Confined-doped fiber for effective mode control fabricated by MCVD process

Abstract

A confined-doped fiber was fabricated by a modified chemical vapor deposition (MCVD) process based on refractive index matching technology. With theory and experiments, we compared the confined-doped fiber and normal-doped fiber. We found that the confined-doped fiber with a core of 35 μm and 0.07 numerical aperture could achieve single-mode output and improve the beam quality from 2.8 to 1.5 in the fiber laser. Meanwhile, it still possesses high laser efficiency and has good stability of beam quality with the increase in pump power. It suggests that the confined-doped fiber with a MCVD process may be the key material for a high-power fiber laser with excellent beam quality.

Novel Dopant Tailored Fibers Using Vapor Phase Chelate Delivery Technique

“…As compared with the previously reported results, the undulations of the present study indicate less successful optimization of the process parameters. [26,27] Figure 4 shows the cross sections of different fibers with a core diameter of 30 AE 2 μm for 125 μm cladding, without any coreÀclad interface imperfection.…”

“…In this study, the overall core-to-cladding ratio (30 μm/125 μm) is higher than the confined core fibers reported in previous works. [25][26][27][28] Such a structure enhances pump absorption by increasing its overlap with the fiber core. The dimensions and NA of both C2 and C3 are found to be in good agreement with the vapor-phase calculation made before fabrication.…”

“…In this study, the inactive passive region of all the fibers comprises aluminoÀsilicate layers, whereas, the previously reported fibers had the germanoÀsilicate ring as the passive region. [25][26][27][28] In the case of GeO 2 -doped silica glass, during the collapsing stage at high temperature (>2000 C), GeO 2 evaporates and leads to the formation of a central dip in the RI profile. [31,32] In addition, the incorporation of aluminoÀsilicate layers as the core glass provides an advantage in terms of minimized stressinduced loss.…”

“…In addition, optimization was done to maintain the repeatability of the process and minimize dopant evaporation during the collapsing stage, which is a common drawback of earlier reported results. [25][26][27] Besides these two challenges, selecting suitable RE concentration was another factor to avoid reduced cladding absorption and the use of long-length fiber during practical application. To achieve the different designs, judicious choice of vapor phase compositions was most important, which was dependent on the sublimator temperature and the gas flow rate.…”

“…[25,26] Later, Liao et al demonstrated a reduced M 2 from 2.8 to 1.5 using 35/400 μm fiber using a similar design using conventional SD technique. [27] Using the same technique, Zhang et al achieved an M 2 of 1.47 using 70% confined core structure in a 33/395 μm Yb codoped with Ce to reduce the photodarkening (PD) effect. [28] However, it is challenging to fabricate a fiber with a customized doping profile with uniform dopant distribution in a repeatable manner.…”