Nippon Telegraph and Telephone Corporation

The Furukawa Electric Co., Ltd.

Takashi Yamamoto

Ryuichi Sugizaki

Kazuhide Nakajima

Taiji Sakamoto

Masaki Wada

Takayoshi Mori

Azusa Urushibara

Hidehiko Takara

Katsunori Imamura

Shinichi Aozasa

Satoki Kawanishi

Tetsuro Inui

Tomohiro Gonda

An object is to provide a multi-core configuration for acquiring a random mode coupling in a case of an arbitrary core refractive index. A multi-core optical fiber according to the present invention is an optical fiber in which two or more core regions are arranged in a clad region having a refractive index at a minimum core interval Λ smaller than a refractive index of the cores, a configuration of the cores is that including one propagation mode, and the core configuration and the core interval are adjusted so that an inter-mode coupling coefficient between adjacent cores is within a range from 0.73 to 120 m.

Multi-core optical fiber and design method

An object of the present invention is to provide an optical transmission system capable of easily controlling a transmission capacity and an optical signal quality even if a MIMO equalizer is provided. The optical transmission system according to the present invention is provided with an N×M MIMO equalizer, includes receivers (N units) equal in number to the spatial multiplexing order L of an optical fiber, and changes the number M of the signal beams of light transmitted through the optical fiber in the range of the spatial multiplex order L or less. The adjustment of the number M of signal beams of light makes it possible to adjust a transmission capacity and a signal quality of the optical transmission system even after construction of the transmission line.

Optical transmission system

An object of the present invention is to provide an optical transmission system capable of controlling a transmission capacity and a signal processing load of a MIMO equalizer, without depending on the number of propagation modes of the optical fiber. The present optical transmission system includes an optical fiberwith the number of spatial modes being L (an integer of 2 or greater), an optical multiplexerconnected to one end of the optical fiberand configured to input M (a natural number of L or less) signal beams of light to the optical fiberand cause the M input signal beams of light to be propagated for each of the spatial modes of the optical fiber, an optical demultiplexerconnected to another end of the optical fiberand configured to demultiplex a propagated beam of light propagated through the optical fiberfor each of the spatial modes of the optical fiber, N (N=L) receiversconfigured to each receive a demultiplexed beam of light obtained by demultiplexing the propagated beam of light, a signal generation apparatusconfigured to generate P (an integer of from M to L) combined signals from the N received signals, and a P×M MIMO equalizerconfigured to receive the P combined signals to output M demodulated signals.

An optical amplifier of the present disclosure includes an optical resonator that includes an amplification fiber capable of amplifying signal light having one or more propagation modes and resonates at least one propagation mode of the signal light amplified by the amplification fiber; an excitation light source that outputs excitation light for exciting the amplification fiber; and a multiplexer that multiplexes the signal light and the excitation light, in which the optical resonator includes a gain clamp setting unit which sets gain clamp for at least one propagation mode out of a plurality of propagation modes resonating in the optical resonator.

Optical amplifier

The optical fiber of the present invention includes a core, and a cladding that is provided on an outer periphery of the core and has a refractive index lower than a refractive index of the core region. In the optical fiber of the present invention, a V value representing a normalized frequency of an LPmode is greater than or equal to 4.8 and less than or equal to 6.4.

Optical fiber and optical transmission system

The optical fiber according to the present disclosure is an optical fiber having a pure silica core which is a step index core through which an LPm1 mode with an effective area of 250 &#x3bc;mor more is propagated by setting a relative refractive index difference to 0.60% or less, considering an effective cutoff condition, and only 2 or more modes or the LPm1 mode are propagated, with the optical fiber as the transmission line.

A differential mode attenuation compensator includes a first multi-mode optical fiber and a third multi-mode optical fiber in which a plurality of propagation modes propagate in a wavelength of a propagating optical signal; and a second multi-mode optical fiber including a core and a clad and arranged with a central axis aligned between the first multi-mode optical fiber and the third multi-mode optical fiber, in which each loss in the plurality of propagation modes is different in the first multi-mode optical fiber and the third multi-mode optical fiber.

Inter-mode loss difference compensator and optical amplifier

An optical transmission system according to the present disclosure is a mode multiplexed optical transmission system using a multi-mode optical fiber in which a plurality of propagation modes propagate as a transmission line, the optical transmission system including an optical fiber transmission line () that includes an optical fiber with two or more propagation modes; and a plurality of mode converters () that are configured to generate mode coupling between at least one pair of the propagation modes, in which a variation in an installation interval of the plurality of mode converters () is equal to or less than a threshold value determined by the transmission line length (Lt) of the optical fiber transmission line ().

In a wavelength division multiplexing optical transmission system, in order to know an influence amount of a temperature dependency of a dispersion slope, a method of monitoring a dispersion variation amount in two or more of wavelength channels is provided. Further, a method of compensating a wavelength dependency of a temperature dependency of the dispersion by providing an appropriate dispersion individually to the channels or summarizingly for all of bandwidths based on the monitored dispersion variation amounts is provided. According to the present invention, in the WDM optical transmission system, a deterioration in a transmission characteristic by influence of a temperature variation of the dispersion slope can be reduced.

Dispersion monitoring method and apparatus and dispersion slope temperature dependency compensation method and apparatus

With a single laser light source, the line width of a beat signal is set to a few tens of kHz or less without it fluctuating over time, and the frequency thereof is set as desired. CW light from a CW laser light source is input into an electroabsorption modulator to which a sine wave electrical signal is applied. A modulation sideband which is made up from line spectra at separations equal to the modulation frequency is generated from the electroabsorption modulator. An optical fiber for higher-order soliton compression broadens the optical spectrum width, and increases the number of line spectra. A tunable wavelength filtering device which is made up from optical fiber gratings and optical circulators chooses two of the line spectra, which are combined by an optical coupler with their beat signal being heterodyne wave detected by a photo-detector.

Growing community of inventors

Tsukuba, Japan

Takashi Yamamoto