Location measurement apparatus, light modulation converter, and light variation location measurement method

1. A location-measurement apparatus that is disposed on one terminal of an optical transmission line, the location-measurement apparatus comprising:

a light source that causes continuous oscillation light to enter one terminal of the optical transmission line, the continuous oscillation light being to propagate a light variation of a first physical amount generated on the optical transmission line to another terminal of the optical transmission line;

a photodetector that detects, on the one terminal of the optical transmission line, light turned back from a light modulation converter provided on the another terminal of the optical transmission line, wherein the light modulation converter obtains the turned-back light by converting the light variation of the first physical amount into a light variation of a second physical amount; and

a processor that calculates a light-variation location generated on the optical transmission line by comparing time variations in the light variation of the first physical amount and the light variation of the second physical amount in the light detected by the photodetector.

2. The location-measurement apparatus according to claim 1 , wherein the processor obtains a cross-correlation between the time variations of the first physical amount and the second physical amount in the detected light, and calculates the light-variation location based on a time difference with a highest correlation between the time variations of the first physical amount and the second physical amount.

3. The location-measurement apparatus according to claim 1 further comprising an optical element that extracts the first physical amount and the second physical amount, wherein

the first physical amount is a light intensity of the light, and the second physical amount is any one of a light phase, polarization, and a frequency.

4. The location-measurement apparatus according to claim 3 , wherein

the light source polarization-multiplexes light having mutually orthogonal polarization components and outputs the light to the optical transmission line,

the optical element extracts the light having the orthogonal polarization components, and

the processor calculates the light-variation location based on the orthogonal polarization components of the light.

5. The location-measurement apparatus according to claim 3 , wherein

the light source polarization-multiplexes light having mutually orthogonal polarization components with different wavelengths and outputs the light to the optical transmission line,

the optical element extracts the light having the orthogonal polarization components with different frequencies, and

the processor calculates the light-variation location based on the orthogonal polarization components of the light.

6. The location-measurement apparatus according to claim 3 , wherein the optical element is an optical hybrid that multiplexes the detected light with reference light to extract a vertically-polarized wave in-phase component, a vertically-polarized wave orthogonal phase component, a horizontally-polarized wave in-phase component, and a horizontally-polarized wave orthogonal phase component, and outputs the components to the photodetector.

7. The location-measurement apparatus according to claim 1 , further comprising a light modulator that adds a pilot signal of one of light variations of a light intensity, a light phase, polarization, and a frequency to light from the light source, and stabilizes the light, wherein the pilot signal serves as a location reference when the time variation is calculated.

8. The location-measurement apparatus according to claim 1 , wherein the processor adds a predetermined delay amount to the second physical amount of the detected light, and identifies the light-variation location based on a delay amount with a highest correlation between the time variations of the first physical amount and the second physical amount.

9. The location-measurement apparatus according to claim 8 , wherein the processor identifies the light-variation location with the highest correlation between the time variations of the first physical amount and the second physical amount, based on the pilot signal, within a range of a cable length of the optical transmission line.

10. The location-measurement apparatus according to claim 1 , wherein

the optical transmission line that is coupled to one terminal of the apparatus includes an optical fiber of an outward path and an optical fiber of a return path,

the optical fiber of the outward path transmits light of the light variation of the first physical amount from the one terminal to another terminal, and

the optical fiber of the return path turns back and transmits light of the light variation of the second physical amount after the conversion by the light modulation converter, and the light of the light variation of the first physical amount, from the another terminal to the one terminal.

11. A light modulation converter that faces a measurement apparatus disposed on one terminal of an optical transmission line and is disposed on another terminal of the optical transmission line, wherein

the measurement apparatus disposed on the one terminal of the optical transmission line includes:

a light source that causes continuous oscillation light to enter the one terminal of the optical transmission line, wherein the continuous oscillation light is to propagate a light variation of a first physical amount generated on the optical transmission line to the another terminal of the optical transmission line;

a photodetector that detects, on the one terminal of the optical transmission line, light turned back from a light modulation converter provided on the another terminal of the optical transmission line, wherein the light modulation converter obtains the turned-back light by converting the light variation of the first physical amount into a light variation of a second physical amount; and

a processor, and

the processor calculates a light-variation location generated on the optical transmission line by comparing time variations in the light variation of the first physical amount and the light variation of the second physical amount in the light detected by the photodetector, and

the light modulation converter comprises an optical element that converts the light variation of the continuous oscillation light with the first physical amount transmitted from the measurement apparatus via the one terminal of the optical transmission line into the light variation of the second physical amount.

12. The light modulation converter according to claim 11 , wherein the optical element converts a light intensity of the first physical amount into any one of a light phase, polarization, and a frequency, as the second physical amount.

13. The light modulation converter according to claim 11 , further comprising a light modulator that adds a pilot signal of any one of light variations of the light intensity, the light phase, the polarization, and the frequency to the light, and stabilizes the light, wherein the pilot signal serves as a location reference when the time variation is calculated.

14. The light modulation converter according to claim 11 , wherein the optical element polarization separates light having mutually orthogonal polarization components included in the transmitted light, and then converts the light variation of the first physical amount into the variation of the second physical amount.

15. The light modulation converter according to claim 11 , wherein the light modulation converter demultiplexes a plurality of wavelengths included in the transmitted light, and then converts the light variation of the first physical amount to the light variation of the second physical amount.

16. A measurement system comprising:

a measurement apparatus that is disposed on one terminal of an optical transmission line; and

a light modulation converter that is disposed on another terminal of the optical transmission line, wherein

the measurement apparatus includes:

a light source that causes continuous oscillation light to enter the one terminal of the optical transmission line, wherein the continuous oscillation light is to propagate a light variation of a first physical amount generated on the optical transmission line to the another terminal of the optical transmission line;

a photodetector that detects, on the one terminal of the optical transmission line, light turned back from a light modulation converter, wherein the light modulation converter obtains the turned-back light by converting the light variation of the first physical amount into a light variation of a second physical amount; and

a processor that calculates a light-variation location generated on the optical transmission line by comparing time variations in the light variation of the first physical amount and the light variation of the second physical amount in the light detected by the photodetector, and

the light modulation converter comprises an optical element that converts the light variation of the continuous oscillation light with the first physical amount transmitted from the measurement apparatus via the one terminal of the optical transmission line into the light variation of the second physical amount.

17. The measurement system according to claim 16 , wherein

the optical element of the light modulation converter converts a light intensity of the first physical amount into any one of a light phase, polarization, and a frequency, as the second physical amount, and

the measurement apparatus includes an optical element that extracts the first physical amount and the second physical amount before and after the conversion by the light modulation converter.

18. The measurement system according to claim 16 , wherein the processor of the measurement apparatus obtains a cross-correlation between the time variations of the first physical amount and the second physical amount in the detected light, and calculates the light-variation location based on a time difference with a high correlation between the time variations of the first physical amount and the second physical amount.

19. A measurement method comprising:

causing continuous oscillation light to enter one terminal of an optical transmission line, wherein the continuous oscillation light is to propagate a light variation of a first physical amount generated on the optical transmission line to another terminal of the optical transmission line;

on the one terminal of the optical transmission line, detecting light turned back from the another terminal of the optical transmission line, the turned-back light obtained by converting the light variation of the first physical amount into a light variation of a second physical amount on the another terminal of the optical transmission line; and

obtaining a light-variation location generated on the optical transmission line by comparing time variations in the light variation of the first physical amount and the light variation of the second physical amount in the detected light.