A Polarization Maintaining Cladding Light Stripper with Ultra-low Backscattering, Based on 20/400-mm Double Clad Fiber

High-power optical fiber laser systems are currently widely used in various applications such as materials processing, medicine, and defense [1]. High-power optical fiber laser technologies employ large mode area (LMA), double clad fibers (DCFs) to increase output power by using a cladding pumping scheme [2]. For the successful implementation of LMA DCF-based high power fiber lasers one of the key components is the cladding light stripper (CLS). It is well-known that a non-negligible amount of residual pump power always exists at the output end of a gain medium based on rare-earth ion-doped LMA DCF after the launched pump beam was used to induce stimulated emission. The residual pump beam together with undesired signal beam within the inner cladding of a LMA DCF is known to degrade output beam quality and potentially damage fiber splicing points. In implementing CLSs, one critical issue is the backward scattering of cladding light since it can induce fiber heating and burning [3]. It was also reported that conventional CLS designs based on randomly roughened surface structures or periodically V-grooved structures are vulnerable to the residual pump backscattering [4, 5].