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 quantum well active layer is doped with 0.3 to 1×10.sup.18/cm.sup.3 of n-type impurity.

The present invention benefits from the determination that pre-selected spectral bandwidths that avoid the spectrum of an electronic transition of a metal/alloy vapor allow for welds substantially free from detritus that may discolor the weld. Accordingly, the present invention provides analytical methods, welding methods and fiber lasers configured to provide high quality metal/alloy welds.

An optical system for suppressing signal noise on an optical fiber, including an input power signal; a pump laser configured to receive the input power signal; a phase modulator coupled to the pump laser configured to modulate, in response to the input power signal, a phase of the pump laser to increase a stimulated Brillouin scattering (SBS) threshold of the pump laser, wherein the pump laser is further configured to: increase a power at the pump laser to be greater than the SBS threshold; generate a back scattering power based on the power of the pump laser being greater than the increased SBS threshold; and limit an output power signal of the pump laser based on the generated back scattering power.

A laser system having a multi-pass amplifier system which includes at least one seed source configured to output at least one seed signal having a seed signal wavelength, at least one pump source configured to output at least one pump signal, at least one multi-pass amplifier system in communication with the seed source and having at least one gain media, a first mirror, and at least a second mirror therein, the gain media device positioned between the first mirror and second mirror and configured to output at least one amplifier output signal having an output wavelength range, the first mirror and second mirror may be configured to reflect the amplifier output signal within the output wavelength range, and at least one optical system may be in communication with the amplifier system and configured to receive the amplifier output signal and output an output signal within the output wavelength range.

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 femtosecond pulse laser apparatus includes a pump light source configured to provide a pump light, a gain medium configured to obtain a gain of a laser light using the pump light, a first curved mirror and a second curved mirror, which are provided at both sides of the gain medium, an output mirror configured to transmit a portion of the laser light and reflect the other portion of the laser light to the gain medium, a mode locking portion configured to generate a femtosecond pulse of the laser light, and an acoustic wave generator configured to provide an acoustic wave into the gain medium so as to adjust self-phase modulation of the laser light.

An optical apparatus for spectrally shaping a laser beam within a fiber MOPA laser is disclosed. The apparatus includes a birefringent optic and a linear polarizer. The laser beam is divided between two orthogonal polarization axes of the birefringent optic having polarization mode dispersion. Propagation of the laser beam through the birefringent optic causes a wavelength-dependent phase shift between components of the laser beam in the two polarization axes. A polarizing direction of the polarizer is oriented between the two polarization axes. Propagation of the polarization-dispersed laser beam through the polarizer modulates the power spectral density of a transmitted portion of the laser beam. This spectral modulation can be tuned to shape a Gaussian spectral distribution from the master oscillator into a uniform spectral distribution for amplification by the power amplifier. The uniform spectrally-shaped laser beam can be amplified to higher powers than the original Gaussian laser beam.

A system has fiber amplifiers that amplify a seed signal into a high power signal. Control circuity drives the fiber amplifiers. An auxiliary broad-linewidth signal can be selectively introduced to mitigate the onset of Stimulated Brillouin Scattering (SBS) when the primary input seed source does not meet the requirements of power and/or linewidth. To determine whether to mitigate SBS, an input photodiode can detect the seed signal, and the control circuity can detect an operational parameter associated with a detected signal indicative of an onset of SBS on the optical path. In response to the detection, the control circuitry introduces an auxiliary broad-linewidth signal from a broad-linewidth source, which can mitigate the onset of SBS on the optical path.

The present invention benefits from the determination that pre-selected spectral bandwidths that avoid the spectrum of an electronic transition of a metal/alloy vapor allow for welds substantially free from detritus that may discolor the weld. Accordingly, the present invention provides analytical methods, welding methods and fiber lasers configured to provide high quality metal/alloy welds.

In some implementations, a monolithic optical fiber may comprise a tapered core having a first diameter at an input end and a second diameter at an output end. The tapered core may comprise a first tapered region at the input end, a second tapered region at the output end, and a central region having a constant diameter that is larger than the first diameter and the second diameter. The first tapered region expands monotonically from the first diameter to the constant diameter of the central region along a length of the first tapered region, and the second tapered region contracts monotonically from the constant diameter of the central region to the second diameter along a length of the second tapered region. The monolithic optical fiber may be used as a delivery fiber to deliver a laser beam from a fiber laser engine to a process head.