A high-precision all-quartz optical fiber FP cavity sensor and its manufacturing method

Abstract

The present invention belongs to the technical field of optical fiber sensors, and specifically relates to a high-fineness all-quartz optical fiber F-P cavity sensor and a manufacturing method thereof. The optical fiber F-P cavity sensor comprises a first optical fiber and a second optical fiber, and also comprises a quartz capillary tube 1; the end face of the first optical fiber close to the second optical fiber is a reflection end face 1, and the reflection end face 1 is a plane and perpendicular to the length direction of the first optical fiber; the end face of the second optical fiber close to the first optical fiber is a reflection end face 2, and the reflection end face 2 is a concave spherical surface; compared with the prior art, the present invention (1) the reflection end face 2 is a concave spherical surface, which plays a focusing role of a concave mirror, offsets the divergence of the light beam in the cavity, thereby matching the reflectivity of the two reflection end faces, allowing the cavity length to be increased, obtaining an interference spectrum with a smaller free spectral range, improving the fringe fineness, improving the resolution, and effectively reducing demodulation instability and jump; (2) the reflection end face 2 can withstand higher temperatures.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber sensors, and in particular relates to a high-fineness all-quartz optical fiber FP cavity sensor and a manufacturing method thereof. Background Art

[0002] In the fields of downhole temperature and pressure monitoring, gas storage temperature and pressure monitoring, and carbon dioxide storage temperature and pressure monitoring in oil and gas development, sensors are needed to monitor downhole temperature, pressure and other parameters in real time. Due to the harsh environment of high temperature, high pressure and corrosion in the well, traditional electronic sensors cannot work stably for a long time in the well. Optical fiber sensors have attracted wide attention for their strong anti-interference ability, corrosion resistance, and good reliability. In particular, optical fiber FP cavity sensors have the advantages of high resolution, large dynamic range, and low drift rate, and are increasingly widely used.

[0003] A widely used type of fiber optic FP cavity sensor is one that places two bare optical fibers with flat end faces in a collimated capillary whose inner diameter matches the diameter of the bare optical fibers. The two bare fiber end faces and the cavity between them form an FP cavity. Changes in physical parameters such as temperature and pressure will cause changes in the length of the FP cavity, thereby causing changes in the spectral fringes. By detecting changes in the spectral fringes by optical methods, the corresponding changes in temperature and pressure can be detected.

[0004] The welding of the optical fiber FP cavity is mainly to fix the optical fiber inserted into the capillary glass tube and the capillary glass tube. The commonly used methods include epoxy resin adhesive bonding, high-frequency CO2 pulse laser hot melting fixation, hydrogen-oxygen flame high-temperature hot melting welding, etc. Among them, Wang Yingying and others invented a "fiber FP cavity sensor manufacturing device", which can heat the capillary glass tube with a hydrogen-oxygen flame welding machine, and at the same time, the capillary glass tube wall collapses inward under the action of exhaust to weld the optical fiber and the capillary glass tube. This welding method firmly welds the capillary glass tube and the optical fiber, has good sealing performance, and can effectively prevent oil, water and gas from penetrating from the welding point to damage the FP cavity, laying a solid foundation for the long-term application of optical fiber FP cavity sensors in harsh environments.

[0005] Although the disclosed technology can obtain a sensor with firm welding, good sealing and leakage prevention by specially manufacturing a device and adopting a high-temperature hot-melt welding method using a hydrogen-oxygen flame, and adopts the welding of optical fiber and quartz capillary with the same material, which has the characteristics of low drift rate, this process generally uses flattening of the optical fiber end face to obtain a lower reflectivity. Due to the divergence of the light beam in the cavity, it will cause reflectivity mismatch of the interference light beam, resulting in only interference spectra with a larger free spectral range. The fringe fineness is low, which limits the further improvement of resolution and will cause demodulation instability and jumps.

[0006] The disclosed methods for improving the reflectivity of the reflecting surface include forming a concave surface at the reflecting end face of the second optical fiber to form a focusing effect through hydrofluoric acid corrosion, femtosecond laser ablation, etc. However, the concave surface formed is small and difficult to match with the beam divergence, and has low sphericity and poor smoothness, which affects the quality of the interference fringes and thus affects the accuracy of the sensor. Summary of the invention

[0007] In view of the above problems, the present invention provides a high-fineness all-quartz optical fiber FP cavity sensor and a manufacturing method thereof.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is: a high-fineness all-quartz optical fiber FP cavity sensor, including a first optical fiber and a second optical fiber, and also including a quartz capillary tube;

[0009] The first optical fiber and the second optical fiber extend into the quartz capillary tube one for a certain distance from both ends of the quartz capillary tube one in the length direction respectively; in the quartz capillary tube one, the first optical fiber and the second optical fiber are both arranged along the axis of the quartz capillary tube one, and the ends of the first optical fiber and the second optical fiber close to each other are separated by a certain distance to form an FP cavity; the end face of the first optical fiber close to the second optical fiber is the reflection end face one, and the reflection end face one is a plane and perpendicular to the length direction of the first optical fiber; the end face of the second optical fiber close to the first optical fiber is the reflection end face two, and the reflection end face two is a concave spherical surface; the first optical fiber and the second optical fiber are respectively fused to the wall of the quartz capillary tube one on one side away from the FP cavity; the end of the first optical fiber away from the FP cavity is connected to the signal receiving end for communication.

[0010] Preferably, the fusion points between the first optical fiber and the second optical fiber on the side away from the FP cavity and a wall of the quartz capillary are the first fusion point and the second fusion point respectively.

[0011] Preferably, the second welding point is spherical.

[0012] Preferably, the quartz capillary tube 1 is a reducer, and the first optical fiber and the second optical fiber are respectively located on the side with a small inner diameter and the side with a large inner diameter of the quartz capillary tube 1.

[0013] Preferably, the first optical fiber and the second optical fiber have the same specifications.

[0014] Preferably, a fiber grating is processed on the side of the first optical fiber close to the FP cavity.

[0015] A method for manufacturing a high-fineness all-quartz optical fiber FP cavity sensor comprises the following steps:

[0016] Step 1: Processing a fiber grating on the side of the first optical fiber close to the FP cavity by femtosecond laser writing; processing the second reflective end face of the second optical fiber, and processing a quartz capillary tube by hot-melt stretching;

[0017] Step 2: Processing the fusion point between the first optical fiber and the second optical fiber on the side away from the FP cavity and the wall of a quartz capillary tube.

[0018] Preferably, the processing of the second reflective end face of the second optical fiber in step 1 comprises the following steps:

[0019] Step 1: cutting the second optical fiber into a planar end face;

[0020] Step 2: clamping the second optical fiber by the first three-dimensional adjustment frame, and clamping the second quartz capillary by the second three-dimensional adjustment frame;

[0021] Step 3: by adjusting the first three-dimensional adjustment frame and the second three-dimensional adjustment frame, the second optical fiber is aligned with the second quartz capillary and the end faces are close to each other;

[0022] Step 4: Install a tungsten steel ball at the end of the second quartz capillary tube near the second optical fiber, wherein the outer diameter of the tungsten steel ball is equal to the inner diameter of the second quartz capillary tube; and adjust the first three-dimensional adjustment frame and the second three-dimensional adjustment frame so that the second optical fiber and the second quartz capillary tube clamp the tungsten steel ball;

[0023] Step 5: The electrode is close to the end face of the second optical fiber close to the tungsten steel ball, and discharges to melt the end face of the second optical fiber and form a second reflective end face.

[0024] Preferably, in step 4, half of the tungsten steel ball enters quartz capillary 2.

[0025] Preferably, the processing method of the second fusion joint is to locally fuse and couple the quartz capillary tube 1 and the second optical fiber together by hot melting, and to locally melt the quartz capillary tube 1 and the second optical fiber by heating with an oxyhydrogen flame and melt them into a spherical shape by surface tension; the processing method of the first fusion joint is to locally fuse and couple the quartz capillary tube 1 and the first optical fiber together by hot melting.

[0026] Compared with the prior art, the advantages and positive effects of the present invention are:

[0027] (1) The second reflective end face of the high-fineness all-quartz optical fiber FP cavity sensor of the present invention is a concave spherical surface with high sphericity, which plays the focusing role of a concave mirror, offsets the divergence of the light beam in the cavity, so that the reflectivity of the two reflective end faces matches, allowing the cavity length to be increased, and an interference spectrum with a smaller free spectral range is obtained, thereby improving the fringe fineness, improving the resolution, and effectively reducing demodulation instability and jumps;

[0028] (2) The reflective end face 2 obtained by the processing method of the reflective end face 2 of the second optical fiber of the present invention is different from the concave surface formed by processes such as coating, and can withstand higher temperatures, thereby allowing the optical fiber FP cavity sensor to be made by high-temperature hot-melting the optical fiber and the quartz capillary tube 1 using a hydrogen-oxygen flame. The hot-melting quartz capillary tube 1 is heated by the hydrogen-oxygen flame to melt the quartz capillary tube 1. At the same time, under the action of exhaust, the wall of the quartz capillary tube 1 collapses inward and is fused together with the optical fiber, which does not affect the reflectivity of the reflective end face 2, thereby ensuring the sensor's characteristics of firm fusion, good sealing, leakage prevention, fusion of the same material, and low drift rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solution of the embodiment of the present invention, the following briefly introduces the drawings required for describing the embodiment. Figure 1 Schematic diagram of the high-fineness all-quartz optical fiber FP cavity sensor provided in Example 1,

[0030] Figure 2 is a schematic diagram of processing the second reflection end face of the second optical fiber,

[0031] Figure 3 Schematic diagram of the high-fineness all-quartz optical fiber FP cavity sensor provided in Example 2.

[0032] Description of reference numerals:

[0033] 100—first optical fiber, 101—reflection end face 1;

[0034] 200—second optical fiber, 201—reflection end face 2,

[0035] 300—quartz capillary tube 1, 301—first fusion point, 302—second fusion point;

[0036] 401—first three-dimensional adjustment frame, 402—second three-dimensional adjustment frame;

[0037] 500—tungsten steel ball, 600—quartz capillary tube II, 700—electrode, 800—fiber Bragg grating. DETAILED DESCRIPTION

[0038] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described below with reference to the accompanying drawings and embodiments.

[0039] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments of the following disclosure.

[0040] Example 1

[0041] The following is combined with Figure 1 The present invention is further described as follows: a high-fineness all-quartz optical fiber FP cavity sensor, such as Figure 1 As shown, it includes a first optical fiber 100 and a second optical fiber 200, and also includes a quartz capillary 300. The first optical fiber 100 and the second optical fiber 200 extend into the quartz capillary 300 for a certain distance from both ends of the length direction of the quartz capillary 300.

[0042] like Figure 1 As shown, in the quartz capillary 300, the first optical fiber 100 and the second optical fiber 200 are both arranged along the axis of the quartz capillary 300, and the ends of the first optical fiber 100 and the second optical fiber 200 close to each other are separated by a certain distance to form an FP cavity.

[0043] like Figure 1 As shown, the end face of the first optical fiber 100 close to the second optical fiber 200 is a reflection end face 101, which is a plane and perpendicular to the length direction of the first optical fiber 100. The end face of the second optical fiber 200 close to the first optical fiber 100 is a reflection end face 201, which is a concave spherical surface.

[0044] like Figure 1 As shown, the first optical fiber 100 and the second optical fiber 200 are respectively fused with the wall of the quartz capillary 300 at one side away from the FP cavity. The end of the first optical fiber 100 away from the FP cavity is connected to the signal receiving end for communication.

[0045] like Figure 1 As shown, the fusion points of the first optical fiber 100 and the second optical fiber 200 away from the FP cavity and the wall of the quartz capillary 300 are respectively the first fusion point 301 and the second fusion point 302. The second fusion point 302 is spherical.

[0046] like Figure 1 As shown, the quartz capillary 300 is a reducer, and the first optical fiber 100 and the second optical fiber 200 are located on the side with a small inner diameter and the side with a large inner diameter of the quartz capillary 300, respectively.

[0047] like Figure 1 As shown, the first optical fiber 100 and the second optical fiber 200 have the same specifications.

[0048] Example 2

[0049] The difference between this embodiment and embodiment 1 is: Figure 3 As shown, a fiber grating 800 is processed on the side of the first optical fiber 100 close to the FP cavity.

[0050] A method for manufacturing a high-fineness all-quartz optical fiber FP cavity sensor comprises the following steps:

[0051] Step 1: Processing the fiber grating 800 on the side of the first optical fiber 100 close to the FP cavity by femtosecond laser writing method, processing the reflection end face 201 of the second optical fiber 200, and processing the quartz capillary 300 by hot-melt stretching.

[0052] Step 2: Processing the fusion point between the side of the first optical fiber 100 and the second optical fiber 200 away from the FP cavity and the wall of the quartz capillary 300.

[0053] In the step 1 of the method for manufacturing a high-fineness all-quartz optical fiber FP cavity sensor, the processing of the second reflective end face 201 of the second optical fiber 200 is as follows: Figure 2 As shown, the following steps are included:

[0054] Step 1: Cut the second optical fiber 200 into a planar end face;

[0055] Step 2: clamp the second optical fiber 200 by the first three-dimensional adjustment frame 401, and clamp the second quartz capillary 600 by the second three-dimensional adjustment frame 402;

[0056] Step 3: by adjusting the first three-dimensional adjustment frame 401 and the second three-dimensional adjustment frame 402, the second optical fiber 200 is aligned with the second quartz capillary 600 and the end faces are close to each other;

[0057] Step 4: Install a tungsten steel ball 500 near the end of the second quartz capillary 600 near the second optical fiber 200, and the outer diameter of the tungsten steel ball 500 is equal to the inner diameter of the second quartz capillary 600. Adjust the first three-dimensional adjustment frame 401 and the second three-dimensional adjustment frame 402 to clamp the second optical fiber 200 and the second quartz capillary 600 to the tungsten steel ball 500;

[0058] Step 5: The electrode 700 is close to the end face of the second optical fiber 200 and the tungsten steel ball 500, and discharges to melt the end face of the second optical fiber 200 and form a second reflective end face 201.

[0059] In the fourth step of the processing method of the second reflective end face 201 of the second optical fiber 200 , half of the tungsten steel ball 500 enters the second quartz capillary 600 .

[0060] The processing method of the second fusion point 302 is to locally fuse and couple the quartz capillary 300 and the second optical fiber 200 together by hot melting, and to locally melt the quartz capillary 300 and the second optical fiber 200 by heating with a hydrogen-oxygen flame and melt them into a spherical shape by using surface tension.

[0061] The first fusion point 301 is processed by partially fusing and coupling the quartz capillary 300 and the first optical fiber 100 together through heat melting.

[0062] The working mode of the high-precision all-quartz optical fiber FP cavity sensor of the present invention is that the cavity between the reflection end face 101 of the first optical fiber 100 and the reflection end face 201 of the second optical fiber 200 is the FP cavity, and the reflection end face 201 is a concave spherical surface. The change of physical parameters such as ambient temperature and pressure will cause the change of the FP cavity length, thereby causing the change of the spectrum stripes. By detecting the change of the spectrum stripes by optical method, the corresponding temperature and pressure change can be detected. By changing the wall thickness of the quartz capillary 300, the pressure sensitivity can be changed.

[0063] Temperature measurement is achieved by writing the fiber Bragg grating 800 at a position of the first optical fiber 200 close to the reflective end face 101 by a femtosecond laser writing method, and the fiber Bragg grating 800 is isolated from pressure interference and is insensitive to pressure in the cavity of the FP in the quartz capillary 300. The temperature parameter measured by the fiber Bragg grating 800 can realize temperature compensation of the optical fiber FP cavity sensor, thereby realizing high-precision measurement of the temperature and pressure dual parameters.

[0064] The above are only preferred embodiments of the present invention and are not intended to limit the present invention in other forms. Any technician familiar with the profession may use the technical contents disclosed above to change or modify them into equivalent embodiments with equivalent changes and apply them to other fields. However, any simple modification or equivalent change made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for manufacturing a high-fineness all-quartz optical fiber FP cavity sensor, characterized in that: The high-fineness all-quartz optical fiber FP cavity sensor comprises a first optical fiber (100), a second optical fiber (200) and a quartz capillary tube (300); The first optical fiber (100) and the second optical fiber (200) extend into the quartz capillary tube (300) for a certain distance from both ends of the quartz capillary tube (300) in the length direction respectively; In the quartz capillary tube 1 (300), the first optical fiber (100) and the second optical fiber (200) are both arranged along the axis of the quartz capillary tube 1 (300), and the ends of the first optical fiber (100) and the second optical fiber (200) close to each other are separated by a certain distance to form an FP cavity; The end face of the first optical fiber (100) close to the second optical fiber (200) is a reflection end face one (101), and the reflection end face one (101) is a plane and perpendicular to the length direction of the first optical fiber (100); the end face of the second optical fiber (200) close to the first optical fiber (100) is a reflection end face two (201), and the reflection end face two (201) is a concave spherical surface; The first optical fiber (100) and the second optical fiber (200) are respectively fused to the wall of a quartz capillary tube (300) at a side away from the FP cavity; the end of the first optical fiber (100) away from the FP cavity is communicatively connected to a signal receiving end; The fusion points of the first optical fiber (100) and the second optical fiber (200) on the side away from the FP cavity and the wall of the quartz capillary tube (300) are respectively a first fusion point (301) and a second fusion point (302); the second fusion point (302) is spherical; The quartz capillary tube (300) is a reducer; the first optical fiber (100) and the second optical fiber (200) are respectively located on the side with a smaller inner diameter and the side with a larger inner diameter of the quartz capillary tube (300); the first optical fiber (100) and the second optical fiber (200) have the same specifications; A fiber grating (800) is processed on a side of the first optical fiber (100) close to the FP cavity; The method for making a high-fineness all-quartz optical fiber FP cavity sensor comprises the following steps: Step 1: processing a fiber grating (800) on the side of the first optical fiber (100) close to the FP cavity by a femtosecond laser writing method; processing the second reflection end face (201) of the second optical fiber (200), and processing a quartz capillary (300) by hot-melt stretching; Step 2: Processing the fusion point between the first optical fiber (100) and the second optical fiber (200) on the side away from the FP cavity and the wall of the quartz capillary tube (300).

2. The method for manufacturing a high-fineness all-quartz optical fiber FP cavity sensor according to claim 1, characterized in that: The processing of the second reflective end face (201) of the second optical fiber (200) in step 1 comprises the following steps: Step 1: cutting the second optical fiber (200) into a planar end face; Step 2: clamping the second optical fiber (200) by the first three-dimensional adjustment frame (401), and clamping the second quartz capillary (600) by the second three-dimensional adjustment frame (402); Step 3: by adjusting the first three-dimensional adjustment frame (401) and the second three-dimensional adjustment frame (402), the second optical fiber (200) is aligned with the second quartz capillary (600) and the end faces are close to each other; Step 4: installing a tungsten steel ball (500) at the end of the second quartz capillary (600) close to the second optical fiber (200), wherein the outer diameter of the tungsten steel ball (500) is equal to the inner diameter of the second quartz capillary (600); and adjusting the first three-dimensional adjustment frame (401) and the second three-dimensional adjustment frame (402) so that the second optical fiber (200) and the second quartz capillary (600) clamp the tungsten steel ball (500); Step 5: The electrode (700) is close to the end face of the second optical fiber (200) close to the tungsten steel ball (500), and discharges to melt the end face of the second optical fiber (200) and form a second reflective end face (201).

3. The method for manufacturing a high-fineness all-quartz optical fiber FP cavity sensor according to claim 2, characterized in that: In the step 4, half of the tungsten steel ball (500) enters the second quartz capillary (600).

4. The method for manufacturing a high-fineness all-quartz optical fiber FP cavity sensor according to claim 1, characterized in that: The processing method of the second fusion point (302) is to locally fuse and couple the quartz capillary tube (300) and the second optical fiber (200) together by hot melting, and to locally melt the quartz capillary tube (300) and the second optical fiber (200) by heating with a hydrogen-oxygen flame and melt them into a spherical shape by using surface tension; The first fusion point (301) is processed by locally fusing and coupling the quartz capillary tube (300) and the first optical fiber (100) together through hot melting.

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