Optical fiber sensing system and optical signal demodulation method

Abstract

The invention relates to an optical fiber sensing system and an optical signal demodulation method. The optical fiber sensing system comprises a plurality of optical fiber sensors; a light source emitting a light signal; the optical transmission module is used for dividing the optical signal into multiple paths of first sub-signals and inputting the first sub-signals into the optical fiber sensors, and is also used for receiving multiple paths of second sub-signals returned by the optical fiber sensors and coupling the second sub-signals to the optical demodulation module; the optical demodulation module comprises a plurality of sub-demodulation units, and one sub-demodulation unit is used for demodulating one path of second sub-signal; the sub-demodulation unit comprises a first photoelectric sensor, a second photoelectric sensor with a first filter and a third photoelectric sensor with a second filter, and the filtering wavelengths of the first filter and the second filter are different. Through the design that the first filter plate and the second filter plate filter wavelengths, the measuring range of the optical fiber sensing system is expanded to the combination of the first filter plate and the second filter plate, so that the purpose of increasing the measuring range is achieved.

Description

Technical Field

[0001] The present invention relates to the field of optical transmission technology, in particular to an optical fiber sensing system and an optical signal demodulation method. Background Art

[0002] Fiber optic sensing measurement technology uses optical signals as carriers. Optical fibers serve as both sensing units and transmission media. The sensing units that have undergone changes in the optical signal will cause the optical signal to carry corresponding information. By demodulating the optical signal, changes in external physical quantities can be inferred. In fiber grating sensing equipment, wavelength demodulation accounts for the vast majority of the cost.

[0003] Traditional demodulation technologies include: spectrometer method, wavelength meter method, interference method, filter method, etc. Among them, the filter method includes tunable filter method, tunable laser method and edge filter method. The tunable filter method has high measurement accuracy and large dynamic response range but high cost. The tunable laser method is similar to the former but the light source cost is too high. In practical applications, the edge filter method has low cost, high demodulation accuracy, large demodulation range and poor stability.

[0004] However, the edge filtering scheme is suitable for general application scenarios in daily structural monitoring, but it is difficult to use in some large-scale strain monitoring. Summary of the invention

[0005] Based on this, it is necessary to provide a fiber optic sensing system and an optical signal demodulation method to address the problem of short measurement range of the edge filtering method.

[0006] In a first aspect, the present application provides a fiber optic sensing system, the fiber optic sensing system comprising:

[0007] Multiple fiber optic sensors;

[0008] A light source, the light source is used to emit a light signal;

[0009] An optical transmission module, used for dividing the optical signal into multiple first sub-signals, and inputting them into each of the optical fiber sensors respectively, and also used for receiving multiple second sub-signals returned by each of the optical fiber sensors and coupling them to the optical demodulation module;

[0010] The optical demodulation module includes a plurality of sub-demodulation units, one of which is used to demodulate one channel of the second sub-signal; the sub-demodulation unit includes a first photoelectric sensor, a second photoelectric sensor having a first filter, and a third photoelectric sensor having a second filter, wherein the first filter and the second filter have different filtering wavelengths; the second sub-signal is transmitted to the first photoelectric sensor, the second photoelectric sensor, and the third photoelectric sensor, respectively.

[0011] In one embodiment, the sub-demodulation unit includes a first beam splitter and a second beam splitter with the same inclination angle, the first beam splitter, the second beam splitter and the third photoelectric sensor are located on the incident path of the second sub-signal in sequence, the first photoelectric sensor is located on the reflection path of the second sub-signal in the first beam splitter, and the second photoelectric sensor is located on the reflection path of the second sub-signal in the second beam splitter.

[0012] In one of the embodiments, the sub-adjustment unit further includes a collimator, and the second sub-signal is incident on the first reflective sheet after passing through the collimator.

[0013] In one embodiment, the sub-demodulation unit further includes a first light-transmitting sheet, wherein the first light-transmitting sheet is disposed on a side of the first beam splitter sheet facing the second beam splitter sheet; and / or,

[0014] The sub-demodulation unit further includes a second light-transmitting sheet, and the second light-transmitting sheet is arranged on the second light-splitting sheet. In one embodiment, the splitting ratio of the first light-splitting sheet and / or the second light-splitting sheet is 20% to 70%.

[0015] In one embodiment, the first filter and the second filter are both bandpass filters, the first center wavelength of the first filter is 1530nm~1544nm, and the second center wavelength of the second filter is 1566nm~1580nm; the falling edge of the filtering curve of the first filter intersects with the rising edge of the filtering curve of the second filter, and the light source is used to emit an optical signal with a wavelength range between the first center wavelength and the second center wavelength.

[0016] In one embodiment, the light source is used to emit an optical signal with a wavelength range of X1nm~X2nm, wherein X1=M+S, X2=NS, M is the value of the first center wavelength, N is the value of the second center wavelength, and S ranges from 1 to 3.

[0017] In one embodiment, the optical transmission module includes a spectrometer and a coupling unit. The spectrometer is connected to the light source and each of the optical fiber sensors, and is used to receive the optical signal and divide the optical signal into multiple first sub-signals, which are input into each of the optical fiber sensors respectively; the coupling unit is connected to each of the optical fiber sensors and each of the sub-demodulation units, and is used to receive the multiple second sub-signals returned by each of the optical fiber sensors and couple to each of the sub-demodulation units.

[0018] In one of the embodiments, it also includes a data processing module, which can obtain the first power signal of the first photoelectric sensor, the second power signal of the second photoelectric sensor and the third power signal of the third photoelectric sensor, so that a first power ratio can be obtained according to the ratio of the second power signal to the first power signal, and a second power ratio can be obtained according to the ratio of the third power signal to the first power signal, and the central wavelength of the second sub-signal can be determined according to the larger one of the first power ratio and the second power ratio to determine the wavelength offset of the optical fiber sensor.

[0019] In a second aspect, the present application further provides an optical signal demodulation method using the optical fiber sensing system, the method comprising the following steps:

[0020] Acquire a first power signal of the first photoelectric sensor, a second power signal of the second photoelectric sensor, and a third power signal of the third photoelectric sensor;

[0021] Obtaining a first power ratio according to a ratio of the second power signal to the first power signal, and obtaining a second power ratio according to a ratio of the third power signal to the first power signal;

[0022] Compare the values ​​of the first power ratio and the second power ratio with a preset threshold range, select the comparison, and select the larger value as the target calculation object;

[0023] The wavelength offset of the optical fiber sensor is determined according to the target calculation object.

[0024] The above-mentioned optical fiber sensing system includes a second photoelectric sensor and a third photoelectric sensor. Based on the different filtering wavelengths of the first filter and the second filter, the second photoelectric sensor and the third photoelectric sensor allow different measurement ranges. Therefore, through the design of the filtering wavelengths of the first filter and the second filter, the measurement range of the optical fiber sensing system is extended to the combination of the first filter and the second filter, thereby achieving the purpose of increasing the measurement range. The optical fiber sensing system provided by the present application encapsulates a large number of passive components with transmission, coupling, splitting, and filtering functions into one, thereby improving the integration of the system, reducing the number of optical fiber fusion splicing times for multi-channel measurement in the edge filtering system, increasing the measurement range of the system, and reducing the number of system components. The above reduces costs, improves production efficiency, and facilitates the later maintenance of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a structural block diagram of a fiber optic sensing system in one embodiment.

[0026] FIG2 is a structural block diagram of a demodulation subunit in one embodiment.

[0027] FIG. 3 is a diagram showing the composition of an optical transmission module in one embodiment.

[0028] FIG. 4 is a flow chart of an optical signal demodulation method according to an embodiment.

[0029] Figure 5 FIG. 4 is a schematic diagram of the filtering range of the first filter and the second filter in one embodiment.

[0030] Figure 6 is a curve of the first power ratio and the second power ratio in one embodiment.

[0031] Description of reference numerals:

[0032] 10. Light emission module; 11. Light source; 20. Light transmission module; 21. Spectrometer; 22. Coupling unit; 30. Sensing unit module; 31. Optical fiber sensor; 40. Light demodulation module; 41. Sub-demodulation unit; 411. First photoelectric sensor; 412. Second photoelectric sensor; 4121. First filter; 413. Third photoelectric sensor; 4131. Second filter; 414. First spectrometer; 415. Second spectrometer; 416. Collimator; 417. First light-transmitting plate; 418. Second light-transmitting plate; 50. Data processing module. DETAILED DESCRIPTION

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0034] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0035] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0036] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0038] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only implementation method.

[0039] Fiber optic sensing measurement technology uses optical signals as carriers. Optical fibers serve as both sensing units and transmission media. After the optical signal is changed by the outside world, the sensing unit will cause the optical signal to carry corresponding information. The change of external physical quantities is inferred by demodulating the optical signal. In discrete sensing technology, the sensing unit of the optical fiber often uses the local etching of the optical fiber as a sensitive unit. When external physical parameters such as temperature, stress, and vibration act on this area, the intensity, phase, wavelength, polarization and other characteristic quantities of the optical signal will change. By extracting one of the characteristic quantities and establishing a connection with the change in the external environmental information, the change in physical quantity can be inverted. Fiber optic sensing technology is widely used in the field of structural monitoring due to its advantages such as lightness, high measurement accuracy, good long-term stability, and strong anti-electromagnetic interference.

[0040] For functional optical fiber sensors, different modulation types can be divided into wavelength modulation, phase modulation, intensity modulation, polarization modulation and spectrum modulation, among which wavelength modulation is the most widely used. In fiber grating sensor equipment, wavelength demodulation accounts for most of the cost, so the research on low-cost wavelength demodulation technology has extremely important application value in practice.

[0041] Some practical demodulation technologies currently include: spectrometer method, wavelength meter method, interference method, filter method, etc. The spectrometer method has a wide dynamic measurement range and high resolution, but it is expensive; the wavelength meter method has a relatively simple structure and is easy to implement, but the dynamic demodulation range is limited; the interference method uses an interferometer to convert the wavelength drift into the phase change for measurement. Its structure is too complex and its reliability is not high compared to other measurement methods, which makes it difficult to use in practical applications; the filter method includes tunable filter method, tunable laser method and edge filter method. The tunable filter method has high measurement accuracy and a large dynamic response range but high cost. The tunable laser method is similar to the former, but the light source cost is too high. The edge filter method has low cost, high demodulation accuracy, large demodulation range and poor stability in practical applications. The edge filter solution is suitable for general application scenarios in daily structural monitoring, but it is difficult to use in some large-scale strain monitoring.

[0042] Based on this, refer to FIG. 1, which shows a framework diagram of an optical fiber sensing system in an embodiment of the present invention. An optical fiber sensing system provided in an embodiment of the present invention includes a light source 11, a plurality of optical fiber sensors 31, an optical transmission module 20, and an optical demodulation module 40. The light source 11 is used to emit an optical signal, and the optical fiber sensor 31 is used to respond to changes in the external environment. The wavelength of the optical fiber sensor 31 is changed based on the changes in the external environment, and then the amount of environmental change is determined according to the amount of change in the wavelength. The optical transmission module 20 transmits the optical signal fed back by the optical fiber sensor 31 to the optical demodulation module 40, which demodulates the optical signal and calculates the amount of change in the external environment based on the amount of change in the wavelength.

[0043] Specifically, the optical transmission module 20 has two functions. One function is to divide the optical signal emitted by the light source 11 into multiple first sub-signals and transmit them to each optical fiber sensor 31. The wavelength of the first sub-signal changes due to environmental changes to obtain a second sub-signal. The second function of the optical transmission module 20 is to couple the multiple second sub-signals returned by each optical fiber sensor 31 to the optical demodulation module 40 for demodulation, thereby obtaining the wavelength change of the second sub-signal relative to the first sub-signal, and then calculating the change in the external environment.

[0044] Referring to FIG. 2 , FIG. 2 shows a block diagram of a sub-demodulation unit 41 in an embodiment. In some embodiments, the optical demodulation module 40 includes a plurality of sub-demodulation units 41 , and one sub-demodulation unit 41 is used to demodulate one second sub-signal. One sub-demodulation unit 41 includes a first photoelectric sensor 411, a second photoelectric sensor 412 having a first filter 4121, and a third photoelectric sensor 413 having a second filter 4131. The first filter 4121 and the second filter 4131 have different filtering wavelengths; the second sub-signal is transmitted to the first photoelectric sensor 411, the second photoelectric sensor 412, and the third photoelectric sensor 413, respectively. In this way, the first photoelectric sensor 411 obtains an unfiltered optical signal as a reference signal, while the second photoelectric sensor 412 and the third photoelectric sensor 413 obtain a filtered signal after filtering. The filtered signal is used as the numerator and the reference signal is used as the denominator to obtain a division result, and the division result is linearly related to the wavelength of the optical signal. Therefore, the wavelength offset fed back by the optical fiber sensor 31 can be determined by the division result, and then the change in the external environment can be determined.

[0045] The wavelength range covered by the filter determines the range of signals that can be demodulated, which directly affects the range of the fiber optic sensing system. If the operating wavelength range of the filter is narrow, the range of the system will also be smaller. However, blindly increasing the wavelength range of the filter will cause the edge of the filter to be relatively flat, which will reduce sensitivity and may not accurately detect small wavelength changes, thus affecting the measurement accuracy. At the same time, more background noise will be introduced in the longer wavelength range, resulting in a decrease in the signal-to-noise ratio. In addition, with a wider wavelength range, the transfer function of the filter may become nonlinear, affecting the accuracy and stability of the measurement. Based on the above considerations, the wavelength range of the filter should be within a reasonable range and cannot be increased indefinitely.

[0046] For scenarios where the external environment changes little, the fiber optic sensing system can determine the fiber wavelength offset based on the reference signal obtained by the first photoelectric sensor 411 and the first filtered signal obtained by the second photoelectric sensor 412; or determine the fiber wavelength offset by the reference signal obtained by the first photoelectric sensor 411 and the second filtered signal obtained by the third photoelectric sensor 413.

[0047] Since the present application includes the second photoelectric sensor 412 and the third photoelectric sensor 413, the second photoelectric sensor 412 and the third photoelectric sensor 413 allow different measurement ranges based on the different filtering wavelengths of the first filter 4121 and the second filter 4131. Therefore, through the design of filtering wavelengths of the first filter 4121 and the second filter 4131, the measurement range of the present optical fiber sensing system is extended to the combination of the first filter 4121 and the second filter 4131, thereby achieving the purpose of increasing the measurement range.

[0048] The above-mentioned fiber optic sensing system encapsulates a large number of passive devices with transmission, coupling, splitting and filtering functions into one, which improves the integration of the system, reduces the number of fiber optic fusion splicing times for multi-channel measurement in the edge filtering system, increases the measurement range of the system, reduces the number of system devices, reduces costs, improves production efficiency, and facilitates the later maintenance of the product.

[0049] Exemplarily, the light source 11 may be configured in the optical transmission module 10. Exemplarily, a plurality of optical fiber sensors 31 may be configured in the sensing unit module 30. Further, the optical fiber sensor 31 may be a wavelength feedback optical fiber sensor 31, including but not limited to using FBG (Fiber Bragg Grating) type, diffraction grating type and FP (Fabry-Perot) cavity type.

[0050] 2, in order to allow the second optical signal to simultaneously enter the first photoelectric sensor 411, the second photoelectric sensor 412, and the third photoelectric sensor 413, in some embodiments, the sub-demodulation unit 41 includes a first beam splitter 414 and a second beam splitter 415 with the same inclination angle, and the first beam splitter 414, the second beam splitter 415, and the third photoelectric sensor 413 are sequentially located on the incident path of the second sub-signal. In this way, the second sub-signal can pass through the first beam splitter 414 and the second beam splitter 415 and enter the third photoelectric sensor 413.

[0051] The first photoelectric sensor 411 is located on the reflection path of the second sub-signal of the first beam splitter 414, and the second photoelectric sensor 412 is located on the reflection path of the second sub-signal of the second beam splitter 415. Thus, when the second sub-signal passes through the first beam splitter 414, part of it passes through the first beam splitter 414, and part of it is reflected to the first photoelectric sensor 411. And part of the second sub-signal that passes through the first beam splitter 414 passes through the second beam splitter 415 and enters the third photoelectric sensor 413, and part of it is reflected to the second photoelectric sensor 412.

[0052] Through the above design, the second sub-signal can enter the first photoelectric sensor 411, the second photoelectric sensor 412 and the third photoelectric sensor 413 respectively. In some embodiments, the sub-adjustment unit further includes a collimator 416, and the second sub-signal is incident on the first reflective sheet after passing through the collimator 416. The collimator 416 reduces the divergence and distortion of the light beam by accurately aligning the incident direction of the second sub-signal, thereby ensuring the uniformity and consistency of the light during the transmission process, thereby improving the resolution and contrast of the image.

[0053] In some embodiments, the sub-demodulation unit 41 further includes a first light-transmitting sheet 417, which is disposed on a side of the first beam splitter 414 facing the second beam splitter 415. In other embodiments, the sub-demodulation unit 41 further includes a second light-transmitting sheet 418, which is disposed on a side of the second beam splitter 415 facing the third photosensor 413.

[0054] The first light-transmitting sheet 417 can improve the transmittance of the second sub-signal of the first beam splitter 414, increase the amount of light entering the second beam splitter 415, avoid interference from stray light, and improve the quality of light received by the subsequent second photoelectric sensor 412 and the third photoelectric sensor 413. The second light-transmitting sheet 418 can improve the transmittance of the second sub-signal of the first beam splitter 414, and improve the quality of light entering the third photoelectric sensor 413.

[0055] In some embodiments, the splitting ratio of the first beam splitter 414 and / or the second beam splitter 415 is 20% to 70%. Within this splitting ratio range, the first beam splitter 414 can ensure that the amount of light reflected to the first photoelectric sensor 411 and the amount of light transmitted to the second beam splitter 415 can meet the detection requirements, and the splitting ratio of the second beam splitter 415 can ensure that the amount of light reflected to the second photoelectric sensor 412 and the amount of light transmitted to the third photoelectric sensor 413 can meet the detection requirements.

[0056] The first filter 4121 and the second filter 4131 are both bandpass filters, the first center wavelength of the first filter 4121 is 1530nm~1544nm, and the second center wavelength of the second filter 4131 is 1566nm~1580nm. Exemplarily, the first center wavelength can be but not limited to 1531nm, 1532nm, 1533nm, 1534nm, 1535nm, 1536nm, 1537nm, 1538nm, 1539nm, 1540nm, 1541nm, 1542nm, 1543nm or 1544nm, etc. The second center wavelength may be, but is not limited to, 1566 nm, 1567 nm, 1568 nm, 1569 nm, 1570 nm, 1571 nm, 1572 nm, 1573 nm, 1574 nm, 1575 nm, 1576 nm, 1577 nm, 1578 nm, 1579 nm or 1580 nm, etc.

[0057] The falling edge of the filtering curve of the first filter intersects with the rising edge of the filtering curve of the second filter, and the light source 11 is used to emit an optical signal with a wavelength range between the first central wavelength and the second central wavelength. In some embodiments, the light source 11 is a C-band or L-band light source 11. Exemplarily, the light source 11 can be a C / L-band broadband light source 11, including but not limited to ASE (Amplified Spontaneous Emission, amplified spontaneous emission light source 11), SLED (Super Luminescent Diode, super luminescent diode) light source 11, etc.

[0058] See also Figure 5 , Figure 5 A schematic diagram of the filtering curves of the first filter 4121 and the second filter 4131 in an embodiment is shown, and the first filter 4121 and the second filter 4131 are both Gaussian filters. The central wavelength of the first filter 4121 is 1541nm±1nm, and the half-height full width is 20nm±1.5nm; the central wavelength of the second filter 4131 is 1573±1nm, and the half-height full width is 20nm±1.5nm. The first filter 4121 has a falling edge from the first central wavelength to the direction of increasing wavelength, and the second filter 4131 has a rising edge from the second central wavelength to the direction of decreasing wavelength. The falling edge of the first filter 4121 and the rising edge of the second filter 4131 intersect. In this way, when the light signal emitted by the light source 11 is between the first central wavelength and the second central wavelength, the measurement range is continuous, and the range can be expanded according to the first filter 4121 and the second filter 4131.

[0059] The light source 11 is used to emit an optical signal with a wavelength range of X1nm~X2nm, wherein X1=M+S, X2=NS, M is the value of the first center wavelength, N is the value of the second center wavelength, and S is in the range of 1~3. Exemplarily, the value of S can be 1, 2 or 3, etc. In this way, X1 is directly separated from the first center wavelength by a certain interval, and X2 is also directly separated from the first center wavelength by a certain interval, thereby avoiding the difficult fitting area.

[0060] Exemplarily, the center wavelength of the first filter is 1541nm±1nm, and the half-maximum full width is 20nm±1.5nm; the center wavelength of the second filter is 1575nm±1nm, and the half-maximum full width is 20nm±1.5nm, and the filtering curves of the first filter and the second filter intersect at 1558nm. The light source 11 is used to emit a light signal with a wavelength range of 1544nm~1572nm, that is, the value of X1 is 1544, and the value of X2 is 1572.

[0061] Since the area near the central wavelength is relatively smooth (about 3nm) and the fitting degree is not good, the maximum difference of the central wavelengths of the two filters is set to 32nm, that is, the difference between 1542nm and 1574nm, so that the area range with good fitting of the falling edge and the rising edge can be selected to avoid the smooth area of ​​the central wavelength, so 36nm is determined, wherein 36nm includes the inconvenient fitting area of ​​14nm (1544nm~1558nm) of the falling edge on the right side of the first filter 4121 + 14nm (1558nm~1572nm) of the rising edge on the left side of the second filter 4131, 2nm (1542nm~1544nm) of the falling edge of the first filter and 2nm (1572nm~1574nm) of the rising edge of the second filter.

[0062] Referring to FIG. 3 , FIG. 3 shows that in some embodiments, the optical transmission module 20 includes a spectrometer 21 and a coupling unit 22. The spectrometer 21 is connected to the light source 11 and each optical fiber sensor 31, and is used to receive an optical signal and divide the optical signal into multiple first sub-signals, and respectively input them into each optical fiber sensor 31; the coupling unit 22 is connected to each optical fiber sensor 31 and each sub-demodulation unit 41, and is used to receive multiple second sub-signals returned by each optical fiber sensor 31 and couple them to each sub-demodulation unit 41.

[0063] Exemplarily, the optical transmission module 20 is composed of a 1*N*2 packaging module, wherein the 1*N packaging module has a splitting function, which splits the optical signal emitted by the power supply into N first sub-signals, and the N*2N packaging module mainly has a coupling function, which can couple the second sub-signal fed back by the optical fiber sensor 31 to the optical demodulation module 40.

[0064] It can be understood that the optical demodulation module 40 can also perform data processing, and process the power signals obtained by photoelectric conversion of the first photoelectric sensor 411, the second photoelectric sensor 412, and the third photoelectric sensor 413. In other embodiments, a data processing module 50 is also included for processing the power signal. The data processing module 50 is electrically connected to the first photoelectric sensor 411, the second photoelectric sensor 412, and the third photoelectric sensor 413, and can obtain the first power signal of the first photoelectric sensor 411, the second power signal of the second photoelectric sensor 412, and the third power signal of the third photoelectric sensor 413, so that the first power ratio can be obtained according to the ratio of the second power signal to the first power signal, the second power ratio can be obtained according to the ratio of the third power signal to the first power signal, and the central wavelength of the second sub-signal can be determined according to the larger one of the first power ratio and the second power ratio to determine the wavelength offset of the optical fiber sensor.

[0065] After the data processing module 50 obtains the first power signal, the second power signal and the third power signal, the first power signal is used as the reference signal, and the second power signal and the third power signal are used as the filtering signal for division calculation. Exemplarily, the ratio K1 of the second power signal to the first power signal is used as the first power ratio, and the ratio K2 of the third power signal to the first power signal is used as the second power ratio. By judging the size of the K1 and K2 values, it is determined which value of K1 and K2 is within a reasonable range, and then a reasonable value is selected as the calculation object to calculate the current wavelength, so as to compare the wavelength of the light signal emitted by the light source 11 with the calculated wavelength, determine the wavelength offset of the optical fiber sensor 31, and further determine the change in the external environment. In this way, K1 and K2 are equivalent to expanding the calculation range of the wavelength.

[0066] Specifically, the K value can be calibrated first. During the calibration, at a constant temperature, a tunable filter is used to send several central wavelengths (simulating the central wavelength of FBG). After the light of different central wavelengths passes through the first beam splitter 414, a proportion of the light reaches the first photoelectric sensor 411 to realize photoelectric conversion and is collected by the circuit to generate a first power signal. The remaining light is reflected by the second beam splitter 415 and passes through the first filter 4121 to reach the second photoelectric sensor 412, generating a second power signal. Part of the light passes through the second beam splitter 415 and the second filter 4131 to reach the third photoelectric sensor 413, generating a third power signal. The value of the first power K1 is obtained by comparing the second power signal to the first power signal, and the value of the second power ratio K2 is obtained by comparing the third power signal to the first power signal. In the traditional tunable filtering method, only one filter is used, that is, only the filtering curve of K1 is obtained, and K1 is used to calculate the wavelength, resulting in a short range.

[0067] In this embodiment, there are two filters, and the transmittance of the filters to light of different central wavelengths is different. For example, see Figure 6 (When the central wavelength of the second optical signal is between 1544nm and 1558nm, the power of the second power signal generated by the second photoelectric sensor 412 gradually decreases as the central wavelength increases (the value of K1 gradually decreases from 1 to 0). When the central wavelength of the second optical signal is between 1558nm and 1572nm, the power of the third power signal generated by the third photoelectric sensor 413 gradually increases as the central wavelength increases (at this time, the second power signal generated by the second photoelectric sensor 412 is close to 0, and the value of K2 gradually increases from 0 to 1). This is due to the selective transmittance of the falling edge and the rising edge of the first filter 4121 and the second filter 4131 to the central wavelength. Therefore, when the temperature is constant, calibration can be performed from 1544nm to 1572nm, and different temperatures can be calibrated according to the actual use environment. Then, the temperature, wavelength, and K value are fitted to establish a mapping relationship table. The temperature can be read using a temperature sensor, and the K value can be obtained through the power ratio, and the wavelength can be calculated.

[0068] Therefore, when the wavelength gradually increases between 1544nm and 1558nm, K1 gradually decreases from 1 to 0 and K2 is close to 0 at this time. Similarly, when the wavelength gradually increases between 1558nm and 1572nm, K2 gradually increases from 0 to 1 and K1 is close to 0 at this time. Therefore, by comparing the values ​​of K1 and K2, the larger value is selected, and then the wavelength is inverted and calculated, thereby achieving a large range measurement. In the second aspect, referring to Figure 4, the present application also provides a method for demodulating optical signals of an optical fiber sensing system, the method comprising the following steps:

[0069] S402 , acquiring a first power signal of the first photosensor 411 , a second power signal of the second photosensor 412 , and a third power signal of the third photosensor 413 .

[0070] S404: Obtain a first power ratio according to a ratio of the second power signal to the first power signal, and obtain a second power ratio according to a ratio of the third power signal to the first power signal.

[0071] S406, comparing the values ​​of the first power ratio and the second power ratio, and selecting the larger value as the target calculation object.

[0072] S408, determining the wavelength offset of the optical fiber sensor 31 according to the target calculation object.

[0073] In the above optical signal demodulation method, the first power ratio is obtained according to the ratio of the second power signal to the first power signal, the second power ratio is obtained according to the ratio of the third power signal to the first power signal, and the wavelength offset of the optical fiber sensor is calculated according to the larger one of the two as the target calculation object. Compared with the solution of using only one filter in the traditional technology, the demodulation method provided in this embodiment can expand the measurement range to the combination of the first filter and the second filter, thereby achieving the purpose of increasing the measurement range.

[0074] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0075] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A fiber optic sensing system, characterized in that: The optical fiber sensing system comprises: Multiple fiber optic sensors; A light source, the light source is used to emit a light signal; An optical transmission module, used for dividing the optical signal into multiple first sub-signals, and inputting them into each of the optical fiber sensors respectively, and also used for receiving multiple second sub-signals returned by each of the optical fiber sensors and coupling them to the optical demodulation module; The optical demodulation module includes a plurality of sub-demodulation units, one of which is used to demodulate one channel of the second sub-signal; the sub-demodulation unit includes a first photoelectric sensor, a second photoelectric sensor having a first filter, and a third photoelectric sensor having a second filter, wherein the first filter and the second filter have different filtering wavelengths; the second sub-signal is transmitted to the first photoelectric sensor, the second photoelectric sensor, and the third photoelectric sensor, respectively.

2. The optical fiber sensing system according to claim 1, characterized in that: The sub-demodulation unit includes a first beam splitter and a second beam splitter with the same inclination angle. The first beam splitter, the second beam splitter and the third photoelectric sensor are located on the incident path of the second sub-signal in sequence. The first photoelectric sensor is located on the reflection path of the second sub-signal in the first beam splitter, and the second photoelectric sensor is located on the reflection path of the second sub-signal in the second beam splitter.

3. The optical fiber sensing system according to claim 2, characterized in that: The sub-demodulation unit further includes a collimator, and the second sub-signal is incident on the first beam splitter after passing through the collimator.

4. The optical fiber sensing system according to claim 2, characterized in that: The sub-demodulation unit further includes a first light-transmitting sheet, wherein the first light-transmitting sheet is disposed on a side of the first beam splitter sheet facing the second beam splitter sheet; and / or, The sub-demodulation unit further includes a second light-transmitting sheet, and the second light-transmitting sheet is disposed on a side of the second beam splitter sheet facing the third photoelectric sensor.

5. The optical fiber sensing system according to claim 2, characterized in that: The splitting ratio of the first beam splitter and / or the second beam splitter is 20% to 70%.

6. The optical fiber sensing system according to claim 1, characterized in that: The first filter and the second filter are both bandpass filters, the first center wavelength of the first filter is 1530nm~1544nm, and the second center wavelength of the second filter is 1566nm~1580nm; the falling edge of the filtering curve of the first filter intersects with the rising edge of the filtering curve of the second filter, and the light source is used to emit an optical signal with a wavelength range between the first center wavelength and the second center wavelength.

7. The optical fiber sensing system according to claim 6, characterized in that: The light source is used to emit an optical signal with a wavelength range of X1nm~X2nm, wherein X1=M+S, X2=NS, M is the value of the first center wavelength, N is the value of the second center wavelength, and S ranges from 1 to 3.

8. The optical fiber sensing system according to claim 1, characterized in that: The optical transmission module includes a spectrometer and a coupling unit, wherein the spectrometer is connected to the light source and each of the optical fiber sensors, and is used to receive the optical signal and divide the optical signal into multiple first sub-signals, which are input into each of the optical fiber sensors respectively; The coupling unit is connected to each of the optical fiber sensors and each of the sub-demodulation units, and is used for receiving the multi-path second sub-signals returned by each of the optical fiber sensors and coupling them to each of the sub-demodulation units.

9. The optical fiber sensing system according to claim 1, characterized in that: It also includes a data processing module, which can obtain the first power signal of the first photoelectric sensor, the second power signal of the second photoelectric sensor and the third power signal of the third photoelectric sensor, so that a first power ratio can be obtained according to the ratio of the second power signal to the first power signal, a second power ratio can be obtained according to the ratio of the third power signal to the first power signal, and a central wavelength of the second sub-signal can be determined according to the larger one of the first power ratio and the second power ratio to determine the wavelength offset of the optical fiber sensor.

10. An optical signal demodulation method using the optical fiber sensing system according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: Acquire a first power signal of the first photoelectric sensor, a second power signal of the second photoelectric sensor, and a third power signal of the third photoelectric sensor; Obtaining a first power ratio according to a ratio of the second power signal to the first power signal, and obtaining a second power ratio according to a ratio of the third power signal to the first power signal; Compare the values ​​of the first power ratio and the second power ratio, and select the larger value as the target calculation object; The wavelength offset of the optical fiber sensor is determined according to the target calculation object.

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