Aspects of the present disclosure are directed to systems, methods, and structures providing for the accurate measurement of guided acoustic-wave Brillouin scattering in optical fiber transmission systems and facilities.

An optical circuit includes: a multicast-and-select (MCS) switch and multiple optical selective devices coupled to output ports of the MCS switch. The selective devices may select a single optical channel by blocking some of wavelengths of light passing therethrough and passing at least one other wavelength. The selective devices may be wave blockers or tunable optical filters. The optical circuit further includes an optical amplifying array, wherein each amplifier has an input port optically coupled to one of the selective devices. At least some of the amplifiers have pump light ports for receiving at least a portion of the pump light from one or more laser pumps or from another of the optical amplifiers, wherein the pumps are capable of providing pump light sufficient to fully saturate all of the rare earth doped optical fibers in the array.

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.

A fiber laser device includes a pumping light source, an amplifying fiber, an input side fiber fusion-spliced on an input side of the amplifying fiber and formed with a HR-FBG, an output side fiber fusion-spliced on an output side of the amplifying fiber and formed with an OC-FBG having a reflectivity smaller than that of the HR-FBG, an output end, and a mode filter, wherein the input side fiber or an intermediate fiber disposed between the amplifying fiber and the input side fiber is fusion-spliced with the amplifying fiber via a fusion splice portion, and at least a portion of the mode filter is disposed in a region between the fusion splice portion and a position separated from the fusion splice portion by a coherence length of beating caused by mode interference of signal light propagating in the amplifying fiber.

An erbium fiber laser produces a beam of ultrashort laser pulses having a center wavelength greater than 780 nanometers, an average power greater than 0.5 watt, and a pulse duration less than 200 femtoseconds. The fiber laser includes an erbium fiber amplifier that is energized by a pump beam having a pump wavelength longer than 1520 nanometers. The pump wavelength is selected to provide uniform gain over the broad spectral bandwidth of a seed beam and minimal gain at shorter wavelengths in the fiber amplifier, thereby overcoming gain narrowing and gain shifting. The pump beam has sufficient power to achieve pump saturation in the fiber amplifier.

Embodiments discussed herein refer to LiDAR systems and methods that enable substantially instantaneous power and frequency control over fiber lasers. The systems and methods can simultaneously control seed laser power and frequency and pump power and frequency to maintain relative constant ratios among each other to maintain a relatively constant excited state ion density of the fiber laser over time.

An active element-doped optical fiber includes a core that includes a first region and a second region. The first region satisfies 0≤r≤0.65d, and the second region surrounds the first region and satisfies 0.65d<r≤d, where d is a radius of the core and r is a distance from a central axis of the core in a radial direction. At least a part of the first region is doped with an active element excited by excitation light, the second region is not doped with the active element, and a shape index is 0.99 or more and less than 1.

A continuous optical beat laser element for generating terahertz (THz) waves and a laser source using same includes periodically poled lithium niobate (ppLN) crystals arranged along a predetermined direction forming a surface generally parallel to the predetermined direction. A Ti diffused region is applied on the surface and an array of gold nanowires are applied on the Ti diffused region to form a gold metal-insulator-metal (MIM) element that optimizes coupling and channeling of THz radiation from the crystals into the gold nanowires. The system provides a simple, stable, compact and cost-effective THz source using a widely tunable C-band SOA-based laser to excite a non-linear photo-mixer to produce terahertz radiation that ranges from 0.8 to 2.51 THz at room temperature. This laser source can be modified into an all fiber-based THz generator by embedding ppLN crystals in a fiber filament configuration resulting in less absorption and producing high output power.

A laser apparatus includes: a laser oscillator that includes a mirror and emits a laser beam; and an external resonator that includes a nonlinear optical crystal that functions as a phase conjugate mirror. The phase conjugate mirror reflects the laser beam and produces a phase conjugate wave that reaches the mirror of the laser oscillator, and the mirror of the laser oscillator and the phase conjugate mirror cause laser oscillation such that a wavelength and a phase of the laser beam oscillated by the laser oscillation are automatically fixed.

A laser tool apparatus includes a tool body; a fiber optic cable disposed in the tool body, the fiber optic cable including a laser head that emits a laser beam; a reshape optic disposed coaxially downstream of the fiber optic, the reshape optic reshaping the laser beam emitted from the laser head; and a flexible cable attached to the reshape optic. The flexible cable flexibly orients the laser beam at a desired angle within a borehole.