Research Of Noise Measurement System Of Semiconductor Laser

In the 1960s, semiconductor lasers were devised, which brings thethriving future of the Optoelectronics fields. Along with the rapid extensionof applied fields, the semiconductor lasers'research and development aregoing forward with a very high speed. By now, the laser diodes have beenwidely used in optical fiber communication, CD, laser printing, informationmemory, medical treatment, pumping solid lasers, measuring, integratedoptics and so on. It becomes more important in advanced technology fields.Then, it is very important to measure the performance of LDs exactly andconveniently and to assess the quality and reliability of LDs. At present, theusual method of screen is electric aging in which all devices are aged with aconstant power or a constant current under high temperature and then theearly failed devices are selected. In the aging, the reliable devices are alsosubject to screening, and the lifetime of devices is affected because of thehot and electric hurt. It can cause batches of devices damage when someaccidence happens, for instance, the out of control system or power cut. Onthe other hand, electric aging is not sensitive for latent defects, for example,some devices after electric aging screening are usually found fail rapidly.Thus, the urgent problems are how to analyses the factors which affect thedevice reliability, and how to select the unqualified devices with a fast,nondestructive and conveniently method.Semiconductor laser noise includes light noise and electric noise ,lightnoise includes phase noise and intensity noise, electric noise includesthermal noise ,shot noise,1/f noise,g-r noise and so on. Electric noiseindicates the defect of material and device, especially, it is very sensitivefor various reliability-dependent defects. So the electric noise is becoming auseful tool to characterize device quality and reliability. Of late years, it hasgiven rise to the person much interest. So since the semiconductor laserswere developed, the people have studied its noise characteristics. Especiallyof late years, with the semiconductor lasers'applying extensively in avariety of domains, the questions of the appliance noise have given rise tothe universal concerns of the people, and the studying about the noise ismore earnest and all-rounder. The low-noise measurement of the semiconductor lasers needsfrequency spectrum analyzer. Because it is very expensive, this paper putforward the noise testing system of semiconductor lasers. The system usesvirtual instruments instead of the analyzer, so the cost of the system isreduced. The system can carry out the function of the time domaindisplaying,the spectral analysis,the spectrum density analysis ,crossspectrum analysis and the frequency response analysis, and select themethods of windowing function and the data averaging according to thesignal feature. We expect the system can carry out the low-noisemeasurements and the reliability evaluation of the semiconductor lasers. First, the article introduces the noise characteristic of semiconductorlasers , especially, the electric noise characteristic is mainly summarized,including the varieties,the features,the generation mechanism and theprincipally applying. Secondly, the measuring methods of noise insemiconductor lasers are introduced, in which the ultralow-noise PC-Basedmeasurement system is especially studied. The system includes thehardware part and the software part: the hardware part adopts four circuits,the preamplifier,the second level amplifying circuit,the filtering circuitand the acquisition card protection circuit. The system is to measureelectrical noise of semiconductor lasers and the other semiconductordevices, and the voltage of noise is very small, usually between several nVand several ten nV. So they need amplifying, in order to achieve thedifferentiating range of the data acquisition card, meanwhile thebackground noise of the amplifier lowers these noise voltages. Because thebackground noise of the system is up to the preamplifier, the systemdescribed by this article uses the Model 5184 produced by the Great BritainEG&G company as the preamplifier, the noise voltage 0.8nV/Hz1/2,thefixed magnification ratio 1000 ,basically satisfying measure demands. Forthe second level amplifying, we apply AD625 amplifier produced by theAD company, the noise voltage 5nV/Hz1/2, the magnification ratio can bemodulated between 1 and 104. Then, the article designs a second-orderlow-pass filtering circuit and the guarding circuit of the acquisition card,acting as preventing from the crossed filtering and protecting theacquisition card, moreover acting as amplifying to certain extent .For thelast data acquisition part ,we use USB 2007 produced by art-controlcompany,it is the board that USB bus is compatible, connected by USBcable with the computer, assembled 14Bit A/D converter on the board. Itprovides quadruple analogue input channels for the users. The input signalrange of A/D converter is ±5V.The USB2007 board has also the 16-roadswitch output and frequency measure functions;The software part is theemphasis of the measuring system. The paper designs a subjunctivespectrum analyzer by imitating some functions of R9211B/C FFT analyzerproduced by the Japanese ADVANTEST company. The major function ofthe analyzer is spectrum analyzing,including the time domain waveformdisplay ,the spectral analysis,the spectrum density analysis,crossspectrum analysis and the frequency response analysis. For the present, weare designing the wavelet analysis and matlab. Moreover the software alsoincludes the functions of filtering,windowing,averaging and so on, inorder that it can perfect analysis functions. The language of LabVIEW 6.0used by compiling software is designed and developed for virtualinstrument by the American National Instrument Company. It is a graphicprogram software for data acquiring,apparatus controlling,data analyzingand data expression. It amplifies the user's ability of making the ownapparatus system at the computer with high efficient and economichardware equipments. LabVIEW,the common data acquisitions and theapparatus equipments are fabricated ,so that the virtual instrument isdesigned .It includes all kinds of functions,whereby making compiling...