With regard to the laser processing of glasses and resins, we explored the possibility of using lasers with wavelengths that have high-internal absorption. Since the wavelengths of lasers available in the market have low-absorption rates, we decided to develop a high-power fiber laser with a 2.8-μm wavelength on our own.
Wavelength stability (2.8 μm ± 1 nm)
Since light absorption by atmospheric moisture occurs around a wavelength of 2.8 μm, the laser light is absorbed, which makes laser processing difficult. Therefore, the laser oscillation wavelength should be fixed at a length that has lower light absorption. For stabilizing the oscillation wavelength of the fiber laser, a fiber Bragg grating (FBG) is used, which constructs a periodic structure in the optic fiber and reflects specific wavelengths of light. However, a quartz fiber, which is usually used, cannot be adopted since it absorbs light of 2.8-µm wavelength. To overcome this, we developed an FBG drawing technology, which draws a periodic structure in the optic fiber for laser oscillation, and it was utilized in the laser oscillator. With this technology, the laser oscillation wavelength is stabilized.
Over 1,000 hours of continuous output
Optic fibers that oscillate middle infrared light are degraded by atmospheric moisture. Especially, when the tip of the optic fiber, which is the emitting port of laser light, is degraded, the light cannot go through, thus stopping laser oscillation. To solve this issue, we have developed a dedicated fusion device and fusion protection technology, so as to fuse non-degrading materials to the tip of the optic fiber. With a fusion protected fiber tip, even a 10-W laser output for more than 1000 hour continuous oscillation is possible.
Increasing output (amplifying)
With higher laser output, the laser processing speed can be increased. Therefore, we are now developing lasers with increased output capacity. For increasing the laser output, an amplifier is required to amplify low-output laser light. In the amplifier, an optical coupler is used, which has been developed to introduce the excitation light from the side of the fiber under the condition that the low-output laser light is coupled to the amplifying fiber.