Derivative Measurement Of High-power Laser Diode And Its Array

High power laser diode (LD) and laser diode arrays (LDA) have been used widely in many fields, such as environment monitor, manufactory, medical treatment, communications, scientific research, military affaires, etc., and the LD is a crucial component which can determine the reliability of the whole laser system. The research on the quality and the reliability of the LDA is vitally significant for fabrication and applications. The usual method of evaluating the quality and the reliability of LDs is by electrical aging. The LD works under the certain temperature and driving current, and the devices with large variation rate of output optical power at certain driving current are screened out. Since every device has to work under the aging conditions for a period in this method, the lifetime of the device will inevitably be shortened. This method has the demerits of the high equipment cost, critical aging condition, long test time. And also it's impossible that the unreliable LDA device was screen out by aging test.The reliability of the LD and the bar is studied by the electrical derivative technology. A measurement system of electrical derivative based on virtual instruments technology is established. The hardware the software and their modification of the system are presented. For example, the voltage is got by the four-wire resistance method; the print and preview function is added to the test program with CFormView base class. The time for the data receiving in the program is adjusted according to the resistance test. The test chambers and the DC powers for both the single LD and the LDA are integrated in one test system and controlled by one PC program. The precision, repetition and convenience of the test system are improved remarkably.More than 100 LDs and several tens of LDAs are measured and analyzed by the test system. According to the characteristic of the bar, the new parameter Q which denotes the ratio of the height to width of the peak on the d2P/dI2~I curve is presented. After compared with the spectrum of device, the work condition of laser diode near the theoshold can be shown with the parameter of Q. The device with a larger value of Q parameter has the better uniformity and reliability. The result shows that the values of h parameters of no-aluminum LD are less than others', and the affection factor is summarized and demonstrated. For better understanding of the work condition of LDA, the virtual bar composed by several LDs parallelly connected is measured by another measurement system. The optic power of every single LD of a virtual bar is tested respectively and the results are transfered to the computer, then dealt with by a program. In this way, the condition of every unit emitting in one LDA is researched. The analysis of the result indicates that the bar with good uniformity has a good reliability. The equivalent circuit of high power bar is established. The bars with different uniformity are simulated by MATLAB software. The simulation results and derivative curves show that the derivative parameters h, m, b, Ith, Q, et al. of the bars are directly interrelated to the uniformity and the reliability of the bar. The values of the parameter should be within a certain range. The device with a good reliability usually coincids the condition mentioned above. On the other hand, the result demonstrates that the derivative measurement is an effective method to evaluate the reliability of laser diode bar. This method is a nondestructive, easy and fast method. The comparison of the values of Q and the result of spectrum from device also proves the conclusion.The parameters and curves of the derivative method correspond to the reliability of the bar. And this method can be used to evaluate the high power LD and LDA nondestructively. The result can help to analyze the mechanism how failure is caused. The prospect of the derivative method is nice according to my research work.