Refsgaardraynor6825

Asymmetric transmission (AT) is useful for polarization manipulation. We report narrowband AT that utilizes a triple-layered symmetric trimeric metasurface with near-field coupling of the dark mode of the Fano resonance. The coupling strength of the dark mode was tuned by using a mid-layer to break the dim AT between two slit layers. The peak transmission of linearly polarized waves and percentage bandwidth reached 0.7719 and 1.26% (numerical simulations) and 0.49 and 1.9% (experiments), respectively. Coupled-mode theory and field patterns are utilized to explain the underlying physical mechanisms of the mid-layer assisted field coupling. These results are useful for Fano-resonance-based devices.We report on the fabrication and optical characterization of erbium-ytterbium co-doped aluminum oxide (Al2O3Er3+Yb3+) waveguides using low-cost, low-temperature deposition and etching steps. We deposited Al2O3Er3+Yb3+ films using reactive co-sputtering, with Er3+ and Yb3+ ion concentrations ranging from 1.4-1.6 × 1020 and 0.9-2.1 × 1020 ions/cm3, respectively. We etched ridge waveguides in 85% pure phosphoric acid at 60°C, allowing for structures with minimal polarization sensitivity and acceptable bend radius suitable for optical amplifiers and avoiding alternative etching chemistries which use hazardous gases. Scanning-electron-microscopy (SEM) and profilometry were used to assess the etch depth, sidewall roughness, and facet profile of the waveguides. The Al2O3Er3+Yb3+ films exhibit a background loss as low as 0.2 ± 0.1 dB/cm and the waveguide loss after structuring is determined to be 0.5 ± 0.3 dB/cm at 1640 nm. Internal net gain of 4.3 ± 0.9 dB is demonstrated at 1533 nm for a 3.0 cm long waveguide when pumped at 970 nm. The material system is promising moving forward for compact Er-Yb co-doped waveguide amplifiers and lasers on a low-cost silicon wafer-scale platform.The fast quasi-adiabatic dynamics (FAQUAD) protocol has proven to be an effective approach to provide shortcuts to adiabatic light evolution in optical waveguides, resulting in short and robust devices. However, the FAQUAD approach of homogeneously distributing device adiabaticity only works for a single mode (polarization, wavelength, or spatial mode group) system. We propose an adiabaticity engineering approach to redistribute the adiabaticity of optical waveguides in multi-mode systems. By engineering the adiabaticity distribution using a single control parameter, we obtain shortcuts to adiabaticity in optical waveguides for multi-mode systems. The concept is applied to the design of a compact polarization-independent adiabatic 3-dB coupler on silicon.Continuous and reversible tuning of the properties of optical metasurfaces, as a functionality that would enable a range of device applications, has been a focus of the metasurface research field in recent years. Tuning mechanisms proposed and demonstrated so far have generally relied upon changing the morphology of a metasurface or the intrinsic properties of its constituent materials. Here we introduce, via numerical simulation, an alternative approach to achieve continuous tuning of gradient metasurface response, and illustrate its potential application to the challenge of continuous beam steering, as required for example in LIDAR and machine vision systems. It is based upon the coherent illumination of a silicon nano-pillar metasurface with two counter-propagating beams. Control of the input beams' relative phase and intensity enables tuning of the individual nano-pillars' electromagnetic response and thereby the phase gradient of the array, which in turn steers the direction of the output beam continuously over an angular range of approximately 9 degrees.Large-area regular laser-induced periodic surface structures (LIPSSs) with a birefringence effect were efficiently produced on a glass surface coated with an indium tin oxide (ITO) film, through irradiation by a femtosecond laser (800 nm, 50 fs, 3 mJ, 1 kHz) focused with a cylindrical lens. The laser fluence of 0.44 J/cm2 on the coated glass was only one-tenth of that on bare glass, which significantly reduced the thermal effect. Moreover, regular LIPSSs with a period as short as 100 nm could be produced efficiently. The retardance of the fabricated LIPSSs was measured to be up to 44 nm, which is eight times that of LIPSSs fabricated on bare glass. The mechanisms of such a large difference of retardance were studied by measuring the nanostructures and the concentration of In3+ ions on the cross section of nano-corrugated surface layer on bare glass and ITO-coated glass.An orbital angular momentum (OAM) dividable on-chip directional coupler design is proposed. To guide OAM modes of topological charge number l = ±1, a waveguide needs to support TE01 and TE10 modes with degeneracy. When a directional coupler is made with such an OAM mode waveguide, it is additionally required to equalize the horizontal-direction coupling strengths of those two OAM constitutive eigenmodes. Base on the coupled mode theory formulation, we have found that this requirement can hardly be satisfied and devised a modified cross-shaped waveguide structure to solve this problem. An example design of OAM mode directional coupler is demonstrated. The coupling length of the designed device is 670 µm, and our numerical simulation showed negligible degradation of OAM mode purity during the operation of complete optical power transfer between two waveguides. To the best of our knowledge, this is the first proposal of the on-chip OAM mode directional coupler. The proposed design approach can be applied to implement various devices for OAM mode-based photonic integrated circuits.Non-uniform thermal load causes performance degradation of crystal X-ray optics. With the development of high-brightness X-ray free-electron lasers, the thermal load on X-ray optics becomes even more severe. To mitigate the thermal load, a quantitative understanding of thermal effects on the optical performance is necessary. We derived an analytical model for monochromator performance under a non-uniform thermal load. This analytical model quantitatively describes the distortion of the rocking curve and attributes different contributions to different factors of thermal load. It provides not only monochromator design insights and considerations, but also a quick estimation of the rocking curve distortion due to thermal load for practical situations such as pump-probe experiments.The higher order (such as the 2nd order and the 4th order) moments of the Mueller matrix elements are important to estimate the polarization mode dispersion (PMD) induced power fluctuations for the forward propagation and the backward scattered signals (e.g. fluctuation of the Raman gain and the Brillouin gain). Current knowledge about the Mueller matrix is limited to the 2nd order moments of its elements in a sufficiently long fiber. In this work, the higher order moments of the Mueller matrix elements of a fiber with arbitrary length is studied analytically. The stochastic differential equations (SDEs) for the moments of the Mueller matrix elements are derived and converted to the related ordinary differential equations (ODEs). Since the ODEs are with the constant coefficients, it is possible to obtain the analytical solutions. The predicted 2nd order moments in a sufficiently long fiber agree well with the existing results. The results of the 4th order moments of the Mueller matrix elements in an arbitrarily long fiber are validated by the numerical simulations with excellent agreement.The obstacle of imaging through multimode fibers (MMFs) is encountered due to the fact that the inherent mode dispersion and mode coupling lead the output of the MMF to be scattered and bring about image distortions. As a result, only noise-like speckle patterns can be formed on the distal end of the MMF. We propose a deep learning model exploited for computational imaging through an MMF, which contains an autoencoder (AE) for feature extraction and image reconstruction and self-normalizing neural networks (SNNs) sandwiched and employed for high-order feature representation. It was demonstrated both in simulations and in experiments that the proposed AE-SNN combined deep learning model could reconstruct image information from various binary amplitude-only targets going through a 5-meter-long MMF. Simulations indicate that our model works effectively even in the presence of system noise, and the experimental results prove that the method is valid for image reconstruction through the MMF. Enabled by the spatial variability and the self-normalizing properties, our model can be generalized to solve varieties of other computational imaging problems.We propose a novel technique based on optical time domain reflectometry for characterizing the losses of transmission modes along few-mode fiber links. The technique estimates the transfer matrix at a crosstalk-inducing point from the measured backscattered waveforms and then eliminates the crosstalk influence of the point on the waveforms. Waveforms that are free from the crosstalk influence enable us to obtain the true losses independently of the crosstalk-inducing point. A proof-of-concept demonstration is performed on an optical fiber with a crosstalk-inducing splice and a bend, and the results show the usefulness of the proposed technique.As the reference radiometric calibration standard of sensors on the Haiyang-1C (HY-1C) satellite platform, the satellite calibration spectrometer (SCS) is equipped with an onboard calibration system composed of double solar diffusers and an erbium-doped diffuser to monitor the postlaunch radiometric response change. Herein, through onboard calibration data analysis, the calibration diffuser performance remains stable without degradation, and the Moderate Resolution Imaging Spectroradiometer (MODIS) on Terra is adopted as a reference to repeatedly verify onboard radiometric calibration results by selecting different dates and reflectance scenes. The SCS equivalent reflectance is obtained by combining the mean digital number (DN) of the SCS crossing area image with the radiometric calibration coefficient. The spectral reflectance is obtained via interpolation and iteration, which is adopted as the actual MODIS incident pupil spectral reflectance because the small imaging time interval can be ignored and almost vertically observed, and it is convoluted with the MODIS spectral response function to obtain the predicted equivalent reflectance. Validation is completed by comparing the predicted MODIS equivalent reflectance to the measured value based on the onboard calibration coefficient. The results show that (1) the difference between the measured and predicted MODIS band equivalent reflectance is between -0.00466 and 0.0039, and (2) the percentage difference between the measured and predicted MODIS band equivalent reflectance ranges from 4.17% and 1.24%, indicating that the calibration system carried on HY-1C can perform high-precision SCS radiometric calibration, meeting the cross-calibration accuracy requirements of other loads on the same platform.We report a ∼3-fold enhancement of third-harmonic generation (THG) conversion efficiency using indium tin oxide (ITO) nanoparticles on the surface of an ultra-high-Q silica microsphere. see more This is one of the largest microcavity-based THG enhancements reported. Phase-matching and spatial mode overlap are explored numerically to determine the microsphere radius (∼29 µm) and resonant mode numbers that maximize THG. Furthermore, the ITO nanoparticles are uniformly bonded to the cavity surface by drop-casting, eliminating the need for complex fabrication. The significant improvement in THG conversion efficiency establishes functionalized ITO microcavities as a promising tool for broadband frequency conversion, nonlinear enhancement, and applications in integrated photonics.