光外差法测量光探测器频率响应的系统校准

通过实验证明了光外差法测量光探测器频率响应特性的一种校准方法的有效性.首先根据光外差法的基本原理详细推导了光探测器频率响应的表达式.发现了激光器调谐过程中的输出不稳定性是影响光外差法测量光探测器频率响应特性结果准确性的主要原因.激光器的输出不稳定性主要表现在输出光的偏振方向、光功率以及光谱不稳定造成的拍频信号线宽变化.实验对两个3dB带宽分别为10GHz和50GHz的探测器进行测量,逐一比较了采用与没有采用相应校准方法的结果,验证了该校准方法的有效性.     

New method for measuring ultrawide frequency response of optical detectors

We propose a simple method which allows for a direct measure of the frequency response of photodetectors up to very high frequencies and avoids some of the problems inherent in the standard time-domain or frequency-domain measurements. This method is based on the detection of the tunable beat frequency obtained by superimposing the EM fields of two monomode semiconductor lasers.     

A transfer standard for measuring photoreceiver frequency response

We have developed a photoreceiver frequency response transfer standard which can be used to measure the optical modulation transfer function of a modulated optical source. It combines a photodiode with an RF power sensor or an amplified receiver with an RF power sensor. It is calibrated with an expanded uncertainty of 0.06 dB (coverage factor=2) using a heterodyne technique at 1.319 μm. We present a theory which allows use of the transfer standard with arbitrary source modulation depth. The calibration is transferred to a SDH/SONET test equipment manufacturer giving a final uncertainty well below the 0.3 dB uncertainty specified by ITU-TS (formerly CCITT) recommendation G.957. The transfer standard may have other applications including calibration of CATV test equipment, light-wave component analyzers, and light-wave spectrum analyzers     

A novel photodetector frequency response measurement techniqueusing an electrooptic modulator

Photodetector frequency response has been measured using an electrooptic modulator in a manner that does not require knowledge of the modulator frequency response. This paper discusses the theory and experimental results for the method and compares them to those obtained by using broadband noise from an optical amplifier     

Silicon p-i-n photodetector using internal reflection method

A semiconductor photodetector is proposed which makes use of an internal reflection method to enhance the photoresponse. This method is to let the incident light be multiply-reflected in the detector so that a long distance is traveled and most of the photon energy is absorbed by the detector. Theoretical analysis of the steady-state and time-dependent photoresponses for a p-i-n photodetector is presented. The photodetector is found to be particularly useful in detection of light with wavelengths near the intrinsic absorption edge. The photodetectors are fabricated from 4000 Ω.cm n-type, oriented silicon wafers. Both sides of the wafer are polished with one side inclined one-half degree with respect to the other. The p+n junction and the ohmic contact are formed by alloy method. The measured photoresponses for wavelengths of 1.0 and 1.1 µm are in reasonable agreement with the theoretical predictions.     

脉冲抽样法测量低频相位差

介绍了一种用脉冲抽样法测量低频相位差的技术。这种技术以可编程逻辑门阵列(FPGA)和单片机为核心,测量的精度达到0.1°。和传统的测相法比较,这种测量方法最大的优点是省去了大量的硬件电路,特别是省去了对速度和漂移特性要求苛刻的整形电路,也省去了鉴相电路、大小相角判别电路,只需增加一个抽样保持电路,给设计、调试带来了方便,而且,这种测量没有传统意义的幅相误差,给整机性能的稳定性和一致性带来了好处。     

Analysis of the frequency response of SAW filters using finite-difference time-domain method

The finite-difference time-domain (FDTD) technique was extended to analyze the frequency response of surface acoustic wave (SAW) filters. In this method, the partial derivatives of quasi-static Maxwell's equations and the equation of motion are discretized to centered finite differences. In addition, the perfectly matched layer boundary condition was applied to reduce spurious reflections. Two structures are considered in this paper. First, the model was applied to analyze the influence of the number of electrodes on the frequency response of a SAW filter fabricated on a zinc oxide (ZnO) substrate. Then, the proposed method was further extended to analyze the frequency response of a ZnO/diamond/Si-layered SAW filter. The simulated results are in a good agreement with the existing experimental data, indicating that the FDTD method was an appropriate approach for modeling SAW devices.     

New method of measuring phase characteristics of antenna using Doppler frequency measurement technique

This paper reports on a new method of measuring the phase characteristics of an antenna using the Doppler frequency measurement technique. With this method, the antenna being tested is rotated at a rate of f/sub sp/ around an axis through its geometrical center, and the phase characteristics of the antenna are calculated from the harmonic components of f/sub sp/ during time variations in the Doppler frequency of radio waves emitted from the antenna. Using this, we obtained three-dimensional phase characteristics of a patch antenna with a root-mean-square error of about 0.5/spl deg/, and confirmed its efficacy through experimental results.     

A simple and novel method for measuring the chirp parameter of anintensity modulated light source

A new and simple method of measuring the chirp parameter α of a modulated light source is presented. The technique involves modulating the optical source in a particular manner, and then directly examining the resulting optical spectrum. This experimental measurement technique allows us to directly measure the phase of the optical signal in the frequency domain. In addition, the method is very easy and accurate. Experimental results demonstrate the use of this measurement technique for measuring the chirp parameter of a source modulated at 10 GHz     

扫频法精确测量高速光调制器频率响应

同微波网络一样,可以用S参数来精确描述光电子器件的性能.根据微波网络的S参数,详细推导了光电子器件的S参数.搭建了40 GHz高速测试系统,利用矢量网络分析仪(带宽40 GHz)和作为参考的标准高速光探测器(带宽45 GHz),测量了宽带光强度调制器(实测带宽35 GHz)的频率响应.理论上,通过S参数和T参数的互相转换,扣除了微波放大器对测试结果的影响.在120 MHz～35 GHz范围内,测得的结果与出厂数据取得了很好的一致性.文中通过合理的简化,得到了光调制器频率响应的简明表达式,从而降低了数据处理的复杂度.     

A thin-film waveguide photodetector using hydrogenated amorphoussilicon

Metal-silicon-metal cladding layers on dielectric waveguides exhibit coupling and absorption characteristics that make them useful as photodetectors for integrated optical applications. Multilayer computer-modeling techniques were applied to waveguide photodetectors in order to investigate field and power distributions, as well as the attenuation and phase response in the guiding region. A waveguide photodetector based on amorphous silicon was fabricated and demonstrated     

A proposed OEIC receiver using MESFET photodetector

An optical receiver configuration based on the concept of using a single optically gated metal-semiconductor-fieid-effect transistor (MESFET) to perform the function of a photodetector and preamplifier has been introduced. The proposed optoelectronic integrated circuit (OEIC) receiver has been analyzed theoretically. A simplified noise model of the receiver has also been developed. Results have been presented for an OEIC receiver based on InGaAs MESFET supposed to be fabricated with matured InGaAs-InP MMIC technology. Theoretical results based on a simplistic noise model reveal that the proposed OEIC receiver has superior performance characteristics over the existing optical receivers     

A novel photodetector using MOS tunneling structures

A metal/oxide/p-Si structure with ultrathin oxide is utilized as a photodetector. At positive gate bias, the dark current of the photodetector is limited by the thermal generation of minority carriers in the inversion layer. The high growth temperature (1000°C) of the gate oxide can reduce the dark current to a level as low as 3 nA/cm². As biased in the inversion layer, the tunneling diode works in the deep depletion region with soft pinning of oxide voltage, instead of the pinning of surface potential, very different from the conventional MOS diode with thick oxide     

A new method for the spectral characterisation of PV modules

This paper presents a new characterisation method for the spectral influence of solar irradiation on photovoltaic (PV) modules, based on a proposed analytical model for the effective responsivity of PV modules. This mathematical tool needs only easily measurable atmospheric parameters and is applicable to different technologies. It allows the calculation of the spectral influence on PV modules under field conditions. It has been observed that this influence depends strongly on sky conditions and also on the PV module tilt angle, its technology, and the time of the year. Opposite effects are observed between cloudy and clear sky conditions, concluding that the former especially favours PV conversion in amorphous silicon modules. Copyright © 1999 John Wiley & Sons, Ltd.     

一种可吸收垂直入射光的管状量子阱红外探测器

基于传统的光刻和化学湿法腐蚀工艺,通过卷曲技术,提出一种三维管状量子阱红外探测器.该管状器件相比于未卷曲的平面器件,在垂直入射光照下,展现了优良的暗电流、黑体响应和光电流响应率特性曲线.当工作温度60 K、偏置电压0.45 V时,管状器件峰值响应率为20.6 mA/W,峰值波长3.62μm,最大量子效率2.3%.从几何光学的角度分析了管状器件的垂直光吸收原理,进而揭示了一种特殊的光耦合方式.测试了不同角度入射光照射下的光电流响应率谱.由于微管的近似圆形对称性,器件具有很宽的视角,有助于红外探测系统的设计.     

一种测量液体中粒子的扩散系数和大小的光散射方法

研究化学大分子或生物大分子(如血红蛋白)的大小、形状和结构是人们感兴趣的问题之。一近十几年来,发展了一些测定技术,例如粘度测定、电泳、超速离心、光散射等,都能测定出大分子的分子量或它的形状。为了研究生物和化学大分子及其反应的动力学性质,往往需要测定大分子的扩散系数。用于测量粒子扩散系数的光子相关技术近年来得到了突飞猛进的发展。本文提出了一种利用计算机控制时间的光散射技术测量大分子的扩散系数和分子大小的方法。利用这种装置我们测量了冻干羊血红蛋白的物理半径。我们所用的光学系统、记录及处理过程都比原先的方法简便得多。     

N~+P photodetector characterization using the quasi-steady state photoconductance decay method

正When a material is irradiated,it becomes more electrically conductive due to the absorption of the electromagnetic radiation.As a result,the number of free electrons and holes changes and raises its electrical conductivity. A simple but interesting phenomenon to characterise a fabricated n~+p photodetector in order to determine its linearity(photoresponse) and photoconductance was employed.Using the transient decay when the irradiation source is switched off,the minority carrier concentration,effective lifetime and surface recombination velocity present at the surface of the detector were measured.     

Wide-bandwidth receiver photodetector frequency responsemeasurements using amplified spontaneous emission from a semiconductoroptical amplifier

The white optical noise (spontaneous-spontaneous beat noise) generated by amplified spontaneous emission from a semiconductor-optical amplifier is used to measure the frequency response of over-wide-bandwidth photodetectors and optical receivers. This technique can be used to characterize optoelectronic components of arbitrarily wide bandwidths     

Wavelength conversion for FM light using light injection induced frequency shift in DFB-LD

A novel wavelength conversion is described. Wavelength conversion of frequency-modulated (FM) light is achieved by combining the lasing frequency shift induced by external light in a DFB-LD and the FM-IM conversion function of a Mach-Zehnder optical filter. In the experiment, 1534 nm FM light is converted to 1550 nm light.<>     

A method for measuring precipitation parameters using radar reflectivity and optical extinction

A method is described by which radar reflectivity and optical extinction are used to determine precipitation parameters, such as liquid water content and rainfall rate, and an exponential approximation to the raindrop size spectrum. The improvement in the accuracy of the results over that which is possible using empirical relations is demonstrated by applying the method to a set of experimentally observed raindrop size spectra. It is also shown that the assumption of an exponential spectrum is not a necessary feature of the method and that any two parameter drop size distribution can be employed.