Modeling On Energy Level And Development Of Driver For Quantum Cascade Laser

At present,the detection of CO toxic gases are mostly adopted laser spectroscopy technology,which is mainly applied quantum cascade laser as light source with the advantages of narrow linewidth,high sensitivity and fast response,and the output characteristics of light source seriously affect the detection accuracy of gas detection system.The output characteristics of the device can be optimized and improved by the establishment of the equivalent circuit model of quantum cascade lasers and the design of the excellent driver.Therefore,it is significant to study the modeling and driver of the quantum cascade lasers.Two aspects have been studied in the paper,in term of the light source of the CO gas detection system-quantum cascade laser.On the one hand,the model of the new two-level quantum cascade laser is established by analyzing the energy level structure,the transition mode and the working mechanism of the quantum cascade laser.The influence of spontaneous emission is considered in the output characteristics of the device,and this model is not only successfully more simplified compared with the traditional equivalent circuit model,but also made up for the shortcomings of the traditional two-level equivalent circuit model.DC,transient and communication of equivalent circuit are analyzed by OrCAD PSpice software,and at the same time the influence factors of its P-I and delay characteristics are analyzed,finally the P-I and delay characteristics of three different wavelength?5?m?9?m?103?m?quantum cascade lasers are verified and compared.The established equivalent circuit model is not only contributed to optimizing device structure,but also helped to design the system of driving power.On the other hand,a driving power is designed for the4.76?m wavelength quantum cascade laser provided by Chinese Academy of Sciences.It is mainly composed of linear soft-start power,signal generator,constant current source,current-limit protection,communication and display module.The driving range of the power is 0-1A,which can realize modulation/scanning function and current-limit protection function,at the same time it can communicate with the computer in real time,which can real-time monitor and storage the data of the laser's working current.The experimental results show that the maximum error between the setting current of driving power and the actual working current is the 0.44m A?within0-1A?,the maximum error of voltage signal by ADC collection is less than±1.8m V,the current stability of the driver when driving different loads?1-10??is 6.0×10^-5,and the current stability of long time?40h?is 3.7×10^-5,this driving power satisfies the driving requirement of quantum cascade laser.Finally the driving power is successfully applied in CO gas detection system,1f signal and 2f signal curves with gas concentration are obtained in combination with the optical system,the gas distribution system and a lock-in amplifier.By linear fitting,the fitting goodness of 1f and 2f are 0.996 and 0.993 respectively?CO gas concentration within 10-100ppm?.The innovation points:1.The equivalent circuit model of the new two-level quantum cascade laser is successfully established,which takes into account the influence of the spontaneous emission in the output characteristics of the laser,and simplifies the model without affecting its performance.2.It is developed that a portable,low cost driver with perfect protection function?soft start protection,over-current protection,reverse protection etc.?for mid-infrared quantum cascade laser,and which is successfully applied to the CO gas detection system.In the case of satisfying the driving demand,the cost is only 1/10¹/100 of the commercial instrument price.