▲2010-2021 China’s laser equipment market
At the same time, the technology of the laser is also rapidly iterating. First, the pump technology is transformed from the 915nm solution with a wider temperature control area to the 976nm solution with higher absorption efficiency. Currently, on the pump technology route of high-power continuous fiber lasers, the 976nm pump Pu technology has become the mainstream technical solution. In addition, in the technology of 10,000-watt lasers, there has always been a battle between “single-channel fiber amplification” and “multi-channel beam synthesis”. The market continues to develop, and comprehensive factors such as technology, cost and efficiency It has become the core factor for the selection of the industrial fiber laser market. Let’s break down the two technical routes.
10,000-watt laser technology route direction
1. Multi-channel beam combination scheme
According to different system structures, fiber lasers can be divided into: direct oscillator structure fiber lasers and master oscillator power amplifier (MOPA) structure fiber lasers. The fiber laser with the direct oscillator structure is simple in structure and only contains a laser oscillator, and the grating selects and outputs the selected specific wavelength.
For a fiber laser with a direct oscillator configuration, it mainly consists of a pair of gratings (low reflection + high reflection), a gain fiber, and several pumps. Multiple beams of pump light are coupled into a gain fiber through a beam combiner, so that the gain fiber is in a state of inversion distribution of the number of particles, so as to realize the stimulated radiation amplification of the light, and finally select a specific wavelength of laser light through the low reflection grating to pass through the output fiber. transmitted to the output header.
▲ Fiber laser based on direct oscillator structure
According to different pumping methods, it can be divided into: forward pumping, reverse pumping and bidirectional pumping. The pump light injection direction is the same as the laser output direction is called forward pumping; the pump light injection direction is the same as the laser output direction opposite to the forward and reverse pumping; the pump light is injected from the forward and reverse directions at the same time. called bidirectional pumping. At present, both GW and IPG use the bidirectional pumping scheme shown in the figure above.
At present, a fiber laser or module with a mainstream direct oscillator structure has a power of about 3KW, and a higher-power laser is combined from one module to another, that is, the light output from multiple modules is coupled through a beam combiner. into a fiber and then output. For example, 12KW is obtained by combining four 3KW modules.
▲ High-power fiber laser with multi-channel beam synthesis scheme
2. Single-channel fiber amplification scheme
The fiber laser with MOPA structure includes a laser oscillator and one or more stages of fiber amplifiers. The wavelength selected by the grating in the oscillator is used as the seed light, and the seed light is amplified under the action of the multistage amplifier, so that the output power can be obtained to a certain degree. improvement.
For such high-power lasers, the power increase is not achieved by increasing the number of modules, but mainly by multi-stage amplifiers. For example, 12KW is obtained through 3-stage amplification.
▲ Single-channel fiber amplification scheme based on MOPA configuration High-power fiber laser
The advantages of multiplexing 10,000-watt lasers
1.The structure of the whole machine is simple and easy to maintain
Since the single-channel amplified high-power laser has only one module, the internal arrangement of light, electricity and water is more complicated. Its control system is relatively more complex, and the oscillator and amplifier need to follow a certain timing relationship when turning on and off: when turning on the laser, the oscillator should be turned on first, and then the amplifier should be turned on from the first stage amplifier; The stage amplifier starts, and the amplifier is turned off step by step forward. Once the timing is out of order, it is very likely to cause serious damage to the laser.
The multi-beam synthesis scheme adopted by GW laser, laser control is relatively simple, there is no timing problem, program control problems, and will not cause damage to the machine. In the event of a laser failure, repairs can be accomplished simply by removing the damaged module and replacing it with a new one. For customers, it saves more maintenance time.
2. Strong anti-return light ability
Different from oscillators, there is no grating at both ends of the gain fiber of the amplifier. The return light when processing high-reflection materials or the reverse light of the post-amplifier is easy to return to the pre-amplifier, which interferes with the work of the pre-amplifier and even causes damage. Therefore, it is necessary to Additional optical isolation measures are added.
GW laser’s multi-beam synthesis scheme, each module has only one oscillator, and there is no reverse light; at the same time, the unique secret of GW laser – ABR anti-high-reflection technology: a single module is equipped with a five-level return light detection and stripping device ;On the basis of the five-level anti-reflection of a single module, each module is equipped with a first-level anti-return light device, which can effectively protect the internal components from damage, ensure the stable operation of the laser, and easily cut gold, silver, Highly reflective materials such as copper and aluminum are suitable for various welding applications.
3. Bidirectional pumping improves system stability
➢Suppress laser noise
For forward and reverse pumping, the pump light is injected into the ytterbium-doped fiber from one end, and the pump light is stronger at the input end of the ytterbium-doped fiber, so the particle inversion excitation is also strong, but due to the absorption factor, the pumping light is strong. The light will be attenuated along the length of the fiber so that gain saturation is reached at a certain fiber length and the noise increases. Bidirectional pumping can make the pump light evenly distributed in the fiber, so that the gain is also distributed evenly in the fiber, so that the noise is reduced.
➢Relieve single-ended pressure
Excessive pump light energy is coupled into the gain fiber, and the initial section of the gain fiber absorbs the pump light a lot, so the fiber temperature is the highest in the initial section, and the fiber melting point bears the largest pressure. Double-end pumping can make the two melting points on both sides of the gain fiber share the pressure, making the system run more stably.
➢Increase the threshold of mode instability
Mode instability is related to the thermal loading of the gain fiber. After the double-end pumping method is adopted, the temperature distribution of the gain fiber can be made more uniform, the thermal effect is weakened, and the threshold value of mode instability is increased.4
. 976nm pumping scheme has obvious advantages
▶ Higher conversion rate
Ytterbium-doped fiber has two strong absorption peaks at 915nm and 976nm, so the pump light band usually selected for ytterbium-doped fiber laser is 915nm or 975nm. Among them, the absorption peak at 975nm is higher, which is about 3 times that of 915nm, so the 1070nm laser with the same power consumes only one third of the 915nm pump light. The pump light is converted from electrical energy, which means that using a 976nm pump source consumes less electrical energy and is more efficient and energy-saving.
▶Lower nonlinear effects
In the continuous single-frequency fiber laser, there are some nonlinear effects, such as stimulated Brillouin scattering, stimulated Raman scattering, and optical Kerr effect, which will degrade the beam quality. Benefiting from the higher absorption peak at 976nm, the gain fiber can be made shorter under the premise of the same absorption efficiency, and reducing the fiber length helps to avoid suppressing nonlinear effects.
Epilogue
GW Laser (GW) is based on 976nm pump technology and multi-channel beam synthesis scheme as the main line, and is committed to improving the power level and beam quality of 10,000-watt lasers; at the same time, it also pays attention to improving the quality and stability of products, reducing product failure rates and The complexity of handling failures. In the future, we will continue to provide customers with high-quality fiber lasers and strong technical support.
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