Step-index high-absorption Yb-doped large-mode-area fiber with Ge-doped raised cladding

Abstract

We report an all-solid large mode area (LMA) step-index fiber offering high absorption and low core numerical aperture (NA) by introducing highly Ytterbium-doped P:Al core and Germanium-doped cladding. The fiber provides core absorption of ~1200 dB/m at 976 nm with a low 0.07 core NA thanks to the raised Ge cladding. Furthermore, matched profiles of P and Al across core is successfully obtained with high concentration of Yb2O3 above 0.4 mol%. The fiber characteristics are routinely achievable by the conventional modified chemical vapor deposition with a solution doping technique. Highly efficient laser with >100 W output power, 86% slope efficiency with respect to launched pump power and a mean M 2 of 1.34 has been demonstrated using the fabricated LMA step-index fiber. We also report 80% laser slope efficiency with 58 W output power (pump power limited) within only 0.5 m of the fiber when pumped by a wavelength-stabilized laser diode.

Influence of GeO2 Content on the Spectral and Radiation-Resistant Properties of Yb/Al/Ge Co-Doped Silica Fiber Core Glasses

“…Linear fitting reveals that the slopes of the density and refractive index are approximately 2.26 × 10 −2 g·cm −3 ·mol −1 and 1.85 × 10 −5 mol −1 . Although Ge co-doping may cause a higher refractive index of the fiber core, the numerical aperture (NA) of the fiber can still be controlled by creating a graded refractive index layer [ 27 , 28 ].…”

High Energy Ultrafast Laser at 2 μm Using Dispersion Engineered Thulium-Doped Fiber

“…In a conventional modified chemical vapor deposition (MCVD) process, ∼7 mol% of Al 2 O 3 is achievable through a solution doping technique. Such amount of Al 2 O 3 concentration raises refractive index to 0.015 [26]. Hence, we set n cor e at 0.015 and adjust r1 to study contribution of waveguide dispersion.…”

Ultra-low NA step-index large mode area Yb-doped fiber with a germanium doped cladding for high power pulse amplification

“…An adiabatically tapered amplifier of <1 m length was used to generate 2 MW peak power pulses [18], but this requires special adaptations and precautions to realize long fiber tapers (i.e.. stripping, cleaning, tapering and recoating of a very long fiber) and leads to unwanted effects such as dopant diffusion and index profile modifications [17,18]. Recently, we have reported a very high absorption step-index Yb-doped LMA fiber made using the conventional modified chemical vapor deposition (MCVD) process combined with the solution doping technique [19]. A high Yb concentration (~0.4 mol % of Yb2O3) was achieved using an equi-molar phosphorus (P) and aluminum (Al) composition that greatly suppresses photodarkening and refractive index increase [20,21].…”

“…In addition, basic characteristics of the Gecladding fiber is discussed which confirm that it behaves very similarly to conventional silica cladding step-index fiber. A series of LMA step-index Yb-doped fibers was fabricated according to the fabrication procedures presented in [19]. The fiber core is comprised of silica doped with Yb, Al and P, while the cladding is doped with Ge to raise the refractive index.…”

“…, The core NA is very well controlled within the range of 0.04-0.05 using our fabrication approach. It is worth noting that the fiber core NA was further reduced from our previous report (NA~0.07) [19] and the fabricated fibers are as readily cleaved and spliced as conventional silica cladding fibers. 1) Table 1 Specifications of the fabricated LMA Yb fibers…”