PRESSURE-MEASURING DEVICE

Abstract

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.

Claims

1-15. (canceled)

16. A device for measuring pressure comprising: an optical fibre comprising a thinned part not comprising a Bragg grating, a laser, referred to as a heating laser, arranged to emit an optical wave, referred to as a heating wave, into the thinned part in order to cause an increase in temperature in the thinned part of the fibre, a measurement means comprising a sensor arranged to measure a backscattered optical wave from an optical wave, referred to as an interrogation optical wave, and coming from the thinned part of the optical fibre, and a processing unit arranged and/or programmed to measure a pressure of a fluid surrounding the thinned part from the measurement of the backscattered wave.

17. The device according to claim 16, wherein the optical fibre does not comprise a Bragg grating and/or wherein the thinned part of the optical fibre does not comprise a metal surface treatment.

18. The device according to claim 16, wherein the heating wave comprises a power of at least twice, preferably at least nine times, the power of the interrogation wave.

19. The device according to claim 16, wherein the sensor of the measurement means comprises a spectrometer.

20. The device according to claim 16, wherein the thinned part comprises a transverse cross-section of less than 50 micrometres, preferably less than or equal to 1 micrometre and/or wherein the thinned part extends along a longitudinal direction of less than 150 millimetres, preferably greater than 20 millimetres and/or less than 120 millimetres.

21. The device according to claim 16, wherein the heating laser comprises an emission wavelength less than or equal to 1650 nanometres, preferably equal to 1550 nanometres?10 nanometres and/or wherein the heating laser is arranged to continuously emit the heating wave.

22. The device according to claim 16, further comprising a coupler arranged to divide the wave emitted by the heating laser into the heating wave and the interrogation wave, said coupler allowing passage of the heating wave and the interrogation wave to the optical fibre in a first direction and allowing passage of the backscattered wave from the thinned part to the measurement means in a second direction.

23. The device according to claim 16, wherein the measurement means comprises a laser, referred to as the measurement laser, arranged to emit an optical wave, referred to as the measurement wave, into the optical fibre, acting as the interrogation wave, the measurement wave preferably comprising a wavelength shift relative to the heating wave less than or equal to 10 nanometres.

24. The device according to claim 23, further comprising a circulator allowing, in a first direction, passage of the heating wave from the heating laser and passage of the measurement wave from the measurement laser into the optical fibre, and allowing, in a second direction, passage of the backscattered wave from the thinned part to the measurement means.

25. The device according to claim 23, wherein the sensor of the measurement means comprises a reflectometer.

26. The device according to claim 16, wherein the backscattered wave comprises a Rayleigh or Raman or Brillouin wave.

27. The device according to claim 16, wherein the processing unit is arranged to measure a vacuum pressure less than or equal to 0.9 bar, preferably less than or equal to 10.sup.?9 bar.

28. The device according to claim 16, further comprising at least one further optical fibre comprising a thinned part, the at least one further optical fibre being connected in series to a free end of the optical fibre.

29. A vacuum pressure measurement system, comprising a gauge placed in an enclosure in which a fluid circulates, said gauge comprising a sensor part comprising a device according to claim 16.

30. A pressure measurement method comprising: emitting, using a laser, referred to as a heating laser, an optical wave, referred to as a heating wave, in a thinned part of an optical fibre in order to cause an increase in temperature in the thinned part of the fibre, measuring, using a sensor belonging to a measurement means, a backscattered optical wave originating from an interrogation optical wave and coming from the thinned part of the optical fibre, and measuring, using a processing unit, a pressure of a fluid surrounding the thinned part from the measurement of the backscattered wave.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0111] Further advantages and features of the invention will become apparent upon reading the detailed description of non-limiting implementations and embodiments, and the following appended drawings.

[0112] FIG. 1 is a schematic representation of a non-limiting exemplary embodiment of an optical fibre arrangement used in a device according to the invention;

[0113] FIG. 2 is a first schematic representation of an exemplary embodiment of a first device according to the invention comprising an optical fibre as described in FIG. 1;

[0114] FIG. 3 is a schematic representation of a non-limiting exemplary embodiment of a second device according to the invention comprising an optical fibre as described in FIG. 1;

[0115] FIG. 4 is a schematic representation of a non-limiting exemplary embodiment of a third device according to the invention comprising a plurality of optical fibres as described in FIG. 1 and connected to each other in series;

[0116] FIG. 5 is a schematic representation of a measurement system according to the invention comprising a device according to the invention as described in FIG. 2 or FIG. 3 or FIG. 4.

DETAILED DESCRIPTION

[0117] Of course, the embodiments described below are by no means limitative. In particular, it is possible to envisage alternatives to the invention comprising only a selection of the characteristics described hereinafter in isolation from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention from prior art. This selection includes at least one preferably functional characteristic without structural details, or with only part of the structural details if this part alone is sufficient to confer a technical advantage or to differentiate the invention from prior art.

[0118] In particular, all the alternatives and embodiments described can be combined with one another, provided there is nothing technically opposed to such a combination.

[0119] In the figures, elements common to several figures retain the same reference.

[0120] FIG. 1 is a schematic representation of an example of an arrangement of an optical fibre 100 used in a device according to the invention.

[0121] The optical fibre 100 comprises a thinned part 102, a non-thinned part 103 and an intermediate zone 105. The non-thinned part 103 surrounds the thinned part 102 of the fibre. The intermediate zone 105 corresponds to the zone connecting the non-thinned part 103 of the fibre 100 to the thinned part 102.

[0122] In particular, the thinned part 102 has a transverse cross-section 104 of less than 50 micrometres (?m). Preferably, the transverse cross-section 104 of the thinned part 102 is less than 1 ?m, for example 0.5 ?m.

[0123] The thinned part 102 extends along a longitudinal direction 106 of less than 150 millimetres (mm), preferably greater than 20 mm and/or less than 120 mm.

[0124] The transverse cross-section 104 of the thinned part 102 is constant along the size of the longitudinal direction 106 of the thinned part 102.

[0125] The size of the longitudinal direction 106 is chosen to promote heat transfer in the thinned part 102 of the optical fibre 100. In the case illustrated in FIG. 1, the thinned part comprises a constant transverse cross-section 104 over 100 mm.

[0126] By way of non-limiting example, the optical fibre 100 is a standard optical fibre, for example a SMF28 type standard optical fibre.

[0127] The optical fibre 100 is made of silica. Preferably, the 100 optical fibre is bare, that is it does not include a protective coating.

[0128] The non-thinned part 103 comprises a transverse cross-section of 125 ?m. By way of non-limiting example, the non-thinned part 103 comprises a core with a diameter of 10 ?m, and a layer surrounding the core referred to as cladding with a diameter of 125 ?m. The thinned part 102 does not include a coating.

[0129] The thinned part 102 of optical fibre 100 does not include a Bragg grating. The optical fibre 100 does not include a Bragg grating.

[0130] The thinned part 102 of the optical fibre 100 does not include any metal surface treatment, such as a metal coating. In particular, the external perimeter of the thinned part 102 is devoid of any metal treatment or metal layer surrounding the thinned part 102.

[0131] FIG. 2 is a first schematic representation of an exemplary embodiment of a device 200 according to the invention comprising an optical fibre 100 as described in FIG. 1.

[0132] The device 200 is a device for pressure measurement and comprises the optical fibre 100. The device 200 also comprises a laser 202, referred to as the heating laser 202, arranged to emit in the optical fibre 100, an optical wave 204, referred to as the heating wave 204, in the thinned part 102. The heating wave 204 propagates in the optical fibre 100, that is along the longitudinal direction 106 of the thinned part 102. The heating wave 204 is arranged to propagate in the optical fibre 100 along a single direction 218, hereinafter referred to as the first direction 218. Consequently, the heating wave 204 only travels one way in the optical fibre 100. No laser cavity is required for performing measurement along the device 200. The thinned part of the fibre extends, for example, over 100 mm. The size of the thinned part is chosen to improve heat transfer in the thinned part 102 of the optical fibre 100. The larger the thinned part 102, the greater the heat transfer. This is all the more advantageous as the heating wave 204 propagates only in the first direction 218 in the optical fibre 100.

[0133] The device 200 also comprises: [0134] a measurement means 206 comprising a sensor 209 arranged to measure a backscattered optical wave 208 originating from an optical wave 210, referred to as the interrogation wave 210 and coming from the thinned part, and [0135] a processing unit 212 arranged and/or programmed to measure a pressure of a fluid (preferably a gas or a mixture of gases), here a gas such as air, surrounding the thinned part 102 from the measurement of the backscattered wave 208.

[0136] The processing unit comprises at least one computer, a central processing or calculator unit, an analog electronic circuit (preferably dedicated), a digital electronic circuit (preferably dedicated), and/or a microprocessor (preferably dedicated), and/or software means.

[0137] The measurement and processing of all the backscattered waves 208 emanating from the thinned part 102 of the fibre 100 enable the pressure measurement to be traced back.

[0138] The heating laser 202 is continuous and single-frequency. Using a continuous laser makes it possible to improve thermal effects in the optical fibre 100, especially in the thinned part 102, as the flow of the heating wave 204 is not interrupted. By way of non-limiting example, the heating laser 202 emits an optical wave at 1550 nm. The heating laser 202 is therefore a laser commonly used in telecommunications, which gives it a good quality-to-price ratio.

[0139] In the device illustrated in FIG. 2, the heating wave 204 and the interrogation wave 210 are derived from the same optical wave 214 emitted by the heating laser 202. The device is therefore very compact, using a single laser to thermally excite and interrogate the optical fibre 100.

[0140] The device 200 comprises a coupler 216 positioned upstream of the optical fibre 100 and downstream of the heating laser 202. The coupler 216 is arranged to divide the wave 214 emitted by the heating laser 202 into the heating wave 204 and the interrogation wave 210. In particular, the coupler 216 allows: [0141] passage of the heating wave 204 and the interrogation wave 210 towards the optical fibre 100 in the first direction 218, and [0142] passage of the backscattered wave 208 from the thinned part 102 to the measurement means 208 in a second direction 220, which is opposite to the first direction 218.

[0143] Thus, only the backscattered wave returns in the direction of the heating laser. The backscattered wave is conveyed via the coupler to the measurement means 206. The optical fibre 100 has a free end 222, opposite to an end connected to coupler 216. The heating wave 204 propagates in the optical fibre 100 and exits the optical fibre 100 at the free end 222 of the optical fibre 100.

[0144] The heating wave 204 comprises a power at least twice, preferably at least nine times, greater than the power of the interrogation wave 210. By way of a non-limiting example, the coupler 216 is arranged to distribute power of the wave 214 emitted by the heating laser 202, for example by distributing 90% of the power of the wave 214 emitted from the heating laser 202 to the heating wave 204 and 10% of the power of the wave 214 emitted from the heating laser 202 to the interrogation wave 210. In this way, only the heating wave 2004 can cause a temperature variation in the optical fibre 100, especially in the thinned part 102 of the optical fibre 100. The interrogation wave 210 does not thermally excite the thinned part 102 of the fibre 100. Thus, interrogation wave 210 can probe temperature without disturbing the thinned part 102 of the optical fibre 100.

[0145] By way of non-limiting example, the heating laser 202 used is a continuous laser emitting a light wave of the order of 100 mW in the wavelength band between 1500 nm and 1600 nm.

[0146] The backscattered wave 208 may contain a Brillouin-type, Raman-type or Rayleigh-type backscattering component.

[0147] The processing unit 212 can be arranged to trace back the pressure measurement via a determination of a temperature variation related to the backscattered wave 208.

[0148] The pressure measurement can then be determined using a table relating temperature to pressure.

[0149] The sensor 209 of the measurement means 206 of the device 200 preferably comprises a spectrometer. The spectrometer receives the backscattered wave 208 for analysis. The spectrometer is an optical reflectometer, also known as an Optical Time Domain Reflectometer (OTDR).

[0150] Preferably, the device 200 is arranged to measure a Brillouin-type backscattered wave 208. The processing unit 212 may comprise a Brillouin effect thermometer arranged to measure pressure from a temperature variation and a table relating the temperature variation to the pressure measurement.

[0151] In this case, the processing unit 212 is arranged to measure a propagation velocity of backscattered wave 208 on the basis of a small shift in length of backscattered wave 208 relative to interrogation wave 210. The small wavelength shift is caused by the Doppler effect. The temperature variation can then be determined using the mathematical relationship Math 1. A frequency (or wavelength) of the optical flow of the backscattered wave, noted F.sub.L, can depend linearly on the temperature of the optical fibre 100 via a local variation of an acoustic velocity.

[0152] In another alternative, the device 200 is arranged to measure a Raman-type backscattered wave 208. The Raman-type backscattered wave 208 comprises an Anti-Stokes wave. In this case, the processing unit 206 can be arranged to measure an intensity variation of the backscattered Anti-Stokes wave 208 with respect to the interrogation wave 210 from which the backscattered wave originates. In this case, processing unit 212 may comprise a Raman effect thermometer. The temperature variation can be traced back using the formula Math 2.

[0153] In another alternative, device 200 is arranged to measure a Rayleigh-type backscattered wave 208.

[0154] The processing unit 212, via the reflectometer, is arranged to measure a variation in the optical losses of the backscattered wave 208 as it propagates through the thinned part 102. Optical losses are measured in decibels (dB). In this case, processing unit 212 may comprise a Rayleigh effect thermometer. The processing unit 212 can retrieve a temperature shift using the formula Math 3. By way of non-limiting example, when the backscattered wave 208 has a center wavelength of 1550 nm, the temperature shift can be equal to ?T=(?0.801? C./GHz)??.

[0155] In an alternative, the processing unit 212 preferably comprises all three types of thermometer (Brillouin effect, Raman effect, and Rayleigh effect).

[0156] Preferably, the device 200 is fully fibred, which facilitates pressure measurements as it is more easily scalable and more secure. Furthermore, this makes it more easily integratable into a measurement system or into any measurement casing arranged to perform pressure measurement.

[0157] In the device 200, the heating wave 204 propagates in the optical fibre 100. Part of the heating wave 204 is absorbed by the material of the optical fibre 100, which causes, due to the convection phenomenon, an increase in temperature in the fibre 100, especially in the thinned part 102 of the optical fibre 100, and in the environment external to the optical fibre 100. In the case of the device 200, the heating wave 204 not absorbed in thinned part 102 is transmitted, propagates in the optical fibre 100 and continues its propagation after optical fibre 100. Only the interrogation wave 210 is backscattered in the thinned part 102 of the optical fibre 100. The backscattered wave 208 comes from backscattering of the interrogation wave 210 by glass impurities (i.e. silica) in the thinned part 102. The backscattered wave 208 carries information about the temperature variation integrated along the thinned part 102 of the optical fibre 100.

[0158] Thus, in the device 200, the heating wave 204 is used to thermally activate the thinned part 102 of the optical fibre 100. The backscattered wave 208 is in turn processed (i.e. analysed) to measure the temperature variation by spectroscopy. The arrangement of the optical fibre 100 promotes temperature increase in the thinned part 102 of the optical fibre 100 and in the environment external to the fibre. Such an arrangement of the optical fibre 100 is simple to implement and inexpensive. The optical fibre 100 is preferably bare, that is it has no coating. Then, pressure measurement using the device 200 does not require introduction of at least one Bragg grating into the thinned part 102 of the optical fibre 100 or into the optical fibre 100. Furthermore, no metal treatment or metal part or other element is required around the thinned part 102 of the optical fibre 100 or around the optical fibre 100. Only the interaction of the heating wave 204 in the thinned part 102 of the fibre 100 causes thermal effects such as an increase in temperature in the thinned part 102. The dimensions, that is transverse cross-section and/or size (i.e. length), of the thinned part are chosen to improve thermal excitation of the thinned part 102 by the heating wave 204.

[0159] By way of non-limiting example, the temperature variation can be measured by device 200 with a sensitivity in the order of one degree (? C.), for example 1? C.

[0160] The processing unit is arranged to measure a vacuum pressure of less than or equal to 0.9 bar, preferably less than or equal to 10.sup.?9 bar.

[0161] The device 200 is a point sensor, performing a point measurement along the optical fibre 100.

[0162] FIG. 3 is a second schematic representation of an exemplary embodiment of a device 300 according to the invention comprising an optical fibre 100 as described in FIG. 1. Only differences from the device 200 illustrated in FIG. 2 will be described.

[0163] The measurement means 206 of the device 300 comprises, in addition to the sensor 209, a laser 302, referred to as the measurement laser 302, arranged to emit an optical wave 304, referred to as the measurement wave 304, into the optical fibre 100. In the device 300, the measurement wave 304 is the same as the interrogation wave 210. The measurement wave 304 is used to interrogate the optical fibre 100. The measurement laser 302 and the sensor 209 may be two distinct or separate elements (i.e., each included in a separate casing) or included in the same element (i.e., included in the same casing).

[0164] The heating laser 204 illustrated in FIG. 3 is similar to that illustrated in FIG. 2. The measurement laser 302 emits a continuous, single-frequency measurement wave 304. Using a continuous measurement wave for the measurement wave 304 enables the optical fibre 100 to be continuously probed. The measurement wave 304 is offset in wavelength from the heating wave 204. The wavelength shift is less than or equal to 10 nanometres (nm), for example 5 nanometres. The emission wavelength of the measurement laser may therefore be 1555 nm. The wavelength offset between the heating wave 204 and the measurement wave 304 makes it easier to distinguish these two waves during the measurements and manipulations required prior to measurement, such as adjustments.

[0165] By way of non-limiting example, the measurement laser 302 is an external cavity laser emitting a continuous electromagnetic wave with a power of 100 mW at a wavelength of 1550 nm.

[0166] In an alternative arrangement 300, the measurement laser 302 can be arranged to emit at least one pulsed measurement wave 304. By way of non-limiting example, the measurement laser 302 may comprise at least one element, for example an optical chopper, to emit at least one pulse from a continuous wave. The pulsed measurement wave 304 is preferably longer than one millisecond (ms), for example it may be 4 ms.

[0167] The device illustrated in FIG. 3 includes a circulator 306.

[0168] The circulator 306 allows, in the first direction 218, passage of the heating wave 204 from the heating laser 204 and passage of the measurement wave 304 from the measurement laser 302 in the optical fibre 100. In the second direction 220, the circulator 306 allows passage of the backscattered wave 208 from thinned part 102 to the measurement means 206.

[0169] The backscattered wave 208 thus comes from backscattering of the measurement wave 304 by structural defects in the thinned part 102. The heating wave 204 emitted by the heating laser 202 therefore serves only to raise the temperature in the thinned part 102 of the optical fibre 100. As in the device 200, the heating wave propagates only once in the optical fibre 100.

[0170] The sensor 209 of the measurement device 206 comprises a reflectometer, for example a LUNA brand ODTR.

[0171] The measurement accuracy of the device 300 is equivalent to the measurement accuracy of the device 200.

[0172] Thus, in the device 300, the heating wave 204 of the heating laser 202 is used to heat the optical fibre 100, especially the thinned part 102 of the optical fibre 100. Temperature measurement is obtained by reflectometry via the sensor reflectometer 209 of the measurement means 206.

[0173] The device 300 can achieve the same measurement performance as the device 200 illustrated in FIG. 2. However, using one laser to thermally excite the fibre 100 and another laser to interrogate the fibre 100 makes it easier to process the pressure measurement, especially to more easily dissociate the heating wave 204 from the interrogation wave 210. Furthermore, it facilitates the control thereof, such as adjustments required for use of the device 300.

[0174] FIG. 4 is a schematic representation of a non-limiting exemplary embodiment of a third device 400 according to the invention. The device 400 comprises: [0175] the device 200 or 300, and [0176] a plurality of optical fibres 100, as illustrated in FIG. 1, and connected to each other in series from the optical fibre 100 of the device 200 or 300, especially from a free (that is unconnected) end 222 of the non-thinned part 103 of the optical fibre 100 of the device 200 or 300.

[0177] By way of non-limiting example, two optical fibres 100 are connected to the device 200 or 300. Of course, this figure can be higher or lower by connecting only one optical fibre 100 to the device 200 or 300. The optical fibres 100 of the device 400 are connected to each other by an optical fibre solder 402 or by a mechanical connection means 402, for example using an optical fibre connector. A standard optical fibre 403 is connected to each non-thinned part 103 of the optical fibre 100 via the weld 402 or mechanical connection means 402. The standard optical fibre 403 is, for example, of the SMF 28 type. Preferably, the standard optical fibre 403 is similar to the non-thinned part 103 of the optical fibre 100.

[0178] The sensor 209 of the measurement means 206 is arranged to measure a plurality of backscattered waves 208 originating from the optical wave 210 propagating in each thinned part 102 of all the optical fibres 100. The processing unit 212 of the device 400 is thus arranged and/or programmed to measure the pressure of the fluid surrounding each thinned part 102 from the measurement of the different backscattered waves 208. The succession of optical fibres 100 connected to each other in series includes a free end 404 to which no physical element is connected. The heating wave 204 and the interrogation wave 210 or the measurement wave 304 (if using device 300) exit through the free end 404.

[0179] In the device 400, the optical fibres 100 are identical. Of course, in one alternative device 400, it may have different optical fibres 100, for example optical fibres 100 comprising different thinned part transverse cross-section 102 and/or thinned part length 102.

[0180] FIG. 5 is a schematic representation of a measurement system 500 according to the invention comprising a device 200, 300, 400 according to the invention as described in FIG. 2 or FIG. 3 or FIG. 4.

[0181] The vacuum pressure measurement system 500 comprises a gauge 502. The gauge 502 is placed in an enclosure 504 in which a gas circulates. The gas comprises air. The gauge 502 includes a sensor part 506 comprising a device 200 or a device 300 as described in FIG. 2 or FIG. 3.

[0182] The vacuum pressure is deduced from the amount of heat transferred by the fibre to the gas contained in the enclosure. The backscattered wave 208 carries this information.

[0183] The vacuum pressure measurement system 500 can achieve measurement ranges for primary and secondary vacuum with a resolution and repeatability at least equivalent, preferably superior, to Pirani gauge-based measurement systems using a heated filament placed in an enclosure whose pressure is to be measured.

[0184] As the sensor part 506 of the measurement system 500 is fibred, especially the measurement part comprised of the optical fibre 100 with the thinned part 102, the system 500 benefits from advantages of the intrinsic properties of optical fibres such as insensitivity to electromagnetic, radio, nuclear waves, etc. Furthermore, the system 500 can be a distributed measurement system 500 in that it can perform measurements over large detection zones by assembling in series several optical fibres 100 with a thinned part 102 along this detection zone, for example by comprising a device 400 described in FIG. 4. The detection zone can be, by way of non-limiting example, in the order of one kilometre or ten kilometres or a hundred kilometres or more.

[0185] Of course, the invention is not limited to the examples just described. Numerous modifications can be made to these examples without departing from the scope of the invention as described.