Measurement Of Dynamic Intrinsic Linewidth Of Interband Cascade Lasers In Its Tuning Process

As a new type of mid-infrared light source,interband cascade laser(ICL),with the properties of low power consumption,high side mode suppression ratio and high quantum efficiency,have been widely deployed in many types of applications such as trace gas spectrum detection and coherent optical communication.And its linewidth properties,which refer to important parameters for characterizing its coherence and spectral purity,are of great significance in its application.Therefore,it is of great importance to perform the dynamic intrinsic linewidth measurement of the interband cascade laser.The main work of this paper includes:Firstly,a measurement method of dynamic intrinsic linewidth was proposed.Combined with the analysis of dynamic linewidth measurement signal model,and fully considered the effects of laser driver current noise and laser temperature noise on linewidth measurement,the measurement method was proposed and the experiment system was designed.The dynamic intrinsic linewidth measurement of ICL was realized,which verified the accuracy and reliability o f the method.Secondly,an Adaptive Initialization Levenberg-Marquardt(AI-LM)fitting algorithm was proposed.The second iterative fitting method was used,and the corresponding fitting parameters of iterative fitting in first iteration was used to predict the relevant parameters of initial value in the second iteration.Combined with the idea of feedback iteration,The optimal iteration initial value was found and the multi-parameter fitting of nonlinear functions was realized.This method effectively reduced the fitting errors due to the unreasonable initial value and improve the fitting result precision.Thirdly,The influence mechanism of the laser parameters on dynamic intrinsic linewidth in ICL was obtained.According to the comparison of the linewidth characteristics under different operating current,It was found that the dynamic intrinsic linewidth decreased with the increasing injection current and the effect mechanism is related to optical power and subject to the gain coefficient of ICL.Based on the analysis of linewidth characteristics at different temperature,the influence mechanism of temperature on dynamic intrinsic linewidth is obtained.Combined the evaluation of linewidth under different tuning frequency,the negative correlation between the ICL intrinsic linewidth and the tuning frequency is clarified.And It was verified the correlation coefficient is affected by the injection current variation.The work is of great significance for the comprehensive understanding of lasers.In this paper,the AI-LM fitting algorithm was proposed and applied to the measurement of the dynamic intrinsic linewidth of the laser.The dynamic intrinsic linewidth measurement of ICL in the current tuning state was realized for the first time.The influence mechanism of tuning current,tuning frequency and working temperature on the intrinsic linewidth of the laser was studied.The work reveal the contribution of operating current,tuning frequency and operating temperature to laser dynamic linewidth,which give us a more comprehensive understanding of lasers and provide technical guidance for laser structure and process optimization.