Research On Widely Tunable External Cavity Quantum Cascade Laser

The mid-infrared laser with wavelength range of 3²5μm has important applications in free space optical communication,infrared countermeasures,trace gas detection and so on.The unipolar quantum cascade laser based on the electronic transition of the guide belt inter-subband has become an ideal source in the infrared band with the advantages of miniaturize-tion,high resolution and high sensitivity.External cavity quantum cascade laser by external optical feedback components chosen mode realizes wide tuning and narrow linewidth,which has shown great application potential in many fields of military and civil,especially the deve-lopment of trace gas detection technology.Baesd on theoretical analysation,scheme design,prototype development and experimental research,this paper has developed a prototype with wavelength of 8¹0μm,and realizes wide tuning and narrow linewidth.Specific contents include:（1）Expound the application of the infrared quantum cascade lasers in the background and demand.Highlight the important application prospect of external cavity quantum cas-cade laser with wide tuning,narrow linewidth,analyzes the research present situation and development trend at home and abroad.（2）Carry out the theoretical analysation of external cavity quantum cascade laser.Based on equivalent cavity optical feedback model and rate equation on the basis of the external cavity quantum cascade laser theory model,analyze the gain and loss,threshold current,output power,and wavelength tuning characteristics of the laser.By using typical values numerical simulation,quantitatively discusse the laser output characteristics and the influence factors of wide tuning.（3）Develope a design of the wide tuning external cascade laser.By studying the cavity structure of the external cavity laser,the light-emittiing characteristics of gain chip,the wave-length tuning characteristics of the blazed grating,the collimation characteristics of path and the temperature stability,design a wide tuning external cavity quantum cascade laser.（4）Develop a miniaturized external cavity quantum cascade laser engineering prototype with wavelength 8¹0μm.Study the output characteristics of the external cavity quantum cascade laser at different grating diffraction angles,temperature and drive current,the power–current characteristics at different wavelengths,line width characteristics and stability.The overall size of the system is 76×54×50mm³.In the pulse mode,temperature 22℃,peak current 2.1A,pulse width 300ns,duty cycle 5%,the maximum tuning range of the laser is334cm^-1,the maximum output power is 17.7mW,the linewidth is less than 1cm^-1 in the entire tuning range,the wavelength fluctuation is less than 0.12cm^-1,and the power fluctuation is less 4%.