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 fiber laser apparatus includes: amplification optical fibers including first and second amplification optical fibers, each of which having different amplification characteristics and including a core to which an active element is doped; one or more cooling plates having a first cooling surface that thermally contacts and cools the first amplification optical fiber and a second cooling surface that thermally contacts and cools the second amplification optical fiber; one or more module boxes including a gain module box that houses the amplification optical fibers and the one or more cooling plates; and an enclosure housing the one or module boxes. The first and second cooling surfaces are disposed at different heights in the gain module box. At least a portion of the first cooling surface overlaps at least a portion of the second cooling surface as viewed along a height direction.

The invention discloses a preparation method and device of active microcrystalline fiber, place the prefabricated rod in the drawing furnace for wire drawing, the drawn fiber is induced by magnetic field in uncoated state and combined with laser treatment technology, the laser beam is focused on the fiber and recrystallized after laser treatment to obtain active microcrystalline fiber. Appropriate laser processing power directly affects the silicate glass fiber in the crystal structure, type, degree of crystallinity, grain size, content, and how much residual phase of glass. Induced by external magnetic field, the thermodynamics and dynamics of crystallization process are changed, make the crystal size distribution is better and uniform, reduce the phenomenon of condensation and makes the grain size is smaller.

An apparatus includes an amplified spontaneous emission source, which in turn includes an optical fiber. The optical fiber includes a solid core and a first end. The solid core includes a silica matrix. The silica matrix includes a rare-earth element and a glass co-dopant. The rare-earth element includes dysprosium or neodymium. The glass co-dopant includes Al.sub.2O.sub.3. The apparatus further includes a laser pump diode coupled to the first end of the optical fiber. The laser pump diode and the optical fiber cooperate to generate a spontaneous spectral emission confined to the solid core. The spontaneous spectral emission includes a simultaneous plurality of spectral regions.

An amplifier operable with an electric drive signal can amplify signal light having a signal wavelength. A laser diode has an active section with input and output facets. The facets are in optical communication with the signal light and are configured to pass the signal light through the laser diode. The active section is configured to generate pump light in response to injection of the electrical drive signal into the active section. The pump light has a pump wavelength different from the signal wavelength. A doped fiber doped with an active dopant is in optical communication with the signal light and is in optical communication with at least a portion of the pump light from the laser diode. The pump wavelength of the pump light is configured to interact with the active dopant of the fiber and thereby amplify the signal light.

An optical amplifier is provided in which adjacent ones of a plurality of cores each containing a rare-earth element and included in an amplifying multi-core optical fiber (MCF) serve as coupled cores at an amplifying wavelength, a connecting MCF is connected to the amplifying MCF, a pump light source is connected to the connecting MCF, and the pump light source pumps the rare-earth element in the amplifying MCF through the connecting MCF.

A laser apparatus according to an aspect of the present disclosure includes a plurality of semiconductor lasers, a plurality of optical switches disposed in the optical paths of the plurality of respective semiconductor lasers, a wavelength conversion system configured to convert pulsed beams outputted from the plurality of optical switches in terms of wavelength to generate wavelength-converted beams, an ArF excimer laser amplifier configured to amplify the wavelength-converted beams, and a controller configured to control the operations of the plurality of semiconductor lasers and the plurality of optical switches, and the plurality of semiconductor lasers are each configured to output a laser beam so produced that wavelengths of the wavelength-converted beams are wavelengths at which the ArF excimer laser amplifier performs amplification and differ from the optical absorption lines of oxygen.

This application discloses an optical amplifier including a Raman fiber amplifier (RFA), a dynamic gain equalizer (DGE), a filter, an erbium-doped fiber amplifier (EDFA), an RFA gain controller, an EDFA gain controller, and an optical amplifier controller. The optical amplifier controller is configured to provide instructions to and receive feedback from the RFA and EDFA gain controllers. The RFA and the EDFA are configured to amplify an optical signal. The RFA gain controller is configured to control the RFA to adjust a gain. The EDFA gain controller is configured to control the EDFA to adjust a gain. The DGE adjusts insertion loss. The filter is configured to filter an amplified spontaneous emission signal produced in an optical amplification process of the RFA.

A figure-8 laser is configured in which gain in the uni-directional loop can be removed while maintaining mode-locked operation with gain only in the bi-directional nonlinear amplifying loop. Simplified self-starting and control over pulse characteristics by controlling gain in the bi-directional loop is made possible.

An amplification fiber which can generate a laser beam in a visible region even when a silica glass is used as a base material of a core of the amplification fiber is realized. An amplification fiber according to an embodiment of the present disclosure includes a core configured to generate a laser beam from an excitation beam in a visible region, and a cladding surrounding the core. The core is composed of a core material including Dy, one or more elements selected from Al, Ge, and P, and a silica glass.