光学测量系统信噪比优化方法研究

在光学测量中常常受低信噪比问题的影响,导致测量结果的不确定度增大。近红外波段双向反射分布函数（BRDF）的测量由于红外信号强度偏弱,易受环境干扰,面临的低信噪比问题尤其突出。光学测量系统的信噪比问题一般产生自探测系统,对于红外测量系统来说,经常使用斩波器、锁相放大器进行弱信号测量,但同时也引入了噪声问题。因此,本文针对近红外波段BRDF测量信噪比问题,从探测器、斩波器、锁相放大器三部分着手,分析噪声来源并针对性地提出抑制方法与优化措施,以提升信号信噪比。优化后的测量系统较优化前抗噪声能力提高,可重复性由优化前的2.1%提升到1.6%。     

锁相放大器在温度传感器校准系统中的应用

本文介绍了锁相放大器的原理和SR380锁相放大器在温度传感器校准系统中的应用。在瞬态温度测量中存在动态误差,需对温度传感器进行校准。温度传感器校准系统加入锁相放大器后,可将低温时的微弱信号检测出来,提高了校准系统的信噪比,拓宽了校准系统的温度下限。     

基于近场技术的微纳尺度热物性测量系统空间分辨率增强

传统的脉冲激光时域热反射系统通常基于远场光学设计,对于微纳米材料热物性测量的空间分辨率约在3μm～10μm范围,不足以满足先进微电子器件和芯片的热物性测试要求.基于近场光学原理,本文研究了提升时域热反射系统空间分辨率的新颖技术方法,并建立了相应的实验系统.实验获得的微纳结构样品测量数据表明,基于近场技术的时域热反射系统...     

WMS温度测量中谐波信号锁相放大器的设计

在波长调制光谱技术(Wavelength Modulation Spectroscopy, WMS)温度测量中,传统的锁相放大器测量谐波信号的振幅必须对被测信号及参考信号的相位单独进行调整。针对这一问题,设计了一种基于高精度平衡调制器AD630进行同步相敏检测的谐波信号的双锁相放大器。与传统的锁相放大器相比,所提双锁相放大器利用正交双通道的平方和检测,可以避免被测信号与参考信号进行严格的相位匹配问题。利用Multisim软件构建仿真模型,包括前置高通滤波器、正交双通道的相敏检波器、低通滤波器等部分。理论计算和仿真结果表明,所提方法能够准确检测微弱一次、二次、四次谐波信号的幅度,检测误差小于5%,具有电路简单、运行速度快、线性度高等优点,能够满足WMS温度测量工程应用。     

锁相放大器校准方法研究

锁相放大器在微弱信号测量中已经得到了广泛的应用,本文通过对锁相放大器基本结构和工作原理的分析,总结出了锁相放大器一般参数的校准方法。     

锁相放大器的校准方法

介绍了锁相放大器的一种校准方法.讨论了锁相放大器的相敏特性、满刻度灵敏度和本机噪声、动态储备、动态范围以及时间常数参数的校准实现方法,结合校准系统对典型参数的测量不确定度进行了评定.     

原子束的调制与质谱信号的锁相放大

在原子束-水蒸汽散射实验中,原子束被调制,四极质谱计的信号由锁定放大器放大。本文将论述该实验的装置。我们已得到的实验结果表明,本底信号被剔除,并可获得良好的信噪比。在约两分钟的持续测量中信号电平的起伏不大于3％。     

基于数字锁相解复用的多通道近红外光并行检测技术

多波长光源照射下微弱光的准确检测是利用近红外漫射光进行人体疾病诊断时所面临的基本问题,而多光源并行检测是实现快速测量所要解决的关键问题之一.基于数字锁相的基本原理,提出了结合单光子计数技术和现场可编程门阵列(FPGA)平台的多通道数字锁相方案,不但可实现微弱光的准确检测,而且可实现多通道实时并行检测.基于此方案,搭建了多通道近红外光检测系统.实验结果表明,所搭建的检测系统对由仿体出射光的检测信噪比为24dB,同时对不同频率编码的光源具有很好的识别度,对不同调制幅度的测量误差小于9.13%.     

用锁相放大器实现电池内阻在线测量

本文对传统的电池内阻测量方法进行了研究比较,提出了用锁相放大器测量电池内阻的新方法,详细阐述了锁相放大器的基本结构与工作原理以及用锁相放大器实现电池内阻测量的实际电路,通过对多种电池内阻的测量以及电池充放电过程中内阻的在线监测,有效地克服了噪声和干扰,快速获得稳定、精确的内阻测量数据,能实现完全的在线检测,并且简化了设计。     

时选窗技术在传声器自由场互易校准中的运用

实验室标准传声器的自由场互易校准是复现声压量值的一种基本方法,在测量过程中需要测试系统具有很高的信噪比.在空气声自由场声压基准装置中采用了步进正弦信号扫描和时间延迟谱技术测量传声器转移阻抗复频率响应,并采用IFFT得到脉冲响应,通过时域窗口消除反射,有效提高了信噪比,在体积较小的消声箱内完成了互易校准.     

Spectral analysis of a sampling optical time-domain reflectometer

A spectral analysis is presented for the backscatter signal of optical time-domain reflectometers (OTDR). Periodic spatial fluctuations in the fiber attenuation produce modulation sidebands in the frequency spectrum of the backscatter signal. Applying the sampling technique to OTDR leads to a considerable improvement of the signal-to-noise ratio (S/N) due to spectrum compression, as a tradeoff with the measurement time. It gives a performance equivalent to digital averaging. Design examples are given at wavelengths of 0.85, 1.3, and 1.55 μm. A practical setup of a sampling OTDR is described     

Scanning near-field optical microscopy signal processing and resolution

To increase the signal-to-noise ratio and to remove the spatially slow varying signals, a lock-in amplifier is often used in scanning probe microscopy. The signal reconstructed from the lock-in data contains the contributions of the evanescent and homogeneous waves that are mixed in the near-field zone (i.e., at a very short distance). The resolution is determined and a method is given to suppress the useless background information. Experimental images of nanoparticles are processed.     

Optical time-domain reflectometer performance improvement using complementary correlated Prometheus orthonormal sequence

The authors deal with the pulse spreading approach using complementary correlated Prometheus orthonormal sequence (CCPONS) to enhance the performance of the optical time-domain reflectometer (OTDR). The approach has the advantage of reduced measurement time when compared with the OTDRs designed using the conventional or Hadamard derived codes. Also, it offers an improved dynamic range when compared with the conventional OTDR. We have demonstrated experimentally a high performance OTDR based on a CCPONS coding scheme and using a low-power Fabry Perot-laser diode. Using a 64-bit CCPONS coding, a one-way signal-to-noise ratio improvement of 3.7 dB was achieved over a conventional OTDR under the same measurement conditions, that is, for the same measurement time (20 000 averages) and same peak power (100 W).     

Quantum radiometry

We review radiometric techniques that take advantage of photon counting and stem from the quantum laws of nature. We present a brief history of metrological experiments and review the current state of experimental quantum radiometry.     

New methods for magnetic susceptibility measurements of solid3He at ultralow temperatures

An ac mutual inductance bridge for magnetic susceptibility measurements of solid³He in a metallic cell at ultralow temperatures is described. A null detector for the bridge was composed of an rf-biased superconducting quantum interference device (rf-SQUID) system and a lock-in amplifier that avoided strong fields of the nuclear demagnetization magnets. A design of a sample cell to reduce eddy currents and allow large skin depths associated with the ac measurements while securing high-thermal conductance is also described. The magnetic susceptibility of solid³He with a hexagonal close-packed structure was measured with this system down to 90 µK. The signal-to-noise ratio was 300 at 300 µK and 1 at 90 mK. The quantity of heat evolved in the susceptibility measurements was less than 3 pW.     

光子多普勒测速系统信号解调方法比较

光子多普勒测速系统具有抗干扰能力强、测速范围大等优点,适用于信噪比低、信号质量差的测量场合。介绍光子多普勒测速系统的工作原理,详细阐述常用的四种信号解调方法——条纹法、相位解调法、短时傅里叶变换法、小波变换法的原理、特点和近几年的研究现状。利用上述四种信号解调方法对简谐振动调制的多普勒信号进行解调仿真,直观地展示不同信号解调方法的优缺点和适用性。实验结果表明,相位解调法最适合用于光子多普勒测速系统振动信号解调。最后讨论了采用递归希尔伯特变换的方法减小相位解调法的正交性误差的可行性,通过仿真实验验证了此方法的有效性。     

Stabilization of electro-optic modulator bias voltage drift using a lock-in amplifier and a proportional-integral-derivative controller in a distributed Brillouin sensor system

In a distributed Brillouin sensor system, it is crucial to keep the pulse energy uniform for a constant signal-to-noise ratio. This means that the variable dc leakage (pulse base) for the electro-optic modulator (EOM) must be locked. We examine two different methods of locking the EOM bias voltage and look at the advantages and disadvantages of each locking method. It is found that the two locking methods, one based on a lock-in amplifier and the other using proportional-integral-derivative control, both have applications in which they excel at locking the pulse base.     

基于石英音叉探针的原子力显微镜测头开发

基于石英音叉探针开发了一种自感应原子力显微镜(AFM)测头。该测头通过自身输出电信号检测悬臂振幅变化,无需外部光学检测部件,易于集成。针对测头设计了微弱电流提取及寄生电容补偿电路。利用商业化锁相放大器实现了对测头幅度信号的获取。在此基础上对测头在调幅模式下的力-距离曲线和分辨力进行了测试。利用锁相放大器内置的PID模块实现了调幅模式下对样品表面形貌的测量。实验证明,该测头灵敏度为0.624 mV/nm,分辨力优于2 nm。