Development Of An Embedded System For Measuring The Electrical Derivative Of Semiconductor Lasers

Since the successful development of semiconductor lasers in the 1960 s,with their progress,they have been applied in more and more fields.Especially the application in fields such as communications,information storage,medical treatment,measurement and military use has placed increasingly higher requirements on performance of semiconductor lasers.It has become an important task to evaluate the reliability of a semiconductor laser unit through correct and efficient measurement of its characteristic parameters.This paper aims to develop a high-performance testing system for high-power semiconductor lasers by focusing on measurement of relevant electrical derivatives.This paper firstly summarizes the development of semiconductor lasers and then briefly introduces the application of such units,as well as the development of relevant electrical derivative measurement.With respect to big drive current of high-power semiconductor lasers,this paper proposes a testing method with variable-step sweep current to measure electrical derivatives of high-power semiconductor lasers to realize fast and correct measurement of photo-electric characteristic parameters under the condition of fewer data collected.Firstly,this paper establishes the experimental environment according to the experimental plan,and designs and makes the driving and sampling circuits of a semiconductor laser unit to realize the sampling of terminal voltage and optical power.Then,it transmits measuring data to the PC through serial ports of the existing single-chip microcomputer,and then processes obtained data through Matlab on the PC.Relevant content includes signal filtering,derivation and research of the variable-step algorithm.Finally,it establishes mathematic models to design relevant algorithm.After successful research of the variable-step algorithm,based on the selected measuring method,this paper designs hardware circuits of the testing system,including control circuits of the single-chip microcomputer,driving and testing circuits of the semiconductor laser unit,power supply circuits,etc.Relevant software is designed with the high level C programming language on the Keil platform.The system is programmed to obtain electric and optical derivatives of collected voltage and optical power data through numerical differentiation,draw data curves,display such curves and relevant parameters on the LCD screen,and store them in the memory card for convenient analysis and treatment on other platforms.In addition,methods such as least square fitting and linear regression are applied to obtain correct parameters such as the threshold current Ith,pre-threshold slope RS1,post-threshold RS2,post-threshold intercept b,junction characteristic parameter m,junction-voltage saturation depth h,slope efficiency ES of optical power curves,and maximum testing optical power Pmax.The testing system developed by this paper can independently measure electrical-derivative parameters of the semiconductor laser unit and draw relevant electrical-derivative characteristic curves,without connection to the PC.Based on testing results we can make the judgment regarding the quality of this semiconductor laser unit.With the variable-step testing method,only 150 sets of data are needed for each laser unit to get its corresponding parameters precisely,with testing time less than 10 seconds.In a word,the system features fast and correct testing,minor damage to the unit and high testing efficiency.