Interferometric all-fiber flow velocity sensor and manufacturing method thereof

Abstract

The invention discloses an interference type all-fiber flow velocity sensor and a manufacturing method thereof, the interference type all-fiber flow velocity sensor comprises a silica fiber, a hollow fiber, a transmission fiber, a shell, an armoring structure and a fiber connector, two ends of the hollow fiber are respectively welded with the silica fiber and the transmission fiber to form a Fabry-Perot cavity for sensing fluid flow velocity, and the Fabry-Perot cavity is marked as a measurement area; the housing is sleeved outside a sensitive assembly composed of the silica fiber, the hollow fiber and the transmission fiber, and is provided with a window for a measurement area. The non-welding end of the transmission optical fiber extends out of the shell, penetrates through the armored structure and then is connected with an optical fiber connector; the optical fiber connector is connected with a demodulation device, and transmits the interference signal to the demodulation device for resolving. The method is simple in process, low in manufacturing cost and high in measurement sensitivity, and is an optimal measurement method for engineering application.

Description

Technical Field

[0001] The invention relates to an interference type all-optical fiber flow velocity sensor and a manufacturing method thereof, in particular to an optical fiber flow velocity sensor based on the Fabry-Perot interference principle, and belongs to the field of optical fiber sensors. Background Art

[0002] Flow velocity is an important physical quantity that characterizes the state of fluid and is one of the important parameters of automatic control. Flow velocity measurement sensors are widely used in industrial production and life. Due to the different requirements of the measurement object, measurement environment and industrial site, flow velocity sensors are also diverse. The current flow velocity measurement technologies mainly include: Pitot tube, hot wire measurement technology, Doppler laser, etc.

[0003] Traditional Pitot tube and hot wire measurement technology mainly rely on electrical methods. The Pitot tube has a long time integral, so it can only measure average changes, but not real-time monitoring. Hot wire technology detects the heat transfer process through the principle of thermal balance, which is difficult to achieve high-temperature flow field application. Doppler laser velocimeter depends on the type of liquid measured and the angle of incident light, so its application field is very limited.

[0004] At the same time, with the increasing maturity of optical fiber production and processing technology, the cost of optical fiber production has dropped significantly. Optical fiber sensors have developed rapidly in recent decades due to their advantages such as small size, high sensitivity, corrosion resistance and intrinsic safety. Optical fiber flow sensors have also been deeply studied by many scholars at home and abroad. Summary of the invention

[0005] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art and provide an interference-type all-fiber flow velocity sensor and a manufacturing method thereof. The sensor is based on the Fabry-Perot interference principle, and causes changes in the interference spectrum through the deformation of the hollow optical fiber caused by the flow velocity. According to the relationship between the interference spectrum and the flow velocity, the flow velocity is monitored, and the process is simple, the manufacturing cost is low, and the measurement sensitivity is high.

[0006] The technical solution of the present invention is: in the first aspect, an interferometric all-fiber flow velocity sensor and a manufacturing method thereof are provided, comprising: a quartz optical fiber, a hollow optical fiber, a transmission optical fiber, a housing, an armored structure and an optical fiber connector, wherein:

[0007] One end of the hollow-core optical fiber is fused with the quartz optical fiber, and the other end is fused with the transmission optical fiber to form a Fabry-Perot cavity, which is used to sense the fluid flow rate and serves as the measurement area;

[0008] The housing is mounted on the outside of the sensitive assembly consisting of the quartz optical fiber, the hollow optical fiber and the transmission optical fiber, and a window is set for the measurement area;

[0009] The non-fused end of the transmission optical fiber extends out of the housing, passes through the armor structure and enters the optical fiber connector;

[0010] The optical fiber connector is connected to the demodulation device to transmit the interference signal to the demodulation device for resolution.

[0011] Preferably, the end faces for fusion splicing the transmission optical fiber and the hollow optical fiber are defined as the first end face of the transmission optical fiber and the first end face of the hollow optical fiber, respectively; the end faces for fusion splicing the hollow optical fiber and the quartz optical fiber are defined as the second end face of the hollow optical fiber and the first end face of the quartz optical fiber, respectively; the other end face of the quartz optical fiber is the second end face of the quartz optical fiber, and the other non-fusion spliced ​​end face of the transmission optical fiber is the second end face of the transmission optical fiber.

[0012] Preferably, the housing is used to protect sensitive components consisting of quartz optical fiber, hollow optical fiber and transmission optical fiber, and its appearance is designed according to actual usage so that it has the function of matching the installation interface to fix the sensor at the measuring point; the material of the housing is the same as the installation interface.

[0013] Preferably, the quartz optical fiber forms effective reflection only at a first end face of the quartz optical fiber, and the other end face is roughened.

[0014] Preferably, the hollow optical fiber is a ring-shaped thin-walled quartz structure, and both end surfaces are polished flat.

[0015] Preferably, the transmission optical fiber should select the optical fiber coating material according to the operating temperature, and the coating material can be selected from any of the following:

[0016] Acrylate, polyimide, aluminum, copper, gold.

[0017] In a second aspect, the present invention provides a method for manufacturing an interferometric all-optical fiber flow velocity sensor, comprising:

[0018] Cutting a transmission optical fiber and a hollow optical fiber of appropriate length, and processing the first end face of the transmission optical fiber by cutting, processing the first end face of the hollow optical fiber by grinding, and fusing the first end face of the transmission optical fiber with the first end face of the hollow optical fiber;

[0019] Cutting a quartz optical fiber of a suitable length, processing the first end face of the quartz optical fiber by cutting, processing the second end face of the hollow optical fiber by grinding, and then fusing the second end face of the hollow optical fiber with the first end face of the quartz optical fiber;

[0020] Roughening the second end face of the quartz optical fiber;

[0021] Adjust the relative position relationship between the sensitive component formed by the quartz optical fiber, the hollow optical fiber and the transmission optical fiber and the housing so that the measuring area is within the window range of the housing, and complete the fixing of the housing and the sensitive component;

[0022] An armored structure is used to encase the transmission optical fiber outside the housing;

[0023] The optical fiber connector is assembled after the second end face of the transmission optical fiber is end-face polished.

[0024] Preferably, when the fluid is a liquid, the airtightness of the fusion joints between the hollow-core optical fiber and the quartz optical fiber and the transmission optical fiber should be tested to prevent the liquid from penetrating into the hollow-core optical fiber.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] (1) The sensitive component of the present invention has a closed structure, and both gas and liquid flow rates can be measured without worrying about the problem of pollution from harsh environments;

[0027] (2) The flow velocity sensor proposed in the present invention is a full quartz optical fiber structure, which has a high upper temperature limit, is resistant to corrosion, oxidation, and electromagnetic interference, and can be applied to harsh working conditions such as high temperature and oxygen. In addition, the sensitive structure is a purely mechanical structure, and there is no problem of high temperature degradation of the optical fiber Bragg grating.

[0028] (3) The present invention has simple process, low manufacturing cost and high measurement sensitivity, and is an optimal measurement method for engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the structure of the interferometric all-optical fiber flow velocity sensor of the present invention;

[0030] Figure 2 This is a schematic diagram of the principle of the interferometric all-optical fiber flow velocity sensor of the present invention;

[0031] Figure 3 Schematic diagram of the relative positions of the optical fiber and the housing of the present invention. DETAILED DESCRIPTION

[0032] The present invention proposes an interference type all-fiber flow velocity sensor, which is based on the Fabry-Perot interference principle. The pressure brought by the fluid flow causes the hollow-core optical fiber to deform, thereby changing the interference spectrum. According to the pre-calibrated relationship between the flow velocity and the interference spectrum, the fluid flow velocity monitoring can be achieved through the change of the interference spectrum: the Fabry-Perot interference is formed by the reflection of the optical fiber end faces at both ends of the hollow-core optical fiber, and the initial interference cavity length is the length of the hollow-core optical fiber; the sensor is inserted into the fluid, and the fluid flow applies pressure to the surface of the hollow-core optical fiber, causing the hollow-core optical fiber to deform, resulting in a change in the interference cavity length; the faster the flow velocity, the greater the pressure, and the more severe the deformation of the hollow-core optical fiber. Therefore, the fluid flow velocity monitoring can be achieved by calibrating the relationship between the flow velocity and the interference cavity length.

[0033] The technical solution of the present invention is as follows: an interference type all-optical fiber flow velocity sensor, comprising: a quartz optical fiber 1, a hollow optical fiber 2, a transmission optical fiber 3, an outer shell 4, an armored structure 5 and an optical fiber connector 6.

[0034] The two ends of the hollow-core optical fiber 2 are fused with the quartz optical fiber 1 and the transmission optical fiber 3 respectively to form a Fabry-Perot cavity for sensing the fluid flow rate, which is recorded as the measurement area. The end faces where the transmission optical fiber 3 and the hollow-core optical fiber 2 are fused are defined as the transmission optical fiber first end face and the hollow-core optical fiber first end face, respectively, and the end faces where the hollow-core optical fiber 2 and the quartz optical fiber 1 are fused are defined as the hollow-core optical fiber second end face and the quartz optical fiber first end face; the other end face of the quartz optical fiber 1 is the quartz optical fiber second end face, and the other non-fused end face of the transmission optical fiber 3 is the transmission optical fiber second end face.

[0035] The housing 4 is mounted on the outside of the sensitive component composed of the quartz optical fiber 1, the hollow optical fiber 2 and the transmission optical fiber 3, and a window is set for the measurement area. The size of the window can ensure that the sensitive component can be exposed. The housing 4 is used to protect the sensitive component composed of the quartz optical fiber 1, the hollow optical fiber 2 and the transmission optical fiber 3. It also has the function of matching the installation interface, and can firmly fix the sensor at the measurement point. The non-fused end of the transmission optical fiber 3 extends out of the housing 4, passes through the armor structure 5 and enters the optical fiber connector 6; the armor structure 5 is used to protect the transmission optical fiber 3 from damage, so that it has better environmental adaptability. The optical fiber connector 6 at the tail end of the transmission optical fiber 3 is used to connect the demodulation device to transmit the interference signal to the demodulation device for resolution.

[0036] The end face (i.e., the first end face of the quartz fiber) where the quartz fiber 1 and the hollow-core fiber 2 are fused should be able to reflect light well. In order to prevent the extra reflection from affecting the quality of the interference spectrum, only the end face (i.e., the first end face of the quartz fiber) where the quartz fiber is fused forms an effective reflection, and the other end face (i.e., the second end face of the quartz fiber) is roughened.

[0037] The hollow core optical fiber 2 is a ring-shaped thin-walled quartz structure, and both ends are polished to achieve end surface flatness, thereby improving the quality of fusion. When the fluid is liquid, the tightness of the fusion joint should be tested to prevent the liquid from penetrating into the hollow core optical fiber 2.

[0038] The transmission optical fiber 3 should select the optical fiber coating material according to the use temperature. Common optical fiber coatings include non-metals such as acrylate and polyimide, and metals such as aluminum, copper, and gold.

[0039] The housing 4 has the functions of protecting sensitive components and matching the installation interface, and can be designed according to actual usage. When manufacturing, homogeneous materials of the installation interface are preferably selected.

[0040] A method for manufacturing an interferometric all-optical flow velocity sensor, the steps are as follows:

[0041] 1) According to actual needs, the transmission optical fiber 3 and the hollow optical fiber 2 are cut to appropriate lengths, and the first end face of the transmission optical fiber is processed by cutting, and the first end face of the hollow optical fiber is processed by grinding, and the first end face of the transmission optical fiber is fused with the first end face of the hollow optical fiber;

[0042] 2) Cutting a quartz optical fiber (1) of a suitable length according to actual needs, processing the first end face of the quartz optical fiber by cutting, processing the second end face of the hollow optical fiber by grinding, and then fusing the second end face of the hollow optical fiber to the first end face of the quartz optical fiber;

[0043] 3) roughening the second end face of the quartz optical fiber;

[0044] 4) Adjust the relative position relationship between the sensitive component formed by the quartz optical fiber 1, the hollow optical fiber 2 and the transmission optical fiber 3 and the housing 4 so that the measuring area is within the window range of the housing 4, and complete the fixing of the housing 4 and the sensitive component;

[0045] 5) using an armor structure 5 to protect the transmission optical fiber 3 outside the housing 4;

[0046] 6) Assemble the second end face of the transmission optical fiber with the optical fiber connector 6 and complete the end face polishing.

[0047] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0048] Example:

[0049] This embodiment produces a fiber optic gas flow rate sensor that can be used in an environment below 300°C. To meet the use requirements, both the quartz fiber and the transmission fiber are polyimide coated single-mode fibers with a diameter of 125μm. The inner diameter of the hollow fiber is 100μm, and the outer diameter of the cladding is 125μm. The armor structure selects a metal threaded tube with an outer diameter of 5mm. The steps for making the fiber optic gas flow rate sensor are as follows.

[0050] (1) Cutting a 1-meter-long transmission optical fiber and a 10-cm-long hollow-core optical fiber, processing the first end face of the transmission optical fiber by cutting, processing the first end face of the hollow-core optical fiber by grinding, and finally welding the first end face of the transmission optical fiber and the first end face of the hollow-core optical fiber. After welding, the hollow-core optical fiber is cut short to 2 mm;

[0051] (2) cutting a 10 cm long quartz optical fiber, processing the first end face of the 10 cm long quartz optical fiber by cutting, processing the second end face of the hollow optical fiber by grinding, and controlling the length of the hollow optical fiber after grinding to be about 1 mm, and finally fusing the second end face of the hollow optical fiber to the end face 1 of the quartz optical fiber;

[0052] (3) Use polyimide coating to re-coat the fusion joint of the optical fiber;

[0053] (4) Cutting the quartz optical fiber to 2 mm using a laser spot and roughening the second end face of the quartz optical fiber;

[0054] (5) Put the housing on the optical fiber, adjust the relative position of the sensitive component and the housing, make the fusion point within the housing window, and apply glue on both sides of the window to fix the optical fiber;

[0055] (6) Cut a metal threaded tube of about 1 m and install it on the second end face of the transmission optical fiber;

[0056] (7) Assemble the optical fiber connector at the second end face of the transmission optical fiber and complete the polishing of the optical fiber connector.

[0057] It should be noted that in the drawings or descriptions, similar or identical parts are all marked with the same figure numbers. The sizes of the parts in the drawings are not proportional to the actual sizes for the convenience of marking. Furthermore, the elements or implementations not shown or described in the drawings are forms known to those of ordinary skill in the art. In addition, although examples of parameters including specific values ​​may be provided herein, it should be understood that the parameters do not need to be exactly equal to the corresponding values, but can be approximated to the corresponding values ​​within an acceptable error tolerance or design constraint.

[0058] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

[0059] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in this field.

Claims

1. An interferometric all-fiber flow velocity sensor, characterized in that include: A quartz optical fiber (1), a hollow optical fiber (2), a transmission optical fiber (3), an outer shell (4), an armor structure (5) and an optical fiber connector (6), wherein: One end of the hollow optical fiber (2) is fused to the quartz optical fiber (1), and the other end is fused to the transmission optical fiber (3) to form a Fabry-Perot cavity for sensing the flow velocity of the fluid as a measurement area; The housing (4) is mounted on the outside of the sensitive component composed of the quartz optical fiber (1), the hollow optical fiber (2) and the transmission optical fiber (3), and a window is set for the measurement area; The non-fused end of the transmission optical fiber (3) extends out of the housing (4), passes through the armor structure (5) and enters the optical fiber connector (6); The optical fiber connector (6) is connected to a demodulation device to transmit the interference signal to the demodulation device for resolution.

2. The interferometric all-fiber flow velocity sensor according to claim 1, characterized in that: The end faces for fusion splicing the transmission optical fiber (3) and the hollow-core optical fiber (2) are defined as the transmission optical fiber first end face and the hollow-core optical fiber first end face, respectively; the end faces for fusion splicing the hollow-core optical fiber (2) and the quartz optical fiber (1) are defined as the hollow-core optical fiber second end face and the quartz optical fiber first end face, respectively; the other end face of the quartz optical fiber (1) is the quartz optical fiber second end face, and the other non-fusion spliced ​​end face of the transmission optical fiber (3) is the transmission optical fiber second end face.

3. The interferometric all-fiber flow velocity sensor according to claim 1, characterized in that: The housing (4) is used to protect the sensitive components consisting of the quartz optical fiber (1), the hollow optical fiber (2) and the transmission optical fiber (3). At the same time, its appearance is designed according to the actual use situation so that it has the function of matching the installation interface and fixing the sensor at the measuring point position; The material of the housing (4) is the same as that of the mounting interface.

4. The interferometric all-fiber flow velocity sensor according to claim 2, characterized in that: The quartz optical fiber (1) forms effective reflection only on the first end face of the quartz optical fiber, and the other end face is roughened.

5. The interferometric all-fiber flow velocity sensor according to claim 1, characterized in that: The hollow optical fiber (2) is a ring-shaped thin-walled quartz structure, and both end surfaces are polished flat.

6. The interferometric all-fiber flow velocity sensor according to claim 1, characterized in that: The transmission optical fiber (3) should select the optical fiber coating material according to the operating temperature. The coating material can be any of the following: Acrylate, polyimide, aluminum, copper, gold.

7. A method for manufacturing an interferometric all-fiber flow velocity sensor, characterized in that include: Cutting a transmission optical fiber (3) and a hollow optical fiber (2) of appropriate length, and processing the first end face of the transmission optical fiber by cutting, processing the first end face of the hollow optical fiber by grinding, and fusing the first end face of the transmission optical fiber with the first end face of the hollow optical fiber; Cutting a quartz optical fiber (1) of suitable length, processing the first end face of the quartz optical fiber by cutting, processing the second end face of the hollow optical fiber by grinding, and then fusing the second end face of the hollow optical fiber to the first end face of the quartz optical fiber; Roughening the second end face of the quartz optical fiber; Adjusting the relative positional relationship between the sensitive component formed by the quartz optical fiber (1), the hollow optical fiber (2) and the transmission optical fiber (3) and the housing (4) so ​​that the measurement area is within the window range of the housing (4), thereby completing the fixing of the housing (4) and the sensitive component; An armored structure (5) is used to encase the transmission optical fiber (3) outside the housing (4); After the second end face of the transmission optical fiber is end-face polished, the optical fiber connector (6) is assembled.

8. The method for manufacturing an interferometric all-optical fiber flow velocity sensor according to claim 7, characterized in that: When the fluid is liquid, the airtightness of the fusion joint between the hollow-core optical fiber (2), the quartz optical fiber (1) and the transmission optical fiber (3) should be checked to prevent the liquid from penetrating into the hollow-core optical fiber (2).

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