Abstract: 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.

Abstract: A fixture for aligning a linear array of optical fiber terminators includes a base and a heightwise stack of positioning devices disposed on the base. Each positioning device includes an anchor secured to a lengthwise wall of a bracket coupled to the base, a terminator holder flexibly coupled to the anchor and having a lengthwise channel for holding a respective optical fiber terminator, and actuators controlling position and yaw of the terminator holder in a plane orthogonal to the heightwise direction. The terminator holder has planar top and bottom surfaces that define a height of the terminator holder and interface with the terminator holder of any adjacent positioning device. The fixture also includes a clamp for clamping the positioning device stack against the base after setting the in-plane position and yaw of each terminator holder. Individual positioning devices may be adjusted or replaced without disturbing the rest of the stack.

Abstract: A dual-grating spectral beam combiner includes a series of sources emitting a respective series of diverging laser beams with mutually parallel center rays offset from each other in a one-dimensional array. The laser beam wavelengths are incremented monotonically across the array. A first diffraction grating receives the diverging laser beams from the sources and diffracts the diverging laser beams to form respective once-diffracted diverging beams with mutually converging center rays. A second diffraction grating is positioned where the center rays of the once-diffracted diverging beams coincide, and diffracts the once-diffracted diverging beams to form a single combined diverging laser beam consisting of twice-diffracted diverging beams. The combined diverging laser beam may be subsequently collimated.

Abstract: A fixture for aligning a linear array of optical fiber terminators includes a base and a heightwise stack of positioning devices disposed on the base. Each positioning device includes an anchor secured to a lengthwise wall of a bracket coupled to the base, a terminator holder flexibly coupled to the anchor and having a lengthwise channel for holding a respective optical fiber terminator, and actuators controlling position and yaw of the terminator holder in a plane orthogonal to the heightwise direction. The terminator holder has planar top and bottom surfaces that define a height of the terminator holder and interface with the terminator holder of any adjacent positioning device. The fixture also includes a clamp for clamping the positioning device stack against the base after setting the in-plane position and yaw of each terminator holder. Individual positioning devices may be adjusted or replaced without disturbing the rest of the stack.

Abstract: 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.

Abstract: The present disclosure relates more to mode mixing optical fibers useful, for example in providing optical fiber laser outputs having a desired beam product parameter and beam profile. In one aspect, the disclosure provides a mode mixing optical fiber for delivering optical radiation having a wavelength, the mode mixing optical fiber having an input end, an output end, a centerline and a refractive index profile, the mode mixing optical fiber comprising: an innermost core, the innermost core having a refractive index profile; and a cladding disposed about the innermost core, wherein the mode mixing optical fiber has at least five modes at the wavelength, and wherein the mode mixing optical fiber is configured to distribute a fraction of the light input at its input end from its lower-order modes to its higher-order modes.

Abstract: An optical apparatus for depolarizing a laser beam within a fiber MOPA laser is disclosed. The apparatus includes a first phase modulator for spectral broadening, a linear polarizer, an optical coupler, a second phase modulator for depolarizing the laser beam, and a polarization-maintaining optical fiber. The optical coupler divides a linearly-polarized portion of the laser beam equally between fast and slow axes of the second phase modulator. The laser beam delivered by the polarization-maintaining optical fiber is truly unpolarized. The apparatus provides independent control of the spectral broadening and the depolarization to mitigate stimulated Brillouin scattering during subsequent amplification. A method for depolarizing a laser beam, using this apparatus, is also disclosed.

Abstract: The present disclosure relates to optical fiber amplifying systems having operability at a wide variety of ambient temperatures and to methods for using them. One aspect of the disclosure is an optical fiber system configured to provide amplified radiation. The system includes an active optical fiber; a plurality of grating-locked pump sources, each having an output optically coupled to the active optical fiber; one or more temperature sensors, configured to measure a temperature associated with one or more of the grating-locked pump sources; and a control system configured to accept measurements from the one or more temperature sensors and, for a desired total pump power output, to provide to one or more of the grating-locked pump sources a set of drive currents suitable to provide the desired total pump power output.

Abstract: A high-power fiber laser produces a compound output beam having a center beam and an annular beam. The center beam and the annular beam are independently adjustable in power and wavelength. The output beam is delivered from an output optical fiber having a center core and a concentric annular core. A fundamental beam generated by a seed laser is amplified by a fiber amplifier and partially converted to a second-harmonic beam by a second-harmonic generator. The residual fundamental beam and second-harmonic beam are separated, attenuated, and selectively coupled into the cores of the output optical fiber.

Abstract: A high-power fiber laser produces a compound output beam having a center beam and an annular beam. The center beam and the annular beam are independently adjustable in power and wavelength. The output beam is delivered from an output optical fiber having a center core and a concentric annular core. A fundamental beam generated by a seed laser is amplified by a fiber amplifier and partially converted to a second-harmonic beam by a second-harmonic generator. The residual fundamental beam and second-harmonic beam are separated, attenuated, and selectively coupled into the cores of the output optical fiber.

Abstract: The present disclosure relates to systems and methods for reducing thermal effects in double-clad clad optical fiber amplifying systems via control of the pump absorption. One optical fiber amplifying system for reducing thermal effects includes one or more first optical pump sources, each configured to output radiation of a pump wavelength, a bridge optical fiber, having an input configured to receive the radiation of the pump wavelength output by the one or more first optical pump sources and an output, and an active optical fiber that has a first end substantially directly coupled to the output of the bridge optical fiber and a second end. The active optical fiber is configured to amplify radiation of the first active wavelength when pumped with radiation of the pump wavelength.

Abstract: The present disclosure relates to thiol-ene based coating compositions and polymeric compositions that are resistant to high temperature, as well as optical fibers coated with such polymeric compositions. In one aspect, the disclosure provides a radiation-curable optical fiber coating composition that includes at least 20 wt % of one or more at least trifunctional ethylenically unsaturated monomers, each having three or more free radical polymerizable ethylenic unsaturations; at least 20 wt % of one or more at least trifunctional thiol monomers, each having three or more free radical polymerizable thiols; and an effective amount of a free radical photoinitiator, wherein the ratio of the number of polymerizable ethylenic unsaturations of the curable composition to the number of polymerizable thiols of the curable compositions is at least about 1.

Abstract: A method for operating a fiber optic gyroscope to measure angular velocity uses a closed-loop modulation scheme. Two-state modulation voltages are applied to an optical modulator and continuously adjusted to maintain a null difference between corresponding demodulated voltages from a photodetector. If one of the modulation voltages reaches a threshold voltage, the continuous nulling adjustment is interrupted briefly while the two-state modulation voltages are reset to values that correspond to relative phases of ?/2 and ??/2 when the gyroscope is stationary, then the continuous adjustment is resumed. This reoccurring resetting, while the gyroscope accelerates or decelerates, substantially increases the dynamic range over which the gyroscope can precisely measure angular velocity.

Abstract: An optical apparatus for depolarizing a laser beam within a fiber MOPA laser is disclosed. The apparatus includes a first phase modulator for spectral broadening, a linear polarizer, an optical coupler, a second phase modulator for depolarizing the laser beam, and a polarization-maintaining optical fiber. The optical coupler divides a linearly-polarized portion of the laser beam equally between fast and slow axes of the second phase modulator. The laser beam delivered by the polarization-maintaining optical fiber is truly unpolarized. The apparatus provides independent control of the spectral broadening and the depolarization to mitigate stimulated Brillouin scattering during subsequent amplification. A method for depolarizing a laser beam, using this apparatus, is also disclosed.

Abstract: The present disclosure relates more particularly to active optical fibers, amplified spontaneous emission (ASE) sources using such active optical fibers, and imaging and detection systems and methods using such ASE sources. In one aspect, the disclosure provides an active optical fiber that includes a rare earth-doped gain core configured to emit radiation at at least a peak wavelength emitted wavelength when pumped with pump radiation having a pump wavelength; a pump core surrounding the gain core; and a cladding surrounding the pump core, wherein the value M=16R2(NA)2/?2 in which R is the gain core radius, NA is the active optical fiber numerical aperture, and ? is the peak emitted wavelength, is at least 50, or at least 100. The present disclosure also provides an optical source that includes the optical fiber coupled to a pump source.

Abstract: The present disclosure relates more to mode mixing optical fibers useful, for example in providing optical fiber laser outputs having a desired beam product parameter and beam profile. In one aspect, the disclosure provides a mode mixing optical fiber that includes a core having a refractive index profile; and a cladding disposed about the core. The core of the mode mixing optical fiber supports at least two (e.g., at least five) guided modes at the wavelength. The mode mixing optical fiber is configured to substantially distribute optical radiation having the wavelength propagating therein (e.g., input at its input end or generated or amplified within the core) among a plurality of the guided modes (e.g., to distribute a substantial fraction of the optical radiation having the wavelength propagating therein from its lower-order guided modes to its higher-order guided modes).

Abstract: The present disclosure relates to methods and apparatuses for providing optical radiation having improved rise/fall times and improved levels of leakage. One method for amplifying optical radiation includes an intermediate stage (220) having an intermediate active optical fiber (222), the intermediate active optical fiber and a final amplifying stage (230) including a final active optical fiber (232), and providing optical radiation to the input of the intermediate active optical fiber, wherein one or more final optical pump sources (235) are together in a low power state such that the optical radiation is substantially absorbed by the intermediate active optical fiber and such that substantially no optical radiation of the amplified wavelength is transmitted by the intermediate stage. The intermediate active optical fiber (222) can then be switched to a transmissive state by switching the final optical pump source(s) (235) to a high power state.

Abstract: A method for operating a fiber optic gyroscope to measure angular velocity uses a closed-loop modulation scheme. Two-state modulation voltages are applied to an optical modulator and continuously adjusted to maintain a null difference between corresponding demodulated voltages from a photodetector. If one of the modulation voltages reaches a threshold voltage, the continuous nulling adjustment is interrupted briefly while the two-state modulation voltages are reset to values that correspond to relative phases of ?/2 and ??/2 when the gyroscope is stationary, then the continuous adjustment is resumed. This reoccurring resetting, while the gyroscope accelerates or decelerates, substantially increases the dynamic range over which the gyroscope can precisely measure angular velocity.

Abstract: Methods and apparatuses for determining the polarization state and for providing polarization control in optical fiber lasers and amplifiers. One embodiment of the invention is an optical fiber amplifying system including a circulator (260) having a first optical port (260a), a second optical port (260b) that is configured to output radiation received from the first optical port, and a third optical port (260c) that is configured to output radiation received from the second optical port; one or more amplifier stages (216) connected in series, together having an optical input (216a) optically coupled to the second port of the circulator, and an optical output (216b); and a polarization detector (240) having an optical input optically coupled to the third port of the circulator. Thereby the polarization state of the amplified radiation can be determined using radiation backscattered from the amplifying stage.

Abstract: The present invention relates generally to high brightness optical fiber systems and, more particularly to optical fiber systems 104 having an optical power module 151 remote from an initial amplifier stage 101. In one aspect of the invention, the optical fiber system comprises a first active optical fiber 102 operatively coupled to one or more first pump sources 104; a first signal optical fiber 110 coupled to the first active optical fiber 102; one or more final pump sources 120; one or more final pump optical fibers 130, coupled to one or more of the final pump sources 120; and spatially separated from the one or more final pump sources 120 and the initial amplifier stage 101 comprising the first active optical fiber 102, a power module 151, comprising a final active optical fiber 150, coupled to the first signal optical fiber 110, said final active optical fiber 150 being coupled to said one or more final pump optical fibers 130.