Method and system for interrogating birefringent fiber Bragg grating sensors using heterodyne optical detection - Patent Application 20070122999

Abstract

A method is described for interrogating at least one sensor of the birefringent fiber Bragg grating (Bi-FBG) type. Such a method includes first illuminating the at least one sensor of the birefringent fiber Bragg grating type Bi-FBG with broadband optical excitation radiation OA and transmitting a reflected light spectrum OR from the at least one sensor of the birefringent fiber Bragg grating type Bi-FBG to a detection photonic integrated circuit PIC. Next, the method includes separating, by a polarizing optical beam splitter configured in the detection photonic integrated circuit PIC, a first component of the reflected optical spectrum OR1 characterized by a first optical polarization generated by birefringence and centered on a first frequency ω1 from a second component of the reflected optical spectrum OR2 characterized by a second optical polarization generated by birefringence and centered on a second frequency ω2. The method further comprises the steps of supplying said wideband optical excitation OA to a detection photonic integrated circuit PIC and obtaining at least two narrowband optical signals (LO1, LO2) based on at least one narrowband optical filtering of said wideband optical excitation emission OA implemented in the detection photonic integrated circuit PIC. The at least two narrowband optical signals (LO1, LO2) include a first optical local oscillator signal LO1 centered on a first local oscillator frequency ωLO1 and a second optical local oscillator signal LO2 centered on a second local oscillator frequency ωLO2. The method then provides the first component OR1 of the reflected light spectrum and the first local oscillator optical signal LO1 to a first optical heterodyne detection means integrated in the detector photonic integrated circuit PIC for heterodyne detection, and detects a first local oscillator frequency ω LO1 and the first frequency ω1 of the first component OR1 of the reflected light spectrum. IFs The method includes obtaining a first electrical signal E1. Similarly, the method further comprises providing the second component of the reflected optical spectrum OR2 and the second local oscillator optical signal LO2 to a second optical heterodyne detection means also integrated in the detection photonic integrated circuit PIC to perform heterodyne detection and to obtain a second local oscillator frequency ω LO2 and the second frequency ω2 of the second component of the reflected light spectrum OR2. IFf The method further includes obtaining a second electrical signal E2 with The method finally comprises: determining a first intermediate frequency ω ω 1 that exhibits a first wavelength shift Δλ 1 of a first component of the reflected light spectrum OR1 having a first polarization relative to a first reference wavelength λ i of a Bragg grating of the sensor of the optical fiber sensor Bi-FBG; IFs determining a second intermediate frequency ω indicative of a second wavelength shift Δλ2 of a second component OR2 of the reflected light spectrum having a second polarization relative to a second reference wavelength λi of the Bragg grating of the optical fiber sensor Bi-FBG; IFf Determine. The aforementioned first wavelength shift Δλ1 and second wavelength shift Δλ2 represent at least one physical magnitude measured by the optical fiber sensor Bi-FBG. Furthermore, a corresponding system for interrogating at least one sensor of a birefringent fiber Bragg grating Bi-FBG is described. Finally, a method and system are described for determining at least two physical magnitudes detectable by a birefringent fiber Bragg grating (Bi-FBG) type sensor using the aforementioned interrogation method.

Description

[Technical Field]

[0001] The present invention relates generally to methods and systems for measuring physical parameters using birefringent Fiber Bragg Grating type sensors.

[0002] More specifically, the present invention relates to methods and systems for querying birefringent fiber Bragg grating (FBG) type sensors (e.g., in birefringent fibers) employing heterodyne optical detection and integrated photonic techniques. [Background technology]

[0003] Fiber Bragg Grating type optical fiber sensors (FBG sensors) are becoming increasingly used to measure physical quantities such as strain and temperature due to their simplicity and accuracy. Such sensors are passive, meaning they must be illuminated by optical radiation and the reflected or transmitted spectrum must be analyzed to obtain a measurement of the desired physical quantity.

[0004] In this field, birefringent fiber Bragg grating (Bi-FBG) sensors have the advantage of providing more information compared to standard fiber FBG sensors because, upon reflection, they generate an optical signal that can be viewed as a combination of two partially independent optical signal components with different optical polarizations, each biased in its own specific and predictable way by one or more physical magnitudes detectable by the sensor.

[0005] Since it is possible to independently detect components of the spectrum reflected by the sensor having optical polarizations that are orthogonal to each other (e.g., associated with the so-called "fast polarization axis" and "slow polarization axis"), it is then possible to detect the wavelength deviation of each of these components from the nominal operating wavelength of the sensor.

[0006] Therefore, a Bi-FBG sensor using a birefringent fiber can obtain more information than a conventional fiber FBG sensor for measuring the physical parameters or physical magnitudes to be detected.

[0007] On the other hand, birefringent fiber FBG sensors require much more complex, and therefore more expensive and bulky, interrogating / querying and processing methods and systems than standard fiber FBG sensors.

[0008] Indeed, the interrogation / query must be performed by optical excitation on at least two different channels, one corresponding to the fast axis polarization and one corresponding to the slow axis polarization (since there are at least two reflected optical signals with different polarizations, each operating at its own frequency / wavelength), which in known solutions is usually done by means of a tunable laser source.

[0009] Furthermore, the entire receiving, filtering and electro-optical processing of the optical signal reflected by the birefringent Bi-FBG sensor is at least repeated compared to the non-birefringent FBG sensor.

[0010] The problems of complexity, cost, and bulkiness that already plague standard fiber FBG sensor interrogation / query systems are even more acutely felt in birefringent fiber Bi-FBG sensor interrogation / query systems and remain at least partially unsolved to date.

[0011] In view of the above, there is a strong need for a system and method for interrogating birefringent fiber Bi-FBG sensors that alleviates the above technical drawbacks and meets the following criteria: (i) compactness and simplicity in construction and use; and (ii) effectiveness in performance.

[0012] Such needs are felt in many technical fields, in particular in which birefringent fiber Bi-FBG sensors offer potentially great advantages in terms of detection capabilities, but which may be hampered in practice by the fact that due to their complexity and bulk, it is difficult, if not impossible, to install birefringent fiber Bi-FBG sensor interrogation systems available in the prior art, which is of course essential for practical applicability. Summary of the Invention

[0013] solution The object of the present invention is to provide a method for interrogating birefringent fiber Bragg grating type sensors, which at least partially overcomes the drawbacks mentioned above with reference to the prior art and is able to meet the aforementioned needs, which are particularly felt in the technical field considered.

[0014] This and other objects are achieved by a method for interrogating at least one sensor of the birefringent fiber Bragg grating type according to claim 1.

[0015] Some advantageous embodiments of such a method are the subject of dependent claims 2-12.

[0016] A further object of the invention is to provide a corresponding system for interrogating at least one sensor of the birefringent fiber Bragg grating (Bi-FBG) type.

[0017] This object is achieved by the process according to claim 16.

[0018] Some advantageous embodiments of such a system are the subject of dependent claims 17 to 29.

[0019] Another object of the present invention is to provide a method for determining at least two physical magnitudes detectable by a birefringent fiber Bragg grating (Bi-FBG) type sensor employing the aforementioned interrogation method.

[0020] This object is achieved by a method according to claim 13.

[0021] Some advantageous embodiments of such a method are the subject of dependent claims 14-15.

[0022] A further object of the present invention is to provide a corresponding system for determining at least two physical magnitudes detectable by a sensor of the Birefringent Fiber Bragg Grating (Bi-FBG) type.

[0023] This object is achieved by a system according to claim 30.

[0024] Some advantageous embodiments of such a system are the subject of dependent claims 31-33. [Brief explanation of the drawings]

[0025] Further features and advantages of the method and system according to the invention will become apparent from the following description of preferred embodiments thereof, given by way of non-limiting illustration with reference to the accompanying drawings, in which:

[0026] [Figure 1] FIG. 1 shows, by means of a functional block diagram, different embodiments of a system for interrogating a sensor of the Birefringent Fiber Bragg Grating (Bi-FBG) type. [Figure 2]FIG. 2 shows by means of a functional block diagram different embodiments of a system for interrogating a sensor of the Birefringent Fiber Bragg Grating (Bi-FBG) type. [Figure 3] FIG. 3 shows by means of a functional block diagram a different embodiment of a system for interrogating a sensor of the Birefringent Fiber Bragg Grating (Bi-FBG) type. [Figure 4] FIG. 4 shows by means of a functional block diagram a different embodiment of a system for interrogating a sensor of the Birefringent Fiber Bragg Grating (Bi-FBG) type. [Figure 5] FIG. 5 shows by means of a functional block diagram a different embodiment of a system for interrogating a sensor of the Birefringent Fiber Bragg Grating (Bi-FBG) type. [Figure 6] FIG. 6 shows by means of a functional block diagram a different embodiment of a system for interrogating a sensor of the Birefringent Fiber Bragg Grating (Bi-FBG) type. [Figure 7] FIG. 7 shows a simplified diagram of some known optical heterodyne detection / reception techniques. [Figure 8] FIG. 8 shows a simplified diagram of some known optical heterodyne detection / reception techniques. DETAILED DESCRIPTION OF THE INVENTION

[0027] In the following, with reference to Figures 1 to 6, a method is described for interrogating at least one sensor of the birefringent fiber Bragg grating (FBG) type (hereinafter, for the sake of brevity, also referred to as birefringent Bi-FBG sensor), for example a sensor of the Bi-FBG type obtained in a birefringent fiber or in an optical fiber zone made birefringent.

[0028] Such a method comprises first irradiating said at least one sensor of the birefringent fiber Bragg grating Bi-FBG type with broadband optical excitation radiation OA, and transmitting in an integrated photonic PIC detection circuit (or device) a reflected light spectrum OR reflected by the at least one sensor of the birefringent fiber Bragg grating Bi-FBG type.

[0029] Next, the method includes separating, by a polarizing optical beam splitter included in the detection photonic integrated circuit PIC, a first component OR1 of the reflected light spectrum, which is produced by birefringence and characterized by a first optical polarization centered at a first frequency ω1, from a second component OR2 of the reflected light spectrum, which is produced by birefringence and characterized by a second optical polarization centered at a second frequency ω2.

[0030] The method further includes providing the wideband optical excitation OA to a detection photonic integrated circuit PIC, and obtaining at least two narrowband optical signals (LO1, LO2) based on at least one narrowband optical filtering of the wideband optical excitation emission OA implemented in the detection photonic integrated circuit PIC.

[0031] At least two narrowband optical signals (LO1, LO2) are oscillated at a first local oscillator frequency ω LO1 a first local oscillator optical signal LO1 centered at ω and a second local oscillator frequency ω LO2 and a second local oscillator optical signal LO2 centered at .

[0032] Next, the method includes providing the first component OR1 of the reflected light spectrum and the first local oscillator optical signal LO1 to a first optical heterodyne detection means integrated in the detection photonic integrated circuit PIC to perform heterodyne detection, and detecting a first local oscillator frequency ω LO1and a first intermediate frequency ω1 of the first component OR1 of the reflected light spectrum. IFs The method includes obtaining a first electrical signal E1.

[0033] Similarly, the method includes providing a second component OR2 of the reflected light spectrum and a second local oscillator optical signal LO2 to a second optical heterodyne detection means also integrated in the detection photonic integrated circuit PIC to perform heterodyne detection, and detecting a second local oscillator frequency ω LO2 and a second intermediate frequency ω2 of the second component OR2 of the reflected light spectrum. IFf The method further includes obtaining a second electrical signal E2 at

[0034] The method finally comprises: ref1 a first intermediate frequency ω that exhibits a first wavelength shift Δλ1 of a first component OR1 of a reflected light spectrum having a first polarization relative to IFs and further comprising determining a second reference wavelength λ ref2 the second intermediate frequency ω2, which indicates a second wavelength shift Δλ2 of the second component OR2 of the reflected light spectrum having a second polarization relative to IFf The method includes determining:

[0035] The aforementioned first wavelength shift Δλ1 and second wavelength shift Δλ2 (indicated by the determined intermediate frequency) represent at least one physical magnitude measured by the optical fiber sensor Bi-FBG.

[0036] According to one embodiment of the method shown in FIG. 1, the aforementioned step of acquiring at least two narrowband optical signals (LO1, LO2) comprises: a local oscillator frequency ω adapted to narrow-band filtering said broadband optical excitation radiation OA by a narrow-band bandpass optical tunable filter OTF incorporated in the detector photonic integrated circuit PIC to act as a local oscillator signal LO; LO obtaining a narrowband optical signal centered at - splitting said narrowband optical signal by an optical beam splitter OSPL configured to make available at two output ports two attenuated replicas of the same narrowband optical signal received as input; Includes:

[0037] In this case, the first local oscillator signal LO1 and the second local oscillator signal LO2 are two identical signals present at the two output ports of the optical beam splitter.

[0038] According to another embodiment of the method shown in FIG. 2, the aforementioned step of acquiring at least two narrowband optical signals (LO1, LO2) comprises: - splitting said broadband optical excitation radiation OA by an optical beam splitter to obtain a first replica of broadband optical excitation radiation and a second replica of broadband optical excitation radiation; narrow-band filtering of said first replica of the broadband optical pump radiation by a first narrow-band bandpass optical tunable filter OTF1 integrated in the detector photonic integrated circuit PIC to a first local oscillator frequency ω LO1 obtaining a first narrowband optical signal centered at - second local oscillator frequency ω LO2 narrowband filtering said second replica of the broadband optical pump radiation by a second narrowband bandpass optical tunable filter OTF2 integrated in the detector photonic integrated circuit PIC to obtain a second narrowband optical signal centered at Includes:

[0039] According to one embodiment of the method, for example, as shown in Figures 1 to 4, the step of performing heterodyne detection and obtaining a first electrical signal E1 includes a step of combining a first component OR1 of the reflected optical spectrum with a first local oscillator optical signal LO1 in an optical waveguide of a first optical coupler OC1 of the first optical heterodyne detection means, and further includes a step of converting the optical signal obtained at the output of the first optical coupler into a respective first electrical signal E1 by a first optoelectronic receiver PD1 of the first optical heterodyne detection means.

[0040] In such an embodiment, the step of performing heterodyne detection and obtaining a second electrical signal E2 includes combining the second component OR2 of the reflected optical spectrum with the second local oscillator optical signal LO2 in the optical waveguide of the second optical coupler OC2 of the second optical heterodyne detection means, and further includes converting the optical signal obtained at the output of the second optical coupler into a respective second electrical signal E2 by the second optoelectronic receiver PD2 of the second optical heterodyne detection means.

[0041] According to one embodiment (shown in FIG. 3 ), each step of performing heterodyne detection to obtain the first electrical signal E1 and the second electrical signal E2 includes, for each heterodyne detection, performing balanced detection using a respective 2x2 optical coupler configured to provide as output two optical signals detected by two respective photodiodes for balanced detection, and each of the first electrical signal E1 and the second electrical signal E2 is obtained as a subtraction of the currents output from the respective photodiodes.

[0042] According to another embodiment of the method (shown in FIG. 4), the step of performing the first heterodyne detection further comprises shifting the phase of the first local oscillator optical signal LO1 in a controlled manner by a first optical phase shifter OPS1 configured in the photonic integrated circuit PIC before input at the first optical coupler OC1.

[0043] Similarly, the step of performing the second heterodyne detection further includes shifting the phase of the second local oscillator optical signal LO2 in a controlled manner by a second optical phase shifter OPS2 configured in the photonic integrated circuit PIC before input at the second optical coupler OC2.

[0044] According to another embodiment of the method (shown in FIG. 5 ), the step of performing heterodyne detection includes injecting a first component OR1 of the reflected optical spectrum and a second component OR2 of the reflected optical spectrum into a single 2×1 optical coupler OC, and generating an intermediate frequency ω 1 representing a difference in frequency deviation between the first component OR1 of the reflected optical spectrum and the second component OR2 of the reflected optical spectrum. IF as an output.

[0045] Heterodyne detection, also called coherent optical detection (or reception) using heterodyne techniques, is a commonly known technique. The following description of a corresponding system according to the invention provides further details in this regard with reference to the embodiments shown in Figures 1 to 6.

[0046] According to the embodiment shown in FIG. 6, the method can interrogate multiple sensors of the birefringent fiber Bragg grating type (Bi-FBG1 to Bi-FBGn) in a cascaded manner, each characterized by a respective nominal operating wavelength (λ1 to λn).

[0047] In such an embodiment, the transmitting step comprises transmitting the total reflected light spectrum ORT reflected from cascaded sensors of birefringent fiber Bragg grating type (Bi-FBG1 to Bi-FBGn) to the detection photonic integrated circuit PIC, and the separating step comprises separating a first component ORT1 and a second component of said total reflected light spectrum ORT.

[0048] The first component ORT1 of the total reflected light spectrum includes a superposition of first components (OR11 to OR1n) having first light polarizations centered around respective first frequencies (ω11 to ω1n).

[0049] The second component ORT2 of the total reflected light spectrum includes a superposition of second components (OR21 to OR2n) having second light polarizations centered around respective second frequencies (ω21 to ω2n).

[0050] In this case, the method comprises: - spectrally separating the first components (OR11 to OR1n) from each other by first frequency discrimination or demultiplexing means AWG1; - spectrally separating the second components (OR21 to OR2n) from each other by second frequency discrimination or demultiplexing means AWG2; - performing a heterodyne detection step on each of said first components (OR11 to OR1n) and each of said second components (OR21 to OR2n) to obtain a respective plurality of first electrical signals E1k and second electrical signals E2k; for each pair of first and second electrical signals E1k and E2k corresponding to each sensor of the birefringent fiber Bragg grating type Bi-FBGk, a first intermediate frequency ω IFs,k and the second intermediate frequency ω IFf,k and performing the aforementioned step of determining:

[0051] According to one embodiment of the method, the first light polarization corresponds to polarization on the "slow polarization axis" (referred to as the "slow axis" for brevity), and the first birefringence peak frequency ω corresponds to a slow-axis birefringence peak frequency ω. The second light polarization corresponds to polarization on a "fast polarization axis" (referred to as the "fast axis" for brevity) that is orthogonal to the first light polarization and orthogonal to the "slow polarization axis," and the second birefringence peak frequency ω corresponds to a fast-axis birefringence peak frequency ω.

[0052] According to one embodiment of the method, the aforementioned first reference wavelength λ ref1 and the aforementioned second reference wavelength λ ref2 corresponds to the two respective nominal operating wavelengths of the sensor of birefringent fiber Bragg grating type Bi-FBG on the two fast and slow channels determined by initial calibration.

[0053] According to another embodiment of the method, the aforementioned first reference wavelength λref1 and the second reference wavelength λ ref2 are coincident and correspond to the reference wavelength λi specified by tuning the narrow bandpass optical tunable filter OTF.

[0054] According to one embodiment of the method, the aforementioned first reference wavelength λ ref1 and a second reference wavelength λ ref2 correspond to two reference wavelengths λi1 and λi2, respectively, which are determined by tuning two narrow bandpass optical tunable filters (OTF1 and OTF2).

[0055] According to another embodiment, the aforementioned first reference wavelength λ ref1 and the second reference wavelength λ ref2 are matched to and correspond to the two respective nominal operating wavelengths of the birefringent fiber Bragg grating (Bi-FBG) type sensor in the two high-speed and low-speed channels.

[0056] Here, a method is described for determining at least two physical magnitudes detectable by a birefringent fiber Bragg grating Bi-FBG type sensor.

[0057] Such a method may involve carrying out a method for interrogating at least one sensor of the birefringent fiber Bragg grating (Bi-FBG) type according to any one of the above-mentioned embodiments, and then interrogating the first intermediate frequency ω as described above. IFs and the second intermediate frequency ω IFf determining at least two physical dimensions based on the processing of

[0058] According to one embodiment of such a method, the two physical quantities that are determined are longitudinal strain and transverse strain.

[0059] According to another embodiment of such a method, the two physical quantities determined are strain and temperature.

[0060] In this regard, further description will be given below with reference to the previously described embodiment regarding a method for measuring two orthogonally polarized Bragg wavelengths reflected by a fiber Bragg grating Bi-FBG sensor characterized by birefringence.

[0061] A periodic and uniform variation of the refractive index of an optical fiber "core" is the simplest form of a Bi-FBG structure. The fundamental property of a Bi-FBG sensor is the existence of a resonance condition, which reflects light at a specific wavelength called the Bragg wavelength (λB), defined as: λB = 2n eff Λ where n eff is the effective refractive index of the fiber, and Λ is the grating period, also called the grating pitch. The Bragg wavelength is determined by the ratio of the grating pitch (Λ) to the effective refractive index of the fiber core (n eff ), and these parameters are sensitive to changes in temperature and strain. Therefore, Bi-FBG sensors can be directly used as strain and temperature sensors.

[0062] If the fiber is birefringent, the effective refractive index experienced by light propagating at two orthogonal polarizations is different, typically n eff-s and n eff-f It is defined as follows.

[0063] Therefore, the two orthogonal polarization spectra reflected by the Bi-FBG sensor in a birefringent fiber are given by Δλ = λs − λf = 2(n eff-s -n eff-f ) · Λ is observed at two different wavelengths with a peak wavelength separation.

[0064] Similar considerations can be made by referring to the corresponding frequency parameter ω instead of wavelength.

[0065] Examples of birefringent fibers used in the fabrication of birefringent Bi-FBG sensors include Panda fiber, TruePhase fiber, bowtie fiber, D-clad fiber, elliptical-core-elliptical-clad fiber, and microstructured highly birefringent optical fiber (MOF).

[0066] Birefringent Bragg gratings can also be induced in optical fibers by femtosecond writing, in which case the birefringence is inscribed only in a limited region of the fiber resulting in a Bi-FBG sensor.

[0067] Birefringent Bi-FBG sensors advantageously enable simultaneous detection of strain and temperature by measuring the Bragg wavelength offset corresponding to the fast and slow axes of light polarization.

[0068] Assuming a linear dependence, the correlation between the Bragg wavelengths λs and λf and the change in temperature and strain can be expressed by the following equation, expressed in matrix form:

number

number

number

number

number

[0069] Therefore, the temperature change ΔT and the strain change Δε can be calculated simultaneously through the inverse matrix.

number

number

[0070] The birefringent Bi-FBG sensor is also capable of distinguishing between transverse and longitudinal strain.

[0071] Indeed, the Bi-FBG sensor exhibits maximum transverse strain sensitivity when its birefringence axes are orthogonal and parallel to the surface: when a transverse load is applied along one of the two birefringence axes, the corresponding reflection peak exhibits maximum transverse strain sensitivity.

[0072] Instead, when the axis is positioned at 45° to the surface, the sensitivity of the Bi-FBG sensor to transverse strain decreases, and the wavelength deviation depends mainly on longitudinal strain.

[0073] This property of birefringent Bi-FBG sensors allows them to distinguish between two types of strain and, advantageously, to measure shear strain. For example, S. Sulejmani et al., "Shear stress sensing with Bragg grating-based sensors in microstructured optical fibers," Opt. Express 21, 20404-20416 (2013), show that the maximum shear strain sensitivity of wavelength separation deviation is obtained when the birefringence axis is aligned at 45°.

[0074] Clearly, therefore, the advantage of the Bi-FBG birefringence sensor is that it can simultaneously detect two different magnitudes due to the information provided by two spectral components of different polarizations.

[0075] With reference to Figures 1 to 6, a system 1 for testing at least one sensor of the birefringent fiber Bragg grating FBG type (hereinafter, for the sake of brevity, also referred to as birefringent Bi-FBG sensor), for example a Bi-FBG type sensor obtained in a birefringent fiber or in an optical fiber zone made birefringent, is described.

[0076] Such a system comprises a broadband optical radiation source BS, an integrated photonic detection device PIC, and electronic processing means 2 operatively connected to the integrated photonic detection device PIC.

[0077] The broadband optical radiation source BS is configured to irradiate at least one sensor of the birefringent fiber Bragg grating Bi-FBG type with broadband optical excitation radiation OA.

[0078] The integrated photonic detection device PIC comprises a first input port C1 operatively connected to said at least one optical fiber sensor of the birefringent fiber Bragg grating Bi-FBG type for receiving the reflected light spectrum OR from said sensor, and a second input port C2 operatively connected to said broadband optical radiation source BS for receiving said broadband optical excitation radiation OA.

[0079] The integrated photonic detection device PIC includes a polarizing optical beam splitter PS, a local oscillator signal generating means, a first heterodyne optical detection means, a second heterodyne optical detection means, a first output port U1, and a second output port U2.

[0080] The polarizing optical beam splitter PS is configured to separate a first component OR1 of the reflected light spectrum, which is generated by birefringence and characterized by a first light polarization centered at a first frequency ω1, from a second component OR2 of the reflected light spectrum, which is generated by birefringence and characterized by a second light polarization centered at a second frequency ω2.

[0081] The local oscillation signal generating means generates a first local oscillation frequency ω LO1 a first local oscillator optical signal LO1 centered at ω LO2 and a second local oscillator optical signal LO2 centered on the first local oscillator optical signal LO1.

[0082] Such local oscillator signal generating means comprises at least one tunable narrow-band optical bandpass filter OTF configured to perform narrow-band optical filtering of said broadband optical excitation radiation OA.

[0083] The first optical heterodyne detection means is configured to receive said first component OR1 of the reflected optical spectrum and said first optical local oscillator signal LO1 and generate, by heterodyne detection or reception techniques, a first local oscillator frequency ω based on the first component OR1 of the reflected optical spectrum and the first optical local oscillator signal LO1. LO1 and a first intermediate frequency ω1 of the first component OR1 of the reflected light spectrum. IFs generates a first electrical signal E1.

[0084] The second optical heterodyne detection means is configured to receive the second component OR2 of the reflected light spectrum and the second optical local oscillator signal LO2, and generate, by a heterodyne detection technique, a second local oscillator frequency ω based on the second component OR2 of the reflected light spectrum and the second optical local oscillator signal LO2. LO2 and a second intermediate frequency ω2 equal to the difference between the second frequency ω2 of the second component OR2 of the reflected light spectrum. IFf A second electrical signal E2 is generated.

[0085] It comprises a first output port U1 configured to make available a first electrical signal E1 and a second output port U2 configured to make available a second electrical signal E2.

[0086] The electronic processing means is operatively connected to the integrated PIC photonic device and receives the first electrical signal E1 and the second electrical signal E2 and generates a first reference wavelength λ ref1 the first intermediate frequency ω 1 , which indicates a first wavelength offset Δλ 1 of the first component OR1 of the reflected light spectrum having a first polarization, relative to IFs is configured to determine

[0087] The electronic processing means further comprises a second reference wavelength λ ref2 the second intermediate frequency ω2, which indicates a second wavelength shift Δλ2 of the second component OR2 of the reflected light spectrum having a second polarization relative to IF2 is configured to determine

[0088] The aforementioned first wavelength shift Δλ1 and second wavelength shift Δλ2 represent at least one physical magnitude measured by the optical fiber sensor Bi-FBG.

[0089] According to one embodiment of system 1 (shown in FIG. 1), the aforementioned means for generating a local oscillator signal includes a tunable narrowband OTF optical filter and an optical beam splitter.

[0090] The narrow-band optically tunable OTF narrow-band filters the aforementioned broadband optical pump radiation OA to generate a local oscillator frequency ω 1 , which is adapted to act as a local oscillator signal LO. LO The optical fiber is configured to generate a narrowband optical signal centered at .

[0091] The optical beam splitter is configured to split the aforementioned narrowband optical signal and make two attenuated replicas of the narrowband optical signal itself received as input corresponding respectively to a first local oscillator signal LO1 and a second local oscillator signal LO2 available at two output ports of the optical beam splitter.

[0092] Some additional details of the foregoing embodiment are described below with reference to FIG.

[0093] As can be seen, the system includes a device for coupling and splitting two orthogonal polarizations corresponding to the fast and slow axes into two optical waveguides.

[0094] The device for splitting the two orthogonal polarizations is, in several possible implementation options, for example, a two-dimensional 2D grating coupler or an edge coupler combined with a polarization rotator and splitter (PSR).

[0095] The system further includes two different integrated photonic circuits that implement a heterodyne detection scheme.

[0096] The two orthogonal polarizations at different frequencies / wavelengths reflected by the birefringent Bi-FBG are separated and coupled into two single-mode waveguides, in which the two signals at different frequencies / wavelengths are analyzed separately.

[0097] The two signals are separately combined with the local oscillator signal by two integrated optical couplers, mixed in an integrated photodiode, and the frequency deviation of the two individual peaks is detected by heterodyne detection.

[0098] As an example shown in Figure 1, light coming from a broadband light source BS is split by an optical splitter ("splitter") OS and sent to both a first port of an optical circulator 3 and an input port of a photonic integrated circuit PIC.

[0099] The birefringent Bi-FBG sensor is interrogated by a broadband light source BS through the second port of the optical circulator, and the reflected optical power from the birefringent Bi-FBG sensor is collected by the third port of the optical circulator and coupled into a chip implementing the PIC integrated photonic circuit.

[0100] The integrated photonic circuit PIC includes an optical coupler C1 and a signal polarization splitter PS (where the polarization splitter, or polarizing optical beam splitter, may include a 2D grating coupler or PSR, as described above) for the fast axis polarization and slow axis polarization reflected by the birefringent Bi-FBG sensor.

[0101] The integrated photonic circuit PIC further includes an additional optical coupler C2 (eg, a one-dimensional grating coupler or an "edge" coupler) configured to couple broadband light into the integrated photonic circuit.

[0102] Photonic integrated circuits (PICs) - at least one tunable optical bandpass OTF filter (e.g., but not limited to, a ring resonator filter) for selecting a desired frequency / wavelength to be used as a local oscillator signal; - at least two optical couplers configured to couple the optical signal and the local oscillator signal into the same waveguide; - at least two integrated photodiodes for heterodyne detection.

[0103] The coupler combines the reflected light from the third port of the optical circulator into the PIC optical chip, and the PS polarization splitter separates the light by sending it into two different optical waveguides. The two orthogonal polarizations reflected from the birefringent Bi-FBG sensor at the fast-axis ωs and slow-axis ωf frequencies are combined and sent into two different waveguides of the PIC integrated photonic circuit.

[0104] According to one implementation option, the scheme further comprises a polarization rotator or a 2D grating coupler for coupling the light separated by the splitter into two waveguides TE.

[0105] The combined broadband light is fed as input to another input port on the PIC chip, where it is filtered by a tunable optical bandpass filter (OTF) to select a specific wavelength.

[0106] According to one implementation option, the tunable filter is based on the extraction (drop) port of a tunable micro-ring resonator.

[0107] The filtered light at the selected wavelength acts as a local LO oscillator, which is split and sent to two different integrated optical couplers OC1 and OC2, where it is combined with light at the frequencies of the slow polarization axis ωs and the fast polarization axis ωf.

[0108] Each coupler combines the frequency of a local LO oscillator with one of two frequencies, ωs and ωf, and the output signals of the optical couplers are fed to integrated photodiodes in a heterodyne configuration.

[0109] The two optical signals and the local oscillator propagate with the same cross section and polarization in the waveguide, providing maximum polarization match for heterodyne detection.

[0110] Two intermediate frequencies ω IFs = ωs - ω LO , and the other side ω IFf = ωf - ω LO The term resulting from the mixing of the two heterodyne detections in carries information about the wavelengths of the reflection peaks of the birefringent Bi-FBG sensor and can be used to detect the wavelength offset of the birefringent Bi-FBG sensor and the wavelength separation between the two peaks corresponding to the slow and fast axes, respectively.

[0111] According to another embodiment of the system (shown in FIG. 2), the aforementioned local oscillator signal generating means comprises an optical beam splitter OSPL, a first tunable narrow band-pass optical filter OTF1, and a second tunable narrow band-pass optical filter OTF2.

[0112] The optical beam splitter OSPL is configured to split said broadband optical excitation radiation OA to obtain a first replica of the broadband optical excitation radiation and a second replica of the broadband optical excitation radiation.

[0113] The first narrowband optically tunable OTF1 narrowband filters the first replica of the broadband optical pump radiation and tunes it to a first local oscillator frequency ω LO1 The optical fiber 10 is configured to generate a first narrowband optical signal LO1 centered at .

[0114] A second narrowband optically tunable OTF2 narrowband filters the second replica of the broadband optical pump radiation and tunes it to a second local oscillator frequency ω LO2 The optical fiber 10 is configured to generate a second narrowband optical signal LO2 centered at .

[0115] Some additional details of the foregoing embodiment are described below with reference to FIG.

[0116] In this case, the PIC device operates at two different frequencies, ω LO1 , ω LO2 The optical fiber includes two different tunable narrow-band optical filters OTF1 and OTF2 configured to select two independent local oscillators.

[0117] Two intermediate frequencies ω for detecting two peaks of wavelength IFs = ωs - ω LO And, ω IFf = ωf - ω LO are independent. According to one implementation option, such frequencies are finely tuned to make the subsequent detection stages easier and more accurate.

[0118] Advantageously, this embodiment using two independent local oscillators provides greater flexibility in the heterodyne detection scheme, as it allows independent control of the intermediate frequency, i.e., the beat frequency between the local oscillator and the "slow" and "fast" polarized optical signals. Such flexibility leads to further benefits, such as allowing the required bandwidth of the photodiode to be reduced, thereby reducing noise at its input and improving the signal-to-noise ratio (SNR) of the measurement.

[0119] According to an embodiment of system 1 (e.g., as shown in Figures 1-3), the first heterodyne detection means includes a first optical coupler OC1 including respective optical waveguides configured to couple the first component OR1 of the reflected optical spectrum with the first local oscillator optical signal LO1, and a first optoelectronic receiver PD1 configured to receive the output optical signal from the first optical coupler OC1 and convert it into a respective first electrical signal E1.

[0120] The second heterodyne detection means includes a second optical coupler OC2 including respective optical waveguides configured to couple the second component OR2 of the reflected optical spectrum with the second local oscillator optical signal LO2, and includes a second optoelectronic receiver PD2 configured to receive the output optical signal from the second optical coupler OC2 and convert it into a respective second electrical signal E2.

[0121] According to various possible implementation options, the first and second heterodyne detection or reception means are implemented by heterodyne detection or reception devices known per se.

[0122] For example, see Rongqing Hui's "Introduction to Fiber-Optic Communications" - 1st Edition, June 13, 2019 (DOI:10.1016 / B978-0-12-805345-4.00009-3), from which the figures in Figures 7 and 8 are excerpted and briefly described below.

[0123] FIG. 7 shows a well-known example of the heterodyne mixing technique, which makes it possible to reduce the frequency of an optical frequency signal to obtain a corresponding intermediate frequency signal that can be easily detected by electronic reception.

[0124] In particular, the mixing of the optical signal and the local oscillator is performed by a photodiode, i.e., the input signal E s (t) and local oscillator E LOThis can be achieved by a detector with a quadratic detection law, where two electromagnetic fields corresponding to (t) respectively are mixed to provide a photocurrent i(t) proportional to the square of the two input electromagnetic fields.

[0125] Input optical signal E s (t) and the local oscillator optical signal E LO (t) can be expressed as follows:

number

number

number

number

[0126] According to another embodiment of the system shown in FIG. 3, the aforementioned first optical coupler OC1 is a 2x2 optical coupler configured to output two optical beat signals resulting from a combination of the first reflected optical spectral component OR1 and the first local oscillator optical signal LO1.

[0127] Furthermore, the aforementioned first optoelectronic receiver B-PD1 includes two photodiodes configured to perform balanced detection, and the first electrical signal E1 is obtained as a subtraction of the emitted currents from the two photodiodes of the first optoelectronic receiver B-PD1.

[0128] Similarly, the aforementioned second optical coupler OC2 is a 2x2 optical coupler configured to output two optical beat signals resulting from the combination of the second reflected optical spectral component OR2 and the second local oscillator optical signal LO2.

[0129] Furthermore, the aforementioned second optoelectronic receiver B-PD2 comprises two photodiodes configured to perform balanced detection, and the second electrical signal E2 is obtained as a subtraction of the emitted currents from the two photodiodes of the second optoelectronic receiver B-PD2.

[0130] According to an implementation option, the balanced heterodyne detection is performed using a balanced detection technique known per se, as shown in FIG.

[0131] In this case, the 1x2 optical coupler is replaced by a 2x2 optical coupler, and the two output ports of the optical coupler are connected to BPD balanced photodetectors.

[0132] Balanced coherent heterodyne detection improves the signal-to-noise ratio (SNR) of the detected signal and avoids unwanted effects of local oscillator intensity noise.

[0133] Specifically, balanced coherent heterodyne detection, shown in Figure 2, uses a 2x2 optical coupler and two photodiodes in parallel. The difference between the two photocurrents provides only one component, the intermediate frequency component, which can be expressed as:

number

[0134] In this configuration, the DC components of the optical signal and the local oscillator signal are advantageously cancelled, which makes it possible to improve the signal-to-noise ratio (SNR) and reduce the undesired influence of excess laser noise (e.g., intensity noise) and non-local effects in the reflection response.

[0135] According to one embodiment of the system shown in Figure 4, the first heterodyne detection means further comprises a first optical phase shifter OPS1 configured to shift the phase of the first optical local oscillator signal LO1 in a controlled manner before input at the first optical coupler OC1, and the second heterodyne detection means further comprises a second optical phase shifter OPS2 configured to shift the phase of the second optical local oscillator signal LO2 in a controlled manner before input at the second optical coupler OC2.

[0136] Thus, in this case, the PIC device integrates two optical phase shifters that can control and modulate the phase of the local optical oscillator signal.

[0137] The phase shifter adds phase control of the local oscillator, the phase of which can be modulated by the phase shifter, which advantageously allows for improved sensitivity of the measurement.

[0138] According to another embodiment of the system shown in Figure 5, optical signals at two frequencies ωs and ωf are combined by a directional coupler. Again, the intermediate frequency for heterodyne detection is ω IFS =ωs-ωf.

[0139] According to one embodiment (shown in Figure 6), the system is configured to query multiple sensors of cascaded birefringent fiber Bragg grating type (Bi-FBG to Bi-FBG), each characterized by a respective nominal operating wavelength (λ to λ).

[0140] In such an embodiment, the PS polarizing optical beam splitter is configured to separate a first component and a second component of the overall ORT reflected light spectrum from a birefringent fiber Bragg grating (Bi-FBG1 to Bi-FBGn) sensor cascade.

[0141] The first component ORT1 of the total reflected light spectrum includes a superposition of first components (OR11 to OR1n) having first optical polarizations centered around respective first frequencies (ω11 to ω1n), and the second component ORT2 of the total reflected light spectrum includes a superposition of second components (OR21 to OR2n) having second optical polarizations centered around respective second frequencies (ω21 to ω2n).

[0142] In this case, the system further includes first and second frequency discrimination means or demultiplexing means, a plurality of first heterodyne detection means, and a plurality of second heterodyne detection means.

[0143] The first frequency discrimination or demultiplexing means AWG1 is arranged to spectrally separate the first components (OR11 to OR1n) from one another.

[0144] The second frequency discrimination or demultiplexing means AWG2 is arranged to spectrally separate the second components (OR21 to OR2n) from one another.

[0145] The first heterodyne detection means is configured to operate on each of the first components (OR11 to OR1n) to obtain a respective one of the plurality of first electrical signals E1n.

[0146] The second heterodyne detection means is configured to operate on each of the second components (OR21 to OR2n) to obtain a respective plurality of second electrical signals E2n.

[0147] According to one implementation option (mentioned in the example shown in Figure 6), both the first and second means of frequency discrimination or demultiplexing are performed by respective integrated "arrayed waveguide grating" (AWG) type devices placed at the output of the polarization splitter, allowing measurements based on WDM (wavelength division multiplexing).

[0148] An AWG device is an optical device for splitting an optical signal containing multiple N wavelengths present at one waveguide input so that it is available at the inputs of N different output waveguides.

[0149] The wavelength peaks reflected from the N birefringent Bi-FBG sensors are coupled into a PIC device, and the N wavelengths corresponding to the fast-axis and slow-axis polarized signals, respectively, are separated and sent to two different waveguides, where the individual wavelengths are filtered and selected for different output ports of the AWG device. The individual wavelengths at each output port of the AWG device can be detected by any of the methods exemplified above with reference to querying a single birefringent Bi-FBG sensor.

[0150] According to another implementation option, the first and / or second means of frequency discrimination or demultiplexing are performed by respective WDM demultiplexing devices of other types known per se.

[0151] According to the implementation option already mentioned above, the aforementioned tunable narrow-band optical bandpass filter OTF is a microring optical resonator filter known per se.

[0152] For example, a ring resonator is a structure in which a fiber or optical waveguide is surrounded in a "loop" configuration; when light of a particular resonant wavelength passes through the ring (or loop) under constructive interference conditions, the intensity of the light increases within the structure, and the light of the given resonant wavelength can be extracted / observed at a monitor port at the extraction port.

[0153] By designing microring resonators and incorporating them into integrated photonic circuits (PICs), they can be used as bandpass filters, optical switches, and optical intensity modulators.

[0154] The resonant wavelength of a microring resonator depends on the refractive index and geometry of the device (e.g., the size of the optical waveguide and the ring diameter), and the resonant wavelength can be tuned by small changes in the refractive index of the optical waveguide, e.g., thermal tuning based on localized microheaters.

[0155] According to one embodiment of the present system, the aforementioned polarizing optical beam splitter PS is a polarizing optical beam splitter manufactured by integrated photonics technology of the two-dimensional grating coupler type.

[0156] According to another implementation option of the system, the aforementioned polarizing beam splitter PS is a polarizing optical beam splitter made by integrated photonics technology of the Polarizing Splitter and Rotator-PSR type.

[0157] Regarding polarization beam splitters, it is worth noting that there are different strategies to couple and propagate orthogonal polarizations of the same light beam inside silicon optical waveguides. The best-known solutions are two-dimensional grating couplers and edge couplers, which combine polarization splitters and rotators (PSRs).

[0158] A two-dimensional grating coupler (2D GC) can be thought of as a superposition of two one-dimensional grating couplers (1D GC), in which two orthogonal polarizations coming from a fiber at the input are coupled into two orthogonally polarized optical waveguides TE, where the two orthogonal polarizations are coupled into optical waveguides where the light propagates with the same polarization.

[0159] In PSR polarization rotators and splitters, a signal containing two orthogonal polarizations is sent to an integrated polarization optical beam splitter, which splits the light into two separate signals with two orthogonal polarizations: TE and TM [e.g., M.R. Watts, H.A. Haus, E.P.I.ppen, "Integrated mode-evolution-based polarization splitter," Opt. Lett. 30, 967-969 (2005)]. The separated TM-polarized signal is sent to a polarization beam rotator, where its polarization is rotated by 90° to become a TE-polarized signal [M.R. Watts, H.A. Haus, E.P.I.ppen, "Integrated mode-evolution-based polarization splitter," Opt. R. Watts, H.A. Haus, "Integrated mode-evolution-based polarization rotators," Opt. Lett. 30, 138-140 (2005)].

[0160] According to one implementation option of the system, each of said first optoelectronic receiver PD1 and / or said second optoelectronic receiver PD2 comprises at least a respective semiconductor photodiode configured to detect and convert into an electrical signal an optical signal of the wavelength considered.

[0161] According to one embodiment, the system further comprises an optical circulator 3 having a first circulator port connected to a broadband optical radiation source BS, a second circulator port connected to a birefringent optical fiber containing a birefringent fiber Bragg grating Bi-FBG type sensor, and a third circulator port connected to an optical input port of a photonic integrated device PIC.

[0162] Such an optical circulator 3 is configured to transmit the broadband optical radiation OA received from a first circulator port to a birefringent optical fiber including a fiber Bragg grating Bi-FBG type sensor via a second circulator port, and further to transmit the spectrum reflected by the birefringent fiber Bragg grating Bi-FBG type sensor received from the second circulator port to an optical input port of the photonic integrated component PIC via a third circulator port.

[0163] According to one embodiment of the system, the first reference wavelength λ ref1 and the aforementioned second reference wavelength λ ref2 corresponds to the two respective nominal operating wavelengths of the birefringent fiber Bragg grating Bi-FBG type sensor on the two fast and slow channels, as determined by initial calibration.

[0164] According to another embodiment of the system, the first reference wavelength λ ref1 and the second reference wavelength λ ref2 are coincident and correspond to the reference wavelength λi specified by tuning the narrow bandpass optical tunable filter OTF.

[0165] According to one implementation option of the system, the aforementioned first reference wavelength λ ref1 and a second reference wavelength λ ref2 correspond to two reference wavelengths λi1 and λi2, respectively, which are determined by tuning two narrow bandpass optical wavelength tunable filters (OTF1 and OTF2).

[0166] According to another embodiment of the method, the first reference wavelength λ ref1 and the second reference wavelength λ ref2 correspond to the two respective nominal operating wavelengths of the birefringent fiber Bragg grating (Bi-FBG) type sensor in the two high-speed and low-speed channels.

[0167] Next, a method is described for determining at least two physical magnitudes detectable by a birefringent fiber Bragg grating Bi-FBG type sensor.

[0168] Such a system comprises a sensor of the birefringent fiber Bragg grating Bi-FBG type and a system for querying at least one birefringent fiber Bragg grating Bi-FBG type according to any one of the above-mentioned embodiments, wherein electronic processing means are adapted to process the detected first intermediate frequency ω IF1 and the second intermediate frequency ω IF2 and determining at least two physical dimensions based on the processing of the signal.

[0169] According to one embodiment, the two physical quantities determined are longitudinal strain and transverse strain.

[0170] According to another embodiment, the two physical quantities determined are strain and temperature.

[0171] According to one embodiment of such a system, a birefringent fiber Bragg grating Bi-FBG type sensor is configured to operate within a brake pad, embedded in a brake caliper, attached to a brake caliper, or embedded in a washer device adapted to be positioned between a brake caliper bracket and a brake caliper.

[0172] The at least two physical magnitudes detected are longitudinal strain and transverse strain, which exist at the point where the birefringent fiber Bragg grating (Bi-FBG) sensor is located and collectively represent the clamping force and / or braking torque acting on the brake caliper.

[0173] It is noteworthy that the objects of the present invention are fully achieved by the above-exemplified method and system due to its functional and structural features.

[0174] Indeed, with reference to the technical problems described in the prior art section, the system according to the present invention is a simple and compact system in which the essential components are integrated (for example in a photonic integrated circuit in PIC technology).

[0175] The system and method for interrogating Bi-FBG sensors made of birefringent fiber according to the present invention meets the following criteria: (i) compactness and simplicity in construction and use, and (ii) effectiveness in performance.

[0176] This is possible because such methods and systems are based on photonic integrated circuits, and the inventive solution involves polarization-based light splitting of the spectrum reflected by the birefringent Bi-FBG sensor followed by double-heterodyne coherent detection (a function that can be achieved with components that can be integrated into PICs).

[0177] Furthermore, the need for a local oscillator (which cannot be incorporated into the PIC) is avoided because a signal substantially similar to that generated by the local oscillator is obtained in the PIC circuit through narrowband optical filtering of a replica of the same broadband optical query radiation.

[0178] From the above, it can be seen that the inquiry system provided by the present invention can be installed in technical fields such as strain and temperature detection of brake calipers, and is very suitable for brake pads.

[0179] In such a situation, the above-mentioned advantages offered by birefringent Bi-FBG sensors are particularly evident, including in particular the ability to simultaneously detect at least two magnitudes or physical parameters (e.g., transverse and longitudinal strain, or strain and temperature).

[0180] To meet fortuitous and particular needs, those skilled in the art may make several modifications and adaptations to the above-described embodiments and may, however, substitute other functionally equivalent elements without departing from the scope of the following claims. All features described above as belonging to one possible embodiment may be implemented independently of other described embodiments.

Claims

1. 1. A method for interrogating at least one sensor of the birefringent fiber Bragg grating type (Bi-FBG), comprising: - illuminating said at least one sensor of the birefringent fiber Bragg grating type (Bi-FBG) with broadband optical excitation radiation (OA); transmitting the reflected light spectrum (OR) reflected by said at least one sensor of the birefringent fiber Bragg grating type (Bi-FBG) to a detection photonic integrated circuit (PIC); - separating, by a polarizing optical beam splitter (PS) configured in said detector photonic integrated circuit (PIC), a first component (OR1) of said reflected light spectrum, which is generated by said birefringence and is characterized by a first light polarization centered on a first frequency (ω1), and a second component (OR2) of said reflected light spectrum, which is generated by said birefringence and is characterized by a second light polarization centered on a second frequency (ω2); - providing said broadband optical excitation radiation (OA) to said detection photonic integrated circuit (PIC); - obtaining at least two narrowband optical signals (LO1, LO2) based on at least one narrowband optical filtering of the wideband optical excitation radiation (OA) performed in the detector photonic integrated circuit (PIC), the at least two narrowband optical signals (LO1, LO2) being at a first local oscillator frequency (ω ＬＯ１ a first local oscillator optical signal (LO1) centered at ω ), and a second local oscillator optical signal (ω ＬＯ２ a second local oscillator optical signal (LO2) centered at - feeding said first component of said reflected light spectrum (OR1) and said first local oscillator optical signal (LO1) to first optical heterodyne detection means integrated in said detector photonic integrated circuit (PIC) for heterodyne detection, and detecting said first local oscillator frequency (ω ＬＯ１ a first intermediate frequency (ω 1 ) equal to the difference between the first frequency (ω 1 ) of the first component (OR 1 ) of the reflected light spectrum and the first intermediate frequency (ω 1 ) of the first component (OR 1 ) of the reflected light spectrum; ＩＦｓ ) acquiring a first electrical signal (E1); - feeding said second component of said reflected light spectrum (OR2) and said second local oscillator optical signal (LO2) to second optical heterodyne detection means integrated in said detector photonic integrated circuit (PIC) for heterodyne detection, and detecting said second local oscillator frequency (ω ＬＯ２ a second intermediate frequency (ω ) equal to the difference between the first frequency (ω ) of the second component (OR ) of the reflected light spectrum and the second frequency (ω ) of the second component (OR ). ＩＦｆ ) acquiring a second electrical signal (E2); - a first reference wavelength (λ ｒｅｆ１ The first intermediate frequency (ω ; λ i ) exhibits a first wavelength shift (Δλ 1 ) of a first component (OR 1 ) of a reflected light spectrum having a first polarization relative to the first intermediate frequency (ω ; λ i ). ＩＦ１ ) the second reference wavelength (λ ) of the Bragg grating of the sensor of birefringent fiber Bragg grating type (Bi-FBG); ｒｅｆ２ ) with respect to the second intermediate frequency (ω ), which exhibits a second wavelength shift (Δλ 2 ) of the second component (OR 2 ) of the reflected light spectrum having a second polarization. ＩＦ２ ) determining The method, wherein the first wavelength shift (Δλ1) and the second wavelength shift (Δλ2) represent at least one physical magnitude measured by a birefringent fiber Bragg grating type (Bi-FBG) sensor.

2. The step of acquiring at least two narrowband optical signals (LO1, LO2) comprises: - narrow-band filtering of said broadband optical excitation radiation (OA) by a narrow-band bandpass optical tunable filter (OTF) integrated in a detection photonic integrated circuit (PIC) to generate a local oscillator frequency (ω) adapted to act as a local oscillator signal (LO); ＬＯ acquiring a narrowband optical signal centered at splitting said narrowband optical signal by an optical beam splitter (OSPL) configured to make available at two output ports two attenuated replicas of the same narrowband optical signal received as input, The first local oscillator signal (LO1) and the second local oscillator signal (LO2) are two identical signals present at the two output ports of the optical beam splitter; The method of claim 1.

3. The step of acquiring at least two narrowband optical signals (LO1, LO2) comprises: - splitting said broadband optical excitation radiation (OA) by an optical beam splitter (OSPL) to obtain a first replica of said broadband optical excitation radiation and a second replica of said broadband optical excitation radiation; - narrow-band filtering the first replica of the broadband optical pump radiation by a first narrow-band bandpass optical tunable filter (OTF1) integrated in the detector photonic integrated circuit (PIC) to tune it to a first local oscillator frequency (ω ＬＯ１ acquiring a first narrowband optical signal centered at - narrow-band filtering the second replica of the broadband optical pump radiation by a second narrow-band bandpass optical tunable filter (OTF2) integrated in the detector photonic integrated circuit (PIC) to tune it to a second local oscillator frequency (ω ＬＯ２ and acquiring a second narrowband optical signal centered at The method of claim 1.

4. the step of performing heterodyne detection and obtaining a first electrical signal (E1) comprises the step of combining a first component (OR1) of the reflected optical spectrum with a first local oscillator optical signal (LO1) in an optical waveguide of a first optical coupler (OC1) of the first optical heterodyne detection means, and further comprising the step of converting the optical signal obtained at the output of the first optical coupler into a respective first electrical signal (E1) by a first optoelectronic receiver (PD1) of said first optical heterodyne detection means; the step of performing heterodyne detection and obtaining a second electrical signal (E2) comprises the step of combining the second component (OR2) of the reflected optical spectrum with a second local oscillator optical signal (LO2) in an optical waveguide of a second optical coupler (OC2) of the second optical heterodyne detection means, and further comprising the step of converting the optical signal obtained at the output of the second optical coupler into a respective second electrical signal (E2) by a second optoelectronic receiver (PD2) of the second optical heterodyne detection means; 4. The method according to any one of claims 1 to 3.

5. each step of performing heterodyne detection to obtain a first electrical signal (E1) and a second electrical signal (E2) includes performing balanced detection using a respective 2x2 optical coupler configured to provide two optical signals as outputs; For each heterodyne detection, the signal is detected by two respective photodiodes for balanced detection, and for each heterodyne detection, each of the first electrical signal (E1) and the second electrical signal (E2) is obtained as a subtraction of the currents output from the respective photodiodes; The method of claim 4.

6. the step of performing first heterodyne detection further comprises a step of shifting the phase of the first local oscillator optical signal (LO1) in a controlled manner by a first optical phase shifter (OPS1) configured in a photonic integrated circuit (PIC) before input at the first optical coupler (OC1); the step of performing second heterodyne detection further comprises a step of shifting the phase of the second local oscillator optical signal (LO2) in a controlled manner by a second optical phase shifter (OPS2) configured in the photonic integrated circuit (PIC) before input at the second optical coupler (OC2); The method of claim 4.

7. The step of performing heterodyne detection is to detect a first component (OR1) of the reflected light spectrum and a second component (OR2) of the reflected light spectrum at an intermediate frequency (ω ＩＦ 2. Injecting a 2×1 optical signal into a single 2×1 optical coupler (OC) configured to generate as an output an optical signal of The method according to any one of claims 1 to 6.

8. 8. A method according to any one of claims 1 to 7, arranged to interrogate a plurality of sensors of cascaded birefringent fiber Bragg grating type (Bi-FBG1 to Bi-FBGn), each characterized by a respective nominal operating wavelength (λ1 to λn), comprising: said transmitting step comprises transmitting the total reflected optical spectrum (ORT) reflected by the cascaded sensors of the birefringent fiber Bragg grating type (Bi-FBG1 to Bi-FBGn) to a detection photonic integrated circuit (PIC); - said separating step comprises separating a first component of the total reflected light spectrum (ORT1) and a second component of the total reflected light spectrum (ORT2); a first component (ORT1) of the total reflected light spectrum comprising a superposition of first components (OR11-OR1n) having first light polarizations centered around respective first frequencies (ω11-ω1n); a second component (ORT2) of the total reflected light spectrum comprising a superposition of second components (OR21-OR2n) having second light polarizations centered around respective second frequencies (ω21-ω2n); The method further comprises: - spectrally separating the first components (OR11 to OR1n) from one another by first frequency discrimination or demultiplexing means (AWG1); - spectrally separating the second components (OR21-OR2n) from one another by second frequency discrimination or demultiplexing means (AWG2); - performing said heterodyne detection step on each of said first components (OR11-OR1n) and each of said second components (OR21 to OR2n) to obtain a respective plurality of first electrical signals (E1k) and second electrical signals (E2k); For each pair of first electrical signals (E1k) and second electrical signals (E2k) corresponding to each sensor of the birefringent fiber Bragg grating type (Bi-FBGk), a first intermediate frequency (ω ＩＦｓ，ｋ ) and the second intermediate frequency (ω ＩＦｆ，ｋ and performing said step of determining (a) the time domain of said signal.

9. the first light polarization corresponds to polarization on the "slow polarization axis" and the first birefringence peak frequency (ω1) corresponds to the slow axis birefringence peak frequency (ωs); the second light polarization corresponds to polarization on a "fast polarization axis" that is orthogonal to the first light polarization and orthogonal to the "slow polarization axis," and a second birefringence peak frequency (ω) corresponds to a fast axis birefringence peak frequency (ω); The method according to any one of claims 1 to 8.

10. The first reference wavelength (λ ｒｅｆ１ ) and the second reference wavelength (λ ｒｅｆ２ ) correspond to the two respective nominal operating wavelengths of the birefringent fiber Bragg grating type (Bi-FBG) sensor on the two high-speed and low-speed channels, as determined by initial calibration; The method according to any one of claims 1 to 9.

11. The first reference wavelength (λ ｒｅｆ１ ) and the second reference wavelength (λ ｒｅｆ２ ) and corresponds to a reference wavelength (λi) determined by tuning a narrow bandpass optical tunable filter (OTF). The method according to any one of claims 2 to 9.

12. The first reference wavelength (λ ｒｅｆ１ ) and the second reference wavelength (λ ｒｅｆ２ ) correspond to two reference wavelengths (λi1, λi2) specified by tuning two narrow bandpass optical wavelength tunable filters (OTF1, OTF2), respectively. The method according to any one of claims 2 to 9.

13. 1. A method for determining at least two physical magnitudes detectable by a sensor of the birefringent fiber Bragg grating type (Bi-Bi-FBG), comprising: - implementing a method according to any one of claims 1 to 12, interrogating at least one sensor of the birefringent fiber Bragg grating type (Bi-FBG); said first intermediate frequency (ω ＩＦｓ ) and the second intermediate frequency (ω ＩＦｆ and determining at least two physical dimensions based on processing of the image.

14. The two physical quantities that are determined are longitudinal strain and transverse strain. The method of claim 13.

15. The two physical quantities that are determined are strain and temperature. The method of claim 13.

16. A system (1) for interrogating at least one sensor of the birefringent fiber Bragg grating type (Bi-FBG), comprising: a broadband optical radiation source (BS) configured to illuminate said at least one sensor of the birefringent fiber Bragg grating type (Bi-FBG) with broadband optical excitation radiation (OA); a detector photonic integrated device (PIC) having a first input port (C1) operatively connected to said at least one sensor of the birefringent fiber Bragg grating type (Bi-FBG) for receiving the reflected light spectrum (OR) from said sensor, and a second input port (C2) operatively connected to said broadband optical radiation source (BS) for receiving said broadband optical excitation radiation (OA), The detecting photonic integrated device (PIC) comprises: a polarizing optical beam splitter (PS) configured to separate a first component (OR1) of said reflected light spectrum, which is produced by birefringence and is characterized by a first light polarization centered on a first frequency (ω1), from a second component (OR2) of said reflected light spectrum, which is produced by birefringence and is characterized by a second light polarization centered on a second frequency (ω2); means for generating local oscillator signals adapted to obtain at least two narrowband optical signals (LO1, LO2), The narrowband optical signal is oscillated at a first local oscillator frequency (ω ＬＯ ;ω ＬＯ１ a first local oscillator optical signal (LO1) centered at ω ), and a second local oscillator optical signal (ω ＬＯ ;ω ＬＯ２ a second local oscillator optical signal (LO2) centered at the means for generating the local oscillator signal includes at least one narrow bandpass optical tunable filter (OTF) configured to perform narrow band optical filtering of the broadband optical excitation radiation (OA); receiving the first component of the reflected optical spectrum (OR1) and the first optical local oscillator signal (LO1); and detecting, by a heterodyne detection technique, the first optical local oscillator frequency (ω ＬＯ１ a first intermediate frequency (ω) equal to the difference between the first frequency (ω) of the first component (OR1) of the reflected light spectrum and the first frequency (ω) of the first component (OR2) of the reflected light spectrum; ＩＦｓ a first optical heterodyne detection means (11) configured to generate a first electrical signal (E1) at receiving the second component of the reflected optical spectrum (OR2) and the second optical local oscillator signal (LO2); and detecting, by heterodyne detection techniques, the second optical local oscillator frequency (ω ＬＯ２ a second intermediate frequency (ω) equal to the difference between the first frequency (ω) and the second frequency (ω) of the second component (OR2) of the reflected light spectrum; ＩＦｆ a second optical heterodyne detection means (12) configured to generate a second electrical signal (E2) at a first output port (U1) configured to make available said first electrical signal (E1) and a second output port (U2) configured to make available said second electrical signal (E2); The system, - electronic processing means (2), operatively connected to the photonic integrated device (PIC) to receive the first electrical signal (E1) and the second electrical signal (E2); The first reference wavelength (λ ) of the Bragg grating of the birefringent fiber Bragg grating type (Bi-FBG) sensor ｒｅｆ１ λi) with a first polarization, exhibiting a first wavelength shift (Δλ1) of a first component of the reflected light spectrum (OR1), ＩＦｓ ) configured to determine Furthermore, the second reference wavelength (λ ) of the Bragg grating of the birefringent fiber Bragg grating type (Bi-FBG) sensor is ｒｅｆ２ ) with respect to the second intermediate frequency (ω ), which exhibits a second wavelength shift (Δλ 2 ) of a second component of the reflected light spectrum (OR 2 ) having a second polarization. ＩＦｆ ) configured to determine The system (1), wherein the first wavelength shift (Δλ1) and the second wavelength shift (Δλ2) represent at least one physical magnitude measured by an optical fiber sensor (Bi-FBG).

17. the means for generating the local oscillator signal comprises: - narrow-band filtering of said broadband optical excitation radiation (OA) and a local oscillator frequency (ω) adapted to act as a local oscillator signal (LO); ＬＯ a narrowband bandpass optical tunable filter (OTF) configured to generate a narrowband optical signal centered at an optical beam splitter (OSPL) configured to split said narrowband optical signal (LO) and make available at two output ports of the optical beam splitter two attenuated replicas of the same narrowband optical signal received as input, said attenuated replicas being attenuated replicas of the same narrowband optical signal received as input and corresponding respectively to a first local oscillator signal (LO1) and a second local oscillator signal (LO2); A system (1) according to claim 16.

18. the means for generating the local oscillator signal comprises: an optical beam splitter (OSPL) configured to split said broadband optical excitation radiation (OA) to obtain a first replica of said broadband optical excitation radiation and a second replica of said broadband optical excitation radiation; - narrow-band filtering the first replica of the broadband optical excitation radiation and aligning it with a first local oscillator frequency (ω ＬＯ１ a first narrowband bandpass optical tunable filter (OTF1) configured to generate a first narrowband optical signal (LO1) centered at - narrow-band filtering the second replica of the broadband optical pump radiation and generating a second local oscillator frequency (ω ＬＯ２ a second narrowband bandpass optical tunable filter (OTF2) configured to generate a second narrowband optical signal (LO2) centered around A system (1) according to claim 16.

19. the first heterodyne detection means a first optical coupler (OC1) including respective optical waveguides configured to couple a first component of the reflected optical spectrum (OR1) and a first local oscillator optical signal (LO1); a first optoelectronic receiver (PD1) configured to receive the output optical signals from the first optical coupler (OC1) and convert them into respective first electrical signals (E1); the second heterodyne detection means a second optical coupler (OC2) including respective optical waveguides configured to couple a second component of the reflected optical spectrum (OR2) and a second local oscillator optical signal (LO2); a second optoelectronic receiver (PD2) configured to receive the output optical signals from the second optical coupler (OC2) and convert them into respective second electrical signals (E2); A system (1) according to any one of claims 16 to 18.

20. the first optical coupler (OC1) is a 2x2 optical coupler and is configured to provide as output two optical beat signals resulting from a combination of a first component (OR1) of the reflected optical spectrum and a first optical local oscillator signal (LO1), the first optoelectronic receiver (B-PD1) comprises two photodiodes configured for balanced detection, the first electrical signal (E1) being obtained as the subtraction of the currents output by the two photodiodes of the first optoelectronic receiver (PD1); the second optical coupler (OC2) is a 2x2 optical coupler and is configured to provide as output two optical beat signals resulting from a combination of a second component (OR2) of the reflected optical spectrum and a second optical local oscillator signal (LO2), the second optoelectronic receiver (B-PD2) comprising two photodiodes configured for balanced detection, the second electrical signal (E2) being obtained as the subtraction of the currents output by the two photodiodes of the second optoelectronic receiver (PD2); 20. A system (1) according to claim 19.

21. the first heterodyne detection means further comprises a first optical phase shifter (OPS1) configured to shift the phase of the first local oscillator optical signal (LO1) in a controlled manner before input at the first optical coupler (OC1); the second heterodyne detection means further comprises a second optical phase shifter (OPS2) configured to shift the phase of the second local oscillator optical signal (LO2) in a controlled manner before input at the second optical coupler (OC2); 20. A system (1) according to claim 19.

22. configured to query a plurality of cascaded sensors of birefringent fiber Bragg grating type (Bi-FBG1 to Bi-FBGn), each sensor characterized by a respective nominal operating wavelength (λ1 to λn); a polarizing beam splitter (PS) configured to separate a first component (ORT1) and a second component (ORT2) of the total reflected light spectrum (ORT) from cascaded sensors of the birefringent fiber Bragg grating type (Bi-FBG1 to Bi-FBGn); the first component (ORT1) of the total reflected light spectrum includes a superposition of first components (OR11-OR1n) having first light polarizations centered around respective first frequencies (ω11-ω1n); a second component (ORT2) of the total reflected light spectrum includes a superposition of second components (OR21-OR2n) having second light polarizations centered at respective second frequencies (ω21-ω2n); The system is first frequency discrimination or demultiplexing means (AWG1) adapted to spectrally separate said first components (OR11 to OR1n) from one another; second frequency discrimination or demultiplexing means (AWG2) adapted to spectrally separate said second components (OR21 to OR2n) from one another; a plurality of first heterodyne detection means configured to operate on each of the first components (OR11 to OR1n) to obtain a respective plurality of first electrical signals (E1n); a plurality of second heterodyne detection means configured to operate on the respective second components (OR21 to OR2n) to obtain a respective plurality of second electrical signals (E2n); A system (1) according to any one of claims 16 to 21.

23. The narrow-band bandpass optical tunable filter (OTF) is an optical microring resonator filter. A system (1) according to any one of claims 16 to 22.

24. The polarizing optical beam splitter (PS) is a polarizing optical beam splitter manufactured by "two-dimensional grating coupler" type integrated photonics technology or "polarizing splitter and rotator - PSR" type integrated photonics technology; A system (1) according to any one of claims 16 to 23.

25. each of the first optoelectronic receiver (PD1) and / or the second optoelectronic receiver (PD2) comprises at least a respective semiconductor photodiode configured to detect and convert into an electrical signal an optical signal at the wavelength considered, A system (1) according to any one of claims 16 to 23.

26. The optical circulator (3) further comprises a first circulator port connected to a broadband optical radiation source (BS), a second circulator port connected to a birefringent optical fiber containing a sensor of the fiber Bragg grating type (Bi-FBG), and a third circulator port connected to an optical input port of a photonic integrated device (PIC), The optical circulator (3) is configured to transmit broadband optical radiation (OA) received from a first circulator port to a birefringent optical fiber including a fiber Bragg grating type (Bi-FBG) sensor via a second circulator port, and further configured to transmit the spectrum reflected by the fiber Bragg grating type (Bi-FBG) sensor received from the second circulator port to an optical input port of a photonic integrated device (PIC) via a third circulator port. A system (1) according to any one of claims 16 to 25.

27. The first reference wavelength (λ ｒｅｆ１ ) and the second reference wavelength (λ ｒｅｆ２ ) correspond to the two respective nominal operating wavelengths of the birefringent fiber Bragg grating type (Bi-FBG) sensor on the two high-speed and low-speed channels, as determined by initial calibration; A system (1) according to any one of claims 16 to 26.

28. The first reference wavelength (λ ｒｅｆ１ ) and the second reference wavelength (λ ｒｅｆ２ ) and corresponds to a reference wavelength (λi) determined by tuning a narrow bandpass optical tunable filter (OTF). A system (1) according to any one of claims 17 to 26.

29. The first reference wavelength (λ ｒｅｆ１ ) and the second reference wavelength (λ ｒｅｆ２ ) correspond to two reference wavelengths (λi1, λi2) respectively specified by tuning two narrow bandpass optical wavelength tunable filters (OTF1, OTF2), A system (1) according to any one of claims 17 to 26.

30. 1. A system for determining at least two physical magnitudes detectable by sensors of the birefringent fiber Bragg grating type (Bi-FBG), comprising: - a sensor of the birefringent fiber Bragg grating type (Bi-FBG), A system (1) according to any one of claims 16 to 29, for interrogating at least one sensor of the birefringent fiber Bragg grating type (Bi-FBG), wherein the electronic processing means (2) are adapted to process the detected first intermediate frequency (ω ＩＦｓ ) and the second intermediate frequency (ω ＩＦｆ and a system (1) further configured to determine the at least two physical dimensions based on processing of system.

31. The two physical quantities that are determined are longitudinal strain and transverse strain.

31. The system of claim 30.

32. The two physical quantities that are determined are strain and temperature.

32. The system of claim 31.

33. a birefringent fiber Bragg grating type (Bi-FBG) sensor configured to operate within a brake pad, or incorporated within a brake caliper, or coupled to a brake caliper, or incorporated into a washer device adapted to be positioned between a brake caliper support and a brake caliper; At least two physical magnitudes to be detected are present at the point where a sensor of the birefringent fiber Bragg grating type (Bi-FBG) is placed, and are generally longitudinal and transverse strains representative of the clamping force and / or braking torque acting on the brake caliper; 32. The system of claim 31.

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