Research On Tunable External Cavity Quantum Cascade Laser In Mid-infrared Waveband

The mid-infrared band external cavity quantum cascade laser(EC-QCL)has a series of unique spectral properties that can be widely used in spectroscopy,gas detection,protein detection,medical diagnosis,free-space optical communication and other fields.In particular,its advantages of wide tuning range(up to hundreds of wave numbers)and good stability make EC-QCL show great potential for applications in many fields.This paper introduces the research progress of the Littrow structure,Littman structure and fiber Bragg grating structure of EC-QCL,and summarizes the development and research results of EC-QCL.the application research of EC-QCL in gas molecule detection,protein detection,industrial detection etc.show its practicality in various fields.It is shown that the use of blazed grating as optical feedback element not only can achieve wide tuning,but also low cost,which is conducive to reduce the complexity of EC-QCL structure,therefore,the use of blazed grating as optical feedback element is the mainstream direction of EC-QCL,and EC-QCL also provides further new options for multi-component detection.In this paper,we will investigate the effect of different blazed gratings on the performance of EC-QCL by using Littrow structure to obtain modular EC-QCL,and then research the ultra-wideband tunable structure of EC-QCL to obtain wider tuning range of EC-QCL.First,we analyze the development status and research application of EC-QCL,and provide an in-depth analysis of the luminescence principle of QCL and the feedback selection mode of its external cavity structure.Second,a 4 μm broad-spectrum tunable EC-QCL module based on the Littrow structure is designed.The 4 μm QCL gain chip is used in the structure,and different external cavity structures are formed using 450 lines/mm and 300 lines/mm blazed gratings,respectively.The output optical power is 7.30 m W at an injection current of 303 m A with a tuning range of 380nm(3774～4154 nm),a side mode rejection ratio(SMSR)of 20 d B,and a high order mode excitation phenomenon when using a 450 lines/mm blazed grating.The EC-QCL output power is 5.24 m W at 303 m A injection current with a tuning range of 297 nm(3779～4076nm),SMSR of 20 d B,and fundamental mode excitation using a 300 lines/mm blazed grating.By comparison,different external cavity structures can be used to obtain EC-QCL performance focusing on different aspects,thus better fitting the corresponding application scenarios.Third,a laser structure with a larger tuning range is obtained.An ultra-wideband tunable EC-QCL based on the combined beam of two gain chips is designed.The EC-QCL is based on the Littrow structure and uses two QCL gain chips with center wavelengths of 4.0 μm and4.6 μm to provide optical gain.The two QCL gain chips work in an alternating and complementary manner to achieve ultra-wide spectrum tuning from 3 ～ 5 μm.The laser operates at a blazed grating rotation angle of 34.54°～46.50° with a wavelength tuning range of 3779～4836 nm(including the 179 nm wavelength tuning gap)at a temperature of 25°C and 303 m A injection current,with a maximum output optical power of 14.12 m W and an SMSR of 20 d B.The laser has the advantages of compactness and ultra-wide tuning range,and is suitable for the development of ultra-broadband portable modular lasers.The laser has the advantages of compact structure and ultra-wide tuning range,and lays the foundation for the development of an ultra-broadband portable and modular mid-infrared EC-QCL.