The Disquisitions Of High-brightness High-power Laser Diode

Recently, more and more attention has been paid to the brightness of laser diode. High-brightness high-power laser diode could be used for optical pumping of solid state lasers and fiber amplifiers, material processing, free space communications, and medical treatment. Tapered laser diode is a promising concept for the combinations of high-power and nearly diffraction-limited beam quality in order to obtain high brightness.In this papar, the photoelectricity seclusion structure of 808nm high power laser bars has been optimally designed and fabricated. 850nm high brightness tapered laser diodes have been designed and fabricated, too. The main contents and results of this paper are as follows:The first one: The current expansion theory considers, the ridge tops and recess could limit the lateral expansion of injection current. The lateral current density distribution of the broad area lasers and the lasers with ridge tops and recess has been simulated by the professional software of Crosslight3D. Laser bars with 808 nm are designed and fabricated based on GaAs/A1GaAs graded-index waveguide separate confinement hetero-structure single quantum well chip (GIRN-SCH-SQW). The enhancement in output power, electro-optical conversion efficiency, the slope efficiency and the spectral properties have been observed in the laser bars with ridge tops and recess. Because restrictions of lateral diffusion of the current enhanced with the deepening of recess, electro-optical properties of the bars are in direct proportion to the etching depth.The second one: 850nm tapered laser diodes are designed and fabricated based on AlGaInAs/AlGaAs GIRN-SCH-SQW chip. The tapered lasers with different lengths of deep etched RW sections have been fabricated. The lengths of RW sections are 750μm, 1000μm and 1250μm, respectively and all the whole cavity length is 2500μm. Through the testing and analysis of the the power-current characteristics, it has been proved the laser with shorter RW section would have better performance in high-power lasers. For the 850nm tapered lasers with the 750μm of RW lengths, under the threshold current density is 490.2A/cm2, the slope efficiency is up to 0.58 W/A and the conversion efficiency reaches 30% at the output power 1.40 W(3A) under pulsed (50μs, 100Hz) condition.The third one: to evaluate the beam quality of the tapered diode lasers, the knife-edge method of ISO standard 11146 was used to measure beam radius and divergence of far field. The high-power 850 nm tapered laser with the 750μm of RW lengths with nearly diffraction-limited beam quality has been obtained. The beam propagation factor M² is only 1.7 and the high brightness is 16.3 MW·cm-2·sr^-1 when the output power is 200 mW. The M² factor and brightness of the laser could keep at 2.8 and 9.9 MW·cm-2·sr^-1 while the output power is 1 W.The last one: a broad laser and a tapered laser of 850 nm with the same width of 125μm, and the same cavity length of 2500μm were fabricated based on the AlGaInAs/A1GaAs chip with GIRN-SCH-SQW structure. The lateral divergence angle, the beam propagation factors M² and the brightness of the tapered laser at the output power of 1 w are 4°, 2.8 and 9.9 MW·cm-2·sr^-1, respectively, which are much better than that of the broad laser. The output power of tapered laser is 1.40 W, and the power of broad laser is 1.59 W under the injection pulse current of 3A. It indicates that the tapered laser has higher beam quality and brightness with high-power.