An optical amplifier repeater system includes an optical fiber propagating a light beam in a plurality of propagation modes and an optical amplifier repeater amplifying the light beam propagated through the optical fiber. The optical amplifier repeater includes an optical demultiplexer demultiplexing the light beam in the plurality of propagation modes propagated through the optical fiber into a plurality of single-mode light beams, an optical amplifier amplifying, by simultaneous pumping, intensities of the plurality of single-mode light beams using a light beam generated by one pumping light source, an optical multiplexer multiplexing the plurality of single-mode light beams amplified by the optical amplifier into a light beam in the plurality of propagation modes, and an optical intensity adjusting unit adjusting the intensity of each of the plurality of single-mode light beams at least one of before or after the amplification by the optical amplifier. The optical intensity adjusting unit performs the adjustment by amplifying or attenuating the optical intensity of each of the plurality of single-mode light beams in an individual optical path through which the single-mode light beam is propagated.

An object is to improve the efficiency of amplification by rare earth ion while maintaining beam quality of output light in a multi-mode fiber doped with rare earth ion. A multi-mode fiber (11) that includes a rare-earth-ion-doped core and that has a normalized frequency of not less than 2.40 includes a filter portion (111) that is formed by bending a partial section of or entirety of the multi-mode fiber (11), the filter portion (111) having a smallest diameter (diameter R1) that is set so that (1) only LP01, LP11, LP21, and LP02 modes propagate or only LP01 and LP11 modes propagate and (2) a loss of a highest-order one of the modes that propagate is not more than 0.1 dB/m.

An amplification fiber which can generate a laser beam in a visible region even when a silica glass is used as a base material of a core of the amplification fiber is realized. An amplification fiber according to an embodiment of the present disclosure includes a core configured to generate a laser beam from an excitation beam in a visible region, and a cladding surrounding the core. The core is composed of a core material including Dy, one or more elements selected from Al, Ge, and P, and a silica glass.

A method for gain control for an optical amplifier module is provided. The method may include receiving an input light signal at a first amplifier. The method may include dynamically adjusting a gain of the input light signal based on feedback monitoring of an output light signal. The method may include receiving the gain adjusted light signal at a second amplifier for output of the optical amplifier module.

A fiber laser producing a beam of ultrashort laser pulses at a repetition rate greater than 200 MHz includes a linear fiber resonator and a fiber branch. Ultrashort laser pulses are generated by passive mode-locking and circulate within the linear fiber resonator. Each circulating laser pulse is split into a portion that continues propagating in the linear fiber resonator and a complementary portion that propagates through the fiber branch and is then returned to the linear fiber resonator. The optical length of the linear fiber resonator is an integer multiple of the optical length of the fiber branch. The repetition rate of the ultrashort laser pulses is the reciprocal of the propagation time of the laser pulses through the fiber branch.

Multi-stage fiber amplifiers can amplify signals from a few Watts to several kilowatts. These amplifiers are limited in power by intensity instabilities resulting from a sequence of nonlinear optical effects. These nonlinear optical effects include stimulated Brillouin scattering (SBS), with produces a high-intensity pulse close to the signal wavelength that propagates backward up the amplifier chain, causing permanent damage to the upstream components. This SBS pulse can be blocked by an optical isolator that blocks backward-propagating light at or near the signal wavelength. At high enough power levels, the SBS pulse can also induce backward-propagating light at wavelengths tens to hundreds of nanometers away from the signal wavelength. This SBS-Pulse Induced Non-linear Spectrum light is outside the isolator's reject band, so it can propagate upstream and de-stabilize the upstream amplifier stages. It can be suppressed using a filter with a broad reject band and a suppression ratio of 30 dB, enabling higher power operation.

Methods and apparatus for processing a substrate. For example, a processing chamber can include a power source, an amplifier connected to the power source, comprising at least one of a gallium nitride (GaN) transistor or a gallium arsenide (GaAs) transistor, and configured to amplify a power level of an input signal received from the power source to heat a substrate in a process volume, and a cooling plate configured to receive a coolant to cool the amplifier during operation.

An apparatus includes an optical amplifier configured to receive an input optical signal and generate an amplified output optical signal. The optical amplifier includes multiple amplifier stages including at least a first amplifier stage and a second amplifier stage. The apparatus also includes a gain clamp configured to accumulate optical power from the first amplifier stage after an optical power level of the input optical signal drops and provide a first portion of the accumulated optical power to the first amplifier stage to clamp a gain applied by the first amplifier stage. The gain clamp is also configured to provide a second portion of the accumulated optical power to the second amplifier stage to adjust a gain applied by the second amplifier stage. The second amplifier stage is configured to amplify the second portion of the accumulated optical power.

A system includes a processor communicatively coupled to an Amplifier Stimulated Emission (ASE) source and an optical receiver, wherein the processor is configured to cause transmission of one or more shaped ASE signals, from the ASE source, on an optical fiber, obtain received spectrum of the one or more shaped ASE signals from the optical receiver connected to the optical fiber, and characterize the optical fiber based in part on a nonlinear skirt and/or center dip depth in the received spectrum of the one or more shaped ASE signals. The one or more shaped ASE signals can be formed by the ASE source communicatively coupled to a Wavelength Selective Switch (WSS) that is configured to shape ASE from the ASE source to form the one or more shaped ASE signals with one or two or multiple peaks and with associated frequency.

An object is to improve the efficiency of amplification by rare earth ion while maintaining beam quality of output light in a multi-mode fiber doped with rare earth ion. A multi-mode fiber (11) that includes a rare-earth-ion-doped core and that has a normalized frequency of not less than 2.40 includes a filter portion (111) that is formed by bending a partial section of or entirety of the multi-mode fiber (11), the filter portion (111) having a smallest diameter (diameter R1) that is set so that (1) only LP01, LP11, LP21, and LP02 modes propagate or only LP01 and LP11 modes propagate and (2) a loss of a highest-order one of the modes that propagate is not more than 0.1 dB/m.