TN型液晶电光调制实验研究

根据TN型液晶的工作原理和光学特性,提出了一种方波电压信号驱动的液晶电光调制实验方法,在此基础上,利用液晶电光效应实验仪,测量了扭曲向列相型液晶在不同频率、不同波形电压激励下的电光曲线和阈值电压,分析了激励电压频率、波形对电光曲线的阈值电压和陡度的影响.对加载于TN型液晶上的3 000 Hz方波实现了正弦波幅度调制,并分析了电光调制结果.此种电光调制方法可用于液晶材料对电信号响应特性的直观显示.     

谐振型光纤陀螺克尔效应误差消除方法研究

对采用方波频率调制数字闭环谐振型光纤陀螺中克尔效应的影响进行了深入的理论分析,〖CM)〗〖JP〗 分析表明，由克尔效应引起的陀螺误差不仅与光纤环内两相反方向光束的光强差有关，而且还依赖于两路光波频率调制的调制幅度,通过适当调节两光束的频率调制幅度，可有效地实现克尔效应误差的消除,这种基于方波频率调制的克尔效应误差消除方法利用了方波调制的特点，通过调节调制幅度实现误差消除，无需额外光学元件，对强度调制器调制频率要求低，是数字谐振型光纤陀螺系统中消除克尔效应误差的有效方法,     

方波调制下自由载流子吸收测量半导体载流子输运参数的时域模型

本文建立了用于测量半导体载流子输运特性(载流子寿命、载流子扩散系数和前表面复合速度)的方波调制下自由载流子吸收(free carrier absorption,FCA)检测技术的时域理论模型.通过数值模拟,分析了在不同调制频率下时域曲线的变化趋势以及各个载流子输运参数对时域曲线的影响.结果表明方波调制下的自由载流子吸收的时域信号对各个参数都用较高的灵敏度,且参数值的测量范围大于频域测量范围.     

激光频率调制线型分析

在激光频率调制的理论分析中,一般采用正弦波调制、正弦波解调,而没有讨论调制和解调的其它情况。本文主要分析了Guass线型吸收的情况下,锯齿波调制、方波解调的一次、二次谐波相检结果和三角波调制、方波解调的一次、二次谐波相检结果,以及调制深度对信号谱形和信号强度的影响。我们发现,在锯齿波调制、方波解调情况下,一次、二次谐波谱形和正弦波调制情况区别很大;但在三角波调制、方波解调情况下,可以获得和正弦波调制、正弦波解市场相似的结论。另外,不同的调制深度对输出的调制谱形也有重要的影响。我们还用甲烷的可调谐 红外光调制吸收光谱实验验证了理论分析结果。最终得到结论：频率调制谱的信号谱形及信号强度与调制波形、解调波形和调制深度均有关系。     

基于麦克斯韦方程的交变电流长螺线管磁场

为了分析方波驱动长螺线管内磁场畸变机理,利用麦克斯韦方程研究了螺线管内外的磁场分布情况。首先,利用麦克斯韦方程,分别建立了正弦波驱动螺线管内外电场、磁场模型,并结合安培环路定律和电磁感应定律选取了合适的边界条件,得到了正弦波驱动长螺线管的磁场分布;其次,通过傅里叶变换将方波信号变换为多个正弦信号叠加的形式,从而得到了方波驱动长螺线管磁场分布;最后,通过仿真试验重点分析了方波驱动信号频率对磁场的影响,并得出结论:方波驱动长螺线管磁场波形会失真、畸变,驱动信号频率较低、距离螺线管轴线距离较近处,磁场的方波特性较好。     

非旋波近似下二能级原子与频率变化光场作用的量子特性

在非旋波近似下,研究了频率随时间变化的相干态光场与二能级原子的相互作用,讨论了光场频率随时间作正弦和方波变化时,原子布居数反转随时间的演化特性。数值计算结果表明,当光场频率不随时间变化时,原子布居数反转的周期随着平均光子数的增大而增大;当光场频率随时间作正弦变化时,原子布居数反转塌缩回复的周期和振幅受到了很大影响,光场频率对演化曲线的振荡频率起到了调制作用;当光场频率随时间作方波变化时,原子布居数反转塌缩回复的周期发生了改变,而且出现了新的塌缩回复现象。     

弹光调制测晶体电光系数的数字锁相实现

在弹光调制测晶体电光系数系统中,对弹光调制器工作控制和调制信号数据处理进行了优化设计,并实现一种灵敏度高、测量快速、成本低和系统集成度高的晶体电光系数测量方案.针对弹光调制及调制信号的特点,采用现场可编程门阵列完成弹光调制器的工作控制和测量数据的提取.现场可编程门阵列提供弹光调制器工作电压信号,控制模数转换器的采样频率,同时产生正弦和余弦参考序列来提取直流项、一倍频项的同向分量和正交分量,并输入计算机中求解得出晶体电光系数.对铌酸锂样品进行了测试,实验结果表明系统重复度和灵敏度为0.0016×10~(-12) m/V,测量速率为1ms/数据点.较其他晶体电光系数测量方法,本文方法具有更高的测量灵敏度和更快的测量速率,为实现弹光调制测量晶体电光系数的智能系统奠定了基础.     

谐振式微光学陀螺偏置频率调制技术研究

谐振式微光学陀螺(RMOG)是一种基于光学Sagnac效应的新型角速度传感器.提出了基于模拟波形连续线性相位调制技术的偏置频率调制.与传统的双频率锯齿波调制以及数字调制方法相比,偏置频率调制消除了由于锯齿波回扫或数字波形中的台阶效应引入的脉冲噪声.从理论上推导了连续线性相位调制波形参数与陀螺的动态范围和灵敏度的关系,得...     

可调谐半导体激光吸收光谱技术的调制参量影响及优化选择

为获得较好的谐波信号,完成不同测量目的,以DFB-760.77nm波长处氧气监测为例,通过改变扫描锯齿信号和调制正弦信号的频率和幅值,讨论了调制参量对二次谐波信号峰-峰值、对称性、谐波信号展宽和信号完整性等判别依据的影响和变化.结果表明:Sinmulink模拟值和实验值相关性较高,当正弦调制信号和锯齿扫描信号频率比值为1 000倍时,可以获得较好的二次谐波信号.该研究为实验系统中调制参量的选取和调制度及系统准确度、稳定性、重复性等性能的优化提供了一定帮助.     

方波磁光调制测量在无机械连接的设备间方位传递中的应用

在航天、军事等领域往往需要传递无机械连接的设备之间的空间方位信息,而传统的方位测量系统测量范围小、测量精度低,难以满足系统高精度大范围传递的要求,为此改变传统方法中的调制方式,将方波磁光调制引入了方位测量系统,建立了基于方波磁光调制的方位测量模型。根据马吕斯定律,建立了方波磁光调制后的输出信号模型,并分析了调制后信号的特点。根据调制后信号的表达式与方位角的关系,推导、建立了调制后信号与方位角之间的关系方程,并利用调制后信号的增减性去除了方程的增根,结合调制前后信号的相位对比扩大了方位角的测量范围,最终得到了基于方波磁光调制的方位测量模型,实现了无机械连接的设备之间方位信息的传递。仿真结果表明,提出的基于方波调制的测量方法与传统方法比较,理论测量精度更高、测量范围更广,这为实现空间方位角高精度大范围测量提供了一种参考。     

Theoretical model for superluminal and slow light in erbium-doped optical fibers: enhancement of the frequency response by pump modulation

Superluminal and slow-light propagation in erbium-doped optical fibers are theoretically modeled. The pump and signal fields are allowed to be intensity modulated at the same frequency, and propagation effects are included in the model. The levels of advancement, delay, and distortion are determined as functions of system parameters such as modulation frequency, input pump power, modulation indexes of the pump and signal powers, input signal power, fiber length, and the relative phase of the pump and signal modulation. Two methods are analyzed for enhancing the frequency response while ensuring that distortion values remain tolerable. The first method assumes no modulation of the pump wave, although the pump power is adjusted for each signal modulation frequency. A flat frequency response for frequencies up to several kilohertz is obtained, although signal advancements are limited to low values. In the second method, the pump power is modulated with a phase that needs to be controlled with respect to that of the signal. Advancements and delays are increased by this procedure, and distortion values remain tolerable. The frequency response is not made worse for advancements and it is improved for delays. Moreover, absorption need not accompany slow light for this method.     

基于PSpice的半导体激光高频调制系统设计

为了实现高频率的调制激光输出,设计了一种驱动系统由信号放大、电流调制、过流保护和具有慢启动功能的直流偏置电路高度集成的半导体激光高频调制系统。此系统采用了结构简单的直接调制方式,运用线性调频的高频信号去控制半导体激光器发射激光的强度,从而实现高频调制。在运用OrCAD/PSpice对高频调制驱动系统进行模拟仿真的基础上,最终研制出的半导体激光高频调制系统实现了频率为40.02 MHz、直流偏置为493.326 mA、正弦波调制电流峰峰值为850 mA的高频调制输出,调制激光平均功率为300 mW。     

Electro-optic holography fringe control using diode laser current modulation

Electro-optic holography (EOH) is a whole field, laser-based, vibration measurement technique. Highly dense, unresolvable fringe patterns often limit the EOH measurement range. This paper presents a technique for increasing the measurement range of an EOH system using diode laser current modulation. This technique is known as frequency translated electro-optic holography (FTEOH). Using diode laser current modulation, the fringe patterns are based on higher-order Bessel functions and the sensitivity of the EOH system can either be increased or decreased. The amount of sensitivity reduction is limited only by the frequency limit of the signal generator that modulates the current supplied to the diode laser. EOH and FTEOH experimental results are presented and shown to closely compare.     

Reconstruction of the first-derivative EPR spectrum from multiple harmonics of the field-modulated continuous wave signal

Selection of the amplitude of magnetic field modulation for continuous wave electron paramagnetic resonance (EPR) often is a trade-off between sensitivity and resolution. Increasing the modulation amplitude improves the signal-to-noise ratio, S/N, at the expense of broadening the signal. Combining information from multiple harmonics of the field-modulated signal is proposed as a method to obtain the first derivative spectrum with minimal broadening and improved signal-to-noise. The harmonics are obtained by digital phase-sensitive detection of the signal at the modulation frequency and its integer multiples. Reconstruction of the first-derivative EPR line is done in the Fourier conjugate domain where each harmonic can be represented as the product of the Fourier transform of the 1st derivative signal with an analytical function. The analytical function for each harmonic can be viewed as a filter. The Fourier transform of the 1st derivative spectrum can be calculated from all available harmonics by solving an optimization problem with the goal of maximizing the S/N. Inverse Fourier transformation of the result produces the 1st derivative EPR line in the magnetic field domain. The use of modulation amplitude greater than linewidth improves the S/N, but does not broaden the reconstructed spectrum. The method works for an arbitrary EPR line shape, but is limited to the case when magnetization instantaneously follows the modulation field, which is known as the adiabatic approximation.     

一种基于两块PEM调制器的光谱测量方法

弹光调制干涉信号范围为百赫兹到数十吉赫兹之间,而由于探测器阵列无法对该等级频率实现有效响应,因此,该情况使弹光调制器在光谱成像工作中受到限制。为了解决该问题,发展了一种使用两块具有相近谐振频率的PEM,并基于该频率差进行光信号调制的方法。该方法将两个弹光调制器分别工作在数值略有差异的频率f₁和f₂上,被测光通过双弹光调制器实现差频调制,因此干涉信号中产生载有被测光的低频调制分量,低频调制频率是以δ_i(σ,t)=δ_0i(σ)sin(ω_it)为基频的一系列倍频信号,该低频调制信号使用普通探测器即可实现探测,再将直流和高频信号滤波后,仅对调制信号后的低频成分进行对应的运算即可得到被测光谱。由于该频率差比所使用PEM的谐振频率低2至3个数量级,因此,该方法可使探测器获得更多的响应时间,而且由于该方法并不需要所使用的两块PEM具有严格一致的谐振频率和相同的光程差,降低了系统本身的设计难度。     

Modulated angle beam ultrasonic spectroscopy for evaluation of imperfect interfaces and adhesive bonds

An experimental method incorporating high frequency pulsed angle beam ultrasonic measurements modulated by low frequency vibrations of a bonded structure is described. This method uses parametric/nonlinear mixing between high and low frequencies to characterize adhesive degradation. It is demonstrated that good quality (undamaged) bonds exhibit little dependence of ultrasonic signature on the overlay of low frequency vibration loads; however, environmentally degraded or imperfect bonds exhibit strong modulation of the resonance frequency of the ultrasonic signal reflected from the bond. The results are interpreted using a model for normal and oblique wave interaction with two nonlinear interfaces separated by an adhesive layer under quasi-static stress modulation.     

Detection performance improvement of photon counting chirped amplitude modulation lidar with response probability correction

Geiger mode avalanche photodiode detector(Gm-APD) possesses the ultra-high sensitivity. Photon counting chirped amplitude modulation(PCCAM) light detection and ranging(lidar) uses the counting results of the returned signal detected by Gm-APD to mix with the reference signal, which makes PCCAM lidar capable of realizing the ultra-high sensitivity, and this is very important for detecting the remote and weak signal. However, Gm-APD is a nonlinear device, different from traditional linear detectors. Due to the nonlinear response of Gm-APD, the counting results of the returned signal detected by Gm-APD are different from those of both the original modulation signal and the reference signal. This will affect the mixing effect and thus degrade the detection performance of PCCAM lidar. In this paper, we propose a response probability correction method. First, the response probability correction model is established on the basis of Gm-APD Poisson probability response model. Then, the response probability correction model is used to adjust the original modulation signal that is used to drive laser, in order to make the counting results of the returned signal detected by Gm-APD better mix with the local reference signal in the same form. Through this method, the detection performance of PCCAM lidar is enhanced efficiently.     

噪声交叉关联强度的时间周期调制对线性过阻尼系统的随机共振的影响

针对由加性、乘性噪声和周期信号共同作用的线性过阻尼系统, 在噪声交叉关联强度受到时间周期调制的情况下,利用随机平均法推导了系统响应的信噪比的解析表达式. 研究发现这类系统比噪声间互不相关或噪声交叉关联强度为常数的线性系统具有更丰富的动力学特性, 系统响应的信噪比随交叉关联调制频率的变化出现周期振荡型随机共振, 噪声的交叉关联参数导致随机共振现象的多样化.噪声交叉关联强度的时间周期调制的引入有利于提高对微弱周期信号检测的灵敏度和实现对周期信号的频率估计. 关键词： 随机共振 周期振荡型共振 噪声交叉关联强度 信噪比     

Resonator fiber optic gyro using the triangle wave phase modulation technique

Based on the Sagnac effect, resonator fiber optic gyro (R-FOG) has potential as a high accuracy inertial rotation sensor. An R-FOG based on the triangle wave phase modulation technique is proposed in this paper. The slope of the demodulation curve near the resonance dip is found to affect the ultimate sensitivity of the gyro. In order to maximize the slope of the demodulation signal, the parameters of the triangle wave are analyzed. By employing Fourier series and the method of field overlapping, the relationship between the demodulation signal and the resonance frequency deviation is analyzed. The optimum values for the modulation frequency and phase modulation index are obtained. And the relationship between the carrier component and the phase modulation index under analysis in this paper shows that the triangle wave phase modulation technique is more advantageous than the traditional modulation technique in reducing the noise induced by backscattering.     

A novel tunable optical oscillator for broadband signals

A tunable optical oscillator that generates signals at the micro- to millimeter-wave band for wireless communication applications is suggested. It uses directly modulated semiconductor lasers, in which sideband modes and four-wave mixing (FWM) conjugate modes are injection locked by the simple control of the applied modulation power. The signals at 15 GHz with phase noise of below ?95 dBc/Hz at an offset frequency of 100 kHz were experimentally obtained. The frequency of the generated signal is tunable, and the maximum achievable signal frequency is limited mainly by the bandwidth of the receiver.