beam splitters are key elements widely used in different optical instruments. This paper introduces the design and simulation of a novel thin-film multilayer polarizing micro beam splitter based on airgap layers (n = 1.002828 at 400 nm). The negligible absorption coefficient of the air over a wide spectral region (κ ≈ 0 from about 200 nm and higher) satisfies the conditions of a perfect low refractive index material (L). Moreover, using titanium dioxide (TiO2) as high refractive index material (H), a very high refractive index contrast is obtained. The micro beam splitter optical structure consists in a 7 optimized multilayer of TiO2 and air, providing a refractive contrast higher than 1.2. The polarizing beam splitter cube is projected in a borosilicate glass substrate (BK7) and the optical multilayer obtained, expressed in multiples of the quarter wavelength optical thickness – QWOT, is 1.6H L 1.1H 1.5L 1.1H L 1.6H. This optical structure ensures the transmission of p- polarization and the reflection of s- polarization, from visible to NIR spectral range, over a bandwidth higher than 170 nm. Additionally, the designed polarizing beam splitter can be fabricated using standard microtechnology fabrication processes.

In this paper we analyze the change of polarization state for a laser optical system which includes a Cassegrain beam expander and several fold mirrors. First, this system operates over a broad spectral band and is with several separated wavelengths, therefore, strong polarization effects will occur at certain waveband. The polarization state changes of different wavelengths at the exit pupil are discussed mainly based on the comparison of their Point Spread Function (PSF) and Strehl Ratio respectively. Then, fold mirrors cause large angles of incidence and can rotate in azimuth and zenith. The amplitude diattenuation and retardance are calculated at different azimuth and zenith of the beam director assembly. In this paper, Code-V commercial optical-engineering software is used to model the polarization behavior for the system. The factors mentioned above, which are spectral bandwidth, angle of incidence of surfaces and systemic coatings, are taken into consideration in the process of simulation. The result of the study shows that the polarization properties at certain wavelength are satisfactory except some other wavelengths are not. This laser system is more sensitive to retardance than to diattenuation. It is concluded that polarization is an important factor that affects the performances of the whole system and the design of laser optical system should take into account the polarization effects.

A focused study on the C-band polarimetric scattering and physical characteristics of frost-flower-covered sea ice was conducted at the Sea-Ice Environmental Research Facility over a three day period. Sea ice was grown in an outdoor pool outfitted with automated sensors to monitor environmental conditions. C-band polarimetric scattering measurements were conducted continuously at a range of incidence angles, and surface roughness statistics were obtained at discrete times using a laser scanner system LiDAR. Four stages of development were identified that exhibited notably different physical and scattering characteristics: 1) initial formation; 2) surface brine expulsion; 3) frost flower growth; and 4) decimation. An optimal polarization and incidence angle is not readily apparent for the purposes of identifying the frost flower development Stages I-III; however, the lower incidence angles (25° and 35°) appear to be most sensitive to the surface brine expulsion. Only the dual-polarization measurements at low incidence angles (e.g., 25°) could be used to identify the onset of the decimation stage. Backscatter increased rapidly during the initial formation, with a local maximum corresponding to ~ 80% areal coverage of frost flowers, followed by a local minimum when the surface was covered by a brine-rich surface layer, connoting that surface brine expulsion may be identified using polarimetric scatterometry.

Our aim was to examine secondary image formation in the anterior segment caused by peripheral light focusing (PLF) in the human cornea, and in particular the crystalline lens. Non-sequential ray-tracing (OptiCAD) was applied to an anatomically based human eye model, which incorporates a gradient index crystalline lens. For analysis of the limbal effect, we varied the incident angle from 100 to 122 degrees, while for the crystalline lens effect, the incident angle was varied from 60 to 90 degrees. The corneal shapes studied included central radii from 7.4 to 8.2 mm with a range of shape factors. In each case, we computed the peak and average intensities, and the area of exposure at the limbus or lens periphery. The computation was repeated with a previous model eye for comparison. For the limbal effect, a peak intensity gain of x22.5 was found at an incident angle of 104 degrees which compares well with previous results. The average intensity gain at this angle was x7.5 over an area of 0.23 mm2. Steeper corneal curvature produced a greater PLF effect. For the crystalline lens effect, maximum UVA (365 nm) intensity gain peaked at x8.6 at 84 degrees with average intensity gain of x2.3. The area of UVA exposure peaked at 4.7 mm2 at 70 degrees. A relatively wide range (30 degrees ) of incident angles produced peak PLF gains of x3 or more in the lens. Significant focusing of light is directed to the nasal limbus, and to a lesser extent to the crystalline lens over a broad range of incident angles. PLF in the nasal cornea is reduced by an order of magnitude when a UV-blocking soft contact lens is used. The concentration levels and intraocular sites of PLF action on UV and visible light suggest a new mechanism of phakic dysphotopsia and lens phototoxicity.

Metasurface-based carpet cloaks although are very thin and have a good performance, are very sensitive to the incident angles and work only for a very narrow range of incident angles. In this paper, we have addressed this issue using PSO algorithm in combination with a deep neural network. A passive single-layer metasurface capable of making objects under it invisible for a wide range of incident angles, 0 to 70 degrees, is designed and optimized using PSO algorithm in combination with a deep neural network. The cloak has been designed and evaluated using full-wave numerical simulations, and the results show a good performance in the mentioned incident angle band.

We present the design and the simulation of an ultracompact high efficiency polarization beam splitter(PBS) based on the properties of the light waves propagating in straight waveguide and composite structure photonic crystal. The splitting properties of the PBS are numerically simulated and analyzed by using the plane wave expansion (PWE)method and finite difference time domain(FDTD) method. The PBS consists of three parts, namely, input waveguide, beam structure and output waveguide. It is shown that a high efficiency and a large separating angle for TE mode and TM mode can be achieved. Owing to these excellent features, including small size and high rate, the PBS makes a promising candidate in the future photonic integrated circuits.

In this paper, we present new results on the controlled directional steering and focusing of surface plasmon polaritons (SPPs) via 1D and 2 D metagratings by changing the angle of incidence, the incident wavelength and polarization. These findings build on previous work of our group on polarization controlled steering of SPPS using fishbone meta gratings and greatly expand on the functionality of the latter using novel designs. First we show that by creating a running wave of polarization along a one dimensional metallic metagrating consisting of subwavelength spaced rotated apertures that propagates faster than the SPP phase velocity, we can generate surface plasmon wakes, which are the two-dimensional analogue of Cherenkov radiation. The running wave of polarization travels with a speed determined by the angle of incidence and the photon spin angular momentum. We utilize this running wave of polarization to demonstrate controlled steering of the wakes by changing both the angle of incidence and the polarization of light, which we measure through near-field scanning optical microscopy. Next we report a simple 2D metagrating design strategy that can be used for focusing, polarization beam splitting, waveguide coupling, and even phase control at the focus of an SPP beam. We experimentally verify our 2D metasurface by creating a four wavelength plasmonic demultiplexer, which also has polarization selectivity (on/off). The wavelength demultiplexer is designed such that each of the four wavelengths is focused to a different spot outside of the structure. Coupling of free space light to SPPs is achieved by milling subwavelength apertures into a thin gold film. This methodology can be easily extended to any wavelength where SPPs exist, for an arbitrary number of wavelengths, and with polarization selectivity and phase control at the focus as well. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.