Birdlorenzen6555

The simulation of the external perturbations performed at the elaborated device proved the applicability of the proposed scheme as a sensor of various physical quantities.The nonlinearity of the light-emitting diode (LED) in underwater wireless optical communication (UWOC) systems is considered the one major limiting factor that degrades the system's performance. Volterra series-based nonlinear equalization is widely employed to mitigate such nonlinearity in communication systems. However, the conventional Volterra series-based model is of high complexity, especially for the nonlinearity of higher-order terms or longer memory lengths. In this paper, by pruning away some negligible beating terms and adaptively picking out some of the dominant terms while discarding the trivial ones, we propose and experimentally demonstrate a sparse pruned-term-based nonlinear decision-feedback equalization (SPT-NDFE) scheme for the LED-based UWOC system with an inappreciable performance degradation as compared to systems without the pruning strategy. Meanwhile, by replacing the self/cross beating terms with the terms formed by the absolute operation of a sum of two input samples instead of the product operation terms, a sparse pruned-term-based absolute operation nonlinear decision-feedback equalization (SPT-ANDFE) scheme is also introduced to further reduce complexity. The experimental results show that the SPT-NDFE scheme exhibits comparable performance as compared to the conventional NDFE (nonlinear decision-feedback equalization) scheme with lower complexity (the nonlinear coefficients are reduced by 63.63% as compared to the conventional NDFE scheme). While the SPT-ANDFE scheme yields suboptimal performance with further reduced complexity at the expense of a slight performance degradation, the robustness of the proposed schemes in different turbidity waters is experimentally verified. The proposed channel equalization schemes with low complexity and high performance are promising for power/energy-sensitive UWOC systems.In this paper, a novel method for simultaneous all-optical sampling and quantization is presented, to the best of our knowledge. This study utilizes the nonlinear Kerr effect in a silicon-based waveguide grating to realize nonlinear filters in which the sampling pulses are affected by the input signal. Compatible with complementary metal-oxide-semiconductor fabrication, in this ultra-compact two-bit quantizer, the footprint is reduced to 90µm2 which, to the best of our knowledge, is the least among recent similar studies.We investigate the polarization characteristics of apophyllite crystals in an attempt to evaluate their potential use for achromatic waveplates. Among the 50 plates that we extracted and polished from natural apophyllite crystals, a few show the sought-for characteristic of birefringence that increases linearly with the wavelength. However, we also find that the crystals among our samples exhibit a sectored structure in their polarization properties, as well as an undesirable degree of spatial nonuniformity.Despite the availability of effective hepatitis B vaccinations, the hepatitis B virus remains a serious global health concern. It is expected that early detection could aid in initiating therapy before the infection progresses to liver damage. A silicon nanowire rectangular optical waveguide has been demonstrated theoretically to detect the surface antigen of hepatitis B "HBsAg" based on label-free surface sensing using finite-element method-based COMSOL Multiphysics. Different procedural segments of the biomarker detection have been mimicked on the surface of a waveguide as adlayers to investigate the device theoretically. Initially, the parameters of the waveguide have been optimized to provide a large interaction of light and bio-analyte, i.e., to provide high sensitivity. The analyses are first performed at the waveguide level based on the light-analyte interaction. Furthermore, performances of the sensor have been obtained by incorporating this waveguide structure in the sensing arm of the Mach-Zehnder interferometer. see more The device structure shows ultra-high surface sensitivities such as phase surface sensitivity of 7.03×2πrad/nm and MZI surface sensitivity of 3421.89 µW/nm with an excellent detection limit of 2.92×10-3pg/mm2 for HBsAg detection. The proposed device can measure the HBsAg concentration as low as 0.00973 ng/mL, which is significantly low to detect the infection in an early stage.Fluorescent digital image correlation (DIC) is becoming popular for measuring 3D profiles and deformations in external surfaces. However, the simultaneous monitoring of interior layers is highly challenging due to the penetrability and refraction of light using monochromatic fluorescence. We propose a color fluorescent speckle pattern (CFSP) method for measuring the internal displacement of transparent objects based on multispectral stereo-DIC and refractive index correction. During sample fabrication, fluorescent speckle patterns exciting different colors are fabricated on both the surface and interior layers of objects. A virtual color stereo-DIC system is utilized to capture the CFSP on the surface and interior layers simultaneously from two different perspectives. Different color channels are practically equivalent to synchronized monochrome vision systems, having separate CFSP in external and internal measurements. In multispectral stereo-DIC calculation, the external surface is initially reconstructed through one channel of the system even if the surface is non-planar. Based on Snell's law and the CFSP method, the internal layer is then reconstructed and corrected by establishing the geometry of the refractive stereo-DIC through another channel. The relative error of the thickness between two planar layers was proved to decrease from 33.4% to 0.7% after refractive index correction. Further experimental results validate the efficacy of this method for correcting the profile of the non-planar arc profile and determining the internal deformations of disc materials.Two-wave mixing adaptive interferometer based on a liquid crystal light valve with a semiconductor GaAs substrate is realized and studied at 1064 nm wavelength. The local response of the dynamic hologram recorded in the liquid crystal layer of the light valve allows for detection of small phase modulations of the object beam. The characteristics of the interferometer are estimated experimentally. The temporal adaptability lies in the subsecond range. The large optical nonlinearity of the cell is favorable for measurements of small displacements with high sensitivity.The effect of the formation of deep minima in frequency characteristics of photon density waves (PDWs) during their propagation in scattering media with different optical characteristics has been studied by statistical Monte Carlo modeling. The simulation was performed for the Henyey-Greenstein scattering phase function with the anisotropy factor value varying in the range of 0-0.93. The dependence of the position and magnitude of the minimum in the frequency response of PDWs on the combination of the parameters of the scattering medium and the distance to the radiation source is demonstrated.We propose a design method for a three-mirror anastigmatic telescope with low misalignment sensitivity and deduce the analytic expression between the misalignment aberration and its optical parameters based on the nodal aberration theory. We establish an optical system as-built performance evaluation model. Using this model as the system's as-built performance evaluation indicator, we can get an optical system that could have both low misalignment sensitivity and good image quality after optimization. The design results of a field bias three-mirror anastigmatic telescope show that the misalignment aberration of the system can be reduced by changing the spacing of the mirrors. When the spacing between the primary mirror and the secondary mirror increases and the spacing from the secondary mirror to the third mirror and the third mirror to the image plane decreases, the misalignment sensitivity will drop significantly. If the mirror spacing is changed by 10%, the misalignment sensitivity of the telescope optimized by our method is only about 85% of that of the traditional method.A simple wideband reflective type linear-cross and linear-circular polarization converter for terahertz (THz) applications is proposed in this paper. The top frequency selective surface (FSS) consists of a thin gold coated figure of eight square loop with the connected strip line corners on a thin grounded polyamide dielectric substrate. For the y/x-polarized incidence, the design exhibits linear-circular conversion with an axial ratio (≤3dB) from 0.49-0.50, 0.60-0.83, 1.16-1.62, and 1.81-1.85 THz with 2.02%, 32.17%, 33.09%, and 2.19% fractional bandwidth (FBW), respectively. In addition, it also performs the linear-cross conversion with a minimum 90% polarization conversion ratio (PCR) from 0.53-0.56, 0.92-1.07, and 1.69-1.75 THz having 5.50%, 15.08%, and 3.49% FBW, respectively. Multiple plasmonic resonances are the reason behind different polarization conversions and are confirmed with surface current distribution profiles of the FSS and ground. The metasurface's performance is stable up to 45° for both transverse electric (TE) and transverse magnetic (TM) oblique incidences. The polarizer's unit cell architecture is compact with structural dimensions of 0.121×0.121×0.041λL3, where λL is the lowest operating frequency's free-space wavelength. The authors believe this design is compact, with angular stable multi-band multi-conversion ability that will significantly impact the THz applications in real time.Ocean color (OC) remote sensing requires compensation for atmospheric scattering and absorption (aerosol, Rayleigh, and trace gases), referred to as atmospheric correction (AC). AC allows inference of parameters such as spectrally resolved remote sensing reflectance (Rrs(λ);sr-1) at the ocean surface from the top-of-atmosphere reflectance. Often the uncertainty of this process is not fully explored. Bayesian inference techniques provide a simultaneous AC and uncertainty assessment via a full posterior distribution of the relevant variables, given the prior distribution of those variables and the radiative transfer (RT) likelihood function. Given uncertainties in the algorithm inputs, the Bayesian framework enables better constraints on the AC process by using the complete spectral information compared to traditional approaches that use only a subset of bands for AC. This paper investigates a Bayesian inference research method (optimal estimation [OE]) for OC AC by simultaneously retrieving atmospheric and oce, which often appears in complex water conditions, was reduced by a factor of 3. The OE-derived pixel-level Rrs(λ) uncertainty estimates were also assessed relative to in-situ data and were shown to have skill.The construction of a guide star catalog is crucial for a star sensor to achieve accurate star map recognition and attitude determination. At present, the methods of a guide star catalog for a large field of view (FOV) star sensor have been relatively mature. However, for a small-FOV star sensor, there are still certain problems, such as a large storage capacity of a guide star catalog, uneven distribution of stars, and easy occurrence of voids. To address these problems, we propose a construction method of a small-FOV star sensor guide star catalog based on the combination of the improved spherical spiral method (ISSM) and extreme learning machine (ELM) named the ISSM-ELM. First, a spiral reference point is used as an optical axis pointing of the star sensor, and the guide stars are preliminarily screened based on the star-diagonal distance between the star and the reference point, and the star-density and magnitude characteristics of the guide star. Then the ELM is used to supplement the guide star empty sky area to construct an integrity guide star catalog.