An optical fiber configured to improve the pump conversion efficiency of an L-band fiber amplifier which uses the multimode pump source. By directly absorbing multimode light including 915 nm, an active fiber core region co-doped with both erbium and ytterbium can provide gain to the L-band signals via stimulated emission. The unwanted C-band amplified spontaneous emission (ASE) light generate from this active fiber core region can be absorbed by another active fiber core region doped with erbium, then provides additional gain to the L-band signals. Active regions and cladding can be configured to match a given spatial mode of the optical signal. Signal-pump combiners with end-coupling or side coupling can be used.

A system, device, and method for laser cooling rare earth doped silica glass using anti-Stokes fluorescence is disclosed. The system includes a rare earth doped and codoped with one or more codopants silica glass; a laser that provides radiation to a first surface and through a body of the rare earth doped silica glass, wherein the laser is tuned from a first wavelength to a second wavelength; and a thermally sensitive device that captures images of the rare earth doped silica glass as the laser is tuned and determines a third wavelength between the first wavelength and the second wavelength where the rare earth doped silica glass is maximumly or near maximumly cooled.

An optical material including: a silica host; and a Praseodymium dopant; wherein the Praseodymium atoms are configured to form nanoclusters in the silica host. In addition, the optical material may include an Ytterbium co-dopant. The nanoclusters include Ge, Te, Ta, Lu and/or F, Cl to minimize multi-phonon quenching. Moreover, the nanoclusters may be encapsulated in a low phonon energy shell to minimize energy transfer to the host matrix.

A new type of all-silica optical fiber is described; a Structured Silica Clad Silica (SSCS) optical fiber, whose cladding is structured to provide mode mixing within the core; and/or to have an average effective refractive index. Its cross-section is essentially symmetrical, it can be used, among other objects, to provide flatter, more speckle-free outputs from fiber lasers, or other limited mode photonic sources. Building the new fiber structure around a rare earth doped laser core provides a better fiber laser/amplifier for cladding pumping. The structured silica cladding contains paired layers, in which a down doped silica layer is followed by a layer of pure, or lesser down-doped, or even up-dope silica, and die number of paired layers is, typically, from 5 to about 25, and, generally, within the paired layers the ratio of thickness of the higher RI layer of silicate the down-doped silica is very broad, lying between about 0.0625 to about 16, depending on the intended use of the SSCS fibers. In some versions, the main core material can be up-doped silica with pure silica or down-doped silica as the primary second component.

A rare earth-doped optical fiber comprises a fluorosilicate core surrounded by a silica cladding, where the fluorosilicate core comprises an alkaline-earth fluoro-alumino-silicate glass, such as a strontium fluoro-alumino-silicate glass. The rare earth-doped optical fiber may be useful as a high-power fiber laser and/or fiber amplifier. A method of making a rare earth-doped optical fiber comprises: inserting a powder mixture comprising YbF.sub.3, SrF.sub.2, and Al.sub.2O.sub.3 into a silica tube; after inserting the powder mixture, heating the silica tube to a temperature of at least about 2000° C., some or all of the powder mixture undergoing melting; drawing the silica tube to obtain a reduced-diameter fiber; and cooling the reduced-diameter fiber. Thus, a rare earth-doped optical fiber comprising a fluorosilicate core surrounded by a silica cladding is formed.

A fiber amplifier is provided, including a pump laser (202), a pump and signal combiner (203), and a few-mode doped fiber (204). The pump laser (202) is configured to output pump light. The pump and signal combiner (203) is configured to couple input few-mode signal light and the pump light into the few-mode doped fiber (204). Refractive indexes of a fiber core of the few-mode doped fiber (204) are distributed to be gradient along a radial direction of a cross section, the fiber core is etched with periodic gratings along an axial direction, and periods of the gratings satisfy a phase matching condition. The fiber amplifier achieves strong coupling and co-amplification between optical signal modes, thereby reducing a differential gain between mode groups.

Example optical amplification apparatus and example signal amplification methods are provided. One example optical amplification apparatus is connected to an optical fiber. The optical amplification apparatus includes a first pump laser and a first gain medium. The first pump laser is configured to emit first pump light. The first gain medium is configured to receive the first pump light and first multi-channel optical signals from the optical fiber; and perform gain amplification on the first multi-channel optical signals based on the first pump light, where the first pump light overlaps each of the first multi-channel optical signals in the first gain medium.

A gain mirror is created for use as an optical amplifier in a solid state ring laser rotation sensor. Such a ring laser includes at least three mirrors for reflecting counter propagating laser beams around a closed loop optical path, wherein at least one of the mirrors is a gain mirror. The gain mirror is formed by applying a thin film of silica, a few half wavelengths thick and doped with Nd isotopes, onto a very high reflectivity mirror and then using a laser diode to pump it with intense light to form a population inversion in Nd.sup.3+ ions. An assembly consisting of this gain mirror and a pump laser diode can be used as an optical amplifier in a solid state ring laser to generate the two counter propagating laser light beams needed to measure rotation.

A solid-state optical amplifier is described, having an active core and doped cladding in a single chip. An active optical core runs through a doped cladding in a structure formed on a substrate. A light emitting structure, such as an LED, is formed within and/or adjacent to the optical core. The cladding is doped, for example, with erbium or other rare-earth elements or metals. Several exemplary devices and methods of their formation are given.

Compact optical frequency sources are described. The comb source may include an intra-cavity optical element having a multi-material integrated structure with an electrically controllable active region. The active region may comprise a thin film. By way of example, the thin film and an insulating dielectric material disposed between two electrodes can provide for rapid loss modulation. In some embodiments the thin film may comprise graphene. In various embodiments of a frequency comb laser, rapid modulation of the CEO frequency can be implemented via electric modulation of the transmission or reflection loss of an additional optical element, which can be the saturable absorber itself. In another embodiment, the thin film can also be used as a saturable absorber in order to facilitate passive modelocking. In some implementations the optical element may be formed on a cleaved or polished end of an optical fiber.