Research On Prism Beam Based Grating External Cavity Semiconductor Laser

External cavity semiconductor laser with single longitudinal mode,narrow linewidth,tunable,high stability and other advantages,in optical storage,optical frequency standard,high resolution laser spectroscopy,atomic physics and other fields has a wide range of applications.Laser linewidth as a main technical specification,has received considerable attention.In this paper,a new method for realizing an external cavity semiconductor laser with narrow linewidth is presented.Firstly,the working principle of external cavity semiconductor lasers is introduced.The basic theoretical knowledge of external cavity linewidth narrowing and continuous tuning is analyzed.At the same time,the principle of prism beam expender and narrowing the laser beam linewidth is studied.A grating external cavity semiconductor laser is designed based on the prism beam expander and completed the machining.Second through the mathematical model of the laser laser frequency stabilization,the stability of the system is simulated.a new control scheme was put forward,completed the long-locked laser.The performance of the laser is tested,and the relationship between the current,wavelength,power and temperature is obtained.In the end,the linewidth parameters of the improved laser and the original laser are compared with the experimental results of the beat frequency experiment and self-heterodyne experiment,further evidence of the superiority of linewidth narrowing with the prism beam expander.Specifically including the following aspects:1.The working principle of external cavity semiconductor laser is summarized.In this chapter,the theoretical analysis and calculation of the laser diode emitting mechanism are introduced,and the role of the external cavity in the tuning and linewidth narrowing is introduced.Through the introduction of selection mode of the grating,the tuning theory of grating external cavity semiconductor laser is analyzed,and presents a scheme of realization of continuous adjustable.Further more,this chapter introduces the filtering technology in the tunable laser,mainly through the dispersion filter element modeling analysis of the beam splitter and the grating.The effect of the dispersion filter on the linewidth narrowing is discussed.Finally,the linewidth expression of the grating external cavity semiconductor laser is calculated.2.The design scheme of the external cavity semiconductor laser based on prism beam expander is introduced.The selection and parameters of each component are determined.The installation method and mechanical structure of the various components are analyzed in detail,and then the mechanical structure of the laser is designed by using SolidWorks software completed the machining and assembly.In addition,the principle of the laser control system is analyzed,especially focusing on the drive circuit and the control circuit.Finally,the entire laser is completed.3.A method for stabilizing laser frequency stabilization is proposed.The dual PID phase locked loop is used to control the piezoelectric ceramics and the temperature control element,and it can also overcome the fast and slow external disturbance at the same time.It can meet the requirement of the long-term lock.Theoretically,the mathematical model of the laser frequency stabilization system is established.According to the influence of environmental factors,the disturbance term is introduced.As a result,the monotonous and continuous changing environment disturbance will cause a steady-state error in this theory model.The simulation results show that the dual PID control can improve the steady-state performance,adjusting time,and overshoot.Finally,the laser lock is locked on the Fabry Perot(F-P)etalon with stable frequency by using the standard PDH.4.The performance of the semiconductor laser is Tested and evaluated,and the relationship between the current,wavelength,power and temperature is obtained by experiment.Further more,using self-heterodyne experiment,the linewidth parameters of the improved laser and the original laser are compared,and the results further proved the advantages of the prism beam expander on the narrow linewidth.At the same time the experimental results of the beat frequency experiment verify the accuracy of the selfheterodyne experiment.At last,the advantages and the need for improving place of the new type structure laser are analyzed.