Optical fiber pressure sensor using thermal pressure sensing
A pressure-measuring device including an optical fibre with a thinned portion, a laser, called the heating laser, arranged to emit an optical wave, called the heating wave, into the thinned portion, a measuring means including a sensor that is arranged to measure a backscattered optical wave that is generated by an optical wave, called the interrogation wave, and that originates in the thinned portion of the optical fibre, and a processing unit arranged and/or programmed to measure a pressure of a fluid, preferably a gas, encircling the thinned portion, on the basis of the measurement of the backscattered wave.
1 . A device for measuring pressure comprising:
an optical fiber comprising a thinned part formed by a reduced transverse cross-sectional area of the optical fiber which functions to transfer heat from the reduced transverse cross-sectional area to a surrounding fluid,
a first laser configured to emit an optical wave into the thinned part in order to cause an increase in temperature in the thinned part of the optical fiber,
a sensor configured to measure a backscattered optical wave coming from a fluid surrounding the thinned part of the optical fiber, and
a processing unit configured to trace back a pressure measurement via a determination of a temperature variation related to the backscattered optical wave.
2 . The device according to claim 1 , wherein the optical fiber does not comprise a Bragg grating and/or wherein the thinned part of the optical fiber does not comprise a metal surface treatment.
3 . The device according to claim 1 , wherein the sensor comprises a spectrometer.
4 . The device according to claim 1 , wherein the thinned part comprises a transverse cross-section of less than 50 micrometers, and the thinned part extends along a longitudinal direction of less than 150 millimeters.
5 . The device according to claim 1 , wherein the first laser has an emission wavelength less than or equal to 1650 nanometers.
6 . The device according to claim 1 , further comprising:
a coupler configured to:
divide the wave emitted by the first laser into a heating wave and an interrogation wave,
allow passage of the heating wave and the interrogation wave to the optical fiber in a first direction, and
allow passage of the backscattered wave from the thinned part to the sensor in a second direction.
7 . The device according to claim 6 , wherein the heating wave comprises a power of at least twice the power of the interrogation wave.
8 . The device according to claim 1 , wherein the sensor comprises:
a second laser configured to emit a second optical wave, into the optical fiber, the second optical wave having a wavelength shift relative to the optical wave less than or equal to 10 nanometers.
9 . The device according to claim 8 , further comprising:
a circulator configured to:
allow, in a first direction, passage of the heating wave from the laser and passage of the measurement wave from the second laser into the optical fiber, and
allow, in a second direction, passage of the backscattered wave from the thinned part to the sensor.
10 . The device according to claim 8 , wherein the sensor comprises a reflectometer.
11 . The device according to claim 1 , wherein the backscattered wave comprises a Rayleigh wave or a Raman wave or a Brillouin wave.
12 . The device according to claim 1 , wherein the processing unit is configured to deduce a vacuum pressure less than or equal to 0.9 bar.
13 . The device according to claim 1 , further comprising:
a second optical fiber comprising a second thinned part, the second optical fiber being connected in series to a free end of the optical fiber.
14 . A vacuum pressure measurement system, comprising:
a gauge placed in an enclosure in which a fluid circulates, said gauge comprising:
an optical fiber comprising a thinned part formed by a reduced transverse cross-sectional area of the optical fiber which functions to transfer heat from the reduced transverse cross-sectional area to a surrounding fluid;
a first laser configured to emit an optical wave into the thinned part in order to cause an increase in temperature in the thinned part of the optical fiber;
a sensor configured to measure a backscattered optical wave coming from a fluid surrounding the thinned part of the optical fiber; and
a processing unit configured to trace back a pressure measurement via a determination of a temperature variation related to the backscattered optical wave.
15 . A pressure measurement method comprising: emitting, using a first laser, an optical wave in a thinned heat transfer part of an optical fiber to cause an increase in temperature in the thinned heat transfer part of the optical fiber, the thinned part being formed by a reduced transverse cross-sectional area of the optical fiber which functions to transfer heat from the reduced transverse cross-sectional area to a surrounding fluid, measuring, using a sensor, a backscattered optical wave coming from a fluid surrounding the thinned heat transfer part of the optical fiber, and measuring tracing back, using a processing unit, a pressure measurement via a determination of a fluid surrounding the thinned part from the measurement of temperature variation related to the backscattered optical wave.