Carrier Injection Control For High-power Laser Chip

Diode lasers have many advantages,such as small size,wide wavelength coverage,high efficiency and good stability.Because of this,diode lasers have been used in a wide range of applications,such as pump sources for solid-state lasers,medical treatment,space communications,materials processing,laser displays and laser weapons.With the continuous development of the application,the requirements for the optoelectronic performance of lasers are no longer limited to high power,but also a high beam quality output while ensuring a high power output.In standard ridge lasers,narrow stripe width lasers can obtain better beam quality but lower maximum output power,while the maximum output power of wide stripe width lasers will be increased,but according to waveguide mode theory,wide stripe lasers will produce more higher order modes,so the lateral beam quality is poor.In addition,the diode laser will be accompanied by thermal lens effect,carrier accumulation effect and lateral leakage in the working process,which will further deteriorate the lateral beam quality.In this paper,the contradictory relationship between strip width and output power and beam quality is attributed to the fact that the standard ridge structure cannot separately confine carriers and optical field in the lateral direction.Therefore,based on the standard ridge structure,the lateral structure is optimized in this paper.The obtained step-ridge structure can realize the separate confinement of carriers and optical field in the lateral direction,weaken the accumulation of carriers at the edge of the injection area,reduce the lateral leakage current,and finally improve the beam quality of the laser.The main work and research results of this paper are as follows.(1)This paper introduces the basic working principle of laser and the basic parameters to judge the performance of laser.The loss path of laser in electro-optical conversion and the factors affecting beam quality are analyzed.The previous improvement methods and achievements are summarized.(2)Using PICS3 D software developed by Crosslight,a slotted ridge structure is designed to address the lateral leakage of carriers.The simulation of the semiconductor laser with different geometrical parameters and different injection area widths is carried out.The structure that can minimize the lateral leakage current needs the groove width as large as possible.In the limit case,the step-ridge structure is evolved.COMSOL software was used to simulate the optical field profile and carrier distribution of the step-ridge structure with different injection width.The simulation results show that the step-ridge structure can realize the lateral separation confinement of carriers and optical field.In the simulation results of this paper,compared with the standard ridge structure,The step-ridge device with the injection area width of 30 μm can reduce the carrier concentration at the edge of the waveguide area by 86.0%,and finally reduce the lateral leakage current by 92.4%.(3)Step-ridge structures with different injection area widths were fabricated for testing.It is worth noting that the fabrication process of the step ridge structure studied in this paper only requires one more photolithography and etching,which is simpler than other structural processes that can reduce lateral leakage.The tests were carried out at room temperature.The power-current characteristics of the laser were measured respectively under quasi-continuous wave and continuous wave conditions,and the beam quality was measured under continuous wave conditions.The test results at 6A show that,the device with injection zone width of 30 μm can keep the power almost unchanged compared with the device with injection zone width of 90 μm,and the beam quality is improved by 56.2%.