稀疏子带的多频段雷达信号融合超分辨距离成像

多频段雷达信号融合是提高目标距离分辨率的一种有效方法,在稀疏子带观测条件下,由于信号频带稀疏,传统的相位补偿和融合成像方法难以应用,为此本文在线性调频信号体制下,基于修正的多重信号选择(MUSIC)算法提出了一种新的参数化融合成像方法.该方法首先对信号离散序列进行均匀采样处理,然后对多个频带的雷达信号统一建模,将相位补偿参数与目标散射中心参数一起估计,理论分析和仿真结果表明该方法能够有效融合多频段的雷达观测信号,改善目标一维距离像的分辨率.     

能带混合量子阱的触发功能和异质谷间转移电子放大器件的研究

运用MonteCarlo理论模拟、二极管除穿伏安特性、器件振荡性能和射频输入信号激励下的放大功能研究了异质谷间转移电子器件中能带混合量子阱的触发功能。理论和实验研究发现，当能带混合量子讲中没有产生足够的异质谷间转移电子效应时，即使有源层中加有足够的电场仍然不能产生振荡。异质谷间转移电子效应成为器件进行射频工作的必要条件。在适当设计的器件中，运用输入射频信号也能激励异质谷间转移电子效应而触发输出放大信号。应用这一原理研制成8mm波段工作的稳态放大器，解决了二极管稳态放大器中的自激振荡问题。最后讨论了利用能带混合量子讲的触发功能来制作新的三端器件和各类功能器件的可能性。     

A Millimeter-Wave Quasi-Optical Circuit for Compact Triple-Band Receiving System

A novel receiver optical system designed for Korean VLBI Network (KVN) has been used for conducting simultaneous millimeter-wave very long baseline interferometry (VLBI) observations at frequencies of 22, 43, 86, and 129 GHz. This multi-frequency band receiver system has been effective in compensation of atmospheric phase fluctuation by unique phase referencing technique in mm-VLBI observations. However, because the original optics system incorporated individual cryogenic receivers in separate cryostats, a rather bulky optical bench of size about 2600 mm x 2300 mm x 60 mm was required. To circumvent difficulties in installation and beam alignment, an integrated quasi-optical circuit incorporating a more compact triple-band receiver in single cryostat is proposed in this paper. The recommended frequency bands of the improved triple-band receiver are K(18–26 GHz) band, Q(35–50 GHz) band, and W(85–115 GHz) band. A frequency-independent quasi-optical circuit for triple band is adopted to obtain constant aperture efficiency as a function of the observed frequencies. The simulation results show that total aperture efficiency of each recommended frequency band is maintained almost constant within 1%. We present the design details of the compact wideband quasi-optical circuit and the triple-band receiver optimized for simultaneous multi-frequency observations.     

Multiple-parameter quantum estimation and measurement of nonselfadjoint observables

A quantum mechanical form of the Cramér-Rao inequality and a minimum-mcan-square-error quantum estimator for multiple parameters are derived, allowing all possible quantum measurements of the received field. The role of nonselfadjoint operators is emphasized in the formulation. Relations of our results to previous work on quantum estimation are discussed. For the estimation of complex mode amplitudes of coherent signals in Gaussian noise, it is shown that the optimal receiver measures the photon annihilation operator, which corresponds to optical heterodyning. This demonstrates the possible optimality of nonselfadjoint operators and clearly indicates the importance of considering more general quantum measurements in quantum signal detection.     

Avibrating-Dipole Technique for Measuring Mlillimeter-Wave Fields in Free Space

EM field measuring techniques, based on the modulated-scattering principle, are well established at microwave frequencies. The main difficulty in extending measurements to the millimeter-wave region is that of scaling the scatterer for operation at these wavelengths. The technique of modulated scattering described in this paper overcomes this limitation. A thin metallic dipole, attached to a vibrating nylon cord, forms the modulated scatterer which interacts with the electric field and gives rise to a phase-modulated reflected wave. The reflected wave is then combined with preference wave in a coherent detection system. The detected signal contains information about the amplitude and phase of the field at the midpoint of the dipole's vibration. An analysis of the technique is presented and the factors affecting the accuracy of measurement are fully discussed. It is shown how the measurement errors can be minimized. Amplitude and phase measurements, taken at a wavelength of 4.8mm, verify the validity and accuracy of the technique.     

Quantum noise and excess noise in optical homodyne and heterodyne receivers

A parallel development of the semiclassical and quantum statistics of multispatiotemporal mode direct, homodyne, and heterodyne detection using an ideal (except for its subunity quantum efficiency) photon detector is presented. Particular emphasis is placed on the latter two coherent detection Configurations. The primary intent is to delineate the semiclassical theory's regime of validity and to show, within this regime of validity, how the quantum theory's signal quantum noise, local oscillator quantum noise, the quantum noise incurred because of subunity detector quantum efficiency, plus (for heterodyning only) image band quantum noise produce the quantitative equivalent of the semiclassical theory's local oscillator shot noise. The effects of classical fluctuations on the local oscillator, and the recently suggested dual-detector arrangement for suppressing these fluctuations, are treated. It is Shown that previous studies of this arrangement have neglected a potentially significant noise contribution.     

New type of raster scan preserves the topology of the image

A raster scan is described that maps a video signal on a square image in a continuous fashion. The scan pattern has no retrace. For spatial low-pass filtering or magnification of the image memory savings are obtained because simultaneous order in the display implies successive order in the video signal.     

基于最低误码率准则及Volterra序列的几何特征均衡器

针对通信系统中带内噪声及干扰的滤波问题,提出一种基于最低误码率准则的非线性几何特征均衡器.考虑到噪声与干扰具有不同的统计特性,本文所建立的均衡模型把匹配滤波器输出映射到特征空间,使信号与干扰在特征空间形成不同的几何特征,再用Volterra序列予以分离,而分离是基于最低误码率准则.仿真表明:对于扩展的二元相移键控信号,在相对强的调频信号、调幅信号及噪声的联合干扰下,匹配滤波器和基于最小均方误差准则的线性均衡器均已失效,而几何特征均衡器仍能表现出良好的性能,并且基于奇次三阶Volterra序列的几何特征均衡器更具实用价值.     

基于NMOS线性图像传感器的光谱数据采集系统设计

基于NMOS线性图像传感器和单片机(MCU)技术设计了一个光谱信号采集系统.介绍了系统的硬件构成及工作原理,详细分析了S3924-512Q图像传感器的结构、工作原理和特点.用PIC16F877A单片机控制A/D转换实现光谱信号数据采集,并给出了程序流程图.通过该系统,实现了特定波段光谱的高精度采集.     

基于量子概率统计的医学图像增强算法研究

 传统的医学图像增强算法存在对噪声敏感且易陷入欠增强或过增强等不足. 本文首先利用量子信号处理基本原理,定义了两种不同的像素量子比特表达形式;然后,针对医学图像的特点,结合3×3邻域像素灰度相关性,提出了一种基于量子概率统计的图像增强算子. 为了优化图像增强的效果,根据子采样图像信息熵自适应确定本算子的灰度阈值参数. 通过主观和客观评价,实验结果表明本文所提出的增强方法考虑了图像全局与局部信息,能更有效地提高医学图像质量.     

Investigation of the parameters of signals reflected from the ionosphere on the basis of regular radio-field measurements performed in the long-wave band

Diurnal and seasonal variations of the signal reflected from the ionosphere are investigated on the basis of regular measurements of the amplitude and phase of the radio field of a reference radio station operating at a frequency of 50 kHz. The reflected signal is extracted from the mixture of the ground-wavel and reflected-wave fields using a special procedure. Effective parameters of an exponential ionospheric model, which characterize the statistical parameters of the signals in the long-wave band at medium distances, are proposed.     

中间带太阳电池进展

中间带太阳电池是第三代光伏发电研究中很热门的研究领域之一。论述了中间带太阳电池的原理,以及实现中间带材料的三种方法,即量子点中间带电池、杂质带电池、高失配合金。量子点中间带太阳电池的红外吸收测量证实中间带太阳电池的基本原理是正确的。介绍了为提高短路电流,采用应力补偿技术,增加量子点层数,增大量子点的吸收系数。目前量子点中间带太阳电池的效率达到18%。阐述了杂质带的机理,研究表明,当Si中掺Ti浓度超过Mott相变浓度时,杂质抑制非辐射复合,有效载流子寿命增加。高失配合金具有不寻常的能带结构,AlGaN材料的带隙接近中间带的理想值,很可能成为下一个研究的热点。     

Dual-channel sis receivers for the iram Plateau de Bure Interferometer

The five antennas of the Plateau de Bure Interferometer have been instrumented with dual-channel receivers in the λ 3 mm and λ 1 mm bands. Polarisation diplexing allows simultaneous observations in the two bands. Each receiver has ambient and cryogenic calibration loads, and one receiver is equipped with a beam switching chopper for total power flux measurements. Typically the receiver noise temperatures are<50 K in both the λ 3 mm band and the λ 1 mm band. Initial observations show that at 115 GHz the sensitivity is doubled compared to the previous receivers, and high quality fringes have been obtained at 230 GHz. Preliminary experiments show that the receiver stability is good enough to correct atmospheric phase variations by monitoring the fluctuations in atmospheric emission at 225 GHz. VLBI fringes have been detected between one 15-m antenna and the IRAM 30-m antenna in Spain.     

基于二阶量子相干的定位与时钟同步方法

纠缠态的光量子对经过两个不同的路径到达一个HOM干涉仪,进行二阶量子相干,可以对两条路径传的信号到达时间差进行飞秒级的精确测量。在这个原理上构建量子定位系统,在4个通道上同时进行二阶量子相干测量,可以精确确定用户在一个坐标系中的空间和时间4维坐标。本文介绍了基于纠缠量子对二阶量子相干的定位和时钟同步的基本原理以及星基量子定位系统的初步方案。     

Calibration study of dual-band Weaver–Hartley receiver architecture

This paper presents a calibration study of dual-band image rejection receiver based on combined Weaver–Hartley architecture, with improved image rejection of first and second image signals. The system implementation is based on dual-band WLAN 802.11 a/g. When the desired signal is at 5.7-GHz band, the 2.4-GHz band becomes the first image signal and vice versa. The output IF frequency is at 30-MHz. The detection of the gain and phase mismatches is based on modeling, extraction of related error signals and correcting them in closed loop. Moreover, we demonstrate an open loop technique to reach the phase and gain correction signals. The correction signals can be digitally stored and applied as digital trimming control on the LO signals. Simulation showed close to 60 dB of image rejection ratio for the first image signal. Second image signal is rejected by a 4-section poly-phase filter.     

电场驱动HgCdTe/CdTe量子阱拓扑相变引起的光吸收增强研究

HgTe/CdTe量子阱是研究拓扑绝缘体新奇物性的一个很好载体。采用Kane八带k·p模型,对电场驱动Hg1-xCdxTe/CdTe量子阱拓扑相变及其相变前后的光吸收性质进行了研究,并使用BHZ模型对吸收系数进行了解析计算和分析。结果表明:在电场能够驱动Hg1-xCdxTe/CdTe量子阱拓扑相变后继续增大电场,其能带可变为墨西哥帽形状,联合态密度将会增强,导致光吸收相比于无电场时显著增强,与解析计算结果相吻合。对于平行界面偏振光(TE)吸收曲线在带边还形成了双峰结构。文章结果可用于新型红外光电探测器、激光器以及频率选择器等量子阱器件的研究和设计。     

An Efficient Group Delay Measurement Method for Frequency Converting System

The existing group delay measurement methods can only get the group delay at a certain aperture or frequency perturbation in one or two measurements. A new method based on comb signal is proposed. If modulo delay ambiguity can be ignored, then the method permits measurement without frequency perturbation of the test signal in one single measurement. The whole phase character of the test band can be obtained, and the group delay characteristics can be calculated by polynomial fitting of the phase curve at diverse aperture. A group delay ambiguity resolution method based on extended Chinese remainder theorem (CRT) is detailed. If modulo delay ambiguity cannot be ignored, then the extended CRT method can be used to obtain the unambiguity delay, releasing the operator from the constraint of keeping the aperture or frequency perturbation small. Computer simulations and field experiments are presented to verify the proposed methods.     

Multicast-enabled high-speed VCSEL technology for flexible data center networks

We experimentally demonstrate the multiple signal modulation on a single class 10 G vertical cavity surface emitting laser (VCSEL) carrier at 1 310 nm for next generation multicast-enabled data center networks. A 10 Gbit/s data signal is directly modulated onto a single mode VCSEL carrier. To maximize carrier spectral efficiency, a 2 GHz reference frequency (RF) clock tone is simultaneously modulated on the VCSEL phase attribute. The inherent VCSEL orthogonal polarization bistability with changing bias current is further exploited in transmission of a polarization based pulse per second (PPS) timing clock signal. Therefore, we simultaneously transmit a 10 Gbit/s directly modulated data, 2 GHz phase modulated RF and a polarization-based PPS clock signals using a single mode 10 GHz bandwidth VCSEL carrier. It is the first time that a single class 10 G VCSEL carrier is reported to transmit a directly modulated data, phase modulated RF clock and polarization based PPS timing signal simultaneously in a single wavelength. A of G.652 single mode fibre (SMF) transmission over 3.21 km is experimentally attained. A receiver sensitivity of ?15.60 dBm is experimentally obtained for the directly modulated 10 Gbit/s data signal. A 3.21-km-long SMF transmission introduces a penalty of 0.23 dB to the data signal. The contribution of a 2 GHz phase modulated RF and a polarization-based PPS clock signal to this penalty is found to be 0.03 dB. An RF single-side band (SSB) phase noise values of ?82.36 dBc/Hz and ?77.97 dBc/Hz are attained without and with simultaneous directly modulated data and polarization-based PPS clock signals respectively for a 3.21-km-long SMF transmission. This work provides an alternative efficient and cost effective technique for simultaneous high-speed multiple information transmission to different network nodes within a data center network through shared network infrastructure.     

基于HBAR的X波段低相噪频率合成方法

基于高次谐波体声波谐振器(HBAR)的高Q值梳谱信号产生的特性提出了一种低相位噪声频率合成方法。该文根据HBAR的工作原理,采用HBAR与声表滤波器级联的方法共同构成低噪声振荡环路直接产生S波段信号,然后通过四倍频模块输出X波段频率信号。采用HBAR与声表滤波器串联的方式提高了带外频响抑制,输出的2.2GHz信号的相位噪声达-118.9dBc/Hz@1kHz,四倍频后得到的X波段信号8.8GHz的相噪达到-107.4dBc/Hz@1kHz。     

基于非厄米和拓扑效应的光场调控机制与光学器件研究进展（特邀）

光的传输与调控是光子集成器件发展的重要基础,光子晶体作为一种新型的光学功能材料,在光操控上有着巨大的潜力。与传统的基于实空间光场叠加原理和倒空间固体能带色散理论的光场调控思想不同,受凝聚态物理中拓扑相概念启发,通过在光子晶体的能带系统研究中引入拓扑相能够提供新颖的光场调控机制和丰富的输运以及光操控性质,如高维度的光场调控等。文中分别从非厄米光子体系和拓扑光子学体系两个方面综述了近年来笔者所在的课题组所取得的研究成果。首先,回顾了光学拓扑研究和光学非厄米研究的背景;其次,介绍了在高阶光子拓扑绝缘体、高阶量子自旋霍尔效应、光子晶体的拓扑场局域以及非厄米体系拓扑光传输等领域的研究进展;最后,对研究结果在相关领域如光量子计算、光通信等的应用发展趋势进行了总结与展望。