Fbg sensor interrogation system

Abstract

The invention proposes an interrogation system for optical fiber sensors of the FBG (Fiber Bragg Grating) type. The system is based on a ring topology fiber laser that includes each FBG sensor as part of its cavity. The change in the reflection wavelength of the sensor is converted into a change in the laser's operating power, which is detected by the system. The multipoint of detection is conducted by means of optical switches, whereas the FBG sensors may have similar or different characteristics in terms of central wavelength and reflectivity.

Description

[0001] DESCRIPTION

[0002] FBG SENSOR INTERROGATION SYSTEM

[0003] The present invention concerns an optical fiber sensor reading system (interrogator) and belongs to the field of optoelectronics and optical fibers. Specifically, it falls within the category of FBG interrogation systems, which convert the wavelength shift caused by FBGs into a change in reflected power.

[0004] Fiber Bragg Grating (FBG) sensors are segments of optical fibers with lengths of the order of a few m illimeters that exhibit maximum reflectivity at a very specific wavelength. This is achieved through periodic modulation of the refractive index of the fiber core at that specific wavelength, a process known as "writing". The wavelength of maximum reflectivity is determined by their construction parameters and changes when the sensor elongates or when its temperature varies. For this reason, FBG sensors find widespread use, primarily as mechanical strain and temperature sensors, with direct applications in monitoring the integrity of buildings and other structures. The measurement of the wavelength shift of the maximum reflectivity of FBGs is carried out using devices called interrogators.

[0005] In current practice, a family of methods for reading FBGs, one of which implements the conversion of wavelength shift to power variation. The technical limitation of these FBG reading methods is related to the limited dynamic range, reduced power, and limited resolution, problems that are solved by the proposed invention.

[0006] Existing FBG reading systems fall into two major categories. The first category includes systems that directly analyze the spectrum of reflected light using spectral analysis setups whereas the second involves systems that convert the wavelength shift of maximum reflectivity into a change of reflected power. [A.Othonos and K.Kalli, Fiber Bragg grating: Fundamental and applications in telecommunications and sensing. Artech House, 1999, R.Kashyap, Fiber Bragg Gratings, Elsevier, 2010, Francis T. S. Yu and Shizhuo Yin, Fiber Optic Sensors, Marcel Dekker, Inc. 2002, U.Tiwari, K.Thyagarajan, M.R.Shenoy, and S.CJain "EDF-Based Edge-Filter interrogation Scheme for FBG Sensors" IEEE Sensors Journal, VOL. 13, NO. 4, (2013). https: / / ieeexplore.ieee.org / document / 63872531. The first and classical approach, consists of a wide-spectrum light emission source that sends light to FBGs through optical fibers, along with a spectral analysis system (usually an optical spectrum analyzer or spectrometer) that records the spectrum of the reflected light. The emission spectrum of the source should cover the range in which the FBGs are designed to operate, typically in the telecommunications wavelength region (around 1550 nm) to leverage optical fiber components that are widely available in the optical communications market. The main drawback of these systems is related to the fact that in the case of multiple monitoring points, each FBG must be designed to reflect at a different wavelength. Consequently, in cases with few monitoring points (such as when monitoring a small building construction), these systems become complex and impractical, since they not only utilize spectral analyzers, which are sophisticated devices, but also because they require sensors with distinct characteristics.

[0007] The above category of FBG interrogation methods include as well the technique that is based on tunable lasers. Specifically, in this technique, the light source that sends light to the FBG through an optical fiber is not a wide-spectrum source, as in the previous case, but rather a monochromatic variable-wavelength laser. The system of the state of the art adjusts the emission wavelength of the laser and record the reflected power for each wavelength, until they detect the maximum reflected power. The drawbacks of this method are similar to the previous one, with the additional consideration of relatively slow scanning speed when multiple FBGs are used to monitor multiple points.

[0008] A variation of the previous isthe reading technique which involves the use of tunable optical filters. These filters are placed at the output of a wide- spectrum light source and allow the transmission of a narrow spectral range with variable central wavelength, effectively simulating a monochromatic variable-wavelength source. This technique has similar drawbacks with the previous ones.

[0009] In the second category of FBG interrogation systems, which includes systems based on the conversion of the strain induced wavelength shift into change of optical power, a reading method based on the use of a linear gradient filter (edge filter) has been proposed. These filters are implemented with a special type of FBGs, called chirped FBGs (CFBGs) and exhibit spectral regions with linear variation of reflectance with wavelength. A broadband source sends light to the FBG sensor and the reflected wavelength passes through the filter. When the reflected wavelength from the sensor changes, the output power of the filter changes accordingly in a linear fashion. In the paper by SHAO Li-yang, SONG Jian-fei, ZHANG A -ping, and HE Sai-ling "Novel FBG triangular filter for interrogating a FBG sensor in dynamic strain measurement" Optoelectronics Letters, Vol.2, No 5, 336- 338, (2006), a filter based on CFBGs is described. In general, these filters are difficult to manufacture and, in addition to the increased cost, show regions of linear reflectance of limited range (which typically does not exceed 1.5 nm), disadvantages which are solved by the proposed invention.

[0010] In the reference by M. Yucel and 0. Koyuncu "Design and implementation of a passive edge filter with high bandwidth and slope" Microw. Opt. Technol. Lett., 61:2572-2578, (2019), https: / / doi.org / 10.1002 / mop.319231-4, an interrogator based on erbium-doped fiber (EDF) has been proposed. Specifically, the EDF behaves as a linear slope filter, leveraging the absorption spectrum of erbium. As a result, it achieves an increased operational bandwidth, enhancing the characteristics of corresponding chirped fiber Bragg grating (CFBG) filters. However, in this context, the EDF operates as a passive component (not in a laser form), and therefore, it falls short in terms of power levels due to increased absorption and losses. tn document CN114812629 (A), published on July 29, 2022, the proposed interrogator relies on a laser structure. However, this technique employs a Sagnac interferometer topology, which induces complexity because it is based on optical phase variations. Additionally, it exhibits limitations in scalability to more than one sensor.

[0011] In a very brief disclosure, the present invention proposes a method for implementing an FBG interrogator which, in combination with FBG sensors that exhibit reflectivity in the 1532-1537 nm range, converts the shifts of the FBG reflectivity spectrum into a linear power variation, without any use of additional optica! filters. The interrogator consists of an Erbium-doped fiber laser in a ring topology, which also includes the FBG sensor. The variation in the maximum reflectivity wavelength of the sensor, due to mechanical strain applied to it or changes in its temperature, is converted into a change in the laser's operating powerwhich is monitored by a simple photodiode. Multiple detection points can be monitored by using multiple similar FBG sensors (in terms of central wavelength and reflectivity) that are sequentially connected to the system via an optical switch. The proposed method is implemented by a corresponding device. The present invention solves the above-mentioned technical problem by simultaneously achieving the increase in power due to the laser topology, the increase in resolution due to the reduction of the emission spectrum of the device and the increase in dynamic range due to operation in wide spectral range of Erbium. The advantages of the invention in relation to the state of the art are the following:

[0012] In contrast to the state-of-the-art existing systems based on spectral analysis, the present invention does not utilize spectral analyzers, tunable lasers or filters, that increase system complexity and cost. Additionally, the invention can operate with multiple sensors of both the same and different inscriptions. Also, the proposed invention exhibits a wide operational spectral range of approximately 5 nm and can cover the entire spectral shift of an FBG sensor under mechanical strain. An additional advantage of the invention is that, due to the ring laser topology, the power levels of the device can be adjusted to compensate for any eventual losses up to the position where the sensor is located. Furthermore, the high response speed of the technique allows real-time monitoring and recording of fast events, such as the vibrations and behavior of constructions during earthquakes. An important additional advantage of the method is the very narrow linewidth of the output light, thanks to the fiber laser topology. This narrow linewidth significantly enhances the system s resolution and in combination with the other advantages reported in the previous paragraphs, it outperforms existing systems that convert wavelength variations into power changes because it simultaneous achieve improvement in operational bandwidth, power level, and resolution.

[0013] The invention can be used for "reading" typically up to 16 sensors, as the system is expandable in case the number of sensors increases or decreases depending on the application. The fabrication of the device straightforward and creates favorable conditions for its extensive use in the structural health monitoring of smal l structures such as buildings, bridges, and other constructions. In these applications, assessing structural integrity can be achieved with just a few monitoring points (typically using 8 to 12 sensors). This approach is particularly relevant in regions with increased seismic activity as Greece, where numerous small-scale constructions exist.

[0014] Due to the low cost of construction and operation, the invention can remain in permanent operation at the installation site. The device is particularly adapted for operation as a networked device to enable remote recording of the behavior and integrity of the monitored structures.

[0015] Finally, converting the variation in the maximum reflectivity wavelength of the FBG into a variation in detected power using the proposed ring laser-based topology provides a larger dynamic range compared to devices based on linear slope filters. Additionally, it offers greater flexibility and simpler implementation, considering that these filters pose implementation challenges and increased fabrication cost.

[0016] The 3 drawings accompanying the invention briefly illustrate the following:

[0017] Figure 1 illustrates the structural diagram of the device-system readout of FBGs which exhibit maximum reflectivity in the 1532-1537 nm region.

[0018] Figure 2 shows the emission spectrum of an Erbium Doped Fiber (E D F) for various optical pumping power levels P1, P2, P3, P4, by means of a Laser Diode (ID) emitting at 980nm.

[0019] Figure 3 shows the linear response of the interrogator fora sensor with a central reflection wavelength at 1534 nm.

[0020] The invention is identified by the Claims accompanying it. The present invention constitutes a method for implementing an FBG interrogator (a system for reading FBG sensors). The method is based on an optical fiber laser with an active fiber segment doped with rare earth elements, where, the FBG sensor is an embedded part of the laser cavity, continuously feeding back the cavity with the power it reflects. The FBG sensor is inscribed to exhibit maximum reflectivity within a spectra! range of the active material emission, where the emission spectrum shows a linear dependence with wavelength. In the implementation example presented here, the laser is implemented with a ring topology and an optical fiber doped with trivalent Erbium ions. This fiber exhibits two linear regions in the emission spectrum: one from 1525 to 1530 nm and another from 1532 to 1537 nm (Figure 2, regions AB & AC) while the FBG sensor shows maximum reflectivity within one of the aforementioned spectral ranges. In this specific implementation example, the FBG operates in the 1532-1537 nm range, but the method can equivaiently be implemented with a sensor exhibiting maximum reflectivity in the 1525- 1530 nm range. Additionally, the method could be implemented using an optica! fiber laser that utilizes alternative active rare earth materials. In this case, the sensor would be designed to exhibit maximum reflectivity within one of the linear regions of the emission spectrum associated with these alternative active rare earth materials. Furthermore, the method could be implemented in a similar manner using a Fabry-Perot laser cavity instead of the ring topology described in this indicative implementation. When the FBG sensor elongates (either positively or negatively) due to mechanical strain or temperature variations, the reflected wavelength will shift, consequently affecting the operating wavelength of the optical fiber laser. Given that the gain of the laser's active material depends on the wavelength, any change in the laser's operating wavelength results in a variation of its output power, which can be detected using a simple photodiode. Consequently, If the rest of the system's parameters remain constant, each measured change in the laser's power can be linearly related to the variation in the reflected wavelength of the sensor that caused it. Subsequently, this allows for the calculation of the mechanical strain applied to the sensor and / or the change in its temperature. As a result, the method converts the spectral shift of the FBG reflection due to mechanical strain or other causes into a linear variation in the power measured by the system, without the use of optical filters. In the implementation example of the inventive idea described here, a ring topology laser with erbium-doped fiber was used, along with an FBG sensor exhibiting maximum reflectivity in the wavelength range between 1532 and 1537 nm. The method is implemented by a device-system that Includes at least the following structural elements:

[0021] 1. Laser Diode (1): emitting light at an indicative wavelength of 980 nm, although other wavelengths (e.g , around 1480 nm) are not excluded.

[0022] 2. Current Controller (2) for the laser diode.

[0023] 3. Temperature Controller (3) for the laser diode.

[0024] 4. Wavelength Division Multiplexing (WDM) Coupler (4) operating at 980 nm and the 1550 nm region.

[0025] 5. An optical fiber doped with trivalent erbium ions (Erbium Doped Fiber - EDF) or other active materials such as ytterbium (Yb) or a combination of active materials.

[0026] 6. Optical Circulator (6) operating in the 1550 nm region.

[0027] 7. Optical Switch (7) with a 1;N configuration at 1550 nm.

[0028] 8. Splitter (8) with an indicative 50%-50% ratio at 1550 nm.

[0029] 9. Photodiode Circuit (9) for optical power detection.

[0030] 10. Microcontroller (10) for circuit control and execution of the measurement software.

[0031] 11. Internet Interface (11) for communication and remote measurement retrieval.

[0032] 12. Single-Mode Fiber (12) connecting the Fiber Bragg Gratings (FBGs) to the interrogator.

[0033] 13. FBGs (13) written on single-mode fibers.

[0034] 14. Wiring for Analog Electrical Signals (14) related to optical power measurement.

[0035] 15. Wiring for Control Signals (15) of the setup.

[0036] 16. Electrical Power Supply (16) for the circuits.

[0037] 17.lnternet (17).

[0038] 18. Central Monitoring Unit (18) for the system. In the application of the inventive idea described here, when referring to materials that operate in the 1550 nm region, it means that this range covers the spectrum from approximately 1520 nm to 1560 nm or 1550 ± 30 nm.

[0039] The invention can be realized and functions in exactly the same way even if an alternative circulator arrangement (such as using an optical coupler) is chosen instead of the original circulator (6).

[0040] As depicted in Figure 1, a 980 nm laser source (1) pumps an optical fiber doped with trivalent erbium ions (Erbium Doped Fiber, EDF) (5) through an optical coupler (4), This optical coupler can couple two wavelength regions at 980 nm and 1550 nm. The length and concentration of the fiber's doping can vary depending on the desired output power of the system and the reflectivity of the FBG sensors.

[0041] The optical pumping (1) of the Erbium-Doped Fiber (EDF) (5) generates an optical spectrum at its output, covering the range from 1520 to 1560 nm. This optical spectrum is directed toward the Fiber Bragg Grating (FBG) sensor (13) through an optical circulator (6), which also operates within the aforementioned spectral range, after passing through the optical switch (7) and the optical fiber (12) (path C-D).

[0042] The Fiber Bragg Grating (FBG) sensor (13) selectively reflects only the wavelength for which it is specifically designed. If the sensor experiences mechanical strain, the reflected wavelength changes. The reflected wavelength returns to the optical circulator (6), via the optical fiber (12) and the optical switch (7) (path D-C), which circulator directs it to the optical splitter (8). The purpose of the optical splitter (8) is to extract a specific percentage of the optical power (usually around 50%) for measuring the system's power. The invention operates in exactly the same manner if an optical splitter (8) with different power extraction ratio is chosen, as designed - for example, a ratio of 60%-40%. The selection of the power extraction percentage from the splitter (8) results from the combination of the ring's losses and the gain exhibited by the Erbium- Doped Fiber (EDF) (5) when pumped by the laser (1). When the gain is balanced by the ring's losses, the operating power of the ring laser stabilizes at a specific level, which is also the power level detected by the photodiode (9). Additionally, the operating power of the laser ring can be adjusted through the choice of the length and the doping concentration of the EDF (Erbium-Doped Fiber) (5) in combination with the laser (1) pump power. The power adjustment provides the capability to compensate for potential losses due to the placement distance of the sensors from the reading device.

[0043] The remaining power within the ring after the optical splitter, passes through the coupler (4) (path G-H) and is reintroduced into the EDF (Erbium-Doped Fiber) (5). This optical wave is amplified as it travels through the EDF (5) (due to stimulated emission) and, after exiting it, is redirected by the circulator (6) back toward the sensor (13) via the optical switch (7) and the optical fiber (12) (path C-D). There, it is reflected once again and follows the same circular path (D-C~E-F-G-H) to be reintroduced into the EDF (5), as described earlier, in a continuous feedback process as typically foreseen in a ring laser topology.

[0044] Apart from the clockwise circular path described earlier, a portion of the generated optical power follows a counterclockwise (anticlockwise) path within the ring. When this counterclockwise wave reaches the circulator (6), it completely bypasses the Fiber Bragg Grating (FBG) sensor (13), thus not contributing to the selection of the laser's operating wavelength. Consequently, it does not lead to power variation due to sensor reflection wavelength shifts; it only contributes to the initial power level of the system. However, the device can operate unidirectionally if an optical isolator is inserted between the circulator (6) and the coupler (8), enforcing only the clockwise path. In this unidirectional mode, the overall operating power level of the arrangement is reduced.

[0045] The continuous successive roundtrips of the optical waves through the ring, continuously amplify the optical input power that enters the EDF (Erbium-Doped Fiber). When this power approaches the saturation level of the gain provided by the EDF, then the gain decreases due to saturation, reaching a value that fully compensates the total losses in the ring according to the theory of the optical fiber-ring laser operation. This gain corresponds to a specific input power value into the EDF, which also determines the final output power of the splitter (8), specifically for the wavelength reflected by the sensor (13). As depicted in Figure 1, the second output of the splitter (8) is connected to a photodiode (9), whose electrical circuit generates an electric voltage proportional to the optical power it receives. This electric voltage is read by an electronic microcontroller (10), which can record the measurement in a file and / or transmit it via the interface (11) and the internet (17) to a central monitoring unit for the sensor (18).

[0046] The sensor (13) is affixed to a location that monitors its elongation (e.g., on the steel reinforcement of a building or a bridge). If the sensor elongates due to the corresponding elongation of the element to which it is attached, then the reflection wavelength will change, changing accordingly the wavelength of the device it is connected to, as mentioned earlier.

[0047] If the sensor is designed such that its reflection wavelength falls within the spectral range from 1532 to 1537 nm, then according to the emission spectrum of the Erbium-Doped Fiber (EOF), the optical power has a linear relationship with the wavelength (Figure 2). As a result, the output power of the device (measured by the photodiode (9)) also exhibits a linear relationship with the wavelength reflected by the Fiber Bragg Grating (FBG) (13). Consequently, when the FBG's reflection wavelength changes due to elongation, the output power varies linearly. In other words, the device converts all changes of reflection wavelength into variations of the optical power. The photodiode (9) detects this optical power variation and converts it through its circuitry into an electrical voltage variation, which is measured by the microcontroller (10). The microcontroller then translates this into the corresponding wavelength change and, correspondingly, into a measurement of elongation or contraction, which is the ultimate purpose (Figure 3).

[0048] The ability to read multiple monitoring points is achieved using a number of similar sensors (13) and by inserting an optical switch (7) between the circulator (6) and the respective FBG sensor (13) (Figure 1). The more outputs the optical switch has, the more sensors (13) it can read. Additionally, some sensors are used to detect and compensate for any temperature changes to which all FBG sensors are sensitive. The switching between sensors is controlled by an electrical signal sent by the microcontroller (10) to the optical switch (7). The microcontroller's software provides the corresponding command to determine which sensor is being read each time.

[0049] The present invention can be used in any application that requires the reading of FBG sensors. It is particularly suitable for continuous monitoring of the structural health of small constructions (where cost is a critical parameter) and cases where estimation can be achieved with only a few monitoring points (e.g., residential buildings, bridges, etc.). The sensors of the device can be attached to beams or other structural elements to monitor their deformation. Their elongation or contraction due to deformation results in a corresponding change in the central reflection wavelength. For example, a reinforced concrete beam could elongate by approximately 2000 microstrains before failure. An FBG sensor with a central wavelength around 1534 nm could be read by the proposed system and measure elongation exceeding 1000 microstrains, as shown in Figure 3. This elongation leads to a corresponding variation in the central wavelength, which is detected by the system through changes in optical power, as depicted in Figure 3. The invention can find applications in other scientific and technological fields, such as biomedicine, wind turbines, shipbuilding, aerospace, flammable fluid and gas transportation systems, environmental measurements, and more.

[0050] Apart from detecting elongation, FBG sensors are also sensitive to temperature. Consequently, the proposed method can be similarly applied to temperature measurement, as well as humidity and pH measurement. Therefore, this invention can also be used for measuring these quantities.

[0051] The method employed by the proposed invention relies on the linear regions (power versus wavelength) in the emission spectrum of materials doped with erbium ions, such as triply ionized erbium (Er3+). However, any other material, such as ytterbium (Yb) or a combination thereof, that can function in a similar manner may also be utilized in the application of this method and harnessed by the proposed invention.

Claims

AMENDED CLAIMS received by the International Bureau on 9 January 2025AMENDED CLAIMS1. A method for reading Fiber Bragg Grating (FBG) sensors that employs a fiber ring laser topology and converts the displacement of the FBG reflection spectrum into a linear power variation, which is characterized by the fact that it is implemented with an erbium-doped active optical fiber laser with a FBG as an integral part of the laser cavity, continuously feeding back the power reflected by the FBG, where the FBG sensor (13) is inscribed to exhibit maximum reflectivity within the spectral emission range of the active doping material of the optical fiber (5), from which the optical fiber laser is constructed, in which spectral range, its emission power exhibits a linear dependence on wavelength, and is determined within the ranges from 1525 nm to 1530 nm or from 1532 nm to 1537 nm, and where when the FBG sensor (13) is positively or negatively elongated due to mechanical stress or temperature change, its reflection wavelength changes and therefore the operating wavelength of the optical fiber laser changes accordingly, since the gain of the active material of the laser depends on the wavelength, changing the operating wavelength of the laser causes a change in its operating power, which is detected by a photodiode device (9), whereas if the other parameters of the system remain constant, then any measured change in laser power is linearly related to the change in the reflection wavelength of the sensor that caused it and subsequently to the calculation of the mechanical stress applied to the sensor and / or the change in its temperature.

2. An FBG sensor interrogation device for carrying out the method ofClaim 1, characterized by the fact that16AMENDED SHEET (ARTICLE 19)it comprises FBGs which are written in one of the spectral ranges from 1525 to 1530 nm or from 1532 to 1537 nm and it consists at least of the following components:Laser diode (1) with an emission wavelength of 980 nm, not excluding other wavelengthsCurrent controller (2) of the diode laserTemperature controller (3) of the diode laserWavelength Division Multiplexing (WDM) coupler at 980 and the 1550nm range Erbium Doped optical Fiber (EDF) (5) or a combination of Erbium and Ytterbium, (Er / Yb)Optical circulator in the 1550nm range (6), alternatively optical coupler1:N optical switch in the 1550nm range (7)Splitter (8) 50% - 50% not excluding other percentages, in the 1550nm rangePhotodiode circuit for receiving optical power (9)Microcontroller for circuit control and running of measurement acquisition software (10)Interface for internet communication and remote measurement download (11)Single mode fiber (12) to connect the FBG to the optical switch (7), by the fact that the diode laser source (1) is connected to the EDF (5) and injects light to it through the optical coupler (4), generating an optical spectrum which is directed to the FBG sensor (13) which is written in the range from 1525 to 1530 nm or from 1532 to 1537 nm, through the optical circulator (6) which also has an operating wavelength range in the above spectral range, after passing through the optical switch (7) and the optical fiber (12), by the fact that the FBG sensor (13) selectively reflects only the wavelength for which it is designed, therefore if the sensor is subjected to mechanical stress, the reflected wavelength changes and returns to the circulator (6), via the optical fiber (12) and the optical switch (7), where the circulator directs it to the optical splitter (8)17AMENDED SHEET (ARTICLE 19)and by the fact that the remaining power in the ring after the optical splitter passes through the coupler (4) and is reintroduced into the EDF (5), this optical wave is amplified due to stimulated emission as it travels through the EDF (5) and after exiting the EDF, it is redirected by the circulator (6) to the sensor (13) via the optical switch (7) and the optical fiber (12) where it is reflected again and following the same cyclic path D-C-E- F-G-H is reintroduced into the EDF (5) in a continuous feedback process.

3. An FBG sensor interrogator according to Claim 2, characterized in that the splitter (8) has different output power ratios, according to the design, by selecting an output power ratio of the splitter (8) according to the total ring loss in combination with the gain exhibited by the EDF fiber (5) when pumped by the laser (1), so that when the gain is compensated by the ring losses, the ring laser reaches the steady state operating power level which is also the power level detected by the photodiode (9).

4. An FBG sensor interrogator according to Claims 2-3, characterized in that the operating power of the ring laser is adjusted by selecting the length and doping density of the EDF fiber (5) in combination with the adjustment of the laser pumping power (1).

5. An FBG sensor interrogator according to Claims 2-4, characterized in that it operates unidirectionally by the introduction into the cavity of an optical isolator between the circulator (6) and the separator (8) so as to enforce only the clockwise direction.

6. An FBG sensor interrogation device according to Claims 2-5, characterized by that it is possible to read several monitoring points with similar sensors (13) and with the introduction of an optical switch (7) between the circulator (6) and the respective FBG sensor (13).18AMENDED SHEET (ARTICLE 19)7. An FBG sensor interrogation system according to Claim 2, characterized in that it comprises: wiring of analogue electrical signals for optical power measurement (14), electrical control signal wiring of the device (15), electrical power supply of the circuits (16), connection to the Internet (17), central unit for monitoring the system (18).19AMENDED SHEET (ARTICLE 19)

Images