更精确地利用光谱自然确定禁带宽度

以建立在能量守恒定律得到的塔克(Tauc)关系为出发点,推算出一个三参数方程用来以光谱实验数据获得更加精确和可靠的材料的禁带宽度.禁带宽度Eg、材料性质指数n及取决于跃迁种类的常量A自然而然地以参数形式出现在这个参数方程中.于是当对实验数据进行最小二乘方非线性拟合后,就能得到表征材料特性的关键指标禁带宽度Eg、材料性质...     

Simple Time and Frequency Dissemination Method Using Optical Fiber Network

This paper describes a simple and cost-effective method of frequency dissemination. In current digital communication networks, node clocks are hierarchically synchronized to the atomic master clock through fiber links. This synchronized network is used as an intermediate link for remote calibration services like the global positioning system common-view method. A prototype reference signal generator has been developed for recovering the communication clock signal and synthesizing a 10-MHz signal from it. The generator output frequency at the client site can be traced to coordinated universal time (UTC) National Metrology Institute of Japan (NMIJ) with some uncertainty, depending on the stability of the node clocks and the distance from the master clock. The stability performance of the generated reference signal has been tested at Okinawa-the farthest prefecture from Tokyo, where the master clock is located (baseline distance of 1500 km). The primary rate (1.544 MHz) for telecommunication services was chosen for the 10-MHz signal generation in the experiment. A sinusoidal phase fluctuation within a one-day period is dominantly observed. This fluctuation is mainly caused by fiber expansion and contraction due to normal daily temperature changes. It degrades the stability (Allan deviation) to the level of 5 X 10^-13 (t = 40 000 s, which is almost half a day). However, the major part of the phase fluctuation can be canceled by averaging a full day's data. In this case, the Allan deviation becomes 1 X 10^-13, which is obtained at Okinawa over ten consecutive days of measurement. The worst average frequency offset relative to UTC (NMIJ) (one-day averaging) is -6.3 X 10^-13. The results indicate that this method promises to be suitable for most applications, providing an uncertainty of less than 1 X 10^-12 at an averaging time of one day.     

Frequency Modulated Continuous Wave System for Optical Fiber Intensity Sensors With Optical Amplification

We report on the use of erbium doped fiber (EDF) amplification to enhance a frequency modulated continuous wave (FMCW) technique for referencing optical intensity sensors located between two Bragg grating structures. The experiment combines the concept of FMCW with the spectrally selective mirror properties of Bragg gratings to interrogate with referencing properties intensity based sensors. The interrogation system without amplification yields a sensor resolution of around 0.078 dB. When the EDF amplifier is introduced into the experimental set up, the sensor sensitivity does not change, but the signal-to-noise ratio is improved, resulting into an enhanced resolution of 0.025 dB. We also obtain a remote sensing operation at a location of 50 km, showing the feasibility of this configuration to be used as a remote sensing application.     

Microprocessor-Based Temperature Monitoring System Using Optical Fibers

This paper describes a microprocessor-based temperature monitoring instrumentation system based on phase modulation principle using interferometric optical sensors system, where the phase of a beam through a temperature sensing fiber (placed in a hot chamber) is compared with that of a beam from a reference fiber placed out side the hot chamber. The sensor system consists of a He-Ne laser source, two beam splitters, two single-mode optical fibers, and two light dependent resistor (LDR)-based timer circuits as detectors. The frequencies of the timer circuits change according to the change in temperature of the hot chamber. A 8085 microprocessor-based system is used to sample the frequencies of the timer circuits.      

Optical Frequency Metrology of an Iodine-Stabilized He-Ne Laser Using the Frequency Comb of a Quantum-Interference-Stabilized Mode-Locked Laser

We perform optical frequency metrology of an iodine-stabilized He-Ne laser using a mode-locked Ti:sapphire laser frequency comb that is stabilized using quantum interference of photocurrents in a semiconductor. Using this technique, we demonstrate carrier-envelope offset frequency fluctuations of less than 5 mHz using a 1 s gate time. With the resulting stable frequency comb, we measure the optical frequency of the iodine transition [¹²⁷I₂ R(127) 11-5 i component] to be 473 612 214 712.96 ± 0.66 kHz, well within the uncertainty of the CIPM recommended value. The stability of the quantum interference technique is high enough such that it does not limit the measurements.     

双层减反射膜镀制半导体光放大器

首次采用ZnSe和MgF2双层减反射膜镀制半导体光放大器，分别测出了两端面的剩余反射比曲线。结果表明，该放大器两端面反射比乘积最小值低于1×10－6，按照O’Mahoney给出的判据，其可用行波单程增益为22dB。     

基于C#的几何量精密测量数据处理系统的开发

介绍了用Visual C#.net开发的几何量精密测量数据处理系统.针对测量数据处理繁琐和难于进行分析的问题,结合相应数据处理方法,用计算机编程进行数据处理,深化了计算机在几何量精密测量数据处理领域中的应用.     

基于四参数正弦拟合的放大器延迟时间的精确测量

针对放大器延迟时间测量时信号幅度相差悬殊的问题,提出了四参数正弦拟合测量方式,以相位差转换成时间差予以实现。对其中的相位周期性带来粗大误差问题,负值幅度带来相位粗大误差问题,测量系统自身通道间延迟修正问题等,进行了分析讨论,并给出了解决方案。对测量结果的不确定度进行了分析。在实际应变放大器上的一组实验结果,验证了所述方法的有效性与可行性。并且发现,放大器的延迟具有内在稳定性,与激励信号的幅度、频率、波形等均无关系。该方法可用于放大器、滤波器、衰减器等线性电路延迟的测量分析。     

Precise Frequency Measurements in Submillimeter and Infrared Region

As a result of frequency stabilization of all the lasers and microwave oscillators in a new multiplication chain consisting of HCN (337 ?m), D2O (84 ?m), CO2/OsO4 (10.53 ?m), CO2 (10.18 ?m), and He-Ne/CH4 (3.39 ?m) lasers signals up to 88 THz have been synthesized with high precision. Owing to phaselocking of HCN and D2O lasers to the primary frequency standard synthesis accuracy of ~1013 up to 30 THz has been achieved for the first time. The frequency of the CO2/OsO4 laser was first measured ?OsO4 = 28 464 676 938.5 ± 1 kHz and the He-Ne/CH4 laser frequency was determined to be ?CH4 = 88 376 181 586 ± 10 kHz.     

反向泵浦光纤喇曼放大器中双重瑞利散射噪声的抑制

研究了反向泵浦光纤喇曼放大器中泵浦和信号和求解方法，并且分析了双重瑞利散射噪声的特性，提出了在考虑反向喇曼光放大作用时，双重瑞利散射噪声的表达式。给出了在加入光隔离器进行抑制后，双重瑞利散射噪声的计算方法，并进行了模拟分析，得出了放置光隔离器的最佳位置。     

微波功率固态放大器负载牵引特性的自动测试

提出了一种新的微波功率固态放大器件负载牵引测试方法和校准方法，研制了自动测试系统，并对该测试方法、校准方法和自动测试系统进行了较为详细的讨论。通过实测，获得了微波功率固态放大器输出功率等值线阻抗圆图，验证了所提出的校准方法、测试方法和自动测试系统测试方案是正确的，并具有实用性。     

在线光纤放大器远程监控方案的研究

研究了一个监控信道方案，用于ＷＤＭ＋ＥＤＦＡ光纤通信系统在线光纤放大器远程监控，并成功地实现了其演示系统，对该方案的实行性进行了论证。     

A Frequency Modulation Based System Using Bilayer Thin-Film Displacement Sensors

A novel method has been used for accurately measuring low voltage signals (~10^-4 V) associated with inductance changes of bilayer thin-film sensors under bending stress. In this paper the architecture of the system is first presented, and then the design ideas and key technologies are followed. Initially, the frequency modulated signals were simulated with superimposed noise signals to test the demodulation performance of the written program. From the results, the expected output of the program was confirmed. Following this, the frequency modulation technique was used with actual sensor signals to measure the displacement of a bilayer thin film sensor. The results from the acquisition were compared with a previously developed amplitude modulation based setup, and it proved that the frequency modulation system provided a robust and accurate solution to evaluate magnetostrictive materials and their application in magnetic sensors     

Velocity Profile Measurement Using Digital Signal Processor-Based Optical Tomography System

The utilization of personal computer together with Data Acquisition System (DAS) as the processing tool in optical tomography systems has been a norm ever since the beginning of process tomography. However, the advancements in silicon fabrication technology nowadays allow the fabrication of powerful digital signal processors (DSPS) at a reasonable cost. This allows the technology to be applied in optical tomography system since data acquisition and processing can be performed within the DSP. Thus, the dependency of personal computer and the DAS to sample and process the external signals can be reduced or otherwise eliminated. The DSP system was customized to control the data acquisition process of 16$,times,$ 16 optical sensors array, arranged in parallel beam projection. The data collected was used to measure the velocity profile using sensor to sensor cross-correlation and pixel to pixel cross correlation.      

基于高斯光脉冲延迟技术的光纤长度精确测量方法

提出了一种基于高斯光脉冲延迟技术的无盲区、高精度光纤长度测量方法。借助光纤延迟环的作用,在高速示波器上可以观察两路具有相对时延的高斯脉冲序列。通过调节脉冲频率可使两路高斯脉冲完全重合,依据此时脉冲频率可计算出光纤长度。脉冲未完全重合则会引入频率测量的误差,而利用脉冲时延与幅度的转换关系,通过脉冲幅度极大值的测量可以精确判断脉冲是否重合。脉冲频率的分辨力达到0.1 Hz,从而提高光纤长度测量的精确度。实验中当光源波长为1296nm时,该方法测量2284.34m G.652单模光纤长度的不确定度为0.04m,测量12726.57m的不确定度为0.24m。     

Optical Spatial Frequency Filtering of Radiographs

The frequency content of a photographic image can be considerably modified by using a suitable optical system. The Fraunhofer diffraction pattern (the Fourier transform) of a transparency is produced by using parallel light from a laser. This spatial frequency spectrum can be differentially filtered to produce a reconstructed image of arbitrary frequency content. The radiographic image is a convolution of the X-ray source with the object under examination. The filtering operation lessens the degrading effect of penumbra by means of a deconvolution with a filter that is representative of the Fourier transform of the X-ray source.

Manufacture of the spatial filter is described and results showing enhancement of detail in radiographs by reduction of penumbra are presented.     

频域光存储和全息术

本文通过分析光谱烧孔的全息探测法,提出了全息频域光存储系统,并分析了系统的特性指标。计算机模拟分析结果表明,全息频域光存储技术是一种大容量并行光存储新技术。