Conventional target localization algorithms for the multiple-input multiple-output (MIMO) radar with widely separated antennas are mainly based on the centralized localization framework, which suffer ...from huge burdens of computation and communication as well as robustness defect in complex environments. To overcome these issues, this paper first considers the MIMO radar with widely separated directional transmitters and omnidirectional receivers generating the bistatic range (BR) and angle of incidence (AOI) measurements for target localization, which is proven that the position of the target can be uniquely determined with one transmitter and one receiver. Then, the distributed localization framework using the hybrid BR and AOI measurements is developed, where each receiver acts as a fusion center extracting the BR and AOI measurements to perform the localization process, and the localization problem is formulated as solving a linear matrix equation. The distributed constrained total least squares (DCTLS) algorithm considering errors in both data matrix and observation vector is proposed for each receiver for target localization. The localization performance regarding the Cramér-Rao lower bound (CRLB) is derived for theoretical analysis. Numerical simulations are performed to validate the efficacy and superiority of the proposed DCTLS algorithm over other typical localization algorithms.
Conventional optical components rely on gradual phase shifts accumulated during light propagation to shape light beams. New degrees of freedom are attained by introducing abrupt phase changes over ...the scale of the wavelength. A two-dimensional array of optical resonators with spatially varying phase response and subwavelength separation can imprint such phase discontinuities on propagating light as it traverses the interface between two media. Anomalous reflection and refraction phenomena are observed in this regime in optically thin arrays of metallic antennas on silicon with a linear phase variation along the interface, which are in excellent agreement with generalized laws derived from Fermat's principle. Phase discontinuities provide great flexibility in the design of light beams, as illustrated by the generation of optical vortices through use of planar designer metallic interfaces.
Broadband Light Bending with Plasmonic Nanoantennas Ni, Xingjie; Emani, Naresh K.; Kildishev, Alexander V. ...
Science (American Association for the Advancement of Science),
01/2012, Letnik:
335, Številka:
6067
Journal Article
Recenzirano
Odprti dostop
The precise manipulation of a propagating wave using phase control is a fundamental building block of optical systems. The wavefront of a light beam propagating across an interface can be modified ...arbitrarily by introducing abrupt phase changes. We experimentally demonstrated unparalleled wavefront control in a broadband optical wavelength range from 1.0 to 1.9 micrometers. This is accomplished by using an extremely thin plasmonic layer (~λ/50) consisting of an optical nanoantenna array that provides subwavelength phase manipulation on light propagating across the interface. Anomalous light-bending phenomena, including negative angles of refraction and reflection, are observed in the operational wavelength range.
Detailed knowledge of the image of the point spread function (PSF) is necessary to optimize astronomical coronagraph masks and to understand potential sources of errors in astrometric measurements. ...The PSF for astronomical telescopes and instruments depends not only on geometric aberrations and scalar wave diffraction but also on those wavefront errors introduced by the physical optics and the polarization properties of reflecting and transmitting surfaces within the optical system. These vector wave aberrations, called polarization aberrations, result from two sources: (1) the mirror coatings necessary to make the highly reflecting mirror surfaces, and (2) the optical prescription with its inevitable non-normal incidence of rays on reflecting surfaces. The purpose of this article is to characterize the importance of polarization aberrations, to describe the analytical tools to calculate the PSF image, and to provide the background to understand how astronomical image data may be affected. To show the order of magnitude of the effects of polarization aberrations on astronomical images, a generic astronomical telescope configuration is analyzed here by modeling a fast Cassegrain telescope followed by a single 90° deviation fold mirror. All mirrors in this example use bare aluminum reflective coatings and the illumination wavelength is 800 nm. Our findings for this example telescope are: (1) The image plane irradiance distribution is the linear superposition of four PSF images: one for each of the two orthogonal polarizations and one for each of two cross-coupled polarization terms. (2) The PSF image is brighter by 9% for one polarization component compared to its orthogonal state. (3) The PSF images for two orthogonal linearly polarization components are shifted with respect to each other, causing the PSF image for unpolarized point sources to become slightly elongated (elliptical) with a centroid separation of about 0.6 mas. This is important for both astrometry and coronagraph applications. (4) Part of the aberration is a polarization-dependent astigmatism, with a magnitude of 22 milliwaves, which enlarges the PSF image. (5) The orthogonally polarized components of unpolarized sources contain different wavefront aberrations, which differ by approximately 32 milliwaves. This implies that a wavefront correction system cannot optimally correct the aberrations for all polarizations simultaneously. (6) The polarization aberrations couple small parts of each polarization component of the light (∼10-4) into the orthogonal polarization where these components cause highly distorted secondary, or "ghost" PSF images. (7) The radius of the spatial extent of the 90% encircled energy of these two ghost PSF image is twice as large as the radius of the Airy diffraction pattern. Coronagraphs for terrestrial exoplanet science are expected to image objects 10-10, or 6 orders of magnitude less than the intensity of the instrument-induced "ghost" PSF image, which will interfere with exoplanet measurements. A polarization aberration expansion which approximates the Jones pupil of the example telescope in six polarization terms is presented in the appendix. Individual terms can be associated with particular polarization defects. The dependence of these terms on angles of incidence, numerical aperture, and the Taylor series representation of the Fresnel equations lead to algebraic relations between these parameters and the scaling of the polarization aberrations. These "design rules" applicable to the example telescope are collected in § 5. Currently, exoplanet coronagraph masks are designed and optimized for scalar diffraction in optical systems. Radiation from the "ghost" PSF image leaks around currently designed image plane masks. Here, we show a vector-wave or polarization optimization is recommended. These effects follow from a natural description of the optical system in terms of the Jones matrices associated with each ray path of interest. The importance of these effects varies by orders of magnitude between different optical systems, depending on the optical design and coatings selected. Some of these effects can be calibrated while others are more problematic. Polarization aberration mitigation methods and technologies to minimize these effects are discussed. These effects have important implications for high-contrast imaging, coronagraphy, and astrometry with their stringent PSF image symmetry and scattered light requirements.
We have detected a spin-dependent displacement perpendicular to the refractive index gradient for photons passing through an air-glass interface. The effect is the photonic version of the spin Hall ...effect in electronic systems, indicating the universality of the effect for particles of different nature. Treating the effect as a weak measurement of the spin projection of the photons, we used a preselection and postselection technique on the spin state to enhance the original displacement by nearly four orders of magnitude, attaining sensitivity to displacements of ∼1 angstrom. The spin Hall effect can be used for manipulating photonic angular momentum states, and the measurement technique holds promise for precision metrology.
We introduce an ultrasensitive label-free detection technique based on asymmetric Fano resonances in plasmonic nanoholes with far reaching implications for point-of-care diagnostics. By exploiting ...extraordinary light transmission phenomena through high-quality factor (Qsolution
We propose a method for designing the multilayer diffractive optical elements (MLDOEs) to improve the polychromatic integral diffraction efficiency (PIDE) in wide angle of incidence. By comparing and ...analyzing the characteristic angle weighted PIDE (CAW-PIDE) in the whole angles of incidence, the optimal microstructure height combination of the MLDOE can be obtained. The optimization process and simulation examples for the single-band and multi-band MLDOE are given. Compared to the conventional method, the PIDE is obviously improved in wide angle of incidence by our method. This optimization method can be applied to different working wavebands, and the image quality of the hybrid optical system with the MLDOE can be improved in wide angle of incidence.
•A method for designing the MLDOEs is presented considering the incident angle.•The mathematical model of microstructure height optimization is established.•This design method can be applied to different wavebands and different types of DOE.•This method can extend the working incident angle range of the MLDOE.
Three major factors lead to the deviation of actual power output of a photovoltaic (PV) panel from the rated value: irradiance, temperature and spectral factor. While the first two are well ...characterized, spectral factor remains less explored. Spectral factor depends on the spectral irradiance as well as the spectral response of the material. So far, normal irradiance is assumed for the estimation of the spectral factor which excludes one major factor, i.e. the angle of incidence (AOI). Here it is demonstrated that AOI has a strong effect on spectral factor due to multiple reasons. For a chosen PV material of monocrystalline Si, the AOI-dependence is obtained through the following parameters: reflectivity of a bare cell and a covered panel, the transmissivities of the cover system and the effective AOI on the PV cell after multiple refractions. When all these factors are incorporated in the estimation of spectral factor, a systematic underestimation (∼4.5%) is observed for the conventional method. Further the modified definition is tested for a chosen location of Kanpur, India for annual variations. Again a significant underestimation is noticed (∼3.5%), the value of which is expected to be higher for higher latitude locations due to greater obliquity of insolation.
The effect of angle of incidence on the absorption and conversion is studied for a monocrystalline silicon solar photovoltaic panel. The spectral factor is demonstrated to be sensitive to the angle of incidence which alters the reflectivity, transmissivity of the cover system and the effective angle of incidence on the layer of photovoltaic material. Display omitted
•AOI-dependence on spectral factor (SF) is estimated for m-Si PV module.•AOI-dependent spectral reflectivity is measured for bare PV cell.•AOI-dependent spectral transmissivity of cover material is measured.•Strong AOI dependence on SF-estimation is observed.•Seasonal variations of SF are illustrated for Kanpur, India.
Photovoltaic insulated glass units (PV-IGUs) possess significant potential for achieving simultaneous power generation, thermal insulation, and natural lighting in buildings. However, the optical ...properties of PV-IGUs are influenced by real-time variations of the Angle of Incidence (AOI), thereby intricately impacting its optical-electrical-thermal performance. Therefore, an optical-electrical-thermal coupling model was developed to evaluate the impact of real-time AOI on the optical-electrical-thermal performance of cadmium telluride (CdTe) PV-IGUs. Through outdoor experiments, the model's accuracy was validated with acceptable errors between experimental and simulated data. After validation, the optical-electrical-thermal performance of PV-IGUs were analyzed under different operational conditions and AOIs. Results revealed that when AOI exceeds 45o, there is a reduction in absorptance up to 60.76% in terms of optical performance. Notable variations were observed across AOIs regarding thermal-electrical performance, with a maximum temperature difference of 16.08 °C for the PV cells and a maximum disparity in power generation of 140.51 Wh/m2 under solar radiation of 800W/m2. Additionally, an increase of AOI and decrease of photovoltaic coverage ratio (PVR) for PV-IGUs result in higher variation of the solar heat gain coefficient (SHGC), reaching up to 69.81% when PVR is 0.1. This study established a reliable foundation for accurately evaluating the performance of PV-IGUs.
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