Rare-Earth-Doped Laser Fiber Fabrication Using Vapor Deposition Technique
Rare-earth (RE)-doped silica-based fiber lasers and amplifiers with very high output power and excellent beam quality are efficient devices for a variety of applications in industry, science, and medicine. Extreme power densities beyond the kW level and complicated fiber structures put high demands on fiber material properties and the preparation technology concerning both efficient laser operation and high-power stability. Silica is the preferred basic material. The host properties can be improved using co-dopants, which influence the optical properties (as refractive index distribution, absorption and emission behavior, optical background losses).
Over the years, alternative technologies to the common modified chemical vapor deposition (MCVD) process have been developed to incorporate REs and the most important co-dopant aluminum (Al) into silica. These fabrication methods differ in process control and regarding the properties of the manufactured preforms and fibers, such as geometry, incorporated level of REs and co-dopants, homogeneity of dopant concentration, and refractive index distribution. Here, two different technologies are described in detail. The MCVD process combined with solution doping is the most widely used and successful technique due to its simplicity and versatility. However, this technology has several limitations concerning geometry, doping and refractive index homogeneity, and the incorporation of very high REs and Al concentrations. One option to overcome these limitations is the MCVD process combined with gas phase doping for REs and Al.
Advantageous and detrimental effects of the relevant technology must be carefully considered for an optimal design for a high-power laser fiber.
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