Study On The High Frequency Modulation Technology Of High Power Semiconductor Laser

Semiconductor laser has the advantages of high reliability,small size,and direct modulation characteristics.The development of semiconductor laser is closely related to the high and new technology of laser communication and laser radar.The direct modulation system of high power semiconductor laser is playing a more important role.Because the quality of the modulation laser determines the performance of the laser high frequency modulation system that is designed by using direct modulation mode,and the quality of the modulated laser depends on the performance of the drive system.So designing the modulation drive system with excellent performance has important practical significance.We studied the factors that affect the high frequency modulation performance of semiconductor laser in the process of direct modulation.The equivalent circuit model of LD is derived from the rate equation of semiconductor laser,which was established by using Pspice.We analyzed the effects of the parasitic parameters,the DC bias and the current modulation intensity on the high frequency modulation characteristics of the laser,and put forward the corresponding methods to improve the performance of the modulation.We designed two laser modulation systems by studying the high frequency modulation characteristics of semiconductor laser.Firstly,we designed a direct modulation system of semiconductor laser without DC bias.We simulated the direct modulation drive system of semiconductor laser and developed a laser modulation system.This system can output modulation laser that frequency is 1MHz and the average power of the laser is 1.1W.Secondly,in order to output high frequency modulation,we designed a high frequency modulation system of semiconductor laser which is composed of a signal magnifying circuit,a current modulation circuit,an over current protection circuit and a DC bias circuit with slow start function.The high frequency modulation drive system of semiconductor laser uses a simple structure of the direct modulation method.The direct modulation method is that control laser intensity of semiconductor laser by using a signal of adjustable frequency.We simulate the high frequency modulation drive system of semiconductor laser by using OrCAD/Pspice.The high frequency modulation system of the semiconductor laser can output laser that frequency is 40 MHz and the average power of the laser is 300 mW.And this drive system of the semiconductor laser output the modulation current that frequency is 40 MHz,DC bias is 493.326 mA and peak value of sine wave modulation is 850 mA.