A filter device includes: an optical fiber that allows light having a predetermined wavelength to propagate in multimode; a first higher-order mode filter that removes at least part of the light in any higher order mode than a predetermined mode in the light in the multimode propagating in the optical fiber; and a fiber Bragg grating that transmits the light having the predetermined wavelength and reflects light having a particular wavelength longer than the predetermined wavelength.

Techniques for managing gain equalization error in optical communication systems are provided. For example, a multi-stage gain correction filter may be configured to at least correct gain equalization error produced by filters with insufficient resolution, for example, conventional non-reflective gain correction technology used in the optical communication systems. The multi-stage filter may include at least a broadband gain correction filter to correct gain equalization error in most of the transmission bandwidth and a narrow band gain correction filter to correction error in a narrow region of the bandwidth. One or more of the multi-stage filters may be implemented in the repeaters of the system (which may be referred to as hybrid GFFs) or may be included in a standalone body (which may be referred to as hybrid GEFs).

An optical device includes a core, a first cladding, a second cladding, a slanted fiber Bragg grating, and a high refractive index material. The first cladding covers the core and has a lower refractive index than the core. The second cladding covers the first cladding and has a lower refractive index than the first cladding. The slanted fiber Bragg grating is formed in the core and couples stimulated Raman scattering light, propagating through the core, to the first cladding. The high refractive index material has a higher refractive index than the second cladding and covers an outer peripheral surface of a removal portion where the second cladding is removed and a portion of the first cladding that covers the region where the slanted fiber Bragg grating is formed in the core.

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 surgical laser system includes a pump module configured to produce pump energy within an operating wavelength, a gain medium configured to convert the pump energy into first laser energy, a non-linear crystal (NLC) configured to convert a portion of the first laser energy into second laser energy, which is a harmonic of the first laser energy, an output, and a first path diversion assembly having first and second operating modes. When the first path diversion assembly is in the first operating mode, the first laser energy is directed along the output path to the output, and the second laser energy is diverted from the output path and the output. When the first path diversion assembly is in the second operating mode, the second laser energy is directed along the output path to the output, and the first laser energy is diverted from the output path and the output.

A fiber laser apparatus includes a pump light source that emits pump light; a pump delivery fiber that guides the pump light; an amplifying optical fiber that is optically coupled to the pump delivery fiber and guides laser light; and a filter element that causes more loss of light of a wavelength range that includes a peak wavelength of at least one of Stokes light and anti-Stokes light than the laser light. The Stokes light and anti-Stokes light result from four-wave mixing involving a plurality of guide modes in a multi-mode fiber that guides the laser light. The filter element is disposed between: the pump delivery fiber and the amplifying optical fiber, the amplifying optical fiber and the multi-mode fiber, or at the multi-mode fiber.

A WDM seed beam source for a fiber laser amplifier system that includes a number of master oscillators that generate seed beams at different wavelengths and a spectral multiplexer that multiplexes all of the seed beams onto a single fiber. An EOM modulates the combined seed beams on the single fiber and a spectral demultiplexer then separates the modulated seed beams into their constituent wavelengths on separate fibers before the seed beams are amplified and spectrally combined. The fiber laser amplifier system includes a separate fiber amplifier that amplifies the separated seed beams, an emitter array that directs the amplified beams into free space, beam collimating optics that focuses the uncombined beams, and an SBC grating responsive to the collimated uncombined beams that spatially combines the collimated uncombined beams.

Techniques for managing gain equalization error in optical communication systems are provided. For example, a multi-stage gain correction filter may be configured to at least correct gain equalization error produced by filters with insufficient resolution, for example, conventional non-reflective gain correction technology used in the optical communication systems. The multi-stage filter may include at least a broadband gain correction filter to correct gain equalization error in most of the transmission bandwidth and a narrow band gain correction filter to correction error in a narrow region of the bandwidth. One or more of the multi-stage filters may be implemented in the repeaters of the system (which may be referred to as hybrid GFFs) or may be included in a standalone body (which may be referred to as hybrid GEFs).

A low-noise amplifier includes a gain medium and two or more amplifier stages. Each amplifier stage includes an optical filter to pass all wavelengths of a respective input optical signal in a given propagation direction over the gain medium and reflect wavelengths above a respective threshold wavelength received in the opposite direction, and a respective Raman pump to inject a pump light centered at a wavelength lower than the threshold wavelength onto the gain medium for transmission in the given direction. A first amplifier stage outputs a first combined optical signal including all wavelengths of the respective input optical signal and a pump light injected by the respective Raman pump. The second amplifier stage receives the first combined optical signal as its input and outputs a second combined optical signal including all wavelengths of the first combined optical signal and a pump light injected by the respective Raman pump.

An example apparatus includes an optical fiber including a core and cladding, the core being situated to propagate an optical beam along a propagation axis associated with the core, and at least one fiber Bragg grating (FBG) situated in the core of the optical fiber, the fiber Bragg grating including a plurality of periodically spaced grating portions situated with respect to the propagation axis so that light associated with Raman scattering is directed out of the core so as to reduce the generation of optical gain associated with stimulated Raman scattering (SRS).