Nippon Telegraph and Telephone Corporation

The University of Tokyo

Ntt Corporation

Nobutomo Hanzawa

Takashi Matsui

Kazuhide Nakajima

Kyozo Tsujikawa

Yuto Sagae

Fumihiko Yamamoto

Hideaki Murayama

Ryota Wada

Taiji Sakamoto

Shinichi Aozasa

Yoko Yamashita

Saki Nozoe

Makito Kobayashi

Ryota Imada

Noriyuki Araki

An object of the present disclosure is to enable behavior of a linear structure in water to be estimated. The present disclosure is an apparatus that: expresses at least one parameter in a plurality of discrete values, and forecasts behavior of a linear structure by using each of the discrete values; acquires behavior of the linear structure detected using an optical fiber; calculates a likelihood between the forecasted behavior of the linear structure and the acquired behavior of the linear structure; updates at least one of the plurality of discrete values on the basis of the likelihood; and calculates behavior of the linear structure by using the updated plurality of discrete values.

Apparatus and methods for calculating the behavior of linear structures

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

A shape measurement system and method for a three-dimensional shape of a linear object over a long distance with high resolution. The shape measurement system comprises: a multicore optical fiber having a center core positioned in the center of the cross section thereof and three or more outer peripheral cores positioned at equal intervals concentrically with respect to and outside of the center core; a measurement device for measuring the backward Brillouin scattered light distribution in the propagation direction of each core of the multicore optical fiber; and an analysis device for calculating position coordinates, in three-dimensional space, of a linear structure having an unknown three-dimensional shape from the backward Brillouin scattered light distributions of a multicore optical fiber positioned along the linear structure having an unknown three-dimensional shape and a multicore optical fiber positioned along a linear structure having a known three-dimensional shape.

Shape measurement system and shape measurement 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 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 object is to provide a beam propagating method capable of satisfying desired output power and a desired propagation distance and a required condition of beam quality and a method of designing an optical fiber designing the structure of an optical fiber. According to the present invention, an effective core cross-sectional area Ais calculated based on desired specification values and, by appropriately adjusting the structure of an optical fiber satisfying the effective core cross-sectional area and the number of modes to be propagated, the structure of the optical fiber is determined. In this way, by controlling the excitation ratio of a high-order mode at the time of coupling laser light in the optical fiber designed as above, light of high-output laser can be propagated a long distance with the beam quality maintained.

Optical fiber design method

An optical fiber that is a photonic crystal fiber in which a plurality of holes is arranged along a longitudinal direction of the optical fiber, having a predetermined bending radius R determined according to a transmission distance L of the optical fiber and optical power output from the optical fiber, and having an inter-hole distance &#x39b; and a ratio d/&#x39b; between a hole diameter d and the inter-hole distance &#x39b; such that light of a predetermined number of modes is transmitted and a bending loss of the light of a fundamental mode with the predetermined bending radius R is equal to or smaller than a predetermined value.

Optical fiber and optical transmission system

An object of the present invention is to provide a structure of an optical fiber capable of satisfying desired requirements of an output power, a propagation distance, and a beam quality. In the design of the PCF of the present invention, the PCF has air holes having diameters d and intervals &#x39b; in an overlapping region where a region of Aof a desired value or more and a cutoff region in a desired higher-order mode overlap each other on a graph where the horizontal axis represents d/&#x39b; and the vertical axis represents &#x39b;, so that it is possible to sufficiently cut off the mode which is the desired higher-order mode or more, and thus, it is possible to select a region where the Ais large.

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Tsukuba, Japan

Nobutomo Hanzawa