Detection of infrared small target based on fusion of multi-filters北大核心CSCD

Aiming at solving accuracy problem of infrared small target detection in sky and ocean background scenarios of infrared image sequences, a novel infrared small target detection based on multi-filters algorithm fusion method is presented in this paper. Firstly infrared small target and imaging, time and space characteristics of the corresponding background noise are analyzed. Tophat algorithm with improved Robinson guard filter are then integrated to highlight target and suppress clutter background by using infrared small target imaging features. Adaptive threshold segmentation is used to extract candidate targets, while Unger smoothing filter and multi-objects association filter are used to eliminate random noise and false targets in the candidate targets. Multiple experiments of infrared small target image sequences are implemented, and experimental results show that proposed method can detect infrared small targets at 99% detection rate with high reliability and good real-time performance. © 2017, Editorial Board, Journal of Applied Optics. All right reserved.     

Validation method of infrared imaging simulation based on recognition range北大核心CSCD

随着红外成像技术的发展和应用,红外系统成像仿真及验证技术越来越受到重视。现有仿真模型验证方法没有考虑到人眼视觉的影响,可能导致严重后果,为了解决这一问题,提出了基于识别距离的红外系统成像仿真模型验证方法。以识别距离作为红外系统成像仿真模型的准确度评价因子,考评仿真图像与实测图像在灰度分布、信噪比、分辨率、成像大小、人眼视觉等方面的综合差异。     

Speech recognition based on a combination of acousticfeatures with articulatory information

The contributions of the static and dynamic articulatory information to speech recognition were evaluated, and the recognition approaches by combining the articulatory information with acoustic features were discussed. Articulatory movements were observed by the Electromagnetic Articulographic System for reading speech, and the speech signals were recorded simultaneously. First, we conducted several speech recognition experiments by using articulatory features alone, consisting of a number of specific articulatory channels, to evaluate the contribution of each observation point on articulators. Then, the displacement information of articulatory data were combined with acoustic features directly and adopted in speech recognition. The results show that articulatory information provides with additional information for speech recognition which is not encoded in acoustic features. Furthermore, the contribution of the dynamic information of the articulatory data was evaluated by combining them in speech recognition. It is found that the second derivative of articulatory information provided quite larger contribution to speech recognition comparing with the second derivative of acoustical information. At last, the combination methods of articulatory features and acoustic ones were investigated for speech recognition. The basic approach is that the Bayesian Network (BN) is added to each state of HMM, where the articulatory information is represented by the BN as a factor of observed signals during training the model and is marginalized as a hidden variable in recognition stage. Results based on this HMM/BN framework show a better performance than the traditional method.     

Application of PWM dimming based on Grassmann optical model北大核心CSCD

针对发光二极管（light-emitting diode,LED）光源颜色和光通量精准调控难度高,在生产应用中,调控操作需在电脑等设备上进行的问题,基于格拉斯曼颜色混合定律,结合脉宽调制(pulse width modulation,PWM)调控LED的特性,建立表示PWM与LED照度关系的数学模型,以STM 32微控制器为核心设计了三基色LED调光调色系统。对系统分别进行单色、双色和3色的混光照度实验,数字照度计的测量值与光照数学模型的理论值对比结果表明,该系统在0~370 lx区间内系统的光源照度误差≤4%,合成光色共16 777 216种,且对光源颜色和光通量的调控操作可直接在系统上完成,无需接入其他设备,减少了操作流程,满足工业视觉检测、农作物补光照明和文化旅游对光源颜色和照度的需求。     

Testing technology of vacuum ultraviolet spectral radiance北大核心CSCD

The spectral radiance of vacuum ultraviolet (UV) target is of crucial significance to plenty of researches including deep space exploration and spacecraft damage test. Two types of test systems and methods for vacuum UV light sources were studied. Through the research of test method for vacuum UV spectral radiance, a corresponding test system was developed, which included vacuum UV standard light source, optical imaging system, light splitting module, vacuum UV detector module, vacuum chamber and data processing system. According to the direct measurement method and the comparative method, the spectral radiance of deuterium lamps was tested and analyzed, the influencing factors and the relative index error of vacuum UV spectral radiance were discussed, and the accurate measurement of vacuum UV spectral radiance in the five wavelength ranges of 121.2 nm, 135.6 nm, 160 nm, 180 nm, 200 nm at 0.01 μW/cm2·nm·sr~1 μW/ cm2·nm·sr was realized. The repeatability of the measurement is 0.001 34, which shows that the proposed test system can realize the test of vacuum UV signal. © 2022 Editorial office of Journal of Applied Optics. All rights reserved.     

Optical design and analysis of illumination system based on augmented reality北大核心CSCD

照明系统是增强现实光学系统的重要组成部分,其体积、照度均匀性、能量利用率直接影响增强现实照明系统的质量,因此在照明系统中对光源二次配光非常重要。针对增强现实系统的自由曲面透镜形式和照明系统开展研究,重点分析准直系统集光角度与体积的对应关系,在对光源准直系统的面型构建详细分析基础上,对中心透射边缘反射的折反射式准直系统的面型进行求解,结合偏微分方程法和划分网格法,设计了自由曲面透镜,该系统与偏振分光棱镜共同组成硅基液晶（liquid crystal on silicon,LCoS）照明系统。仿真分析结果表明:系统照度均匀性达到91.96%,若不计偏振影响,照明系统光学效率达到66.6%。该系统具有结构简单紧凑、体积小、质量轻、照度均匀性高等特点,满足增强现实眼镜的需求。     

Jamming effectiveness analysis of quad-element detector based on Monte Carlo method北大核心CSCD

Quad-element detector is a key sensor of the third generation infrared seeker. In order to implement effective jamming to the seeker, this paper firstly discusses the detection mechanism, and secondly proposes the interference strategy which disturbs the auto gain control (AGC) circuit working.The jamming process is then simulated and analyzed.Finally, the average effective jamming ratio is acquired by Monte Carlo method when frequency difference exists, or duty cycle varies, or phase changes on jamming laser.The simulation conclusions are as follows: at the same or multiple frequency with the seeker and 0.25 duty cycle, high power jamming laser can lead the AGC circuit working abnormal; moreover, adjusting the pulse laser phase can influence the jamming effect and destroy the signal extraction logic, finally, the deception is achieved.The analysis and results of this paper are of theoretical significance for the development of laser directional infrared countermeasure system. © 2018, Editorial Board, Journal of Applied Optics. All right reserved.     

Prediction model of K2CsSb photocathode reflectivity based on LSTM北大核心CSCD

针对目前K₂CsSb光阴极制备过程中无法预判光阴极生长状态的问题,提出一种基于长短期记忆（LSTM）循环神经网络的K₂CsSb光阴极反射率预测模型。一维原始反射率数据集经过清洗、筛选、序列化等预处理手段后重构为二维数据输入模型。为充分利用反射率数据在时序上高度相关的特性,采用双层LSTM网络提取特征,预测结果通过全连接层输出,以均方误差（MSE）作为模型预测效果的评判标准。实验结果表明,该模型的网络结构合理且在不同数据集下的表现良好,预测准确率可达99.21%。该模型可运用在K₂CsSb光阴极的制作过程中,通过反射率预测值反馈调节工艺参数以趋近目标走势,对提高光阴极性能具有促进作用。     

Large-aperture collimated wavefront evaluation based on sparse subaperture北大核心CSCD

A wavefront evaluation method based on sparse subaperture was proposed for the collimated wavefront of 300 mm aperture wavelength-tuned interferometer. The method used the wavefront data of sparse aperture to construct a uniform and equally spaced subaperture arrangement model and utilized the simultaneous fitting algorithm to realize the reconstruction of the full-aperture collimated wavefront. The change rules of subaperture spacing and subaperture size on the reconstruction accuracy were analyzed by the numerical calculation, and the optimized subaperture arrangement way was obtained. Finally, an optimized subaperture arrangement with a subaperture size of 10.8 mm and an adjacent subaperture center spacing of 9.72 mm was used for the sparse subaperture evaluation of 300 mm aperture collimated wavefront. The simulation results show that the optimized sparse subaperture evaluation wavefront residual peak valley (PV) value is 0.001 6λ and the residual root mean square (RMS) value is 1.689 3e−4 λ. Copyright ©2022 Journal of Applied Optics. All rights reserved.     

Existence detection of blanket jamming based on fractal characteristics in FRFT domain北大核心CSCD

This paper addresses the existence detection of blanket jamming based on fractal features in fractional Fourier transform （FRET） domain. Firstly, the existences of fractal features of three typical jamming signals are analyzed, and box dimension and information dimension are employed to describe fractal features quantitatively. Then the differences of fractal characteristics between blanket jamming and white Gaussian noise （WGN） in FRFT domain are described, and a detector to detect the jamming is proposed. At last, simulations are done to verify that the algorithm is effective preferable.     

High-precision detection technology of NO concentration based on UV differential-adaptive interference cancellation北大核心CSCD

In order to realize high-precision monitoring of vehicle emission, a high-precision and wide-range NO measurement method was proposed. Aiming at the problem that the absorption peaks of SO2 and NO in emission overlapping in the UV band, and it was impossible to directly perform single-component gas inversion, the differential optical density (DOD) of mixed gas in the NO sensitive band (200 nm～230 nm) was first calculated by the ultraviolet differential optical absorption spectroscopy (UV-DOAS) method. Then, the adaptive interference cancellation technology was introduced to achieve rapid separation of mixed gas DOD. Finally, the least square method was used to perform the concentration inversion of separated NO. This method could achieve rapid inversion of NO concentration (volume fraction of gas) in the range of 100×10−6 to 3 000×10−6. After testing, the absolute value of the relative error of inversion is less than 10% in the concentration range of 100×10−6 to 200×10−6, and less than 5% in the concentration range of 300×10−6 to 3 000×10−6. This method has the characteristics of large measurement range and fast speed, and can meet the measurement requirements of NO concentration in the range of 3 000×10−6 in vehicle emission. © 2022 Editorial office of Journal of Applied Optics. All rights reserved.     

Reconstruction method of computational ghost imaging based on non-local generalized total variation北大核心CSCD

鬼成像是一种能够透过大雾等恶劣环境的成像技术。针对传统鬼成像重建图像存在噪声较多、图像对比度较低等问题,将非局部广义全变分方法用于鬼成像的图像重建之中,提出基于非局部广义全变分的计算鬼成像重建方法。所提方法构造了一种非局部相关性权重设计梯度算子,将其代入全变分重建算法中,使得重建的图像能有效去除噪声的同时实现细节较好的还原。首先在不同条件下进行仿真模拟,得到所提方法的峰值信噪比相对其他方法提升1 dB左右,且具有更好的主观视觉效果,进而设计并搭建实验平台对算法的有效性进行验证,实验结果证明了所提方法在去除噪声和细节重建等方面的优越性。     

Design of broadband hybrid fiber amplifier based on particle swarm optimization algorithm北大核心CSCD

基于铒/镱共掺光纤放大器（erbium-ytterbium doped fiber amplifier, EYDFA）的理论模型和受激拉曼散射效应的分析理论,利用EYDFA和拉曼光纤放大器（Raman fiber amplifier, RFA）的增益谱互补特性,研究并设计了EYDFA与二阶多泵浦RFA相结合的混合放大器结构。为了得到高增益和低平坦度的混合放大器,引入了粒子群算法优化泵浦光波长和功率。仿真结果表明:在不使用增益均衡器的条件下,所设计的混合光纤放大器在输出端得到了近似相等的输出光功率,在90 nm的带宽范围内平均增益为38.78 dB,增益平坦度为1.1 dB,为混合放大器的设计和优化提供了参考。     

Real-time positioning technology of train based on optical fiber coherent Rayleigh backscattering北大核心CSCD

With the rapid growth of railway mileage in China, the degree of heavy load of railway wagons continues to increase. An interference technology based on Rayleigh backscattering signal in optical fiber was proposed by using existing communication optical cables along railway lines. When the fiber vibrated slightly, the phase and refractive index of the fiber at disturbed position changed, which resulting in the Rayleigh backscattering light. By performing differential calculation on the Rayleigh signal curves before and after the operation, the location of the interference light intensity signal corresponded to the location of the disturbances was obtained. Based on this method, the recognition and positioning of railway vehicles were realized. By collecting and analyzing the time-domain and frequency-domain signal, the signal strength, train length, the number of carriages and other characteristics were extracted, and the model of railway vehicles were accurately recognized. Compared with traditional positioning technologies, this technology could realize long-distance monitoring, and the sensing fiber was buried underground on both sides of the railway, which was conducive to the concealment and protection of optical fiber. Experimental results show that the positioning error of the system is within ±10 m, and the detection of railway speed and position within 25 km can be realized. © 2022 Editorial office of Journal of Applied Optics. All rights reserved.     

Selection and optimization of mirror structure of off-axis two-mirror afocal system北大核心CSCD

According to the structural characteristics of aspheric off-axis two-mirror optical system, the imaging characteristics of the system were analyzed by using primary aberration theory. Based on the characteristics of different aspheric surfaces, the vector expression of system aberrations was derived. Using the Seidel coefficients, the primary wave aberration of systems were expanded and values of system aberration for different aspheric surface shapes were specifically calculated. After the evaluation index of the off-axis structure was determined, the imaging qualities of different surface shape combinations were compared. Then the optimal surface shape selection method was analyzed by quantitative comparison results. The results show that compared with other reflector combination methods, the spherical aberration, coma and astigmatism of the off-axis double paraboloid system are all 0, the wavefront RMS is much better than λ/14 (λ=0.587 6 μm), and the Strehl ratio is greater than 0.8. According to the calculation results, it not only has a stronger ability to suppress multiple primary aberrations, but also can effectively compress the volume of the system. Copyright ©2022 Journal of Applied Optics. All rights reserved.     

Interferometry measurement of LG beam propagation parameters in near field北大核心CSCD

Laguerre-Gaussian (LG) vortex beam has orbital angular momentum (OAM). Recurrence propagation formulae of LG beam through optical system with aperture is analyzed in near field. Phase difference change of LG beam with different orders passing double slit is calculated. Forked diffraction grating on computer is employed to diffract fundamental-mode Gaussian beam, which gives rise to LG vortex beam with different orders. LG beam spot through aperture system and double slit interference pattern are captured via CCD camera. Experimental measurement of LG beam propagation characteristics is conducted in near field. Fork diffraction grating 4 mm×5 mm are displayed on SLM at 1 m distance laser, grating density is about 16 lines/mm. LG hollow beam is generated when size of LG dark spot is between 0.5 mm and 0.9 mm, and width of radius ratio is 0.2. Double slit width is 0.2 mm while double seam spacing is 0.5 mm, in this way clear interference fringes are obtained. Results can be used in optical communication information encoded optical vortex orbital angular momentum. © 2017, Editorial Board, Journal of Applied Optics. All right reserved.     

Differential confocal measurement method of linear scanning based on dual linear array camera北大核心CSCD

针对目前微观三维表面形貌测量技术中存在检测效率和测量范围较小的问题,提出一种基于双线阵相机的线扫描差动共聚焦三维形貌测量方法。采用线扫描光源,利用线扫描拼接算法,分别合成焦前和焦后图像;再利用差动算法获得样本位于测量区域的差动图像,结合预先刻度的轴向响应曲线,完成样本的三维形貌还原,实现大范围高效测量。实验结果证明:基于双线阵相机的线扫描差动共聚焦三维形貌测量方法在相同时间内测量范围和测量效率分别是白光干涉仪的16.48倍和6.59倍,并且该方法在测量过程中不需要停顿,只需实现一次对焦,就可以对样品进行连续不间断的扫描检测。研究成果为满足智能制造中在线在位、实时高效、大范围测量的检测需求提供依据。     

Night vision dense crowd counting based on mid-term fusion of thermal imaging features北大核心CSCD

为了提高人群计数模型对尺度和光噪声的鲁棒性,设计了一种多模态图像融合网络。提出了一种针对夜间人群统计模型,并设计了一个子网络Rgb-T-net,网络融合了热成像特征和可见光图像的特征,增强了网络对热成像和夜间人群特征的判断能力。模型采用自适应高斯核对密度图进行回归,在Rgb-T-CC数据集上完成了夜视训练和测试。经验证网络平均绝对误差为18.16,均方误差为32.14,目标检测召回率为97.65%,计数性能和检测表现优于当前最先进的双峰融合方法。实验结果表明,所提出的多模态特征融合网络能够解决夜视环境下的计数与检测问题,消融实验进一步证明了融合模型各部分参数的有效性。     

Natural color low-level-light EBAPS imaging system based on three-color LCTF北大核心CSCD

The high-sensitivity electron bombarded active pixel sensor (EBAPS) not only has the characteristics of high gain and high sensitivity of vacuum imaging devices, but also has the digital characteristics of solid-state imaging devices, which greatly improves the level of night vision imaging. A natural color low-level-light EBAPS imaging system was built based on three-color liquid crystal tunable filter (LCTF). According to the characteristics of low-level-light images, the color enhancement processing such as grayscale stretching, white balance, and color correction was performed on the color images obtained by the system. The experimental results show that the system can realize the natural low-illumination color imaging that reflects the color characteristics of the scene itself, which can effectively improve the observation effect of the characteristics of the target scene at night, and can realize the color imaging under 5×10−4 lx illumination. © 2022 Editorial office of Journal of Applied Optics. All rights reserved.     

MPPC low-level-light imaging enhancement algorithm based on sub-window box filtering北大核心CSCD

针对多像素光子计数器(MPPC)进行微光成像时,图像受光照不足和噪声影响出现的图像亮度低、对比度差、边缘模糊等问题,提出一种基于子窗口盒式滤波的自适应微光图像处理算法。为了减少算法运行时间的同时突出图像的边缘细节信息,利用子窗口盒式滤波器对图像进行分层得到基础层和细节层;对基础层图像采用自适应阈值直方图均衡化拉伸对比度,细节层图像采用自适应增益控制方式进行增强;根据基础层图像中有效灰度值个数占总灰度的比值自适应确定融合系数,将基础层图像与细节层图像融合得到增强后图像。通过微光实验平台设置3组不同照度的微光环境进行实验仿真,验证了本文算法在保持边缘信息和增强细节方面获得了更好的效果。实验结果表明本文算法在标准差、信息熵、平均梯度等客观评价方面优于改进前算法,提升了微光图像的成像效果。