An optical amplifier of the present disclosure includes a rare-earth doped fiber including a plurality of cores, in which a v value of the plurality of cores of the rare-earth doped fiber is less than 2.405, the plurality of cores has a core pitch of a normalized coupling coefficient of 1.010.sup.3 or more, and on injection of excitation light into a clad part of the rare-earth doped fiber in a state of being bent at a predetermined bending radius, propagating light in the rare-earth doped fiber is amplified with mode-dependent gain characteristics dependent on the bending radius.

A tunable laser that includes an array of parallel optical amplifiers is described. The laser may also include an intracavity NM coupler that couples power between a cavity mirror and the array of parallel optical amplifiers. Phase adjusters in optical paths between the NM coupler and the optical amplifiers can be used to adjust an amount of power output from M1 ports of the NM coupler. A tunable wavelength filter is incorporated in the laser cavity to select a lasing wavelength.

Amplifier device (20) configured to amplify an input signal (SE2), the device comprising: a wavelength or frequency demultiplexer (22) configured to demultiplex the input signal (SE2) into N intermediate signals (SI21, SI22, SI23) with N greater than or equal to 2, a set of N amplifiers (AMP1, AMP2, AMP3), each amplifier being configured to receive one of the N intermediate signals (SI21, SI22, SI23) and generate an amplified signal (SI21amp, SI22amp, SI23amp), a wavelength or frequency multiplexer (24) configured to receive and multiplex the N amplified signals (SI21amp, SI22amp, SI23amp) into an output signal (SS2),
wherein the amplifying device (20) comprises a temperature control device (26) of the set of N amplifiers (AMP1, AMP2, AMP3), the temperature control device (26) configured to control that the temperature of at least one amplifier is different from that of at least one of the other amplifiers.

Embodiments of an optical amplification apparatus are disclosed which include a first optical amplifier, a second optical amplifier, and a mode exchanger. The first optical amplifier is connected to an input port of the mode exchanger, and the second optical amplifier is connected to an output port of the mode exchanger. The first optical amplifier is configured to amplify optical signals carried in a plurality of transmission modes of a few-mode fiber, the plurality of transmission modes of the few-mode fiber may be grouped into N groups, each group includes two transmission modes, and N is a positive integer greater than or equal to 1. The mode exchanger is configured to exchange the two transmission modes carrying optical signals in each group. The second optical amplifier is configured to amplify the optical signals that are carried in the two transmission modes in each group and whose modes are exchanged.

A device for modulation of an optical signal includes an active layer configured to provide electrically controlled gain of the optical signal; an electrode layer arranged to extend along the active layer, wherein the electrode layer comprises a plurality of separate electrodes associated with respective parts of the active layer, wherein each electrode have a size of a cross-section in the electrode layer smaller than a wavelength of the optical signal and neighboring electrodes are separated by a distance smaller than the wavelength of the optical signal; wherein an electrical signal to each of the electrodes is controllable for locally modulating an imaginary part of a refractive index of the active layer by locally controlling an electrical signal in the active layer.

In various embodiments, the disclosure relates to an electro-optical device that includes an optical amplifier and a photonic assembly. The optical amplifier may include a first encapsulation layer defining a first bonding surface, and an erbium-doped Si.sub.3N.sub.4 waveguide, wherein the erbium-doped Si.sub.3N.sub.4 waveguide disposed within the first encapsulation layer. The photonic assembly may include a substrate, a second encapsulation layer defining a second bonding surface, the second encapsulation layer disposed on the substrate, a modulator, one or more photodetectors, and a waveguide. In various embodiments, the modulator, the one or more photodetectors and the waveguide are disposed within the second encapsulation layer. The one or more regions of the first bonding surface are bonded to the one or more regions of the second bonding surface in various embodiments. The Si.sub.3N.sub.4 waveguide is optically coupled to the waveguide in various embodiments.

A single-material-double-process parametric laser-wavelength converter includes a pump-laser source, a nonlinear optical material, a first optical reflective element, and a second optical reflective element. The pump-laser source is configured to emit a pump-laser pulse light. The nonlinear optical material receives the pump-laser pulse and generates a signal-laser pulse and a partially depleted pump-laser pulse through optical parametric amplification. The first optical reflective element is configured to reflect the signal-laser pulse back to the same nonlinear optical material. The second optical reflective element is configured to reflect the partially depleted pump-laser pulse back to the same nonlinear optical material. With an appropriate adjustment on the reflecting path lengths, the nonlinear optical material is configured to receive the temporally synchronized signal-laser pulse and the partially depleted pump-laser pulse to generate an idler output through difference frequency generation. Both optical parametric amplification and difference frequency generation occur in the same nonlinear optical material.

1.55 m all-fiber laser based on tapering of ultra-large mode area fiber is provided, which can increase the fiber mode area, significantly enhance energy, and achieve high energy, high beam quality, narrow linewidth pulsed light, and all-fiber. The overall structure achieves an integration of the fiber laser system by fiber fusion. In the fiber laser seed source system continuous seed light output from a distributed feedback laser with an integrated isolator is modulated into pulsed light with controllable repetition rate and pulse width by an acousto-optic modulator. After amplification by a single-mode erbium-doped fiber amplifier, the signal light is amplified to an order of ten milliwatts and injected into a fiber pre-amplifier. In the fiber pre-amplifier, signal light is amplified to the order of hundreds of milliwatts by two stages of erbium-ytterbium co-doped gain fiber.

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.

Example optical amplification apparatuses 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.