## 留言板

Investigating polarization changes in a turbulent atmosphere holds great significance because polarization is one of the most important parameters in laser communication. Based on the extended Huygens-Fresnel principle and the unified theory of coherence and polarization, an analytical expression for the degree of polarization (DoP) in partially coherent Airy-Gaussian beams propagating in a slanted turbulent atmosphere is derived. It is then used to study the dependence of polarization changes in turbulent parameter, coherence length, zenith angle, truncation and distribution factor. The polarization between the slanted and horizontal paths is also compared. Compared with horizontal turbulence, the beams traverse a longer distance to recover their initial polarization in slanted turbulence. An increase in the zenith angle, receiving height and truncation factor, or a decrease in the coherence length can increase the DoP. A smaller distribution factor or a higher coherence length is beneficial to reducing the effect of the zenith angle on the polarization. Analysis of the influence of the distribution factor on polarization also shows that maintaining the polarization of a Gaussian beam with higher coherence in a horizontally turbulent atmosphere has a greater advantage to that of a pure Airy beam from the view of keeping polarization invariance. The results in this paper may be useful for studying atmospheric communication, and show that optical information encoding can be achieved by selecting appropriate parameters.

Quasi-distributed fiber sensing systems play an important role in the fields of civil engineering, energy surveying, aerospace, national defense, chemicals, etc. Interrogation technology for quasi-distributed fiber sensing systems based on microwave photonics is widely used in high-speed and high-precision signal demodulation and sensor positioning in optical fiber multiplexing systems. Compared to conventional optical wavelength interrogation, this technology greatly improves system demodulation rate and compensates for the defects of traditional sensor positioning methods. This paper introduces the recent research progress of quasi-distributed fiber sensing interrogation technology based on microwave photonics; compares and analyzes the advantages and disadvantages of several existing microwave demodulation systems from the perspective of their fiber grating quasi-distributed sensing and fiber Fabry-Perot quasi-distributed sensing systems, respectively; and provides a summary of the prospective direction of future research in quasi-distributed fiber sensing interrogation technology based on microwave photonics.

Lanthanide ion doped upconversion luminescence is limited by the small absorption cross-section and narrow absorption band of lanthanide ions, which results in weak luminescence. Recently, a dye-sensitized method has proven to be an effective strategy of increasing upconversion luminescence. However, simply attaching dye molecules to nanoparticles with classic Yb-doped nanostructures cannot effectively activate the sensitizing ability of the dye molecules. In response to this problem, we designed Nd-sensitized core/shell/shell (NaYF4: Yb/Er (20/2%)@ NaYF4: Yb (10 %)@ NaYF4: Nd (80 %)) nanostructures, compared with the classic IR-806 sensitized NaYF4: Yb/Er nanostructure, their upconversion luminescence (500 to 700 nm) was approximately enhanced by a factor of 38. Through analysis of the nanostructure’s emission and luminescence lifetime data, the enhancement was confirmed by the effective overlap of Nd absorption with the emission of near-infrared dye molecules and the protective effects of the shell structure on the luminescent center (the lifetime of Er (4S3/24I15/2) was increased by 1.7 times). In addition, we found that the doping Yb3+ in the outermost layer will decrease the dye-sensitized luminescence intensity. Furthermore, this Nd-sensitized core/shell/shell also achieved enhancement in the sensitized upconversion luminescence of the luminescence centers of Ho and Tm, which establishes a foundation for enhanced dye-sensitized upconversion luminescence.

Resolution in a confocal microscope is limited by the diffraction limit. Structured modulation has been proven to be able to achieve super-resolution in confocal microscopy, however, its limited speed in image acquisition limits its applicability in practical applications. In order to improve its imaging speed, we introduce a method that can achieve rapid super-resolution confocal microscopy by combining line-scanning and structured detection. A cylindrical lens is used to focus the light into a line, and a digital mask with a sinusoidal function is used to modulate the descanned image in the light detection arm. Unlike the virtual structured method, there is no need for a subsequent frequency shift process. In order to improve the isotropic resolution of the system, a scanning angle of 0 ° and 90 ° is achieved by rotating the sample. Simulation and experiment results indicate that the spectrum wolth of coherent transfer function expands and the resolution is 1.4 times as large as that of a conventional confocal microscope. This method increases the system’s imaging acquisition speed 104-fold when compared with a confocal structured modulation microscope that uses spot-scanning.

Surface plasmon polariton is a mode of electromagnetic surface waves that exists on two dielectric cross-sections (usually a metal and an insulator) with opposite signs of dielectric constant, which can break the diffraction limit. In an appropriate optical waveguide structure composed of metal and dielectric, light can be trapped at the subwavelength scale. Here, we propose an approach that integrates dielectric waveguiding with plasmonics by finite-element simulation. The hybrid optical waveguide consists of an active ZnO nanowire separated from a metal surface by a nanoscale dielectric gap (10 nm). The coupling between the surface plasmonic and waveguide modes allows energy to be stored and propagated in the subwavelength dielectric gap. The leaky modes of the ZnO nanowire lose part of their energy to the continuum of the dielectric layer during propagation. Due to gain guiding, the hybrid electric leaky mode makes it possible to observe leaky-mode lasing. This approach could lead to the true integration of subwavelength lasers based on nanoscale semiconductor-based plasmons and photonics.

Acoustic-to-seismic coupling landmine detection technology based on the unique mechanical characteristics of landmines and the acoustic-to-seismic coupling principle has broad application prospects in safe and effective detection of landmines. However, a significant amount of work must be done to study the practical landmine detection system. Among them, the acoustic coupled surface vibration signals are very weak and complicated, which has always been a challenging problem to detect such signals accurately and quickly. In this paper, the non-contact laser measurement techniques of surface vibrations based on the principle of the acoustic-to-seismic coupling landmine detection technology were reviewed, including laser Doppler interferometry, electronic speckle pattern interferometry and laser self-mixing interferometry, etc., and the application feasibility of electronic speckle-shearing pattern interferometry in acoustic-to-seismic coupling landmine detection was explored.

目的  为了解决空间光电跟瞄系统在真空环境下的多光轴标校问题，  方法  本文首先基于空间光电跟瞄系统的多光轴一致性检测精度要求，设计了一套多光轴标校系统。接着，对多光轴标校系统各子系统进行了详尽的误差分析，并给出了关键子系统的误差影响抑制方法。然后，对通信技术试验卫星三号的空间光电跟瞄系统进行了实验室环境与真空环境下的技术测试，分析了多光轴标校系统在两种测试环境下的误差来源以及测试精度，并给出了测试结果。最后，对多光轴标校系统进行了精度验证。  结果  最终结果表明：本文设计的多光轴标校系统在实验室测试环境下的标校精度为0.998″，收发平行度标定误差为1.165″；在真空测试环境下的标校精度为1.219″，收发平行度标定误差为1.359″，  结论  完全满足空间光电跟瞄系统1.5″的多光轴检测精度要求，为相关工程应用提供了技术支持。

目的  红提糖度和含水率是重要的内部品质衡量指标，传统的检测方法均为破坏性生化检测。  方法  本文研究基于可见/近红外透射光谱技术的红提糖度和含水率的无损检测方法。采集360个红提样本并分别利用标准正态变量变换（Standard Normal Variable transformation，SNV）、SavitZky-Golay卷积平滑处理法（SavitZky-Golay，S_G）等光谱预处理方法建立PLSR模型，确定最好的光谱预处理方法，分别采用一次降维（GA、SPA、CARS、UVE）和二次降维组合（CARS-SPA、UVE-SPA、GA-SPA）七种数据降维方法对光谱进行特征变量提取，分别建立红提糖度和含水率的偏最小二乘回归算法(Partial Least Squares Regression，PLSR)和最小二乘支持向量机（Least Squares Support Vector Machine，LSSVM）含量检测模型并对比分析模型的优劣。  结果  结果表明，红提糖度和含水率的最优PLSR模型波长提取方法为GA-SPA-PLSR，最优模型的预测集相关系数分别为0.958、0.938；红提糖度和含水率的最优LSSVM模型波长提取方法分别为CARS-SPA-LSSVM、UVE-SPA-LSSVM，最优模型的预测集相关系数分别为0.969、0.942；LSSVM所建模型的效果好于PLSR所建模型，但模型的运算时间较长。  结论  研究结果表明：基于可见/近红外技术无损检测红提糖度和含水率的方法可行，且两种最优检测模型预测的精度较高，都能满足检测要求。在不同应用下，可选择不同模型，PLSR所建最优模型的运算时间较短，适合在线快速检测；LSSVM的检测性能最佳，可更加准确地检测红提糖度和含水率。

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Terahertz technology is indispensable in plenty of fields due to the abundant interactions between terahertz waves and matter. In order to meet the needs of terahertz applications, the development of highly sensitive and portable terahertz detectors based on distinctive physical mechanisms and various materials with excellent properties are urgently required. Black arsenic-phosphorus is a novel two-dimensional material that has a tunable band gap and transport characteristics with varying chemical composition, which has gained widespread interest in optoelectronic applications. Recent research on b-AsxP1-x mainly focuses on infrared detection, while the detection of terahertz has not yet been applied. Herein, an antenna-coupled terahertz detector based on exfoliated multilayer black arsenic-phosphorus is demonstrated. The terahertz response performance of the detector reflects two different mechanisms, which have a competitive relationship in the detection process. In particular, the detection mechanism can be tailored by varying the chemical composition of black arsenic-phosphorus. By balancing the band gap and carrier mobility, a responsivity of over 28.23 V/W and a noise equivalent power of less than 0.53 nW/Hz1/2 are obtained at 0.37 THz. This implies that black arsenic-phosphorus has great potential in terahertz technology.
2021, 14(1): 196-205.   doi: 10.37188/CO.2020-0062
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One-dimensional (1D) semiconductor nanowires have shown outstanding performance in nano-electronics and nano-photonics. However, the electrical properties of the nanowire transistors are very sensitive to interactions between the nanowires and substrates. Optimizing the device structure can improve the electrical and photodetection performance of nanowire transistors. We report a suspended In2O3 nanowire transistor fabricated by one-step lithography, showing a high mobility of 54.6 cm2V−1s−1 and a low subthreshold swing of 241.5 mVdec−1. As an ultraviolet photodetector, the phototransistor shows an extremely low dark current (~10−13 A) and a high responsivity of 1.6×105 A•W−1. This simple and effective method of suspending the channel material of a transistor can be widely used in manufacturing high-performance micro-nano devices.
2021, 14(1): 206-212.   doi: 10.37188/CO.2020-0153
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Hybrid graphene/semiconductor phototransistors have attracted great attention because of their ultrahigh responsivity. However, the specific detectivity (D*) for such hybrid phototransistors obtained from source-drain electrodes is assumed to be 1/f noise. In this paper, D* of ~1.82×1011 Jones was achieved from source-gate electrodes. Compared with the same device which was measured from source-drain electrodes, D* was improved by ~500 times. This could be attributed to the carrier trapping and detrapping processes having been screened by the Schottky barrier at the interface. The rise and decay times were 4 ms and 37 ms, respectively. The temporal response speed also correspondingly improved by ~2 orders of magnitude. This work provides an alternative route toward light photodetectors with high specific detectivity and speed.
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Zinc sulfide (ZnS) crystal is one of the important materials used to make the wide-spectrum infrared window. The ultrafast laser technology for manufacturing the nanopores with high aspect ratio provides an important approach to fabricate the photonic devices such as mid-infrared waveguide Fourier transform spectrometer etc. In this paper, a 40-times-demagnification ultrafast laser direct-writing system was built with a 4f system and a Gaussian-Bessel beam generated by a quartz axicon and a Yb:KGW laser source that operated at a wavelength of 1030 nm, a repetition rate of 100 kHz and a pulse width tunable from 223 fs to 20 ps. When the pulse energy was changed from 36 μJ to 63 μJ and the pulse duration was changed from 12.5 ps to 20 ps, the nanopore structure with a diameter of 80~320 nm was successfully written on the ZnS crystal. The surface morphology, diameter and depth of the nanopores were determined by FIB (Focused Ion Beams) ablation and SEM (Scanning Electron Microscopy) imaging. The influence of laser pulse energy and pulse width on the nanopores was studied. The results show that when the pulse width is 20 ps and the pulse energy is 48 µJ, the depth of a nanopore is about 270 µm.

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2019, 12(4): 731-740.   doi: 10.3788/CO.20191204.0731

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2019, 12(4): 701-718.   doi: 10.3788/CO.20191204.0701

ISSN 2095-1531

CN 22-1400/O4

CODEN ZGHUC8