US 12,313,449 B2
Optical pulse test method and optical pulse test equipment
Yoshifumi Wakisaka, Musashino (JP); Daisuke Iida, Musashino (JP); and Hiroyuki Oshida, Musashino (JP)
Assigned to NIPPON TELEGRAPH AND TELEPHONE CORPORATION, Tokyo (JP)
Appl. No. 17/766,494
Filed by NIPPON TELEGRAPH AND TELEPHONE CORPORATION, Tokyo (JP)
PCT Filed Oct. 17, 2019, PCT No. PCT/JP2019/040821
§ 371(c)(1), (2) Date Apr. 4, 2022,
PCT Pub. No. WO2021/075015, PCT Pub. Date Apr. 22, 2021.
Prior Publication US 2023/0175884 A1, Jun. 8, 2023
Int. Cl. G01H 9/00 (2006.01)
CPC G01H 9/004 (2013.01) 12 Claims
OG exemplary drawing
 
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

OG Complex Work Unit Math
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,
Fν(t) represents a time waveform of a phase change in an arbitrary section of the measured optical fiber,
Fν(ƒν) represents a function obtained by a Fourier transform of Fν(t),
ƒνmax represents a maximum value of a frequency range occupied by Fν(ƒν),
C(t) represents an absolute value of a phase change between a time point t and a time point t+TN,
Cmax(TN) represents a maximum value of C(t) when arbitrarily changing the time point t,
Cmax−1(Fν) represents an inverse function of Cmax(TN),
Fν represents a difference between a maximum value and a minimum value of Fν(t),
TN represents intervals of optical pulses in the optical pulse sequence, and
Cmax−1(Π) represents the intervals TN of the optical pulses when an absolute value of a magnitude of phase change is Π.