Advanced Optical Systems (United States)

Modern optical systems prioritize precision and resolution, increasing demand for large-aperture mirrors. To enhance manufacturing efficiency, we propose a multi-robot collaborative optical manufacturing technology utilizing the Preston equation. Our study correlates the rotational speed of lapping tools with material removal. For a 1450 mm diameter mirror, the process achieved a 61.96% reduction in total manufacturing time to 52 hours over eight cycles. The surface quality within the central 90% aperture was simultaneously improved, with the PV value decreasing from 80.14λ to 5.42λ (λ = 632.8 nm) and the RMS value decreasing from 8.19λ to 0.75λ.. These findings confirm that the three-robot system effectively shortens manufacturing time, providing insights for advancing intelligent optical manufacturing and enhancing production capabilities..

Metasurface-based solar concentrators offer significant potential to effectively capture broadband, wide-angle sunlight without an extra tracking system, making them a promising pathway for advanced solar energy utilization. Currently, how to mass-produce nanostructures on large-area surfaces is both a research hotspot and a technical challenge. Therefore, a manufacturing method has been proposed that utilizes nanoimprint lithography for mass-producing surface nanopatterns on concentrators, followed by etching techniques to transfer these patterns onto TiO₂ substrates. However, masks fabricated via nanoimprint lithography suffer from issues such as irregular shapes, weak adhesion between the mask and the substrate, and fragmentation during the etching process. Furthermore, the constraints imposed by the material properties of TiO₂ and the size inhomogeneity of nanopatterns mean that achieving large-area etching of nanopatterns with high aspect ratios and high uniformity remains a significant challenge. To address these challenges, this study proposes a method that employs reactive ion etching (RIE) technology incorporating sidewall protection and ion-assisted etching processes. This approach effectively resolves the issues of low etching rate and insufficient selectivity encountered in other etching methods. A 4-inch concentrator has been successfully fabricated, achieving high-aspect- ratio nanostructures with a maximum etching depth of 400 nm. Furthermore, the etched TiO₂ nanostructures can achieve sidewall angles exceeding 89°, even when the mask quality is imperfect. These results demonstrate that RIEbased processes enable high-efficiency, high-precision nanofabrication of metasurface concentrators.

We discuss the requirements, concepts, simulations, implementation, and calibration of two dual Fabry-Perot (FPI)-based imaging spectropolarimeters, CRISP and CHROMIS, at the Swedish 1-m Solar Telescope, and CRISP2, which is under construction. These instruments are optimised for a large field of view and high cadence at the expense of a moderate spectral resolution, and use a combination of a high-resolution and a low-resolution etalon together with an order-sorting prefilter to define the bandpass. The overall design is made robust and stable by tailoring the low-resolution etalon reflectivity to accommodate expected cavity errors from both etalons, by using a compact optical design that eliminates the need for folding mirrors, and enclosing the entire system within a single container sealed by lenses. By using a telecentric design based on lenses rather than mirrors, image degradation by the FPI system is negligible, as shown in a previous publication, and the throughput of the system is maximised. The initial alignment, and maintaining that alignment over time, is greatly simplified. Moreover, the telecentric design allows the full calibration and/or modelling of essential system parameters to be carried out without interfering with the optical set-up or the cameras. We also discuss briefly the polarimeters developed for CRISP and CHROMIS. The high performance of CRISP and CHROMIS has been demonstrated in an earlier publication through measurements of the granulation contrast and comparisons with similar measurements simultaneously made through broadband continuum filters. Here, we focus on the aspects of the design that are central to enabling high performance and robustness, but also discuss the calibration and processing of the data, and use a few examples of processed data to demonstrate the achievable image and data quality. We put forward a proposal for a similar conceptual design for the European Solar Telescope and conclude by discussing potential problems of the proposed approach to designs of this type. Some aspects of these FPI systems may also be of interest outside the solar community.

This work presents an efficient Maxwell solver which integrates an iterative boundary condition scheme with the Runge-Kutta propagation method, enabling effective handling of boundary value problems. This new method is termed to the Runge-Kutta Iterative Solution (RKIS), which accurately computes near-field distributions for EUV masks while requiring substantially less memory than the Rigorous Coupled-Wave Analysis (RCWA). Coupled with the Abbe imaging model, RKIS enables efficient simulation of far-field imaging through thick masks. It delivers accuracy compared with established methods with a significantly reduced computational cost, offering a practical solution for advanced lithography applications with rigorous electromagnetic simulation.

Bonnet polishing, a cost-effective and high-precision polishing technique with remarkable adaptability, is widely utilized in the precision machining of complex curved surfaces. However, mid-spatial frequency (MSF) error residuals significantly constrain its convergence efficiency in form error correction and ultimate machining accuracy. This paper investigates the influence of tool removal function characteristics on MSF errors during bonnet polishing. Initially, the theoretical removal functions under varying tool and process conditions were derived through finite element simulations, with the computational framework grounded in Preston's law, Hertzian contact mechanics, and kinematic analysis. Subsequently, a spectral-domain simulation model was developed to quantify MSF error residuals on optically finished surfaces based on the characterized removal functions. The simulation results indicate that under conditions of larger curvature bonnets and lower air pressure, the MSF error residuals are smaller. Finally, experiments were conducted on a high-precision flat fused silica element with a diameter of 100mm to validate the MSF prediction model, and the experimental results showed good consistency with the simulation results. The findings of this study provide critical guidance for suppressing MSF errors in high-precision bonnet polishing applications.

Nonlinear wavelength conversion based on four-wave mixing (FWM) is a key function for optical signal processing in photonic integrated systems. Although various integrated waveguide platforms have been proposed for on-chip wavelength converters, it remains a great challenge to realize efficient broadband wavelength conversion using a low-power pump due to the lack of sufficient nonlinear gain in waveguides. To address this challenge, we develop centimeter-scale long, low-loss, spiral nanowaveguides on a highly nonlinear AlGaAs-on-insulator (AlGaAsOI) platform. Through dedicated waveguide dispersion engineering, we demonstrate a broadband wavelength conversion with a 3-dB bandwidth over 130 nm at the telecom bands and a flat conversion efficiency over −10 dB in the whole band, using a single continuous-wave low-power pump of ∼18 dBm. A theoretical analysis not only shows excellent agreement with our experimental results but also reveals a viable route for further performance improvement by reducing the propagation loss and/or tailoring the dimension of waveguides. The demonstrated high-performance wavelength converters provide a practical solution for compact and power-efficient wavelength conversion in optical signal processing. Furthermore, our work highlights the great potential of highly nonlinear AlGaAsOI nanowaveguides in chip-scale χ(3)-based nonlinear applications with ultrahigh performance.

Traditional metasurface design approaches largely rely on the prior knowledge of researchers and iterative trial-and-error methods using full-wave simulations, resulting in lengthy and inefficient processes. Deep-learning techniques, such as tandem neural networks (TNNs) and generative networks, show considerable promise in addressing the inverse-design problem. However, TNN faces challenges in creating high-freedom structures and neglects learning one-to-many mappings in inverse problems. The denoising diffusion probabilistic model (DDPM), while superior to other generative networks in generation precision and quality, is hindered by slow structure generation. This paper proposes a novel metasurface design method called the tandem generative network (TGN) to realize accurate and efficient high-degree-of-freedom meta-atom design. TGN constructs an original probabilistic generative model and generates free-form meta-atoms by sampling from the probability space. TGN-generated patterns are validated to produce matching transmittance with an average mean absolute error of 0.0356, achieving decreases of 38% and 86% compared to DDPM and TNN, respectively. Furthermore, the generation speed of TGN is 2990 times faster than that of DDPM. By employing the first probabilistic generative model for metasurface design, TGN paves new avenues in deep learning for inverse design, providing a swift and accurate means to design complex meta-atom structures with desired electromagnetic properties.

Here, we applied direct laser-induced periodic surface structuring to drive the phase transition of amorphous silicon (a-Si) into nanocrystalline (nc) Si imprinted as regular arrangement of Si nanopillars passivated with a SiO2 layer. By varying the laser beam scanning speed at a fixed pulse energy, we successfully tailored the resulting unique surface morphology of the formed LIPSSs that change from ordered arrangement of conical protrusions to highly uniform surface gratings, where sub-wavelength scale ripples decorate the valleys between near-wavelength scale ridges. Along with the surface morphology, the nc-Si/SiO2 volume ratio can also be controlled via laser processing parameters allowing the tailoring of the optical properties of the produced textured surfaces to achieve anti-reflection performance or partial transmission in the visible spectral range. Diverse hierarchical LIPSSs can be fabricated and replicated over large-scale areas opening a pathway for various applications including optical sensors, nanoscale temperature management, and solar light harvesting. By taking advantage of good wettability, enlarged surface area and remarkable light-trapping characteristics of the produced hierarchical morphologies, we demonstrated the first LIPSS-based surface enhanced fluorescent sensor that allowed the identification of metal cations providing a sub-nM detection limit unachievable by conventional fluorescence measurements in solutions.

N-H activation is crucial for NH3-assisted selective catalytic reduction (SCR) and selective catalytic oxidation (SCO) of NH3 in exhaust emission treatment of the diesel engine. Copper-exchanged CHA-type zeolites show high performance for N-H activation, however, the atomic-level understanding of the activation mechanism is inaccessible. In this work, we use density functional theory (DFT) calculations to investigate the origin of high activity through electronic structures, magnetic properties and the N-H bond of NH3 activation on the naked Cu2+ as the active site in Cu-SSZ-13. Fe, Co and Ni-SSZ-13 were also systematically studied for comparison. The incorporation of transition metal ions leads to high-spin d-states around the Fermi level. The magnetic moment of 3.858, 2.889, 1.920 and 0.946 μB is observed for Fe, Co, Ni, and Cu-SSZ-13, respectively. A distorted square planar crystal field is found. For Cu-SSZ-13, the electronic configuration of Cu2+ ensures the lowest unoccupancy of b1g (dx2-y2), enabling to receive electrons from base NH3 and thus activate the N-H bond with a barrier of 1.26 eV significantly lower than that in Fe, Co and Ni-SSZ-13. These findings may provide fundamental insights into the high activity and selectivity of Cu-SSZ-13 catalysts for NOx removal and NH3 oxidation at high temperature.

Demonstrated are 1060 nm microelectromechanical-systems-based tunable vertical-cavity surface-emitting lasers (MEMS-VCSELs) with a 100 nm continuous tuning range under repetitively scanned operation at rates beyond 500 kHz and a 90 nm continuous tuning range under static operation. These devices employ a thin strained InGaAs multiple quantum well active region integrated with a fully oxidised GaAs/AlxOy bottom mirror and a suspended dielectric top mirror. The devices are optically pumped via 850 nm light. These ultra-widely tunable lasers represent the first MEMS-VCSELs reported in this wavelength range, and are ideally suited for application in ophthalmic swept-source optical coherence tomography.