相位敏感光时域反射仪的振动全程敏感研究

研究相位敏感光时域反射仪振动检测时, 高功率激光脉冲的入射使得光电探测器产生饱和现象而导致光纤前端振动传感不敏感, 低功率又满足不了远距离检测的需求。为了解决这一问题, 采用一种新型传感结构的方法进行了理论分析和实验验证。根据入射功率的高低对光纤分段检测, 通过相应的数据处理, 实现了光纤振动全程敏感的结果。同时, 为了进一步提高该系统的振动灵敏度和信噪比, 对比分析了雪崩二极管检测与利用低噪声光电二极管检测的结果, 并比较了声光调制器与半导体光放大器的实验效果。结果表明, 当测量距离为38km时, 相比雪崩二极管检测, 利用低噪声光电二极管与掺铒光纤放大器有更高的信噪比; 相比声光调制器, 利用半导体光放大器能得到更高信噪比。该新型传感结构为光纤传感器领域的科学研究和工程应用提供了很好的参考。     

干涉型光纤传感器直流相位跟踪检测系统的改进

对干涉型光纤传感器直流相位跟踪检测系统进行了分析和改进，通过在检测系统中加入简单的电路模块，使系统的幅频响应特性得到改善。建立了Michelson光纤干涉型传感系统，实验结果与理论分析相吻合。     

A vibrationally compensated far infrared laser interferometer for plasma density measurements

A modulated far-infrared laser interferometer which is presently operating on the PDX experiment at Princeton is described. The interferometer geometry permits the characterization of inside “D”, outside “D” as well as circular discharges. To achieve this versatility, a titanium corner cube reflector, mounted inside the PDX vacuum vessel is used in conjunction with a second visible wavelength interferometer for vibration corrections. In addition, the use of room temperature quasi-optical Schottky diodes in the far-infrared interferometer is reported. The minimum detectable line average density of the system is ～5×10¹¹ cm^?3.     

Four-port homodyne receiver for optical fibre communications comprising phase and polarisation diversities

A new four-port homodyne receiver for optical fibre communications is proposed and studied experimentally. It comprises phase-and polarisation-diversity schemes, removing the need for phase locking and polarisation control. The bit-error-rate measurement is also reported.     

Performance analysis and experiment of a homodyne receiverinsensitive to both polarization and phase fluctuations

A detailed bit-error-rate analysis of a differential phase-shift keying (DPSK) homodyne receiver which comprises polarization and phase diversities is presented. It is shown that both the requirement for the laser linewidth and the receiver sensitivity are approximately equal to those of a conventional DPSK heterodyne receiver. The insensitivity of the receiver to the polarization state of the incoming signal is also investigated both theoretically and experimentally     

大气湍流引起CO_2激光自差通信系统相位起伏的研究

本文对CO_2激光自差通信系统接收中频信号相位受大气湍流的随机起伏进行的理论与实验研究表明,该系统有助于克服大气湍流对接收中频信号相位的随机起伏,由大气湍流带来的随机相位噪声可不予考虑。     

An optical homodyne technique for measurement of amplitude and phase of subangstrom ultrasonic vibrations

An optical homodyne technique is utilized to measure sub-angstrom dynamic mechanical deformations. For measurement in the frequency domain, where synchronous detection is used both the amplitude and phase of the mechanical signal can be measured with a high sensitivity; displacements less than 10^-2Å were measured with normal environment acoustic noise. Measurement in the time domain is also feasible with reduced sensitivity.     

Development and application of the Fraunhofer-diffraction method for measurements of plasma density fluctuations using infrared lasers

This paper is concerned with systematic developments of the Fraunhofer-diffraction method for studies of plasma density fluctuations in high-temperature plasmas using infrared lasers, namely (i) development of the general theory of the Fraunhofer-diffraction method, (ii) measurements of fluctuations propagating in an azimuthal direction, (iii) measurements of fluctuation intensities, and (iv) application in measurements on high-temperature plasmas.     

应用于污泥处理的等离子体动态匹配电源的研究

随着等离子体技术应用在污泥处理中的不断深入,对于等离子体电源性能的要求也越来越高,因此文中重点研究了污泥处理装置中的等离子体电源的动态匹配功能。采用三相不可控整流电路,IGBT全桥逆变电路,DC侧Buck斩波功率调节和频率自动跟踪算法的策略。最后通过Simulink对电源系统进行仿真,验证了系统的正确性和动态匹配算法的有效性。     

Confirmation of abnormally high electron density in a transient mercury-vapour plasma by laser-interferometer measurements

An optical interferometer which employs a low-power (100 ?W) beam from a frequency stabilised He-Ne laser has been used to find the effective change in path length due to the transient plasma in terms of fractional fringe shift. The results confirm the magnitude of electron density previously deduced from the extrapolated microwave results and indicate a distinct time lag in the buildup of maximum electron density with respect to the transient current maximum. This implies a fall in drift velocity of electrons from the current peak to the electron-density peak which is a function of the degree of ionisation achieved.     

Electron density and temperature measurements of the ignited mode plasma in a thermionic converter

Spectroscopic measurements of the electron density and temperature have been made on a planar thermionic converter operated in the quasi-saturation region of the ignited mode. The effects of several independent converter variables on the electron density were investigated quantitatively. From this investigation it was found that the emitter temperature and current density were the most significant parameters affecting the electron density. Collector temperature, cesium vapor pressure, and interelectrode spacing were less important. Complete electron density profiles and electron temperature profiles were obtained and compared to conditions characteristic of local thermodynamic equilibrium (LTE). A representative case indicated the measured temperature, 2600°K, was only 200°K higher than required for complete LTE in the region of the peak electron density. This corresponds to an electron density approximately 45 percent below the equilibrium value.     

Biomechanical measurements to characterize the oral phase ofdysphagia

Dysphagia is a disorder of the swallowing mechanism and presents a major problem in the rehabilitation of stroke patients and head injured patients. The authors have identified several biomechanical parameters that characterize the oral musculature and have developed techniques to quantify these parameters in normal and dysphagic patients. These parameters include lip closure pressure, lip interface shear force, tongue thrust, and swallow pressure. Significant differences were found in each of these parameters measured in normal and dysphagic patients. The quantitative measurements may aid the physician in choosing the appropriate therapy during the course of recovery.     

Applications of temperature phase measurements to IC testing

This work analyses the applicability of silicon surface temperature phase measurements as a test observable when a device acting as a heat source dissipates a modulated power function. Specifically, this paper considers two different functions: the phase shift of the temperature waveform as a function of frequency and distance, and the slope of the temperature phase shift versus distance as a function of frequency. Different cases are analyzed in order to show the potential of both functions, including experimental results obtained from a specific integrated circuit (IC). The conclusions will show that samples of the phase function can be used to locate devices acting as heat sources, and that the slope function can be used to extract information regarding the heat flow path in the IC, and, therefore, regarding the structure of the IC.     

A new profiling technique applicable to the measurements sensitive to the free-carrier concentration rather than the depletion-layer thickness

A novel profiling procedure where the free-carrier concentration is the primary measured quantity is demonstrated. This method allows the depth profiling of the dopant concentration and other properties such as trap energy levels and generation lifetime by measurements monitoring such parameters as surface conductivity, surface photovoltage, reflectance, transverse acoustoelectric voltage (TAV), and Hall voltage. Nondestructive profiling is also possible by contactless methods, e.g., TAV measurements. The distinct difference between the pulsed capacitance-voltage (C-V) measurement and the proposed procedure is that in the former the measurable physical quantity is the depletion-layer width which is modulated by an external field. In the technique proposed here, the carrier concentration as a function of bias field is monitored and the depletion-layer width is then calculated. The theoretical analysis leading to the evaluation of the depletion width as a function of bias field is presented along with an experimental example, utilizing the nondestructive TAV measurement.     

Submillimeter laser interferometer for high density plasma diagnostic

There are presented the results of investigation of the one-channel homodyne laser interferometer λ=119 µm made on the basis of the hollow dielectric beamguide and quasioptical functional devices. The interferometer is designed for determination of the plasma electron density of the TOKAMAK-7. The density response threshold is 0.7% from the expected plasma density and the phase difference measurement total error is 5°     

In vivo inductive phase shift measurements to detect intraperitoneal fluid

Four different volumes of physiological saline were infused into the abdominal cavity of rats and the resulting inductive phase shift in the bulk of the abdomen was measured with a noncontact electrical induction system, built to measure phase shift in the bulk of the body in the frequency range from 1 MHz to 8.5 MHz. This experimental study shows that inductive bulk measurements of phase shift have the potential to detect changes in intraperitoneal fluid in vivo with measurements made at frequencies higher than approximately 1 MHz. The experiments also show that the bulk phase shift increases as a function of frequency and fluid volume in a way that is qualitatively consistent with earlier theoretical predictions.     

Automated image analysis for bone density measurements using computed tomography

Quantitative trabecular bone density (TBD) measurements in the appendicular skeleton, using computer tomography, are described. Pixel-value frequency histograms are generated, to determine the spatial coordinates of the centers of mass distribution for both bones in the image field. A line joining these centers is used as an axis for subsequent enhancement of horizontal image features, and for radial fan searches, to separate bone images in the analysis field. One bone image is then deleted and the outer contour of the remaining bone is determined using cross-correlation and mathematical morphology operators. This contour is then used as a template to calculate average linear attenuation coefficients (LACs) over 1-pixel-wide annuli for TBD calculation. Data from 33 individual subjects (1251 images) have been processed using both automatic and manual analysis methods. Both methods give the same numerical values for TBD, but the automatic method has slightly better precision. The analysis method is general and is adaptable to other imaging situations.     

EPD measurements for low dislocation density GaAs and InP substrates

The Japan Manufacturers' Society of Compound Semiconductor Materials (JAMS-CS) performed etch pit density (EPD) round robin evaluations of undoped semi-insulating GaAs substrates for three years from 1986 to 1988 [1]. More than ten years have passed since then, and with applications for semiconductor lasers escalating, the market for low dislocation density substrate is increasing rapidly. EPD measurements for low dislocation density substrates are obviously different from that of a conventional semi-insulating GaAs substrate with EPD around 1.0 × 10⁴ cm⁻².     

A DCN laser interferometer for electron density measurements of plasmas

The main characteristic of this interferometric system is such that the systems can be used for DCN laser (λ=195μm, 190μm) and also for HCN laser (λ=337μm) by changing the work medium, regulating the temperature of tube wall and adjusting the optic path, without changing any optic element.