Studies On 970nm High Brightness High Power Tapered Semiconductor Laser

High-power and high-brightness semiconductor lasers（LDs）have broad application prospects in laser processing,free-space communications,medical,pumped solid-state and fiber lasers,etc.Tapered semiconductor laser（TLD）has higher beam quality and Optical Catastrophe Damage（COD）threshold,which can achieve high brightness and high power output.In this work,TLDs with different geometries are simulated and optimized by numerical simulation,and the optimization of the fabrication process and output characteristics of the separated contacts tapered laser（SC-TLD）are deeply studied.The specific work is as follows:1.Aiming at the design of TLD devices,the main reasons that affect the quality of TLD beams are analyzed:beam self-focusing,filament phenomenon,etc.,and the ways to effectively improve TLD beam quality are given.The low mode gain（LMG）epitaxial waveguide structure has a small optical confinement factor（Γ<2%）,which can effectively reduce the occurrence of nonlinear effects such as self-focusing.Through the simulation of symmetric and asymmetric waveguide structures,it is found that the asymmetric waveguide structure can better deviate the optical field from the active region,reduce the phenomenon of lasing high-order modes due to mode competition in the LD,and the structure has a higher COD threshold,which can improve the output power and reduce the far-field divergence angle of the device to a certain extent.2.A simulation of tapered semiconductor lasers has been done based on the wide-angle differential beam propagation method（WA-FD-BPM）in this work.The effects of structural parameters（such as ridge etching depth,taper angle,different ridge/taper length ratio,taper etching depth,and front cavity reflectance）on the beam quality and P-I-V characteristics of the device are analyzed in detail.The analysis shows that the geometric loss of the tapered waveguide is the main factor leading to the decrease in the slope efficiency of the device,and the optical pumping effect is an important factor affecting the deterioration of the beam quality.The beam quality can be improved by reducing the reflectivity of the front cavity surface of the device.3.In order to improve the beam quality of the device,avoid the self-focusing phenomenon,we fabricate the 970 nm SC-TLDs with different cavity lengths(L_RW=750μm,L_Tap=1250/3250/5250μm)of LMGs,by optimizing the semiconductor fabrication process and process.An analysis of the effects of injection current in the Ridge region and Tapered region on the output characteristics of SC-TLDs with different structures was studied.The results show that the same as the simulation results,the geometric loss of the tapered region is the main reason for decreasing the slope efficiency of the device and increasing the threshold current;the size of the injected current in the ridge region affects the optical gain of this part,and the appearance of high-order modes is the main factor to reduce the beam quality of the device.When the cavity length of the prepared device is L=4mm,the maximum output power is 5.15 W without COD and saturation,and the measured beam quality factor M² and brightness when I_RW=200 m A and I_Tap=6 A are 2.13 and 143.2 MW·cm^-2·Sr^-1,high-brightness and high-power output of the device is achieved.The research content of this paper has certain theoretical value and guiding significance for the design and research of tapered semiconductor lasers.