# US 10,871,648 B2 · Optical fiber design method

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- Number: US 10,871,648 B2
- Document ID: US10871648B2
- Status: Granted
- Kind: B2
- Application number: 15/771,040
- Filed: 2016-11-17
- Published: 2018-11-29
- Granted: 2020-12-22
- Earliest claimed: 2015-12-10
- Assignees: Nippon Telegraph and Telephone Corporation
- Applicants: Nippon Telegraph and Telephone Corporation
- Inventors: Takashi Matsui; Kazuhide Nakajima; Kyozo Tsujikawa; Fumihiko Yamamoto
- Web page: https://patentgrep.com/patent/US10871648B2

## CPC

- G02B 27/0012: {Optical design, e.g. procedures, algorithms, optimisation routines}
- G02B 6/02: Optical fibres with cladding {with or without a coating}
- G02B 6/02323: {Core having lower refractive index than cladding, e.g. photonic band gap guiding}
- G02B 6/02338: {Structured core, e.g. core contains more than one material, non-constant refractive index distribution in core, asymmetric or non-circular elements in core unit, multiple cores, insertions between core and clad}
- G02B 6/02347: {Longitudinal structures arranged to form a regular periodic lattice, e.g. triangular, square, honeycomb unit cell repeated throughout cladding}
- G02B 6/02357: {Property of longitudinal structures or background material varies radially and/or azimuthally in the cladding, e.g. size, spacing, periodicity, shape, refractive index, graded index, quasiperiodic, quasicrystals}
- G02B 6/02361: {Longitudinal structures forming multiple layers around the core, e.g. arranged in multiple rings with each ring having longitudinal elements at substantially the same radial distance from the core, having rotational symmetry about the fibre axis}
- G02B 6/02376: {Longitudinal variation along fibre axis direction, e.g. tapered holes}
- G02B 6/032: with non solid core or cladding {(G02B6/02295 takes precedence)}
- G02B 6/42: Coupling light guides with opto-electronic elements
- G06F 2111/10: Numerical modelling
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)

## Abstract

An optical fiber design method according to the present invention is a design method of a photonic crystal fiber having a plurality of holes arranged in the optical fiber along a longitudinal direction, in which a required effective cross-sectional area is calculated from a light wavelength, a transmission distance, and output power such that, in a cross section, a hole ratio which is an area of the holes per unit area is larger in a central side than in an outer side in a portion corresponding to a cladding, and a fiber structure (hole diameter and hole interval) corresponding to the effective cross-sectional area is calculated.

## Claims

### Claim 1

An optical fiber design method for designing a photonic crystal fiber having a plurality of holes arranged in the optical fiber along a longitudinal direction, in which, in a cross section, a hole ratio which is an area of the holes per unit area is larger in a central side than in an outer side in a portion corresponding to a cladding, the method comprising:
determining a wavelength of a light propagated in the photonic crystal fiber, a power Pth of the light propagated in the photonic crystal fiber, and a propagation distance L through which the light is propagated in the photonic crystal fiber;
calculating a required effective cross-sectional area Aeff of the photonic crystal fiber by utilizing a Mathematical Formula (C5) based on the power Pth and the propagation distance L and a Raman gain coefficient gR;
calculating an effective cross-sectional area Aeff from a diameter d and an interval Λ of the holes of the photonic crystal fiber,
plotting the required effective cross-sectional area Aeff on a graph representing the interval Λ of the holes on a horizontal axis and a ratio (d1/d) of a diameter d1 of the holes on the central side and the diameter d of holes adjacent to the holes in the central side from the outer side thereof or a ratio (d/Λ) of the diameter d and the interval Λ of the holes on a vertical axis,
detecting the diameter d and the interval Λ of the holes of the Aeff satisfying or exceeding the required Aeff;
determining a region of allowable bending radius with which a basic mode can be propagated in the photonic crystal fiber;
detecting an overlapping region in the graph, the overlapping region in which a non-propagating region in which a desired propagation mode is not propagated, the region of the allowable bending radius, and a region based on a product of power of light from a laser oscillator and the propagation distance L overlap; and
determining the interval Λ and the ratio (d1/d) or the interval Λ and the ratio (d/Λ) in the overlapping region as a structure of the photonic crystal fiber,
wherein said Mathematical Formula (C5) is expressed as:
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Mathematical
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P
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