A uniform temperature profile is provided across the width of the core of a ribbon fiber laser or amplifier by the use of insulating elements at the core edges and a spatially variable gain in the fiber core. High average power ribbon fibers, enable a variety of applications such as practical laser cutting and beam combining.

A first fiber is connected to a first end of a third fiber doped with a rare earth element, and a second fiber is connected to a second end of the third fiber. In the third fiber doped with the rare earth element, a central portion of a core is more heavily doped with the rare earth element than a peripheral portion of the core is.

Fiber-based gain elements, such as fiber lasers, fiber amplifiers, and the like, that have higher power and better frequency stability than can be achieved in the prior art are presented. Embodiments include a fiber-based gain element having a first portion in which anti-Stokes fluorescence (ASF) reduces its temperature below that of an ambient environment and a second portion whose temperature is not reduced below that of the ambient environment, which are thermally coupled so heat can flow from the second portion into the first portion, thereby reducing the average temperature of the gain element. In some embodiments, a core configured to provide optical gain is thermally coupled with a first cladding configured to exhibit ASF cooling via an intervening cladding layer that acts to confine a first pump signal to the core.

Disclosed herein is a method comprising injecting light of a first wavelength .sub.1 into a wavelength division multiplexer; injecting light of a second wavelength .sub.2 into the wavelength division multiplexer; combining the light of the first wavelength .sub.1 and the light of the second wavelength .sub.2 in the wavelength division multiplexer to produce light of a third wavelength .sub.3; and reflecting the light of the third wavelength .sub.3 in a dual-Brillouin peak optical fiber that is in communication with the wavelength divisional multiplexer; wherein the dual-Brillouin peak optical fiber has at least two Brillouin peaks, such that an amplitude A.sub.1 of at least one of said Brillouin peaks is within 50% to 150% of an amplitude A.sub.2 of another Brillouin peak 0.5A.sub.2A.sub.11.5A.sub.2; wherein the dual-Brillouin peak optical fiber generates a Brillouin dynamic grating that reflects an improved back-reflected Brillouin signal of the combined light.

A multi-clad optical fiber design is described in order to provide low optical loss, a high numerical aperture (NA), and high optical gain for the fundamental propagating mode, the linearly polarized (LP) 01 mode in the UV and visible portion of the optical spectrum. The optical fiber design may contain dopants in order to simultaneously increase the optical gain in the core region while avoiding additional losses during the fiber fabrication process. The optical fiber design may incorporate rare-earth dopants for efficient lasing. Additionally, the modal characteristics of the propagating modes in the optical core promote highly efficient nonlinear mixing, providing for a high beam quality (M.sup.2<1.5) output of the emitted light.

An optical element is provided. The optical element may comprise a material, the material being a matrix and a set of particles included in the matrix, the material having a molar fraction of SiO.sub.2 higher than or equal to 65 percent, each particle having a dimension smaller than or equal to 80 nanometers.

This disclosure enables laser-based gain elements, such as fiber lasers, fiber amplifiers, and the like, that have higher power and better frequency stability than can be achieved in the prior art. Embodiments disclosed herein include a fiber-based gain element having a first portion in which anti-Stokes fluorescence (ASF) reduces its temperature below that of an ambient environment and a second portion whose temperature is not reduced below that of the ambient environment. The fiber-based gain element is arranged such that the first and second portions are thermally coupled so heat can flow from the second portion into the first portion, thereby reducing the average temperature of the gain element. In some embodiments, a core configured to provide optical gain is thermally coupled with a first cladding configured to exhibit ASF cooling via an intervening cladding layer that acts to confine a first pump signal to the core.

An amplification optical fiber includes: a core; an inner cladding having a refractive index lower than a refractive index of the core, wherein an active element pumped by pumping light is entirely doped to the core, and a relative effective refractive index difference of light in an LP01 mode is greater than or equal to 0.05% and a relative effective refractive index difference of light in an LP21 mode is less than 0.05% in light propagating through the core.

Large mode area optical fibers include cores that are selected to be smaller than a core size associated with a minimum mode field diameter of a lowest order mode. Cross-sectional shape of such cores can be circular or annular, and a plurality of such cores can be used. Gain regions can be provided in cores or claddings, and selected to produce a selected state of polarization.

A mode-locked fiber laser device is provided in the disclosure. The mode-locked fiber laser device includes a non-linear loop mirror, an optical splitter and a uni-directional loop. The uni-directional loop includes a polarization beam splitter and a Faraday rotator. The uni-directional loop is coupled to the non-linear loop mirror by the optical splitter to form a figure-8 optical path. A first output laser pulse output by the optical splitter is propagated to the polarization beam splitter. After being rotated 45 degrees by a Faraday rotator, the first output laser pulse is propagated back to the non-linear loop mirror to form a laser resonator. A second output laser pulse output by the optical splitter is propagated to the Faraday rotator to rotate the second output laser pulse 45 degrees, and the polarization beam splitter reflects the second output laser pulse to the outside of the mode-locked fiber laser device.