Apparatus and methods for mitigating transverse mode instabilities (TMI) in high power fiber amplifiers that does not depend on active feedback loops. The apparatus and method involve the modulation of the amplitude and/or phase of selected spatial mode components of an input signal beam to increase the TMI threshold of the amplifier. Once the desired modal adjustments are made, the beam is input to a mode multiplexer whereupon an optimized output beam can be input to the active fiber of the amplifier system. By increasing the TMI threshold of the amplifier, the amplifier can be operated at higher power before TMI sets in. A control stage of the fiber amplifier system includes (a) a (seed) beam splitting section; (b) an amplitude and phase control component; and (c) a mode multiplexer that maps multiple individual signal beams to different fiber modes.

A mounting surface defines a branching channel, the branching channel having a main channel and one or more sub-channels branching off the main channel. An optic fiber is affixed to the mounting surface, the optic fiber including a cladding layer and an interior surrounded by the cladding layer, wherein part of the optic fiber is suspended over the main channel. A clad light stripper includes one or more discontinuities in an outer surface of the cladding layer of a suspended section of the optic fiber, the one or more outer surface discontinuities to release a portion of the process light. The one or more subchannels include a first sub-channel having an ingress located to capture released light from an individual one of the one or more discontinuities and trap at least a portion thereof.

The present embodiment relates to an optical amplifier and the like having a structure for enabling efficient use of pumping light while avoiding complication of a device structure. In such an optical amplifier, since pumping light from a pumping light source is supplied to each core of an amplification MCF, a coupling MCF in which adjacent cores form a coupled core is arranged between the amplification MCF and the pumping light source. The pumping light source is optically connected to a specific core of the coupling MCF, and pumping light is coupled from the specific core to remaining cores except the specific core in the coupling MCF before pumping light is supplied to each core of the amplification MCF. This enables coupling of pumping light between optically connected cores between the amplification MCF and the coupling MCF.

Signal combined optical fiber devices, systems, and methods for reducing signal spectrum pumping of Raman spectrum. Power of a Raman component in an output of a signal combined fiber laser system may be reduced by diversifying peak signal wavelengths across a plurality of signal generation and/or amplification modules that are input into a signal combiner. In some examples, fiber laser oscillators that are to have their output signals combined to reach a desired cumulative system output power are tuned to output signal bands of sufficiently different wavelengths that signal from separate ones of the oscillators do not collectively pump a single Raman band. With the combined signal component comprising different peak signal wavelengths, the Raman component of combined output may have multiple peak wavelengths and significantly lower power than in systems where signals of substantially the same signal peak wavelength are combined.

Pump reflectors for use in cladding-pumped fiber systems, such as laser or amplifier systems, are provided. The pump reflector includes an optical fiber segment having at least one core and at least one cladding. A cladding Bragg grating is written by femtosecond inscription in the optical fiber segment, and extending across at least a portion of the cladding. The cladding Bragg grating has a reflectivity profile encompassing the spectral profile of the pump and a spatial profile encompassing the pump spatial distribution in the cladding. A method of manufacturing a pump reflector using femtosecond light pulses is also provided.

The present technology provides large mode area optical fibers engineered to have normal dispersion around 1600 nm, enabling high power Raman amplification at eye safer wavelengths. The fibers can have a main core and one or more side cores disposed relative to the main core so that modes of the main core and the one or more side cores hybridize into supermodes with modified dispersion.

An optical apparatus includes one or more pump sources situated to provide laser pump light, and a gain fiber optically coupled to the one or more pump sources, the gain fiber including an actively doped core situated to produce an output beam, an inner cladding and outer cladding surrounding the doped core and situated to propagate pump light, and a polymer cladding surrounding the outer cladding and situated to guide a selected portion of the pump light coupled into the inner and outer claddings of the gain fiber. Methods of pumping a fiber sources include generating pump light from one or more pump sources, coupling the pump light into a glass inner cladding and a glass outer cladding of a gain fiber of the fiber source such that a portion of the pump light is guided by a polymer cladding surrounding the glass outer cladding, and generating a single-mode output beam from the gain fiber.

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 amplifying optical fiber includes a common cladding comprising a radius defining a glass portion of the amplifying optical fiber and having a relative refractive index Δ.sub.4. At least one waveguide extends through the common cladding The at least one waveguide includes a core region, an inner cladding region encircling and directly contacting the core region, and a depressed cladding region encircling and directly contacting the inner cladding region. The core region includes from greater than or equal to about 500 ppm and less than or equal to about 10,000 ppm Er.sub.2O.sub.3 and has core maximum relative refractive index Δ.sub.1max. The inner cladding region includes an inner cladding relative refractive index Δ.sub.2. The depressed cladding region includes a minimum depressed relative refractive index Δ.sub.3min such that Δ.sub.1max>Δ.sub.2>Δ.sub.3min and Δ.sub.4>Δ.sub.3min.

In some implementations, a master oscillator power amplifier (MOPA) system may include one or more pump laser sources, a power amplifier, and a multicore oscillator that includes an input side coupled to the one or more pump laser sources and an output side coupled to the power amplifier. In some implementations, the multicore oscillator may include an active fiber, including an inner cladding, an outer cladding surrounding the inner cladding, and multiple active fiber cores, embedded in the inner cladding, to convert pump light into signal light. In some implementations, the multicore oscillator may include multiple first reflectors that are each configured to operate as a high reflector on the input side of the oscillator, and multiple second reflectors that are each configured to operate as an output coupler on the output side of the oscillator.