Vertical Cavity Surface Emitting Laser Integrated Micro-Optics Onto Surface

The inherent advantages,longitudinal single mode emission,circular beam shape,ultra-low threshold currents and power consumption,make the vertical cavity surface emitting laser?VCSEL?to be the economical-and energy efficiency-light source in the areas of optical fiber communications,optical interconnection,high-speed laser,laser printing and light detection and ranging?LiDAR?.However,the multi-transverse-mode operation,intrinsic large divergence angle and poor beam quality suffered by the unprocessed VCSEL raise the cost for beam-shaping,packaging and optical fiber coupling,restrict the application areas.Improving the transverse mode property,compressing the far-field divergence angle and obtaining high beam quality are of crucial importance for practical application.In my work,the finite-different time-domain method was applied to model the complete micro-lens integrated VCSEL and non-periodic wide-angle beam steering high index contrast grating?HCG?integrated VCSEL array.The influence of micro-lens on the modal property,far-field patterns and beam quality factor of micro-lens integrated VCSEL was investigated in our simulation.The direction of beam emitting with designed defection angles was simulated in our proposed non-periodic HCG integrated VCSEL array.1.Device model and simulationsWe built a photonics micro-cavity model in FDTD software to simulate a complete micro-lens integrate VCSEL.In the simulation model,the dipole source was deviated from the center of the VCSEL mesa,the aspheric constant and diameter of the micro-lens were set to be 2 and 9?m respectively.To simplify the difficulty of modelling the micro-lens with alternating material and layer thickness,a homogeneous GaAs aspherical micro-lens was used for displace the practical etched distributed Bragg reflector?DBR?micro-lens.In the simulations,we just changed the height of the micro-lens to obtain the micro-lens with different curvature radius.The modal property of the VCSEL integrated with different curvature radius?with micro-lens height 100nm,150nm,200nm,250nm,300nm and 350nm.?was investigated.The curvature radius of micro-lens less than 40.63?m and larger than50.70?m was beneficial to the micro-lens VCSEL emitting fundamental mode.2.high beam quality monolithic micro-lens VCSEL fabrication and characterizationThe diffusion limited wet chemical etching method was applied to etch the micro-lens on the output window of the top-emitting VCSEL.The wet chemical etchant was a mixture of H₂O₂,HBr,CH₃OH and H₂O at the ratio of 1:1:1:10 in volume.In our work,the etch rate was slowed down and kept at a steady value in the static undisturbed environment by decreasing the temperature of the mixture liquid,that was came true by putting the beaker with etchant in the ice water and maintaining it for some time.The methanol was added to dissolve the producing Br₂ molecular and make it adhere to the etching surface better for smoother etching surface.The spatial variation in the etching rate at the edge and the center region of the circular-hole enabled an aspherical profile on the surface of emitting window to be formed.Eventually,the VCSELs integrated with micro-lens with curvature radius31.78?m and 55.63?m were fabricated in our work.The modal property,P-I-V characteristic,and far-field divergence angle and beam quality factor M² for three types of VCSEL,VCSEL with curvature radius 31.78?m,VCSEL with curvature radius 55.63?m and reference VCSEL,were compared.The minimum beam quality1.9,minimum far-field divergence angle 4.2°and single-mode lasing spectra with side mode suppression ratio?SMSR?were obtained from the VCSEL with curvature radius31.78?m,and this VCSEL with threshold current 1.2mA and maximum output power1.3mW.3.multi-angle beam steering non-periodic high index contrast grating integrated VCSELThe non-periodic high-index contrast grating with a given period and duty was designed to manipulate the wave-front phase shift of the beam and further realize multi-angle beam steering.The finite difference time domain method was used to simulate the grating bars with a specific sorting order,and the beam steering angles of-10.644°,-21.176°,-28.307°,10.644°,21.447°,and 28.418°were obtained.Based on the multi-angle steering high contrast grating?HCG?array,a vertical cavity surface emitting laser?VCSEL?source with multi-deflection angle beam steering ability was proposed to meet the requirement of wide-field light detection and ranging source.The tiny and easy integration of wide-angle emitting VCSEL light source system can cater to the compact and miniature LiDAR systems.