This paper describes the observation of a fiber fuse observed in the core of a high-power high-NA, all-glass, double-clad fiber. Fiber fuse is a phenomenon that results in a specific type of
catastrophic destruction of an optical fiber-core from the point of initiation toward the light
source. It is so named because its appearance is very similar to a burning fuse. In this paper, we
examine the origin or the initiation source for the fiber fuse observed in the double-clad fiber.
Furthermore, we propose a two-step thermal mechanism for the fiber-fuse generation in optical
Suppressing nonlinear effects such as stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS) in high
power fiber amplifiers and lasers is crucial for scaling up output power well beyond kW levels. The paper uses a
sophisticated model to analyze many different fiber amplifier designs and compare their performance. The systematic
modeling reveals many interesting results and shows that a co-pumped amplifier can be optimized by carefully choosing
fiber lengths and applying additional heating to the fiber. It also explains why the amplifier configuration can make
great impacts on SBS characteristics. In addition, a single-polarized fiber having an effective area of 206 μm<sup>2</sup> and cutoff
wavelength of 1100 nm is designed to suppress SRS and provide better polarization properties. The systematic
modeling concludes that in general a counter-pumped fiber amplifier has the lowest nonlinear effects and is less sensitive
to the fiber length comparing with the co-pumped amplifiers. However, the co-pumped amplifier is easy to integrate
with an all-fiber-based pump combiner without risking LD damage and it can be heated to increase SBS threshold by a
factor of 1.7.
High power fiber lasers have been recently demonstrated at the kilowatt level. The
spectral linewidths of these lasers oscillators can exceed 20 nm. Whereas, such broad
spectra are fine for many applications, such as materials processing where raw power is
the primary requirement, other applications, including coherent beam combination,
harmonic generation, or gravitational wave detection, require high powers beams with
much narrower linewidths. Amplification of narrow linewidth signals in optical fibers is
limited by stimulated Brillouin scattering (SBS). We discuss novel fiber designs that limit
SBS allowing the amplification of narrow linewidth signals to kilowatt power levels.
This paper reviews different fiber design approaches for high power lasers. First, we discuss the conventional step index
profile design and methods for achieving single mode operation in high power lasers such as bending, helical core fibers
and Yb dopant profile designs. Then we present new design approaches for reducing the SBS through profile and glass
composition designs. Finally, we describe fiber designs to achieve single polarization and at the same time to mitigate
the SRS effect.
This paper outlines recent work at Corning Incorporated on fiber composition design and fabrication of a SBS-managed, large-mode-area (LMA), Yb-doped double-clad fiber for high-power, narrow-linewidth fiber laser applications. Through a detailed theoretical analysis for the SBS threshold in optical fibers, an Aluminum/Germanium (Al/Ge) counter-graded fiber-core composition profile has been proposed and demonstrated for reducing the SBS effect, via the reduced-overlap between optical and acoustic modes in the fiber design. Such Al/Ge counter-graded-composition-profile design overcomes the limitation in a multilayer fiber-core approach, in terms of the low-loss fiber fabrication. The new compositionally SBS-managed, LMA Yb-doped double-clad laser fiber fabricated through the new design, has shown more than ~7 dB improvement in SBS threshold over the conventional LMA fiber design. The new fiber offers exceptionally low passive-loss characteristics, and has been demonstrated with uncompromised high laser efficiency for high-power, narrow-linewidth fiber laser applications.
Single transverse mode fiber lasers have recently achieved output powers at the kilowatt level. These breakthroughs can be attributed to the maturation of high power diode pump technology at 980 nm and the use of large mode area (LMA) fibers. In the continous wave (cw) operation regime, LMA fibers, through their reduction of device length and increase of the effective area, have been effective in the reduction of deleterious nonlinear optical effects such as stimulated Raman scattering (SRS). The use of LMA fiber has been less effective in the suppression of stimulated Brillouin scattering (SBS), for which the threshold can be several orders of magnitude lower than for SRS. In this work we use refractive index profiles and index modifying dopant distributions for the mitigation of SBS. Our theoretical and modeling efforts led to an experimentally demonstrated increase in SBS threshold of 2.5 dB for single mode fiber and 6 dB for LMA amplifier fiber. We discuss the use of this SBS-suppressive fiber in the demonstration of a high-power,
narrow linewidth fiber amplifier.
This paper reviews and presents the recent specialty fiber research and development conducted at Corning Incorporated
towards high-power and high-brightness fiber lasers. These include the fabrication of all glass-composition, high-NA,
Yb-doped double-clad laser fibers, and also of double-clad single-polarization laser fibers for further improved
brightness in laser beam quality through innovative fiber designs. These have led to the 1st all-glass, high NA, Yb-doped
high-power double-clad fiber made by an all-vapor-phase fiber-preform process in the world, and also the highbrightness,
single-polarization double-clad high power laser fiber.
We have demonstrated high power, linearly polarized output from an
all-fiber laser using an integrated polarizing fiber. In this
paper, we will detail the design, fabrication and operation of the
single polarization fiber as well as the fiber laser experiments.
This paper reviews recent progress and presents new designs and experimental results on single polarization (SP) fibers. The design concept for achieving SP propagation and approaches using either stress induced birefringence or hole-assisted geometrical birefringence for realizing single polarization fibers are described. Designs of hole-assisted SP fibers with either dual holes or a central hole are discussed in details. Effects of fiber parameters on SP fiber performance such as bandwidth, cutoff wavelength, mode field area are analyzed. Results on fabrication and characterization of dual-hole-assisted SP fibers are presented. SP operating windows centered at wavelength from 900 to 1600 mm with bandwidths from 18 to 55 nm are realized. Applications of SP fibers for single mode fiber lasers to produce linear polarized laser output are demonstrated with extinction ratio of 17-20 dB.
We review current work on fiber laser systems at Corning. In particular, we describe design and performance of all-glass double-clad laser fibers, broad-area laser pumps, and pump coupling optics. We discuss our approaches using single-polarization fiber and low-nonlinearity photonic band gap fiber as technologies for developing the next generation of high-power fiber lasers.
Glass fiber lasers were invented in the 60's by Elias Snitzer at Americal Optical, soon after the invention of the first solid-state glass laser. However, it was not until the 80's when these waveguide devices were deployed in industrial applications, driven largely by the technological success of the semiconductor laser diode, which provided practical and efficient pumps, and by the advent of low loss rare-earth-doped optical fiber.