The Response Characteristics Of Semiconductor Lasers Based On Rate Equations

High-speed modulated semiconductor lasers as a light source are key components in optical fiber communication systems; it is very active in its research. The pros and cons of Communication system performance are decided on the dynamic characteristics of the laser, so trying to use convenient and effective method to simulate and study operating characteristics of the light source, the factors that come to affect the performance of lasers will be got. It is vitally important to improve its performance, at the same time it can provides theoretical basis for optimizing the design and development of high-speed laser modulation bandwidth.In this paper, we studies the response characteristics of distributed feedback laser diodes(DFB-LD) mainly from the transient response and the modulation response based on rate equation theory, and establishes the equivalent circuit model of laser, simulating by two software MATLAB and PSpice.First of all, the rate equations of DFB-LD are established based on the traditional rate equations and the structure characteristics of DFB-LD, considering emphatically the spontaneous emission and gain saturation effect. On this basis, the SIMULINK model of rate equations is established used to analyze the effects on the transient response of lasers about the injection current and gain saturation factor. Then the rate equations are been used to differential analysis for the simple analysis of laser characteristics, we derive the relationship between modulation response (intensity modulation and frequency modulation), relaxation oscillation frequency and DFB-LD structure characteristic parameters under small signal approximation, and do simulation analysis using MATLAB software. The effects of the delay time, relaxation oscillation, gain saturation items, electrical parasitic parameters and temperature on the modulation characteristics are discussed emphatically, and the limited role of the phenomenon of frequency chirp to communication is studied, and has put forward the corresponding improvement measures. Research results provide theoretical basis on improving the high-frequency modulation characteristics and optimizing the device structure for DFB-LD.Lastly, in order to improve the design efficiency of semiconductor lasers, computer simulation methods for laser are researched: establishing small-signal equivalent circuit model based on rate equations of lasers and emphatically taking into account the gain saturation effect and the parasitic parameters. Simulating using general-purpose circuit simulation software PSpice and the outcome is more accurate, intuitive and easy to operate comparing with MATLAB simulation.