Optics express最新文献

This paper extensively utilizes fine three dimensional environmental data obtained from laser point clouds. Based on theories such as geometrical optics and effective roughness theory, a deterministic wireless channel model is established, which integrates higher-order diffuse scattering. This model is referred to as the ray tracing fusion with higher-order diffuse scattering model. To expedite the collision calculation between rays and the scene, this paper introduces a combined approach of voxelization and signed distance field, resulting in a remarkable 16-fold improvement in computational speed. Moreover, aiming to balance accuracy and efficiency, the paper systematically analyzes the optimization computation parameters of the model. Finally, the proposed model is validated using measurement data in the frequency range of 1 GHz to 6 GHz in mountainous terrain. The results indicate that the predicted outcomes of the proposed model have an accuracy within 6 dB compared to the measurement results, and are superior to ITU-R P.1546, which is an international standard recommended by the International Telecommunication Union for modeling electromagnetic wave propagation in undulating terrain. This provides necessary technical support for network planning and optimization.

We discuss the implementation and performance of a plug-play adaptive optics (AO) module for commercial microscopes comprising indirect wavefront sensing, and a deformable phase plate (DPP) located directly between the objective and the turret. With the DPP at this location, the system closely resembles a pupil-AO scheme, in which effective aberration correction is only possible within the isoplanatic patch. We overcome this limitation by estimating the aberration profiles at multiple field points in parallel and correcting them in sequence to obtain a 2D array of high-quality sub-aperture images. These are then stitched together to form a corrected full-field image. To minimize the measurement time without compromising correction quality, we propose an empirical method to identify the size of the isoplanatic patch, which is both sample and system dependent. Matching the field segment size to that of the isoplanatic patch provides the best compromise between consistent correction quality across the image and measurement time. We demonstrate the performance of the developed system in a commercial microscope using synthetic samples and discuss the performance and limitations of the system.

Transparent crystalline scintillators such as cerium-doped YAG or LuAG are widely used in X-ray imaging for the indirect detection of X-rays. The application of reflective coatings on the front side to improve the optical gain is common practice for flat panel detectors with CsI or Gd₂O₂S powder scintillators but still largely unknown for crystalline scintillators such as LuAG. This work shows experimentally and quantitatively how a black and reflective coating on the X-ray side of a 2 mm LuAG:Ce scintillator improves the image quality compared to a 2 mm LuAG:Ce scintillator without a coating. The measurements have been done for two different distances, with 2 m and 29.7 m on the BM18 beamline of the European Synchrotron. The Modulation Transfer Function (MTF) and the Signal-to-Noise-Ratio (SNR²) power spectrum as well as contrast-to-noise ratio are used for comparing image quality. Propagation-based phase contrast strongly enhances the SNR² amplitudes (gain ≈10 from 2 m to 29.7 m object-detector distance) of the raw images' spectrum independent of the scintillator coating. For both detector positions, the reflective coating is able to raise SNR² by up to 80% through the improved optical gain, while black coating does the opposite (decrease SNR² by 20%) with respect to no coating. With the tested optical setups, changes in MTF /sharpness between the coatings are minor. Comparing CNR² in CT scans of a multi-material sample, in this case an electric motor, we observe the reflective coating yielding better material contrast for plastic and air. Application and effect of Wiener-deconvolution, along with Paganin-type phase retrieval, are also discussed in the context of CT image quality.

Compared to mechanical ones, liquid crystal (LC) beam deflectors present several advantages, such as non-mechanical control, compactness, and low power consumption, making them a viable alternative. In this work, we demonstrate an LC-based polarization-dependent, electrically tunable beam deflector, which is a composite blazed grating fabricated using a single-step photopolymerization-induced phase separation (PIPS) technique. We investigated the effect of different factors on the performance of the deflector, including the thickness of the upper substrate, the grating period, and the cell gap. The prepared sample demonstrated a diffraction angle of 2°6', and a diffraction efficiency of 40.0%. Unlike previous ones, our proposed fabrication technique for the LC beam deflector provides many benefits, such as simplicity, cost-effectiveness, and large-area production.

Space division multiplexing (SDM) systems using few-mode fibers (FMF) are essential for next-generation fiber optic communications. Optical amplifiers with low noise, minimal differential modal gain (DMG), and minimal differential spectral gain (DSG) are essential for these systems. In this work, we present a method to design and optimize a two-stage few-mode erbium-doped fiber amplifier (FM-EDFA) using a joint DMG-DSG minimization approach. This methodology involves the pumping profile design and the gain flattening filter design. Simulation results show the two-stage FM-EDFA achieves DMG and DSG below 2.8 dB and 0.42 dB, respectively, with an optical signal-to-noise ratio above 19 dB across the C-band, enabling a system capacity of 48.6 Tbps. This work reveals the effectiveness of this two-stage FM-EDFA for optical amplification in the context of SDM systems.

Thin-film lithium niobate (TFLN) waveguides have emerged as a pivotal platform for on-chip spontaneous parametric down-conversion (SPDC), serving as a crucible for the generation of entangled photon pairs. The periodic poling of TFLN, while capable of generating high-efficiency SPDC, demands intricate fabrication processes that can be onerous in terms of scalability and manufacturability. In this work, we introduce a novel approach to the generation of entangled photon pairs via SPDC within TFLN waveguides, harnessing the principles of modal phase-matching (MPM). To address the challenge of efficiently exciting pump light typically in a higher-order mode, we have engineered a mode converter that couples two asymmetrically dimensioned waveguides. This converter adeptly transforms the fundamental mode into a higher-order mode, demonstrating a conversion loss of 1.55 dB at 785 nm with a 3 dB bandwidth exceeding 30 nm. Subsequently, we have showcased the device's capabilities by characterizing the pair generation rate (PGR), coincidences-to-accidentals ratio (CAR), and spectral profile of the entangled photon source. Our findings present a simplified and versatile method for the on-chip generation of entangled photon sources, which may pave the way for the application in the realms of quantum information processing and communication technologies.

This paper presents the design of an integrated metasurface antenna, which combines a central radiating patch with a quadru-arc (QAS) structure. The metasurface antenna simultaneously achieves high-gain radiation and complex scattering functionality. The modulation of the radiation function is primarily achieved through phase manipulation of the power division feed network, while modulation of the X-polarization scattering function is mainly accomplished by adjusting the arc of the QAS. The effectiveness of this design is verified by designing two metasurface antennas with distinct functionalities. The feed network phases are arranged in a checkerboard pattern in the first approach, resulting in four-beam radiation with a gain of 16 dBi per beam. Additionally, the scattering component utilizes eight scattering structures with a phase difference of 45 degrees to form a 3-bit coding, enabling vortex beam scattering. The second configuration arranges the feed network in phase with the deflected beam, resulting in a deflected beam radiation pattern characterized by a gain of 22.3 dBi. The scattering function is optimized using a simulated annealing-genetic algorithm for phase alignment, resulting in the achievement of RCS reduction across a wide bandwidth range of 8-24 GHz. The proposed metasurface antenna is ultimately fabricated and subjected to rigorous measurements.

Latent image calculation for large-area masks is an indispensable but time-consuming step in lithography simulation. This paper presents LIC-CGAN, a fast method for three-dimensional (3D) latent image calculation of large-area masks using deep learning. Initially, the library of mask clips and their corresponding latent images is established, which is then used to train conditional generative adversarial networks (CGANs). The large area layout is divided into mask clips based on local pattern features. If a mask clip matches one from the training library, its latent image can be obtained directly. Otherwise, the CGANs are employed to calculate its local latent image. Finally, all local latent images are synthesized to simulate the entire latent image. The proposed method is applied to lithography simulations for display panels, demonstrating high accuracy and a speed-up of 2.5 to 4.7 times compared to the rigorous process.

An achromatic extended depth-of-field (EDOF) system can obtain clear scene information that is crucial for target recognition, dynamic monitoring, and other applications. However, the imaging performance of most optical systems is depth-variant and wavelength-variant, which leads to the generation of chromatic aberrations. Traditional optical design and image post-processing algorithms cannot effectively eliminate these chromatic aberrations. Here, we propose a deep configurable multiple virtual lenses optimization method that embeds four virtual lenses in parallel conjugated with a real lens. Combined with a lens fusion recovery network (LFRNet), it compensates for chromatic aberrations at different depths to achieve achromatic EDOF imaging. Trainable virtual optics can eliminate chromatic aberrations and overcome the limitations of traditional optics. The proposed framework reduces the optical design complexity and improves the imaging quality of a simple optical system. We validate our method using a singlet lens, and the experimental results show that the reconstructed images have an average peak signal-to-noise ratio (PSNR) improvement of 12.1447 dB and an average structural similarity index measure (SSIM) improvement of 0.2465. The proposed method opens a new avenue for ultra-compact, high-freedom, high-efficiency, and wholly configurable deep optics design, and empowers various advanced applications, such as portable photography and other complex vision tasks.

A transport of intensity equation (TIE) based three-dimensional (3D) fluorescence imaging using photon-counting detection was proposed for low light-level bioimaging applications. The number of photons required to achieve the quantitative phase measurement using the proposed system was investigated experimentally and numerically. Results show that the feasibility of reconstructing phase information with an average number of photons is greater than about 9 per pixel in our plant cells.