Research On Non-destructive Test For Semiconductor Lasers And Laser Arrays

With the development of optoelectronic technology, high power semiconductor lasers (LDs) and laser arrays (LD arrays) have been used widely in military affaires, medical treatment, communications, etc., and the quality and reliability of the LD devices are of great importance to the application system. Reliability research on semiconductor lasers are of vital significance to both manufacture and application. The usual method to evaluate the quality of LDs is to carry out electrical aging tests by increasing temperature and driving current, and screen out the 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. In this method, even the devices of high reliability will also have to undergo electrical aging tests for a certain length of time, which shortens the devices'lifetime undoubtedly.This thesis originates from a high technology key project (No.200403001-4) of Jilin Province. The goal of the project is to establish a test system for high power semiconductor lasers and laser arrays, mainly using the technology of electrical derivative.This paper summarizes the reliability research methods of semiconductor lasers and then points out that the electrical derivative technology is a simple, fast and nondestructive method to estimate the LDs'reliability. On the base of the former measurement methods for electrical derivative, this paper proposes a new measurement method based on virtual instruments technology, and has designed a test system on NI virtual instruments development platform. The system can measure V～I, IdV/dI～I, P～I, dP/dI～I d2P/dI2～I etc. of LDs and provide parameters such as threshold current, equivalent series-wound resister, characteristic parameter of junction, junction voltage saturation parameter etc. to evaluate the quality and reliability of the 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 validity of the electrical derivative method to evaluate the quality of LDs has been proved by electrical aging tests, which show that most of the LDs with high reliability have normative electrical derivative curves and proper parameters. Those with small Ith, m, b, etc. and big h are usually devices of high reliability. 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 LDs, have not been embodied by the parameters we have acquired. The paper discusses on the problem that the high power InGaAsP/InGaP/GaAs lasers have small junction voltage saturation parameters, which belongs to the latter exception. The analysis show that the weak carrier limit of the InGaAsP/InGaP/GaAs lasers leads to the increase of minor carrier leakage and the decrease of junction voltage saturation parameters'value.Then the paper tries to generalize the technology of electrical derivative to test the array devices nondestructively. A test system has been established which can acquire the LD arrays'electrical derivative curves and the related parameters similar to those of the single LDs'. We have carried out electrical derivative tests for several batches of LD arrays of different reliability, and analyzed the characteristic of their curves and parameters. The analysis results indicate the feasibility of the electrical derivative method to evaluate the LD arrays'reliability. The results also points out that the reliability criterions for LD arrays are similar to those for LDs, that is, those with small Ith, m, b, etc. and big h are usually devices of high reliability. The method, which can directly prove the validity of electrical derivative method to evaluate LD arrays'reliability, is electrical aging tests. Because of the great power consumption and high cost, it's nearly impossible for us to carry out electrical aging tests on batches of LD arrays. So we try to study the relationship between LD arrays'electrical derivative parameters and their reliability using the tests on parallel connected LDs. We have summarized the reliability criterions for LD arrays according to the theoretical, simulated and experimental results, and the conclusion is basically the same with our former prediction. Though it cannot replace the electrical aging tests completely, the tests on parallel connected LDs can simulate the LD arrays'behavior to a certain extent, which can offer references for the criterions of LD arrays'reliability.In order to eliminate the affection of the noise during the course of electrical derivative measurement, the nonlinear diffusion equation is applied 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. Experiment results indicate that the method can effectively reduce the noise in electrical derivative data and preserve the dip at threshold.