Optical fiber type sensor and method for manufacturing optical fiber type sensor

Abstract

To provide an optical fiber type sensor that can stabilize an optical coupling state and can increase optical coupling efficiency even with a configuration to irradiate an element with excitation light through an optical fiber, the element having a lattice defect that emits fluorescent light upon incident of excitation light.SOLUTION: An optical fiber type sensor 1 comprises: a light source 3 that emits excitation light GL; an optical fiber 10 on one end of which the excitation light GL is incident; a diamond substrate 2 that is provided in contact with the other end of the optical fiber 10 and has a color center emitting fluorescent light RL upon incident of the excitation light GL; and a photodetector 4 that measures the intensity of the fluorescent light RL. When the optical fiber 10 and the diamond substrate 2 are not in contact with each other, the other end of the optical fiber is convex, and when the optical fiber 10 and the diamond substrate 2 are in contact with each other, at least part of the convex portion is deformed into a flat shape.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical fiber sensor and a method for manufacturing an optical fiber sensor. [Background technology]

[0002] A sensor that measures magnetic field strength based on the principle of optically detected magnetic resonance (ODMR) using an element with fluorescent lattice defects, such as a diamond substrate with an NV center, which is a material having color centers (see, for example, Non-Patent Document 1). In this sensor, green light is irradiated onto the NV center as excitation light, and microwaves are frequency-swept to detect red fluorescence emitted from the NV center. When microwaves of a resonant frequency are irradiated onto the NV center, electron spin resonance occurs in the NV center, reducing the intensity of the fluorescence emitted from the NV center. Here, the magnetic field causes Zeeman splitting in the NV center, resulting in two points of fluorescence intensity reduction corresponding to the number of energy levels split during the microwave frequency sweep. Because the Zeeman splitting in the NV center occurs with a magnitude proportional to the magnetic field strength, the difference in microwave frequencies corresponding to the two points of fluorescence intensity reduction (hereinafter referred to as the resonant frequency difference) increases in proportion to the magnetic field strength. This allows magnetic field strength to be detected based on the resonant frequency difference.

[0003] In the sensor described in Non-Patent Document 1, excitation light is propagated from a light source to a diamond substrate via a multimode fiber, and the tip of the multimode fiber is fixed to the diamond substrate with an ultraviolet-curable adhesive.

[0004] As means for joining an optical fiber to other optical elements such as a substrate, there are those that use adhesives as in the non-patent literature (Patent Document 1), and those that use a structure called a bulb-tipped fiber in which the tip of the optical fiber is processed into a spherical shape (Patent Documents 2 to 4). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 64-29809 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-188107 [Patent Document 3] Japanese Patent Application Publication No. 05-134134 [Patent Document 4] Japanese Patent Application Publication No. 05-134138 [Non-patent literature]

[0006] [Non-Patent Document 1] Yang Gao, Chaoqun Xu, Kui Huang, Yuting Gao, Nankai Wu, Zhong Yi, “Research and Experiment on the System of Miniaturized Diamond NV Center Ensemble Magnetometer Based on Fiber Coupling”, 2021 IEEE 15th International Conference on Electronic Measurement & Instruments(ICEMI) Summary of the Invention [Problem to be solved by the invention]

[0007] In the structure in which an optical fiber is fixed to a substrate with an adhesive, as in Non-Patent Document 1 and Patent Document 1, the labor and time required for applying and curing the adhesive is significant, resulting in a long manufacturing time. Furthermore, when using an adhesive, the expansion / contraction of the adhesive due to heat must be taken into consideration, and there is also the problem that the optical coupling state between the optical fiber and the diamond substrate is difficult to stabilize depending on the operating temperature. On the other hand, in the structure in which a bulb-tipped fiber is fixed to a substrate, as in Patent Documents 2 to 4, the tip of the optical fiber is heated and melted when processing the tip into a spherical shape, making it difficult to control the shape of the tip, which places restrictions on the shape and results in low optical coupling efficiency.

[0008] In view of the above circumstances, the present invention aims to provide an optical fiber sensor and a method for manufacturing the same that can stabilize the optical coupling state and increase the optical coupling efficiency even in a structure in which excitation light is irradiated via an optical fiber to an element having lattice defects that emit fluorescence when excitation light is incident thereon. [Means for solving the problem]

[0009] The optical fiber sensor of the present invention is an optical fiber sensor comprising: a light source that irradiates excitation light; an optical fiber that is arranged on the optical path of the excitation light and into which the excitation light is incident at one end; an element having a contact surface that contacts the other end of the optical fiber and having lattice defects that emit fluorescence when the excitation light is incident through the optical fiber; and a measurement unit that measures the intensity of the fluorescence; when the optical fiber and the element are not in contact, at least one of the other end of the optical fiber and the contact surface of the element is convex, and when the other end of the optical fiber and the contact surface of the element are butted together and in contact with each other, at least a portion of the convex portion is deformed into a flat shape due to the butting.

[0010] The present invention also provides a method for manufacturing an optical fiber sensor, which includes a light source that irradiates excitation light, an optical fiber that is arranged on the optical path of the excitation light and into which the excitation light is incident at one end, an element having a contact surface that contacts the other end of the optical fiber and having lattice defects that emit fluorescence when the excitation light is incident through the optical fiber, and a measurement unit that measures the intensity of the fluorescence, wherein the optical fiber and the element are configured such that at least one of the other end of the optical fiber and the contact surface of the element is convex when not in contact with each other, and the other end of the optical fiber and the contact surface of the element are butted together to deform the convex portion into a flat shape, thereby connecting the other end of the optical fiber and the element. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an optical fiber sensor and a method for manufacturing the same that can stabilize the optical coupling state and increase the optical coupling efficiency even in a structure in which excitation light is irradiated via an optical fiber to an element having lattice defects that emit fluorescence when the excitation light is incident thereon. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram showing an outline of an optical fiber sensor according to an embodiment of the present invention; [Figure 2] FIG. 1 is a diagram schematically showing the crystal structure of a diamond substrate having an NV center. [Figure 3] 1A and 1B are diagrams for explaining the principle of measuring magnetic field strength using an optical fiber sensor. [Figure 4] 10 is a graph showing the relationship between the point at which the intensity of fluorescence decreases during a microwave frequency sweep, the microwave frequency, and the magnetic field strength. [Figure 5] 2 is a cross-sectional view (a cross-sectional view perpendicular to the axial direction of the optical fiber) showing the optical fiber of FIG. 1. [Figure 6] FIG. 2 is an enlarged view showing the contact portion between the optical fiber and the diamond substrate in FIG. 1, in which the optical fiber is shown in a cross section parallel to the axial direction. [Figure 7]FIG. 6 shows a state where the optical fiber and the diamond substrate are not in contact with each other. [Figure 8] FIG. 7 is a diagram showing a conventional optical fiber sensor, and corresponds to FIG. 6. [Figure 9] FIG. 7 is a diagram showing a conventional optical fiber sensor, and corresponds to FIG. 6. [Figure 10] FIG. 8 is a diagram showing a modified example of the optical fiber sensor, and corresponds to FIG. 7. [Figure 11] FIG. 8 is a diagram showing another modified example of the optical fiber sensor, and corresponds to FIG. 7. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described below in accordance with preferred embodiments. Note that the present invention is not limited to the embodiments shown below and can be modified as appropriate without departing from the spirit of the present invention. In addition, in the embodiments shown below, some components are omitted from illustration and description, but for the details of the omitted technologies, publicly known or well-known technologies are applied as appropriate within the scope of not causing any contradictions with the content described below.

[0014] First, an outline of an optical fiber sensor 1 according to an embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a diagram showing an outline of the optical fiber sensor 1 according to an embodiment of the present invention. Fig. 1 illustrates a sensor that measures the strength of a surrounding magnetic field as the optical fiber sensor 1. The optical fiber sensor 1 shown in Fig. 1 comprises a light source 3, an optical fiber 10, a diamond substrate 2 (element), and a photodetector 4 (measurement unit). The optical fiber sensor 1 also comprises a fluorescence reflection filter 12, a microwave irradiator 6, a magnetic field generator 7, and a control unit 5.

[0015] The light source 3 is a semiconductor laser or the like that emits green excitation light GL (Green Light). The optical fiber 10 is a waveguide that transmits the excitation light GL emitted from the light source 3 and may be made of quartz or resin. The optical fiber 10 is installed on the optical path of the excitation light GL, and the excitation light GL is incident on one end. The diamond substrate 2 is a diamond substrate that has NV centers as lattice defects, which are a type of color center that emits red fluorescence RL (Red Light) when the excitation light GL is incident on it. The diamond substrate 2 is installed in contact with the other end of the optical fiber 10, and the excitation light GL is incident on it via the optical fiber 10. Note that in Figure 1, the fluorescence RL enters the optical fiber 10 and propagates through it. The photodetector 4 is a measurement unit that measures the intensity of the fluorescence RL and is installed on the optical path of the fluorescence RL. The fluorescence reflection filter 12 is a wavelength-selective filter that reflects the fluorescence RL emitted from the optical fiber 10 toward the photodetector 4 and transmits the excitation light GL. The fluorescence reflection filter 12 is located between the light source 3 and the optical fiber 10, and on the optical path of the fluorescence RL and excitation light GL. In Figure 1, the fluorescence reflection filter 12 is tilted at a predetermined angle with respect to the optical axis of the optical fiber 10. This allows the excitation light GL emitted from the light source 3 to pass through, while reflecting the fluorescence RL emitted from the optical fiber 10 toward the photodetector 4. The microwave irradiator 6 is an irradiation unit that irradiates the diamond substrate 2 with microwaves while sweeping the frequency. The magnetic field generator 7 is a device that generates a DC magnetic field around the diamond substrate 2. The control unit 5 is a computer that measures the magnetic field strength and controls the frequency of the microwaves irradiated by the microwave irradiator 6. Specifically, the control unit 5 controls the operation of the light source 3, the photodetector 4, the microwave irradiator 6, and the magnetic field generator 7, and measures the ambient magnetic field strength from the relationship between the frequency of the microwaves irradiated by the microwave irradiator 6 and the intensity of the fluorescence RL measured by the photodetector 4. The control unit 5 also uses the magnetic field generator 7 to intentionally generate a magnetic field of a predetermined strength as needed to expand the magnetic field measurement range.

[0016] In this way, the optical fiber sensor 1 irradiates the NV center with the excitation light GL and sweeps the frequency of the microwave to mainly measure the magnetic field intensity of the measurement target. The measurement principle will be described with reference to FIGS.

[0017] Figure 2 is a diagram showing a schematic diagram of the crystal structure of a diamond substrate 2 having an NV center. As shown in Figure 2, the NV center is a complex impurity defect consisting of a pair of nitrogen (N) that has entered a substitutional position of carbon in the diamond lattice and a vacancy (V) that has been removed from the carbon atom adjacent to this nitrogen. This NV center is in a neutral charge state NV 0 Capture one electron from NV - Then, the magnetic quantum number m S = -1, 0, +1 electron spin triplet states are formed.

[0018] FIG. 3 is a diagram for explaining the principle of measuring magnetic field intensity B using the optical fiber sensor 1. As shown in FIGS. 2 and 3, the NV center emits red fluorescence RL when irradiated with green excitation light GL. The intensity of this fluorescence RL depends on the magnetic quantum number m of the electron spin of the NV center electron. S Compared with the case where the electron is excited from the state of =0, the level at which electron spin resonance occurs (magnetic quantum number m S =±1 state), it becomes smaller.

[0019] For example, when a microwave MW with a resonant frequency (approximately 2.8 GHz) is irradiated onto an NV center when the magnetic field strength is zero, Zeeman splitting does not occur, and the level at which electron spin resonance (ESR) occurs is a single degenerate level. Some of the electrons photoexcited from this level return to the ground state via non-radiative transition and do not contribute to light emission. Therefore, when electrons in the NV center are excited from the level at which electron spin resonance occurs, the intensity of the fluorescence RL decreases.

[0020] Figure 4 is a graph showing the relationship between the intensity drop points of the fluorescence RL during frequency sweep of the microwave MW and the frequency of the microwave MW and the magnetic field strength B. As shown in this graph, when the magnetic field strength B is 0, there is only one point where the intensity of the fluorescence RL drops, whereas when the magnetic field strength B is a value B1, B2, B3 (B3>B2>B1>0) greater than 0, there are two points where the intensity of the fluorescence RL drops. The two points where the intensity of the fluorescence RL drops are the m S = ±1 are the frequencies of microwaves MW corresponding to the levels m S The levels of =±1 undergo Zeeman splitting so that the energy difference increases in proportion to the magnitude of the external magnetic field strength. Therefore, the frequency difference Δf (=f2-f1) between the two points increases in proportion to the magnetic field strength B. Therefore, the magnetic field strength B can be calculated from the magnitude of the frequency difference Δf. In this way, the optical fiber sensor 1 can measure the magnetic field strength B from the relationship between the intensity of the fluorescence RL and the frequency of the microwave MW. This is the principle of measuring magnetic field strength B using the optical fiber sensor 1.

[0021] Next, the structure of the contact portion between the optical fiber 10 and the diamond substrate 2, which is a characteristic part of the optical fiber sensor 1, will be described with reference to Fig. 1 and Fig. 5 to Fig. 7. Fig. 5 is a cross-sectional view (a cross-sectional view perpendicular to the axial direction of the optical fiber) showing the optical fiber of Fig. 1. The optical fiber 10 shown in Fig. 1 comprises a core 10A and a cladding 10B as shown in Fig. 5.

[0022] A light source 3 is disposed opposite one end of the optical fiber 10, specifically the end face of the core 10A, via an optical system such as a lens (not shown), and excitation light GL is incident on the core 10A from the light source 3. The excitation light GL is not emitted from the core 10A but propagates to the other end of the core 10A. A diamond substrate 2 is in contact with the other end of the core 10A (see FIG. 6), and the excitation light GL is incident on the NV center of the diamond substrate 2 from the core 10A.

[0023] Red fluorescence RL emitted from the NV center of the diamond substrate 2 enters the core 10A of the optical fiber 10. The fluorescence RL that entered the core 10A exits one end of the optical fiber 10 and is reflected by the surface of the fluorescence reflection filter 12 toward the photodetector 4. The photodetector 4 receives the fluorescence RL.

[0024] FIG. 6 is an enlarged view showing the contact area between the optical fiber 10 and the diamond substrate 2 in FIG. 1. FIG. 7 shows the state of FIG. 6 in which the optical fiber 10 and the diamond substrate 2 are not in contact. As shown in FIGS. 6 and 7, the diamond substrate 2 has a contact surface 33 that contacts the other end 31 of the optical fiber 10. Furthermore, when the optical fiber 10 and the diamond substrate 2 are not in contact, at least one of the other end 31 of the optical fiber 10 and the contact surface 33 of the diamond substrate 2 is convex. In FIG. 7, the other end 31 of the optical fiber 10 is convex. Furthermore, the other end 31 of the optical fiber 10 and the diamond substrate 2 are butted together as indicated by the white arrow in FIG. 7, thereby coming into contact with each other as shown in FIG. 6. When the optical fiber 10 and the diamond substrate 2 are in contact with each other as shown in FIG. 6, at least a portion of the convex portion of the other end 31 is deformed into a flat shape by the butting. A mechanical process such as polishing can be used to make the other end 31 of the optical fiber 10 convex. The term "convex" used herein means that the cross section parallel to the butting direction is, for example, an arc-shaped shape.

[0025] As described above, in the optical fiber sensor 1, the other end 31 of the optical fiber 10 and the contact surface 33 of the diamond substrate 2 are butted against each other. Furthermore, the convex portion formed on the other end 31 of the optical fiber 10 is pressed against the other end 31 and deformed into a flat shape during contact. In this configuration, the optical fiber 10 and the diamond substrate 2 can be tightly attached simply by butting them together, making it difficult for an air gap to form at the connection between the diamond substrate 2 and the optical fiber 10. Therefore, the optical fiber sensor 1 can reduce reflection loss at the connection between the diamond substrate 2 and the optical fiber 10 and stabilize the optical coupling state at the connection between the diamond substrate 2 and the optical fiber 10. Furthermore, the optical fiber sensor 1 does not require the melting process required for the connection, as is the case with bulb-tipped fibers. Therefore, the optical fiber sensor 1 allows for easy shape control of the tip, is not limited by its shape, and can enhance the optical coupling efficiency at the connection between the diamond substrate 2 and the optical fiber 10. Furthermore, since the optical fiber sensor 1 does not require any other substances, such as adhesives, at the connection between the diamond substrate 2 and the optical fiber 10, the diamond substrate 2 and the optical fiber 10 can be connected in a shorter time than when adhesives or other materials are used. Furthermore, compared to when an adhesive is used, the problem of expansion / contraction due to heat is less likely to occur, and the optical coupling state between the diamond substrate 2 and the optical fiber 10 can be stabilized.

[0026] The reason why the optical coupling state is stable will be specifically explained with reference to FIGS. 8 and 9. FIGS. 8 and 9 are diagrams showing a conventional optical fiber sensor and correspond to FIG. 6. When both the diamond substrate 2 and the optical fiber 10 are flat, as shown in FIG. 8, if the axis of the optical fiber 10 is tilted with respect to the normal direction of the diamond substrate 2, only the end of the optical fiber 10 will be in close contact with the diamond substrate 2. Therefore, an air gap G will be created between the non-contact portions. When the gap G is created, the boundary between the diamond substrate 2 and the gap G becomes the interface between the diamond and the air. Furthermore, the boundary between the gap G and the optical fiber 10 becomes the interface between the air and the optical fiber 10. Because a portion of the excitation light GL and the fluorescence RL is reflected at the interface, the creation of the gap G causes Fresnel reflection, reducing the optical coupling efficiency between the optical fiber 10 and the diamond substrate 2. On the other hand, since the other end 31 of the optical fiber sensor 1 of this embodiment is convex, even if the axis of the optical fiber 10 is tilted with respect to the normal direction of the diamond substrate 2, the convex portion is pressed against the diamond substrate 2 and deformed into a flat shape, resulting in close contact without the creation of the gap G. Therefore, the optical fiber sensor 1 can stabilize the optical coupling state between the diamond substrate 2 and the optical fiber 10.

[0027] On the other hand, when the optical fiber 10 is fixed to the diamond substrate 2 with an adhesive 41 as shown in FIG. 9 , no gap G occurs. However, the manufacturing of the optical fiber sensor 1 requires labor and time for applying and curing the adhesive 41, which increases the manufacturing time. Furthermore, when using the adhesive 41, thermal expansion / contraction of the adhesive 41 must be taken into consideration. Therefore, the wider the temperature range in which the optical fiber 10 is used, the more difficult it is to stabilize the optical coupling state between the optical fiber 10 and the diamond substrate 2. On the other hand, the optical fiber sensor 1 of this embodiment does not involve any other substance, such as the adhesive 41, at the connection between the diamond substrate 2 and the optical fiber 10. Therefore, the diamond substrate 2 and the optical fiber 10 can be connected in a shorter time than when the adhesive 41 is used. Furthermore, compared to when the adhesive 41 is used, the problem of thermal expansion / contraction is less likely to occur, and the optical coupling state at the connection between the diamond substrate 2 and the optical fiber 10, in this case, between the other end 31 and the contact surface 33, can be stabilized regardless of changes in the ambient temperature.

[0028] The structure for butting one of the diamond substrate 2 and the optical fiber 10 against the other is not particularly limited, as long as it can apply a stress sufficient to deform the convex portion into a flat shape when butted. For example, the optical fiber sensor 1 may include a separate pressing member that elastically deforms like a spring on at least one of the diamond substrate 2 and the optical fiber 10. Alternatively, the optical fiber sensor 1 may be configured such that the optical fiber 10 itself functions as a spring, for example, by bending the optical fiber 10 into a springy shape such as a mountain shape. The curvature of the convex portion is not particularly limited because it depends on the material, but it may be sufficient as long as it is pressed by butting and deforms into a flat shape. For example, a radius of curvature of approximately 25 mm is sufficient. In this case, if the material of the optical fiber 10 is glass (SiO2), a pressing force of 0.5 kgf or more can be applied to flatten the butted portion.

[0029] Furthermore, when the optical fiber 10 and the diamond substrate 2 are butted against each other, it is not necessary for the entire convex portion to be deformed into a flat shape.

[0030] FIG. 7 illustrates a structure in which the other end 31 of the optical fiber 10 is convex and the contact surface 33 of the diamond substrate 2 with the optical fiber 10 is flat when the optical fiber 10 and the diamond substrate 2 are not in contact with each other. However, the optical fiber sensor 1 is not limited to the structures shown in FIGS. 6 and 7 . The optical fiber sensor 1 may be configured such that at least one of the other end 31 of the optical fiber 10 and the contact surface 33 of the diamond substrate 2 with the optical fiber 10 is convex when the optical fiber 10 and the diamond substrate 2 are not in contact with each other. This point will be explained with reference to FIGS. 10 and 11 . FIG. 10 is a diagram showing a modified optical fiber sensor and corresponds to FIG. 7 . FIG. 11 is a diagram showing another modified optical fiber sensor and corresponds to FIG. 7 . As shown in FIG. 10 , the other end 31 of the optical fiber 10 may be flat and the contact surface 33 of the diamond substrate 2 with the optical fiber 10 may be convex when the optical fiber 10 and the diamond substrate 2 are not in contact with each other. 11, both the other end 31 of the optical fiber 10 and the contact surface 33 of the diamond substrate 2 with the optical fiber 10 may be convex, with the optical fiber 10 and the diamond substrate 2 not in contact with each other. As a means for making the contact surface 33 of the diamond substrate 2 with the optical fiber 10 convex, mechanical processing such as polishing may be used.

[0031] When the optical fiber 10 and the diamond substrate 2 are not in contact with each other, whether the other end 31 of the optical fiber 10 or the contact surface 33 of the diamond substrate 2, or both, should be convex can be appropriately selected taking into account the advantages of each. For example, in a structure in which the other end 31 of the optical fiber 10 is convex and the contact surface 33 of the diamond substrate 2 is flat, as shown in FIG. 7, the optical fiber 10, which has a lower hardness than the diamond substrate 2, is processed into a convex shape, which is advantageous in that wear on the processing tool can be reduced. On the other hand, in a structure in which the other end 31 of the optical fiber 10 is flat and the contact surface 33 of the diamond substrate 2 is convex, as shown in FIG. 10, the tip of the optical fiber 10 is not processed, which is advantageous in that the optical properties of the optical fiber 10 are not affected by heat, stress, etc. during processing. Furthermore, in a structure in which both the other end 31 of the optical fiber 10 and the contact surface 33 of the diamond substrate 2 are convex, the two convex portions can be deformed flat even if the deformation amount of each of the two convex portions is smaller than in a case in which there is only one convex portion. Therefore, even if the pressing force when butting is weakened, the convex portions can be flattened and brought into close contact, which is advantageous in that it increases the options for the pressing structure.

[0032] Next, a brief description of the manufacturing method of the optical fiber sensor 1 will be given. First, as shown in FIG. 7, an optical fiber 10 and a diamond substrate 2 having an NV center are prepared. At least one of the other end 31 of the optical fiber 10 and the contact surface 33 of the diamond substrate 2 is prepared so that it has a convex shape. Furthermore, the other end 31 of the optical fiber 10 is butted against the contact surface 33 of the diamond substrate 2, and the convex portion is deformed into a flat shape, thereby connecting the other end 31 of the optical fiber 10 to the diamond substrate 2. Furthermore, the light source 3, photodetector 4, fluorescence reflection filter 12, microwave irradiator 6, magnetic field generator 7, and control unit 5 shown in FIG. 1 are prepared. Next, the prepared light source 3 is positioned so that excitation light GL enters the optical fiber 10. Furthermore, the fluorescence reflection filter 12 is positioned opposite the tip surface of the core 10A of the optical fiber 10 and is on the optical path of the fluorescence RL. Next, the photodetector 4 is positioned on the optical path of the fluorescence RL reflected by the fluorescence reflection filter 12. The microwave irradiator 6 and magnetic field generator 7 are positioned near the surface of the diamond substrate 2 opposite the contact surface 33 with the optical fiber 10. Finally, the light source 3, the photodetector 4, the microwave irradiator 6, and the magnetic field generator 7 are electrically connected to the control unit 5. This completes the description of the method for manufacturing the optical fiber sensor 1.

[0033] As described above, the optical fiber sensor 1 of this embodiment includes a light source 3, an optical fiber 10, a diamond substrate 2, and a photodetector 4. When the optical fiber 10 and the diamond substrate 2 are not in contact with each other, at least one of the other end 31 of the optical fiber 10 and the contact surface 33 of the diamond substrate 2 with the optical fiber 10 is convex. On the other hand, when the other end 31 of the optical fiber 10 and the contact surface 33 of the diamond substrate 2 are butted together, at least a portion of the convex portion is deformed into a flat shape by the butting. In this configuration, the optical fiber 10 and the diamond substrate 2 are butted together, and the convex portion formed on one side is pressed by the butting and deformed into a flat shape when they are in contact. Therefore, simply butting the optical fiber 10 and the diamond substrate 2 together can achieve tight contact without any gaps. This reduces reflection loss at the connection between the diamond substrate 2 and the optical fiber 10.

[0034] Furthermore, since this embodiment does not require the process of melting the other end 31 of the optical fiber 10 as in the bulb-tipped fiber, the shape of the tip can be easily controlled, there are no shape restrictions, and the optical coupling efficiency at the connection between the diamond substrate 2 and the optical fiber 10 can be improved. Furthermore, since no other substance such as an adhesive 41 is interposed at the connection between the diamond substrate 2 and the optical fiber 10 in this embodiment, the diamond substrate 2 and the optical fiber 10 can be connected in a shorter time than when an adhesive 41 or the like is used. Furthermore, compared to when an adhesive 41 is used, problems of thermal expansion / contraction are less likely to occur, and the optical coupling state at the connection between the diamond substrate 2 and the optical fiber 10 can be stabilized over a wider temperature range. Thus, the optical fiber sensor 1 can stabilize the optical coupling state and improve the optical coupling efficiency even in a structure in which excitation light GL is irradiated via the optical fiber 10 onto an element (diamond substrate 2) having lattice defects that emits fluorescence RL when excitation light GL is incident thereon. Furthermore, the optical fiber sensor 1 can stabilize the optical coupling state and improve the optical coupling efficiency even in a structure in which fluorescence RL is incident on the optical fiber 10.

[0035] On the other hand, in this embodiment, when the optical fiber 10 and the diamond substrate 2 are not in contact with each other, the other end 31 of the optical fiber 10 is convex, and the contact surface 33 of the diamond substrate 2 with the optical fiber 10 is flat. In this configuration, the optical fiber 10 and the diamond substrate 2 are butted against each other, and the convex portion formed on the other end 31 of the optical fiber 10 is pressed against the contact surface 33 of the diamond substrate 2 during the butting, and is deformed into a flat shape. In this configuration, the optical fiber 10, which has a lower hardness than the diamond substrate 2, is processed into a convex shape, so wear on the processing tools can be suppressed.

[0036] Furthermore, in this embodiment, when the optical fiber 10 and the diamond substrate 2 are not in contact with each other, the other end 31 of the optical fiber 10 may be flat, and the contact surface 33 of the diamond substrate 2 with the optical fiber 10 may be convex. In this configuration, the optical fiber 10 and the diamond substrate 2 are butted against each other, and the convex portion formed on the contact surface 33 of the diamond substrate 2 is pressed against the other end 31 of the optical fiber 10 during butting, thereby deforming it into a flat shape. In this configuration, the other end 31 of the optical fiber 10 is not machined into a convex shape, so there is no risk of the optical properties of the optical fiber 10 being changed by heat, stress, etc. applied when the other end 31 of the optical fiber 10 is machined.

[0037] In this embodiment, when the optical fiber 10 and the diamond substrate 2 are not in contact with each other, both the other end 31 of the optical fiber 10 and the contact surface 33 of the diamond substrate 2 with the optical fiber 10 may be convex. In this configuration, the optical fiber 10 and the diamond substrate 2 are butted together, and the convex portions formed on the contact surface 33 between the other end 31 of the optical fiber 10 and the diamond substrate 2 are pressed by the butt contact, causing both to be deformed into a flat shape. In this configuration, the two convex portions are butted together to deform, so the amount of deformation of each of the two convex portions can be reduced compared to when one convex portion is pressed against a flat portion. Therefore, even if the pressing force when butting together is weak, the convex portions can be flattened and tightly attached, increasing the options for the pressing structure.

[0038] Furthermore, in the manufacturing method of the optical fiber sensor 1 according to this embodiment, the optical fiber 10 and the diamond substrate 2 are used such that at least one of the other end 31 of the optical fiber 10 and the contact surface 33 of the diamond substrate 2 with the optical fiber 10 is convex when not in contact. Furthermore, in the manufacturing method of the optical fiber sensor 1 according to this embodiment, the other end 31 of the optical fiber 10 is connected to the diamond substrate 2 by butting the optical fiber 10 against the diamond substrate 2 and deforming the convex portion into a flat shape. In this configuration, the optical fiber 10 and the diamond substrate 2 are butted against each other, and the convex portion formed on one side is pressed by the butt joint and deformed into a flat shape when in contact. Therefore, the optical fiber 10 and the diamond substrate 2 can be tightly attached simply by butting them against each other, which reduces reflection loss at the connection between the diamond substrate 2 and the optical fiber 10 and stabilizes the optical coupling state between the diamond substrate 2 and the optical fiber 10.

[0039] Furthermore, the method for manufacturing the optical fiber sensor 1 according to this embodiment does not require a step of melting the other end 31 of the optical fiber 10 as in the case of a bulb-tipped fiber. Therefore, the shape of the tip can be easily controlled, there are no shape restrictions, and the optical coupling efficiency at the connection between the diamond substrate 2 and the optical fiber 10 can be improved. Furthermore, in the method for manufacturing the optical fiber sensor 1 according to this embodiment, no other substance such as the adhesive 41 is interposed at the connection between the diamond substrate 2 and the optical fiber 10, so the diamond substrate 2 and the optical fiber 10 can be connected in a shorter time than when the adhesive 41 is used. Furthermore, compared to when the adhesive 41 is used, problems of thermal expansion / contraction are less likely to occur, and the optical coupling state at the connection between the diamond substrate 2 and the optical fiber 10 can be stabilized over a wider temperature range.

[0040] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and modifications may be made within the scope of the spirit of the present invention, and publicly known or well-known technologies may be combined as appropriate.

[0041] For example, in this embodiment, a substrate having an NV center is exemplified as the diamond substrate 2, but the diamond substrate 2 is not limited to a substrate having an NV center as long as it has lattice defects that emit fluorescence RL when irradiated with excitation light GL. For example, the diamond substrate 2 may be a diamond substrate having an SnV color center consisting of tin (Sn) and vacancies V, an SiV color center consisting of silicon (Si) and vacancies V, or a GeV color center consisting of germanium (Ge) and vacancies V.

[0042] Furthermore, in this embodiment, the optical fiber 10 has been exemplified as having a single clad structure including the core 10A and the clad 10B, but the optical fiber 10 may have a double clad structure.

[0043] Furthermore, in this embodiment, a magnetic sensor is exemplified as the optical fiber sensor 1, but the present invention can also be applied to a fluorescent temperature sensor or the like that generates a temperature signal from the center position of two resonance frequencies.

[0044] Furthermore, in this embodiment, the diamond substrate 2 is exemplified as an element, but the element is not limited to the diamond substrate 2. For example, SiC having spin defects called silicon vacancies may be used as the element. [Explanation of symbols]

[0045] 1: Optical fiber sensor 2: Diamond substrate (element) 3:Light source 4: Photodetector (measurement unit) 5: Control section 10: Optical fiber 31: Other end 33: Contact surface GL: Excitation light RL: Fluorescent

Claims

1. an optical fiber sensor including a light source that irradiates excitation light; an optical fiber that is provided on an optical path of the excitation light and into which the excitation light is incident at one end; an element having a contact surface that contacts the other end of the optical fiber and that has lattice defects and that emits fluorescence when the excitation light is incident via the optical fiber; and a measuring unit that measures the intensity of the fluorescence, When the optical fiber and the element are not in contact with each other, at least one of the other end of the optical fiber and the contact surface of the element is convex, An optical fiber type sensor characterized in that when the other end of the optical fiber and the contact surface of the element are butted together and in contact with each other, at least a portion of the convex portion is deformed into a flat shape due to the butting.

2. 2. The optical fiber sensor according to claim 1, wherein the other end of the optical fiber is convex and the contact surface of the element is flat when the optical fiber and the element are not in contact with each other.

3. 2. The optical fiber sensor according to claim 1, wherein the other end of the optical fiber is flat and the contact surface of the element is convex when the optical fiber and the element are not in contact with each other.

4. 2. The optical fiber sensor according to claim 1, wherein both the other end of the optical fiber and the contact surface of the element are convex when the optical fiber and the element are not in contact with each other.

5. 1. A method for manufacturing an optical fiber sensor comprising: a light source that irradiates excitation light; an optical fiber that is provided on an optical path of the excitation light and into which the excitation light is incident at one end; an element having a contact surface that contacts the other end of the optical fiber and having lattice defects that emits fluorescence when the excitation light is incident via the optical fiber; and a measurement unit that measures the intensity of the fluorescence, The optical fiber and the element are configured so that at least one of the other end of the optical fiber and the contact surface of the element is convex when not in contact with each other, A method for manufacturing an optical fiber sensor, characterized in that the other end of the optical fiber and the element are connected by butting the other end of the optical fiber with the contact surface of the element and deforming the convex portion into a flat shape.

Images