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.
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.
With certain emitter beam quality and BPP allowed by fiber, we have derived a spatial beam combination structure that approaches the BPP limit of the fiber. Using the spatial beam combination structure and polarization beam combination, BWT has achieved 1.1KW output from a fiber (one end coated) with NA 0.22 and core diameter of 200μm. The electro- optical efficiency is nearly 47%. Multiple emitters with wavelength of 976nm are packaged in a module with size of 600 ×350×80mm3.
With continuous increase in output power of fiber lasers, small volume, low weight, high electro-optic efficiency and high brightness diode laser pump source has become the trend of development. Using spatial beam combining and polarization beam combining methods, BWT has developed a compact pump laser achieving 600W level out of a fiber of 0.22 NA and 200 μm core diameter. At 12A, electro-optical efficiency is higher than 49%. Its brightness is higher than that of the commercially available 158W pump from BWT.
KEYWORDS: Semiconductor lasers, Mirrors, Diffraction gratings, High power lasers, Beam shaping, High power fiber lasers, Electro optics, Energy efficiency, Diffraction, Reflectivity, Polarization, Collimation
Spectral beam combination expands the output power while keeps the beam quality of the combined beam almost the same as that of a single emitter. Spectral beam combination has been successfully achieved for high power fiber lasers, diode laser arrays and diode laser stacks. We have recently achieved the spectral beam combination of multiple single emitter diode lasers. Spatial beam combination and beam transformation are employed before beams from 25 single emitter diode lasers can be spectrally combined. An average output power about 220W, a spectral bandwidth less than 9 nm (95% energy), a beam quality similar to that of a single emitter and electro-optical conversion efficiency over 46% are achieved.
In this paper, Rigorous Coupled Wave analysis is used to numerically evaluate the influence of emitter width, emitter pitch and focal length of transform lens on diffraction efficiency of the grating and spectral bandwidth.
To assess the chance of catastrophic optical mirror damage (COMD), the optical power in the internal cavity of a free running emitter and the optical power in the grating external cavity of a wavelength locked emitter are theoretically analyzed.
Advantages and disadvantages of spectral beam combination are concluded.
We developed a high brightness fiber coupled diode laser module providing more than 140W output power from a
105μm NA 0.15 fiber at the wavelength of 915nm.The high brightness module has an electrical to optical efficiency
better than 45% and power enclosure more than 90% within NA 0.13. It is based on multi-single emitters using optical
and polarization beam combining and fiber coupling technique. With the similar technology, over 100W of optical power
into a 105μm NA 0.15 fiber at 976nm is also achieved which can be compatible with the volume Bragg gratings to
receive narrow and stabilized spectral linewidth. The light within NA 0.12 is approximately 92%.
The reliability test data of single and multiple single emitter laser module under high optical load are also presented and
analyzed using a reliability model with an emitting aperture optimized for coupling into 105μm core fiber. The total
MTTF shows exceeding 100,000 hours within 60% confidence level. The packaging processes and optical design are
ready for commercial volume production.
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