Environmental characteristic measurement device and environmental characteristic measurement method

1. An environmental property measurement apparatus for measuring an environmental property in a length direction using a few mode fiber having a plurality of multiplexed modes as a measurement optical fiber by analyzing a Brillouin frequency shift using a Brillouin optical time domain analysis method, the environmental property measurement apparatus comprising:

a first unit configured to input probe light in a desired mode to one end of the measurement optical fiber;

a second unit configured to input to an other end of the measurement optical fiber, a light pulse in the desired mode as a pump light pulse with respect to the probe light, the light pulse having a frequency difference corresponding to a Brillouin frequency shift of the measurement optical fiber relative to the probe light on a high frequency side; and

a third unit configured to input second probe light having the frequency difference corresponding to the Brillouin frequency shift of the measurement optical fiber relative to the probe light on a low frequency side to the other end of the measurement optical fiber, the second probe light being probe light with respect to the probe light in another mode different from the desired mode.

2. The environmental property measurement apparatus according to claim 1 ,

wherein the second unit comprises a first light frequency control unit and the third unit comprises second light frequency control unit,

wherein the first light frequency control unit is configured to control a light frequency such that the frequency difference corresponding to the Brillouin frequency shift of the measurement optical fiber relative to the probe light is provided to the light pulse, and

the second light frequency control unit is configured to control the light frequency such that the frequency difference corresponding to the Brillouin frequency shift of the measurement optical fiber relative to the probe light is provided to the second probe light.

3. The environmental property measurement apparatus according to claim 1 , further comprising:

a double side band modulation unit,

wherein the second unit comprises a first optical fiber unit, and the third unit comprises a second filtering unit,

wherein the second unit is configured to select a high frequency side of two side bands which the double sided band modulation unit generates with the first optical filter to control a light frequency such that the frequency difference corresponding to the Brillouin frequency shift of the measurement optical fiber relative to the probe light is provided to the light pulse, and

the third unit is configured to select a low frequency side of the two side bands with the second optical filter unit to control the light frequency such that the frequency difference corresponding to the Brillouin frequency shift of the measurement optical fiber relative to the probe light is provided to the second probe light.

4. The environmental property measurement apparatus according to claim 1 , further comprising:

a double side band modulation unit and a reflective optical filter unit,

wherein the double side band modulation unit is configured to generate two side bands, and

the reflective optical filter unit is configured to reflect one of the two side bands and transmit the other of the two sides bands, and

the second unit is configured to select a high frequency side of the two side bands reflected or transmitted by the reflective optical filter unit to control a light frequency such that the frequency difference corresponding to the Brillouin frequency shift of the measurement optical fiber relative to the probe light is provided to the light pulse, and

the third unit is further configured to select a low frequency side of the two side bands reflected or transmitted by the reflective optical filter unit to control the light frequency such that the frequency difference corresponding to the Brillouin frequency shift of the measurement optical fiber relative to the probe light is provided to the second probe light.

5. An environmental property measurement method for measuring an environmental property in a length direction using a few mode fiber having a plurality of multiplexed modes as a measurement optical fiber by analyzing a Brillouin frequency shift using a Brillouin optical time domain analysis method, the environmental property measurement method comprising:

inputting probe light in a desired mode to one end of the measurement optical fiber;

inputting to an other end of the measurement optical fiber, a light pulse in the desired mode as a pump light pulse with respect to the probe light, the light pulse having a frequency difference corresponding to a Brillouin frequency shift of the measurement optical fiber relative to the probe light on a high frequency side; and

inputting second probe light having the frequency difference corresponding to the Brillouin frequency shift of the measurement optical fiber relative to the probe light on a low frequency side from the other end of the measurement optical fiber, the second probe light being probe light with respect to the probe light in another mode different from the desired mode.