The blue semiconductor laser with a wavelength range of 450nm has developed rapidly in recent years. For high-reflective and high-thermal conductive materials represented by copper, gold and high-strength aluminum, the absorption rate of blue laser is 5-10 times than infrared lasers. Blue laser can achieve high-quality and consistent welding results, stable melt pools and no spatter. With the development of blue semiconductor laser technology, there is a growing demand for higher brightness and reliability. Based on the practical application background, we have designed and implemented a stable high-brightness blue laser. Through BPP theory and ZEMAX simulation calculation, 48pcs TO-packaged 5.5W blue lasers are coupled into a 105μm core diameter 0.22NA fiber using polarization and optical fiber coupling technology. More than 250W output power is obtained with coupling efficiency exceeds 90% and electro-optical efficiency exceeds 35%. The high brightness blue laser has passed various reliability tests including accelerated aging for 7000 hours, 85°C high temperature storage, -40°C low temperature storage, -20°C to approximately 70°C temperature cycling test, vibration and mechanical shock test. The stable high-brightness blue laser finds significant applications in medical, 3D printing and welding.
With the development of fiber lasers, the weight, power and brightness of fiber coupled semiconductor lasers are increasingly required. Low SWAP (low size and weight and power-efficient) laser diode has been a major focus of research. This paper mainly introduces the latest development of BWT low-SWaP products. In 2023, BWT introduces products with a power to mass ratio of 2.3W/g. By optimizing the optical path, increasing the power of the single chip, optimizing the structural design, and changing the material, BWT has introduced a higher brightness low-SWaP wavelength stabilized pumps. relying on a proprietary architecture of spatial and polarization multiplexing with multi-emitters.
On last year’s SPIE conference, BWT has launched a pump source in weight around 500g, which was locked at 976nm, output 420W from a 135μm diameter and NA 0.22 fiber. In order to meet the need of higher output power pumping of fiber lasers, BWT has achieved 650W output from a 135μm diameter and NA0.22 fiber with a diode laser locked at 969nm and 982nm based on dense spatial beam combination (DSBC) and wavelength beam combination. In the absorption spectrum of Yb3+ ions, 969nm and 982nm have lower absorption coefficients than 976nm,. The active fiber with the same doping concentration will produce less heat accumulation per unit length, which has an obvious effect on improving the TMI threshold (transverse mode instability) and increasing the single-mode fiber laser power. With the enhancement of pump source brightness and the improvement of active fiber doping process and wave-guide structure, the power of single mode fiber laser directly pumped by diode laser is expected to exceed 10kW in the future.
A compact high-brightness blue laser is designed and developed. Through BPP theory and ZEMAX simulation, 18pcs TO-packaged 5W blue lasers are coupled into a 113μm core diameter 0.15NA optical fiber using polarization and optical fiber coupling technology. More than 75W output power is obtained, coupling efficiency exceeds 88%. Optical fiber end face spot with uniformity of more than 90% can be achieved by coupling the square optical fiber, which provides an ideal light source for medium power applications with high beam quality requirements such as gold foil welding and cutting, wire stripping, medical, etc.
BWT introduced the idea of dense spatial beam combination(DSBC) and proved it experimentally with kW level pump source. Currently, the output power of single emitters has reached 15W~30W@BPP≈5-12mm·mrad with electro-optical efficiency<60%. This makes it possible for the high-power pump source with optical fiber output to maintain high brightness, small volume, and light weight. With commercial available chips, BWT achieved 420W output locked at 976nm from a fiber of 135μm core diameter and NA0.22, and mass of ≈500g. Also 1000W output at 976nm (or 915nm) from a 220μm core diameter 0.22NA fiber is obtained and mass of ≈400g. In the future, with increasing diode chip brightness and electro-optical efficiency, the pump source with high power and mass ratio will have an important role in small size and high power fiber lasers, which will become an active driver for defence and industrial applications.
At SPIE 2020 conference, we presented a blue diode laser that provides 200W output from a 200μm core diameter 0.22 NA fiber. Blue laser with high power and high brightness is the best choice for higher efficiency demanded by industrial processing. Based on 7 modules each provides 160W from a 105μm core diameter 0.22 NA fiber (NA 0.15/0.22 power ratio >93%), using fiber beam combining, 1000W output is achieved from a 330μm core diameter 0.22 NA fiber. And the aging test of 160 W unit modules was carried out. 1000W high brightness blue laser source is an ideal choice for processing (welding, 3D printing, etc) of non-ferrous metals, especially copper.
In this study,the chip bonding processes for various chips from various chip suppliers around the world have been
optimized to achieve reliable chip on sub-mount for high performance. These chip on sub-mounts, for examples, includes
three types of bonding, 8xx nm-1.2W/10.0W Indium bonded lasers, 9xx nm 10W-20W AuSn bonded lasers and 1470 nm
6W Indium bonded lasers will be reported below. The MTTF@25℃ of 9xx nm chip on sub-mount (COS) is calculated
to be more than 203,896 hours. These chips from various chip suppliers are packaged into many multiple single emitter
laser modules, using similar packaging techniques from 2 emitters per module to up to 7 emitters per module. A
reliability study including aging test is performed on those multiple single emitter laser modules. With research team’s 12
years’ experienced packaging design and techniques, precise optical and fiber alignment processes and superior chip
bonding capability, we have achieved a total MTTF exceeding 177,710 hours of life time with 60% confidence level for
those multiple single emitter laser modules. Furthermore, a separated reliability study on wavelength stabilized laser
modules have shown this wavelength stabilized module packaging process is reliable as well.
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