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976nm pumped fiber laser achieves 85% optical efficiency
The industrial fiber laser market is growing rapidly, and this momentum will continue to be maintained in the next five to ten years. Semiconductor lasers as their core components need to be re-examined.
The market for medium and low power fiber lasers is fierce, and the market for high power fiber lasers needs to be developed.
With the increasing homogenization of medium and low power fiber lasers (output power below 1500 watts) and increasingly fierce market competition, many leading fiber laser manufacturers have begun to turn their attention to high-power fiber lasers (output power of 1500 watts or more). The market wants to achieve greater success. In the past, a semiconductor laser of 915 nm was used as the pump source of the fiber laser. Although the 915 nm laser has a wavelength drift coefficient of 0.3 nm/° C., the absorption source of the gain active fiber in the 915 nm is wide, and the laser pump source is subjected to the ambient temperature. The affected central wavelength drift has little effect on the absorption efficiency of the gain fiber, and the fiber laser is not sensitive to the working environment temperature. Therefore, the 915 nm band pumping scheme is widely recognized in the medium and low power fiber laser market.
The 915 nm band pumping scheme has limitations in the development of high power fiber lasers.
When designing a high-power fiber laser solution, the drawbacks of using the 915nm pump source in the past have begun to stand out. Due to the low absorption efficiency of the gain active fiber in the 915 nm band, in order to achieve higher power output of the whole fiber laser, it is technically required to use a higher 915 nm pump power and a longer active fiber, which will lead to developers. Have to face the nonlinear effects of fiber, loss of light and light efficiency, increased difficulty in thermal management, rising cost per wattage and many other difficulties. When the output power exceeds a certain level, the 915nm pumping scheme will become extremely complicated and eventually fail. High power fiber lasers therefore require a more efficient industrial pumping scheme.
The optical fiber conversion efficiency of the fiber laser using the everbright 976nm pump source can reach 85%.
The use of the 976 nm pumping scheme will well address the above-mentioned problems in the development of high power fiber lasers. The efficiency of the gain-active fiber for pump light in the 976nm band is 2-3 times that of the pump light in the 915nm band (Figure 1): due to higher absorption efficiency, the length of the gain-active fiber is shorter, and the nonlinear effect of the fiber is lower. It also saves some material costs.
FIG 1 ytterbium absorption lasing spectrum
Under the same pump power input, after several third-party verifications in the fiber laser industry, the light-to-light conversion efficiency increased by 10% under the working conditions after replacing the non-wavelength-locked 976nm pump source of everbright . 85% (Figure 2): This means that the developer's return on investment in pump light has increased by 10%, and today, when profits are precious, this will be a huge competitive advantage.
Fig. 2 Comparison of oblique efficiency of 915/976nm pumped erbium-doped fiber
The 976nm chip has higher reliability than the 915nm chip.
As far as the semiconductor laser itself is concerned, the 976 nm chip is more reliable than the 915 nm chip and has a longer life expectancy. Although the GaAs epitaxial crystal material has a slightly better photoelectric conversion efficiency in the 915 nm, the photon energy is lower due to the longer wavelength of 976 nm, and the cavity surface damage threshold of the high-brightness semiconductor laser chip under high current operating conditions is improved. In other words, the 976nm chip has a lower probability of cavity surface optical catastrophic damage (COD) than the 915nm band chip, and the chip itself is more reliable. Therefore, the 976nm semiconductor laser pump source as a core device also improves the reliability and life expectancy of the fiber laser machine.
In the past, the 976nm pump source was applied to industrial fiber lasers, and the whole machine was greatly affected by the ambient temperature.
In the research market, the use of 976nm to develop high-power or even megawatt fiber laser applications has been relatively mature. In the industrial market, the development of high-power fiber lasers by the 976nm pump source has just begun to spread.
In the past, the main reason for restricting the industrial application of 976nm pump source is that the absorption peak of the gain active fiber in the 976nm is narrow: when the temperature of the working environment changes, the drift of the center wavelength of the pump source causes the absorption rate of the gain active fiber to change greatly, which is easy. This leads to fluctuations in the performance of the fiber laser. The industrial use environment is complicated. In the past, low-power fiber lasers used air-cooling to cool the pump source, and the temperature control capability was limited. As a compromise, developers are actively or forced to use the 915nm with a wide absorption peak but lower absorption efficiency to reduce the impact of ambient temperature changes on overall machine performance. The 976nm pump source with VBG wavelength locking is generally used for scientific research purposes due to high cost, and large-scale industrial promotion is not accepted.
Now,there are no technical barriers to the application of the 976nm pump source to high-power fiber lasers, and the solution has been validated in batches.
The difference is that high-power fiber lasers basically use industrial water-cooled machines for forced water circulation refrigeration. Even with non-wavelength-locked 976nm pump sources, the cooling power, temperature control level and cost of existing water-cooled machines have fully met the requirements of fiber lasers. Pump source temperature control requirements. Due to the higher light-to-light conversion efficiency in the 976 nm, the laser has less heat rejection, and in fact the system thermal management pressure is smaller.
After a year and a half of application demonstrations at several third parties, it shows that the high-fiber laser in the industrial market uses the non-wavelength-locked 976nm pump source of everbright. There is no technical and cost application obstacle, and the ambient temperature is on the whole system. The performance impact is weak and controllable, and it has a strong competitive advantage in cost performance.
Everbright 976nm pump source has advanced indicators, stable and reliable performance, and is available in the market through mass verification.
Figure 3 135μm 160W test data
Figure 4 105μm 130W test data
Figure 5 200μm 800W test data
Figure 6 105μm 130W Wavelength lock test data
Everbright high-brightness 976nm fiber-coupled module uses 976nm single-tube chip produced by everbright. It achieves high-brightness fiber-coupled output through precise optical package and strict process control: the current output of 105μm fiber is 160. Tile (Figure 4), 135μm fiber output is up to 200W (Figure 3), 200μm fiber up to 800W (Figure 5), actual NA test 95% up to 0.18; center wavelength can be controlled at ± 2 nm, The spectral width is less than 5 nanometers. After nearly two years of market incubation verification and continuous iteration improvement, the series of 976nm products have been stably supplying large quantities to the fiber laser market. Everbright also provides a wavelength-locked 976nm fiber-coupled module with a maximum output of 130 watts for 105μm fiber (Figure 6). The actual NA test is 95% less than 0.18.
The 976nm pumping solution has obvious advantages and will gradually become the mainstream of the market.
In short, the 976nm semiconductor laser is applied to the high-power fiber laser in the industrial market. Due to the elimination of the nonlinear effect of the fiber, nearly 85% of the light-to-light conversion efficiency is achieved, the whole system is weakly affected by the ambient temperature, and the reliability of the semiconductor laser itself is higher. Many advantages will be more and more valued and welcomed. In the long term, with the scale application of the 976nm fiber-coupled module, it is believed that the product technology level will continue to improve, and low-cost 976nm wavelength locking on components will become a reality.