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Bound states in the continuum (BICs) can be derived from a generalized waveguide condition in which the total internal reflection is substituted by coherent perfect reflection. Coherent perfect reflection can occur in the truncated photonic crystal (PhC) due to the interference of different Bloch modes. Based on the coherent reflection, BICs can be constructed by the bulk Bloch modes of PhC slabs. In contrast to the determination of BICs from the topological vortices of far-field radiation, this interpretation from coherent reflection can give the spatial field profile in detail in the near field. We show that the BICs can be characterized by the indices (or number of nodes) of their constituent Bloch modes. Moreover, all the guided resonances in addition to BICs can also be labelled by these mode indices. It is found that for the guided resonances the mode indices can change suddenly on the same frequency band. Our results may have potential applications in guided-wave optics and enhanced light-matter interaction.A polydimethylsiloxane film patterned by a self-assembled array has been demonstrated as a strain sensor. A monolayer of 580 nm polystyrene spheres prepared by convective deposition was the template to transfer a periodic pattern to a polydimethylsiloxane (PDMS) film. Optical diffraction through the stretched PDMS film, enabled strain sensing perpendicular and parallel to the stretching direction, with sensitivities of 1.7 nm/% strain and 4.0 nm/% strain, respectively. The PDMS film was used as a vibration sensor at 50 Hz.The distance and velocity measurement can be obtained by the round-trip time and Doppler effect on the down-chirp and the up-chirp of the linear frequency-modulated waveform (LFMW), but false targets will appear in a multi-target situation, resulting in erroneous detection. Here, we report a photonics-assisted approach to realize unambiguous simultaneous distance and velocity measurement in multi-target situations utilizing a dual-band symmetrical triangular LFMW. Dual-band observation invariance is proposed, to effectively resolve the false targets. The de-chirped signals can be obtained from parallel de-chirping processing to the dual-band echoes. By measuring and calculating the beat frequencies of the de-chirped signals in the two frequency bands, the actual parameter measurements can be acquired according to the authenticity criterion. In the experiments, detections to three targets are performed, and the distance and velocities are acquired without false targets. The absolute measurement errors of the distance and the velocity are less than 9 mm and 0.16 m/s, respectively. These results show the feasibility of the proposed approach.Optical tweezers find applications in various fields, ranging from biology to physics. One of the fundamental steps necessary to perform quantitative measurements using trapped particles is the calibration of the tweezer's spring constant. This can be done through power spectral density analysis, from forward scattering detection of the particle's position. In this work we propose and experimentally test simplifications to such measurement procedure, aimed at reducing post-processing of recorded data and dealing with acquisition devices that have frequency-dependent electronic noise. In the same line of simplifying the tweezer setup we also present a knife-edge detection scheme that can substitute standard position sensitive detectors.Conventional models of Er/Yb co-doped fibers assume all ytterbium ions are equally involved in the energy transfer with erbium ions, governed by a singular transfer rate. This would predict output power clamping once ytterbium parasitic lasing starts, contrary to the observations that the output continued to grow albeit at a slower rate. One study explained this using elevated temperature at high powers. Our study, however, shows that elevated temperature and mode-dependent effects only play insignificant roles. A new model is developed based on the existence of isolated ytterbium ions, which can explain all the observed experimental behaviors.During the past few years, a lot of efforts have been devoted in studying optical analog computing with artificial structures. Up to now, much of them are primarily focused on classical mathematical operations. How to use artificial structures to simulate quantum algorithm is still to be explored. In this work, an all-dielectric metamaterial-based model is proposed and realized to demonstrate the quantum Deutsch-Jozsa algorithm. The model is comprised of two cascaded functional metamaterial subblocks. The oracle subblock encodes the detecting functions (constant or balanced), onto the phase distribution of the incident wave. Then, the original Hadamard transformation is performed with a graded-index subblock. Both the numerical and experimental results indicate that the proposed metamaterials are able to simulate the Deutsch-Jozsa problem with one round operation and a single measurement of the output eletric field, where the zero (maximum) intensity at the central position results from the destructive (constructive) interference accompanying with the balance (constant) function marked by the oracle subblock. NIBRLTSi The proposed computational metamaterial is miniaturized and easy-integration for potential applications in communication, wave-based analog computing, and signal processing systems.In this paper, a new method combining carrier transport in semiconductors with an RF equivalent circuit was put forward to simulate the frequency response of an avalanche photodiode (APD). The main trade-off between the gain-bandwidth product (GBP) and the dark current was analyzed to optimize the structure of an APD; and a separated absorption, grading, charge, multiplication, charge, transit (SAGCMCT) structure with 120 nm balanced InAlAs multiplication layer was proposed to reduce the dark current and improve the frequency response. The fabricated triple-mesa type back-illuminated InGaAs/InAlAs APD achieved the properties of low dark current of 6.7 nA at 0.9Vb and high GBP over 210 GHz.Modeling techniques for light-shaping systems with freeform surface are presented from a physical-optics point of view. We apply the modeling techniques to different light-shaping systems with freeform surfaces designed by "ray mapping method". The simulation results show that the design is not always valid. Diffraction effects occur, especially in paraxial situations. We discuss the accuracy of the design via physical-optics simulation, and find an explanation in the geometric-optics assumption of the design algorithm being sufficient only if the optical system results in homeomorphic behavior for the electric field between the input and target.
My Website: https://www.selleckchem.com/products/nibr-ltsi.html
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