Research On The Lateral Beam Quality Of High-power Broad-area Diode Lasers

High power diode lasers with broad-area(BA)waveguide have desirable properties in terms of high output power,good reliability,long lifetime,compact size,wide wavelength range and so on,thus it is a widely used laser source.However,the BA diode lasers operate with multi-mode in the lateral direction(parallel to the epitaxial layer),deteriorating the beam quality.In addition,with the increasing of injection current,the lateral far-field is broaden,which limits further applications.Therefore,we introduced some micro-structures to the BA diode lasers and improved the lateral beam quality.In addition,the sensitivity of lateral far-field on the current was decreased greatly.The BA diode lasers with micro-structures have numerous advantages,like low cost,easy fabrication,suitable for mass production.This lays a good foundation on the development of high power high beam quality diode lasers.The objective of this thesis is to improve the lateral beam quality of high power BA diode lasers.The main work is follows:1)For BA diode lasers,the method of effective index approximation is used to solve the carrier-diffusion equation and the wave equation self-consistently.Then we comprehensive research the impact of different lateral modes on the near-and far-fields and obtain approaches of optimizing lateral beam quality.2)The lateral ridge waveguide(LRW)structure is introduced to a BA diode laser.The BA diode lasers with LRW structure and without were fabricated and the influences of LRW on the output power,near-and far-field were investigated.The best overall performance is obtained from the BA laser with length of 20% the cavity length.Due to the small gain fluctuation,the output power increases by 3% and more uniform near field is obtained.The optimized LRW laser successfully decreases the lateral divergence from 10.54° to 8.51° at 4 A current.Meanwhile,limiting the lateral divergence rise to 0.13° per ampere of current increase,compared to 1.27°/A for the standard BA diode laser.3)The spatial current modulation(SCM)structure is applied to BA diode laser after optimizing by software(LASTIP and PICS3D).The SCM structure forms a two-dimensional current flow,resulting in periodical gain-loss along lateral and longitudinal directions.Therefore,current spreading and the carrier density accumulated at the mesa edges are reduced.The BA diode lasers with SCM structure and without were fabricated with 64 ?m width and 1240 ?m cavity length.The beam parameter product(BPP)of SCM laser is decreased by 36.5% and injection current insensitive lateral divergence is realized.At the same time,the line-width is decreased about 45%,which is in accordance with simulation.4)Based on the doping distribution and waveguide characteristic of BA photonic crystal laser,a ladder-like groove structure(LLGS)is proposed.The etched groove removes the gap layer near the injection current area,resulting in suppression of lateral current spreading.The other etched groove forms an index step in lateral direction,which increases the threshold of high-order modes.84 ?m wide stripe and 1700 ?m long cavity devices with and without structure were fabricated and tested.Comparing with stand laser,about 15.4% improvement in output power and 25.2% decrease in lateral BPP is realized.