A system for measuring multiple physical parameters at the measurement point using multimode fiber

Abstract

The present invention relates to the field of measuring physical parameters using multimode optical fibers. The present invention relates to a system for measuring P physical parameters at one or more measurement points using one or more multimode optical fibers. According to the present invention, the system (10) comprises: a light source (11) configured to generate a source optical signal; a multimode measuring optical fiber (16) configured to transmit optical signals in at least M predetermined second propagation modes different from each other, M being an integer greater than or equal to P, the measuring optical fiber (16) comprising a measuring portion (18) configured to reflect an optical signal whose wavelength is variable according to the physical parameter to be measured; a detection device (17) configured to measure the wavelength of the optical signal reflected by the measuring portion; and optical modules (13, 14, 15) configured to generate M optical signals from the source optical signal, the optical signals being injected into the measuring optical fiber (16) so that each optical signal propagates in a second propagation mode, the optical modules further configured to transmit the reflected optical signals to the detection device (17).

Description

Technical Field

[0001] The present invention relates to the field of measuring physical parameters using optical fibers, and to a system for measuring multiple physical parameters at one or more measurement points using one or more multimode optical fibers.

[0002] The present invention is particularly applicable to measuring temperature and deformation at a point in a structure using an optical fiber with a Bragg grating, but is more generally applicable to measuring any physical parameter that can be quantified by a sensitive element of an optical fiber, such as a Bragg grating or a Fabry-Perot cavity. The measurement of the physical parameter can also be based on Rayleigh scattering, the Raman effect, or Brillouin scattering. Background Art

[0003] Fiber Bragg grating (FBG) fiber sensors offer a suitable solution for measuring temperature and deformation at one or more points on a structure, particularly when the space available for integrating sensors is limited or when these sensors are subject to significant thermal and / or mechanical stresses. Fiber Bragg grating (FBG) sensors comprise an optical fiber with at least one FBG inscribed on a portion of the fiber, referred to as the measurement portion. Depending on the thermomechanical stresses applied to this portion, the FBG patterns become more or less spaced apart. Consequently, the Bragg wavelength of the reflected light beam varies depending on these stresses. Determining the shift in the Bragg wavelength relative to a reference wavelength makes it possible to measure physical parameters in the measurement portion. To measure temperature and deformation, two optical fibers are typically used. A first fiber, containing a first FBG, is freely mounted in a capillary tube, subject only to thermal stresses. A second fiber, containing a second FBG, is attached to the structure, subject to deformation caused by both thermal and mechanical stresses. Solving two systems of equations with two unknowns allows the determination of each unknown: temperature and deformation. Fiber optic sensors can optionally measure a large number of physical parameters. However, they must include as many optical fibers as the number of physical parameters to be measured. This makes sensor integration and installation relatively complex.

[0004] Another solution for measuring two physical parameters at one point with the aid of a Bragg grating fiber sensor is to discern the polarization of the electric field of the signal passing through the fiber. In transverse electric (TE or S) polarization, the Bragg grating has a sensitivity to deformation K S,ε and the sensitivity to temperature K S,θ In transverse magnetic polarization (TM or P), the Bragg grating has a sensitivity to deformation K P,ε and the sensitivity to temperature K P,θ Therefore, for a single Bragg grating, the deformation and temperature at that Bragg grating can be determined. However, this solution is limited to determining only two physical parameters. This solution is more complex to implement due to the need to maintain the polarization of the signal in the fiber.

[0005] It has also been proposed to use a multi-core optical fiber whose cores have different sensitivities to different physical parameters to be measured. A description of this solution is given in the article by Li Chao et al., “Simultaneous measurement of refractive index, strain, and temperature based on a four-core fiber combined with a fiber Bragg grating”, Optics & Laser Technology, Vol. 90, 2017, pp. 179-184. This solution is relatively complex to implement because it is necessary to identify multi-core optical fibers with different sensitivities to different physical parameters to be measured. In addition, the connection of this type of optical fiber is not standardized, making its interface particularly complex.

[0006] Therefore, the above solutions for measuring multiple physical parameters at a measuring point are not entirely satisfactory. The object of the present invention is to propose a technique for measuring multiple physical parameters by means of a compact sensor with a relatively simple structure, allowing its design, manufacture and use in any type of industry. Summary of the Invention

[0007] To this end, the present invention is based on the differentiated utilization of different signal propagation modes in a multimode optical fiber. The multimode optical fiber has a sensitive element in its measuring section, which is configured to reflect optical signals in different propagation modes, with wavelengths or wavelength shifts that vary depending on the physical parameter to be measured. Since the wavelength shift also varies depending on the propagation mode, the solution of the equations makes it possible to determine each physical parameter using a single optical fiber and in a single measuring section of that fiber.

[0008] More specifically, the present invention first relates to a system for measuring P physical parameters using a multimode optical fiber, where P is an integer greater than or equal to 2. The system includes: a light source, a multimode measurement optical fiber, a detection device, and an optical module.

[0009] The light source is configured to generate a source light signal.

[0010] The multimode measuring optical fiber is configured to transmit optical signals in at least M predetermined second propagation modes different from each other, where M is an integer greater than or equal to P. The measuring optical fiber includes a measuring portion configured to reflect an optical signal whose wavelength is variable according to a physical parameter to be measured.

[0011] The detection means is arranged to measure the wavelength of the optical signal reflected by the measuring portion.

[0012] The optical module is configured to generate M optical signals from a source optical signal. These optical signals are injected into the measurement optical fiber so that each optical signal propagates in a second propagation mode. The optical module is also configured to transmit the reflected optical signal to the detection device.

[0013] The light source can be a broadband light source or an adjustable light source. Preferably, the light source has a bandwidth sufficient to measure multiple wavelengths. For example, the bandwidth is greater than or equal to 3 nm.

[0014] The measurement fiber must be a multimode fiber. It can be slightly multimode, i.e., have physical properties that cause the number of propagation modes to vary from a few to dozens of modes, or strongly multimode, i.e., have physical properties that cause the number of propagation modes to vary from dozens to hundreds of modes.

[0015] The measuring section of the measuring fiber acts as a sensitive element. It is configured to reflect an optical signal whose wavelength varies depending on the physical parameter being measured. In other words, it is configured to reflect each incident optical signal as a reflected optical signal with a wavelength that depends on the different physical parameters being measured. The sensitivity parameters of the measuring section to different physical parameters vary depending on the signal propagation mode. Therefore, for a given change in the physical parameter, the change in wavelength of the reflected signal relative to the incident signal will vary depending on the propagation mode. Therefore, knowing the wavelengths of the different reflected optical signals enables the determination of the different physical parameters by solving a system of equations.

[0016] According to a first specific embodiment, an optical module includes M transmission optical fibers and a mode multiplexer.

[0017] Each transmission optical fiber is arranged to transmit an optical signal in a first predetermined propagation mode.

[0018] A mode multiplexer is connected to the M transmission optical fibers on the one hand and to the measurement optical fiber on the other hand, and is configured to transmit optical signals received from the transmission optical fibers to the measurement optical fibers by converting each first propagation mode into a second propagation mode, and is configured to transmit each reflected optical signal received from the measurement optical fibers to the transmission optical fibers by converting each second propagation mode into a first propagation mode associated with the transmission optical fibers.

[0019] According to the present invention, the mode multiplexer performs both multiplexing and demultiplexing functions. Therefore, it can be referred to as a "mode multiplexer / demultiplexer." However, for the sake of simplicity, the mode multiplexer will be referred to herein simply as a "mode multiplexer." On the one hand, the mode multiplexer enables the generation of optical signals with different propagation modes for the measurement fiber. On the other hand, the wavelength information associated with each propagation mode can be recovered on the different receiving channels (in this case, the M transmission fibers), thereby facilitating the determination of these wavelengths. The mode multiplexer establishes a one-to-one correspondence between a first propagation mode of each transmission fiber and a second propagation mode of the measurement fiber.

[0020] An example of a mode multiplexer according to the invention is described in patent application US 2017 / 010463 A1.

[0021] Advantageously, the transmission fiber is a single-mode fiber. Thus, each first propagation mode is a fundamental mode. The transmission fiber can also be a multimode fiber. However, a single mode is used in each transmission fiber.

[0022] According to a first alternative of the first specific embodiment, the measurement system further comprises an optical splitter arranged to receive the source optical signal, split the source optical signal into M optical signals, and transmit the optical signal to each transmission fiber in a first propagation mode associated with the transmission fiber.

[0023] The optical splitter distributes the power of the source optical signal across all transmission fibers. The distribution may be equal or unequal.

[0024] The optical splitter may also be configured to receive reflected optical signals received from the transmission optical fiber, add the reflected optical signals to obtain a reconstructed optical signal, and transmit the reconstructed optical signal to the detection device. The measurement system may also include an optical circulator configured to transmit the source optical signal from the light source to the optical splitter, and transmit the reconstructed optical signal to the detection device.

[0025] According to a second alternative to the first embodiment, the measurement system further comprises an optical switch arranged to receive the source optical signal, temporally split the source optical signal into M optical signals, and transmit the optical signal to each transmission optical fiber in a first propagation mode associated with the transmission optical fiber.

[0026] The optical switch may also be configured to receive reflected optical signals received from the transmission optical fiber, temporally combine the reflected optical signals to obtain a reconstructed optical signal, and transmit the reconstructed optical signal to the detection device. The measurement system may also include an optical circulator configured to transmit the source optical signal from the light source to the optical switch, and transmit the reconstructed optical signal to the detection device.

[0027] In an alternative embodiment of the present invention, the detection device includes K detectors, where K is an integer greater than or equal to 2 and less than or equal to M, and each detector is configured to measure the wavelength of one or more reflected optical signals received from one or more transmission optical fibers. Each detector is connected to the transmission optical fiber, for example, via an optical circulator. The optical circulator is configured to transmit each optical signal from the optical splitter or optical switch to a mode multiplexer, and transmit each reflected optical signal from the mode multiplexer to the detector.

[0028] When the operating spectral range of the mode multiplexer is too limited for the number of physical parameters to be measured, and therefore too limited for the number of second propagation modes to be generated, multiple mode multiplexers can be used. Mode multiplexers are defined for a specific spectral width, typically 10 to 30 nm. However, the spectral width of the source light signal can exceed this value and reach 50 to 100 nm. In this case, the size of the mode multiplexer cannot cover the entire operating range of the light source. Therefore, the use of multiple mode multiplexers makes it possible to cover the entire spectral range of the light source. For example, for a light source emitting light between 1520 and 1580 nm (i.e. a spectral width of 60 nm), three mode multiplexers can be used, the first mode multiplexer operating between 1520 and 1540 nm, the second mode multiplexer operating between 1540 and 1560 nm, and the third mode multiplexer operating between 1560 and 1580 nm.

[0029] Therefore, according to the second specific embodiment, the optical module includes: X first transmission optical fibers, second multimode transmission optical fibers, Y third transmission optical fibers, a fourth multimode transmission optical fiber, a first mode multiplexer, a second mode multiplexer, a source-side optical splitter or a source-side optical switch, and a measurement-side optical splitter or a measurement-side optical switch.

[0030] X is an integer greater than or equal to 2, and each first transmission optical fiber is configured to transmit an optical signal in a first predetermined propagation mode.

[0031] The second multimode transmission optical fiber is configured to transmit optical signals in at least X second predetermined propagation modes that are different from each other.

[0032] Y is an integer greater than or equal to 2, each third transmission optical fiber is configured to transmit an optical signal in a third predetermined propagation mode, and the sum of X and Y is equal to M.

[0033] The fourth multimode transmission optical fiber is arranged to transmit optical signals in at least Y second predetermined propagation modes that are different from each other and from the X second propagation modes.

[0034] The first mode multiplexer is connected to the X first transmission optical fibers on the one hand and to the second transmission optical fibers on the other hand. The first mode multiplexer is configured to transmit optical signals received from the first transmission optical fibers to the second transmission optical fibers by converting each first propagation mode into one of the X second propagation modes, and is configured to transmit each reflected optical signal received from the second transmission optical fibers to one of the first transmission optical fibers by converting each second propagation mode into a first propagation mode associated with the first transmission optical fibers.

[0035] The second mode multiplexer is connected to the Y third transmission optical fibers on the one hand and to the fourth transmission optical fibers on the other hand. The second mode multiplexer is configured to transmit the optical signals received from the third transmission optical fibers to the fourth transmission optical fibers by converting each third propagation mode into one of the Y second propagation modes, and is configured to transmit each reflected optical signal received from the fourth transmission optical fibers to one of the third transmission optical fibers by converting each second propagation mode into a third propagation mode associated with the third transmission optical fibers.

[0036] The source-side optical splitter is configured to receive a source optical signal, split the source optical signal into X+Y optical signals, transmit the optical signal to each first transmission optical fiber in a first propagation mode associated with the first transmission optical fiber, and transmit the optical signal to each third transmission optical fiber in a third propagation mode associated with the third transmission optical fiber. The source-side optical switch is configured to receive the source optical signal, split the source optical signal in time into X+Y optical signals, transmit the optical signal to each first transmission optical fiber in the first propagation mode associated with the first transmission optical fiber, and transmit the optical signal to each third transmission optical fiber in the third propagation mode associated with the third transmission optical fiber.

[0037] The measurement-side optical splitter is configured to receive optical signals from the first and second mode multiplexers, add these optical signals to obtain a common optical signal, and transmit the common optical signal to the measurement optical fiber. It is also configured to receive the reflected common optical signal, split the reflected common optical signal into two optical signals, and transmit each of these optical signals to one of the first and second mode multiplexers. The measurement-side optical switch is configured to receive optical signals from the first and second mode multiplexers, temporally combine these optical signals to obtain a common optical signal, and transmit the common optical signal to the measurement optical fiber. It is also configured to receive the reflected common optical signal, split the reflected common optical signal into two optical signals, and transmit each of these optical signals to one of the first and second mode multiplexers.

[0038] The first transmission optical fiber and / or the third transmission optical fiber is a single-mode optical fiber, and each first propagation mode and / or each third propagation mode is a fundamental mode.

[0039] The source-side optical splitter may include a first-order optical splitter, a first second-order optical splitter, and a second second-order optical splitter.

[0040] The first-order optical splitter is configured to receive a source optical signal and split the source optical signal into a first intermediate optical signal and a second intermediate optical signal.

[0041] The first second-order optical splitter is configured to receive a first intermediate optical signal, split the intermediate optical signal into X optical signals, and transmit an optical signal to each first transmission fiber in a first propagation mode associated with the first transmission fiber.

[0042] The second second-order optical splitter is configured to receive the second intermediate optical signal, split the intermediate optical signal into Y optical signals, and transmit the optical signal to each third transmission fiber in a third propagation mode associated with the third transmission fiber.

[0043] The source-side optical switch may include: a first-order optical switch, a first second-order optical switch, and a second second-order optical switch.

[0044] The first-order optical switch is configured to receive a source optical signal and temporally split the source optical signal into a first intermediate optical signal and a second intermediate optical signal.

[0045] The first second order optical switch is configured to receive a first intermediate optical signal, temporally split the intermediate optical signal into X optical signals, and transmit an optical signal to each first transmission fiber in a first propagation mode associated with the first transmission fiber.

[0046] The second second-order optical switch is configured to receive the second intermediate optical signal, temporally split the intermediate optical signal into Y optical signals, and transmit the optical signal to each third transmission fiber in a third propagation mode associated with the third transmission fiber.

[0047] In a particular embodiment, the measuring system further comprises a processing unit configured to measure the wavelength of the optical signal reflected by the measuring portion and P×M predetermined sensitivity parameters K PP (j,i) to determine each of the P physical parameters, each sensitivity parameter K PP (j,i) represents the physical parameter PP of the measurement portion for the second propagation mode i j sensitivity, where i is an integer between 1 and M, and j is an integer between 1 and P.

[0048] Each optical splitter can be configured to receive reflected optical signals, add these optical signals, and transmit them to another component. Specifically, the source-side optical splitter can be configured to receive X+Y reflected optical signals, add these optical signals to obtain a reconstructed optical signal, and transmit the reconstructed optical signal to the detection device.

[0049] Similarly, each optical switch can be configured to receive reflected optical signals, temporally combine these optical signals, and transmit them to another component. Specifically, the source-side optical switch can be configured to receive X+Y reflected optical signals, temporally combine these optical signals to obtain a reconstructed optical signal, and transmit the reconstructed optical signal to the detection device.

[0050] Preferably, the operating ranges of the first mode multiplexer and the second mode multiplexer do not overlap and are included in the spectral range of the light source.

[0051] The measurement system according to the first and second specific embodiments enables measurement of multiple physical parameters at the measurement section of a single multimode optical fiber. However, the present invention is applicable to measurement of multiple physical parameters at the measurement sections of multiple multimode optical fibers.

[0052] Therefore, the present invention also relates to a system for measuring P+Q physical parameters using a multimode optical fiber, where P and Q are two integers greater than or equal to 2. The system includes: a light source, a first multimode measurement optical fiber, a second multimode measurement optical fiber, a detection device, and an optical module.

[0053] The light source is configured to generate a source light signal.

[0054] The first multimode measurement optical fiber is configured to transmit optical signals in at least M second predetermined propagation modes different from each other, where M is an integer greater than or equal to P. The first measurement optical fiber includes a first measurement portion configured to reflect an optical signal whose wavelength is variable according to a physical parameter to be measured.

[0055] The second multimode measurement optical fiber is configured to transmit optical signals in at least N predetermined fourth propagation modes that are different from each other, where N is an integer greater than or equal to Q. The second measurement optical fiber includes a second measurement portion that is configured to reflect an optical signal whose wavelength is variable according to a physical parameter to be measured.

[0056] The detection means are arranged to measure the wavelength of the light signal reflected by each measuring optical fibre.

[0057] The optical module is configured to generate M+N optical signals from the source optical signal, wherein the M optical signals are injected into the first measurement optical fiber such that each optical signal propagates in a second propagation mode, and the N optical signals are injected into the second measurement optical fiber such that each optical signal propagates in a fourth propagation mode. The optical module is further configured to transmit the reflected optical signals to a detection device.

[0058] According to certain embodiments, the optical module includes: M first transmission optical fibers, a first mode multiplexer, N second transmission optical fibers, a second mode multiplexer, and an optical splitter or an optical switch.

[0059] M is an integer greater than or equal to P, and each first transmission optical fiber is configured to transmit an optical signal in a first predetermined propagation mode.

[0060] The first mode multiplexer is connected to the M first optical fibers on the one hand and to the first measurement fiber on the other hand. The first mode multiplexer is configured to transmit optical signals received from the first transmission fibers to the first measurement fiber by converting each propagation mode into a second propagation mode, and is configured to transmit each reflected optical signal received from the first measurement fiber to the first transmission fiber by converting each second propagation mode into a first propagation mode associated with one of the first transmission fibers.

[0061] N is an integer greater than or equal to Q, and each second transmission optical fiber is configured to transmit an optical signal in a third predetermined propagation mode.

[0062] The second mode multiplexer is connected to the N second transmission optical fibers on the one hand and to the second measurement fiber on the other hand. The second mode multiplexer is configured to transmit the optical signals received from the second transmission optical fibers to the second measurement fiber by converting each third propagation mode into a fourth propagation mode, and is configured to transmit each reflected optical signal received from the second measurement fiber to the second transmission optical fiber by converting each fourth propagation mode into the third propagation mode associated with one of the second transmission optical fibers.

[0063] The optical splitter is configured to receive a source optical signal, split the source optical signal into M+N optical signals, transmit the optical signal to each first transmission optical fiber in a first propagation mode associated with the first transmission optical fiber, and transmit the optical signal to each second transmission optical fiber in a third propagation mode associated with the second transmission optical fiber. The optical switch is configured to receive a source optical signal, split the source optical signal in time into M+N optical signals, transmit the optical signal to each first transmission optical fiber in the first propagation mode associated with the first transmission optical fiber, and transmit the optical signal to each second transmission optical fiber in the third propagation mode associated with the second transmission optical fiber.

[0064] The first transmission optical fiber and / or the second transmission optical fiber may be a single-mode optical fiber, and each first propagation mode and / or each third propagation mode may be a fundamental mode.

[0065] The optical splitter may include a first-order optical splitter, a first second-order optical splitter, and a second second-order optical splitter.

[0066] The first-order optical splitter is configured to receive a source optical signal and split the source optical signal into a first intermediate optical signal and a second intermediate optical signal.

[0067] The first second-order optical splitter is configured to receive a first intermediate optical signal, split the intermediate optical signal into M optical signals, and transmit the optical signal to each first transmission fiber in a first propagation mode associated with the first transmission fiber.

[0068] The second second-order optical splitter is configured to receive the second intermediate optical signal, split the intermediate optical signal into N optical signals, and transmit the optical signal to each second transmission fiber in a third propagation mode associated with the second transmission fiber.

[0069] The optical switch may include: a first-order optical switch, a first second-order optical switch, and a second second-order optical switch.

[0070] The first-order optical switch is configured to receive a source optical signal and temporally split the source optical signal into a first intermediate optical signal and a second intermediate optical signal.

[0071] The first second-order optical switch is configured to receive a first intermediate optical signal, temporally split the intermediate optical signal into M optical signals, and transmit an optical signal to each first transmission fiber in a first propagation mode associated with the first transmission fiber.

[0072] The second second-order optical switch is configured to receive the second intermediate optical signal, temporally split the intermediate optical signal into N optical signals, and transmit the optical signal to each second transmission fiber in a third propagation mode associated with the second transmission fiber.

[0073] The measurement system may further include a processing unit configured to measure the wavelength of the optical signal reflected by the optical fiber, P×M predetermined sensitivity parameters K PP (j, i) and Q×N predetermined sensitivity parameters K PP (l,k) to determine each of the P+Q physical parameters, each sensitivity parameter K PP (j,i) represents the physical parameter PP of the first measurement part for the second propagation mode i j where i is an integer between 1 and M, j is an integer between 1 and P, and each sensitivity parameter K PP (l, k) represents the physical parameter PP of the second measurement part for the fourth propagation mode k l where k is an integer between 1 and N, and l is an integer between 1 and Q.

[0074] Various optional features and advantages associated with the system described above for measuring P physical parameters using multimode optical fiber are applicable to the system for measuring P+Q physical parameters using multimode optical fiber.

[0075] In each measurement system according to the present invention, each measurement portion includes, for example, a Bragg grating or a Fabry-Perot cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Other characteristics, details and advantages of the invention will become apparent on reading the following description which is given by way of example only and with reference to the accompanying drawings, in which:

[0077] Figure 1 A first example of a system for measuring P physical parameters using a multimode optical fiber according to the present invention is shown;

[0078] Figure 2 A second example of a system for measuring a physical parameter using a multimode optical fiber according to the present invention is shown, the measuring system comprising a plurality of detectors;

[0079] Figure 3 A third example of a system for measuring P physical parameters using a multimode optical fiber according to the present invention is shown, the measurement system comprising a common detector having two propagation modes;

[0080] Figure 4 A fourth example of a system for measuring P physical parameters using a multimode optical fiber according to the present invention is shown, wherein the measurement system includes two optical multiplexers;

[0081] Figure 5 An example of a system for measuring P+Q physical parameters using two multimode optical fibers according to the present invention is shown. DETAILED DESCRIPTION

[0082] Figure 1 A first example of a system for measuring physical parameters using a multimode optical fiber according to the present invention is shown. The measurement system 10 enables measurement of P physical parameters, where P is an integer greater than or equal to 2. The measurement system includes a light source 11, an optical circulator 12, an optical switch 13, M single-mode optical fibers 14, a mode multiplexer / demultiplexer 15 (hereinafter referred to as "mode multiplexer 15"), a multimode optical fiber 16, and a detection device 17. The number M is an integer greater than or equal to P. In Figure 1In the example shown, optical fiber 14 enables transmission of optical signals in fundamental mode. However, the measurement system according to the present invention enables the use of multimode optical fibers. Therefore, signals are transmitted in each optical fiber according to a single propagation mode, referred to as the "first propagation mode." This first propagation mode can vary depending on the optical fiber. Multimode optical fiber 16 is configured to transmit optical signals in at least M second predetermined propagation modes that are different from each other. The multimode optical fiber includes a Bragg grating 18 in a portion thereof, referred to as the "measurement portion." Light source 11 can be a broadband light source or a tunable light source. For example, a broadband light source has a bandwidth greater than or equal to 3 nm. Optical circulator 12 receives a source optical signal from light source 11 at a first input / output terminal and transmits the source optical signal to a second input / output terminal for optical switch 13. Optical switch 13 is configured to receive the source optical signal, temporally split the signal into M identical optical signals, and transmit one of these optical signals in fundamental mode to each optical fiber 14. An optical splitter can be used in place of optical switch 13. The optical splitter divides the power of the source optical signal to generate M identical optical signals. A mode multiplexer 15 is connected to the optical fiber 14 and the multimode optical fiber 16. The mode multiplexer is configured to transmit an optical signal received from the optical fiber 14 to the multimode optical fiber 16 by converting each first propagation mode into one of M second propagation modes. The mode multiplexer is also configured to transmit each reflected optical signal received from the multimode optical fiber 16 to one of the optical fibers 14 by converting each second propagation mode into a fundamental mode. Each reflected optical signal is directed by the mode multiplexer 15 to the optical fiber 14 from which it originated, thereby establishing a one-to-one correspondence between each optical fiber 14 and the second propagation mode of the multimode optical fiber. A detection device 17 is configured to measure the wavelength of the reflected optical signal transmitted by the optical fiber 14.

[0083] The measurement system 10 may further comprise a processing unit (not shown) configured to determine the wavelength of the reflected light signal determined by the detection device 17 and P×M predetermined sensitivity parameters K PP (j,i) to determine each of the P physical parameters. Each sensitivity parameter K PP (j, i) represents the physical parameter PP of the Bragg grating 18 for the second propagation mode i j sensitivity, where i is an integer between 1 and M, and j is an integer between 1 and P.

[0084] The physical parameters are determined by the solution of a system of M equations with P unknowns, each equation of mode i being written as:

[0085]

[0086] Where Δλ i It represents the change of the wavelength of the optical signal associated with mode i relative to the reference wavelength.

[0087] When the number of parameters to be measured is less than the number of modes (P < M), the system of equations is overdetermined. Then, at least some of the physical parameters can be determined multiple times, enabling these physical parameters to be determined more precisely.

[0088] Figure 2 A second example of a system for measuring P physical parameters using a multimode optical fiber according to the present invention is shown. The essential difference between the measurement system 20 according to this embodiment and the measurement system 10 described in the reference Figure 1 is that the detection device 17 is formed by M independent detectors 171, 172,... 17 M The measurement system 20 includes M optical circulators 121, 122,... 12 M . Each optical circulator 12 i is connected to two portions of an optical fiber 14 and a detector 17 i such that each optical signal from the optical switch 13 is transmitted to the mode multiplexer module 15, and each reflected optical signal from the mode multiplexer 15 is transmitted to the associated detector 17 i . The processing unit can similarly recover the wavelengths of the different reflected optical signals in order to determine the P physical parameters at the Bragg grating 18.

[0089] Figure 3 A third example of a system for measuring P physical parameters using a multimode optical fiber according to the present invention is shown. The essential difference between the measurement system 30 according to this embodiment and the measurement system 20 described in the reference Figure 2 is that the detection device 17 is composed of a number of detectors strictly less than M. The measurement system 30 still includes M optical circulators 12 i . The measurement system also includes one or more signal combiners. In this case, the measurement system includes a signal combiner 19 12 which is connected to the optical circulators 121 and 122 so as to receive the reflected optical signals transmitted by two optical fibers 14, and is arranged to add or combine these signals in time and transmit them to the detector 17 12 . The other detectors 17 i receive a single reflected optical signal.

[0090] Figure 4A fourth example of a system for measuring P physical parameters using multimode optical fibers according to the present invention is shown. Measurement system 40 further includes a light source 11, an optical circulator 12, a multimode optical fiber 16, and a detection device 17. The measurement system also includes a first-order optical switch 41, a first second-order optical switch 131, a second second-order optical switch 132, X first single-mode transmission optical fibers 44, second multimode transmission optical fibers 421, Y third single-mode transmission optical fibers 45, a fourth multimode transmission optical fiber 422, a first mode multiplexer 151, a second mode multiplexer 152, and a measurement-side optical switch 43. Optical switch 41 is configured to receive a source optical signal and temporally split it into a first intermediate optical signal and a second intermediate optical signal. Similar to optical switch 13, first optical switch 131 is configured to receive the first intermediate optical signal, temporally split it into X optical signals, and transmit each optical signal to a transmission optical fiber 44. Second optical switch 132 is configured to receive the second intermediate optical signal, temporally split it into Y optical signals, and transmit each optical signal to a transmission optical fiber 45. The first transmission optical fiber 44 and the third transmission optical fiber 45 are each configured to transmit optical signals in fundamental mode. The total number of the first and third transmission optical fibers (X+Y) is equal to M, where M is greater than or equal to P. The first transmission optical fiber 421 is configured to transmit optical signals in at least X second predetermined propagation modes, each of which is different from the other and selected from the M second propagation modes of the multimode optical fiber 16. The fourth transmission optical fiber 422 is configured to transmit optical signals in at least Y second predetermined propagation modes, each of which is different from the other and from the X second propagation modes, and selected from the M second propagation modes of the multimode optical fiber 16. A first mode multiplexer 151 is connected to the transmission optical fibers 44 and the second transmission optical fibers 421. The first mode multiplexer is configured to transmit each optical signal received from the transmission optical fiber 44 to the second transmission optical fiber 421 by converting the fundamental mode into one of the X second propagation modes, and to transmit each reflected optical signal received from the second transmission optical fiber 421 to one of the transmission optical fibers 44 by converting each second propagation mode into the fundamental mode. The second mode multiplexer 152 is connected to the transmission optical fiber 45 and the fourth transmission optical fiber 422. On the one hand, the second mode multiplexer is configured to transmit each optical signal received from the transmission optical fiber 45 to the fourth transmission optical fiber 422 by converting the fundamental mode into one of Y second propagation modes, and on the other hand, to transmit each reflected optical signal received from the fourth transmission optical fiber 422 to one transmission optical fiber 45 by converting each second propagation mode into the fundamental mode.The measurement-side optical switch 43 is configured to, on the one hand, receive the X optical signals from the first mode multiplexer 151 and the Y optical signals from the second mode multiplexer 152, temporally combine these optical signals to obtain a common optical signal, and transmit the common optical signal to the multimode optical fiber 16; and, on the other hand, receive the reflected common optical signal, temporally split the common optical signal into two optical signals, and transmit each optical signal to one of the first and second mode multiplexers 151 and 152.

[0091] Figure 5An example of a system for measuring P+Q physical parameters using two multimode optical fibers according to the present invention is shown. Measurement system 50 further includes a light source 11, an optical circulator 12, and a detection device 17. The measurement system also includes a first-order optical switch 41, a first second-order optical switch 131, a second second-order optical switch 132, a first mode multiplexer 151, and a second mode multiplexer 152, identical to those of measurement system 40. Measurement system 50 also includes M first single-mode transmission fibers 54, N second transmission fibers 55, a first multimode measurement fiber 161, and a second multimode measurement fiber 162. First optical switch 131 is configured to receive a first intermediate optical signal from optical switch 41, temporally split the first intermediate optical signal into M optical signals, and transmit each optical signal to a transmission fiber 54. Second optical switch 132 is configured to receive a second intermediate optical signal from optical switch 41, temporally split the second intermediate optical signal into N optical signals, and transmit each optical signal to a transmission fiber 55. The first transmission fiber 54 and the third transmission fiber 55 are each configured to transmit optical signals in a fundamental mode. The first measurement fiber 161 is configured to transmit optical signals in at least M second predetermined propagation modes that are different from one another, where M is an integer greater than or equal to P, and includes a first Bragg grating 181. The second measurement fiber 162 is configured to transmit optical signals in at least N fourth predetermined propagation modes that are different from one another, where N is an integer greater than or equal to Q, and includes a second Bragg grating 182. The N fourth propagation modes may be the same as or different from the M second propagation modes. A first mode multiplexer 151 is connected to the transmission fiber 54 and the first measurement fiber 161. The first mode multiplexer is configured to transmit each optical signal received from the transmission fiber 54 to the measurement fiber 161 by converting the fundamental mode into one of the M second propagation modes. Furthermore, the first mode multiplexer is configured to transmit each reflected optical signal received from the first measurement fiber 161 to one of the transmission fibers 54 by converting each second propagation mode into the fundamental mode. A second mode multiplexer 152 is connected to the transmission fiber 55 and the second measurement fiber 162. The second mode multiplexer is configured, on the one hand, to transmit each optical signal received from the transmission optical fiber 55 to the measurement optical fiber 162 by converting the fundamental mode into one of N fourth propagation modes, and, on the other hand, to transmit each reflected optical signal received from the second measurement optical fiber 162 to one transmission optical fiber 55 by converting each fourth propagation mode into the fundamental mode.

[0092] The measuring system 50 may further comprise a processing unit (not shown) configured to determine the wavelength of the reflected light signal determined by the detection device 17, the P×M predetermined sensitivity parameters K PP (j, i) and Q×N predetermined sensitivity parameters K PP (l,k) to determine each of the P and Q physical parameters. Each sensitivity parameter K PP(j, i) represents the physical parameter PP of the Bragg grating 181 in the second propagation mode i j where i is an integer between 1 and M and j is an integer between 1 and P. Each sensitivity parameter K PP (l, k) represents the sensitivity of the physical parameter PP1 of the Bragg grating 182 to the fourth propagation mode k, where k is an integer between 1 and N, and l is an integer between 1 and Q.

Claims

1. A measurement system for measuring P physical parameters using a multimode optical fiber, where P is an integer greater than or equal to 2, comprising: a light source (11) arranged to generate a source light signal, A multimode measuring optical fiber (16) configured to transmit optical signals in at least M predetermined second propagation modes different from one another, M being an integer greater than or equal to P, the measuring optical fiber (16) comprising a measuring portion (18) configured to reflect an optical signal having a variable wavelength according to a physical parameter to be measured, Detection device (17, 171, 172, 17 M 、17 12 ), the detection device is configured to measure the wavelength of the light signal reflected by the measuring portion, and Optical modules (13, 131, 132, 14, 15, 151, 152, 41, 421, 422, 43, 44, 45), the optical modules being configured to generate M optical signals from the source optical signal, the optical signals being injected into the measuring optical fiber (16) so that each optical signal propagates in a second propagation mode, the optical modules being further configured to transmit the reflected optical signals to the detection device (17, 171, 172, 17 M 、17 12 ); The optical module includes: X first transmission optical fibers (44), X being an integer greater than or equal to 2, each first transmission optical fiber being configured to transmit an optical signal in a first predetermined propagation mode, a second multimode transmission optical fiber (421), the second multimode transmission optical fiber being configured to transmit optical signals in at least X second predetermined propagation modes that are different from each other, Y third transmission optical fibers (45), Y being an integer greater than or equal to 2, each third transmission optical fiber being configured to transmit an optical signal in a third predetermined propagation mode, the sum of X and Y being equal to M, a fourth multimode transmission optical fiber (422) configured to transmit optical signals in at least Y second predetermined propagation modes that are different from each other and from the X second propagation modes, a first mode multiplexer (151) connected to the X first transmission optical fibers (44) on the one hand and to the second transmission optical fibers (421) on the other hand, the first mode multiplexer being configured to transmit optical signals received from the first transmission optical fibers to the second transmission optical fibers by converting each first propagation mode into one of the X second propagation modes, and being configured to transmit each reflected optical signal received from the second transmission optical fibers to one of the first transmission optical fibers by converting each second propagation mode into a first propagation mode associated with the first transmission optical fibers, a second mode multiplexer (152) connected to the Y third transmission optical fibers (45) on the one hand and to the fourth transmission optical fiber (422) on the other hand, the second mode multiplexer being configured to transmit an optical signal received from the third transmission optical fiber to the fourth transmission optical fiber by converting each third propagation mode into one of the Y second propagation modes, and being configured to transmit each reflected optical signal received from the fourth transmission optical fiber to one of the third transmission optical fibers by converting each second propagation mode into a third propagation mode associated with the third transmission optical fiber, a source-side optical splitter (131, 132, 41) or a source-side optical switch (131, 132, 41), the source-side optical splitter being configured to receive the source optical signal, split the source optical signal into X+Y optical signals, transmit the optical signal to each first transmission optical fiber (44) in a first propagation mode associated with the first transmission optical fiber, and transmit the optical signal to each third transmission optical fiber (45) in a third propagation mode associated with the third transmission optical fiber; the source-side optical switch being configured to receive the source optical signal, split the source optical signal in time into X+Y optical signals, transmit the optical signal to each first transmission optical fiber (44) in the first propagation mode associated with the first transmission optical fiber, and transmit the optical signal to each third transmission optical fiber (45) in the third propagation mode associated with the third transmission optical fiber, and A measurement side optical splitter (43) or a measurement side optical switch (43), the measurement side optical splitter being configured to receive optical signals from the first mode multiplexer (151) and the second mode multiplexer (152), add these optical signals to obtain a common optical signal, and transmit the common optical signal to the measurement optical fiber (16); and being configured to receive a reflected common optical signal, split the reflected common optical signal into two optical signals, and transmit each of these optical signals to the first mode multiplexer and the second mode multiplexer (151). , 152), the measurement side optical switch is configured to, on the one hand, receive optical signals from the first mode multiplexer (151) and the second mode multiplexer (152), temporally combine these optical signals to obtain a common optical signal, and transmit the common optical signal to the measurement optical fiber (16); and, on the other hand, is configured to receive a reflected common optical signal, temporally split the reflected common optical signal into two optical signals, and transmit each of these optical signals to one of the first mode multiplexer and the second mode multiplexer (151, 152).

2. The measurement system according to claim 1, wherein: The optical module includes: M transmission optical fibers (14), each transmission optical fiber being configured to transmit an optical signal in the first predetermined propagation mode, and a mode multiplexer (15) connected to the M transmission optical fibers (14) on the one hand and to the measurement optical fiber (16) on the other hand, the mode multiplexer being configured to transmit optical signals received from the transmission optical fibers to the measurement optical fibers by converting each first propagation mode into a second propagation mode, and to transmit each reflected optical signal received from the measurement optical fibers to the transmission optical fibers by converting each second propagation mode into a first propagation mode associated with a transmission optical fiber.

3. The measurement system according to claim 2, wherein: The transmission optical fiber (14) is a single-mode optical fiber, and each first propagation mode is a fundamental mode.

4. The measuring system according to any one of claims 2 and 3, wherein: The measurement system further comprises an optical splitter (13) configured to receive the source optical signal, split the source optical signal into M optical signals, and transmit the optical signal to each transmission optical fiber (14) in a first propagation mode associated with the transmission optical fiber.

5. The measurement system according to claim 4, wherein: The optical splitter (13) is further configured to receive reflected light signals received from the transmission optical fiber (14), add the reflected light signals to obtain a reconstructed light signal, and transmit the reconstructed light signal to a detection device (17). The measurement system (10) further comprises an optical circulator (12) configured to transmit the source optical signal from the light source (11) to the optical splitter (13) and to transmit the reconstructed optical signal to the detection device (17).

6. The measuring system according to any one of claims 2 and 3, wherein: The measurement system further comprises an optical switch (13) configured to receive the source optical signal, temporally split the source optical signal into M optical signals, and transmit the optical signal to each transmission optical fiber (14) in a first propagation mode associated with the transmission optical fiber.

7. The measurement system according to claim 6, wherein: The optical switch (13) is further configured to receive reflected optical signals received from the transmission optical fiber (14), temporally combine these reflected optical signals to obtain a reconstructed optical signal, and transmit the reconstructed optical signal to the detection device (17). The measurement system (10) further comprises an optical circulator configured to transmit the source optical signal from the light source to the optical switch and to transmit the reconstructed optical signal to the detection device.

8. The measuring system according to any one of claims 2 and 3, wherein: The detection device includes K detectors (171, 172, 17 M 、17 12 ), K is an integer greater than or equal to 2 and less than or equal to M, and each detector is configured to measure the wavelength of one or more reflected light signals received from one or more transmission optical fibers (14).

9. The measurement system according to claim 1, wherein: The first transmission optical fiber (44) and / or the third transmission optical fiber (45) are single-mode optical fibers, and each first propagation mode and / or each third propagation mode is a fundamental mode.

10. The measuring system according to any one of claims 1 to 3 or 9, wherein: The measuring system further comprises a processing unit, which is configured to calculate the wavelength of the optical signal reflected by the measuring part and P×M predetermined sensitivity parameters K PP (j,i) to determine each of the P physical parameters, each sensitivity parameter K PP (j,i) represents the physical parameter PP of the measurement portion for the second propagation mode i j sensitivity, where i is an integer between 1 and M, and j is an integer between 1 and P.

11. A measurement system for measuring P+Q physical parameters using a multimode optical fiber, where P and Q are two integers greater than or equal to 2, the system comprising: a light source (11) arranged to generate a source light signal, a first multimode measuring optical fiber (161) configured to transmit optical signals in at least M predetermined second propagation modes different from one another, M being an integer greater than or equal to P, the first measuring optical fiber comprising a first measuring portion (181) configured to reflect an optical signal having a variable wavelength according to a physical parameter to be measured, a second multimode measurement optical fiber (162) configured to transmit optical signals in at least N predetermined fourth propagation modes different from one another, N being an integer greater than or equal to Q, the second measurement optical fiber comprising a second measurement portion (182) configured to reflect an optical signal having a variable wavelength according to a physical parameter to be measured, a detection device (17) arranged to measure the wavelength of the optical signal reflected by each measuring optical fiber (161, 162), and Optical modules (131, 132, 151, 152, 41, 54, 55) are configured to generate M+N optical signals from a source optical signal, the M optical signals being injected into a first measuring optical fiber (161) such that each optical signal propagates in a second propagation mode, and the N optical signals being injected into a second measuring optical fiber (162) such that each optical signal propagates in a fourth propagation mode, and the optical modules are further configured to transmit reflected optical signals to the detection device (17).

12. The measurement system according to claim 11, wherein: The optical module includes: M first transmission optical fibers (54), M being an integer greater than or equal to P, each first transmission optical fiber being configured to transmit an optical signal in a first predetermined propagation mode, a first mode multiplexer (151) connected to the M first optical fibers (54) on the one hand and to the first measuring fiber (161) on the other hand, the first mode multiplexer being configured to transmit optical signals received from the first transmission fibers (54) to the first measuring fiber (161) by converting each propagation mode into a second propagation mode, and to transmit each reflected optical signal received from the first measuring fiber (161) to the first transmission fiber (54) by converting each second propagation mode into a first propagation mode associated with one of the first transmission fibers, N second transmission optical fibers (55), N being an integer greater than or equal to Q, each second transmission optical fiber being configured to transmit an optical signal in a predetermined third propagation mode, a second mode multiplexer (152) connected to the N second transmission optical fibers (55) on the one hand and to the second measurement optical fiber (162) on the other hand, the second mode multiplexer being configured to transmit optical signals received from the second transmission optical fibers (55) to the second measurement optical fibers (162) by converting each third propagation mode into a fourth propagation mode, and to transmit each reflected optical signal received from the second measurement optical fibers (162) to the second transmission optical fibers (55) by converting each fourth propagation mode into a third propagation mode associated with one of the second transmission optical fibers, and An optical splitter (41) or an optical switch (41) is configured to receive a source optical signal, split the source optical signal into M+N optical signals, transmit the optical signal to each first transmission optical fiber (54) in a first propagation mode associated with the first transmission optical fiber (54), and transmit the optical signal to each second transmission optical fiber (55) in a third propagation mode associated with the second transmission optical fiber (55); and the optical switch is configured to receive a source optical signal, split the source optical signal in time into M+N optical signals, transmit the optical signal to each first transmission optical fiber in the first propagation mode associated with the first transmission optical fiber, and transmit the optical signal to each second transmission optical fiber in the third propagation mode associated with the second transmission optical fiber.

13. The measurement system according to claim 12, wherein: The first transmission optical fiber (54) and / or the second transmission optical fiber (55) is a single-mode optical fiber, and each first propagation mode and / or each third propagation mode is a fundamental mode.

14. The measuring system according to any one of claims 11 to 13, wherein: The measuring system further comprises a processing unit, wherein the processing unit is configured to measure the wavelength of the optical signal reflected by the optical fiber, P×M predetermined sensitivity parameters K PP (j, i) and Q×N predetermined sensitivity parameters K PP (l,k) to determine each of the P+Q physical parameters, each sensitivity parameter K PP (j,i) represents the physical parameter PP of the first measurement portion for the second propagation mode i j where i is an integer between 1 and M, j is an integer between 1 and P, and each sensitivity parameter K PP (l, k) represents the physical parameter PP of the second measurement part for the fourth propagation mode k l where k is an integer between 1 and N, and l is an integer between 1 and Q.

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