Vibration measuring instrument and vibration measurement method
The present disclosure relates to a vibration measuring instrument that repeatedly injects a plurality of light pulses with different optical frequencies into an optical fiber, and performs distributed acoustic sensing-phase (DAS-P). In the vibration measuring instrument, light pulses having a waveform with a spectral side lobe smaller than a side lobe of a rectangular wave are used as the plurality of light pulses.
1 . A vibration measuring instrument, comprising:
a light source interfaced with an optical modulator, where the light source and the optical modulator cooperatively operate to repeatedly inject a plurality of light pulses with different optical frequencies into an optical fiber,
a light receiver configured to receive scattered light; and
a signal processing device interfaced with the light receiver and performs distributed acoustic sensing-phase (DAS-P), wherein light pulses having a waveform with a spectral side lobe smaller than a side lobe of a rectangular wave are used as the plurality of light pulses.
2 . The vibration measuring instrument according to claim 1 , wherein
the plurality of light pulses includes a plurality of pulse pairs including a component of a main optical frequency and a component of a compensation optical frequency, and
a center of a main lobe of a main optical frequency included in one of the pulse pairs is set at a frequency position located at a valley of a side lobe component of a main optical frequency included in another.
3 . The vibration measuring instrument according to claim 1 , comprising
a single sideband modulator that generates the plurality of light pulses by modulating continuous light using a modulation signal.
4 . The vibration measuring instrument according to claim 3 , wherein
an envelope of each modulation frequency component of the modulation signal has a raised cosine waveform.
5 . The vibration measuring instrument according to claim 3 , wherein
a modulation frequency component of the modulation signal is used, to separate, for each of the plurality of light pulses, scattered light generated from the plurality of light pulses scattered by the optical fiber.
6 . The vibration measuring instrument according to any one of claims 3 , wherein
a passband width in a bandpass filter for separation for each of the plurality of light pulses is determined by a full width at half maximum (FWHM) of a raised cosine waveform.
7 . A vibration measuring method, comprising:
repeatedly injecting a plurality of light pulses with different optical frequencies into an optical fiber using a light source of a vibration measurement instrument, and
performing, using a signal processing device of the vibration measurement instrument, distributed acoustic sensing-phase (DAS-P), wherein the plurality of light pulses are configured with a waveform having a spectral side lobe smaller than a side lobe of a rectangular wave.