Research On High Efficiency 980 Nm Vertical External Cavity Surface Emitting Semiconductor Lasers

Optically-pumped vertical external cavity surface emitting laser(VECSEL)has both advantages of high conversion efficiency of semiconductor laser and easy transverse mode control of solid-state laser.It can achieve high-power laser output and near-diffraction-limited beam quality,and has flexible external cavity structure.By adding optical elements in the cavity,various functions such as frequency doubling,mode locking,wavelength tuning can be realized.Thanks to the rich wavelength coverage range of semiconductor material band engineering technology,VECSEL can output lasers from visible light to infrared band,thus attracting wide attention in recent years and becoming a hot research direction of semiconductor lasers.VECSEL can obtain much higher output power than conventional vertical cavity surface emitting semiconductor lasers,but its conversion efficiency is relatively low.This thesis mainly focuses on how to improve the conversion efficiency of opticallypumped vertical external cavity surface emitting semiconductor lasers,a key scientific problem.Taking 980 nm VECSEL as an example,we carried out research on highefficiency VECSEL principle and chip design,lateral lasing principle and suppression research and high-efficiency VECSEL preparation and performance analysis.The research contents are as follows:(1)Research on optically-pumped VECSEL principle and chip designThe working principle of optically-pumped VECSEL gain chip was systematically studied.PICS3 D software was used to simulate the influence of different well compositions and thicknesses on emission wavelength and gain.The optimization of composition and thickness was completed and periodic gain structure was realized.The analysis method of reflectivity of reflector was explored.Based on transmission matrix theory,the reflectivity of distributed Bragg reflector(DBR)and dual-band distributed Bragg reflector(DBM)were simulated respectively.The influence of curvature radius of external output coupling mirror and external cavity length on spot diameter on gain chip was studied.The main heat sources of VECSEL and common methods of heat management for VECSEL are analyzed.Based on solid heat transfer theory,the heat dissipation capacity of two structures: substrate-removed bottom-emitting structure and bonded high thermal conductivity diamond heat sink were simulated respectively.The performance of gain chip was studied.(2)Research on lateral lasing phenomenon suppressionThe principle of lateral lasing phenomenon generation was explored,as well as its influence on VECSEL output efficiency.Several methods for suppressing lateral lasing phenomenon were studied at present,and proposed for the first time a lateral laser suppression method using large gain and cavity mode detuning.A 30 nm detuned VECSEL gain chip was designed and fabricated.By controlling temperature to adjust detuning degree,lateral lasing output intensity at working temperature 0°C、10°C、20°C were measured by side measurement respectively.The experimental results show that lateral lasing output intensity decreases,and 0°C has more obvious suppression effect than other two temperatures.It is concluded that large detuning between gain and cavity mode structure is conducive to suppress lateral lasing phenomenon.(3)Preparation and performance analysis of 980 nm high-efficiencyVECSEL Based on the research on suppression of lateral lasing phenomenon,the design optimization for gain chip was carried out,and a bottom-emitting structure980 nm gain chip was fabricated.A 25 nm large mismatch between gain peak wavelength with cavity mode wavelength was introduced,a DBM reflector with higher absorption for pump light than DBR reflector,and bonded high thermal conductivity diamond heat sink to reduce thermal resistance.A straight-type cavity for output test,the highest output power at-15°C.When pump power is 90 W,output power reaches 34 W.Maximum slope efficiency is 47%,optical-optical conversion efficiency about 47%.Output power and efficiency are leading in China.In addition,a high-efficiency VECSEL with in-well pumping at 1150 nm was also fabricated.The highest output power at-10°C,is 3 W when pump power is 27 W.Maximum slope efficiency is 46%,optical-optical conversion about 16%.