激光陀螺锁区最小化控制技术

通过分析激光陀螺锁区的形成原因,给出了锁区最小化控制的基本原理.由激光陀螺谐振腔相向传播光束的输出特性,说明了常规锁区控制方案存在的缺点.从激光陀螺基本方程推导出锁区误差判别信号,提出了基于拍频信号和腔长信号迭加放大的高信噪比锁区控制方案,对交变偏频和常值偏频激光陀螺均适用.运用该项技术,实现了对某型激光陀螺的全温范围内的锁区最小化控制.     

激光陀螺锁区最小化控制技术

通过分析激光陀螺锁区的形成原因,给出了锁区最小化控制的基本原理.由激光陀螺谐振腔相向传播光束的输出特性,说明了常规锁区控制方案存在的缺点.从激光陀螺基本方程推导出锁区误差判别信号,提出了基于拍频信号和腔长信号迭加放大的高信噪比锁区控制方案,对交变偏频和常值偏频激光陀螺均适用.运用该项技术,实现了对某型激光陀螺的全温范围内的锁区最小化控制.     

机抖激光陀螺锁区补偿的理论研究

二频机抖陀螺具有较高的精度,但在每个抖动周期需要两次通过锁区,会丢失部分信息,从而带来了过锁误差.噪声注入只能将误差随机化,并不能从根本上消除误差.根据锁区方程阐述了锁区对机抖陀螺精度的影响.对二频机抖陀螺的锁区补偿方案进行了理论研究.采用零速率点恒加速近似得到了过锁误差的信号表征方法.数值分析表明该锁区补偿方法在各种...     

激光陀螺锁区的谐波测量方法

锁区对速率偏频激光陀螺的性能有重要影响,而高精度的锁区测最依然是一个难题.从激光陀螺闭锁方程出发,通过理论近似的方法得到了锁区与激光陀螺输出信号谐波的近似关系.在此基础卜提出了一种激光陀螺锁区的谐波测量方法,进而通过闭锁方程的严格数值解进行了修正和误差分析.最后利用谐波测量法测量了某一激光陀螺的锁区大小,结果表明精度能够优于5%.     

基于PMAC运动控制器的激光雕刻控制系统设计

为了实现激光雕刻切割机的灵活控制,提出了一种基于PMAC运动控制器的激光雕刻控制系统方案。PMAC运动控制器通过Pcomm32通信驱动程序接收工控机的指令数据,并将控制量传递给伺服驱动器,控制两个交流伺服电机的运转,同时伺服驱动器接收伺服电机的位置反馈信号,进行位置补偿,从而达到电机位置的精确控制。对运动控制模块进行了设计,并给出运动了程序基本结构。该方案结构简单,可靠性好,控制方式灵活,加工效率得到了大幅度的提高。     

数字相位测距仪信号源的研究与设计

在相位激光测距仪中,信号初始相位的相对稳定性对测距仪的测量精度非常重要.对于如何得到全同步的主振信号、本振信号、差频参考信号以及填充脉冲,给出了采用单片机控制频率合成器(DDS)直接数字频率合成芯片,直接滤波以及FPGA软件模拟DDS原理三种不同的方案,最后对这三种方案进行了比较.直接滤波法实现起来简单且成本较低,适合测量精度不是很高的系统.另外两种方案可用于测量精度较高的系统,但是成本较高.     

不同传感信号对风电叶片载荷智能控制影响研究

本文在自主搭建的DTEF(柔性尾缘襟翼)"智能叶片"仿真实验平台的基础上,讨论了三种不同传感信号方案,即信号来自叶片挥舞方向加速度,叶尖位移和叶根挥舞力矩,对控制效果影响。首先,本文分析了四组不同位置处加速度信号对控制效果的影响,接着对比了三种传感器信号方案的优劣,最后详细分析了相关流动控制机理。通过详细的讨论,本文得出结论:1)由于复杂流动分离和变桨作用,导致风力机叶片在Ⅱ区运行时选取加速度传感信号越靠近叶尖,控制效果越差,与Ⅲ区运行时相反;2)三种传感器信号方案中,选取叶根挥舞力矩为传感信号时控制效果最佳,相比原有主机控制最大降低载荷12.0%~22.5%;3)DTEF的作用扰乱了控制前叶片流动-结构间较好的同步性,削弱了叶片系统间的气弹耦合作用,从而有效地减少了叶轮受载。     

基于半导体光放大器的非归零信号时钟恢复

提出了一种基于半导体光放大器加窄带光纤光栅滤波器，将非归零信号转换为伪归零信号，再把伪归零信号注入到主动锁模环行腔激光器进行时钟提取的非归零信号时钟恢复方案.利用该方案实现了10 Gb/s伪随机非归零信号的全光时钟恢复，对工作原理和结果进行了分析和讨论.实验证明该方案具有结构简单，调整容易，输出波形好的特点.     

三路光纤放大器相干合成技术的实验研究

实验上实现了三路保偏光纤放大器稳定的锁相控制，达到相干合成的输出目的.介绍了实验方案，详细阐述了相位检测与控制的方法并以一路信号光为例给出了相位噪声的测量结果.最后给出了相干合成的远场图样并对其影响因素加以简单分析.实验表明，利用提出的方案增加相干合成的路数是可行的. 关键词： 光纤放大器 相干合成 锁相     

非等幅OTDM信号的全光时钟提取

理论上推导了非等幅均匀复用的OTDM信号中时钟分量与各路脉冲幅度的关系式,并分别从频域和时域的角度给出了利用以半导体光放大器（SOA）作为调制器的锁模光纤激光器进行时钟提取的物理机制,对时钟提取的物理过程给出了形象解释.实验上通过利用锁模光纤激光器成功地从非等幅均匀复用的8×2.5 GHz OTDM信号中提取了2.5 GHz单路时钟和20 GHz群路时钟光脉冲.利用该方案提取的时钟脉冲稳定性好,对偏振态不敏感,是较理想的时钟源.此技术可用于高速OTDM信号的时钟提取.     

Femtosecond pulse-shape modulation at kilohertz rates

We demonstrate a new scanning femtosecond pulse-shaping technique that allows pulse shapes to be modulated at kilohertz rates. This technique is particularly useful for lock-in measurements in which the signal is synchronized with the alternating pulse shapes. The pulse-shape lock-in technique is demonstrated in resonant coherent anti-Stokes Raman scattering, where it is shown to significantly improve the ratio of the resonant signal to both the nonresonant background and to noise.     

Coherent Beam Combination of Three Fiber Amplifiers with Multi-dithering Technique

Coherent beam combination of three W-level fiber amplifiers with multi-dithering technique is demonstrated. The multi-dithering technique is used for phase control in two channels. In the experiment, two channels are modulated by sine wave with 70 kHz and 100 kHz respectively, and two regular commercial DSP lock-in amplifiers and an industrial computer are used for electric signal processing in the feedback loop. The fringe contrast is advanced from 12% to 81%, and 78% coherent combination efficiency is obtained when the feedback loop is closed.     

Method for In-Vivo Fluorescence Imaging Contrast Enhancement through Light Modulation

Early diagnosis is one of the most important factors that increase the therapeutic potential of the disease. Diagnoses conducted by conventional equipment are expensive, time-consuming, burdensome to patients, and do not have high success rates. Diagnostic methods have also been investigated using nanoparticles. However, there have been no significant improvements in the early diagnosis of disease. The diagnosis technique proposed in this paper consumes less time, is more cost-effective, and more accurate. It uses a new concept—a low-intensity fluorescence molecular imaging system with a lock-in technique. This study applied the lock-in technique to basic research in contrast enhancement and optimization. This improved fluorescence distribution analysis, resulting in increased resolution of optical molecular imaging for early diagnosis of disease. An experimental lock-in fluorescence imaging system, which used a variety of fluorescent dyes, achieved signal amplification 100 times greater than that of a conventional fluorescence imaging system. The results of this study demonstrate that the lock-in technique could significantly improve optical molecular imaging technology, making it possible to achieve early diagnosis of disease.     

Experimental study of inspection on a metal plate with defect using ultrasound lock-in thermographic technique

The ultrasound lock-in thermographic technique was developed to detect interfacial defects and cracks in a metal plate. Discrete correlation method (DCM), Fourier transformation method (FTM), Short Time Fourier transformation (STF) and Discrete Wavelet Transformation (DWT) algorithms were used to extract the characteristic information of the thermal wave signal generated by ultrasonic wave modulated. It is found that STF and DWT algorithms are available for analyzing the thermal wave signal generated by ultrasonic wave modulated due to higher signal–noise ratio. Experiments were performed to investigate the effect on the amplitude contrast and phase angle contrast by the ultrasound transducer position, initial sonotrode action force and modulation frequency, respectively. Experimental results show that transducer position closed to the defect, higher initial sonotrode action force loaded and optimal modulation frequency selected are help to detect the defects of metal plate using ultrasound lock-in thermographic technique.     

Approach to optical interference fringes reduction in diode laser absorption spectroscopy

The advantage of a new scheme for balanced detection has been investigated to reduce the influence of optical interference fringes when performing diode laser gas absorption spectroscopy employing lock-in amplifiers and pigtailed lasers. The influence of the fringes has been reduced by comparing the lock-in 2 f signal due to the gas sample with that of a reference beam. The frequency regions outside the absorption feature have been used to obtain information on the interference fringe impact on the signal of interest. We have demonstrated an efficient way to reduce the influence of such fringes by employing this technique combined with non-linear signal processing methods. The different steps of the algorithm are presented. In the experimental arrangement presented, a reduction of the optical interference fringes by about 10 times is achieved, as demonstrated in measurements on molecular oxygen around 761 nm. The new technique is compared with an analog technique for balanced detection and certain advantages of the computer algorithm are pointed out. In particular, the emerging field of gas spectroscopy in scattering solid media strongly benefits from the technique presented. PACS 42.55.Px; 39.30.+w; 42.25.Hz     

Measurement of the decay lengths of the near-field signal in tapping mode

In near-field optics, the use of vertical vibration of the probe is of great interest in order to prevent the tip crash, in tapping mode. The optical signal is often obtained through a lock-in amplifier using a feedback on this vertical vibration. Therefore, harmonics of the optical signal are available. The reconstruction of the near-field signal, from these harmonics, enables the knowledge of the vertical variations of the near-field signal, without the use of the slower technique of approach curves or the use of photocounter. In this work, we use this reconstruction to measure the vertical decay lengths of the near-field data with the Prony’s and the simplex methods. We compare both methods and we discuss the results in terms of filtering by the lock-in.     

Research on thermal wave processing of lock-in thermography based on analyzing image sequences for NDT

Lock-in thermography, an active IR thermography technique for NDT, is based on propagation and reflection of thermal waves which are launched from the surface into the inspected component by absorption of modulated radiation. In this paper, thermal wave image sequences were sampled by a Cedip JADE MWIR 550 FPA infrared camera. Thermal wave signal processing algorithms are investigated to obtain information on subsurface defects. The Fourier transform, four-point correlation, and digital lock-in correlation algorithms are applied to extract the amplitude and phase of thermal wave’s harmonic component. A novel method called the time constant method (TCM) is proposed to analyze subsurface defects by using lock-in thermography. The experimental results confirm the thermal wave signal processing algorithms’ efficiency on subsurface defect detection.     

Application of infrared lock-in thermography for the quantitative evaluation of bruises on pears

An infrared lock-in thermography technique was adjusted for the detection of early bruises on pears. This mechanical damage is usually difficult to detect in the early stage after harvested using conventional visual sorting or CCD sensor-based imaging processing methods. We measured the thermal emission signals from pears using a highly sensitive mid-infrared thermal camera. These images were post-processed using a lock-in method that utilized the periodic thermal energy input to the pear. By applying the lock-in method to infrared thermography, the detection sensitivity and signal to noise ratio were enhanced because of the phase-sensitive narrow-band filtering effect. It was also found that the phase information of thermal emission from pears provides good metrics with which to identify quantitative information about both damage size and damage depth for pears. Additionally, a photothermal model was implemented to investigate the behavior of thermal waves on pears under convective conditions. Theoretical results were compared to experimental results. These results suggested that the proposed lock-in thermography technique and resultant phase information can be used to detect mechanical damage to fruit, especially in the early stage of bruising.     

Resonant photoacoustic gas sensing by PC-based audio detection

A new and simple technique for data acquisition and processing in an experiment of resonant photoacoustic detection is presented. It is based on the use of the sound card of a desk or laptop computer for digitizing the signal from a microphone enclosed in an acoustical cavity and further processing by a high-resolution fast Fourier transform. The system is applied to the detection of NO₂ traces in air at atmospheric pressure with an amplitude-modulated visible laser and the results are compared with those obtained by a lock-in amplifier. For the same acquisition time the results for the ultimate measurable concentration were 50 ppbV with this system and 130 ppbV with a lock-in amplifier. PACS 42.62.Fi; 82.80.Kq; 43.60.+d