System composition of high-power fiber laser

System composition of high-power fiber laser
1、 System composition
The high-power fiber laser consists of four parts: pump source, pump combiner, gain fiber, and laser output head
1.1 Pump source: The output power of a single laser die is only 10W~50W, and 6~50 dies will be integrated and packaged according to demand; If there are a large number of chips, spatial beam combining and polarization beam combining will be combined to increase power. The power of a single pump source ranges from tens to hundreds of watts, and to achieve kilowatt level output, more than 10 pump sources need to be connected in series (such as the Ruike laser using a combination of 11 pump sources).
1.2 Pump combiner: Produced through fiber fusion splicing technology, multiple pump modules are optically coupled into the same fiber.
1.3 Gain fiber: with a length often exceeding 30 meters, it will be coiled and fixed on the heat dissipation plate, often using ytterbium doped double cladding structure: core diameter of 10-20 μ m, single mode/few mode waveguide, doped with ytterbium ions; The inner cladding diameter reaches 400 μ m and is used for transmitting multi-mode pump light.
1.4 Laser Output Head: Responsible for the final laser output and can be connected to processing equipment through a standard interface.
2、 Core working principle
2.1 Resonator for optical amplification: composed of a pair of fiber Bragg gratings (FBGs): a high reflection grating (reflectivity>99%) reflects light of the target wavelength (such as 1080nm) back to the gain fiber; Output coupled grating (reflectivity 10%~50%) partially reflects to maintain oscillation, and partially transmits to form output. Pump light excites ytterbium ions to produce spontaneous emission, and photons that meet the wavelength requirements are repeatedly amplified between gratings, ultimately forming stable laser output.
2.2 Mode selection ensures beam quality: On the one hand, relying on the waveguide limitation of the small diameter core layer, only low loss transmission of the fundamental mode is allowed; On the other hand, by utilizing the high overlap between the fundamental mode and the gain medium (ytterbium ions), as well as the high loss characteristics of higher-order modes, combined with fiber bending design to further filter out higher-order modes, high-quality fundamental mode output with M ² approaching 1 is ultimately achieved