Abstract: Fiber amplifier and/or mode filter including a linearly birefringent LMA fiber coiled at a radius of curvature over a bend length to differentiate a fundamental optical mode from supported higher-order modes through bending losses. The LMA fiber may be a polarization-maintaining (PM) fiber having a variety of geometrical core shapes and cladding configurations. In some embodiments, the birefringent LMA fiber includes a radially asymmetric core that is angularly rotated over a length of the coiled fiber to ensure bending losses are experienced in orthogonally oriented higher-order modes associated with some orientation relative to the core orientation. In some embodiments, the fiber coiling is two-dimensional with bending occurring only about one axis. In some embodiments, an asymmetric core is pre-spun to a predetermined axial spin profile. In some embodiments, angular rotation of the core is achieved through mechanically twisting an un-spun fiber over a length of the coil.

Abstract: Gain switched laser diode pulses are used as seed pulses for optical pulse generation. ASE is reduced by applying a prebias to the laser diodes at an amplitude less than that associated with a laser diode threshold. An electrical seed pulse having an amplitude larger than that associated with laser threshold is applied within about 10-100 ns of the prebias pulse. The resulting laser diode pulse can be amplified in a pumped, rare earth doped optical fiber, with reduced ASE.

Abstract: A pulse shaper includes a seed laser situated to emit laser pulses, an amplitude modulator situated to receive one or more laser pulse bursts from the seed laser, and a pulse signal generator situated to send a seed pulse signal with a predetermined delay to the seed laser so that the seed laser emits the laser pulses in one or more laser pulse bursts at a selected frequency with each laser pulse burst having a selected number of laser pulses and a selected temporal spacing between laser pulses in the laser pulse burst and situated to send an amplitude pulse signal so that the amplitude modulator adjusts the amplitude of at least one laser pulse in each laser pulse burst.

Abstract: A pulse shaper includes a seed laser situated to emit laser pulses, an amplitude modulator situated to receive one or more laser pulse bursts from the seed laser, and a pulse signal generator situated to send a seed pulse signal with a predetermined delay to the seed laser so that the seed laser emits the laser pulses in one or more laser pulse bursts at a selected frequency with each laser pulse burst having a selected number of laser pulses and a selected temporal spacing between laser pulses in the laser pulse burst and situated to send an amplitude pulse signal so that the amplitude modulator adjusts the amplitude of at least one laser pulse in each laser pulse burst.

Abstract: Fiber amplifier and/or mode filter including a linearly birefringent LMA fiber coiled at a radius of curvature over a bend length to differentiate a fundamental optical mode from supported higher-order modes through bending losses. The LMA fiber may be a polarization-maintaining (PM) fiber having a variety of geometrical core shapes and cladding configurations. In some embodiments, the birefringent LMA fiber includes a radially asymmetric core that is angularly rotated over a length of the coiled fiber to ensure bending losses are experienced in orthogonally oriented higher-order modes associated with some orientation relative to the core orientation. In some embodiments, the fiber coiling is two-dimensional with bending occurring only about one axis. In some embodiments, an asymmetric core is pre-spun to a predetermined axial spin profile. In some embodiments, angular rotation of the core is achieved through mechanically twisting an un-spun fiber over a length of the coil.

Abstract: 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).

Abstract: An optical amplification system is disclosed which includes a seed source providing a seed beam, and a chirally coupled core fiber amplifier optically coupled to the seed beam and configured to convert the coupled seed beam into an amplifier output beam, wherein the polarization of the seed beam is controllably launched into the chirally coupled core fiber in order to reduce nonlinearities in the amplifier output beam. Peak output powers in excess of 500 kW can be realized for short-pulsed single-mode beams having mode field diameters greater than 30 ?m.

Abstract: High power fiber lasers include large or very large mode area active fibers. Mode preserving pump combiners are situated to counter-pump the active fiber using one or more pump sources. The mode preserving pump combiners preserve single mode propagation in a signal fiber, and such combiners can be identified based on optical spectra, beam quality, or temporal response. Active fibers can also be included in a pump combiner so that the active fiber is splice free from an input end that receives a seed pulse to an output end. Peak powers of over 100 kW can be obtained.

Abstract: 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).

Abstract: Nonlinear optical systems include fiber amplifiers using tapered waveguides such as optical fibers that permit multimode propagation but produce amplification and oscillation in a fundamental mode. The tapered waveguides generally are provided with an active dopant that is pumped with an optical pump source such as one or more semiconductor lasers. The active waveguide taper is selected to taper from a single or few mode section to a multimode section, and a seed beam in a fundamental mode is provided to a section of the waveguide taper associated with a smaller optical mode. An amplified beam exits the waveguide taper at a section associated with a larger optical mode. The amplified beam is directed to nonlinear conversion optics such as one or more nonlinear crystals to produce high peak power and high beam quality converted light using second or third harmonic generation, or other nonlinear processes.

Abstract: Pulse power can be stabilized by applying spectrally narrow pulses to a laser diode during gain switching. An injection locking laser with a narrow emission bandwidth is tuned to a gain bandwidth of a laser diode to be gain switched. The injection locking emission is pulsed to provide locking pulses that are attenuated and then coupled to a laser diode. A gain switching pulse drive is applied to the laser diode in the presence of the attenuated locking pulses. The gain switched output is then stabilized with respect to pulse energy and pulse amplitude, and is suitable as a seed pulse for lasers to be used in materials processing.

Abstract: An optical amplification system is disclosed which includes a seed source providing a seed beam, and a chirally coupled core fiber amplifier optically coupled to the seed beam and configured to convert the coupled seed beam into an amplifier output beam, wherein the polarization of the seed beam is controllably launched into the chirally coupled core fiber in order to reduce nonlinearities in the amplifier output beam. Peak output powers in excess of 500 kW can be realized for short-pulsed single-mode beams having mode field diameters greater than 30 ?m.

Abstract: Hybrid laser systems include fiber amplifiers using tapered waveguides and solid-state amplifiers. Typically, such systems represent a technically simple and low cost approach to high peak power pulsed laser systems. The tapered waveguides generally are provided with an active dopant such as a rare earth element that is pumped with one or more semiconductor lasers. The active waveguide taper is selected to taper from a single or few mode section to a multimode section. A seed beam in a fundamental mode is provided to a section of the waveguide taper associated with a smaller optical mode, and an amplified beam exits the waveguide taper at a section associated with a larger optical mode. The waveguide taper permits amplification to higher peak power values than comparable small mode area fibers. The fiber amplified beam is then directed to a solid state amplifier, such as a thin disk or rod-type laser amplifier.

Abstract: Pulse power can be stabilized by applying spectrally narrow pulses to a laser diode during gain switching. An injection locking laser with a narrow emission bandwidth is tuned to a gain bandwidth of a laser diode to be gain switched. The injection locking emission is pulsed to provide locking pulses that are attenuated and then coupled to a laser diode. A gain switching pulse drive is applied to the laser diode in the presence of the attenuated locking pulses. The gain switched output is then stabilized with respect to pulse energy and pulse amplitude, and is suitable as a seed pulse for lasers to be used in materials processing.

Abstract: Gain switched laser diode pulses are used as seed pulses for optical pulse generation. ASE is reduced by applying a prebias to the laser diodes at an amplitude less than that associated with a laser diode threshold. An electrical seed pulse having an amplitude larger than that associated with laser threshold is applied within about 10-100 ns of the prebias pulse. The resulting laser diode pulse can be amplified in a pumped, rare earth doped optical fiber, with reduced ASE.

Abstract: High power fiber lasers include large or very large mode area active fibers. Mode preserving pump combiners are situated to counter-pump the active fiber using one or more pump sources. The mode preserving pump combiners preserve single mode propagation in a signal fiber, and such combiners can be identified based on optical spectra, beam quality, or temporal response. Active fibers can also be included in a pump combiner so that the active fiber is splice free from an input end that receives a seed pulse to an output end. Peak powers of over 100 kW can be obtained.

Abstract: Hybrid laser systems include fiber amplifiers using tapered waveguides and solid-state amplifiers. Typically, such systems represent a technically simple and low cost approach to high peak power pulsed laser systems. The tapered waveguides generally are provided with an active dopant such as a rare earth element that is pumped with one or more semiconductor lasers. The active waveguide taper is selected to taper from a single or few mode section to a multimode section. A seed beam in a fundamental mode is provided to a section of the waveguide taper associated with a smaller optical mode, and an amplified beam exits the waveguide taper at a section associated with a larger optical mode. The waveguide taper permits amplification to higher peak power values than comparable small mode area fibers. The fiber amplified beam is then directed to a solid state amplifier, such as a thin disk or rod-type laser amplifier.

Abstract: Nonlinear optical systems include fiber amplifiers using tapered waveguides such as optical fibers that permit multimode propagation but produce amplification and oscillation in a fundamental mode. The tapered waveguides generally are provided with an active dopant that is pumped with an optical pump source such as one or more semiconductor lasers. The active waveguide taper is selected to taper from a single or few mode section to a multimode section, and a seed beam in a fundamental mode is provided to a section of the waveguide taper associated with a smaller optical mode. An amplified beam exits the waveguide taper at a section associated with a larger optical mode. The amplified beam is directed to nonlinear conversion optics such as one or more nonlinear crystals to produce high peak power and high beam quality converted light using second or third harmonic generation, or other nonlinear processes.

Abstract: 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).