A distributed bragg reflector based sensor for object monitoring

Abstract

A Distributed Bragg Reflector, DBR, based sensor is presented. The DBR based sensor comprises a housing and a DBR comprised within an optical fiber. The housing comprises a cavity. The optical fiber is arranged through the housing. A sensor part of the optical fiber comprising the DBR is arranged within the housing with the DBR being located within the cavity. The housing may be used to accommodate different types and / or a plurality of DBRs. Examples of a DBR are a Fiber Bragg Grating, FBG, and a Fabry-Pérot etalon, FPE.

Description

[0001] A Distributed Bragg Reflector based sensor for object monitoring

[0002] Technical field

[0003] The present disclosure relates to sensors. More specifically, the present disclosure relates to Distributed Bragg Reflector (DBR) based sensors for monitoring objects. Furthermore, the present disclosure relates to a housing of such DBR based sensor, a chainable sensor array of such DBR based sensors, and a measurement system based on such DBR based sensors.

[0004] Background

[0005] Fiber Bragg Gratings (FBGs) are a type of DBRs, i.e. , a structure formed from multiple layers of alternating materials with varying refractive index, or by periodic variation of some characteristic (such as height) of a dielectric waveguide, resulting in periodic variation in the effective refractive index in the guide. A DBR, in particular an FBG, can be constructed in a short segment of optical waveguide, such as an optical fiber, to reflect a particular wavelength range of light and to transmit all others (i.e., the DBR is tuned to or is responsive to that particular wavelength range). This is achieved by creating the aforementioned periodic variation in the refractive index of the fiber core, which generates a wavelength-specific dielectric mirror and reflects light. DBRs can be used as sensors (DBR sensors) in an optical waveguide, by emitting light into the waveguide towards those DBRs and analyzing the light reflected from the DBR sensors. A DBR can thus be used as a sensor by the fact that its reflected wavelength is a direct result of DBR material changes from the environment (change in index, geometric variation), such that observing a shift in wavelength response by means of illumination and detection of reflectance or transmission constitutes a sensor measurement of the DBR’s environment. This process of detection, analysis or monitoring is often called DBR sensing or interrogation and is a way of measuring.

[0006] Typical applications of DBR sensing may include temperature analysis (as the length and dielectric constant of the optical waveguide increases with temperature) and strain analysis of physical bodies when the waveguide is attached to the body to act as an optical strain gauge, e.g., for structural health monitoring, although other types of applications may also be considered.

[0007] FBG based sensors find applications in various fields such as structural health monitoring in civil engineering, aerospace, oil and gas infrastructures, chemical industry infrastructures, biomedical sensing, and many more where accurate and reliable sensing in potentially harsh environments is required, or object monitoring for improvement of process efficiency. Non-limiting examples of objects that can be monitored using FBG sensors include pipelines, chemical reactors, dam and high- voltage transformers. FBG sensors offer high accuracy and precision in measuring parameters like strain, temperature, pressure, and more. They can detect very small changes in these parameters with great reliability.

[0008] FBG sensors allow multiple sensors to be multiplexed along a single optical fiber. This means several sensing points can be monitored using a single fiber, reducing complexity and costs in installations.

[0009] FBG sensors are typically highly durable and resistant to degradation, making them suitable for long-term monitoring in challenging environmental conditions. Moreover, FBG sensors can be made very small and lightweight, making them suitable for applications where space and weight are critical factors.

[0010] Existing DBR based sensors are typically designed for small size applications requiring a complex manufacturing process, resulting in a suboptimal sensor operating ranges and higher costs. Moreover, the manufacturing process of known DBR based sensors is often complex, further contributing to higher costs.

[0011] Summary

[0012] A summary of aspects of certain examples disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects and / or a combination of aspects that may not be set forth. The present disclosure aims to overcome the drawbacks identified in the background section. In particular, the present disclosure aims to provide an improved DBR sensor for measuring various parameters of or at an object, such as temperature and / or vibrations. The DBR sensor of the present disclosure may be used in a chainable sensor array for different types of DBR based sensors.

[0013] In an embodiment, a DBR based sensor is presented. The DBR based sensor may include a housing and a DBR included within an optical fiber. The housing may include a cavity. The optical fiber may be arranged through the housing. A sensor part of the optical fiber including the DBR may be arranged within the housing, with the DBR being located within the cavity.

[0014] In an embodiment, the housing may include two parts. Each part of the housing may include a part of the cavity. When the two parts are put together, they may form the cavity and the housing.

[0015] In an embodiment, the sensor part of the optical fiber may include a DBR temperature sensor. The sensor part may have a curvature within the cavity.

[0016] In an embodiment, the sensor part of the optical fiber does not touch the housing.

[0017] In an embodiment, the sensor part of the optical fiber may include a DBR vibration sensor.

[0018] In an embodiment, the housing may further include a vibration enhancing element that is attached to a wall of the cavity on a first end of the vibration enhancing element.

[0019] In an embodiment, the vibration enhancing element may touch the optical fiber.

[0020] In an embodiment, the vibration enhancing element may include a weight on a second end of the vibration enhancing element opposite of the first end.

[0021] In an embodiment, the DBR based sensor may be a combined DBR sensor including two or more DBRs arranged within the cavity of the housing, the DBRs being arranged within the housing for different types of measurements.

[0022] In an embodiment, the two or more DBRs may be located in different optical fibers.

[0023] In an embodiment, the two or more DBRs may be located in one optical fiber.

[0024] In an embodiment, the two or more DBRs include: aDBR based temperature sensor; a DBR based vibration sensor; a DBR based shock sensor; a DBR based acceleration sensor; a DBR based tilt sensor; a DBR based strain sensor; a DBR based humidity sensor and / or a DBR based curvature sensor.

[0025] In an embodiment, the DBR based sensor may be an FBG based sensor.

[0026] In an embodiment, the DBR based sensor may be a Fabry-Perot etalon (FPE) based sensor. According to an aspect of the present disclosure, a housing of a DBR based sensor is presented. The housing may include a cavity. The housing may be arranged for accommodating an optical fiber through the housing. The housing may be arranged for accommodating a sensor part of the optical fiber including the DBR arranged within the housing, with the DBR being located within the cavity.

[0027] In an embodiment, the housing may include two parts. Each part of the housing may include a part of the cavity. When the two parts are put together, they may form the cavity and the housing.

[0028] In an embodiment, the housing may further include a ring arranged around the cavity and over the optical fiber for holding the optical fiber in place within the housing.

[0029] In an embodiment, one or both of the two parts may include a groove for accommodating the ring.

[0030] In an embodiment, one or both of the two parts may include one or more studs for keeping the ring in place.

[0031] According to an aspect of the present disclosure, a chainable sensor array is presented. The chainable sensor array may include one or more DBR based sensors having one or more of the above-described features.

[0032] According to an aspect of the present disclosure, a measurement system is presented. The measurement system may include a chainable sensor array as described above and an interrogator device coupled to the chainable sensor array.

[0033] Brief description of the Drawings

[0034] Embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbol indicate corresponding parts, in which:

[0035] Fig. 1 shows an example DBR sensor based measurement system based on a chainable sensor array; Figs. 2A-2B show a 3D model of an example housing of a DBR sensor;

[0036] Fig. 3A shows a three-dimensional (3D) model of an example embodiment of a DBR temperature sensor;

[0037] Fig. 3B shows an abstract two-dimensional (2D) representation of an example DBR temperature sensor;

[0038] Fig. 4A shows a 3D model of an example housing of a DBR vibration sensor;

[0039] Fig. 4B shows a 3D model of an example embodiment of a DBR vibration sensor;

[0040] Fig. 5 shows a 3D model of an example embodiment of a combined DBR temperature and DBR vibration sensor; and

[0041] Figs. 6A-6B show 3D models of example parts of a housing of a DBR sensor.

[0042] The figures are intended for illustrative purposes only, and do not serve as restriction of the scope of the protection as laid down by the claims.

[0043] Detailed description

[0044] It will be readily understood that the components of the embodiments as generally described herein and illustrated in the appended figures could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of various embodiments, as represented in the figures, is not intended to limit the scope of the present disclosure but is merely representative of various embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

[0045] The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the present disclosure is, therefore, indicated by the appended claims rather than by this detailed description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

[0046] Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present disclosure should be or are in any single example of the present disclosure. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present disclosure. Thus, discussions of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same example.

[0047] Furthermore, the described features, advantages, and characteristics of the present disclosure may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize, in light of the description herein, that the present disclosure may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the present disclosure. Reference throughout this specification to "one embodiment," "an embodiment," or similar language means that a particular feature, structure, or characteristic described in connection with the indicated embodiment is included in at least one embodiment of the present disclosure. Thus, the phrases "in one embodiment," "in an embodiment," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0048] In a practical implementation of the present disclosure, at least some of, preferably all of, the DBRs may, e.g., be FBGs. An FBG is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. This is achieved by creating a periodic variation in the refractive index of the optical fiber core, which generates a wavelengthspecific dielectric mirror.

[0049] A fundamental principle behind the operation of an FBG is Fresnel reflection, where light traveling between media of different refractive indices may both reflect and refract at the interface. The refractive index will typically alternate over a defined length. The reflected wavelength is called the Bragg wavelength (AB) .

[0050] Known applications of FBG technology include optical communication applications, sensing applications and wavelength-specific reflector applications. The present disclosure uses FBG technology in sensing applications.

[0051] The Bragg wavelength is known to be sensitive to strain and to temperature, and FBGs have been developed that can be used as sensing elements in optical fiber sensors. In an FBG sensor, the measurand causes a shift (AAB) in the Bragg wavelength. The relative shift (AAB / AB) in the Bragg wavelength due to an applied strain (E) and / or a change in temperature (AT) may be approximately by the following equation: AAB / AB = CS £ + CT AT. Here, Cs is a coefficient of strain, which is related to a strain optic coefficient, and CT is a coefficient of temperature, which depends on a thermal expansion coefficient of the optical fiber and a thermo-optic coefficient.

[0052] An FBG sensor may thus be used to detect the applied strain (E) and / or changes in the temperature (AT) at the FBG sensor. A detection of an applied strain may be indicative of a pressure. A detection of changes in the applied strain may be indicative of vibrations. Information obtained from the FBG sensor is particularly useful when obtained periodically over time, enabling pressure sensing applications, temperature sensing applications and / or vibration sensing applications.

[0053] Alternatively or additionally, at least some of, preferably all of, the DBRs may, e.g., be FPEs.

[0054] DBR sensors may be used in terminated sensor arrays and chainable sensor arrays.

[0055] Terminated sensor arrays include one or more DBRs protected by a stiff tube or jacket decoupling strain artefacts. A limitation of terminated sensor arrays is the inability to chain multiple arrays and the limited maximum length of the stiff element.

[0056] Chainable sensor arrays typically include of one or more DBRs, each encapsulated into a transducer element.

[0057] For temperature readings it may be important to avoid interference from strain on the DBR, in particular with FBGs. Strain, and in particular changes in strain, can cause noise on the Bragg wavelengths that are measured for the temperature readings. Thin metal, plastic or ceramic tubes protecting the FBG sensor from strain typically only reduce the strain response rather than completely void it. Achieving a strain relief by fixation of the optical fiber by directly gluing it inside a tube can also result in nonlinear responses of the sensor.

[0058] On the other hand, for vibration readings external vibrations may be guided to the DBR. Strain relief is typically not desired for vibration sensors.

[0059] The present disclosure presents DBR sensors, which may be used for sensing, e.g., temperature, vibrations, shock, acceleration, tilt, strain, humidity and / or curvature, and which may be used in chainable sensor arrays, without the above identified drawbacks.

[0060] Fig. 1 shows an example of a measurement system 100 according to an aspect of the present disclosure. The measurement system 100 may include an interrogator device 110 coupled to an optical fiber 102 including a chainable sensor array 120. In this example, the chainable sensor array 120 includes three DBR sensors 122, 124, 126, but there can be any number of DBR sensors included in the chainable sensor array 120, e.g., 1 , 50, 64, 100, hundredths or thousands of DBR sensors. The chainable sensor array 120 may include different types of DBR based sensors, such as a mix of FBG and FPE based sensors.

[0061] The interrogator device 110 may include a broadband light source 112 for generating an input spectrum of light into the optical fiber 102. For example, each FBG sensor 122, 124, 126 may reflect part of the input spectrum, which may be detected at a wavelength detection system 114 of the interrogator device 110 as Bragg wavelengths.

[0062] The DBR sensor 122, 124, 126 may be used to measure temperature fluctuations over time. If, e.g., a first Bragg wavelength ABI corresponds to the reflected light from a first FBG sensor 122, the Bragg wavelength ABI may be analyzed to determine if and to what extent the temperature changes and / or detect a strain or changes in strain at the first FBG sensor 122 in time. Hereto, the Bragg wavelength ABI may be converted to a digital signal using any known analog-to-digital converter (ADC) system and the digital signal may be processed using any suitable computer system (not shown in Fig. 1).

[0063] The periodicity of the measurements may depend on the measurement application. The measurements may be performed continuously, at a periodicity in the order of microseconds, at a periodicity in the order of seconds, at a periodicity in the order of minutes, at a periodicity in the order of hours, or at any other suitable frequency. In a preferred embodiment, the measurements are performed at a periodicity in the order of 20 microseconds to 1 millisecond, which may be considered a continuous monitoring.

[0064] The chainable sensor array 120 may be used for monitoring objects. In an example use case, the chainable sensor array 120 may be used for monitoring objects, such as pipelines, where fluctuations in temperature at or along the object may be measured. In another example use case, the chainable sensor array 120 may be used for monitoring vibrations at objects, such as pipelines or machines, where fluctuations in strain at or along the object may be measured. Preferably, but not necessarily, some or all of the DBR sensors 122, 124, 126 are applied equidistantly in the chainable sensor array.

[0065] When analyzing the information obtained from the wavelength detection system 114, further sensory data may be taken into account to, e.g., compensate for fluctuations in temperature of a fluid flowing through an object (e.g., fluctuations in the temperature of a liquid in a pipeline) and / or compensate for fluctuations in temperature around the object (e.g., environmental temperature fluctuations). The analysis of the data, including the analysis of the data from the Bragg wavelengths ABI and / or any further sensory data, is outside the scope of the present disclosure and will not be further described.

[0066] In an example embodiment, a DBR sensor 122, 124, 126 is presented that is designed for optimal heat transfer towards the DBR of the DBR sensor 122, 124, 126. Where known DBR sensors are typically designed to follow the temperature of a substrate and / or require the DBR to follow the temperature of the optical fiber, the DBR sensor 122, 124, 126 of the present disclosure has been designed differently. It has been found that conductivity is not a driving factor of heat transfer, but thermal radiation is a key component of the heat transfer. With this knowledge, an improved DBR sensor 122, 124, 126 is designed, which enclosure (herein also referred to as ‘housing’) is not directly fixated to the DBR sensor part including the DBR of the DBR sensor 122, 124, 126. This DBR sensor can measure temperature changes by detecting thermal radiation, typically including a heat exchange via thermal convection. Thus, the sensor part including the DBR is not fixated to a substrate, which advantageously enables very effective strain decoupling, while enabling the DBR sensor 122, 124, 126 to operate as an effective temperature sensor.

[0067] In another example embodiment, an DBR sensor 122, 124, 126 is presented that is designed for optimal vibration transfer towards the DBR of the DBR sensor 122, 124, 126. In another embodiment, the DBR sensor 122, 124, 126 may include two or more of: a DBR temperature sensor; a DBR vibration sensor; a DBR based shock sensor; a DBR based acceleration sensor; a DBR based tilt sensor; a DBR based strain sensor; a DBR based humidity sensor and / or a DBR based curvature sensor, either in separate optical fibers or combined in a single optical fiber.

[0068] Fig. 2A is a 3D model of an example embodiment of a housing 200 of a DBR sensor 122, 124, 126. The housing 200 includes two parts 210, 220. Features of one of these parts 210 will be described. In this example, the other part 220 may be identical to the first part 210 and the two parts 210, 220 may be combined to form the housing 200, e.g., by clamping the two parts 210, 220 together. Part 210 is shown in isolation in Fig. 2B. When the two parts 210, 220 are put together, the housing 200 includes a cavity 230.

[0069] The part 210 may include one or more protrusions 212, preferably laterally arranged to a through hole 216 for accommodating a protective tubing of the optical fiber 102. In the example of Fig. 2A and 2B, the part 210 has two protrusions 212. The protrusions 212 may a ridged surface for improved fixation to the other part 220.

[0070] The part 210 of the housing 200 may further include one or more protrusion receptors 214, preferably laterally arranged to through hole 218 for accommodating further protective tubing of the optical fiber 102. In the example of Fig. 2A and 2B, the part 210 has two protrusion receptors 214.

[0071] The protrusion receptors 214 are arranged to receive the protrusions of the other part 220. The protrusions 212 are arranged to be inserted into the protrusion receptors of the other part 220. When the two parts 210, 220 are put together, the two parts 210, 220 will be clamped together by the protrusions 212 frictionally fixed within the protrusion receptors 214. At the same time, the protective tubing in the through holes 216, 218 will be clamped within the through holes 216, 218 and thus to the housing 200.

[0072] Advantageously, a DBR sensor including a housing 200 as shown in Fig. 2A may be assembled in a time efficient manner because of the few production steps involved in putting together such DBR sensor. Moreover, because both sides 210 and 220 may be similar or identical, production of the DBR sensor is cost efficient, as the DBR sensor will include few different components. Although less preferred, the housing may be designed differently, e.g., as two parts that are screwed or glued together.

[0073] The housing 200 may be used for accommodating various types of DBR based sensors, including, but limited to, a DBR based temperature sensor, a DBR based vibration sensor, a DBR based strain sensor, a DBR based shock sensor, a DBR based acceleration sensor, a DBR based tilt sensor, a DBR based strain sensor, a DBR based humidity sensor, a DBR based curvature sensor and / or a DBR based pressure sensor. Different DBR based sensors may be combined within a single housing 200, and more specifically withing the cavity 230 of a single housing 200.

[0074] Figs. 3A-3B show an example embodiment of a DBR temperature sensor 300. Fig. 3A shows a 3D model of the DBR temperature sensor 300. The DBR temperature sensor 300 includes a housing 310, which may be similar or identical to the housing 200 of Fig. 2, and a cavity 312 within the housing 310.

[0075] An optical fiber in a protective tubing 322 is fed through the housing 310, such that the sensor part 320 of the optical fiber including the DBR without the protective tubing 322 resides within the cavity 312. While the tubing 322 may be fixated, e.g., clamped, to the housing 310, the sensor part 320 is not fixated to the housing 310 and preferably loosely resides within the cavity 312, i.e. , without any pulling force from the tubing 322 to minimize strain on the sensor part 320. Preferably, the sensor part 320 is arranged within the cavity 312 without touching the housing 310 to avoid external vibrations resulting in vibration noise to reach the sensor part 320 through the housing 310.

[0076] Fig. 3B is an abstract 2D representation of the example DBR sensor 300. The housing 310 including the cavity 312, the tubing 322 and the sensor part 320 are shown. The DBR of the sensor part 320 is depicted as S1 in Fig. 3B. At and between the locations F2 and F3, the optical fiber, which is routed inside the tubing through the cavity 312, resides stress-free inside the cavity 312 of the housing 310, preferably without touching the housing 310. The tubing 322 may be fixated to the housing 310 by using the housing 310 as crimping element. By using the housing 310 as crimping tool, the tubing 322 may be fixated to the DBR sensor 300 without the need of intermediate assembly steps. In the example of Fig. 3B, the tubing 322 is fixated to the housing 310 at locations F1 and F4 using the clamping force of the housing 310 itself. While fixating the tubing 322 to the housing 310 using clamping force is preferred, other fixation methods may be used. For example, the tubing 322 may be glued to the housing 310 at locations F1 and F4. The tubing 322 may be a stiff tubing, e.g., made from Polytetrafluoroethylene (PTFE).

[0077] Figs. 4A-4B show an example embodiment of a DBR vibration sensor 400. Fig. 4A shows a 3D model of a first part 410 of a housing of the DBR vibration sensor 400. The DBR vibration sensor 400 typically includes two parts that, when fixated to each other, form the housing of the sensor. The housing of the DBR vibration sensor 400 may be based on the housing 200 of Fig. 200. The first part 410 of the housing may include a cavity 412. The first part 410 may further include a vibration enhancing element 430, e.g., in the form of a spring element such as a leaf spring. The vibration enhancing element 430 may be attached to a side wall 432 of the cavity 412. The second part of the housing is typically without such spring element.

[0078] A shown in Fig. 4B, an optical fiber in a protective tubing 422 may be fed through the housing, such that the sensor part 420 of the optical fiber including the DBR without the protective tubing 422 resides within the cavity 412. The tubing 422 may be fixated, e.g., clamped, to the housing 410 when the two parts of the housing are put together.

[0079] In the cavity 412, the optical fiber touches the vibration enhancing element 430. Thus, vibrations reaching the housing of the DBR vibration sensor 400 may be enhanced by the vibration enhancing element 430 before reaching the sensor part 420. Vibrations may result in strain on the optical fiber and ultimately on the DBR, which may be detected as vibrations.

[0080] In an example embodiment, a weight 434 may be added to the loose end of the vibration enhancing element 430. The added weight 434 may increase the sensitivity of the DBR vibration sensor 400. The weight 434 may be added on top of or below the vibration enhancing element 430. The weight 434 may be added as a separate weight applied to the vibration enhancing element 430. Alternatively, the loose end of the vibration enhancing element 430 may be made heavier, e.g., by making it thicker or wider.

[0081] A DBR temperature sensor, such as the DBR temperature sensor 300 of Fig. 3, and a DBR vibration sensor, such as the DBR vibration sensor 400 of Fig. 4, may be combined in a single housing, such as housing 200 of Fig. 2. In an example embodiment shown in Fig. 5, a combined DBR sensor 500 (only a first part 510 similar to first part 210 or 410 is shown) includes a first optical fiber 520 with a DBR for temperature measurements, similar to the embodiment of Figs. 3A- 3B, and a second optical fiber 522 with an DBR for vibration measurements, similar to the embodiment of Figs. 4A-4B. For optimal temperature measurements, the first optical fiber 520 should not touch the second optical fiber 522 or the vibration enhancing element 530. Also shown are the cavity 512 of the housing of the combined DBR sensor 500 and a protective tubing 522.

[0082] In another example embodiment (not shown), a DBR for temperature measurements and a DBR for vibration measurements, or any other types of DBR based sensors, may be included in a single optical fiber and both arranged in a single cavity of the housing of the combined DBR sensor.

[0083] With reference to Figs. 6A-6B, in an example embodiment, a ring 602, e.g., rubber ring, may be placed on the optical fiber 102, e.g., covering locations F2, F3 of the optical fiber as shown in Fig. 3B or at similar locations on the optical fiber in Fig. 4B. The rubber ring may be located around the cavity. The rubber ring 602 may be used to fixate the optical fiber 102 to the first part 610 of the housing.

[0084] The ring 602 may be kept in place within the housing in various manners. In the example of Fig. 6A, the part 610 of the housing may include a groove 604 for accommodating the ring 602. The other part of the housing may be identical to the first part 610 and also include such groove 604. In another example embodiment shown in Fig. 6B, the part 610 of the housing may include one or more protrusions or studs 606 for keeping the ring 602 in place. The part 610 may further include one or more stud receptors 608 for receiving the studs from the other part when put together. The example embodiment of Fig. 6B may further include a groove 602.

[0085] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope thereof.

Claims

CLAIMS1. A Distributed Bragg Reflector, DBR, based sensor (122, 124, 126) comprising a housing (200) and a DBR (320, 420, 520, 522) comprised within an optical fiber (102), wherein the housing comprises a cavity (230, 312, 412, 512), wherein the optical fiber is arranged through the housing, and wherein a sensor part of the optical fiber comprising the DBR is arranged within the housing, with the DBR being located within the cavity.

2. The DBR based sensor according to claim 1 , wherein the housing comprises two parts (210, 220), wherein each part of the housing comprises a part of the cavity, and wherein the two parts are put together to form the cavity and the housing.

3. The DBR based sensor according to claim 1 or claim 2, wherein the sensor part of the optical fiber comprises a DBR temperature sensor (320), and wherein the sensor part has a curvature within the cavity.

4. The DBR based sensor according to claim 3, wherein the sensor part of the optical fiber does not touch the housing.

5. The DBR based sensor according to claim 1 or claim 2, wherein the sensor part of the optical fiber comprises a DBR vibration sensor (420).

6. The DBR based sensor according to claim 5, wherein the housing further comprises a vibration enhancing element (430) that is attached to a wall (432) of the cavity on a first end of the vibration enhancing element.

7. The DBR based sensor according to claim 6, wherein the vibration enhancing element touches the optical fiber.

8. The DBR based sensor according to claim 6 or claim 7, wherein the vibration enhancing element comprises a weight (434) on a second end of the vibration enhancing element opposite of the first end.

9. The DBR based sensor according to claim 1 or claim 2, wherein the DBR based sensor is a combined DBR sensor (500) comprising two or more DBRs arranged within the cavity of the housing, the two or more DBRs being arranged within the housing for different types of measurements.

10. The DBR based sensor according to claim 9, wherein two or more DBRs are located in different optical fibers.

11. The DBR based sensor according to claim 9, wherein two or more DBRs are located in one optical fiber.

12. The DBR based sensor according to any one of the claims 9-11 , wherein the two or more DBRs include: a DBR based temperature sensor; a DBR based vibration sensor; a DBR based shock sensor; a DBR based acceleration sensor; a DBR based tilt sensor; a DBR based strain sensor; a DBR based humidity sensor and / or a DBR based curvature sensor.

13. The DBR based sensor according to any one of the preceding claims, wherein the DBR based sensor is one of: a Fiber Bragg Grating, FBG, based sensor; and a Fabry-Perot etalon, FPE, based sensor.

14. A housing (200) of a Distributed Bragg Reflector, DBR, based sensor (122, 124, 126), wherein the housing comprises a cavity (230, 312, 412, 512), wherein the housing is arranged for accommodating an optical fiber (102) through the housing,and wherein the housing is arranged for accommodating a sensor part of the optical fiber comprising the DBR arranged within the housing, with the DBR being located within the cavity.

15. The housing according to claim 14, wherein the housing comprises two parts (210, 220), wherein each part of the housing comprises a part of the cavity, and wherein the two parts are put together to form the cavity and the housing.

16. The housing according to claims 14 or claim 15, further comprising a ring (602) arranged around the cavity and over the optical fiber for holding the optical fiber in place within the housing.

17. The housing according to claim 16, wherein one or both of the two parts comprises a groove (604) for accommodating the ring.

18. The housing according to claim 16 or claim 17, wherein one or both of the two parts comprises one or more studs (606) for keeping the ring in place.

19. A chainable sensor array (120) comprising one or more DBR based sensors according to any one of the claims 1-13.

20. A measurement system (100) comprising a chainable sensor array (120) according to claim 19 and an interrogator device (110) coupled to the chainable sensor array.

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