Sm3+-doped bismuthate glasses and proton-implanted near-infrared waveguides

Sm3+-doped bismuthate glass has been synthesized by means of the classic melt-quenching technique. Its optical properties were characterized, which included refractive index, absorption and fluorescence spectra. The measured data suggest that the Sm3+-doped bismuthate glass is suitable for optoelectronic applications. A Sm3+-doped bismuthate glass waveguide operating at 1.539 mu m has been manufactured by using the proton implantation with a 0.4 MeV energy and a 8.0 x 10(16) ions.cm(-2) fluence for the first time to our knowledge. The effective refractive indices of the propagation modes for the glass waveguide were obtained by the m-line technique. The energy loss caused by the collision of the irradiated protons and the nuclei of the target Sm3+-doped bismuthate glass was calculated by the SRIM 2013. The refractive index profile and the near-field guided mode distribution for the waveguide structure were fitted through the reflectivity calculation method (RCM) and the FD-BPM method, respectively. The proton-implanted Sm3+-doped bismuthate glass waveguide is an alternative for an integrated device in the telecommunication band.</p

Optimized design of an emerging optical imager using compressive sensing

The emerging optical imager utilizes Fourier-domain interferometry and can reduce system weight, size and power by an order of magnitude compared to conventional optical telescopes at the same resolution. The compressive sensing theory demonstrates that incomplete and noisy measurements may actually suffice for accurate reconstruction of compressible or sparse signals. In this paper, we propose an optimized design of the emerging optical imager based on compressive sensing theory. It simplifies data acquisition structure and reduces data transmission burden. In addition, the system robustness is improved.</p

Mirrors fabricated with CFRP composites by replication technology

To realize ultra-lightweight ratio, mirrors were fabricated with CFRP (carbon fiber reinforced plastic composites) by replication technology. The replication technology was aimed to improve surface accuracy. Though replication technique, the surface accuracy was improved to 0.098 &lambda; (&lambda;=632.8nm, RMS), and the roughness of 1.9 nm (Ra) can be achieved. The CFRP mirror presented poor dimension stability, the surface accuracy increased gradually in air. In order to solve this problem, a polymer coating was carried on mirror surface. The polymer coating exhibited better dimension stability, the surface accuracy can be maintained under 0.15 &lambda; for more than 200 days. &copy; 2019 SPIE.</p

Optimization design and performance test of optical antenna for laser communication

Laser communication has many outstanding advantages, such as high optical gain, high anti-interception, high anti-interference ability and high communication rate, it is an important technical method to solve the problem of high speed communication. The optical antenna is responsible for the reception and transmission of the signal, which is an important part of the laser communication terminal. Based on the general research situation at home and abroad, from the aspect of system SNR and efficiency, this article has determined some targets such as receiving / emission efficiency, wave aberration and ability of off-Axis stray light suppression; combined with specific application requirements, we have determined the basic parameters such as communication wavelength: 1545nm, aperture: 100mm, FOV: 0.1 degrees, optical magnification: 15 times. According to the above parameters, a set of reasonable optical antenna system has been designed and the test equipment is set up to measure, the test results are all satisfied. This paper has some reference value for the design and test of laser communication optical antenna. &copy; 2019 SPIE.</p

Modified phase diversity technique to eliminate Poisson noise for reconstructing high-resolution images

Phase diversity technique (PD) is a widely known method to estimate wave-front aberration of optical imaging system and to obtain reconstructed high-resolution image after degradation. However, when detecting weak or low light object in space, Poisson noise, as the main source of noise, has a serious impact on the accuracy of the PD&#39;s two main function. Hence, we firstly propose a modified PD combined with Non-local Means (NLM) algorithm to reduce the sensitivity of PD towards the Poisson noise. The numerical simulations demonstrate that our approach compared with the traditional PD has a significant improvement in terms of both the wave-front residual root-mean-square error (RMS) and the structural similarity index metrics (SSIM). The wave-front residual RMS decreases by approximately 51% across the Poisson noise levels ranging from 24.48 dB to 61.02 dB. The overall decline range of SSIM significantly decreases from 47% to 17%, and the average of SSIM increases from 84% to 91%. The modified PD would be useful in the AO system with active Poisson noise. &copy; 2019 COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.</p

Controllable dot-matrix marking on titanium alloy with anti-reflective micro-structures using defocused femtosecond laser

This paper reports on the fabrication of marking units of controllable size ranging from 300 to 500 &mu;m equipped with anti-reflective micro-structures using defocused femtosecond laser on titanium alloy TC4. The results show that the range of diameters of marking units (laser ablation-based craters) goes through three stages with the increase of the pulse number. The craters are too shallow for the first stage and too deep for the third stage to meet the criterion of depth, so the second stage turns out to be the optimal stage of parameter selection, where the diameter and depth of marking units are within a desired range with modification of laser energy and defocusing amount. Besides meeting the marking requirements of the size and morphology, the anti-reflective micro-structures with great color difference are formed on the surface of marking units, which contributes to the high recognition rate. Compared with the conventional marking methods, this method has a great recognition rate without recast layer and micro-cracks. Therefore, the femtosecond laser-based processing would provide a new marking technology with high efficiency and quality. ? 2019 Elsevier Ltd</p

Optical system design for wide-angle airborne mapping camera with diffractive optical element

With the development of the digital airborne photogrammetry technology, the more performances of the optical system for airborne mapping camera are required, such as the longer focal and the wider field of view (FOV). At the same time, the secondary spectrum correction becomes more important and difficult for the optical system design. A high performance optical system of airborne mapping camera with 200mm focus and 2&omega;=60&deg; FOV is designed in this paper. The range of work wavelength is from 430nm to 885nm. A two-layer HDOE with negative dispersive characteristic is used to eliminate the secondary spectrum in the process of optical system design. The diffraction efficiency of the designed two-layer HDOE is up to 90%. From the result of design, the MTFs in whole fields are over 0.5 at 90lp/mm, which shows that the system has a great image quality. Meantime, the thermal analysis is done at the temperature range between-20&deg;C and 40&deg;C. As a result, MTF curves of the system at-20&deg;C ?40&deg;C show that a great image quality is kept, which meets the design requirements. ? 2019 SPIE.</p

A Sparse Constrained Graph Regularized Nonnegative Matrix Factorization Algorithm for Hyperspectral Unmixing

由于受到高光谱遥感图像传感器平台的限制,图像的空间分辨率受到一定影响,这导致高光谱遥感图像的像元通常是多种地物的混合,也叫做混合像元。混合像元的存在制约了高光谱遥感图像的准确分析和应用领域。采用高光谱解混技术可将混合像元分解为纯净的物质光谱(Endmember,端元)和每种物质光谱所对应的混合比例(Abundance,丰度),为获取更多更精细的光谱提供了可能。这对高精度的地物分类识别、目标检测和定量遥感分析等研究领域具有重要的意义。因此,解混技术成为高光谱遥感图像领域的一个研究热点。基于线性光谱混合模型(linear spectral mixing model, LMM),提出了一种端元丰度联合稀疏约束的图正则化非负矩阵分解(endmember and abundance sparse constrained graph regularized nonnegative matrix factorization, EAGLNMF)算法。该算法通过研究基于非负矩阵分解(nonnegative matrix factorization, NMF)的方法,结合图正则化理论来考虑高光谱数据内部的几何结构,将端元光谱稀疏约束和丰度稀疏约束应用于其中,从而能够对高光谱数据的内部流形结构进行更为有效的表达。首先,构造了EAGLNMF算法的损失函数,采用VCA-FCLS方法进行初始化,然后,设定相关参数,包括图正则化权重矩阵参数、端元光谱稀疏约束因子和丰度矩阵稀疏约束因子,最后,通过推导得到了端元矩阵与丰度矩阵的迭代公式,并且设置了迭代停止条件。该方法不受图像中是否有纯像元的限制。实际上,在现行高光谱遥感传感器平台情况下,高光谱遥感图像中几乎不存在纯像元,因此, EAGLNMF方法为高光谱遥感图像的实际应用提供了一种思路。采用合成的高光谱数据,构造了4个实验来分析该方法的可行性和有效性,实验将该算法与VCA-FCLS,标准NMF及GLNMF等经典的解混算法进行比较,通过光谱角距离(spectral angle distance, SAD)和丰度角距离(abundance angle distance, AAD)这两个度量标准来进行比较。实验1是总体分析实验。在固定的信噪比和固定端元数目的情况下,用以上三种经典方法与EAGLNMF同时进行解混。实验2是SNR影响分析实验。在固定端元数目和不同信噪比的情况下,用这四种方法进行解混。实验3端元数目分析实验。在固定信噪比和不同端元数目的情况下,用四种方法进行解混,并且将结果进行对比。实验结果发现提出的EAGLNMF方法在提取端元精度和估计丰度精度上都更为准确。同时,实验4是稀疏因子分析实验。对端元稀疏约束和丰度稀疏约束之间的影响因子进行分析,实验结果表明引入的端元稀疏约束对于解混结果也具有较好的影响,并且端元稀疏约束和丰度稀疏约束之间的影响因子也对解混结果具有一定影响。最后,将该算法应用于AVIRIS所采集的真实高光谱图像数据,将其解混结果与美国地质勘探局光谱库中光谱进行匹配对比,其提取的平均端元精度相比于其他三种方法要稍好。</p

Single-wavelength-tunable and dual-wavelength-switchable Tm-doped fiber soliton laser based on single-walled carbon nanotubes

We propose a single-wavelength-tunable and dual-wavelength-switchable Tm-doped fiber soliton laser with single-walled carbon nanotubes. The laser can deliver single-wavelength mode-locked pulse tunable from 1892 nm to 1924 nm. Dual-wavelength mode-locking operation can also be achieved by increasing pump power and rotating the polarization controller (PC), meanwhile the wavelength can be switched between 1883/1894 nm and 1905/1910 nm. Both the tunable and switchable operations are realized with great ease by solely adjusting the parameters of PC. The proposed Tm-doped fiber laser can operate in two mode-locking states, which is helpful for further understanding of the mode-locking mechanism and useful for practical applications.</p

Optimization investigation for high-power 1034 nm all-fiber narrowband Yb-doped superfluorescent source

An optimization for all-fiber narrowband Yb-doped superfluorescent source with a central wavelength shorter than 1040 nm is conducted theoretically and then verified experimentally using steady-state rate equations. Theoretical investigation indicates that with the increase in fiber length, signal power presents one peak value, but the ratio of signal power to output power is decreasing monotonously. Moreover, a filter with high extinction ratio and a gain fiber with high absorption coefficient can have gain suppression on a long wavelength. One all-fiber superfluorescent source is built experimentally on the basis of the theoretically optimized parameters. The source achieves an output power of 214.64 W with a central wavelength of 1034.18 nm and signal&ndash;noise ratio of 30 dB. The output power of the source can have further power scaling with considerable available pump power. &copy; 2019 Elsevier B.V.</p