Abstract: An amplification optical fiber includes: a core; an inner cladding having a refractive index lower than a refractive index of the core, wherein an active element pumped by pumping light is entirely doped to the core, and a relative effective refractive index difference of light in an LP01 mode is greater than or equal to 0.05% and a relative effective refractive index difference of light in an LP21 mode is less than 0.05% in light propagating through the core.

Abstract: An amplification optical fiber includes: a core; an inner cladding having a refractive index lower than a refractive index of the core, wherein an active element pumped by pumping light is entirely doped to the core, and a relative effective refractive index difference of light in an LP01 mode is greater than or equal to 0.05% and a relative effective refractive index difference of light in an LP21 mode is less than 0.05% in light propagating through the core.

Abstract: An optical device includes a first medium which (i) has a refractive index lower than (a) a refractive index of an outermost shell part in a first outer shell removed area of a first optical fiber and (b) a refractive index of an outermost shell part in a second outer shell removed area of a second optical fiber and (ii) surrounds an entire side surface of the first outer shell removed area. Moreover, the optical device includes a second medium which (i) has a refractive index higher than a refractive index of an outermost shell part in the second outer shell removed area and (ii) surrounds at least a part of a side surface in the second outer shell removed area. The second outer shell removed area has a diameter larger than a diameter in the first outer shell removed area.

Abstract: A fiber laser system with a fiber laser device including a fiber laser; a laser output end part; and a delivery fiber. The delivery fiber is constituted by a double cladding fiber. An SFBG is provided on the output end side of the delivery fiber, which reflects part of laser light propagating in the core of the delivery fiber to thereby couple the part of the laser light with a backward-propagating cladding mode propagating in a first cladding in a backward direction. A backward-propagating cladding mode detecting section is provided on the input end side of the delivery fiber, which detects the intensity of backward-propagating light in a cladding mode, which light is the part of the laser light coupled by the SFBG with the backward-propagating cladding mode.

Abstract: An optical device includes a first medium which (i) has a refractive index lower than (a) a refractive index of an outermost shell part in a first outer shell removed area of a first optical fiber and (b) a refractive index of an outermost shell part in a second outer shell removed area of a second optical fiber and (ii) surrounds an entire side surface of the first outer shell removed area. Moreover, the optical device includes a second medium which (i) has a refractive index higher than a refractive index of an outermost shell part in the second outer shell removed area and (ii) surrounds at least a part of a side surface in the second outer shell removed area. The second outer shell removed area has a diameter larger than a diameter in the first outer shell removed area.

Abstract: An object of the present invention is to provide an optical fiber amplifier capable of suppressing oscillation of ASE. The optical fiber amplifier includes a second amplifier fiber 30 doped with a rare earth element; a second pumping source 26 that supplies pump light to the second amplifier fiber 30; a storage unit 40 for storing a relationship between oscillation threshold pump power and temperature of the second amplifier fiber 30, the oscillation threshold pump power being power of the pump light which causes oscillation of ASE in a different wavelength range from a signal wavelength range produced by the second amplifier fiber 30; and a temperature controller 38 for controlling the temperature of the second amplifier fiber 30 so that the oscillation threshold pump power is higher than the power of the pump light outputted by the second pumping source 26, by referring to the relationship stored in the storage unit 40.

Abstract: An object of the present invention is to provide an optical fiber amplifier capable of suppressing oscillation of ASE. The optical fiber amplifier includes a second amplifier fiber 30 doped with a rare earth element; a second pumping source 26 that supplies pump light to the second amplifier fiber 30; a storage unit 40 for storing a relationship between oscillation threshold pump power and temperature of the second amplifier fiber 30, the oscillation threshold pump power being power of the pump light which causes oscillation of ASE in a different wavelength range from a signal wavelength range produced by the second amplifier fiber 30; and a temperature controller 38 for controlling the temperature of the second amplifier fiber 30 so that the oscillation threshold pump power is higher than the power of the pump light outputted by the second pumping source 26, by referring to the relationship stored in the storage unit 40.