An objective of the present invention is to provide an amplification fiber having a cladding excitation configuration that improves amplification efficiency and an optical amplifier. An amplification fiber (10) according to the present invention is a multi-core amplification fiber having, from one end (E1) to the other end (EE), a plurality of cores (11b) in a cladding (11a), and a total distance from the one end (E1) to the other end (EE) in which rare earth ions are doped differs depending on the types of cores (11b). The cores (11b) are preferably disposed such that the cores of the same type are not adjacent to each other. By arranging the types of the cores in this manner, requirements for inter-core crosstalk can be mitigated since the bands of signal light in the adjacent cores are different. As a result, a density of cladding excitation light can be increased by shortening the inter-core distance, and thus the amplification efficiency can be improved.

A photonic device is configured with a photonic integrated circuit (PIC), a plurality of fiber-based gain mediums in optical communication with the PIC, and at least one optical pump outputting pump light coupled into two or more gain mediums. At least one of the fiber-based gain media and the PIC form a hybrid resonant optical cavity there between operative to lase light into the PIC. The gain media further include one or more fiber amplifiers amplifying light signals coupled into and decoupled from the PIC. The photonic device is integrated with Si photonic passive and active photonic elements, while ail fiber links between the gain media and PIC are free from these elements.

A gain adjuster, a gain adjustment method, and an optical line terminal are provided, to separately adjust a gain of a to-be-adjusted optical signal. The gain adjuster includes a light spot conversion component and a gain medium that are sequentially coupled. The gain adjuster further includes a pump laser. The light spot conversion component is configured to adjust light spot sizes of at least some optical signals in received optical signals to output a first optical signal transmitted in space. The pump laser is configured to excite the gain medium. The gain medium is configured to adjust a gain of the first optical signal to output a second optical signal.

An EHz ultrafast modulated pulse scanning laser and a distributed fiber sensing system. A plurality of phase-shift gratings are engraved on a doped fiber, the phase-shift gratings having different central window wavelengths and a wavelength interval between the adjacent central window wavelengths being a preset fixed value. When a pump light emitted by a pump laser source is coupled by a wavelength division multiplexer and enters the doped fiber, a single-mode narrow-linewidth laser light having multiple wavelengths with a wavelength interval being a preset fixed value can be generated, by using the phase-shift gratings graved on the doped fiber. The ultrafast modulation is completed by using a time-domain control method based on an EOM. An internally frequency converted pulse light formed by splicing pulse lights whose frequencies linearly increase is obtained, thus forming the EHz ultrafast modulation of a distributed feedback fiber laser. In this way, a coherence length of an output laser light is increased while a frequency of the laser light is remained.

A macroscopic entanglement state in which a polarization state has a strong quantum correlation is realized by use of a macroscopic laser light. A laser oscillator includes a ring resonator having an optical fiber ring, an optical amplifier for maintaining an amplitude of a laser pulsed light propagating on the optical fiber ring, and three optical fibers that are connected with respective polarization controllers, and, after changing a polarization state of the laser pulsed light being a qubit extracted at a predetermined branch ratio from the optical fiber ring by the polarization controllers, couples the changed laser pulsed light whose polarization state has been changed with the laser pulsed light propagating on the optical fiber ring, and each polarization controller rotates the polarization state of the laser pulsed light with an S1 axis, an S2 axis, and an S3 axis, which are orthogonal to each other, as a rotation axis.

An optically amplified repeater system includes optical transmission paths, a multi-channel optical amplifier, one or more Raman amplification pumping light sources, and a wavelength multiplexer. The multi-channel optical amplifier includes K simultaneous pumping light sources, N optical amplification media, and one or more optical couplers, and simultaneously amplifies, with the K simultaneous pumping light sources, light intensities of optical signals that pass through the N optical amplification media and propagate through the optical transmission paths. Light intensities of the wavelength band of the optical signals is Raman amplified by the Raman amplification pumping light. A light intensity of the Raman amplification pumping light output from the one or more Raman amplification pumping light sources is determined in accordance with characteristic differences between the optical signals passing through the optical transmission paths.

A single-mode micro-laser based on a single whispering gallery mode optical microcavity and a preparation method thereof described includes: preparing a desired single whispering gallery mode optical microcavity doped with rare earth ions or containing a gain material such as quantum dots, wherein an optical microcavity configuration include a micro-disk cavity, a ring-shaped microcavity, and a racetrack-shaped microcavity; a material type include lithium niobate, silicon dioxide, silicon nitride, etc.; preparing an optical fiber cone or an optical waveguide of a required size which can excite high-order modes of the optical microcavity, such as a ridge waveguide and a circular waveguides; and coupling, integrating, and packaging the optical fiber cone or the optical waveguide with the microcavity. A pump light is coupled to the optical fiber cone or the optical waveguide to excite a compound mode with a polygonal configuration.

Embodiments of the present disclosure provide example multi-core fiber interleavers, example optical fiber amplifiers, example transmission systems, and example transmission methods. One example multi-core fiber interleaver includes a first port, a second port, a third port, and a fourth port, respectively adapted to be coupled to a first multi-core fiber, a second multi-core fiber, a third multi-core fiber, and a fourth multi-core fiber. A first subset of a plurality of first cores is coupled to a first subset of a plurality of second cores. A first subset of a plurality of third cores is coupled to a first subset of a plurality of fourth cores. A second subset of the plurality of fourth cores is coupled to a second subset of the plurality of second cores. A second subset of the third cores is coupled to a second subset of the first cores.

An optical amplifying fiber includes: at least one core portion including a rare earth element added therein; an inner cladding portion surrounding the at least one core portion, the inner cladding portion having a refractive index lower than a maximum refractive index of the at least one core portion; and an outer cladding portion surrounding the inner cladding portion, the outer cladding portion having a refractive index lower than the refractive index of the inner cladding portion, the inner cladding portion including different refractive index regions each having a refractive index different from a refractive index of a region adjacent to that different refractive index region.

An optical resonator, a constituent part of the optical resonator, and a laser device that enable a reduction in size even if a wavelength band limiting element is disposed in the optical resonator, are provided.

An optical resonator including: a laser medium that is disposed between a pair of reflection members, and emits emitted light that has been excited by excitation light that has been predetermined; and a wavelength band limiting element that is disposed on a side of emission of the emitted light between the pair of reflection members, includes two reflection flat faces that are orthogonal to an optical axis of the laser medium, and limits a wavelength band of the emitted light, in which the wavelength band limiting element is disposed in a position that prevents a resonance component outside an intended wavelength range of the wavelength band limiting element from being generated between a reflection member on a laser beam emission side from among the pair of reflection members and the wavelength band limiting element.