Optical fiber characteristics measuring apparatus and optical fiber characteristics measuring method

Patent metadata

Field	Value
Publication number	US-11326981-B2
Application number	US-201816233836-A
Country	US
Kind code	B2
Filing date	Dec 27, 2018
Priority date	Dec 27, 2017
Publication date	May 10, 2022
Grant date	May 10, 2022

Abstract

An optical fiber characteristics measuring apparatus includes: a light source that outputs frequency-modulated continuous wave of light; a first optical branching unit that branches the continuous light into pump light and reference light; a second optical branching unit that outputs backscattered light generated by making the pump light incident from one end of an optical fiber to be measured, wherein the backscattered light is Brillouin scattering in the optical fiber; a detector that detects interference light of the backscattered light and the reference light; a measuring unit that measures characteristics of the optical fiber by using a detection signal output from the detector; and a controller that controls the light source to change modulation frequency of the continuous light in units of one period or half a period of a modulation period corresponding to the modulation frequency.

First claim

What is claimed is:

1. An optical fiber characteristics measuring apparatus comprising:
a light source that outputs frequency-modulated continuous wave of light;
an optical splitter that branches the continuous light into pump light and reference light;
an optical circulator that is connected to the optical splitter and an optical fiber to be measured and that outputs backscattered light generated by making the pump light incident from one end of the optical fiber, wherein the backscattered light is Brillouin scattering in the optical fiber;
a detector that detects interference light of the backscattered light and the reference light;
a calculator that calculates characteristics of the optical fiber by using a detection signal output from the detector; and
a controller that controls the light source to change, before the detector detects the interference light of the backscattered light and the reference light, modulation frequency of frequency modulation of the continuous light in terms of discrete steps of one period or half a period of a modulation period corresponding to the modulation frequency.

2. The optical fiber characteristics measuring apparatus according to claim 1 ,
wherein the controller controls the light source to change modulation amplitude of the continuous light together with the modulation frequency.

3. The optical fiber characteristics measuring apparatus according to claim 2 ,
wherein the controller changes the modulation frequency and the modulation amplitude such that spatial resolution in a longitudinal direction of the optical fiber is constant regardless of change of the modulation frequency and the modulation amplitude.

4. The optical fiber characteristics measuring apparatus according to claim 3 ,
wherein the controller changes the modulation frequency and the modulation amplitude such that a product of the modulation amplitude and the modulation frequency before change is equal to a product of the modulation amplitude and the modulation frequency after the change.

5. The optical fiber characteristics measuring apparatus according to claim 2 ,
wherein the controller changes the modulation frequency and the modulation amplitude such that spatial resolution in a longitudinal direction of the optical fiber is different from each other for each of the optical circulator and the optical splitter.

6. The optical fiber characteristics measuring apparatus according to claim 2 ,
wherein the controller changes the modulation frequency and the modulation amplitude such that the modulation frequency and a combination of the modulation frequency and the modulation amplitude are different from each other for each of the optical circulator and the optical splitter.

7. The optical fiber characteristics measuring apparatus according to claim 1 , further comprising:
an optical gate that brings an optical path between the optical circulator and the optical splitter into a disconnected state or a connected state under control of the controller.

8. The optical fiber characteristics measuring apparatus according to claim 7 ,
wherein the controller controls the optical gate to shape the pump light into pulsed light having a pulse width of one period or half a period of the modulation period.

9. The optical fiber characteristics measuring apparatus according to claim 8 ,
wherein, when the optical path between the optical circulator and the optical splitter is in the disconnected state, the controller controls, based on a return time of the backscattered light, the light source to generate the reference light that interferes with the backscattered light by changing the modulation frequency of the continuous light in units of one period or half a period of the modulation period corresponding to the modulation frequency.

10. The optical fiber characteristics measuring apparatus according to claim 9 ,
wherein, when the optical splitter makes first pump light and second pump light incident on the optical fiber, the detector detects the interference light of (i) the backscattered light obtained by the pulsed light modulated by the controller, corresponding to the first pump light and (ii) the reference light generated by the light source based on the return time of the backscattered light, corresponding to the first pump light, and
the calculator calculates the characteristics of the optical fiber by making the second pump light incident on the optical fiber without waiting for return of the backscattered light corresponding to the first pump light.

11. The optical fiber characteristics measuring apparatus according to claim 9 ,
wherein the controller controls a change order of the modulation frequency in a case of shaping the pump light into the pulsed light to be different from a change order of the modulation frequency in a case of obtaining the reference light.

12. The optical fiber characteristics measuring apparatus according to claim 9 ,
wherein the controller controls a change order and change timing of the modulation frequency in a case of shaping the pump light into the pulsed light to be respectively the same as a change order and a change timing of the modulation frequency in a case of obtaining the reference light.

13. An optical fiber characteristics measuring method, comprising:
changing modulation frequency of frequency modulation of frequency-modulated continuous wave of light output from a light source, before detecting interference light of backscattered light and reference light, in terms of discrete steps of one period or half a period of a modulation period corresponding to the modulation frequency;
detecting interference light of backscattered light and reference light, wherein the backscattered light is generated by making modulation frequency-changed light incident on one end of an optical fiber to be measured, the backscattered light is Brillouin scattering in the optical fiber, and frequency of the reference light is modulated in units of one period or half a period of the modulation period; and
measuring characteristics of the optical fiber by using a detection result of the interference light.

14. The optical fiber characteristics measuring method according to claim 13 , further comprising:
obtaining the reference light by changing modulation frequency of the continuous light in units of one period or half a period of the modulation period corresponding to the modulation frequency based on a return time of the backscattered light.

15. The optical fiber characteristics measuring method according to claim 13 , further comprising:
shaping the modulation frequency-changed continuous light into pulsed light having a pulse width of one period or half a period of the modulation period and being incident from the one end of the optical fiber.

Assignees

• Yokogawa Electric Corp

Inventors

• Furukawa Osamu

Classifications

• G01M5/0091

  by using electromagnetic excitation or detection · CPC title

• G01L1/242

  the material being an optical fibre · CPC title

• G01K11/32

  using changes in transmittance, scattering or luminescence in optical fibres · CPC title

• G01M11/083

  by using an optical fiber in contact with the device under test [DUT] · CPC title

• G01K11/322

  using Brillouin scattering · CPC title