Measurement Of Electrical Derivative And Research On Reliability Of Semiconductor Laser

Optoelectronic technology has become an important part in modern high technology, which are vital to national economic development, defense construction, communications, etc. With the development of opotoelectronic technology, semiconductor lasers has been widely used in optical fiber communications, optical sensing, information storage, medical treatment, laser printing, etc. and the quality and reliability are important to the application system. Therefore, research on reliability of semiconductor lasers are of vital significance to both manufacture and application.At present, the usual method to evaluate the quality of semiconductor lasers is to carry out electrical aging tests by increasing temperature and driving current, and screen out devices with large variation rate of output optical power at certain driving current or those with large variation rate of driving current at certain output optical power. This method has a long period and the reliable semiconductor lasers are easily damaged, besides the price of this apparatus is expensive and complicated for operating. So, research on method to estimate the semiconductor lasers'reliability has become more important in nowadays.Electrical derivative method is an excellent method to test semiconductor lasers'performance. It can be used to study junction characteristic parameter, junction voltage saturation characteristic, parallel leakage channel, carrier divulaging, serial linear resistance, nonlinear resistance, current spreading and non-radiative recombination centers, these parameters are closely related to reliability of semiconductor lasers. Compared with traditional electrical aging method, devices which have been first sorted by electrical derivative method, then using electrical aging method to test, can reduce the aging number and improve the efficiency of aging set. This paper is based on electrical derivative method, design a system to extract electrical derivative parameters and study relations between parameters and reliability of semiconductor lasers. This paper summarizes the significance of research on reliability of semiconductor lasers, show the role of electrical derivative method in it, and then analyzing characteristics of V～I, P～I, IdV/dI～I, dP/dI～I curves and parameters of semiconductor lasers. Based on digital method, design an system to extract electrical derivative parameters. There are two schemes, one is based on PC-DAQ scheme, using data acquisition card; the other is based on PC-MCU scheme, using high-precision digital to analog, analog to digital converters. Although the former has high precision, it is too expensive, on the other hand, the latter can not only meet requirements of system, but also has a high perfomance price ratio. On the base of latter measurement method, this paper designs an electrical derivative parameters extracting system, composed of MSP430F149, digital to analog module, voltage controlled current source, photoelectric converting module, analog to digital module and PC. In the system, high-precision D/A, A/D is an key, which determines the whole performance of system, so we choose 16-bit converters. Voltage controlled current source is used to transfer voltage signal from D/A to current signal, in order to provide semiconductor lasers with step scanning current. The role of photoelectric converting module is collecting optical power of semiconductor lasers for subsequent processing. The working principle of whole system is: 16-bit D/A is controlled by MSP430F149 to generate 0～5V analog voltage signal, then amplifiy it to 0～10V, deliver it to voltage controlled current source, to provide 0～2A current siganl for semiconductor lasers. Once there is current, semiconductor lasers bring junction voltage and luminescence. Using photoelectric converting module to tranfer optical signal to electric signal. After that, 16-bit A/D convert junction voltage and optical power to digital signal, then via RS-232 serial port, delivering data to PC. Finally in the PC, design application interface to display electrical derivative curve and abstract electrical derivative parameters.This system using Visual C++ 6.0 as platform, design an application interface to display V～I, P～I, IdV/dI～I, dP/dI～I curves and electrical derivative parameters of semiconductor lasers. In serial port communication, we use MSComm activex to send and get data. In interface displaying, median filter, numerical differentiation and curve fitting are applied to display curves and extract parameters. Besides, on the base of partial differential equation, we use nonlinear diffusion filtering method to denoise the electrical derivative data according to its denoising theory. The specialty of this method is that it can protect the curves'characteristic from distortion and effectively reduce the noise in electrical derivative data and preserve the dip at threshold.The system can measure V～I, IdV/dI～I, P～I, dP/dI～I of semiconductor lasers and provide parameters such as threshold current Ith, junction characteristic parameter m, junction voltage saturation parameter h, intercept b, peak, etc. to evaluate the quality and reliability of devices. Several batches of high power semiconductor lasers of different structure have been tested and the results indicate excellent performance and stability of the system. The experiments show that most of semiconductor lasers with high reliability have normative electrical derivative curves and proper parameters. Those with small Ith, m, b, peak. are usually devices of high reliability. For junction voltage saturation parameter h, it has different value by its internal structure. As for high power AlGaAs/GaAs semiconductor lasers, with high reliability devices have junction characteristic parameter m between 1.3～2.0, junction voltage saturation parameter h between 20～50mv, intercept b between 0～0.04; As for high power InGaAsP/InGaP/GaAs semiconductor lasers, with high reliability devices have junction characteristic parameter m between 1.4～2.0, junction voltage saturation parameter h between 0～5mv, intercept b between 0～0.05. But there also have exceptions sometimes. For example, some devices with proper electrical derivative parameters have been proved to have poor quality by electrical aging tests while some other devices with bad parameters proved to be high reliable. Perhaps there are some other factors, which lead to the degradation of semiconductor lasers, have not been embodied by the parameters we have acquired. It needs further study in future.