Optical fiber test method and optical fiber test device

Patent metadata

Field	Value
Publication number	US-11719599-B2
Application number	US-201917762185-A
Country	US
Kind code	B2
Filing date	Oct 10, 2019
Priority date	Oct 10, 2019
Publication date	Aug 8, 2023
Grant date	Aug 8, 2023

Abstract

This disclosure describes inputting pulsated pump light in a fundamental mode or a first higher-order mode into one end of an optical fiber under test constructed by connecting two optical fibers in series; inputting probe light having an optical frequency difference within a Brillouin frequency shift range with respect to the pump light into the other end of the optical fiber under test in the fundamental mode or the first higher-order mode; measuring a Brillouin gain distribution related to a distance of transmitted light intensity of probe light output from the one end into which the pump light was input; and calculating each inter-modal coupling efficiency at the connection point of the optical fiber under test.

First claim

The invention claimed is:

1. An optical fiber test method, comprising performing:
a Brillouin gain coefficient acquisition procedure of acquiring a Brillouin gain coefficient that is unique to an optical fiber under test;
a pump light pulse input procedure of pulsating pump light of an optical frequency that enables the pump light to propagate both as fundamental mode light and as first higher-order mode light and inputting the pulsated pump light into one end of the optical fiber under test constructed by connecting two optical fibers in series in either a fundamental mode or a first higher-order mode;
a probe light input procedure of inputting probe light having an optical frequency shifted by a given frequency v within a Brillouin frequency shift range with respect to the optical frequency of the pump light into the other end of the optical fiber under test in either a fundamental mode or a first higher-order mode;
a measurement procedure of measuring a Brillouin gain distribution related to a distance from the one end into which the pump light was input based on transmitted light intensity of the probe light output from an end surface into which the pump light was input;
a transmittance acquisition procedure of acquiring a transmittance of the probe light at a connection point of the optical fiber under test by using the Brillouin gain distribution measured in the measurement procedure; and
a calculation procedure of substituting the acquired Brillouin gain coefficient and the acquired transmittance into a first mathematical expression representing a transmittance at the connection point that occurs in a Brillouin gain distribution in a fundamental mode and a second mathematical expression representing a transmittance at the connection point that occurs in a Brillouin gain distribution in a first higher-order mode according to each mode and simultaneously setting the first and second mathematical expressions to calculate at least one of a coupling efficiency between the fundamental modes, a coupling efficiency between the fundamental and first higher-order modes, or a coupling efficiency between the first higher-order modes.

2. The optical fiber test method according to claim 1 , wherein any one of expression (C1) and expression (C2) below is used as the first mathematical expression and the other is used as the second mathematical expression;

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where T j represents a transmittance obtained from a mode j component.

3. The optical fiber test method according to claim 1 , wherein
the calculation procedure further includes
logarithmically transforming the coupling efficiency between the fundamental modes and the coupling efficiency between the first higher-order modes to calculate a loss for each mode, and
logarithmically transforming the coupling efficiency between the fundamental mode and the first higher-order mode to calculate inter-modal crosstalk.

4. An optical fiber test method, comprising performing:
a Brillouin gain coefficient acquisition procedure of acquiring a Brillouin gain coefficient that is unique to an optical fiber under test;
a pump light pulse input procedure of pulsating pump light of an optical frequency that enables the pump light

Assignees

• Nippon Telegraph & Telephone

Inventors

• Nakamura Atsushi
• Oda Tomokazu
• Iida Daisuke
• Oshida Hiroyuki
• Wakisaka Yoshifumi

Classifications

• G01M11/39 Primary

  in which light is projected from both sides of the fiber or waveguide end-face · CPC title