A structure includes: an optical fiber including a large-diameter section that is larger in diameter than a remainder of the optical fiber; and a glass block joined to a first end face of the large-diameter section of the optical fiber. The large-diameter section includes a tapering section that: includes, as part of a surface thereof, a sloping surface sloping at an angle of more than 0° and less than 90° to an optical axis of the optical fiber; and is disposed in a portion other than the first end face.

A hybrid optical amplifier is proposed that includes a preamplifier element formed of single-clad Ho-doped optical fiber and a power amplifier element formed of single-clad Tm-doped (or Tm—Ho co-doped) optical fiber. The preamplifier is used to impart gain to an input signal propagating at a wavelength λ.sub.S in the presence of a first pump beam operating at λ.sub.P1, creating an amplified output over a defined transmission bandwidth. The power amplifier element is disposed at the output of the preamplifier element and provides an additional level of gain to the output of the preamplifier element in the presence of a second pump beam operating at λ.sub.P2. A passband filter may be used between the preamplifier and the power amplifier to ensure that only wavelength components within the defined transmission bandwidth are applied as an output to the power amplifier.

A ring cavity laser source, a tunable ring cavity laser source and a method of fabricating a ring cavity laser source. The fiber ring cavity laser source comprises a fiber pigtailed pump laser; a fiber-based gain medium; a fiber-based circulator; a fiber-based coupler, wherein an input fiber port of the fiber-based coupler is coupled to a first end of the fiber-based gain medium, a first output fiber port of the fiber-based coupler is coupled to a first fiber port of the fiber-based circulator, and a second output fiber port of the fiber-based coupler is configured for extracting a laser output of the fiber ring cavity laser source; a fiber-based reflector coupled to a second fiber port of the fiber-based circulator; and a fiber-based combiner, wherein a first input fiber port of the fiber-based combiner is coupled to the fiber pigtailed pump laser, a second input fiber port of the fiber-based combiner is coupled to a third fiber port of the fiber-based circulator, and an output fiber port of the fiber-based combiner is coupled to a second end of the fiber-based gain medium; wherein the fiber-based reflector is configured for wavelength tuning of the laser output.

The present technology provides large mode area optical fibers engineered to have normal dispersion around 1600 nm, enabling high power Raman amplification at eye safer wavelengths. The fibers can have a main core and one or more side cores disposed relative to the main core so that modes of the main core and the one or more side cores hybridize into supermodes with modified dispersion.

A tunable narrow-linewidth photo-generated microwave source based on polarization control includes a high-reflectivity fiber grating, a high-gain fiber, a low-reflectivity polarization-maintaining fiber grating, a stress adjusting device, a single-mode semiconductor pump laser, an optical wavelength division multiplexer, a polarization beam splitter, a polarization controller, an optical coupler, and a photoelectric detector. Birefringence distribution in the low-reflectivity polarization-maintaining fiber grating is controlled by adjusting a stress magnitude of the stress adjusting device to the low-reflectivity polarization fiber grating, thereby controlling a laser frequency working in different polarization modes in a resonant cavity, and a tunable narrow-linewidth photo-generated microwave source is generated by a beat-frequency technology using a dual-wavelength narrow-linewidth laser with variable frequency intervals.

Provided is a single-crystal fiber including a waveguide structure for a wavelength to be subjected to optical amplification, in which at least one end of the single-crystal fiber is planar, an angle θ between a normal to a facet of the single-crystal fiber and an optical axis of the single-crystal fiber satisfies a relationship of θ=90°−tan.sup.−1(n.sub.2/n.sub.1), where n.sub.1 represents a refractive index of a medium of a space that uses the single-crystal fiber, and n.sub.2 represents a refractive index of the single-crystal fiber for a guided light beam having a polarization direction parallel with a plane that includes the normal to the facet and the optical axis, and a diameter Dx in an X-direction and a diameter Dy in a Y-direction of a cross-section of the single-crystal fiber perpendicular to the optical axis satisfies a relationship of (n.sub.2/n.sub.1)0.9≤Dx/Dy≤(n.sub.2/n.sub.1)1.1.

An amplifying optical fiber includes a common cladding comprising a radius defining a glass portion of the amplifying optical fiber and having a relative refractive index Δ.sub.4. At least one waveguide extends through the common cladding The at least one waveguide includes a core region, an inner cladding region encircling and directly contacting the core region, and a depressed cladding region encircling and directly contacting the inner cladding region. The core region includes from greater than or equal to about 500 ppm and less than or equal to about 10,000 ppm Er.sub.2O.sub.3 and has core maximum relative refractive index Δ.sub.1max. The inner cladding region includes an inner cladding relative refractive index Δ.sub.2. The depressed cladding region includes a minimum depressed relative refractive index Δ.sub.3min such that Δ.sub.1max>Δ.sub.2>Δ.sub.3min and Δ.sub.4>Δ.sub.3min.

Systems and methods include a radiation source configured to generate a first waveform, a first separator configured to separate the first waveform into linearly polarized second and third waveforms, a first modulator configured to modulate at least one of a phase and a polarization of the second waveform to generate a fourth waveform, a second modulator configured to modulate at least one of a phase and a polarization of the third waveform to generate a fifth waveform, a first combiner configured to combine the fourth and fifth waveforms to generate a sixth waveform, an amplifier configured to amplify the sixth waveform to generate a seventh waveform, a second separator configured to separate the seventh waveform into a plurality of amplified waveforms, and beam directing optics configured to direct the plurality of amplified waveforms to form an output waveform at a target location.

An apparatus and method for cooling an optical fiber, comprising impinging electromagnetic radiation from a laser on an optical fiber comprising a core, in which the electromagnetic radiation is substantially confined, and a cladding, in thermal communication with the core, configured to provide optically activated cooling of the core via the electromagnetic radiation from the laser.

A fiber laser apparatus includes: a short-length type fiber to which an active element is added and that has a length of 300 mm or less: a ferrule attached to an end of the fiber; and a housing that accommodates the fiber and supports the fiber with the ferrule. Each of the housing and the ferrule is composed of a material having a first thermal expansion coefficient that is equal to or have a predetermined difference from a second thermal expansion coefficient of a raw material of the fiber. The predetermined difference between the first and second thermal expansion coefficients is within −8.6×10.sup.−6 to 11.4×10.sup.−6/K.