An active coronagraph using a liquid crystal array for exoplanet imaging:principle and testing

High-contrast imaging coronagraphs, used for the detection of exoplanets, have always adopted passive coronagraph optical components. It is therefore impossible to actively optimize the coronagraphs to achieve their best performance. To solve this problem, we propose a novel high-contrast imaging coronagraph which combines a liquid crystal array （LCA） for active pupil apodization and a deformable mirror （DM） for phase correction. The LCA we use is an amplitude-only spatial light mod- ulator. The LCA is well calibrated and compensates for its amplitude non-uniformity and nonlinear intensity responsivity. We measured the imaging contrasts of the coron- agraph system with the LCA only and without the DM deployed. Imaging contrasts of 10-4 and 10-5 can be reached at an inner working angular distance of 2.5 and 5A/D, respectively. A simulation shows that the phase errors on the coronagraph pupil limit the contrast performance. The contrast could be further improved if a DM is deployed to correct the phase errors induced by the LCA and coronagraph optics.

Low-Strain Damage Imaging Detection Experiment for Model Pile Integrity Based on HHT

With the advancement of computer and mathematical techniques,significant progress has been made in the 3D modeling of foundation piles.Existing methods include the 3D semi-analytical model for non-destructive low-strain integrity assessment of large-diameter thin-walled pipe piles and the 3D soil-pile dynamic interaction model.However,these methods have complex analysis procedures and substantial limitations.This paper introduces an innovative and streamlined 3D imaging technique tailored for the detection of pile damage.The approach harnesses the power of an eight-channel ring array transducer to capture internal reflection signals within foundation piles.The acquired signals are subsequently processed using the Hilbert-Huang Transform(HHT),a robust analytical tool known for its effectiveness in handling non-stationary signals.Through the development of a sophisticated multi-channel ring array imaging algorithm,this technique empowers engineers and researchers to identify various pile defects,including their specific type,precise location,and obtain detailed 3D imaging representations.The findings of this research offer a valuable blend of theoretical insights and practical guidance,significantly advancing the state-of-the-art in the realm of concrete pile integrity inspection.By simplifying and enhancing the assessment process,this innovative approach not only addresses the complexities of existing methods but also contributes to the overall safety and reliability of concrete engineering structures.

Cross-talk-free integral imaging three-dimensional display based on a pyramid pinhole array

We propose a cross-talk-free integral imaging 3D display based on a pyramid pinhole array. The pyramid pinhole array is used to provide a point light source array. Since the generated point light source array is behind a transmission-type display panel that displays an elemental image array, the pseudoscopic problem can be resolved. By setting the appropriate parameters for the pyramid pinhole array, the cross talk can be eliminated.We experimentally verify the reconstruction of the orthoscopic and cross-talk-free 3D images using the proposed 3D display.

Crosstalk-free integral imaging display based on double plano-convex micro-lens array

A crosstalk-free integral imaging display consisting of a display panel and double piano-convex micro-lens array is proposed. The double piano-convex micro-lens array includes two micro-lens arrays, A and B. Micro-lens array A is used to eliminate crosstalk by completely reflecting crosstalk lights. Micro-lens array B, located near microqens array A, is used to display three-dimensional images. Computer simulations based on ray-tracing are conducted. Crosstalk-free reconstruction images may be clearly observed from the simulation results.

Depth extraction method with high accuracy in integral imaging based on moving array lenslet technique

In order to improve depth extraction accuracy, a method using moving array lenslet technique(MALT) in pickup stage is proposed, which can decrease the depth interval caused by pixelation. In this method, the lenslet array is moved along the horizontal and vertical directions simultaneously for N times in a pitch to get N sets of elemental images. Computational integral imaging reconstruction method for MALT is taken to obtain the slice images of the 3 D scene, and the sum modulus(SMD) blur metric is taken on these slice images to achieve the depth information of the 3 D scene. Simulation and optical experiments are carried out to verify the feasibility of this method.

High-definition colorful perovskite narrowband photodetector array enabled by laser-direct-writing

Narrowband photodetectors as specific spectral sensing pixels have drawn intense attention in multispectral detection due to their distinct characteristic of filter-free spectrum discrimination,in which the emerging halide lead perovskites witness a booming development in their performance and wavelength-selectivity from blue to near-infrared light.However,the challenge in integrating perovskite narrowband photodetectors on one chip imposes an impediment on practical application.In this work,the combination of laser-direct-writing and ion exchange is proposed as an efficient way to fabricate high-definition colorful sensing array with perovskite narrowband photodetector unit as pixel.Under laser irradiation,the photolysis of halocarbon solvent(CHCl_(3),CH_(3)CH_(2)I,etc)releases the halide ions,which brings the ion exchange and gives rise to slow-varying bandgap in single perovskite photoactive film.This ion exchange can be controlled via laser irradiation time and focus point,thus enabling precisely engineerable bandgap.By optimizing the process,it is successfully applied to develop patterned perovskite narrow blue and green photodetectors array with a high-definition of~53 ppi.We believe this result will make a great step forward to integrate multifunctional perovskite devices on one chip,which will pave the way for perovskite optoelectronic device to the commercial application.

Infrared Photodetectors and Image Arrays Made with Organic Semiconductors

Combining the strategies of introducing larger heteroatom,regio-regular backbone and extended branching position of side-chain,we developed polymer semiconductors(PPCPD)with narrow band-gap to construct the photosensing layer of thin-film photodiodes and image arrays.The spectral response of the resulting organic photodiodes spans from the near ultra-violet to short-wavelength infrared region.The performance of these short-wavelength infrared photodiodes in 900–1200 nm range achieved a level competitive with that of indium gallium arsenide-based inorganic crystalline detectors,exhibiting a specific detectivity of 5.55×1012 Jones at 1.15µm.High photodetectivity and quantum efficiency in photodiode with amorphous/nanocrystalline thin-films of 100–200 nm thickness enabled high pixel-density image arrays without pixel-level-patterning in the sensing layer.1×256 linear diode arrays with 25µm×25µm pixel pitch were achieved,enabling high pixel-density short-wavelength infrared imaging at room temperature.

Short-working-distance optical imaging system and method for surface detection of underwater structures

In the surface imaging of underwater structures, long working distance will reduce image quality due to the turbidity of water. To acquire high definition and large field of view(FOV) images for surface detection, a short-working-distance underwater imaging system is proposed based on camera array. A multi-view calibration and rectification method is developed. A look-up table(LUT) method and a multi-resolution spline(MRS) method are applied to stitch array images real-time and seamlessly.Experiments both in the air and in the water are conducted. Strength and weakness of the LUT and MRS methods are discussed.Based on the results, the effectiveness in surface detection of underwater structures is verified.

High-repetition-rate pulsed fiber laser based on virtually imaged phased array

High-repetition-rate(HRR) pulsed fiber lasers have attracted much attention in various fields. To effectively achieve HRR pulses in fiber lasers, dissipative four-wave-mixing mode-locking is a promising method. In this work, we demonstrated an HRR pulsed fiber laser based on a virtually imaged phased array(VIPA), serving as a comb filter. Due to the high spectral resolution and low polarization sensitivity features of VIPA, the 30 GHz pulse with high quality and high stability could be obtained. In the experiments, both the single-waveband and dual-waveband HRR pulses were achieved. Such an HRR pulsed fiber laser could have potential applications in related fields, such as optical communications.

Computer generated hologram from full-parallax 3D image data captured by scanning vertical camera array(Invited Paper)

Full-parallax light-field is captured by a small-scale 3D image scanning system and applied to holographic display. A vertical camera array is scanned horizontally to capture full-parallax imagery, and the vertical views between cameras are interpolated by depth image-based rendering technique. An improved technique for depth estimation reduces the estimation error and high-density light-field is obtained. The captured data is employed for the calculation of computer hologram using ray-sampling plane. This technique enables high-resolution display even in deep 3D scene although a hologram is calculated from ray information, and thus it makes use of the important advantage of holographic 3D display.

A novel 2-dimensional cosmic ray position detector based on a CsI(Na) pixel array and an ICCD camera

A novel 2-D cosmic ray position detector has been built and studied. It is integrated from a CsI（Na） crystal pixel array, an optical fiber array, an image intensifier and an ICCD camera. The 2-D positions of one cosmic ray track is determined by the location of a fired CsI（Na） pixel. The scintillation light of these 1.0× 1.0 mm CsI（Na） pixels is delivered to the image intensifier through fibers. The light information is recorded in the ICCD camera in the form of images, from which the 2-D positions can be reconstructed. The background noise and cosmic ray images have been studied. The study shows that the cosmic ray detection efficiency can reach up to 11.4%, while the false accept rate is less than 1%.

用于紫外线成像和无线报警的水凝胶基可伸缩、高稳定性和高性能的光电传感器

柔性可穿戴的紫外线探测器在个体紫外线暴露监测、智能仿生眼和军事领域受到广泛关注.然而,传统不可拉伸的材料和器件结构设计限制了设备在可动态变形的人体皮肤和非平面表面上的精确监测应用和稳定附着.在本研究中,我们提出了基于氧化铜/碳-水凝胶-氧化锌/碳的新型应变隔离异质结构的本征可拉伸(拉伸应变或弯曲高达150%)紫外线探测器,该探测器具有高灵敏度(开/关比为2100%)、高稳定性(大于4000次循环),以及快速响应和恢复时间(分别为1.5和4 s).值得注意的是,该探测器通过水凝胶桥在氧化铜/碳和氧化锌/碳电极之间引入的p-n结能带结构,以及离子导电水凝胶中I^(-)/I_(3)^(-)的电化学反应机制,显著提高了其载流子效率和紫外线响应强度.本文通过集成传感器与所设计的电路板,进一步开发了一种无线紫外线报警系统,用于紫外线强度超标警报.此外,本文还设计了一种光电传感器阵列,并将其用作视网膜假体,以实现对环境紫外线强度的实时监测和成像.本文基于水凝胶基异质结构为开发可穿戴、可拉伸的光电紫外线传感器单元和成像阵列提供了一种新的可行方法.

VIPA-based two-component detection for a coherent population trapping experiment

We demonstrate a two-component detection of a coherent population trapping(CPT)resonance based on virtually imaged phased array(VIPA).After passing through a VIPA,the two coupling lights with different frequencies in the CPT experiment are separated in space and detected individually.The asymmetric lineshape is observed experimentally in the CPT signal for each component,and the comparison with the conventional detection is presented.The shift of the CPT resonant frequency is studied with both the two-component and one-component detections.Our scheme provides a convenient way to further study the CPT phenomenon for each frequency component.