A refractive index micro-ring sensor based on multi-core fiber taper and a measuring method thereof

Abstract

The application relates to a refractive index micro-ring sensor based on a multi-core fiber taper and a measuring method thereof. The refractive index micro-ring sensor based on the multi-core fiber taper mainly comprises a light source, a single-core fiber, a first multi-core fiber coupler, a multi-core fiber taper, a second multi-core fiber coupler and a spectrometer; the middle part of the multi-core fiber taper is smaller than the two ends, so that a fiber taper area is formed in the middle part of the multi-core fiber, and a micro-ring is formed around the waist part of the fiber taper area; wherein: the output end of the light source is connected with one end of the single-core fiber; the other end of the single-core fiber is connected with one fan-in end of the first multi-core fiber coupler; the fan-out end of the first multi-core fiber coupler is connected with one end of the multi-core fiber; the other end of the multi-core fiber is connected with the fan-out end of the second multi-core fiber coupler; and one fan-in end of the second multi-core fiber coupler is connected with the spectrometer. Compared with the existing fiber refractive index sensor, the application has higher integration and improved sensitivity.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber sensing technology, in particular to a refractive index micro-ring sensor based on a multi-core fiber taper and a measuring method thereof. BACKGROUND

[0002] Optical fiber sensors are widely used in chemical process detection, liquid density measurement, water quality detection, biomedical diagnosis and treatment, etc. due to their high sensitivity, high real-time performance and anti-electromagnetic interference, and can achieve measurement tasks that electromagnetic sensors cannot perform.

[0003] Refractive index is an important concept in the field of optics and an important property of optical materials, often reflecting density, composition, crystal orientation, and other physical and chemical properties. It has important significance in environmental pollution monitoring and industrial process monitoring. Refractive index sensors based on tapered optical fibers have been widely studied due to their simple structure, easy preparation, and low cost.

[0004] However, in order to increase the sensitivity, a reference optical fiber arm is often added to the tapered optical fiber to increase the sensitivity using the vernier effect. Although the effect is significant, it greatly reduces the integration of the system and limits the application of the tapered optical fiber refractive index sensor in a narrow environment. In order to ensure the stability of the reference arm, additional protective packaging and stable equipment are often required, further increasing the cost.

[0005] Therefore, how to overcome the defects of the prior art and solve at least part of the above technical problems is a difficult problem to be solved in the technical field. SUMMARY

[0006] In view of the defects in the prior art or the need for improvement, the present application provides a refractive index micro-ring sensor based on a multi-core fiber taper and a measuring method thereof, which can overcome the limitation of the complex structure of the existing optical fiber refractive index sensor and further improve the measurement sensitivity of the refractive index sensor.

[0007] The present application adopts the following technical solutions:

[0008] In a first aspect, the present application provides a refractive index micro-ring sensor based on a multi-core fiber taper, comprising a light source, a single-core optical fiber, a first multi-core optical fiber coupler, a multi-core fiber taper, a second multi-core optical fiber coupler, and an optical spectrum analyzer; the multi-core fiber taper has a smaller diameter in the middle than at both ends to form a fiber taper region in the middle of the multi-core fiber taper, and the waist part of the fiber taper region forms a micro-ring, wherein:

[0009] An output end of the light source is connected to one end of the single-core optical fiber for injecting the optical signal into the single-core optical fiber; the other end of the single-core optical fiber is connected to one fan-in end of the first multi-core optical fiber coupler for conducting the optical signal into the first multi-core optical fiber coupler; the fan-out end of the first multi-core optical fiber coupler is connected to one end of the multi-core optical fiber for conducting the optical signal into the multi-core optical fiber; the other end of the multi-core optical fiber is connected to the fan-out end of the second multi-core optical fiber coupler for conducting the optical signal into the second multi-core optical fiber coupler; one fan-in end of the second multi-core optical fiber coupler is connected to the optical spectrometer so that the optical spectrometer receives the optical signal and displays the spectrum.

[0010] In some embodiments, the multi-core optical fiber comprises an optical signal injection region, a sensing region, and an optical signal receiving region, wherein:

[0011] The input end of the optical signal injection region is connected to the fan-out end of the first multi-core optical fiber coupler, and the output end of the optical signal injection region is connected to the input end of the sensing region; the output end of the sensing region is connected to the input end of the optical signal receiving region; and the output end of the optical signal receiving region is connected to the fan-out end of the second multi-core optical fiber coupler.

[0012] In some embodiments, the diameter of the middle part of the sensing region is smaller than the diameters of the input end and the output end of the sensing region, and the middle part of the sensing region is wound out of a micro-ring.

[0013] In some embodiments, the optical signal injection region comprises a first fiber core group, a first cladding, and a first coating layer, wherein:

[0014] The first cladding surrounds the first fiber core group, and the first coating layer is wrapped outside the first cladding.

[0015] In some embodiments, the sensing region comprises a second fiber core group, a second cladding, and a second coating layer, wherein:

[0016] The second cladding surrounds the second fiber core group, and the second coating layer is wrapped outside the second cladding.

[0017] The diameter of the second cladding of the middle part of the sensing region is smaller than the diameters of the second claddings of the two end parts of the sensing region, and the spacing between each fiber core in the second fiber core group of the middle part of the sensing region is smaller than the spacing between each fiber core in the second fiber core group of the two end parts of the sensing region.

[0018] In some embodiments, the second coating layer is stripped off in the middle part of the sensing region, and the second coating layer is retained in the two end parts of the sensing region.

[0019] In some embodiments, the light signal receiving region comprises a third core group, a third cladding layer, and a third coating layer, wherein:

[0020] The third cladding layer surrounds the third core group, and the third coating layer surrounds the outside of the third cladding layer.

[0021] In some embodiments, the multicore optical fiber comprises a weakly coupled multicore optical fiber.

[0022] In some embodiments, the light source comprises a wide-spectrum light source.

[0023] In a second aspect, the present application provides a measurement method of a refractive index micro-ring sensor based on a multicore optical fiber taper, applied to the refractive index micro-ring sensor based on a multicore optical fiber taper of the first aspect, the measurement method comprising: inputting the light signal generated by the light source into the single-core optical fiber, and inputting the light signal into one core of the first core group of the multicore optical fiber through the first multicore optical fiber coupler, when the light signal is transmitted to the second core group of the multicore optical fiber, power coupling occurs in the fiber taper region, the light signal enters each core, and after different actions with the outside at the micro-ring, interference occurs between the light signals; inputting the sensing light signal into the optical spectrum analyzer through the second multicore optical fiber coupler, and obtaining the change of the refractive index of the outside through the drift of the interference spectrum.

[0024] Compared with the prior art, the present application has the beneficial effects that: a refractive index micro-ring sensor based on a multicore optical fiber taper and a measurement method thereof are provided, the structure of the refractive index sensor is innovated from the aspects of design, a multicore optical fiber is adopted, multiple optical fiber channels are combined in the same cladding layer, the compactness of the system is improved, the multicore optical fiber is thinned along the extension direction of the optical fiber to form a fiber taper region, the waist part of the taper is wound into a micro-ring, the difference of the actions of each core with the outside is increased, the power coupling between the cores of the weakly coupled optical fiber is enhanced, multi-beam interference is realized, the sensitivity is increased, and the refractive index sensor is suitable for high-sensitivity refractive index sensing in a narrow space. Compared with the existing optical fiber refractive index sensor, the sensor provided by the present application has higher integration and improved sensitivity. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0026] Figure 1 A structure schematic diagram of a refractive index micro-ring sensor based on a multicore optical fiber taper is provided for the embodiment 1 of the present application.

[0027] Figure 2 A multi-core fiber micro-ring structure schematic diagram provided for the embodiment 1 of the present application;

[0028] Figure 3 A light signal injection area cross-section schematic diagram provided for the embodiment 1 of the present application;

[0029] Figure 4 A sensing area cross-section schematic diagram provided for the embodiment 1 of the present application;

[0030] Figure 5 A light signal receiving area cross-section schematic diagram provided for the embodiment 1 of the present application;

[0031] Figure 6 A multi-core fiber tapering schematic diagram provided for the embodiment 1 of the present application;

[0032] Figure 7 A measurement principle schematic diagram of the refractive index micro-ring sensor based on multi-core fiber tapering provided for the embodiment 1 of the present application;

[0033] Figure 8 A measurement method flow chart of the refractive index micro-ring sensor based on multi-core fiber tapering provided for the embodiment 2 of the present application. DETAILED DESCRIPTION

[0034] In the description of the present application, the terms "inner", "outer", "longitudinal", "lateral", "upper", "lower", "left", "right", "top", "bottom" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and do not require the present application to be constructed and operated in a particular orientation, therefore should not be understood as a limitation of the present application.

[0035] The present application will be described in detail below with specific embodiments. The following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made. These are within the scope of protection of the present application. It should be noted that if there is no conflict, each feature in the embodiments of the present application can be combined with each other, and all within the scope of protection of the present application. In addition, although the functional modules may be divided in the device schematic diagram, and the steps shown or described may be executed in a different order from the order shown in the flow chart or described in some cases.

[0036] Unless otherwise defined, all technical and scientific terms used in the present disclosure have the same meanings as those commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Furthermore, various embodiments of the application can be described hereinafter in terms of technical features. No description in terms of technical features is intended to limit the scope of the application to that described in the specification. The technical features described hereinafter can be combined in any suitable manner in one or more embodiments or examples.

[0037] Unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an open, non- limiting sense, as meaning "including, but not limited to." As used herein in the description of the application, the terms "embodiment" or "embodiments," "exemplary embodiment" or "exemplary embodiments," "example" or "examples," and "specific example" or "specific examples" mean or refer to a particular feature, structure, material, or characteristic that is included in at least one embodiment or example of the disclosure. Such terms do not necessarily refer to the same embodiment or example, though they can. Embodiments of the present application are directed to each individual feature, structure, material, or characteristic of the description and drawings. In addition, any one or more of the features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples. The following detailed description is made with reference to the accompanying drawings, of which:

[0038] For the purpose of the present application, technical solutions and advantages, the following will be further described in detail in combination with the drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. The present application will be described in detail below with reference to the accompanying drawings and examples.

[0039] Example 1:

[0040] As Figure 1As shown, the embodiment of the present application provides a refractive index micro-ring sensor based on multi-core fiber taper, which comprises a light source 1, a single-core fiber 2, a first multi-core fiber coupler 3, a multi-core fiber taper 4, a second multi-core fiber coupler 5 and a spectrometer 6; the middle part of the multi-core fiber taper 4 is smaller in diameter than the two ends, so as to form a fiber taper zone in the middle part of the multi-core fiber taper 4, and the waist part of the fiber taper zone is wound into a micro-ring, wherein: the output end of the light source 1 is connected with one end of the single-core fiber 2, for injecting an optical signal into the single-core fiber 2; the other end of the single-core fiber 2 is connected with a fan-out end of the first multi-core fiber coupler 3, for conducting the optical signal into the first multi-core fiber coupler 3; the fan-out end of the first multi-core fiber coupler 3 is connected with one end of the multi-core fiber taper 4, for conducting the optical signal into the multi-core fiber taper 4; the other end of the multi-core fiber taper 4 is connected with a fan-out end of the second multi-core fiber coupler 5, for conducting the optical signal into the second multi-core fiber coupler 5; one fan-in end of the second multi-core fiber coupler 5 is connected with the spectrometer 6, so that the spectrometer 6 receives the optical signal and displays a spectrum.

[0041] In the above scheme, the multi-core fiber 4 can be divided into an optical signal injection area, a sensing area and an optical signal receiving area. Along the extension direction of the fiber, the middle part of the multi-core fiber 4 is stretched, the diameter is reduced, and a fiber taper zone is formed, and the waist part is wound into a micro-ring. The optical signal power couples in the sensing area, and due to the different responses of the core positions to the external refractive index changes, finally there is a multi-beam interference signal in each core at the output end of the multi-core fiber 4. The refractive index is measured by observing the drift of the spectrum, which increases the sensitivity while reducing the volume. The refractive index sensor provided by the present application has higher integration and increased sensitivity, and the structure is simpler, which can be applied to environmental monitoring, biological medical treatment and chemical process fields.

[0042] Specifically, the refractive index sensor provided by the present application comprises a wide-spectrum light source, a single-core fiber, two multi-core fiber couplers, a multi-core fiber and a spectrometer, and the structure of the multi-core fiber can be divided into three parts. Referring to Figure 2 As shown, in some embodiments, the multi-core fiber 4 comprises an optical signal injection area 4-1, a sensing area 4-2 and an optical signal receiving area 4-3, wherein: the input end of the optical signal injection area 4-1 is connected with the fan-out end of the first multi-core fiber coupler 3, the output end of the optical signal injection area 4-1 is connected with the input end of the sensing area 4-2; the output end of the sensing area 4-2 is connected with the input end of the optical signal receiving area 4-3; and the output end of the optical signal receiving area 4-3 is connected with the fan-out end of the second multi-core fiber coupler 5.

[0043] In some embodiments, the diameter of the middle part of the sensing region 4-2 is smaller than the diameter of the input end and the output end of the sensing region 4-2, and the middle part of the sensing region 4-2 is wound into a micro-ring.

[0044] Referring to Figure 3 In some embodiments, as shown, the light signal injection region 4-1 includes a first core group 4-1-1, a first cladding layer 4-1-2, and a first coating layer 4-1-3, wherein the first cladding layer 4-1-2 surrounds the first core group 4-1-1, and the first coating layer 4-1-3 surrounds the outside of the first cladding layer 4-1-2.

[0045] Referring to Figure 4 In some embodiments, as shown, the sensing region 4-2 includes a second core group 4-2-1, a second cladding layer 4-2-2, and a second coating layer, wherein the second cladding layer 4-2-2 surrounds the second core group 4-2-1, and the second coating layer surrounds the outside of the second cladding layer 4-2-2; it should be noted that part of the second coating layer of the sensing region 4-2 is stripped off, Figure 4 The cross section shown is the cross section after the second coating layer is stripped off. The diameter of the second cladding layer 4-2-2 of the middle part of the sensing region 4-2 is smaller than the diameter of the second cladding layer 4-2-2 of the two end parts of the sensing region 4-2; and the spacing between each core in the second core group 4-2-1 of the middle part of the sensing region 4-2 is smaller than the spacing between each core in the second core group 4-2-1 of the two end parts of the sensing region 4-2. Specifically, along the extension direction of the optical fiber, the middle part of the second core group 4-2-1 and the second cladding layer 4-2-2 are stretched, the diameter is reduced, and a fiber taper region is formed, and the waist part is wound into a micro-ring. Specifically, referring to Figure 6 As shown, the coating layer of the middle part of the multi-core optical fiber 4 can be removed, the diameter of the middle part of the multi-core optical fiber 4 is reduced by the hot melting tapering method by placing a heat source on the part where the coating layer is stripped off, and then the tapered multi-core optical fiber 4 is wound up, and a fiber micro-ring is formed at the waist part.

[0046] In some embodiments, the second coating layer of the middle part of the sensing region 4-2 is stripped off, and the second coating layer of the two end parts of the sensing region 4-2 is retained.

[0047] Referring to Figure 5 In some embodiments, as shown, the light signal receiving region 4-3 includes a third core group 4-3-1, a third cladding layer 4-3-2, and a third coating layer 4-3-3, wherein the third cladding layer 4-3-2 surrounds the third core group 4-3-1, and the third coating layer 4-3-3 surrounds the outside of the third cladding layer 4-3-2.

[0048] In some embodiments, the multicore optical fiber 4 comprises a weakly coupled multicore optical fiber, the transmission of the pre-taper light in each core is independent, and there is no coupling between the cores, that is, there is no coupling between each core in the multicore optical fiber 4.

[0049] In some embodiments, the light source 1 comprises a wide-spectrum light source.

[0050] In some embodiments, the micro-ring structure of the sensing area 4-2 is a single fiber ring.

[0051] In some embodiments, the micro-ring structure of the sensing area 4-2 has no fiber joints.

[0052] In some embodiments, the number of fiber rings and the number of joints of the sensing area 4-2 can be any number of groups

[0053] Reference Figure 7 As shown, the working principle of the sensor is that when the optical signal is transmitted from the optical signal injection area 4-1 to the taper waist of the sensing area 4-2, due to the thinning of the optical fiber and the decrease of the core spacing, the power coupling between each core is enhanced, and the optical signal is gradually distributed in each core; when the signal is conducted to the micro-ring of the sensing area 4-2, due to the different spatial positions of each core and the different bending degrees, the additional phase of the external environment to the light signal in the core is different; with the continuation of the power coupling, multi-beam interference occurs in each core of the multicore optical fiber, and finally the signal is conducted backward from the optical signal receiving area 4-3.

[0054] In summary, the embodiment of the present application provides a refractive index micro-ring sensor based on multicore optical fiber tapering, which has the following advantages: from the aspects of the structure design of the refractive index sensor, a multicore optical fiber is adopted, multiple optical fiber channels are combined in the same cladding, and the compactness of the system is improved; and along the extension direction of the optical fiber, the multicore optical fiber is thinned to form a fiber taper area, and the taper waist part is wound into a micro-ring, which increases the difference of the action of each core with the outside world and enhances the power coupling between the cores of the weakly coupled optical fiber, realizes multi-beam interference, and thus increases the sensitivity, and is suitable for high-sensitivity refractive index sensing in a narrow space. Compared with the existing optical fiber refractive index sensor, the sensor provided by the present application has higher integration and improved sensitivity.

[0055] Embodiment 2

[0056] On the basis of the refractive index micro-ring sensor based on multicore optical fiber tapering provided in the above embodiment 1, the embodiment 2 of the present application provides a measurement method of the refractive index micro-ring sensor based on multicore optical fiber tapering.

[0057] Reference Figure 8 As shown, the measurement method of the refractive index micro-ring sensor based on multicore optical fiber tapering comprises the following steps:

[0058] Step 100: the light signal generated by the light source 1 is transmitted into the single-core optical fiber 2, and is transmitted into one core of the first core group 4-1-1 of the multi-core optical fiber 4 through the first multi-core fiber coupler 3. In this step, the light signal generated by the light source 1 is the light signal generated by a wide-spectrum light source.

[0059] Step 200: when the light signal is transmitted into the second core group 4-2-1 of the multi-core optical fiber 4, power coupling occurs in the fiber taper region, the light signal enters into each core, and after different interactions with the outside at the micro-ring, interference occurs between the light signals.

[0060] Step 300: the sensing light signal is input into the optical spectrum analyzer 6 through the second multi-core fiber coupler 5, and the change of the refractive index of the outside is obtained through the drift of the interference spectrum. In this step, the change of the refractive index of the outside will cause the drift of the spectrum, and the measured value of the refractive index can be obtained through the corresponding relationship.

[0061] The measurement method of the refractive index micro-ring sensor based on the multi-core fiber taper provided by the present application is further described below with a specific example.

[0062] The sensor of the present embodiment comprises a wide-spectrum light source, a single-core optical fiber, two seven-core fiber couplers, a seven-core optical fiber, and an optical spectrum analyzer. It should be noted that, with reference to Figure 3 , Figure 4 and Figure 5 , the multi-core optical fiber 4 in the present embodiment is a seven-core optical fiber, the seven cores of the seven-core optical fiber have one at the center and the other six are arranged on the circumference of the core at the center with the same spacing; and the seven-core optical fiber is tapered so that the middle diameter of the seven-core optical fiber is smaller than the diameters of the two ends, so as to form a fiber taper region in the middle of the seven-core optical fiber, and a micro-ring is formed around the waist of the fiber taper region. In addition, the first multi-core fiber coupler 3 and the second multi-core fiber coupler 5 used in the present embodiment are both seven-core fiber couplers, so as to correspond to the seven-core optical fiber; the first multi-core fiber coupler 3 is a first seven-core fiber coupler in the present embodiment, and the second multi-core fiber coupler 5 is a second seven-core fiber coupler in the present embodiment. The light source 1 used in the present embodiment is a wide-spectrum light source. In the specific connection and arrangement, the output end of the wide-spectrum light source is connected to the input end of the single-core optical fiber, for injecting the light signal into the single-core optical fiber; the output end of the single-core optical fiber is connected to one fan-out end of the first seven-core fiber coupler, for transmitting the light signal into the first seven-core fiber coupler; the fan-out end of the first seven-core fiber coupler is connected to the input end of the seven-core optical fiber, for transmitting the light signal into the seven-core optical fiber; the output end of the seven-core optical fiber is connected to the fan-out end of the second seven-core fiber coupler, for transmitting the light signal into the second seven-core fiber coupler; and one fan-in end of the second seven-core fiber coupler is connected to the optical spectrum analyzer, so that the optical spectrum analyzer receives the light signal and displays the spectrum.

[0063] Reference is made to Figure 2 As shown in the figure, the seven-core optical fiber of the embodiment includes an optical signal injection region 4-1, a sensing region 4-2, and an optical signal receiving region 4-3, wherein: the input end of the optical signal injection region 4-1 is connected with the fan-out end of the first seven-core fiber coupler, the output end of the optical signal injection region 4-1 is connected with the input end of the sensing region 4-2; the output end of the sensing region 4-2 is connected with the input end of the optical signal receiving region 4-3; the output end of the optical signal receiving region 4-3 is connected with the fan-out end of the second seven-core fiber coupler. The diameter of the middle part of the sensing region 4-2 is smaller than the diameters of the input end and the output end of the sensing region 4-2, and the middle part of the sensing region 4-2 is wound into a micro-ring.

[0064] Reference is made to Figure 3 As shown in the figure, the optical signal injection region 4-1 of the seven-core optical fiber of the embodiment includes a first fiber core group 4-1-1, a first cladding layer 4-1-2, and a first coating layer 4-1-3, wherein: the first cladding layer 4-1-2 surrounds the first fiber core group 4-1-1, and the first coating layer 4-1-3 surrounds the outside of the first cladding layer 4-1-2.

[0065] Reference is made to Figure 4 As shown in the figure, the sensing region 4-2 of the seven-core optical fiber of the embodiment includes a second fiber core group 4-2-1, a second cladding layer 4-2-2, and a second coating layer, wherein: the second cladding layer 4-2-2 surrounds the second fiber core group 4-2-1, and the second coating layer surrounds the outside of the second cladding layer 4-2-2; the diameter of the second cladding layer 4-2-2 of the middle part of the sensing region 4-2 is smaller than the diameters of the second cladding layer 4-2-2 of the two end parts of the sensing region 4-2; the spacing between each fiber core in the second fiber core group 4-2-1 of the middle part of the sensing region 4-2 is smaller than the spacing between each fiber core in the second fiber core group 4-2-1 of the two end parts of the sensing region 4-2. Specifically, along the extension direction of the optical fiber, the middle part of the second fiber core group 4-2-1 and the middle part of the second cladding layer 4-2-2 are stretched, the diameter is reduced, forming an optical fiber taper region, and the taper waist part is wound into a micro-ring. The middle part of the sensing region 4-2 of the seven-core optical fiber of the embodiment is stripped of the second coating layer, and the two end parts of the sensing region 4-2 of the seven-core optical fiber of the embodiment retain the second coating layer.

[0066] Reference is made to Figure 5 As shown in the figure, the optical signal receiving region 4-3 of the seven-core optical fiber of the embodiment includes a third fiber core group 4-3-1, a third cladding layer 4-3-2, and a third coating layer 4-3-3, wherein: the third cladding layer 4-3-2 surrounds the third fiber core group 4-3-1, and the third coating layer 4-3-3 surrounds the outside of the third cladding layer 4-3-2.

[0067] Specifically, reference is made to Figure 6As shown, along the extension direction of the optical fiber, a section of the sensing area 4-2 of the seven-core optical fiber in the embodiment is stripped of the coating, and then a heat source is placed on the section of the seven-core optical fiber stripped of the coating, while the seven-core optical fiber is stretched, the diameter of the section of the seven-core optical fiber is reduced by the hot-melt tapering method, so that a taper is formed in the middle of the seven-core optical fiber. Then the seven-core optical fiber after the tapering is coiled to form a fiber micro-ring at the waist of the taper. In an embodiment of the present application, the micro-ring structure of the sensing area 4-2 can be a single fiber ring; in an embodiment of the present application, the micro-ring structure of the sensing area 4-2 can be a fiber knot-free; in an embodiment of the present application, the number of fiber rings and knots of the sensing area 4-2 can also be any combination of numbers.

[0068] Finally, the light source transmits the optical signal to a group of cores in the light signal injection area through the single-core optical fiber and the first seven-core optical fiber coupler, the cores transmit the optical signal to the sensing area, and power coupling occurs in the sensing area. Because the positions of the cores are different, the degree of change of the optical signal in each core caused by the change of the external refractive index is different. With the continuous coupling of the optical signals, a multi-beam interference signal will finally appear in each core, as shown. Figure 7 The sensing optical signal is transmitted to the optical spectrum analyzer through the second seven-core optical fiber coupler, and the measured change of the refractive index is obtained according to the frequency change of the spectrum drift.

[0069] In summary, the embodiment of the present application provides a measurement method of a refractive index micro-ring sensor based on a multi-core optical fiber taper, which has the following advantages: innovation from the structure design of the refractive index sensor itself, adoption of a multi-core optical fiber taper, combination of multiple optical fiber channels in the same cladding, improvement of the compactness of the system; along the extension direction of the optical fiber, the multi-core optical fiber is thinned to form an optical fiber taper area, and the waist part is coiled into a micro-ring, which increases the difference between each core and the outside world and enhances the power coupling between the cores of the weakly coupled optical fiber, realizes multi-beam interference, and thus increases the sensitivity, which is suitable for high-sensitivity refractive index sensing in a narrow space. Compared with the existing optical fiber refractive index sensor, the sensor provided by the present application has higher integration and improved sensitivity.

[0070] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not limited to them; under the idea of the present application, the technical features of the above examples or different examples can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above, which are not provided in details for simplicity; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A refractive index micro-ring sensor based on multi-core fiber taper, characterized by, The application relates to a light source (1), a single-core optical fiber (2), a first multi-core optical fiber coupler (3), a multi-core optical fiber (4) with a tapered section, a second multi-core optical fiber coupler (5) and a spectrometer (6); the diameter of the middle section of the multi-core optical fiber (4) is smaller than the diameters of the two ends of the multi-core optical fiber (4), so that a fiber taper section is formed in the middle section of the multi-core optical fiber (4), and the waist section of the fiber taper section is wound to form a micro ring. The output end of the light source (1) is connected to one end of the single-core optical fiber (2) for injecting a light signal into the single-core optical fiber (2); the other end of the single-core optical fiber (2) is connected to a fan-out end of the first multi-core optical fiber coupler (3) for transmitting the light signal into the first multi-core optical fiber coupler (3); the fan-out end of the first multi-core optical fiber coupler (3) is connected to one end of the multi-core optical fiber (4) for transmitting the light signal into the multi-core optical fiber (4); the other end of the multi-core optical fiber (4) is connected to a fan-out end of the second multi-core optical fiber coupler (5) for transmitting the light signal into the second multi-core optical fiber coupler (5); and one fan-in end of the second multi-core optical fiber coupler (5) is connected to the spectrometer (6) so that the spectrometer (6) receives the light signal and displays the spectrum.

2. The refractive index micro-ring sensor based on multi-core fiber tapering according to claim 1, characterized in that, The multi-core optical fiber (4) comprises a light signal injection section (4-1), a sensing section (4-2) and a light signal receiving section (4-3). The input end of the light signal injection section (4-1) is connected to the fan-out end of the first multi-core optical fiber coupler (3), the output end of the light signal injection section (4-1) is connected to the input end of the sensing section (4-2), the output end of the sensing section (4-2) is connected to the input end of the light signal receiving section (4-3), and the output end of the light signal receiving section (4-3) is connected to the fan-out end of the second multi-core optical fiber coupler (5).

3. The refractive index micro-ring sensor based on multi-core fiber taper according to claim 2, characterized in that, The diameter of the middle section of the sensing section (4-2) is smaller than the diameters of the input end and the output end of the sensing section (4-2), and the middle section of the sensing section (4-2) is wound to form a micro ring.

4. The refractive index micro-ring sensor based on multi-core fiber taper according to claim 2, characterized in that, The light signal injection section (4-1) comprises a first fiber core group (4-1-1), a first cladding layer (4-1-2) and a first coating layer (4-1-3). The first cladding layer (4-1-2) surrounds the first fiber core group (4-1-1), and the first coating layer (4-1-3) surrounds the outside of the first cladding layer (4-1-2).

5. The refractive index micro-ring sensor based on multi-core fiber taper according to claim 2, characterized in that, The sensing section (4-2) comprises a second fiber core group (4-2-1), a second cladding layer (4-2-2) and a second coating layer. The second cladding layer (4-2-2) surrounds the second fiber core group (4-2-1), and the second coating layer surrounds the outside of the second cladding layer (4-2-2). The diameter of the second cladding (4-2-2) of the middle part of the sensing region (4-2) is smaller than the diameter of the second cladding (4-2-2) of the two end parts of the sensing region (4-2); the distance between each core in the second core group (4-2-1) of the middle part of the sensing region (4-2) is smaller than the distance between each core in the second core group (4-2-1) of the two end parts of the sensing region (4-2).

6. The refractive index micro-ring sensor based on multi-core fiber tapering according to claim 5, characterized in that, The second coating layer is removed from the middle part of the sensing region (4-2), and the second coating layer is retained on the two end parts of the sensing region (4-2).

7. The refractive index micro-ring sensor based on multi-core fiber taper according to claim 2, characterized in that, The light signal receiving region (4-3) comprises a third core group (4-3-1), a third cladding (4-3-2) and a third coating layer (4-3-3), wherein: The third cladding (4-3-2) surrounds the third core group (4-3-1), and the third coating layer (4-3-3) surrounds the outside of the third cladding (4-3-2).

8. The refractive index micro-ring sensor based on the tapering of a multi-core optical fiber according to any of claims 1-7, characterized in that, The multicore optical fiber (4) comprises a weakly coupled multicore optical fiber.

9. The refractive index micro-ring sensor based on multiple-core fiber tapering according to any one of claims 1-7, characterized in that, The light source (1) comprises a wide-spectrum light source.

10. A measurement method of a refractive index micro-ring sensor based on a multi-core fiber taper, applied to the refractive index micro-ring sensor based on a multi-core fiber taper according to any one of claims 1-9, characterized in that, The application comprises: The light signal generated by the light source (1) is transmitted into the single-core optical fiber (2), and then into one core of the first core group (4-1-1) of the multicore optical fiber (4) through the first multicore fiber coupler (3); when the light signal is transmitted into the second core group (4-2-1) of the multicore optical fiber (4), power coupling occurs in the fiber taper region, the light signal enters each core, and after different interactions with the outside at the micro-ring, interference occurs between the light signals; the sensing light signal is input into the optical spectrum analyzer (6) through the second multicore fiber coupler (5), and the change of the refractive index of the outside is obtained through the drift of the interference spectrum.

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