2024

• Record 85 of
  
  Title:Imaging-based measurement of lunar dust velocity and particle size
  
  Author(s):Dai, YiDan; Xue, Bin; Zhao, YiYi; Tao, JinYou; Yang, JianFeng
  Source: APPLIED OPTICS  Volume: 63  Issue: 9  DOI: 10.1364/AO.516801  Published: 2024  
  Abstract:This paper introduces an optical-mechanical system designed for the dynamic detection and analysis of lunar dust, typically characterized as particles under 20 micrometers on the lunar surface. The system's design is both compact and lightweight, aligning with the payload constraints of lunar exploration missions. It is capable of real-time tracking and recording the motion of lunar dust at various altitudes, a crucial capability for understanding the environmental dynamics of the lunar surface. By capturing images and applying sophisticated algorithms, the system accurately measures the velocity and size of dust particles. This approach significantly advances the quantitative analysis of lunar dust, especially during agitation events, filling a critical gap in our current understanding of lunar surface phenomena. The insights gained from this study are not only pivotal for developing theoretical models of lunar surface air flow disturbances and dust movement but also instrumental in designing effective dust mitigation and hazard avoidance strategies for future lunar missions, thereby enhancing both scientific knowledge and the engineering applications in lunar exploration. (c) 2024 Optica Publishing Group
  Accession Number:
  ISSN: 1559-128X
  eISSN: 2155-3165
• Record 86 of
  
  Title:Optical design of a visible/short-wave infrared common-aperture optical system with a long focal length and a wide field-of-view
  
  Author(s):Yan, Aqi; Chen, Weining; Li, Qianxi; Guo, Min; Wang, Hao
  Source: APPLIED OPTICS  Volume: 63  Issue: 9  DOI: 10.1364/AO.517643  Published: 2024  
  Abstract:Addressing the urgent need for long-distance dim target detection with a wide field-of-view and high sensitivity, this paper proposes a visible and short-infrared dual-band common-aperture optical system characterized by a broad field and extended focal length. To achieve system miniaturization and high-sensitivity target detection, the visible and infrared optical systems share a Ritchey-Chretien primary and secondary mirror. The primary optical path is segmented into visible light (0.45-0.75 mu m) and short-wave infrared (SWIR) (2-3 mu m) bands by a dichroic spectral splitter prism. The SWIR optical system utilizes four short-wave cooled infrared detectors, and wide-field stitching is achieved using a field-of-view divider. While ensuring the high cold-shield efficiency of cooled infrared detectors, this common-aperture optical system delivers visible and SWIR dual-band images with expansive fields, elongated focal lengths, and sizable apertures. The visible-light optical system has a focal length of 277 mm, a fieldof-view of 2.3 degrees x 2.3 degrees , and an entrance pupil diameter of 130 mm. Meanwhile, the SWIR optical system features a focal length of 480 mm, a field-of-view of 2.26 degrees x 1.8 degrees and an entrance pupil diameter of 160 mm. The design outcomes suggest that the imaging quality of the optical system approaches the diffraction limit. This visible/SWIR common-aperture optical system exhibits high sensitivity, a large field-of-view, compact structure, and excellent imaging quality, thereby meeting the requirements for long-distance dim target detection and imaging. (c) 2024 Optica Publishing Group
  Accession Number:
  ISSN: 1559-128X
  eISSN: 2155-3165
• Record 87 of
  
  Title:An efficient multi-scale transformer for satellite image dehazing
  
  Author(s):Yang, Lei; Cao, Jianzhong; Chen, Weining; Wang, Hao; He, Lang
  Source: EXPERT SYSTEMS  Volume:   Issue:   DOI: 10.1111/exsy.13575  Published: 2024  
  Abstract:Given the impressive achievement of convolutional neural networks (CNNs) in grasping image priors from extensive datasets, they have been widely utilized for tasks related to image restoration. Recently, there is been significant progress in another category of neural architectures-Transformers. These models have demonstrated remarkable performance in natural language tasks and higher-level vision applications. Despite their ability to address some of CNNs limitations, such as restricted receptive fields and adaptability issues, Transformer models often face difficulties when processing images with a high level of detail. This is because the complexity of the computations required increases significantly with the image's spatial resolution. As a result, their application to most high-resolution image restoration tasks becomes impractical. In our research, we introduce a novel Transformer model, named DehFormer, by implementing specific design modifications in its fundamental components, for example, the multi-head attention and feed-forward network. Specifically, the proposed architecture consists of the three modules, that is, (a) multi-scale feature aggregation network (MSFAN), (b) the gated-Dconv feed-forward network (GFFN), (c) and the multi-Dconv head transposed attention (MDHTA). For the MDHTA module, our objective is to scrutinize the mechanics of scaled dot-product attention through the utilization of per-element product operations, thereby bypassing the need for matrix multiplications and operating directly in the frequency domain for enhanced efficiency. For the GFFN module, which enables only the relevant and valuable information to advance through the network hierarchy, thereby enhancing the efficiency of information flow within the model. Extensive experiments are conducted on the SateHazelk, RS-Haze, and RSID datasets, resulting in performance that significantly exceeds that of existing methods.
  Accession Number:
  ISSN: 0266-4720
  eISSN: 1468-0394
• Record 88 of
  
  Title:Single-photon ranging lidar based on multi-repetition-rate pulse train correlation and accumulation
  
  Author(s):Kang, Yan; Wang, Xiaofang; Zhang, Tongyi; Zhao, Wei
  Source: OPTICS LETTERS  Volume: 49  Issue: 6  DOI: 10.1364/OL.511411  Published: 2024  
  Abstract:A single-photon lidar based on multi-repetition-rate pulse train correlation and accumulation is proposed, and a ranging experiment is conducted on a 32 m target. By accumulating the correlation ranging results of pulse trains with internal spacings of 80, 100, and 125 ns, the signal-to-noise ratio of the cross correlation function is improved by about three-fold, which enables our method to improve the ranging precisions by more than 20% compared with the single repetition-rate method, and the shorter the acquisition time, the more obvious the advantage will be. Experimental results show that at an acquisition time of 0.01 s, our method can still achieve a ranging precision of 2.59 cm, while the single repetition-rate method can no longer obtain effective ranging results at this time. This method will be of great significance for realizing high -speed, large-scale unambiguous single-photon lidar ranging. (c) 2024 Optica Publishing Group
  Accession Number:
  ISSN: 0146-9592
  eISSN: 1539-4794
• Record 89 of
  
  Title:Stable Ultrashort Pulse Generation Using a Coiled and Tapered Few-Mode-Fiber Polarization Controller as a Saturable Absorber
  
  Author(s):Zhao, F. Y.; Hu, X. H.; Zou, F. M.; Zhang, T.; Wang, Y. S.; Lan, J. Q.
  Source: JOURNAL OF RUSSIAN LASER RESEARCH  Volume: 45  Issue: 1  DOI: 10.1007/s10946-024-10189-3  Published: 2024  
  Abstract:We present a coiled and tapered graded-index few-mode-fiber (FMF) polarization controller (PC) as a saturable absorber (SA) in an all-fiber laser. We obtain the 845 fs ultrashort pulse with a signal-to-noise ratio (SNR) of 65 dB, using a tapered graded-index FMF of 40 cm in the cavity. The spectrum is centered at 1588.2 nm with a 3 dB spectral bandwidth of 4.04 nm. Furthermore, a Q-switched mode-locked state is observed between 140 and 360 mW of the pump power in the cavity. The results further demonstrate the application of a coiled and tapered graded-index FMF PC as a SA for stable high-energy ultrashort pulse formation and provide a technical method for generating ultrashort pulses.
  Accession Number:
  ISSN: 1071-2836
  eISSN: 1573-8760
• Record 90 of
  
  Title:Ultralow-Noise K-Band Soliton Microwave Oscillator Using Optical Frequency Division
  
  Author(s):Niu, Rui; Hua, Tian-Peng; Shen, Zhen; Wang, Yu; Wan, Shuai; Sun, Yu Robert; Wang, Weiqiang; Zhao, Wei; Guo, Guang-Can; Zhang, Wenfu; Liu, Wen; Hu, Shui-Ming; Dong, Chun-Hua
  Source: ACS PHOTONICS  Volume: 11  Issue: 4  DOI: 10.1021/acsphotonics.3c01247  Published: 2024  
  Abstract:Compact, low-noise microwave oscillators are required throughout a wide range of applications such as radar systems, wireless networks, and frequency metrology. Optical frequency division via an optical frequency comb provides a powerful tool for low-noise microwave signal generation. Here, we experimentally demonstrate an optical reference down to 26 GHz frequency division based on the dissipative Kerr soliton comb, which is generated on a CMOS-compatible, high-index doped silica glass platform. The optical reference is generated through two continuous wave lasers locked to an ultralow expansion cavity. The dissipative Kerr soliton comb with a repetition rate of 26 GHz acts as a frequency divider to derive an ultralow-noise microwave oscillator, with a phase noise level of -101.3 dBc/Hz at a 100 Hz offset frequency and -132.4 dBc/Hz at a 10 kHz offset frequency. Furthermore, the Allan deviation of the oscillator reaches 6.4 x 10(-13) at a 1 s measurement time. Our system is expected to provide an ultralow-noise microwave oscillator for future radar systems and the next generation of wireless networks.
  Accession Number:
  ISSN: 2330-4022
  eISSN:
• Record 91 of
  
  Title:Domain Adaptation of Anchor-Free object detection for urban traffic
  
  Author(s):Yu, Xiaoyong; Lu, Xiaoqiang
  Source: NEUROCOMPUTING  Volume: 582  Issue:   DOI: 10.1016/j.neucom.2024.127477  Published: 2024  
  Abstract:Modern detectors are mostly trained under single and limited conditions. However, object detection faces various complex and open situations in autonomous driving, especially in urban street scenes with dense objects and complex backgrounds. Due to the shift in data distribution, modern detectors cannot perform well in actual urban environments. Using domain adaptation to improve detection performance is one of the key methods to extend object detection from limited situations to open situations. To this end, this article proposes a Domain Adaptation of Anchor -Free object detection (DAAF) for urban traffic. DAAF is a crossdomain object detection method that performs feature alignment including two aspects. On the one hand, we designed a fully convolutional adversarial training method for global feature alignment at the image level. Meanwhile, images can generally be decomposed into structural information and texture information. In urban street scenes, the structural information of images is generally similar. The main difference between the source domain and the target domain is texture information. Therefore, during global feature alignment, this paper proposes a method called texture information limitation (TIL). On the other hand, in order to solve the problem of variable aspect ratios of objects in urban street scenes, this article uses an anchor -free detector as the baseline detector. Since the anchor -free object detector can obtain neither explicit nor implicit instance -level features, we adopt Pixel -Level Adaptation (PLA) to align local features instead of instance -level alignment for local features. The size of the object has the greatest impact on the final detection effect, and the object scale in urban scenes is relatively rich. Guided by the differentiation of attention mechanisms, a multi -level adversarial network is designed to perform feature alignment of the output space at different feature levels called Scale Information Limitation (SIL). We conducted cross -domain detection experiments by using various urban streetscape autonomous driving object detection datasets, including adverse weather conditions, synthetic data to real data, and cross -camera adaptation. The experimental results indicate that the method proposed in this article is effective.
  Accession Number: 127477
  ISSN: 0925-2312
  eISSN: 1872-8286
• Record 92 of
  
  Title:Monolithic PMN-39PT nanograting-assisted second harmonic generation enhancement
  
  Author(s):Li, Tianlun; Liu, Xin; Lu, Yang; Gao, Duorui; Zhang, Kai; Gan, Xuetao; Wei, Xiaoyong; Xu, Zhuo; Zhang, Lei
  Source: OPTICS EXPRESS  Volume: 32  Issue: 6  DOI: 10.1364/OE.510869  Published: 2024  
  Abstract:Second harmonic generation plays a vital role in frequency conversion which mutually promotes the laser technology and allows the wavebands extension of new coherent source. The monolithic crystals are supposed to be a superior choice for harmonic generation due to long interaction distance, however, the phase-mismatch brought a sharp reduction in the conversion efficiency. Although birefringent phase-matching and quasi-phase-matching techniques are commonly utilized to fill the phase gap in monolithic crystals, these techniques are limited by the natural refractive index of crystal and the domain engineering, respectively. In recent years, subwavelength structures evolve as a flexible scheme to realize phase matching by engineering the geometry features of crystals. Here, structured nanogratings are designed and fabricated on a monolithic PMN-39PT (Pb(Mg1/3Nb2/3)O3-0.39PbTiO3) substrate, a novel ferroelectric crystal with promising optical prospect, for enhancing second harmonic generation, where birefringent or quasi phase-matching is hard to achieve. The nanograting-assisted second harmonic generation enhancement is observed which is not limited by the availability of thin crystalline films. Meanwhile, a boost in the second harmonic signal synchronously promotes the cascading third harmonic generation. This method may provide an alternative solution for enhanced harmonic generation on monolithic substrates and develop potential nonlinear optical materials for frequency conversion.
  Accession Number:
  ISSN: 1094-4087
  eISSN:
• Record 93 of
  
  Title:Theoretical derivation and application of empirical Harvey scatter model
  
  Author(s):Ma, Zhanpeng; Wang, Hu; Chen, Qinfang; Xue, Yaoke; Yan, Haoyu; Liu, Jiawen
  Source: OPTICS EXPRESS  Volume: 32  Issue: 6  DOI: 10.1364/OE.519414  Published: 2024  
  Abstract:Starting from the Rayleigh -Rice perturbation theory, this paper derives the empirical Harvey scatter model and ABg scatter model applied extensively in optical analysis software packages and verifies the shift -invariant behavior of the scattered radiance in direction cosine space. Using data obtained from multi -wavelength laser scatterometer on carbon nanotube black coating and pineblack coating, we establish the polynomial model based on the sine of the scattering angle plus the sine of the specular reflection angle, i.e., sin 0s+sin 00 and the dual -Harvey model based on sin 0s -sin 00 , respectively. The models are in good accordance with the experimental data and further extend the valid range of empirical models. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
  Accession Number:
  ISSN: 1094-4087
  eISSN:
• Record 94 of
  
  Title:Generation of arbitrarily structured optical vortex arrays based on the epicycle model
  
  Author(s):Tai, Yuping; Fan, Haihao; Ma, Xin; Wei, Wenjun; Zhang, Hao; Tang, Miaomiao; Li, Xinzhong
  Source: OPTICS EXPRESS  Volume: 32  Issue: 6  DOI: 10.1364/OE.521250  Published: 2024  
  Abstract:Optical vortex arrays (OVAs) are complex light fields with versatile structures that have been widely studied in large-capacity optical communications, optical tweezers, and optical measurements. However, generating OVAs with arbitrary structures without explicit analytical expressions remains a challenge. To address this issue, we propose an alternative scheme for customizing OVAs with arbitrary structures using an epicycle model and vortex localization techniques. This method can accurately generate an OVA with an arbitrary structure by predesigning the positions of each vortex. The influence of the number and coordinates of the locating points on customized OVAs is discussed. Finally, the structures of the OVA and each vortex are individually shaped into specifically formed fractal shapes by combining cross-phase techniques. This unique OVA will open up novel potential applications, such as the complex manipulation of multiparticle systems and optical communication based on optical angular momentum.
  Accession Number:
  ISSN: 1094-4087
  eISSN:
• Record 95 of
  
  Title:Optimal design of a gravitational wave telescope system for the suppression of stray light
  
  Author(s):Liang, Rong; Zhou, Xiaojun; Xu, Huangrong; Wu, Dengshan; Li, Chenxi; Yu, Weixing
  Source: APPLIED OPTICS  Volume: 63  Issue: 8  DOI: 10.1364/AO.502610  Published: 2024  
  Abstract:For gravitational wave detection, the telescope is required to have an ultra-low wavefront error and ultra -high signal-to-noise ratio, where the power of the stray light should be controlled on the order of less than 10 - 10 . In this work, we propose an alternative stray light suppression method for the optical design of an off-axis telescope with four mirrors by carefully considering the optimal optical paths. The method includes three steps. First, in the period of the optical design, the stray light caused by the tertiary mirror and the quaternary mirror is suppressed by increasing the angle formed by the optical axes of the tertiary mirror and the quaternary mirror and reducing the radius of curvature of the quaternary mirror as much as possible to make sure the optical system provides a beam quality with a wavefront error less than lambda/ 80. Next, the stray light could satisfy the requirement of the order of 10 - 10 when the level of roughness reaches 0.2 nm, and the pollution of mirrors is controlled at the level of CL100. Finally, traditional stray light suppression methods should also be applied to mechanics, including the use of the optical barrier, baffle tube, and black paint. It can be seen that the field stop can efficiently reduce stray light caused by the secondary mirror by more than 55% in the full field of view. The baffle tube mounted on the position of the exit pupil can reduce the overall stray light energy by 5%, and the difference between the ideal absorber (absorption coefficient is 100%) and the actual black paint (absorption coefficient is 90%) is 3.2%. These simulation results are confirmed by the Monte Carlo method for a stray light analysis. Based on the above results, one can conclude that the geometry structure of the optical design, the quality of mirrors, and the light barrier can greatly improve the stray light suppression ability of the optical system, which is vital when developing a gravitational wave telescope with ultra-low stray light energy. (c) 2024 Optica Publishing Group
  Accession Number:
  ISSN: 1559-128X
  eISSN: 2155-3165
• Record 96 of
  
  Title:High-performance reconstruction method combining total variation with a video denoiser for compressed ultrafast imaging
  
  Author(s):Pei, Chengquan; Li, David Day-Uei; Shen, Qian; Zhang, Shian; Qi, Dalong; Jin, Chengzhi; Dong, Le
  Source: APPLIED OPTICS  Volume: 63  Issue: 8  DOI: 10.1364/AO.506058  Published: 2024  
  Abstract:Compressed ultrafast photography (CUP) is a novel two-dimensional (2D) imaging technique to capture ultrafast dynamic scenes. Effective image reconstruction is essential in CUP systems. However, existing reconstruction algorithms mostly rely on image priors and complex parameter spaces. Therefore, in general, they are time-consuming and result in poor imaging quality, which limits their practical applications. In this paper, we propose a novel reconstruction algorithm, to the best of our knowledge, named plug-in-plug-fast deep video denoising net-total variation (PnP-TV-FastDVDnet), which exploits an image's spatial features and correlation features in the temporal dimension. Therefore, it offers higher-quality images than those in previously reported methods. First, we built a forward mathematical model of the CUP, and the closed-form solution of the three suboptimization problems was derived according to plug-in and plug-out frames. Secondly, we used an advanced video denoising algorithm based on a neural network named FastDVDnet to solve the denoising problem. The peak signal-to-noise ratio (PSNR) and structural similarity index measure (SSIM) are improved on actual CUP data compared with traditional algorithms. On benchmark and real CUP datasets, the proposed method shows the comparable visual results while reducing the running time by 96% over state-of-the-art algorithms. (c) 2024 Optica Publishing Group
  Accession Number:
  ISSN: 1559-128X
  eISSN: 2155-3165