Photodetector Equivalent Circuit Model And Parameter Extraction

The rapid development of optical fiber communication technology put forward a great demand of the sensitivity, the response rate and the reliability of optical fiber communication systems. Simple combination of discrete optoelectronic devices has been difficult to achieve the desired results. High-speed,highly integrated optoelectronic integrated circuit (OEIC) has become a hot research. The equivalent circuit model of discrete optoelectronic devices for accurate simulation of OEIC is indispensable, photodetector is a key part of optical receiver of OEIC, so the study of equivalent circuit model of photodetector is of great significance. This paper established the equivalent circuit models of the avalanche photodetector (APD) and PIN photodetector, at the same time, the study of simulation analysis and parameter extraction were done.First, this paper describes the working principle of the optical detector, and discussed the basic parameters of it, including responsivity, quantum efficiency, dark current, noise current, response time and bandwidth characteristics. To provide a sufficient theoretical basis of he follow-up study, a detailed analysis of the average avalanche gain and the distribution of electric field of APD were done.Then, based on the working principle and performance parameters of photodetector, a new APD equivalent circuit is established, which included the dark current, noise current and parasitic effects. It can accurately reflect the performance of the device. In order to verify the accuracy of the model, the equivalent circuit module of APD was builted in the PSpice software. Based on the module, the basic parameters of the APD were simulated, Structural parameters on the performance of APD are discussed, APD package structure parameter optimization problem is studied. From the analysis we get: APD gain, bandwidth were mutual restraint, the bandwidth product is approximately a constant in the high-gain region gain; the structure parameters of the layers determines the performance of APD, rational design of the thickness of each layer are needed to get APD with ideal performance; during the process of Optimized structure design of the package, the appropriate choice of the length of gold wire can improve the effect of APD frequency response. Finally, from the basic physical structure of PIN photodetector, we established a small-signal equivalent circuit model of PIN photodetector. Some improvements were made to Adaptive genetic algorithm, and based on the genetic algorithm toolbox (gatbx) of matlab, adaptive genetic algorithm program was prepared. the parameters of the equivalent circuit model of PIN photodetector were extracted by using adaptive genetic algorithm. the effective of the parameter extraction method and the rationality of the equivalent circuit model of PIN photodetector has been proved through comparing the test curves and the calculated curves of the S21 parameter.