Method and system for interrogating fiber Bragg grating type optical fiber sensors using a tunable optical bandpass filter

Abstract

Method and system for interrogating fiber Bragg grating-based optical fiber sensors using a tunable optical bandpass filter. A method for interrogating at least one fiber Bragg grating-based optical fiber sensor is described. The method includes the steps of illuminating the fiber Bragg grating-based optical fiber sensor with broadband excitation optical radiation OA, transmitting an optical spectrum transmitted or reflected by the fiber Bragg grating sensor FBG to at least one tunable optical bandpass filter BPF having a first out-port 1 and a second out-port 2 that are complementary to each other, tuning the optical bandpass filter BPF at a fixed operating wavelength according to the nominal operating wavelength of the fiber Bragg grating of the FBG sensor, detecting a respective first optical signal L1 exiting the first out-port 1 of the optical bandpass filter, and converting the first optical signal L1 by a first optoelectronic receiver PD1 into a respective first electrical signal E1 representative of a wavelength shift Δλ of the spectrum reflected or transmitted by the Bragg grating of the FBG optical fiber sensor relative to the nominal operating wavelength. The method includes detecting a second optical signal L2, spectrally complementary to the first optical signal L1, exiting a second transmit port 2 of the optical bandpass filter BPF, and converting the second optical signal L2 by a second optoelectronic receiver PDT into a respective second electrical signal E2 representative of an optical reference power, the second electrical signal E2 being substantially independent of the filtering wavelength and having a dependence on the power of the broadband excitation optical radiation and on losses in the overall optical path equal to that experienced by the respective first electrical signal E1. The method also includes determining a wavelength shift Δλ of the spectrum reflected or transmitted by the optical fiber sensor FBG relative to a nominal operating wavelength based on the detected first and second electrical signals, such that detection of the first electrical signal is compensated for variations in the optical radiation power and losses in the optical path.A corresponding system for interrogating at least one optical fiber sensor of the Fiber Bragg Grating type FBG is also described, in which the aforementioned optical bandpass filter BPF and the aforementioned first and second optoelectronic receivers PD1, PDT are integrated in a photonic integrated circuit ("photonic integrated circuit" - PIC).

Description

[Technical Field]

[0001] The present invention generally relates to a method and system for measuring physical parameters by using fiber Bragg grating type optical fiber sensors.

[0002] More particularly, the present invention relates to a method and system for interrogating fiber Bragg grating type optical fiber sensors using tunable optical bandpass filters. [Background technology]

[0003] Fiber Bragg grating-based optical fiber sensors (FBG sensors) are increasingly being used to measure physical quantities such as strain and temperature due to their simplicity and high accuracy. Such sensors are passive and must be illuminated by optical radiation and their reflected or transmitted spectrum analyzed to measure the physical quantity of interest.

[0004] Indeed, variations in the detected physical size cause a shift in the spectrum and / or the reflection peak wavelength of the FBG sensor, so the most common known solutions require scanning a range of wavelengths to determine the results.

[0005] Typically, in known solutions, this can be done in two alternative ways: illumination by a wavelength-tunable light source (e.g., a tunable laser) and broadband reception, i.e., broadband illumination and reception by an electrically or optically tunable receiver (e.g., an Arrayed Waveguide Grating, AWG, or spectrometer).

[0006] In other words, either the transmitter or the receiver must be a tuning device that, for each interrogation of the FBG sensor, performs a wavelength scan by sequentially tuning optically or electrically over a range of operating wavelengths.

[0007] This leads to important drawbacks, both related to the complexity of the required equipment (e.g., a tunable laser on transmit and a spectrometer on receive) and to the slow response and limited dynamics due to the time window for sequential tuning of the wavelength range, which can also be large.

[0008] One possible evolution on the receiving side comes from the use of tunable optical filters (e.g., microring resonator filters with one or two rings for each single filter in some configurations). However, because the operation of such a system involves adjusting the tunable optical filters by periodically performing continuous scanning of the FBG sensor's spectrum around a center wavelength to identify the FBG sensor's spectral peak, such a solution also suffers from relatively slow dynamics. Therefore, the dynamic performance of such devices depends on the relatively slow scanning speed of the microring's resonant wavelength.

[0009] Another problem that appears with this solution (as well as the other previously mentioned known solutions) comes from the effect of spurious power variations due to laser emission power fluctuations and spurious variable losses in the optical path covered by the light beam.

[0010] In light of the above, there is a strong need for a system and method for interrogating FBG sensors that can alleviate the aforementioned technical problems obtained with integrated optics and that meets the following criteria: (i) compact and simple structure and use, (ii) fast response and improved dynamic performance, (iii) higher tolerance to spurious losses and / or fluctuations in optical illumination power, (iv) low cost, and (v) robustness to harsh environments.

[0011] Such a need is felt for methods of interrogating FBG sensors used in a wide range of applications, including the important application of measurements performed on pads and calipers in brake systems.

[0012] As already mentioned, the above needs are not fully met by the solutions currently offered by the prior art.

[0013] It is an object of the present invention to provide a method for interrogating optical fiber sensors of the fiber Bragg grating type using a tunable optical bandpass filter, which makes it possible to at least partially overcome the above-mentioned drawbacks described with reference to the prior art and to address the above-mentioned needs particularly felt in the art. Summary of the Invention

[0014] These and other objects are achieved by a method for interrogating optical fiber sensors of the fiber Bragg grating type using a tunable optical bandpass filter according to claim 1.

[0015] Some advantageous embodiments of such a method are the subject of dependent claims 2 to 7.

[0016] It is also an object of the present invention to provide a corresponding system for interrogating fiber optic sensors of the fiber Bragg grating type using tunable optical bandpass filters.

[0017] This object is achieved by a system according to claim 8.

[0018] Some advantageous embodiments of such a system are the subject of dependent claims 9 to 22.

[0019] 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: [Brief explanation of the drawings]

[0020] [Figure 1]FIG. 1 shows, by way of a functional block diagram, an embodiment of a system for interrogating fiber Bragg grating type optical fiber sensors according to the invention. [Figure 2] FIG. 2 shows, by way of a functional block diagram, an embodiment of a system for interrogating fiber Bragg grating type optical fiber sensors according to the invention. [Figure 3] FIG. 3 shows, by way of a functional block diagram, an embodiment of a system for interrogating fiber Bragg grating type optical fiber sensors according to the invention. [Figure 4] FIG. 4 shows, by way of a functional block diagram, an embodiment of a system for interrogating fiber optic sensors of the fiber Bragg grating type according to the invention. [Figure 5] FIG. 5 shows, by way of a functional block diagram, an embodiment of a system for interrogating fiber optic sensors of the fiber Bragg grating type according to the invention. [Figure 6] FIG. 6 is a functional diagram of an optical bandpass filter included in one embodiment of a system according to the present invention, and further illustrates an example of the optical spectrum entering the optical filter, exiting the first drop port of the optical filter, and exiting the second transmit port of the optical filter. [Figure 7] FIG. 7 is a structural diagram of an optical microring resonator bandpass filter configured in one embodiment of the system. [Figure 8A] FIG. 8A is a diagram showing the spectra emerging from the first drop port and the second transmit port of the optical filter when a wideband optical signal is injected into the input. [Figure 8B] FIG. 8B is a diagram showing the spectra emerging from the first drop port and the second transmit port of the optical filter when a wideband optical signal is injected into the input. [Figure 9] FIG. 9 shows the reflection spectrum of the optical fiber sensor FBG and an example of narrowband sampling by the optical bandpass filters of FIGS. [Figure 10]FIG. 10 is a diagram showing the spectra from the first output port and the second transmission port of the optical filter when the optical spectrum reflected by the optical fiber sensor FBG is incident on the input. [Figure 11] FIG. 11 is a diagram showing the spectra from the first output port and the second transmission port of the optical filter when the optical spectrum reflected by the optical fiber sensor FBG is incident on the input. [Figure 12] FIG. 12 is a diagram showing an enlarged view of the spectra of FIGS. 10 and 11 in detail, and FIG. 12 is a diagram showing an enlarged view of the spectra of FIGS. [Figure 13] FIG. 13 shows, by way of functional block diagram, two further respective embodiments of a system for interrogating a fiber Bragg grating type optical fiber sensor according to the invention. [Figure 14] FIG. 14 shows, by way of functional block diagram, two further respective embodiments of a system for interrogating a fiber Bragg grating type optical fiber sensor according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] A method for interrogating at least one optical fiber sensor of the Fiber Bragg Grating type FBG (hereinafter also referred to as "FBG sensor" for the sake of brevity) will now be described with reference to FIGS.

[0022] The method includes the steps of first illuminating the at least one optical fiber sensor of a fiber Bragg grating type FBG with broadband excitation optical radiation OA, and sending the optical spectrum OT transmitted or the optical spectrum OR reflected by the at least one optical fiber sensor of a fiber Bragg grating type FBG to at least one tunable optical bandpass filter BPF having a first out-port 1 and a second out-port 2 complementary to each other.

[0023] The method also includes tuning the optical bandpass filter BPF at a constant operating wavelength λ i according to a nominal operating wavelength of the fiber Bragg grating of the optical fiber sensor FBG.

[0024] The method then includes detecting each first optical signal L1 exiting the first drop port 1 of the optical bandpass filter, wherein such first optical signal is a narrowband optical filtering of the transmission spectrum OT or reflection spectrum OR of the fiber Bragg grating of the optical fiber sensor FBG around a certain operating wavelength λi of the optical bandpass filter BPF.

[0025] Next, the method provides for converting, by a first optoelectronic receiver PD1, the aforementioned first optical signal L1 into a respective first electrical signal E1 representative of the spectrum reflected or transmitted by the Bragg grating of the optical fiber sensor FBG by a wavelength shift Δλ relative to the nominal operating wavelength.

[0026] In different embodiments, this first electrical signal E1 is a current or a voltage.

[0027] In a preferred embodiment, the first electrical signal E1 is representative of (or corresponds to) an electrical voltage that is proportional to the optical power incident on the first optoelectronic receiver PD1, and is therefore related to (e.g., proportional to) the aforementioned wavelength shift Δλ of the spectrum reflected or transmitted by the optical fiber sensor FBG.

[0028] The method then includes detecting a second optical signal L2, spectrally complementary to the first optical signal L1, emerging from a second transmit port 2 of the optical bandpass filter BPF, and converting such second optical signal L2 by a second optoelectronic receiver PDT into a respective second electrical signal E2 representative of an optical reference power, the second electrical signal being substantially independent of the filtering wavelength and having a dependence on the power of the broadband excitation optical radiation and on losses throughout the optical path equal to that experienced by the first optical signal.

[0029] In different embodiments, such second electrical signal E2 is a current or a voltage.

[0030] In a preferred embodiment, the second electrical signal E2 represents (or corresponds to) a voltage proportional to the optical power incident on the second optoelectronic receiver PDT.

[0031] Finally, the method provides for determining a wavelength shift Δλ of the spectrum reflected or transmitted by the Bragg grating of the optical fiber sensor FBG relative to the nominal operating wavelength based on the detected first electrical signal E1 derived from the optical signal L1 exiting the first drop port 1 of the optical bandpass filter BPF and based on a second electrical signal E2 representative of the detected reference optical power derived from the second optical signal L2 output from the second transmit port 2 of the optical bandpass filter BPF, whereby the detection of the first electrical signal is compensated for power variations of the broadband excitation optical radiation and loss variations on the optical path.

[0032] The determined wavelength shift Δλ of the spectrum reflected or transmitted by the Bragg grating is representative of the physical magnitude measured by the optical fiber sensor FBG.

[0033] The optical bandpass filter BPF, the first optoelectronic receiver PD1, and the second optoelectronic receiver PDT are integrated into a photonic integrated circuit (PIC).

[0034] In typical operating conditions, the optical bandpass filter BPF is designed to have a narrower bandwidth (typically much narrower) than the bandwidth of the transmission or reflection spectrum of the FBG sensor, i.e., the FBG sensor is similarly selected to be much larger than the bandwidth of the optical bandpass filter (as shown in Figures 9 to 12). This feature ensures that the total optical power detected by the second transmission port of the filter remains substantially constant over the detection range of the physical dimensions measured by the FBG sensor.

[0035] The optical bandpass filter BPF is adjusted during initial setup to favorably position the resonance of the optical filter with respect to the spectrum of the FBG sensor (e.g., not limited to the approximately linear region of the response of the FBG sensor as disclosed further below).

[0036] After tuning, the optical bandpass filter BPF operates by keeping the tuned wavelength constant and filters the optical spectrum reflected or transmitted by the FBG sensor at the determined wavelength λi. Variations in the peak wavelength and the overall optical spectrum reflected or transmitted by the FBG sensor, i.e., the shift Δλ, due to the physical phenomenon to be measured, result in variations in the part of the optical spectrum filtered by the optical bandpass filter, which ultimately determines optical power variations at the output of the optical bandpass filter, which can be correlated in a known manner with the wavelength shift / variation of the spectrum of the FBG sensor.

[0037] According to one embodiment of the method, the tunable optical bandpass filter BPF has a third input port 3 different from the aforementioned first outgoing port 1 and second outgoing port 2. In this case, the sending step comprises sending the optical spectrum sent OT or reflected OR by at least one optical fiber sensor of the Fiber Bragg Grating type FBG to said third input port 3 of the tunable optical bandpass filter BPF.

[0038] According to one embodiment, the method uses as optical bandpass filters optical microring resonator filters (ie "microring resonator MRRs"), which are disclosed in more detail below in the description of the system according to the invention.

[0039] According to the embodiment illustrated below, the optical micro-ring resonator filter is of a single ring type and has one optical ring 8 .

[0040] According to another embodiment, the optical microring resonator filter is of the double-ring type and has two optical rings (as shown, for example, in the scientific paper "Low-Power-Consumption Integrated Tunable Filters for WDM Switching Applications in Silicon Photonics" by Manganellira - IEEE Photonics Technology Letters, Vol. 30, No. 18, September 15, 2018).

[0041] According to one embodiment, the method uses as the first optoelectronic receiver PD1 and the second optoelectronic receiver PDT first and second photodiodes, respectively, which are shown in more detail below in the description of the system according to the invention.

[0042] According to a preferred embodiment, the adjusting step comprises adjusting the optical bandpass filter BPF in such a way that, at a constant operating wavelength λi, which is located in a linear or nearly linear region of the nominal reflection or transmission spectrum of the fiber Bragg grating of the optical fiber sensor FBG, a shift or variation in wavelength ΔL of the reflection or transmission spectrum of such optical fiber sensor of the fiber Bragg grating type FBG corresponds to a linear or nearly linear variation in the power or intensity of the first optical signal. This situation is illustrated in Figures 9 to 12.

[0043] According to an embodiment, the method comprises interrogating at least one optical fiber sensor of the fiber Bragg grating type having a reflection spectrum with a linear shape, for example a chirped fiber Bragg grating.

[0044] According to the embodiment shown in FIG. 1, the method comprises interrogating only one optical fiber sensor of the Fiber Bragg Grating type FBG operating in the reflection spectrum OR of the FBG sensor.

[0045] According to another embodiment, shown in FIG. 2, the method provides for interrogating only one optical fiber sensor of the Fiber Bragg Grating type FBG, operating on the transmission spectrum OT of the FBG sensor.

[0046] According to a further embodiment (shown in FIG. 3), the method includes interrogating a plurality of optical fiber sensors of fiber Bragg grating type FBG1-FBGn in a cascade, each characterized by a respective nominal operating wavelength λ1-λn.

[0047] In this case, the sending step includes transmitting the entire optical spectrum transmitted or reflected by the cascade of fiber Bragg grating type optical fiber sensors FBG1-FBGn to the cascade of tunable optical bandpass filters BPF1-BPFn, and the adjusting step includes adjusting each of the optical bandpass filters BPF1-BPFn around a respective wavelength λ1-λn corresponding to one of the nominal operating wavelengths of each of the fiber Bragg grating type optical fiber sensors FBG1-FBGn.

[0048] The step of detecting at least one first optical signal L1 includes detecting a plurality of first optical signals L11 to L1n output from respective first outlets of the optical bandpass filters BPF1 to BPFn at respective operating wavelengths λ1 to λn held constant, and the conversion step includes converting the plurality of first optical signals L11 to L1n into a respective plurality of first electrical signals E11 to E1n by a plurality of first optoelectronic light receiving elements PD1 to PDn (e.g., composed of first photodiodes).

[0049] The step of detecting the second optical signal L2 comprises detecting an optical signal exiting from a second transmit port 2 of the last optical bandpass filter (BPFn) of the cascade of optical bandpass filters, and the step of converting comprises converting said second optical signal L2 into a respective second electrical signal E2 by a second optoelectronic receiver PDT.

[0050] The determining step comprises determining a wavelength shift Δλi relative to a nominal operating wavelength of the spectrum of the reflected OR or transmitted OT by each of the fiber Bragg grating type optical fiber sensors FBG1 to FBGn based on the detected plurality of first electrical signals E11 to E1n and the detected second electrical signal E2.

[0051] According to another embodiment (shown in FIG. 4), the method comprises interrogating only one optical fiber sensor of the Fiber Bragg Grating type FBG over a wide range of wavelengths.

[0052] In this case, the transmitting step includes conveying the optical spectrum transmitted or reflected by the fiber Bragg grating type FBG optical fiber sensor to a cascade of tunable optical bandpass filters BPF1 to BPFn, and the adjusting step includes adjusting each of the optical bandpass filters BPF1 to BPFn at a respective operating wavelength λ1 to λn that is kept constant and belongs to a wide wavelength range of the optical spectrum transmitted or reflected by the FBG sensor.

[0053] The step of detecting at least one first optical signal includes detecting a plurality of first optical signals L11 to L1n output from a first output port 1 of each of the optical bandpass filters BPF1 to BPFn, and the step of converting at least one first optical signal includes converting the plurality of first optical signals L11 to L1n into a plurality of first electrical signals E11 to E1n, respectively, by a plurality of first optoelectronic receivers PD1 to PDn (e.g., consisting of first photodiodes).

[0054] The step of detecting the second optical signal L2 comprises detecting an optical signal exiting from a second transmit port 2 of the last optical bandpass filter BPFn of the cascade of optical bandpass filters, and the step of converting the second optical signal L2 comprises converting this second optical signal into a respective second electrical signal E2 by a second optoelectronic receiver PDT.

[0055] The determining step includes determining a peak of a reflection wavelength or a transmission wavelength of the FBG sensor within the wide wavelength range based on the detected plurality of first electrical signals E11 to E1n and the detected second electrical signal E2.

[0056] According to a preferred embodiment, each of the first electrical signals E1i (belonging to the group E11 to E1n) represents a voltage proportional to the optical power incident on the respective optoelectronic receiver Pdi (belonging to the group of optoelectronic receivers PD1 to PDn), and therefore related (e.g. proportional) to a respective wavelength shift Δλi of the spectrum reflected or transmitted by the respective optical fiber sensor FBGi (belonging to the group of sensors FBG1 to FBGn).

[0057] According to a further embodiment (shown in FIG. 5 ), the method further comprises, before the conveying step, a step of splitting the total optical power by an optical splitter D and sending a part thereof to a third optoelectronic receiver PDD to obtain a third electrical signal E3 adapted to support further compensation.

[0058] As described above (and depicted in Figure 6), an optical bandpass filter, e.g., a micro-ring resonator, filters out a portion of the signal reflected (or transmitted) by the FBG sensor at the resonant frequency of the resonant ring on the take-off port 1 ("drop port") of the optical micro-ring filter, and also makes it possible to obtain a transmitted spectrum (corresponding to the spectrum of the FBG sensor without the aforementioned filtering portion) on the transmit port 2 ("thru port") of the optical micro-ring filter.

[0059] In summary, as disclosed above, this method is based on an optical bandpass filter having two complementary ports and two photodetectors, one at each of such complementary ports.

[0060] In particular, in one embodiment, one or more two-port micro-ring resonators are used to interrogate a single FBG sensor or multiple FBG sensors, with two photodetectors integrated for each micro-ring resonator connected to the two "drop" and "through" output ports of the micro-ring resonator.

[0061] 1 to 14, a system 10 for interrogating at least one optical fiber sensor of the Fiber Bragg Grating FBG type will now be described.

[0062] Such a system comprises at least one optical fiber sensor of the Fiber Bragg Grating (FBG) type, a broadband optical radiation source S, at least one tunable optical bandpass filter BPF, a first optoelectronic receiver PD1, a second optoelectronic receiver PDT and electronic processing means 4.

[0063] The broadband optical radiation source S is configured to illuminate at least one optical fiber sensor of the Fiber Bragg Grating type FBG with broadband excitation optical radiation OA.

[0064] According to different possible embodiments of the system, the broadband optical radiation source S may comprise a superluminescent LED (SLED) or the spontaneous amplified emission (AE) of an erbium-doped optical amplifier (EDFA).

[0065] According to an embodiment, the broadband optical radiation source S is a component external to the photonic integrated circuit PIC in which the optical bandpass filter BPF and the first and second optoelectronic receivers PD1 and PDT are integrated.

[0066] According to another embodiment (for example shown in FIG. 13), the broadband optical radiation source S is integrated in a photonic integrated circuit PIC, in which the optical bandpass filter BPF and the first and second optoelectronic receivers PD1 and PDT are integrated. For this purpose, suitable integration technologies can be used. These technologies are known, for example, from silicon-on-insulator SOI technology, based on semiconductors from the III-V group (see, for example, the scientific article "Hybrid Silicon Laser Technology, A Thermal Perspective" - ​​MN Sysak et al. - IEEE Journal of Selected Topics in Quantum Electronics, Vol. 17, No. 6, Nov. / Dec. (IEEE Journal of Selected Topics in Quantum Electronics, Vol. 17, No. 6, Nov. / Dec., 2011).

[0067] At least one tunable optical bandpass filter BPF has a first drop port 1 and a second transmit port 2 that are complementary to each other, and further has a third input port 3 (different from the first drop port 1 and the second transmit port 2) operatively connected to at least one optical fiber sensor of a Fiber Bragg Grating type FBG for receiving the optical spectrum transmitted OT or reflected OR by such sensor.

[0068] The optical bandpass filter BPF has a tunable wavelength range with a constant operating wavelength λ i depending on the nominal operating wavelength of the fiber Bragg grating of the optical fiber sensor FBG.

[0069] A first optoelectronic receiver PD1 is operatively connected to the first drop port 1 of the optical bandpass filter BPF and configured to receive a respective first optical signal L1 and convert such first optical signal L1 into a respective first electrical signal E1, the first optical signal being a narrowband optically filtered transmission spectrum OT or reflection spectrum OR of the fiber Bragg grating of the optical fiber sensor FBG at a fixed operating wavelength of the optical filter.

[0070] A second optoelectronic PDT receiver is operatively connected to the second transmit port 2 of the optical bandpass filter BPF for receiving a second optical signal L2, and it is configured to convert said second optical signal L2 into a respective second electrical signal E2 representative of an optical reference power that is substantially independent of the filtering wavelength and whose dependence on the power of the broadband excitation optical radiation and on losses in the overall optical path is equal to the dependence experienced by the first optical signal.

[0071] The electronic processing means 4 is operatively connected to the aforementioned first and second optoelectronic receivers PD1 and PDT, and is configured to determine, based on the detected first electrical signal E1 derived from the first optical signal L1 and based on the second electrical signal E2 derived from the first optical signal L2 and representative of the detected reference optical power, a wavelength shift Δλ of the spectrum of the reflected OR or transmitted OT by the Bragg grating of the optical fiber sensor FBG relative to the nominal operating wavelength, whereby the detection of the first electrical signal is compensated for fluctuations in the power of the broadband excitation optical radiation and fluctuations in losses on the optical path.

[0072] Said wavelength shift Δλ of the spectrum reflected or transmitted by the Bragg grating is representative of the physical magnitude measured by the optical fiber sensor FBG.

[0073] The optical bandpass filter BPF and the first and second optoelectronic receivers PD1 and PDT are integrated in a photonic integrated circuit ("Photonic Integrated Circuit" - PIC).

[0074] According to different embodiments, such a first electrical signal E1 is a current or a voltage.

[0075] In a preferred embodiment, the first electrical signal E1 represents (or corresponds to) a voltage proportional to the optical power incident on the optoelectronic receiver and is therefore related to (e.g., proportional to) the aforementioned wavelength shift Δλ of the spectrum reflected or transmitted by the optical fiber sensor FBG.

[0076] According to one embodiment of the system, the optical bandpass filter BPF is an optical microring resonator filter (ie, a "microring resonator MRR").

[0077] As already disclosed, according to two possible embodiments, the optical microring resonator filter is of a single ring type and consists of a single ring 8, or the optical microring resonator filter is of a double ring type and consists of two optical rings.

[0078] A ring resonator is a closed loop of optical waveguide. When light of a specific resonant wavelength passes through the ring by constructive interference, the intensity of the light increases inside the ring, and the light (of the resonant wavelength) can be extracted and observed from the extraction / monitoring port of the ring resonator filter.

[0079] As shown in Figure 6, after injecting a broadband input spectrum into the input port 3 of the micro-ring resonator 6, only the resonant wavelength of the ring 6 is extracted from the output port 1. This is because the light component at the resonant wavelength propagates within the closed ring by constructive interference.

[0080] Conversely, all other non-resonant wavelengths in the input spectrum are transmitted through transmission port 2 of the BPF resonator filter.

[0081] In this way, the two spectra output from the output port 1 and the transmission port 2 of the microring resonator filter BPF are complementary to each other, and the resonator ring functions as a bandpass filter for the output port 1.

[0082] The resonant wavelength of a microring resonator depends on the refractive index of the material and the geometry of the device (waveguide dimensions and ring diameter), and the resonant wavelength can be varied in a controlled manner, i.e., tuned, by small modifications of the refractive index of the light guide, e.g., by thermal tuning based on localized microheaters 9 (e.g., as shown in Figure 7).

[0083] It is worth noting that the output port 1 of the optical bandpass filter BPF converts the shift Δλ of the operating wavelength of the FBG sensor due to the variation of the physical parameter to be measured into a power variation (fluctuation of the optical power upstream of the photodiode, see Figure 7) that is detected by the integrated photodetector or photodiode. The output port 2 of the optical bandpass filter BPF outputs a retro-reflected signal with a spectrum complementary to the signal coming out of the output port 1.

[0084] Because the width of the optical band of the FBG sensor is larger (typically much larger) than the bandwidth of the filter, the power at the output of send port 2 is approximately equal to the total power of the spectrum of the FBG sensor (in other words, the part that is filtered and extracted at drop port 1 is negligible with respect to the total power).

[0085] Therefore, differential detection, which takes into account dual detection at both ports (dropout and transmission) of the optical bandpass filter, enables measurements that are not affected by spurious fiber losses or power fluctuations of light sources such as lasers.

[0086] According to an embodiment (e.g., shown in FIG. 7), the optical micro-ring resonator 6 can be wavelength tuned by the thermo-optic effect of the silicon (in which the micro-ring resonator is integrated), i.e., by applying a voltage or power command signal, the transfer function of the wavelength filter (i.e., the spectrum of the "drop" port depicted in FIG. 8A) can be shifted.

[0087] In some typical implementations, application of a signal on the order of a few volts, dissipating tens of milliwatts of thermal power on a microring resonator filter with a radius of a few tens of microns, can induce a spectral shift of between 5 and 8 nm.

[0088] In the example shown in Figure 8A, the spectrum of the out-coupling port of the micro-ring resonator filter is shown in the wavelength range between 1540 nm and 1565 nm. Being a resonant filter, the spectrum is periodic and has a determined free spectral range (FSR), which in the example of Figure 8 is equal to 10 nm. The optical micro-ring resonator filter is designed so that the FSR parameter is larger than the maximum shift Δλ of the operating wavelength of the FBG sensor.

[0089] The example shown in Figure 8B shows the spectrum of the transmit port of a microring resonator filter over the same wavelength range between 1540 nm and 1565 nm. Because it is again a resonant filter, the spectrum is periodic and the FSR (Free Spectral Range) is determined, which in the example of Figure 8B is also equal to 10 nm. As already disclosed above, the extraction spectrum (Figure 8A) and the transmission spectrum (Figure 8B) are complementary to each other.

[0090] FIG. 9 is a diagram showing an example of the reflection spectrum of the optical fiber sensor FBG and the spectrum of the transmission port 2 of the optical bandpass filter BPF.

[0091] 10 and 11 are diagrams showing the spectra that emerge from the first output port 1 and the second transmission port 2 of the optical filter when the optical spectrum reflected by the optical fiber sensor FBG is incident on the input.

[0092] FIG. 12 shows an enlarged view of the details of the spectra of FIGS. 10 and 11 near wavelength λi.

[0093] From a structural point of view, microring resonators are compact and flexible devices that can be integrated into photonic integrated circuits (PICs) on different technological platforms, such as photonics on silicon (Si) or InP, and furthermore, integrated photodetectors that can provide high-speed broadband response can be obtained on the same platform.

[0094] As already mentioned, in some embodiments the optical circulator 5 and / or the broadband optical radiation source S may also be integrated on the same platform.

[0095] Referring to one or more of the aforementioned optical fiber sensors in fiber Bragg grating technology (hereinafter also defined as "FBG" sensors), it can be noted that FBG sensors are highly sensitive and versatile optical devices for measuring various physical parameters, such as strain and temperature. FBG sensors are in their simplest form sensors, obtained by spatially periodic modulation of the refractive index inscribed in the "core" of an optical fiber.

[0096] FBG sensors exploit the existence of a resonant state that reflects incident light at the so-called "Bragg wavelength," λB, defined as λB = 2neffΛ, where neff is the effective refractive index of the fundamental mode of the optical fiber and Λ is the spatial pitch (periodicity) of the grating.

[0097] The operating principle of the FBG sensor is that when the effective refractive index or grating pitch changes due to external influences such as strain or temperature, the operating wavelength (Bragg wavelength) shifts by Δλ. BThis is based on the nature of the change and can be derived from Equation 1.

[0098]

number

[0099] where Δλ B =λ―λ B is the reference Bragg wavelength λ B where k is the scale factor and α is the change in Bragg wavelength with respect to T is the thermo-optic coefficient. The Bragg wavelength shift has a linear dependence on the longitudinal strain ε, with a sensitivity approximately equal to 1.0 2 pm / με, and a temperature change has a sensitivity equal to approximately 11 pm / °C for silicon fibers in the 1550 nm range. Such a dependence can be particularly large in the range of strain and temperature change and can have nonlinear characteristics that depend on the particular type of FBG sensor considered.

[0100] FBG sensors are "passive" sensors that do not require power supply but are activated by illumination, i.e., by sending optical activation radiation at an appropriate wavelength (e.g., the Bragg wavelength) down a section of optical fiber that results in a grating within the sensor. In response, the FBG sensor reflects or transmits an optical (i.e., photonic) signal that depends not only on the incident radiation but also on the strain and temperature conditions experienced by the grating itself. In various embodiments of the method exemplified below, such an optical signal can be a transmitted optical signal (or optical spectrum) or a reflected optical signal (or optical spectrum).

[0101] According to a particular embodiment of the system 10, the at least one optical fiber sensor of the fiber Bragg grating type FBG may be an optical fiber sensor of the fiber Bragg grating type having a reflection spectrum with a linear shape.

[0102] This embodiment takes advantage of the highly linear shape of the response of the FBG sensor as a linear reflection filter, ensuring enhanced dynamic interrogation performance and a wide dynamic range for strain or temperature measurements. The use of an FBG sensor with a linear response also simplifies the calibration of the interrogator.

[0103] According to an embodiment of the system 10, said first optoelectronic receiver PD1 consists of (or is made up of) a first photodiode, and said second optoelectronic receiver PDT consists of (or is made up of) a second photodiode.

[0104] The first and second photodiodes are, for example, semiconductor photodiodes of a type known per se, designed to detect and convert optical signals at the wavelengths considered into electrical signals.

[0105] According to the embodiment shown in FIG. 1, the system 10 is configured to interrogate only one optical fiber sensor of the Fiber Bragg Grating type FBG, acting on the reflection spectrum OR of the FBG sensor.

[0106] According to another embodiment shown in FIG. 2, the system 10 is configured to interrogate only one optical fiber sensor of the Fiber Bragg Grating type FBG, acting on the transmission spectrum OT of the FBG sensor.

[0107] According to another embodiment shown in FIG. 3, the system comprises a plurality of cascaded optical fiber sensors of the fiber Bragg grating type FBG1-FBGn, each characterized by a respective nominal operating wavelength λ1-λn, and a plurality of cascaded tunable optical bandpass filters BPF1-BPFn (i.e., the transmit port of a filter is connected to the input port of the next one provided in succession). The plurality of tunable optical bandpass filters BPF1-BPFn are each tunable around a respective wavelength corresponding to a respective one of the nominal operating wavelengths λ1-λn of the optical fiber sensors of the fiber Bragg grating type FBG1-FBGn.

[0108] The system 10 further comprises a plurality of optoelectronic receivers (PD1 to PDn) configured to receive the plurality of first optical signals L11 to L1n and convert such plurality of first optical signals L11 to L1n into a respective plurality of first electrical signals E11 to E1n, and a second optoelectronic receiver PDT operatively connected to the second transmit port 2 of the last optical bandpass filter BPF of the cascade of second optical bandpass filters to receive the second optical signal L2 and convert it into a respective second electrical signal E2.

[0109] In this case, the electronic processing means 4 is configured to determine a wavelength shift ΔL relative to the nominal operating wavelength of each of the spectra reflected or transmitted by each of the optical fiber sensors of the fiber Bragg grating type FBG1 to FBGn based on the detected plurality of first electrical signals E11 to E1n and second electrical signal E2.

[0110] In such an embodiment, the i-th BPF ring resonator filter is tuned at a wavelength λi for interrogating the i-th FBGi sensor, and each single BPF i bandpass filter is tuned at a different wavelength λi, and the combined acquisition of signals by the N photodetectors provides a measurement of the wavelength peak of each of the N different FBG sensors.

[0111] According to another embodiment (shown in FIG. 4), the system 10 consists of at least one optical fiber sensor of the Fiber Bragg Grating FBG type, suitable for operating and interrogating along a wide range of wavelengths.

[0112] In this case, the system 10 further comprises a plurality of cascaded tunable optical bandpass filters BPF1 to BPFn, each tunable at a respective operating wavelength λ1 to λn that remains constant and that falls within the aforementioned broad wavelength range of the optical spectrum that is transmitted or reflected by the sensor.

[0113] The system further comprises a plurality of first optoelectronic receivers PD1 to PDn configured to receive the plurality of first optical signals L11 to L1n into a respective plurality of first electrical signals E11 to E1n, and a second optoelectronic receiver PDT operatively connected to a second transmit port 2 of the last optical bandpass filter BPF of the cascade of optical bandpass filters, for receiving the second optical signal L2 and converting it into a respective second electrical signal E2.

[0114] In this case, the electronic processing means 4 is configured to determine the peak of the reflection wavelength or transmission wavelength of the FBG sensor in the wide wavelength range based on the detected plurality of first electrical signals E11 to E1n and the detected second electrical signal E2.

[0115] In such an embodiment, a single FBG sensor can be interrogated when extreme environmental conditions (e.g., thermal runaway) cause large variations in the wavelength peak. Multiple acquisitions with N photodetectors at the N out-coupling ports of the ring resonator provide measurements of the peak wavelength along a wide range of wavelength variations due to, for example, large changes in temperature or strain.

[0116] According to an embodiment, in reference to the case where there are multiple optical filters, a CWDM (Coarse WDM) demultiplexer is used to provide different optical filters (instead of arranging them in cascade), which can advantageously reduce losses on the optical path. Usefully, the i-th channel of the CWDM demultiplexer can be used to query the Bragg wavelength λi of the i-th optical fiber sensor FBGi to be tunable within the optical band of the corresponding i-th channel.

[0117] According to a preferred implementation option, each of the first electrical signals E1i (belonging to the group E11 to E1n) represents an electrical voltage proportional to the optical power incident on the respective optoelectronic receiver Pdi (belonging to the group of optoelectronic receivers PD1 to PDn) and therefore correlated (e.g. proportional) to a respective wavelength shift Δi of the spectrum reflected or transmitted by the respective optical fiber sensor FBGi (belonging to the group of sensors FBG1 to FBGn).

[0118] It should be noted that in embodiments including multiple optical bandpass filters, each of the optical bandpass filters is used as a fixed filter and not as a tunable filter (tuning is performed only during initialization, not during operation).

[0119] Furthermore, in such an embodiment, the free spectral range must be greater than the sum of the tuning excursions allowed for each of the optical bandpass filters. To this end, the radius R of the ring can be defined during design by considering the following relationship, which connects such radius R to the free spectral range FSR:

[0120]

number

[0121] According to a further embodiment (shown in FIG. 5 ), the system 10 further comprises an optical band splitter D arranged upstream of the tunable optical filter BPF and a third optoelectronic receiver PDD, the optical band splitter D configured to split the total optical power and send a portion thereof to the third optoelectronic receiver PDD, the third optoelectronic receiver PDD configured to obtain a third electrical signal E3 adapted to support further compensation.

[0122] According to the embodiment shown in Figures 1 to 5, the system 10 further comprises an optical circulator 5 having a first port connected to a broadband optical radiation source S, a second port connected to an optical fiber F including an optical fiber sensor of the Fiber Bragg Grating type FBG, and a third port connected to at least one optical bandpass filter BPF.

[0123] The optical circulator 5 is configured to transmit the broadband optical radiation S received by the first port to the optical fiber F including the optical fiber sensor FBG via the second port, and it is further configured to transmit the reflection spectrum OR received by the second port by the optical fiber sensor of the Fiber Bragg Grating type FBG to at least one optical bandpass filter BPF through the third port.

[0124] According to one embodiment, the optical circulator 5 is a component external to the photonic integrated circuit PIC in which the optical bandpass filter BPF and the first PD1 and second optoelectronic receiver PDT are integrated.

[0125] According to another embodiment, the optical circulator 5 is integrated into a photonic integrated circuit PIC in which the optical bandpass filter BPF, the first PD1 and the second optoelectronic receiver PDT are integrated. For this purpose, any suitable integration technology known per se can be used, for example based on magneto-optical materials and bonding technology on a silicon-on-insulator SOI technology platform (for example, as shown in the scientific paper "Broadband TE Optical Isolators and Circulators in Silicon Photonics through CE: YIG Bonding" - P. Pintus et al., Journal of Lightwave Technology, Vol. 37, No. 5, March 1, 2019).

[0126] According to an embodiment of the system 10, each sensor of the at least one optical fiber sensor of the Fiber Bragg Grating type FBG is configured to detect a strain acting at the location where the sensor is located.

[0127] According to some important use cases of the system, the fiber optic sensors of the fiber Bragg grating type FBG are configured to act in a brake pad, or are integrated into or coupled to a brake caliper, or are integrated into a washer device adapted to be arranged between a brake caliper support and a brake caliper, wherein the at least one strain detected by the at least one fiber optic sensor of the fiber Bragg grating type FBG is representative of a clamping force and / or a braking torque acting on the brake caliper.

[0128] According to an embodiment, the electronic processing means 4 consist of at least one electronic processor or microprocessor 40 of a type known per se, adapted to store and execute software programs.

[0129] According to different embodiments (as shown in Figures 1 to 5), the system 10 can be composed of further electronic systems known per se, such as, for example, an ADC analog-to-digital converter, a transimpedance amplifier 41, an ASIC 42 device for conditioning the electrical signal, and appropriate optical connections (shown as continuous lines in Figures 1 to 5) and electrical connections (shown as dotted lines in Figures 1 to 5).

[0130] According to another possible embodiment, the functional block 42 is intended as a block for conditioning the analog signal (i.e., adapting the converted and amplified signal), and the functional block 40 is a digital signal conversion and processing block 40, providing at output the processed data on an appropriate interface / bus.

[0131] According to an embodiment, the functional block 40 and, at least in part, the functional block 42 may be obtained by a single integrated circuit, for example of the ASIC or FPGA type.

[0132] Different experimental or analytical approaches can be used, referring to the relationship between the power detected at the output port 1 of the optical bandpass filter and the wavelength shift Δλ of the FBG sensor.

[0133] For example, based on the measurements performed during characterization, a table (e.g., a look-up table) can be stored in the electronic processing means (e.g., conversion and processing block 40) that establishes a relationship between the measured voltage values ​​and the shift values ​​of the peak wavelength of the FBG sensor.

[0134] According to another embodiment, the following simplified analytical relationship may be considered:

[0135] The optical spectrum seen by the photodetector SOPT(λ) is proportional to the product of the spectra of the FBG sensor and the microring resonator MRR (at the extraction port) through a constant C:

[0136]

number

[0137] The measured optical power is the integral of the wavelength, λ FBG Depends on.

[0138]

number

[0139] Power compensation made possible by detecting the optical signal at the transmit port of the optical bandpass filter can be performed, for example, by normalizing the power detected at the drop port to the power detected at the transmit port.

[0140] According to another embodiment, it is possible to normalize the difference between the power detected at the drop port and the power detected at the transmit port to the sum of the power detected at the drop port and the power detected at the transmit port.

[0141] According to an embodiment, the method and system of the present invention includes active control and relative electronic compensation of the chip's temperature, enabling its operation over a wide temperature range, for example in environments with elevated thermal excursions.

[0142] As will be noted, the objects of the present invention are fully achieved by the above-disclosed method and system, due to its functional and structural features.

[0143] Indeed, with reference to the technical problems mentioned in the section describing the prior art, the system according to the invention is a simple and compact system in which the essential components are integrated (for example in an optical integrated circuit in PIC technology).

[0144] This integration can be carried out with silicon technology, and the system according to the invention is particularly suited to the integration of both optical and electronic circuits in a hybrid chip manufactured using the same process.

[0145] Furthermore, if desired, the above technical solution also allows for the integration of broadband light sources and / or optical circulators in the same integrated circuit in which optical filters and photodetectors are integrated, providing significant design flexibility.

[0146] Furthermore, the systems and methods of the present invention work by keeping constant the wavelength of an optical bandpass filter (which is adjusted only during an initialization step) that captures the portion of the spectrum transmitted or reflected by the FBG sensor. As such spectrum shifts due to effects related to the variable being measured, the constant wavelength sampling by the microring optical filter records the shift in the form of fluctuations in the detected power.

[0147] Thus, the dynamic performance does not depend on the adjustment time of the optical bandpass filter, but only on the speed of the photodetector block, thus providing a faster dynamic response with respect to the previously mentioned known solutions.

[0148] Furthermore, systems and methods according to the present invention utilize simultaneous detection of optical power at both the drop and transmit ports and have improved tolerance to spurious losses and / or fluctuations in optical illumination power.

[0149] It should also be noted that the claimed solution involves narrowband optical filtering of the transmission or reflection spectrum of the FBG optical fiber sensor around the operating wavelength (e.g., unlike that obtained using a solution based on a Fabry-Perot filter, the bandwidth of which can be compared to that of the optical signal of the FBG sensor being interrogated). The fact that the bandwidth of the spectrum reflected by the interrogated FBG sensor is larger than the linewidth of the resonance spectrum of the optical filter used in the present solution (especially much larger in embodiments involving the use of a microring optical resonator filter) offers various advantages, including the possibility to perturb the spectrum emerging from the transmit port of the filter as little as possible, and to be able to select the "finesse" of the resonance spectrum of the optical filter as an important design parameter in order to improve the performance of the interrogator in terms of spectral dynamic resolution.

[0150] The method and system described above also make it possible to obtain a response over a wide reception band, which in fact depends on the reception band of the photodiode used, i.e. on components that are able to act over a very wide band (for example, PIN-type integrated photodiodes are known, which use germanium as the absorbing material, which has a band from MHz up to 40 GHz. For the application considered here, it is necessary to observe phenomena with a band of a few hundred KHz or less, which is easily guaranteed by the system according to the invention).

[0151] Other advantages of the method and system according to the invention are the low power consumption of the integrated devices on the PIC, compatibility with CMOS manufacturing processes for the manufacture of PIC optical chips and EIC electronic chips, and the ability to operate along a wide temperature range obtained by active control of the chip temperature and electronic compensation for operation in high thermal deviation environments.

[0152] To meet fortuitous and specific needs, those skilled in the art can make several modifications and adaptations to the above-described embodiments and substitute other functionally equivalent elements without departing from the scope of the following claims. Each feature described as belonging to a possible embodiment can be obtained independently of the other embodiments described.

Claims

1. 1. A method for interrogating a fiber Bragg grating (FBG) optical fiber sensor, comprising: illuminating the fiber Bragg grating (FBG) optical fiber sensor with broadband excitation optical radiation (OA); sending an optical spectrum (OT) transmitted through the fiber Bragg grating (FBG) optical fiber sensor or an optical spectrum (OR) reflected by the fiber Bragg grating (FBG) optical fiber sensor to a tunable optical bandpass filter (BPF) having a first drop port (1) and a second transmission port (2) that are complementary to each other; tuning the optical bandpass filter (BPF) at a fixed operating wavelength (λi) according to a nominal operating wavelength of the fiber optic sensor (FBG) of the fiber Bragg grating type (FBG); detecting a first optical signal (L1) exiting from the first drop port (1) of the optical bandpass filter (BPF), the first optical signal (L1) being a narrowband optical filtering of an optical spectrum (OT) transmitted through the fiber Bragg grating (FBG) optical fiber sensor or an optical spectrum (OR) reflected by the fiber Bragg grating (FBG) optical fiber sensor around the fixed operating wavelength (λi) of the optical bandpass filter (BPF); converting the first optical signal (L1) by a first optoelectronic receiver (PD1) into a first electrical signal (E1) representing a wavelength shift (Δλ) of an optical spectrum (OT) transmitted through the fiber Bragg grating (FBG) optical fiber sensor or an optical spectrum (OR) reflected by the fiber Bragg grating (FBG) optical fiber sensor relative to the constant operating wavelength (λi); detecting a second optical signal (L2) exiting the second transmit port (2) of the optical bandpass filter (BPF), the second optical signal (L2) being spectrally complementary to the first optical signal (L1); converting said second optical signal (L2) into a second electrical signal (E2) by a second optoelectronic receiver (PDT), said second electrical signal (E2) representing a reference optical power, said reference optical power being substantially independent of a filtering wavelength and having a dependence on the power of broadband pump optical radiation and on losses over an optical path, said dependence being equal to the dependence experienced by said first optical signal; determining a wavelength shift (Δλ) of an optical spectrum (OT) transmitted through or an optical spectrum (OR) reflected by the Fiber Bragg Grating (FBG) optical fiber sensor relative to the constant operating wavelength (λi) based on the detected first electrical signal (E1) derived from the first optical signal (L1) exiting the first drop port (1) of the optical bandpass filter (BPF) and based on the second electrical signal (E2) representing the detected reference optical power derived from the second optical signal (L2) output from the second transmit port (2) of the optical bandpass filter (BPF), wherein the detection of the first electrical signal is compensated for fluctuations in the power of broadband excitation optical radiation and fluctuations in optical path loss, the determined wavelength shift (Δλ) of the optical spectrum (OT) transmitted through the fiber Bragg grating (FBG) optical fiber sensor or the optical spectrum (OR) reflected by the fiber Bragg grating (FBG) optical fiber sensor represents a physical magnitude measured by the fiber optic sensor (FBG); The method, wherein the optical bandpass filter (BPF), the first optoelectronic receiver (PD1), and the second optoelectronic receiver (PDT) are integrated in a photonic integrated circuit (PIC).

2. the optical bandpass filter (BPF) comprises a third input port (3) different from the first drop port (1) and the second transmission port (2); 2. The method of claim 1, wherein the sending step sends an optical spectrum (OT) transmitted through the fiber Bragg grating (FBG) optical fiber sensor or an optical spectrum (OR) reflected by the fiber Bragg grating (FBG) optical fiber sensor to the third input port (3) of the optical bandpass filter (BPF).

3. The method of claim 1 or 2, wherein the optical bandpass filter (BPF) is an optical microring resonator filter.

4. the adjusting step includes adjusting the optical bandpass filter (BPF) at the constant operating wavelength located in a linear or nearly linear region of an optical spectrum transmitted through or reflected from the FBG optical fiber sensor (OT or OR); 4. The method of claim 1, wherein a wavelength shift or variation of the optical spectrum (OT) transmitted through or reflected by the Fiber Bragg Grating (FBG) optical fiber sensor corresponds to a linear or nearly linear variation of the power or intensity of the first optical signal (L1).

5. configured to interrogate a plurality of cascaded fiber optic sensors of the Fiber Bragg Grating type (FBG1-FBGn); wherein the plurality of optical fiber sensors (FBG1-FBGn) are characterized by their respective nominal operating wavelengths (λ1-λn), the sending step includes sending a total transmitted light spectrum (OT) or a total reflected light spectrum (OR) from the plurality of cascaded optical fiber sensors (FBG1-FBGn) of the optical fiber sensor (FBG) to a plurality of cascaded optical bandpass filters (BPF1-BPFn); the adjusting step includes adjusting each of the plurality of optical bandpass filters (BPF1 to BPFn) to about a respective wavelength (λ1-λn) corresponding to one of the nominal operating wavelengths (λ1-λn) of the plurality of fiber optic sensors (FBG1-FBGn) of the fiber Bragg grating type; the step of detecting the first optical signal (L1) includes detecting a plurality of first optical signals (L11 to L1n) output from the first drop ports of each of the plurality of optical bandpass filters (BPF1 to BPFn) at respective operating wavelengths held constant; the converting step includes converting the plurality of first optical signals (L11 to L1n) into a plurality of first electrical signals (E11 to E1n) by a plurality of first photodiodes (PD1 to PDn), respectively; the step of detecting the second optical signal (L2) includes detecting, by the second optoelectronic receiver (PDT), an optical signal exiting from the second transmit port of the last optical bandpass filter (BPFn) of the cascaded optical bandpass filters, and converting the second optical signal (L2) into the second electrical signal (E2); 5. The method of claim 1, wherein the determining step includes determining a wavelength shift (Δλi) relative to a nominal operating wavelength of each of the spectra reflected or transmitted by each of the plurality of optical fiber sensors (FBG1-FBGn) based on the detected plurality of first electrical signals (E11-E1n) and the detected second electrical signal (E2).

6. configured to interrogate only one fiber optic sensor of the Fiber Bragg Grating type (FBG) over a wide wavelength range; the sending step includes sending the optical spectrum (OT) transmitted through the fiber Bragg grating (FBG) optical fiber sensor or the optical spectrum (OR) reflected by the fiber Bragg grating (FBG) optical fiber sensor to a plurality of cascaded tunable optical bandpass filters (BPF1 to BPFn); the adjusting step includes adjusting each of the plurality of optical bandpass filters (BPF1 to BPFn) at a respective operating wavelength (λ1 to λn) that is kept constant and that falls within a wide wavelength range of an optical spectrum (OT) transmitted through the fiber Bragg grating (FBG) optical fiber sensor or an optical spectrum (OR) reflected by the fiber Bragg grating (FBG) optical fiber sensor; the step of detecting the first optical signal (L1) includes detecting a plurality of first optical signals (L11 to L1n) output from the first drop ports of each of the plurality of optical bandpass filters (BPF1 to BPFn); the step of converting the first optical signal (L1) includes converting the plurality of first optical signals (L11 to L1n) into a plurality of first electrical signals (E11 to E1n) by a plurality of first photodiodes (PD1 to PDn); The step (L2) of detecting the second optical signal includes detecting an optical signal output from the second transmit port (2) of the last optical bandpass filter (BPFn) of the plurality of cascaded optical bandpass filters (BPF1 to BPFn); the step of converting the second optical signal (L2) includes converting the second optical signal (L2) into the second electrical signal (E2) by the second optoelectronic receiver (PDT); 5. The method of claim 1, wherein the determining step includes determining a peak of a reflection wavelength or a transmission wavelength of the fiber Bragg grating (FBG) optical fiber sensor within the wide wavelength range based on the detected plurality of first electrical signals (E11 to E1n) and the second electrical signal (E2).

7. 7. The method according to claim 1, wherein, before the sending step, the total optical power is split by an optical splitter (D) and a part thereof is sent to a third optoelectronic receiver (PDD).

8. A system (10) for interrogating a fiber optic sensor of the Fiber Bragg Grating type (FBG), comprising: The system (10) comprises: the optical fiber sensor of the fiber Bragg grating type (FBG); a broadband optical radiation source (S) configured to illuminate the fiber optic sensor of the Fiber Bragg Grating type (FBG) with broadband excitation optical radiation (OA); a tunable optical bandpass filter (BPF) having a first drop port (1) and a second transmission port (2) that are complementary to each other, and further having an input port (3) different from the first drop port (1) and the second transmission port (2), the tunable optical bandpass filter (BPF) operatively connected to the fiber Bragg grating (FBG) optical fiber sensor to receive an optical spectrum (OT) transmitted through the fiber Bragg grating (FBG) optical fiber sensor or an optical spectrum (OR) reflected by the fiber Bragg grating (FBG) optical fiber sensor; The optical bandpass filter (BPF) is tunable over a wavelength range with a constant operating wavelength (λi) according to the nominal operating wavelength of a fiber Bragg grating of the fiber Bragg grating type (FBG); The system (10) also includes: a first optoelectronic receiver (PD1) operatively connected to the first drop port (1) of the optical bandpass filter (BPF) and configured to receive respective first optical signals (L1) and convert the first optical signals (L1) into respective first electrical signals (E1), wherein the first optical signals (L1) are narrowband optical filtering of an optical spectrum (OT) transmitted through the fiber Bragg grating (FBG) optical fiber sensor or an optical spectrum (OR) reflected by the fiber Bragg grating (FBG) optical fiber sensor at a certain operating wavelength of the optical bandpass filter (BPF); a second optoelectronic receiver (PDT) operatively connected to the second transmission port (2) of the optical bandpass filter (BPF) for receiving a second optical signal (L2), and configured to convert the second optical signal (L2) into a respective second electrical signal (E2) so as to obtain a reference power value that is substantially independent of a filtering wavelength and whose dependence on the power of broadband excitation optical radiation and on losses throughout the optical path is equal to the dependence experienced by the first optical signal (L1); an electronic processing means (4) operatively connected to the first optoelectronic receiver (PD1) and the second optoelectronic receiver (PDT) and configured to determine, based on a detected first electrical signal (E1) derived from the first optical signal (L1) and based on the second electrical signal (E2) derived from the second optical signal and representing a detected reference optical power, a wavelength shift (Δλ) of an optical spectrum (OT) transmitted through or reflected by the Fiber Bragg Grating (FBG) optical fiber sensor relative to the nominal operating wavelength; the wavelength shift (Δλ) of the optical spectrum (OT) transmitted through the fiber Bragg grating (FBG) optical fiber sensor or the optical spectrum (OR) reflected by the fiber Bragg grating (FBG) optical fiber sensor represents a physical magnitude measured by the fiber Bragg grating (FBG) optical fiber sensor; A system (10), characterized in that the optical bandpass filter (BPF), the first optoelectronic receiver (PD1), and the second optoelectronic receiver (PDT) are integrated in a photonic integrated circuit (PIC).

9. The system (10) of claim 8, wherein the optical bandpass filter (BPF) is an optical microring resonator filter.

10. The system (10) of claim 9, wherein the optical microring resonator filter is a single-ring type consisting of one optical ring.

11. The system (10) of claim 9, wherein the optical micro-ring resonator filter is of a double-ring type consisting of two optical rings.

12. The system (10) of any of claims 8 to 11, wherein the broadband optical radiation source (S) is integrated into the photonic integrated circuit (PIC).

13. 13. The system (10) of any of claims 8 to 12, wherein the optical fiber sensor is a fiber Bragg grating type (FBG) optical fiber sensor having a linear shaped reflection spectrum.

14. a plurality of cascaded fiber Bragg grating type (FBG1-FBGn) optical fiber sensors, each characterized by a nominal operating wavelength (λ1-λn); a plurality of cascaded tunable optical bandpass filters (BPF1-BPFn), each tunable about a respective wavelength (λ1-λn) corresponding to a respective one of the nominal operating wavelengths of the plurality of fiber Bragg grating type (FBG1-FBGn) optical fiber sensors; a plurality of first optoelectronic receivers (PD1 to PDn) configured to receive a plurality of first optical signals (L11 to L1n) and convert the plurality of first optical signals (L11 to L1n) into a respective plurality of first electrical signals (E11 to E1n); a second optoelectronic receiver (PDT) operatively connected to the second transmit port (2) of the last optical bandpass filter (BPFn) of the plurality of tunable optical bandpass filters (BPF1-BPFn), for receiving the second optical signal (L2) and converting it into a second electrical signal (E2); 13. The system (10) of any one of claims 8 to 12, wherein the electronic processing means (4) is configured to determine a wavelength shift (Δλ) relative to the nominal operating wavelength of each of the spectra reflected or transmitted by each of the plurality of fiber Bragg grating type (FBG1 to FBGn) optical fiber sensors based on the plurality of first electrical signals (E11 to E1n) and the second electrical signal (E2).

15. a fiber optic sensor of the Fiber Bragg Grating type (FBG) that can be interrogated and operates over a wide range of wavelengths; a plurality of cascaded tunable optical bandpass filters (BPF1-BPFn), each tunable at a respective operating wavelength (λ1-λn) that remains constant and that belongs to a wide wavelength range of the optical spectrum transmitted or reflected by the optical fiber sensor; a plurality of first optoelectronic receivers (PD1 to PDn) configured to convert a plurality of first optical signals (L11 to L1n) into a respective plurality of first electrical signals (E11 to E1n); a second optoelectronic receiver (PDT) operatively connected to the second transmit port (2) of the last optical bandpass filter (BPFn) of the plurality of tunable optical bandpass filters (BPF1-BPFn), for receiving the second optical signal (L2) and converting it into a respective second electrical signal (E2); 14. The system (10) of claim 12 or 13, wherein the electronic processing means (4) is configured to determine a peak reflected or transmitted wavelength of the optical fiber sensor in the wide wavelength range based on the plurality of first electrical signals (E11 to E1n) and the second electrical signal (E2).

16. an optical band splitter (D) arranged upstream of the optical bandpass filter (BPF), and a third optoelectronic receiver (PDD); 16. The system (10) of any of claims 8 to 15, wherein the optical band splitter (D) is configured to split the total optical power and send a portion thereof to the third optoelectronic receiver (PDD).

17. 17. The system (10) of claim 16, wherein each of the first optoelectronic receiver (PD1) and / or the second optoelectronic receiver (PDT) and / or the third optoelectronic receiver (PDD) comprises a semiconductor photodiode configured to detect and convert an optical signal at the wavelength considered into an electrical signal.

18. an optical circulator (5) having a first port connected to the broadband optical radiation source (S), a second port connected to an optical fiber (F) including the optical fiber sensor of the fiber Bragg grating type (FBG), and a third port connected to the optical bandpass filter (BPF); 18. The system (10) of claim 8, wherein the optical circulator (5) is configured to transmit broadband optical radiation (OA) received from the first port to an optical fiber (F) including the optical fiber sensor (FBG) via the second port, and further configured to transmit a spectrum reflected by a fiber Bragg grating (FBG) optical fiber sensor received from the second port to the optical bandpass filter (BPF) via a third port.

19. 20. The system (10) of claim 18, wherein the optical circulator (5) is integrated into the photonic integrated circuit (PIC).

20. a plurality of cascaded fiber Bragg grating type (FBG1-FBGn) optical fiber sensors, each characterized by a nominal operating wavelength (λ1-λn); a coarse WDM wavelength division demultiplexer configured to demultiplex the spectrum transmitted or reflected by the plurality of fiber Bragg grating type (FBG1-FBGn) optical fiber sensors and provide optical signals of different wavelengths (λi) at respective i-th output ports; a plurality of tunable optical bandpass filters (BPF1-BPFn), each connected to the output of the coarse WDM wavelength division demultiplexer to receive a respective optical signal at a respective wavelength (λi), each tunable about a respective wavelength (λi) corresponding to a respective one of the nominal operating wavelengths of the fiber Bragg grating (FBG) optical fiber sensor; a plurality of first optoelectronic receivers (PD1 to PDn) configured to receive a plurality of first optical signals (L11 to L1n) and convert the plurality of first optical signals (L11 to L1n) into a respective plurality of first electrical signals (E11 to E1n); a plurality of second optoelectronic receivers (PDTs) each operatively connected to a second transmission port (2) of each of the ith optical bandpass filters (BPFi) connected to a respective ith output of the coarse WDM wavelength division demultiplexer, for receiving and converting each of the second optical signals (L2) into a respective second electrical signal (E2); 13. The system (10) of any one of claims 8 to 12, wherein the electronic processing means (4) is configured to determine a wavelength shift (Δλ) relative to a nominal operating wavelength of each of the spectra reflected or transmitted by each of the plurality of fiber Bragg grating type (FBG1-FBGn) optical fiber sensors based on the detected plurality of first electrical signals (E11-E1n) and the second electrical signal (E2).

21. 21. The system (10) of claim 20, wherein each of the plurality of fiber Bragg grating type (FBG1-FBGn) optical fiber sensors is configured to detect contamination acting on a location where the sensor is located.

22. 22. The system (10) of claim 21, wherein the plurality of fiber optic sensors of the fiber Bragg grating type (FBG1-FBGn) are configured to operate within a brake pad, integrated into a brake caliper, coupled to a brake caliper, or integrated into a washer device adapted to be positioned between a brake caliper support and a brake caliper, and wherein at least one strain detected by the plurality of fiber optic sensors of the fiber Bragg grating type (FBG1-FBGn) is representative of a clamping force and / or a braking torque acting on the brake caliper.

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