High power diode lasers are widely used as the pump sources for fiber lasers and solid-state lasers, or the light sources for direct diode laser systems. The lateral brightness of diode lasers is the key parameter for the optical system with fiber coupling. The lateral brightness of a typical broad area diode laser is limited by the far-field booming rather than optical power at high operation current. In this paper, the far-field booming theory will be analyzed based on experimental observation of carrier density distribution and temperature profile along lateral direction. The temperature nonuniformity and the resulting thermal lens effect are supposed to be the dominate factor. We develop a novel high brightness laser diode structure with properly designed contact metal layer to modify the thermal conductivity profile. The thermal simulation indicate that the thermal lens effect is suppressed and the lateral far-field angle is reduced. Laser diodes with 230 μm emitter width and optimized structure are fabricated and the optical properties is investigated. The lateral far-field angle is reduced at current over 40A The optical power with same lateral brightness is increased up to 20%. This structure gives a promising high brightness solution for high power laser diode with power over 35 W. Chips with longer cavity length obtain higher power up to 51W.
High power diode lasers are widely used as the pump sources for fiber lasers and solid-state lasers, or the light sources for direct diode laser systems. To meet the emerging needs of fiber lasers, solid state lasers and direct diode laser systems, diode lasers are moving towards higher volume manufacturing, along with higher performance and lower cost. In this paper, we will present our progresses in these areas. We have set up a 6" GaAs wafer production line for high power diode laser chips, which includes MOCVD epitaxy and wafer fabrication. With the 6" wafer production line, we are producing multi-million chips per month for fiber laser pumping. The 6" wafers show great uniformity and reproducibility. Device performance is outstanding, with near 70% efficiency and high CW roll-over power.
Fiber-coupled diode modules have various applications in material processing and fiber laser pumping because of their high efficiency and high reliability. Commercial fiber-coupled diode modules using spatial beam combining and polarization beam combining cannot be employed in high-brightness applications, for example metal cutting, which demands a laser power exceeding 1 kW with a BPP of a few mm*mrad. Dense wavelength beam combining (DWBC) technology showed the possibility of further scaling-up the output power of fiber-coupled diode modules while maintaining the same beam quality that allows for fiber-coupled diode modules to be used in high-brightness applications. The efficiency, reliability, and brightness of fiber-coupled diode modules can be improved by using single emitters instead of laser diode bars as power sources in DWBC. Two types of high-brightness 100 µm/0.22 NA 2 kW fiber-coupled diode modules employing single-emitter-based DWBC technology, which have a wavelength range from 953 to 991 nm with 50% efficiency and a narrower wavelength range with 48% efficiency respectively, were developed for material processing and Raman fiber amplifier pumping. Furthermore, we combined 15 high-brightness 100 μm/0.22 NA 1.4 kW fiber-coupled diode modules into a 600 μm/0.22 NA fiber, achieving more than 22 kW at the output.
High power density VCSELs are attracting attentions in the field of LiDAR applications. Multi-junction VCSEL is the key technology to obtain high power density. High slope efficiency, high filling factor and small divergence angle are the straight-forward research directions to realize this high performance multi-junction VCSEL array. We optimize the epitaxial design and fabrication process, such as tunnel junction, oxidation layer and array layout. The progress on high performance multi-junction VCSEL array emitting around 940 nm is reported. Selectively oxidized, top-emitting VCSEL emitter array with 59.7% power conversion efficiency and slope efficiency of 8.3 W/A are developed as the basic laser source targeting at the LiDAR applications. The fabricated VCSEL array devices with emitting area of 234*250 um2 exhibit power density higher than 1800 W/mm2 and divergence angle lower than 21 degree (1/e2) with 15A peak current, 10kHz 10 nano-second pulsed (FWHM) driver.
High brightness, high efficiency laser sources become more and more promising in diode laser applications for fiber laser pumping and materials processing. Dense wavelength beam combining (DWBC) technology has great advantages over other beam combining technologies as the brightness is significantly improved. However, the brightness and efficiency of DWBC technology based on laser diode bars are naturally limited by the laser source due to smile effect and low polarization ratio. By employing single emitter based DWBC technology and optimizing the optical design, a laser diode module capable of delivering above 600 W at 976 nm in a 0.22 NA 100/120 fiber is developed and 48% power conversion efficiency is achieved. The maximal power conversion efficiency, 51%, is reached at 400 W output. The intrinsic wavelength stabilization of DWBC technology allows the use of the module for efficiently pumping.
Vertical cavity surface emitting laser (VCSEL) have recently emerged as highly promising electro optic device in 3D sensing and Lidar due to excellent properties such as high reliability, attractive high power performance, design flexibility and low manufacturing costs. To become a dominant player in serving the consumer electronics and driverless cars markets, we develop 6-inch VCSEL production line include device design, epitaxial growth and device-fabrication. By optimizing the device structure and manufacturing process, high power and high efficiency VCSEL devices are developed. We demonstrate that the maximum power conversion efficiency of the triple active regions VCSEL with 61.6%. In this paper, we will present you the evolution of VCSEL manufacturing technology and device characterization.
The paper reports on the design and development of an innovative high power and high brightness laser diode module that is capable of delivering more than 350 W at 976 nm in a standard 0.2 NA 50/125 fiber and 95% of power is in 0.15 NA. This module combines Everbright's multi-emitter modules assembled with 50 μm ridge width 976 nm laser diode chips through dense wavelength beam combining (DWBC) and polarization combining. The intrinsic wavelength stabilization of DWBC technology allows the use of the module for efficiently pumping Yb-doped fiber lasers.
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