Optical sensing system

Abstract

An optical sensing system is disclosed that includes an optical fiber, a light source, a first interrogator, and a second interrogator. The optical fiber includes one or more optical sensors. The light source is disposed at a first end of the optical fiber and is configured to direct light to the one or more optical sensors. The first interrogator is disposed at the first end of the optical fiber. The second interrogator is disposed at an opposite second end of the optical fiber. The first interrogator is configured to receive reflected light from the one or more optical sensors, and the second interrogator is configured to receive transmitted light from the one or more optical sensors.

Description

Technical Field

[0001] This invention relates to an optical sensing system for sensing strain or temperature, and to vehicles, such as aircraft, that include the optical sensing system. Background Technology

[0002] The aircraft may include fiber Bragg sensors for sensing strain to determine loads and torques for safety-critical applications. Summary of the Invention

[0003] A first aspect of the present invention provides an optical sensing system comprising: an optical fiber including one or more optical sensors; a light source disposed at a first end of the optical fiber, wherein the light source is configured to direct light to one or more optical sensors; a first interrogator disposed at the first end of the optical fiber; and a second interrogator disposed at the opposite second end of the optical fiber, wherein the first interrogator is configured to receive reflected light from one or more optical sensors, and the second interrogator is configured to receive transmitted light from one or more optical sensors.

[0004] Optionally, one or more optical sensors are configured to sense changes in strain or temperature along the optical fiber.

[0005] Optionally, the first interrogator and the second interrogator are configured to analyze light received from one or more optical sensors to determine changes in strain or temperature along the optical fiber.

[0006] Optionally, the optical sensing system includes a comparison unit configured to compare strain or temperature determined by a first interrogator and a second interrogator.

[0007] Optionally, the optical sensing system includes another light source located at a second end of the optical fiber, which is configured to direct light to one or more optical sensors in the event of a failure of the light source.

[0008] Optionally, one or more optical sensors are fiber Bragg grating sensors.

[0009] Optionally, the optical fiber includes at least two optical sensors configured to operate at two different frequency ranges.

[0010] Optionally, the first interrogator and the second interrogator are the same interrogator, each of which is configured to operate in a different operating mode.

[0011] Alternatively, optical fibers may be embedded in or attached to safety-critical systems of the aircraft.

[0012] A second aspect of the invention provides a method for sensing strain or temperature, the method comprising: directing light to one or more optical sensors, the one or more optical sensors being included in an optical fiber; receiving transmitted light from one or more optical sensors at a first interrogator located at one end of the optical fiber; and receiving reflected light from one or more optical sensors at a second interrogator located at the other end of the optical fiber.

[0013] Optionally, one or more optical sensors are configured to sense changes in strain or temperature along the optical fiber.

[0014] Optionally, the method includes analyzing light received from one or more optical sensors by each of the first interrogator and the second interrogator, and determining changes in strain or temperature along the optical fiber.

[0015] Optionally, the method includes comparing the strain or temperature determined by each of the first interrogator and the second interrogator.

[0016] Optionally, the method includes: setting a light source at one end of an optical fiber and setting another light source at the opposite end of the optical fiber, using the light source to direct light to one or more optical sensors, and using the other light source to direct light to one or more optical sensors in the event of a failure of the light source.

[0017] Optionally, the method includes: setting a light source at one end of an optical fiber and setting another light source at the opposite end of the optical fiber, using the light source to guide light to one or more optical sensors, and using the light source or the other light source to guide light to one or more optical sensors.

[0018] Optionally, one or more optical sensors are fiber Bragg grating sensors.

[0019] Optionally, the optical fiber includes at least two optical sensors configured to operate at two different frequency ranges.

[0020] Optionally, the first interrogator and the second interrogator are the same interrogator, each of which is configured to operate in a different operating mode.

[0021] Alternatively, optical fibers may be embedded in or attached to safety-critical systems of the aircraft.

[0022] A third aspect of the invention provides an aircraft that includes the system of the first aspect.

[0023] Optionally, the system senses changes in strain or temperature of aircraft components. Attached Figure Description

[0024] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0025] Figure 1 A schematic diagram of an optical sensing system according to an example is shown;

[0026] Figure 2 This is a flowchart illustrating an example of a method for sensing strain or temperature; and

[0027] Figure 3 This is a view of an aircraft including an optical sensing system, based on an example. Detailed Implementation

[0028] Reference Figure 1 The diagram shows a schematic of an optical sensing system 100 according to an example. The optical sensing system 100 includes an optical fiber 130, a light source 120, a first interrogator 110a, and a second interrogator 110b.

[0029] Optical fiber 130 includes optical sensor 140. In this example, the optical sensor is a fiber Bragg grating (FBG) sensor, which includes a periodic variation of the refractive index of the core of optical fiber 130 along a segment of the length of optical fiber 130. In other examples, optical sensor 140 may be a distributed sensor (e.g., operating based on the principles of Rayleigh, Brillouin, or Raman scattering), a long-period grating sensor, or a tilted grating sensor.

[0030] The wavelength of the light band reflected from the optical sensor 140 depends on the strain of the optical fiber 130 in which the optical sensor is located and / or the temperature experienced by the optical sensor. FBG sensors are advantageous because they are lightweight and the spacing between FBG elements can be less than 1 mm. The FBG sensors are directly etched into the core of the optical fiber 130. Depending on the application, the optical fiber 130 may include multiple optical sensors. For example, the optical fiber 130 may include two optical sensors 140. Each of the two optical sensors can be configured to operate at different frequency ranges. Alternatively, the optical fiber 130 may include multiple optical sensors forming a continuous grating. Thus, a large number of sensing points can be located in a small area. The optical fiber 130 may include a large number of optical sensors, such as more than 1000 FBG sensors. Alternatively, the optical fiber 130 may include a small number of optical sensors, such as 10 FBG sensors.

[0031] Optical fiber 130 can be embedded in or attached to structures such as safety-critical systems in aircraft. Optical sensor 140 is sensitive to changes in strain and / or temperature of the structure. The strain and / or temperature of the structure are determined by analyzing the optical properties of optical sensor 140.

[0032] When a mechanical force is applied to the optical fiber 130, the optical properties of the optical sensor 140 change. Specifically, if the optical sensor 140 is an FBG sensor, the grating spacing of the FBG sensor changes when a mechanical force is applied. Therefore, the emission wavelength of the FBG sensor changes. For example, if compression is applied to the FBG sensor, the grating spacing decreases, causing a blue shift in wavelength. Conversely, if tension is applied to the FBG sensor, the grating spacing increases, causing a red shift in wavelength. The optical properties of the optical sensor 140 can also change when the temperature of the optical fiber 130 changes. Specifically, a change in temperature can cause a change in the refractive index of the optical sensor. In some cases, temperature changes in the optical fiber 130 can additionally or alternatively cause the optical sensor to thermally expand or contract.

[0033] A light source 120 is positioned at the first end of an optical fiber 130 and configured to direct light toward an optical sensor 140. For example, a first interrogator 110a may include the light source 120. The light source 120 may be a tunable laser. In another example, the light source 120 may be a broadband light source or a broadband light source with a tunable narrowband filter.

[0034] A first interrogator 110a is positioned at a first end of optical fiber 130, while a second interrogator 110b is positioned at the opposite second end of optical fiber 130. The first interrogator 110a is configured to receive reflected light from optical sensor 140, and the second interrogator 110b is configured to receive transmitted light from optical sensor 140. Each interrogator 110a, 110b is configured to determine the strain and / or temperature at optical sensor 140 based on the received light. Specifically, the first interrogator 110a is configured to determine the strain and / or temperature at optical sensor 140 based on the received reflected light, and the second interrogator 110b is configured to determine the strain and / or temperature at optical sensor 140 based on the received transmitted light. The optical characteristics of optical sensor 140 can be represented as a spectrum. For example, if optical sensor 140 is an FBG sensor, the optical characteristics can represent the pattern or spacing of the grating of the FBG sensor. In use, the optical sensor receives light from a light source 120 that emits the full wavelength spectrum. Light passes through optical fiber 130 and reaches optical sensor 140. The properties of the light are modified by the optical sensor, and a spectrum is obtained. The properties of the light can be, for example, the spectrum of wavelengths. The strain and / or temperature determined by interrogators 110a and 110b can be used to determine the behavior or properties of the structure to which optical fiber 130 is attached. For example, strain can be used to determine the load or torque for safety-critical applications of the structure.

[0035] In summary, each interrogator 110a, 110b includes at least one photometer and is configured to determine the strain and / or temperature of the structure to which the optical fiber 130 is attached based on the light received from the optical sensor 140 at the photometer. The photometer may be, for example, a wavelength meter, a photodetector, or a photodiode such as an avalanche photodiode or a PIN diode.

[0036] Interrogator 110a may include a primary beam splitter, multiple secondary beam splitters, a light source 120, a processor, multiple photometers, and an analog-to-digital converter. The processor may be communicatively connected to the photometers.

[0037] Light source 120 can be arranged to output light to a primary beam splitter. The primary beam splitter splits the light received from light source 120 into two parts, which are then fed to a first-stage beam splitter and a second-stage beam splitter, respectively. The portion of light received from the primary beam splitter is transmitted from the first-stage beam splitter through an optical sensor 140. The reflected light from the optical sensor 140 returns through the first-stage beam splitter to a first photometer, and the reflected light from the optical sensor 140 returns through the second-stage beam splitter to a second photometer.

[0038] In embodiments where the light source is a broadband light source, the photometer, or each photometer, may be a wavelength meter configured to measure the wavelength of light reflected from the optical sensor 140. The processor processes the wavelength measured by the photometer and converts the measured wavelength (e.g., via calibration) into mechanical force or thermal energy applied to the sensor.

[0039] In embodiments where light source 120 is a tunable narrowband light source (e.g., a tunable laser in this embodiment), the photometer, or each photometer, can be a photodetector or a photodiode such as an avalanche photodiode or a PIN diode, configured to measure the intensity of light reflected from optical sensor 140. An analog-to-digital converter is arranged to convert the analog photodiode signal into a digital signal, which is then provided to a processor. In this example, the processor is arranged to control the tunable laser to continuously emit light of different wavelengths while monitoring the light intensity signal received from the photodiode. Therefore, the processor can determine for which emission wavelength the highest intensity of reflected light was detected, and thereby determine the wavelength of light most reflected by the optical sensor at that point in time. The processor can then convert the determined wavelength (e.g., through calibration) into a mechanical force or thermal energy applied to the sensor.

[0040] It should be understood that although two secondary beam splitters and two associated photometers are described in the above example, in other examples, any number of beam splitters and associated photometers may exist. For example, depending on the number of optical sensors required, there may be a pair of secondary beam splitters and an associated photometer for each optical sensor. In some examples, as mentioned above, only one photometer and an associated secondary beam splitter may exist for all optical sensors.

[0041] The first interrogator 110a and the second interrogator 110b can be the same interrogator, each configured to operate in a different operating mode. In this example, the first interrogator 110a is configured to operate in a mode that detects and analyzes reflected light, while the second interrogator 110b is configured to operate in a mode that detects and analyzes transmitted light. The second interrogator 110b may include another light source that is turned off. Alternatively, the light source of the first interrogator 110a and the other light source of the second interrogator 110b can operate alternately. In this configuration, one of the interrogators continues to detect reflected light, while the other interrogator detects transmitted light. Then, each of the interrogators 110a and 110b alternates between reflected and transmitted light depending on which light source is turned on. Light source 120 and the other light source can be the same. Additionally or alternatively, in the event of a failure of light source 120, the other light source can be used to replace light source 140. In this way, if the optical sensing system 100 is part of a safety-critical application for the aircraft, common-mode failures can be avoided because if one of the light sources fails, the other light source can be used as a backup light source.

[0042] Similarly, in the event of a failure in either the first interrogator 110a or the second interrogator 110b, the other interrogator can continue to measure the strain and / or temperature of the optical fiber 130, thus preventing common-mode failure in safety-critical applications. Furthermore, as described above, having one of the two interrogators 110a, 110b analyze reflected light while the other detects transmitted light prevents common-mode failure. In effect, operating the first interrogator 100a and the second interrogator 110b in two different modes provides a simple way to obtain two different measurement results.

[0043] The optical sensing system 100 may include a comparison unit 150 configured to compare strain or temperature results determined by a first interrogator 110a and a second interrogator 110b. The first interrogator 110a and the second interrogator 110b may be connected to the comparison unit 150, which may be, for example, a computer, and receives the analysis results from each of the first interrogator 110a and the second interrogator 110b. If a difference exists between the results from the first interrogator 110a and the second interrogator 110b, the comparison unit may be restarted. Alternatively or additionally, the first interrogator 110a and the second interrogator 110b may be restarted. If a difference persists between the results after restarting, the system 100 may record or indicate a fault or failure. In another example, each of the first interrogator 110a and the second interrogator 110b may be connected to another comparison unit, which again compares the analysis results of each of the first interrogator 110a and the second interrogator 110b. If one of the comparison units fails, providing a pair of comparison units can provide a degree of redundancy.

[0044] Reference Figure 2 The diagram shows a flowchart of a method 200 for sensing strain or temperature according to an example. This method can be implemented using the optical sensing system 100 described above.

[0045] Method 200 includes, at a first block 202, directing light to one or more optical sensors 140, which are included in optical fibers 130. Each optical sensor may be an FBG sensor. Additionally or alternatively, different optical sensors may have different optical characteristics. For example, different optical sensors may operate at different frequency ranges (i.e., have different frequency responses). Optical fibers 130 may be embedded in or attached to safety-critical systems such as landing gear, braking systems, engine control systems, etc., to sense strain applied to the optical fibers 130 by the safety-critical system or the temperature of the safety-critical system.

[0046] Light can be directed from light source 120 to optical sensor 140. Alternatively, if the method is implemented in a safety-critical application, light can be directed from two light sources to optical sensor 140, each operating alternately for a predetermined time. For example, one light source can be positioned at one end of optical fiber 130, while another light source is positioned at the opposite end of optical fiber 130. In another example, light can be directed to optical sensor 140 using a light source positioned at one end of optical fiber 130, and another light source can be used to direct light to one optical sensor in the event of a light source failure. Thus, one of the two light sources can be used as a backup light source.

[0047] Method 200 further includes receiving transmitted light from optical sensor 140 at a first interrogator 110a located at one end of optical fiber 130 at a second block 204, and receiving reflected light from optical sensor 140 at a second interrogator 110b located at the other end of optical fiber 130 at a third block 206.

[0048] For example, the first interrogator 110a and the second interrogator 110b can be the same, but each interrogator operates in a different mode. In particular, the first interrogator 110a can operate in a mode that enables the analysis of the received transmitted light, and the second interrogator 110b can operate in a mode that enables the analysis of the received reflected light.

[0049] In the example, the first interrogator 110a and the second interrogator 110b receive transmitted light and reflected light, respectively, from the optical sensor 140. Each interrogator 110a, 110b analyzes the light received from the optical sensor and determines the strain and / or temperature applied to the optical fiber 130 based on the received light. For example, the first interrogator 110a and the second interrogator 110b can analyze the wavelength spectrum representing the characteristics of the optical sensor 140.

[0050] Method 200 may include an additional step of receiving strain or temperature results determined by each of the first interrogator 110a and the second interrogator 110b at a comparison unit and comparing the two results. In the event of a difference between the two results, method 200 may include an additional step of shutting down or restarting the comparison unit and / or one or both of the first interrogator 110a and the second interrogator 110b.

[0051] Figure 3 This is a view of an aircraft 1000 including an optical sensing system 100, based on an example. The aircraft 1000 may include any of the optical systems 100 described above.

[0052] Aircraft 1000 may include one or more optical sensing systems 100, each having optical fibers 130 attached to a safety-critical application. For example, the optical fibers 130 may be attached to the aircraft 1000's braking system, landing gear control system, engine control system, or fuel system. Each optical sensing system 100 may be used to sense strain or temperature in a safety-critical system of aircraft 1000. For example, one optical sensing system 100 may be used to sense strain applied by the aircraft 1000's wing load mitigation system.

[0053] The optical sensing system 100 described herein provides a means for a failure condition to occur only when at least two failures occur in the system. Specifically, the optical sensing system 100 described herein prevents common-mode failures in safety-critical systems. Furthermore, other advantages include limiting the necessary hardware development while ensuring safety. For example, as described above, two identical interrogators can be used, each operating in a different mode. Similarly, two identical light sources can be used, one to replace the other in case of failure, or each light source can be used alternately. One interrogator receives reflected light, while the other receives transmitted light. Furthermore, each interrogator can alternate between receiving reflected light and receiving transmitted light. Thus, in the event of damage or cut of the optical fiber, reflected light can continue to be received at one interrogator. Additionally, the optical fiber 130 may include optical sensors 140 operating at different frequencies. If one optical sensor fails, the other can continue to operate. Therefore, this application provides a simple way to obtain the redundancy necessary for safety-critical applications.

[0054] Although some embodiments of the invention have been described in the context of use within aircraft, it should be understood that the invention is applicable in other applications, including transportation vehicles other than aircraft, such as spacecraft, automobiles, rail vehicles, and watercraft.

[0055] The above embodiments should be understood as illustrative examples of the present invention. It should be understood that any feature described with respect to any embodiment can be used alone or in combination with other described features, and can also be used in combination with one or more features of any other embodiment, or in any combination of any other embodiment. Furthermore, equivalents and modifications not described above may be employed without departing from the scope of the invention as defined by the appended claims.

[0056] It should be noted that, unless otherwise explicitly stated, the term “or” as used herein should be interpreted as “and / or”.

Claims

1. An optical sensing system, comprising: Optical fibers, which include one or more optical sensors; A light source is placed at the first end of the optical fiber, wherein the light source is configured to direct light to the one or more optical sensors; A first interrogator is positioned at the first end of the optical fiber; and A second interrogator is positioned at the opposite second end of the optical fiber. The first interrogator is configured to receive reflected light from the one or more optical sensors, and the second interrogator is configured to receive transmitted light from the one or more optical sensors. The first interrogator and the second interrogator are configured to analyze light received from the one or more optical sensors to determine changes in strain or temperature along the optical fiber, and The optical sensing system further includes a comparison unit configured to compare strain or temperature determined by the first interrogator and the second interrogator.

2. The optical sensing system according to claim 1, wherein, The one or more optical sensors are configured to sense changes in strain or temperature along the optical fiber.

3. The optical sensing system according to any one of the preceding claims, wherein, The optical sensing system includes another light source located at a second end of the optical fiber and configured to direct light to the one or more optical sensors in the event of a failure of the light source.

4. The optical sensing system according to any one of the preceding claims, wherein, The one or more optical sensors are fiber Bragg grating sensors.

5. The optical sensing system according to any one of the preceding claims, wherein, The optical fiber includes at least two optical sensors configured to operate at two different frequency ranges.

6. The optical sensing system according to any one of the preceding claims, wherein, The first interrogator and the second interrogator are the same interrogator, and each interrogator is configured to operate in a different operating mode.

7. The optical sensing system according to any one of the preceding claims, wherein, The optical fibers are embedded in or attached to the safety-critical systems of the aircraft.

8. A method for sensing strain or temperature, comprising: Directing light to one or more optical sensors, wherein the one or more optical sensors are included in optical fibers; Transmitted light from one or more optical sensors is received at a first interrogator, which is located at one end of the optical fiber; The second interrogator receives reflected light from one or more optical sensors and is located at the other end of the optical fiber. Each of the first interrogator and the second interrogator analyzes the light received from the one or more optical sensors and determines the strain or temperature change along the optical fiber; as well as The strain or temperature determined by each of the first interrogator and the second interrogator will be compared.

9. The method according to claim 8, wherein, The one or more optical sensors are configured to sense changes in strain or temperature along the optical fiber.

10. The method according to claim 8 or 9, wherein, The method includes: setting a light source at one end of the optical fiber and setting another light source at the opposite end of the optical fiber, using the light source to guide light to one or more optical sensors, and using the other light source to guide light to one or more optical sensors in the event of a failure of the light source.

11. The method according to any one of claims 8 to 9, wherein, The method includes: setting a light source at one end of the optical fiber and setting another light source at the opposite end of the optical fiber; using the light source to guide light to one or more optical sensors; and using the light source or the other light source to guide light to one or more optical sensors.

12. The method according to any one of claims 8 to 11, wherein, The one or more optical sensors are fiber Bragg grating sensors.

13. The method according to any one of claims 8 to 12, wherein, The optical fiber includes at least two optical sensors configured to operate at two different frequency ranges.

14. The method according to any one of claims 8 to 13, wherein, The first interrogator and the second interrogator are the same interrogator, and each interrogator is configured to operate in a different operating mode.

15. The method according to any one of claims 8 to 14, wherein, The optical fibers are embedded in or attached to the safety-critical systems of the aircraft.

16. An aircraft comprising an optical sensing system according to any one of claims 1 to 7.

17. The aircraft according to claim 16, wherein, The optical sensing system senses changes in strain or temperature of the aircraft's components.

Images