Nippon Telegraph and Telephone Corporation

Yuto Sagae

Kazuhide Nakajima

Takashi Matsui

Nobutomo Hanzawa

Taiji Sakamoto

Kyozo Tsujikawa

Atsushi Nakamura

Hiroyuki Oshida

Daisuke Iida

Tomokazu Oda

Shinichi Aozasa

Yoko Yamashita

Saki Nozoe

Ryota Imada

Noriyuki Araki

An object of the present invention is to provide an evaluation method and an evaluation device for easily determining whether or not a structural parameter of a multi-core fiber satisfies a desired connection loss value (a specification). The evaluation method according to the present invention includes a step of measuring center coordinates of each core with the center coordinates when a clad is approximated by a circle as an origin in an observed cross-sectional structure of the multi-core fiber to be objected, obtaining a length of a line segment connecting the origin and the center of each core and an angle formed by two line segments connecting the origin and two adjacent cores, and judging whether or not a desired connection loss characteristic is satisfied on the basis of whether or not the values satisfy a predetermined determination formula.

Evaluation method and evaluation device for multi-core fiber

The optical fiber according to the present invention includes, in a cross section of the optical fiber, one core region () and a cladding region () that is arranged on an outer periphery of the core region. The cladding region is a medium that has a lower refractive index than that of the core region and also has a smaller refractive index wavelength dispersion than that of the core region. The optical fiber has a solid core and therefore, allows more reduction in the Rayleigh scattering loss compared to an optical fiber having a hollow core. In addition, since the optical fiber adopts, for the cladding region, a medium that has a smaller refractive index wavelength dispersion than that of the core region, it allows a reduction in the wavelength dispersion of n.

Optical fiber

The present invention is to provide a multi-core optical fiber that can expand its transmission wavelength band, and extend its transmission distance by reducing crosstalk, and also provide a method for designing the multi-core optical fiber. A multi-core optical fiber according to the present invention includes: four cores that are arranged in a square lattice pattern in a longitudinal direction; and a cladding region that is formed around the outer peripheral portions of the cores and has a lower refractive index than the cores, the absolute value of the relative refractive index difference between the cores and the cladding region being represented by A. In the multi-core optical fiber, the diameter of the cladding region is 125+1 μm, the cutoff wavelength is 1.45 μm or shorter, the mode field diameter MFD at a wavelength of 1.55 μm is 9.5 to 10.0 μm, the bending loss at a wavelength of 1.625 μm and with a bending radius of 30 mm is 0.1 dB/turns or smaller, and the inter-core crosstalk at the wavelength of 1.625 μm is −47 dB/km or smaller.

Multi-core optical fiber and design method

Provided are an LPFG and an optical transmission system in which a mode conversion amount does not depend on a polarization state and an electric field distribution. The LPFG according to the present invention includes cavity rows (-and-) of cavitiesperiodically arranged in a core regionof the few-mode fiberat a position away from a central axis z of the core regionin parallel with the central axis z. Each of the cavity rows (-and-) is located at a different position in a longitudinal direction of the few-mode fiber(where the position in a z direction is different), and the cavity rows (-and-) are located at positions shifted by 90° on a cross section of the core regionwith the center of the cross section of the core region(the intersection of an x-axis and a y-axis) as an origin.

Long period fiber grating and optical transmission system

The purpose of the present invention is to provide an optical fiber evaluation equipment and an optical fiber evaluation method that evaluate the center of a cladding of an MCF and a deviation of the center of each core of the MCF from a design value with ease and high accuracy. The optical fiber evaluation equipment according to the present invention approximates the outside diameter of a cladding by a circle, based on a cross-sectional image of an MCF, and determines the center of the circle as the center of the cladding. In addition, the optical fiber evaluation equipment according to the present invention obtains the center coordinates of cores with an origin at the center of the circle, rotates the cross-sectional image so as to minimize a difference between the center coordinates and design coordinates of each core, and derives the minimum value thereof as the amount of deviation of the center of each core.

Optical fiber evaluation device and optical fiber evaluation method

An optical fiber testing method is presented for measuring the change amount for the wave number k of a Brillouin Frequency Shift ν in stimulated Brillouin scattering generated in the same acoustic mode with respect to each target propagation mode. In this way, the ratio of the change amount measured at each propagation mode is acquired as the group delay ratio between the modes.

Optical fiber evaluation method and optical fiber evaluation apparatus

An object of the present invention is to provide an HAF having a structure in which the number of air holes is decreased to be smaller than that of a PCF and Rayleigh scattering loss may be more reduced than that in the existing HAF. The HAF according to the present invention includes a core portion having a uniform optical refractive index; a cladding portion having a uniform optical refractive index and surrounding the core portion; and a plurality of air holes arranged in two layers at positions configuring hexagonal closest packing excluding the core portion within the cladding portion along a longitudinal direction of the hole-assisted fiber, wherein a center-to-center spacing of the air holes is a sum of a radius Rin of an inscribed circle inscribed in the air holes in an inner layer and a radius d/2 of the air hole, and a radius 'a' of the core portion and a relative refractive index difference Δ between the core portion and the cladding portion are present within a range where Rn, which is a ratio of a Rayleigh scattering coefficient Rsmf of a single mode optical fiber and an effective Rayleigh scattering coefficient Reff of the hole-assisted fiber, is equal to or less than 0.92.

Hole assisted optical fiber

An objective is to provide an acoustic mode propagation speed measurement method and an acoustic mode propagation speed measurement device capable of measuring a propagation speed of an acoustic mode without cutting or processing an optical fiber wire. According to the present invention, an acoustic mode propagation speed measurement method includes: acquiring a frequency shift spectrum of Brillouin scattered light generated in an optical fiber; fitting the frequency shift spectrum using a Gauss function; acquiring a spectral full-width at half maximum w from a fitted curve using the Gauss function; and calculating a propagation speed Vof an acoustic mode of the optical fiber by substituting the acquired spectral full-width at half maximum w into a linear function of the spectral full-width at half maximum w and the propagation speed Vof the acoustic mode.

Acoustic mode propagation speed measurement method and acoustic mode propagation speed measurement device

An objective of the present invention is to provide an optical communication system and an optical communication method that can reduce even a delay generated in processing of obtaining a transfer function for correcting distortion in digital coherent transmission. In the optical communication system according to the present invention, pilot data for estimating a transfer function for a transmission channel is transmitted through a transmission channel with a short transmission delay time, a transfer function of the transmission channel is estimated before receiving transmission data, and the transfer function is applied to other transmission channels.

Optical communication system and optical communication method

An optical fiber includes a core, a first clad that is provided on an outer circumferential portion of the core and has a refractive index lower than that of the core, and a second clad that is provided on an outer circumferential portion of the first clad and has a refractive index lower than that of the first clad. In the optical fiber, a mode field diameter at a wavelength of 1.55 &#x3bc;m is equal to or greater than 11.5 &#x3bc;m, a cutoff wavelength is equal to or less than 1.53 &#x3bc;m, a bending loss at a bending radius of 30 mm and a wavelength of 1.625 &#x3bc;m is equal to or less than 2.0 dB/100 turns, and a delay time of transmission light per unit length at a wavelength of 1.55 &#x3bc;m is equal to or less than 4.876 &#x3bc;s/km.

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Tsukuba, Japan

Yuto Sagae