An optical fiber includes a core and a cladding. An effective area A.sub.eff of light of a fundamental mode, having a wavelength of 1070 nm and propagating through the core, is 500 μm.sup.2 or more. A numerical aperture NA of the core satisfies the following formula:

NA≥(1.3×10.sup.−11×a.sup.4/b.sup.6).sup.1/6

where a (m) is a radius of the core and b (m) is a radius of the cladding. A V value, that is a waveguide parameter of the optical fiber, satisfies the following formula:

V≤1.3583×b.sup.−0.2555.

An optical semiconductor device outputting a predetermined wavelength of laser light includes a quantum well active layer positioned between a p-type cladding layer and an n-type cladding layer in thickness direction. The optical semiconductor device includes a separate confinement heterostructure layer positioned between the quantum well active layer and the n-type cladding layer. The optical semiconductor device further includes an electric-field-distribution-control layer positioned between the separate confinement heterostructure layer and the n-type cladding layer and configured by at least two semiconductor layers having band gap energy greater than band gap energy of a barrier layer constituting the quantum well active layer. The optical semiconductor device is applied to a ridge-stripe type laser.

A system includes multiple first thulium-doped fiber lasers each configured to generate pumplight. The system also includes a second thulium-doped fiber laser configured to receive the pumplight from the first thulium-doped fiber lasers and a seed signal. The second thulium-doped fiber laser is also configured to amplify the seed signal using the pumplight. The first thulium-doped fiber lasers are configured to forward-pump the second thulium-doped fiber laser. The second thulium-doped fiber laser includes a fiber gain medium, where the fiber gain medium includes a core doped with thulium and a cladding. The fiber gain medium is longitudinally up-tapered such that a diameter of the core and a diameter of the cladding increase along at least a portion of a length of the fiber gain medium.

A fiber optic ring laser, and non-transitory computer readable medium for using a fiber optic ring laser are disclosed. The disclosed fiber optic ring laser includes a semiconductor booster optical amplifier (BOA), as a gain medium; a Fiber Fabry Perot Tunable Filter (FFP-TF), as a wavelength selection element; an optical isolator (ISO) to insure unidirectional operation of the fiber optic ring laser; and a polarization controller (PC) for attaining an optimized polarization state in order to achieve a stable-generated output in terms of output power and wavelength, wherein the BOA, the FFP-TF, the ISO and the PC are coupled to form a ring configuration that implements a continuously tunable booster amplifier-based fiber ring laser.

Binary-phase-shift-key, phase-modulated waveforms with gigahertz bandwidths, suitable for kilowatt-class fiber amplifiers, can be narrowed back to the source laser’s linewidth via second-harmonic, sum-frequency, or difference-frequency generation in a second-order nonlinear crystal. The spectrum of an optical signal phase-modulated with a pseudo-random bit sequence (PRBS) waveform recovers its original optical spectrum when frequency-doubled using second-harmonic generation (SHG). Conceptually, the PRBS waveform is cancelled by the SHG process, and the underlying laser spectrum is converted to the second-harmonic wavelength as though the PRBS modulation were not present. The same cancellation is possible with sum-frequency generation (SFG) and difference frequency generation (DFG), making it possible to construct high-power, narrow-linewidth lasers at wavelengths from the visible to the long-wave infrared. Using ytterbium-, erbium-, thulium-, and neodymium-doped fibers with SHG, SFG and DFG processes allows generation of high-power beams with very narrowband optical spectra and wavelengths from below 400 nm to beyond 5 .Math.m.

A method for providing spectral beam combining (SBC) including generating a plurality seed beams each having a central wavelength and a low fill factor profile, where the wavelength of all of the seed beams is different; amplifying the seed beams; causing the amplified beams to expand as they propagate so as to be converted from the low fill factor profile to a high fill factor profile where the high fill factor profile tapers to a lower value at a perimeter of each beam; causing a wavefront of the converted beams to flatten to provide a plurality of adjacent SBC beams having different wavelengths with minimal overlap and a minimal gap between the beams; collimating the SBC beams; and directing the collimated SBC beams onto an SBC element that spatially diffracts the individual beam wavelengths and directing the beams in the same direction as a combined output beam.

A hybrid coherent beam combining (CBC) and spectral beam combining (SBC) fiber laser amplifier system including a beam shaper array assembly and a beam source that provides a plurality of beams having a low fill factor profile. The assembly includes an input beam shaper array having a plurality of rectilinear input cells positioned adjacent to each other that are shaped to cause the beam to expand as it propagates away from the input array to be converted from the low fill factor profile to a high fill factor profile. The assembly further includes an output beam shaper array having a plurality of output cells positioned adjacent to each other that are shaped to cause the beam to stop expanding so that the output array provides a plurality of adjacent beams with minimal overlap and a minimal gap between the beams.

A coherently beam combining (CBC) fiber laser amplifier system including beam shaper array assembly and a beam source that provides a plurality of beams having a low fill factor profile. The assembly includes an input beam shaper array having a plurality of input cells positioned adjacent to each other that are shaped to cause the beam to expand as it propagates away from the input array to be converted from the low fill factor profile to a high fill factor profile and cause the profile to taper to a lower value at a perimeter of each input array cell. The assembly further includes an output beam shaper array having a plurality of output cells positioned adjacent to each other that are shaped to cause the beam to stop expanding so that the output array provides a plurality of adjacent beams with minimal overlap and a minimal gap between the beams.

An optical semiconductor device outputting a predetermined wavelength of laser light includes a quantum well active layer positioned between a p-type cladding layer and an n-type cladding layer in thickness direction. The optical semiconductor device includes a separate confinement heterostructure layer positioned between the quantum well active layer and the n-type cladding layer. The optical semiconductor device further includes an electric-field-distribution-control layer positioned between the separate confinement heterostructure layer and the n-type cladding layer and configured by at least two semiconductor layers having band gap energy greater than band gap energy of a barrier layer constituting the quantum well active layer. The optical semiconductor device is applied to a ridge-stripe type laser.

A method and system for amplifying optical signals includes generating idler signals for input signals using an optical pump at a first non-linear element (NLE). An intermediate stage including a Raman amplifier performs pump amplification using the output from the first NLE along a single optical path. Optical power monitoring of the input signals may be used for power equalization. The intermediate stage may include a wavelength selective switch for a certain degree of phase modulation. The phase-sensitive amplified signal is generated at a second NLE using the optical pump. Optical power monitoring of the input signals may be used for power equalization and other control functions to achieve low-noise operation.