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.

Fiber optic amplification includes a photonic crystal fiber coupled to a pump laser through a first coupler. The pump laser emits a first electromagnetic radiation wave into the photonic crystal fiber at a first oscillation frequency and a second electromagnetic radiation wave into the photonic crystal fiber at a second oscillation frequency equaling the first oscillation frequency. The first and second electromagnetic radiation waves interact to generate a signal comprising an electromagnetic radiation wave at a third oscillation frequency and an idler comprising a fourth electromagnetic radiation wave at a fourth oscillation frequency to be generated and amplified through parametric amplification. Parametric amplification is achieved by four wave mixing. The photonic crystal fiber emits a parametric output signal based on the four wave mixing. A nonlinear crystal frequency doubles the parametric output signal through second-harmonic generation.

The present disclosure generally relates optical amplifier modules. In one form for example, an optical amplifier module includes a booster optical amplifier configured to increase optical power of a first optical signal. The module also includes a preamp optical amplifier configured to increase optical power of a second optical signal and a pump laser optically coupled to the booster optical amplifier and the preamp optical amplifier. The pump laser is configured to provide a booster power to the booster optical amplifier and a preamp power to the preamp optical amplifier, the preamp power is effective to induce a gain in optical power to provide a target optical power of the second optical signal from the preamp optical amplifier, and the booster power is dependent on the preamp power.

In some implementations, a waveguide may comprise an inner core to receive a first beam and an outer core surrounding the inner core to receive a second beam that is displaced from the first beam by an offset. The outer core may comprise a beam guiding region that rotationally expands over a length of the waveguide into an annulus that concentrically surrounds the inner core or a partial annulus that partially surrounds the inner core. For example, the beam guiding region may be defined by one or more low refractive index features that have a varied orientation and/or a varied shape over the length of the waveguide such that the second beam enters the waveguide as an offset beam and exits from the waveguide as a ring-shaped beam or a partial ring-shaped beam.

The present invention benefits from the determination that pre-selected spectral bandwidths that avoid the spectrum of an electronic transition of a metal/alloy vapor allow for welds substantially free from detritus that may discolor the weld. Accordingly, the present invention provides analytical methods, welding methods and fiber lasers configured to provide high quality metal/alloy welds.

An optical fiber amplification apparatus is disclosed, including an optical receiving port, a first optical output port, a second optical output port, a gain medium, a pump laser, reflection films, and a transmission-reflection film. The pump laser activates a function of the gain medium to amplify an optical signal. A multiplexed optical signal including a first-waveband optical signal and a second-waveband optical signal is incident onto the gain medium. The reflection films enable the multiplexed optical signal to be reflected back and forth in the gain medium. After the first-waveband optical signal reaches a first target gain, the first-waveband optical signal is output from the gain medium to the first optical output port. The second-waveband optical signal is amplified in the gain medium. After the second-waveband optical signal reaches a second target gain, the second-waveband optical signal is output from the gain medium to the second optical output port.

An optical fiber amplification apparatus is disclosed, including an optical receiving port, a first optical output port, a second optical output port, a gain medium, a pump laser, reflection films, and a transmission-reflection film. The pump laser activates a function of the gain medium to amplify an optical signal. A multiplexed optical signal including a first-waveband optical signal and a second-waveband optical signal is incident onto the gain medium. The reflection films enable the multiplexed optical signal to be reflected back and forth in the gain medium. After the first-waveband optical signal reaches a first target gain, the first-waveband optical signal is output from the gain medium to the first optical output port. The second-waveband optical signal is amplified in the gain medium. After the second-waveband optical signal reaches a second target gain, the second-waveband optical signal is output from the gain medium to the second optical output port.

A stimulated Raman scattering (SRS) spectrometer for real-time, high-resolution molecular analysis of gases is based on two hollow-core fibres illuminated by a single high-power, short-pulse laser pump. The first fibre is prefilled with high-concentration target gases. Interaction of each target gas inside the first fibre, with the laser pump, generates Raman signals corresponding to the target gases. The combined beam of the Raman signals and the pump laser beam is directed into the second fibre containing the measured target gases. Interaction of each target gas with the combined beam generates the Stimulated Raman Growth (SRG), i.e., amplification of the Raman signal, which is proportional to the corresponding target gas concentration. A receiver subsystem receives the beam from the second fibre, spectrally separates it to wavelengths corresponding to each target gas, extracts the SRG value corresponding to each target gas and calculates the concentration of each target gas.

An optical amplification apparatus includes a plurality of input ends configured to receive a plurality of first optical signals with different wavelengths, a plurality of output ends configured to output a plurality of second optical signals obtained by amplifying the first optical signals, and a first pump source configured to provide a first pump light for amplifying the first optical signals. The apparatus also includes a first multi-port wavelength division multiplexing coupler having a plurality of first connection ports connected to the input ends. The apparatus further includes a first optical fiber connection cable connecting the first pump source with the first multi-port wavelength division multiplexing coupler. The first optical fiber connection cable is configured to transmit the first pump light. The apparatus additionally includes an active optical fiber connection cable having an active doped fiber for transmitting and amplifying a plurality of third optical signals.

An optical amplifying fiber includes: at least one single core portion doped with a rare-earth element; an inner cladding portion configured to enclose the at least one core portion, the inner cladding portion having a lower refractive index than maximum refractive index of each core portion; and an outer cladding portion configured to enclose the inner cladding portion, the outer cladding portion having a lower refractive index than refractive index of the inner cladding portion, wherein the inner cladding portion includes a plurality of air bubbles.