Optical pulse test method and optical pulse test equipment

Patent metadata

Field	Value
Publication number	US-12313449-B2
Application number	US-201917766494-A
Country	US
Kind code	B2
Filing date	Oct 17, 2019
Priority date	Oct 17, 2019
Publication date	May 27, 2025
Grant date	May 27, 2025

Abstract

An object of the present invention is to propose a design method of a minimum value N of the number of multiplexed frequencies that is necessary for measuring an object vibrational frequency according to DAS-P while taking into consideration a trade-off between a measurement distance and an upper limit of a measurable vibrational frequency. When a phase change of an arbitrary section of a measured optical fiber is represented by A×sin(2πfvt), N=4Zfv/ν is satisfied when A is smaller than π/2 but N=2Zfv/(ν·Arcsin (π/2A)) is satisfied when A is equal to or larger than π/2, where fv represents vibrational frequency, t represents time, Z represents a length of the measured optical fiber (a measurement distance), and ν represents the speed of light inside the measured optical fiber.

First claim

The invention claimed is:

1. An optical pulse test method comprising:
inputting an optical pulse sequence of which the number of wavelength multiplexes is N and in which optical pulses with different optical frequencies are arranged at temporally regular intervals to one end of a measured optical fiber;
receiving scattered light of each wavelength having returned to the one end of the measured optical fiber;
observing a vibration of the measured optical fiber as a time variation of a phase component of the scattered light; and
determining the number of wavelength multiplexes N as a minimum value satisfying Math. C1 as follows

[

Math
.

C1

]



When
⁢

F
υ

(
t
)

<
π

(
C1
)

N
≥

4
⁢

Zf
υ
max

v

when
⁢

F
υ

(
t
)

≥
π

N
>

2
⁢
Z

vC
max

-
1

(
π
)

where
t represents time,
Z represents a length of the measured optical fiber (measurement distance),
ν represents the speed of light inside the measured optical fiber,
F ν (t) represents a time waveform of a phase change in an arbitrary section of the measured optical fiber,
{tilde over (F)} ν (ƒ ν ) represents a function obtained by a Fourier transform of F ν (t),
ƒ ν max represents a maximum value of a frequency range occupied by {tilde over (F)} ν (ƒ ν ),
C(t) represents an absolute value of a phase change between a time point t and a time point t+T N ,
C max (T N ) represents a maximum value of C(t) when arbitrarily changing the time point t,
C max −1 (F ν ) represents an inverse function of C max (T N ),
F ν represents a difference between a maximum value and a minimum value of F ν (t),
T N represents intervals of optical pulses in the optical pulse sequence, and
C max −1 (Π) represents the intervals T N of the optical pulses when an absolute value of a magnitude of phase change is Π.

2. The optical pulse test method according to claim 1 , comprising:
forming the optical pulse by arranging M-number of minute optical pulses with different optical frequencies at shorter intervals than optical pulse intervals of the optical pulse sequence; and
setting the number M of the minute optical pulses so that 1/√M times a noise level is equal to or lower than a predetermined value.

3. The optical pulse test method according to claim 2 , comprising:
inputting, before inputting the optical pulse sequence to the one end of the measured optical fiber, a correction optical pulse sequence in which optical pulse pairs in which optical pulses with different optical frequencies are arranged at shorter intervals than optical pulse intervals of the optical pulse sequence are arranged to the one end of the measured optical fiber; and
calculating a correction value of the phase component of the scattered light by Math. C2,

[

Math
.

C2

]



ϕ
⁡
(

i
⁡
(

m
′

)

,

i
⁡
(
m
)

)

=

arg
[

1
P

⁢

∑

p
=
1

P

R
[

arg
⁢

{

r

i
⁡
(
m
)

(

z
,

Assignees

• Nippon Telegraph & Telephone

Inventors

• Wakisaka Yoshifumi
• Iida Daisuke
• Oshida Hiroyuki

Classifications

• G01H9/004 Primary

  using fibre optic sensors (light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125) · CPC title