Vapor phase doping process for fabrication of rare earth doped optical fibers: Current status and future opportunities

Abstract

Emerging application of rare‐earth (RE) doped optical fibers in high power lasers requires preforms with stringent geometrical and optical properties. This in turn demands more versatile and reliable process technology which brought Vapor Phase Doping (VPD) into prominence. This technology has immense potential to overcome fiber fabrication related challenges viz, dopant‐rich phase separation, RE uniformity in radial as well as longitudinal direction, “star‐like” defect elimination from core‐clad boundary and refractive index (RI) adjustment which results in improved beam quality and power stability of fiber laser. Further, high power lasers demand LMA active fibers with large core diameter and low numerical aperture (NA) which is easily producible by VPD method as it permits deposition of multiple RE doped core layers in a reproducible “in situ” manner. So, the prime focus is to optimize process technology to produce low RI, large core fibers. This article gives an overview of the comprehensive effort made by the global researchers to overcome challenges of VPD method and to demonstrate a standardized process technology for RE doping in silica glass preform.