噪声免疫腔增强光外差分子饱和光谱线型的理论分析

噪声免疫腔增强光外差分子光谱(NICE-OHMS)作为世界上最灵敏的光谱技术可以被应用到痕量气体检测、频率标准、原子分子光谱以及超灵敏引力波测量等领域中,高精细度谐振腔吸收池的使用在增长激光与腔内物质相互作用路径的同时,极大的提高了腔内激光功率,这就会饱和低气压下的气态样品吸收线从而获得亚多普勒光谱结构,因此NICE-OHMS技术不仅具有高灵敏、还具有超高分辨的优点。该研究基于光与二能级分子相互作用的密度矩阵理论对NICE-OHMS技术中包含亚多普勒的多普勒展宽光谱线型进行了理论推导,获得了光谱线型的表达式,同时以该表达式对光谱线型进行了数值模拟,其中调制频率、饱和参量、频率调制系数分别设置为384 MHz,10和0.2。由模拟结果可见吸收光谱由两个边带的吸收信号构成,在包络上存在四个亚多普勒饱和结构;色散光谱由载频以及边带的色散三者决定,并在包络上存在五个亚多普勒饱和结构,获得了与已有实验一致的结果。最后重点分析了不同探测相位、不同饱和参量下的NICE-OHMS光谱线型尤其是亚多普勒结构的变化,由于饱和参量按照调制系数分配给载频和边带,因此虽然载频饱和参量很大,但NICE-OHMS吸收光谱幅度变化不大,主要是由于该光谱信号只与边带饱和参量有关,可以看出NICE-OHMS多普勒展宽信号具有饱和效应免疫的特性,与已有实验结果也符合较好。为更进一步的实验研究提供了必要的理论基础。     

基于一阶时滞混沌系统参数辨识的保密通信方案

基于参数调制原理,针对一阶时滞Logistic混沌系统设计了相应的参数观测器,仅传递单路信号就可以成功辨识出系统中的未知参数,从而恢复出调制在参数中的模拟信号,并在此基础上采用不同频率信号代替“0”或“1”,设计出具体的数字保密通信方案.数值仿真验证了本方法的有效性. 关键词： 观测器 混沌保密通信 参数调制 滤波     

Entropy control in discrete-and continuous-time dynamic systems

The dynamics of a modified logistic mapping are considered for a system with the order parameter modulated by an external signal. It is shown that the Kolmogorov-Sinay entropy changes with changing modulation depth, while the harmonic signals and white noise can be used as a modulating signal. The conditions for the excitation of regular and strange nonchaotic attractors in the phase space are established.     

Resolution enhancement in a reflection mode near-field optical microscope by second-harmonic modulation signals

The motion of the probe tip in a near-field scanning optical microscope, dithered by vibration of a tuning fork, can modulate the reflection signal from the sample surface not only at the fundamental dithering frequency but also at its second harmonic. By lock-in amplification of these modulated signals, enhanced optical images are obtained, even with an uncoated fiber probe. In particular, accurate optical images with higher resolution are obtained when the second-harmonic signal is detected, which results from the parametric modulation of the tip-sample separation at the double frequency of the horizontal dithering motion of the tip. Using a DVD ROM with a track pitch of 0.74 mum as a test sample, we observed that the sharp edges around the pits are clearly resolved with the second-harmonic signals and obtained enhanced resolution of ~70 nm full width at half-maximum.     

Navigation signal structure based on complex carrier modulation

Signal structure design is an important part of satellite navigation system research,which directly affects navigation performance.Signal performance parameters are analyzed and performances of BPSK modulated signals and BOC modulated signals are compared.Aiming at requirements of high navigation precision and high anti-jamming ability,a new navigation signal structure based on complex carrier modulation is proposed and performances of the signal are researched with different parameters.A synchronization al...     

基于粒子滤波的单通道正弦调频混合信号分离与参数估计

以单通道正弦调频(SFM)混合信号为研究对象,提出了基于粒子滤波的正弦调频混合信号分离与参数提取方法.针对正弦调频混合信号频率无跳变的特征,提出了一种基于粒子滤波的相位差解混叠算法,并通过源信号相位差解决了本算法中粒子滤波高维状态空间降维问题,提出了一种适合高维状态空间的似然函数模型,比较固定长度粒子估计值和真实值误差,进而准确衡量粒子权重.通过在重采样后引入MCMC转移,解决了静止参数下粒子多样性降低问题,有效提高粒子滤波迭代收敛速度.从而在先验知识仅已知信号调制方式的情况下,完成对单通道正弦调频混合信号的参数提取,并通过重构信号完成正弦调频混合信号分离.最后通过仿真分析发现,该方法能够有效的实现正弦调频混合信号的分离与参数估计.     

Wavelength modulation absorption spectrometry from optically saturated collision-broadened transitions

A theoretical investigation of the influence of optical saturation on wavelength modulation absorption spectrometry (WMAS) signals from collision-broadened transitions is presented. Expressions are derived for the nth Fourier coefficient of the analytical detector signal, and thereby also for the nth harmonic signal from a WMAS instrumentation (i.e. the nf-WMAS signal), from a wavelength modulated collision-broadened transition exposed to optical saturation. The flux- (or irradiance-) and modulation-amplitude dependences of the nf-WMAS signal on resonance are scrutinized in detail. It is shown that the nth Fourier coefficient of the wavelength modulated analytical detector signal from an optically saturated collision-broadened transition can be written as a product of a flux-dependent (φ) bleaching function, given by (1+φ/φ_sat)^-1 and identical to that appearing for ordinary, unmodulated absorption spectrometry (AS), and a flux-, detuning-, and modulation-amplitude-dependent wavelength modulated peak-normalized saturation-broadened Lorentzian lineshape function, specific for the WMAS technique. It is found that the nf-WMAS signal on resonance decreases faster than an ordinary AS signal as a function of laser flux when smaller-than-optimum modulation amplitudes are used, but slower when larger-than-optimum modulation amplitudes are used. When optimum (or close-to-optimum) modulation amplitudes are being used, on the other hand, the flux dependence of the WMAS signal resembles to a large degree that of ordinary AS. The conditions for when WMAS from collision-broadened transitions has the same flux dependence as ordinary AS are identified.     

基于伪相关函数的多级电平编码符号信号通用无模糊跟踪方法

针对新一代全球导航卫星系统(GNSS)中多级电平编码符号(MCS)信号存在的跟踪模糊问题,本文提出了一种通用的MCS信号无模糊跟踪方法.首先推导了不同MCS信号互相关函数的统一表达式,并给出了伪相关函数的定义;然后深入分析了实现无模糊跟踪需要满足的约束条件,推导了两路参考信号的通用构造方法以及相互之间的关系,为具体MCS信号的求解提供了极大的便利;进而给出了利用本文方法的GNSS接收机码跟踪环路模型.作为MCS信号的特例,分别讨论了本文方法在四种二进制偏移载波信号跟踪中的应用.仿真结果表明,本文方法能够有效解决MCS信号的跟踪模糊问题,具有良好的性能和广阔的应用前景.     

适合传输快变信息信号的混沌调制保密通信

提出一种新的混沌调制通信方法.利用一个自适应控制器跟踪信息信号的误差对产生混沌载波的发射系统进行参数调制.同时，信息信号直接与混沌载波相乘作为发射信号驱动接收系统.在接收端，另一个自适应控制器维持收发系统的混沌同步并恢复出信息信号.由于同步误差与信息信号无关，从而实现了大幅度、快时变信息信号的混沌调制通信.理论分析和数值模拟的结果表明该方法增强了低维混沌系统的通信保密性. 关键词： 混沌调制 保密通信 自适应控制器 蔡氏电路     

表面热透镜技术测量光学薄膜样品表面热变形

给出了连续调制激励光照射下光学薄膜样品表面热变形场的理论分布,并由此定义了表面热透镜(STL)信号。根据表面热透镜理论实验测量了一个BK7基底高反膜样品的形变,给出了表面热透镜信号随调制频率的变化曲线。实验结果表明:在采用的STL实验构型中,探测了最小1.985 nm的直流形变,对应不调制时的形变为3.97 nm,相应的形变探测灵敏度达到了10 pm量级;直流形变与功率成线性关系;交流表面热透镜信号随着频率增大而减小,在高频端近似成线性减小。     

基于受激布里渊散射的宽带宽和高精度的微波频率瞬时测量

提出了一种基于受激布里渊散射效应的瞬时频率测量方法.未知信号经过强度调制作为泵浦光,矢量网络分析仪产生的信号经过相位调制作为扫描信号光,当泵浦光和扫描信号光之间满足相位匹配条件时,受激布里渊散射效应发生并实现相位调制到强度调制的转换,未知信号的频率被测量.实验验证可以测量0.5 GHz-27 GHz的微波信号的频率,最大误差小于20 MHz.     

Investigation of broadcasting signal overlay using high-frequency filtering characteristics of RSOA in ASE seeded WDM access network

The simultaneous baseband and broadcasting signal transmission based on wavelength division multiplexing-passive optical network access network are proposed and their experimental verifications are shown. Amplified spontaneous emitting source modulated by broadcasting signal in radio frequency band at reflective semiconductor optical amplifier is provided as seed source for wired signal modulation. The filtered amplified spontaneous emitting source is aligned to each channel and modulated by the downlink baseband signal at RSOA. Simultaneous downstream transmission of baseband and broadcasting signals over 23-km SMF is experimentally verified. Mutual interference between broadcasting and baseband signals, nonlinearity by two tone analysis, and performance variation on temperature are investigated.     

Characterization and analysis of coded excitation ultrasound parameters for rock properties

Coded excitation technology(CET) can effectively enhance the penetration and resolution of ultrasonic testing.To analyze the influence of rock properties on pulse compression performance(PCP) of coded excitation signals(CES),a numerical simulation,and an ultrasonic experiment on different rock samples are performed;and the detection ability of several CESs are also investigated and compared.The results of experiments showed that the loss of the signal-to-noise ratio(SNR) of Barker coded signal with tapered linear frequency modulated carrier(BTLFM) is always less than Barker coded signal with sine carrier(BS),while the resolution loss of BTLFM is lower than tapered linear frequency modulated signal(TLFM).In sum,the results not only verifiy the effectiveness of CET,but also provide a basis for the parameter settings of coded signals used in rock ultrasonic testing.     

Effects of temporal envelope modulation on acoustic signal recognition in a vocal fish, the plainfin midshipman.

Amplitude modulation is an important parameter defining vertebrate acoustic communication signals. Nesting male plainfin midshipman fish, Porichthys notatus, emit simple, long duration hums in which modulation is strikingly absent. Envelope modulation is, however, introduced when the hums of adjacent males overlap to produce acoustic beats. Hums attract gravid females and can be mimicked with continuous tones at the fundamental frequency. While individual hums have flat envelopes, other midshipman signals are amplitude modulated. This study used one-choice playback tests with gravid females to examine the role of envelope modulation in hum recognition. Various pulse train and two-tone beat stimuli resembling natural communication signals were presented individually, and the responses compared to those for continuous pure tones. The effectiveness of pulse trains was graded and depended upon both pulse duration and the ratio of pulse to gap length. Midshipman were sensitive to beat modulations from 0.5 to 10 Hz, with fewer fish approaching the beat than the pure tone. Reducing the degree of modulation increased the effectiveness of beat stimuli. Hence, the lack of modulation in the midshipman's advertisement call corresponds to the importance of envelope modulation for the categorization of communication signals even in this relatively simple system.     

Statistical approach to multiple-q modulated structures: average Patterson analysis

Using a statistical approach, the average unit cells have been constructed for modulated structures with different types of modulation, from simple sinusoidal to square-wave functions. The obtained unit cells fully describe diffraction intensities of the main reflections and their satellites. A universal distribution, valid for different lengths of the modulation vector, has been found. Average Patterson functions have been constructed and used to distinguish between different types of modulation.     

调制无线电信号的分形特征研究

调制方式的不同以及信号受到功率放大器的非线性变换决定了调制无线电信号的形状存在着差异,提取这些差异特征是信号识别的基础. 基于分形理论提取信号特征是一种新的方法,本文模拟了在不同信噪比条件下,通过计算调制无线电信号的方差分形维以及Mandelbrot奇异分形维谱,将信号的调制特征以及非线性变换特征投射到分形特征空间. 数值仿真结果表明,不同调制方式、非线性变换对应了分形特征空间中的不同位置. 这些结果表明分形理论能够有效提取无线电信号的调制特征以及功率放大器的特征,对信号的调制方式以及个体特征识别具有一定 关键词： 无线电 信号 分形特征 识别     

Power penalty in multitone radio-over-fibre system employing direct and external modulation with optical amplifiers

This paper presents a multitone RoF system employing a central station and a remote antenna station to transmit modulated microwave or mm-wave signals. Two configurations of the system employing direct and external modulation are presented. First, at the central station, the modulating signal is directly and externally modulated at 1549.5 and 1550.5 nm, respectively, and the combined signal is then transmitted using wireless mode. In the second configuration, the combined signal is transmitted over 20 km to the remote antenna station using optical fibre connectivity. At the remote antenna station, both channel wavelengths are separated and amplified with an EDFA and SOA and are detected. The demonstration results show that there exists a small power penalty between the direct and the external modulation. But a large power penalty is reported depending upon the choice of optical amplifier viz. EDFA or SOA. Better performance is recorded in later case. The results also show that power is being distributed among the operating frequency and sidebands adjacent to it after transmission over a fibre link.     

Magnetic field modulation spectroscopy of rubidium atoms

The magnetically modulated saturation absorption profile is studied for a wide range of external DC magnetic field. The salient features of Doppler-free signal generated by laser frequency modulation and atomic energy level modulation are compared. The DC offset of the signal profile is found to be unstable as the external DC magnetic field is changed. The technical difficulty of tuning laser frequency under locked condition over a large frequency span is discussed along with possible solutions.