Yb-doped large mode area fibers with depressed clad and dopant confinement

Abstract

Large mode area fibers with depressed-index cladding layer and confinement of rare-earth dopants can provide effective suppression of high-order modes. A polarization-maintaining Yb-doped double-clad fiber with 35/250 µm core/clad diameter has been fabricated from conventional methods according to this design. The fiber which has an effective mode area close to 500 µm 2 yields near diffraction-limited output with beam quality factor M 2 close to 1.1 when tested as a power amplifier with a coherent seed light source. Beam pointing measurements provide further evidence for near single-mode behavior as the pointing fluctuations are shown to be negligible once the fiber is coiled to a given diameter.

35/250 ytterbium-doped LMA polarization-maintaining fiber for high average and high peak power amplifiers

“…The effective mode area of the fundamental mode was calculated at 430 µm 2 from the measured index profile. The radial profile of the inner cladding region, featuring an index depression beside the core, yields a greater bending loss differential between the fundamental mode and higher-order modes [3]. Thus the fiber need not be coiled as tightly as conventional LMA fibers with stepindex profiles, reducing the long-term stress fatigue on the fiber and avoiding severe bend-induced mode distortion.…”

“…The ytterbium dopants are further confined to the center of the core to increase gain saturation and promote amplification of the fundamental mode. In addition, higher-order modes (HOMs) will suffer greater propagation losses thanks to our proprietary design, with the depressed-index radial profile of the inner cladding beside the core region [3]. The 35/250 Yb-doped polarizationmaintaining LMA fiber described herein ensures outstanding beam quality, an essential requirement for chirped-pulse amplification and laser harmonics generation.…”

High-power single-frequency depressed-cladding, confined-doping Yb3+ fiber amplifier

“…Furthermore, this fiber design is directly compatible to our inhouse fiber processing techniques such as endcap splicing and cladding light stripper (CLS) writing. This fiber has been used before by Roy et al 9 up to power levels of 60W. Here, we present a master oscillator power amplifier (MOPA) system for further power scaling with this fiber up to 400W and investigate the amplifier's properties for the applicability in gravitational wave detectors.…”

“…Refractive index profile and doping scheme of the depressed-cladding, confined core specialty fiber. Derived from Roy et al 9 .…”