Optical fiber state measuring device and optical fiber state measuring method

An optical fiber state measurement method for measuring temperature, strain, or vibration of an optical fiber to be measured, the optical fiber state measurement method comprising, in order:

• by using a first reference optical fiber and a second reference optical fiber that have an optical fiber length longer than that of the optical fiber to be measured, have a constant Brillouin frequency shift amount different from that of the optical fiber to be measured in a steady state of temperature or a non-application state of strain or vibration with respect to the same incident wavelength, and have constant Brillouin frequency shift amounts different from each other with respect to the same incident wavelength,
• a test light incidence step of causing pulsed measurement test light to be incident on the optical fiber to be measured, and causing continuous light having the same wavelength as the measurement test light or pulsed first reference test light and pulsed second reference test light to be incident on the first reference optical fiber and the second reference optical fiber;
• a scattered light input step in which pulsed measurement Brillouin scattered light is input from the optical fiber to be measured, and continuous light or pulsed first reference Brillouin scattered light and second reference Brillouin scattered light are input from the first reference optical fiber and the second reference optical fiber;
• a beat frequency detection step of multiplexing the measurement Brillouin scattered light and the first reference Brillouin scattered light to detect a first beat frequency thereof, and multiplexing the measurement Brillouin scattered light and the second reference Brillouin scattered light to detect a second beat frequency thereof;
• and
• a shift amount change detection step of detecting a direction, that is, a sign, of a change in a Brillouin frequency shift amount of the optical fiber to be measured from the steady state or the non-application state to a non-steady state or an application state based on the first beat frequency and the second beat frequency in a steady state of a temperature or a non-application state of strain or vibration of the optical fiber to be measured and in the non-steady state of a temperature or the application state of strain or vibration of the optical fiber to be measured.