A device for coupling a multicore/multimode fiber that can transmit a large quantity of information. This multicore/multimode fiber coupling device has a first fiber group (11), a first light converging system (13), a first mode converter (15), a second fiber group (21), a second light converging system (23), and light converging system (33) for multicore fibers. By means of the first mode converter (15), light from the first fiber group (11) is subjected to mode conversion en masse. A space coupling system (33) for multicore fibers transmits light derived from the second fiber group (21) and light derived from the first fiber group (11) subjected to mode conversion to the multicore fibers (31).

The optical amplifier, which amplifies wavelength multiplexed signal light, comprises: a multi-core optical fiber which includes cladding and a first core and a second core disposed in the cladding, and which is doped with rare-earth ions; an excitation light source for supplying excitation light to the cladding of the multi-core optical fiber; and a wavelength demultiplexing means for separating the wavelength bands of the wavelength multiplexed signal light that has propagated through the first core. The signal light of a relatively long wavelength band among a plurality of wavelength bands separated by the wavelength demultiplexing means is caused to propagate through the second core, and is then multiplexed with the signal light of a relatively short wavelength band among the plurality of wavelength bands separated by the wavelength demultiplexing means, and the resultant multiplexed signal light is output.

Systems and methods include an optical switch system which provides a combination of LED arrays, PDs, imaging fiber cables, and crosspoint switch on a single chip. The system includes one or more input ports with each input port configured to connect to an input fiber bundle. The system additionally includes one or more output ports with each output port configured to connect to an output fiber cable, wherein each of the input fiber bundle and the output fiber cable include a plurality of fiber cores. An electrical crosspoint switch is connected to the one or more input ports and the one or more output ports, wherein the electrical crosspoint switch is configured to connect a given input port to a corresponding output port, including all signals in the input fiber cable to the corresponding output fiber cable.

An optical amplifier that amplifies an incident WDM signal and includes cores having an amplification medium, the optical amplifier includes: a wavelength demultiplexer configured to demultiplex the incident WDM signal into wavelength bands and introducing the demultiplexed WDM signals into the cores separately; a wavelength multiplexer configured to multiplex amplified optical signals propagated through the cores and outputting the multiplexed signal; and an wavelength demultiplexing controller configured to monitor an amplification rate of a specific wavelength band of an amplified WDM signal or a scale associated with an amplification rate of a specific wavelength band, demultiplexing, from the incident WDM signal, an optical signal of a wavelength band having relatively-small optical amplification efficiency according to a monitoring result, and controlling demultiplexing performed by the wavelength demultiplexer in such a way as to amplify, with a relatively-large amplification rate, the optical signal of the wavelength band having relatively-small optical amplification efficiency.

It is an object of the present invention to provide a multicore optical fiber, a design method for the multicore optical fiber and an optical transmission method using the multicore optical fiber including four cores having a standard cladding diameter of 1251 m for an existing single mode optical fiber covering several thousands of kilometers of transmission. The multicore optical fiber according to the present invention disposes two-stage claddings with different refractive indices around each core, and designates as a predetermined range, a core radius a1, a radius a2 of a first cladding region surrounding each core, specific refractive index 1 relative to the core of the first cladding region and a specific refractive index 2 relative to the core of a second cladding region including four cores and the first cladding region.

A multi-core fiber amplifier includes: a first optical multiplexer that couples excitation light with first signal light of a first wavelength band and second signal light of a second wavelength band, and outputs coupled light; a first amplifier that includes a rare-earth doped multi-core fiber, inputs output light from the first optical multiplexer, and amplifies and outputs the first signal light; a first optical demultiplexer that demultiplexes output light from the first amplifier into the first signal light, and the second signal light and the excitation light, and outputs demultiplexed light; a second amplifier that includes a rare-earth doped multi-core fiber, inputs the second signal light and the excitation light from the first optical demultiplexer, and amplifies and outputs the input second signal light; and a second optical multiplexer that multiplexes the first signal light from the first optical demultiplexer and the second signal light from the second amplifier.

In a network using MCF, in order to provide a technology which enables a standby system path to be easily constructed, this optical network includes: an active system path which is connected by means of a first multi-core optical fiber, and is a path between a transmission node that transmits an optical signal and a reception node that receives the optical signal; and the standby system path which is composed by means of a plurality of second multi-core optical fibers, which are different from the first multi-core optical fiber, and is a path switchable from the active system path between the transmission node and the reception node, wherein cores, which are switching destinations of the plurality of cores of the first multi-core optical fiber, are disposed at a plurality of respective unused cores of the second multi-core optical fibers.

A transmission direction determination apparatus includes: a first lens configured to collimate light propagating from one multi-core fiber of two multi-core fibers to the other multi-core fiber of the two multi-core fibers; a second lens configured to focus the light that has propagated from the first lens; a partially reflective mirror configured to reflect part of the collimated light and including a first surface and a second surface; a first photodetector disposed on a side of the first surface of the partially reflective mirror and configured to measure an intensity of signal light reflected by the partially reflective mirror; and a second photodetector disposed on a side of the second surface of the partially reflective mirror and configured to measure an intensity of signal light reflected by the partially reflective mirror.

It is an object of the present invention to provide a multicore optical fiber, a design method for the multicore optical fiber and an optical transmission method using the multicore optical fiber including four cores having a standard cladding diameter of 1251 m for an existing single mode optical fiber covering several thousands of kilometers of transmission. The multicore optical fiber according to the present invention disposes two-stage claddings with different refractive indices around each core, and designates as a predetermined range, a core radius a1, a radius a2 of a first cladding region surrounding each core, specific refractive index 1 relative to the core of the first cladding region and a specific refractive index 2 relative to the core of a second cladding region including four cores and the first cladding region.

An optical signal transmitting device comprises an optical transmitter and a mode converter. The optical transmitter transmits a multi-path transmitted initial optical signal to the mode converter, wherein the initial optical signal comprises a first optical signal and a second optical signal both having a first wavelength, and a third optical signal having a second wavelength different from first wavelength. The mode converter is configured to perform phase conversion on the incident initial optical signal to obtain and reflect a first target optical signal, which is single-path transmitted and comprises the third optical signal, the first optical signal transmitted in a first mode, and the second optical signal transmitted in a second mode different from the first mode.