sensor

Abstract

To provide a sensor capable of irradiating an element having an NV center with exciting light and also enhancing light gathering efficiency of fluorescent light emitted by the element.SOLUTION: A sensor comprises: a diamond element 2 which has a color center irradiated with exciting light GL to emit fluorescent light RL; a light source 3 emitting the exciting light GL; an optical sensor 4 receiving the fluorescent light RL; a core 10A propagating the exciting light GL emitted by the light source 3 up to the diamond element 2; and a double-clad fiber 10D having a first clad 10B propagating the fluorescent light RL emitted at the color center arranged outside the core 10A toward the optical sensor 4 and a second clad 10C arranged outside the first clad 10B.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a sensor. [Background technology]

[0002] A sensor is known that measures magnetic fields using the principle of optically detected magnetic resonance (ODMR) with a diamond element having an NV center (see, for example, Non-Patent Document 1). In this sensor, green light is irradiated onto the NV center as excitation light, and microwaves are irradiated onto the NV center while sweeping the frequency, and the red fluorescence emitted from the NV center is detected. In this sensor, when microwaves at the resonance frequency are irradiated onto the NV center, electron spin resonance occurs in the NV center, and the brightness of the fluorescence emitted from the NV center decreases. Here, the magnetic field causes Zeeman splitting in the NV center, resulting in at least two points of fluorescence brightness reduction during microwave frequency sweep. Since the Zeeman splitting in the NV center occurs in a magnitude proportional to the magnetic field strength, the difference in microwave frequencies corresponding to the two points of fluorescence brightness reduction (hereinafter referred to as frequency split) increases in proportion to the magnetic field strength. As a result, the magnetic field strength can be detected based on the magnitude of this microwave frequency split.

[0003] In the sensor described in Non-Patent Document 1, excitation light is propagated from the light source to the diamond element via a multimode fiber, and fluorescence is propagated from the diamond element to the photodetector via the same multimode fiber. [Prior art documents] [Patent Documents]

[0004] [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) [Overview of the project] [Problems that the invention aims to solve]

[0005] The core diameter of multimode fibers is large, ranging from tens to hundreds of micrometers. Therefore, the use of multimode fibers can increase the light collection efficiency of the core of the fluorescence emitted from the diamond element. However, in multimode fibers, light of various modes propagates. Therefore, when mounted on an object that vibrates, the interference state between modes changes as the propagating mode changes in the multimode fiber, resulting in excessive modal noise. This modal noise significantly affects the optical properties of the excitation light, degrading the performance of the diamond element's excitation by the excitation light.

[0006] On the other hand, from the perspective of suppressing modal noise, it is conceivable to use single-mode fibers. However, single-mode fibers have a relatively small core diameter of 10 μm or less, resulting in low collection efficiency of fluorescence emitted in all directions from the diamond element. Therefore, the use of single-mode fibers reduces the sensitivity of the sensor.

[0007] In view of the above circumstances, the present invention aims to provide a sensor that can suitably irradiate an element having a color center such as an NV center with excitation light, and can increase the light collection efficiency of the fluorescence emitted from the element.

Means for Solving the Problem

[0008] The sensor of the present invention includes an element having a color center that emits fluorescence upon irradiation with excitation light, a light source that emits the excitation light, a light receiving unit that receives the fluorescence, a core that propagates the excitation light emitted from the light source to the element, a first cladding that is disposed outside the core and propagates the fluorescence emitted by the color center toward the light receiving unit, and a double-clad fiber having a second cladding disposed outside the first cladding.

Advantages of the Invention

[0009] According to the present invention, excitation light can be suitably irradiated onto an element having a color center such as an NV center, and the light collection efficiency of the fluorescence emitted from the element can be increased.

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is a diagram showing an outline of a sensor according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram schematically showing the structure of a diamond element having an NV center. [Figure 3] FIG. 3 is a diagram for explaining the principle of a diamond quantum sensor that includes a diamond element having an NV center and measures the magnetic field strength or the like based on the principle of optically detected magnetic resonance. [Figure 4] FIG. 4 is a graph showing the relationship between the luminance decrease point of fluorescence during microwave frequency sweeping, the microwave frequency, and the magnetic field strength. [Figure 5] FIG. 5 is a cross-sectional view showing a double-clad fiber. [Figure 6] FIG. 6 is a diagram showing a state in which excitation light is incident on a diamond element from the tip surface of a double-clad fiber. [Figure 7] FIG. 7 is a diagram showing a state in which fluorescence is radiated from a portion of a diamond element excited by excitation light. [Figure 8]Figure 8 shows the fluorescence state within the diamond element. [Figure 9] Figure 9 is a cross-sectional view showing that some of the fluorescence emitted from the excited portion of the diamond element is focused onto the first cladding. [Figure 10] Figure 10 is a perspective view showing the tip of a double-clad fiber and a diamond element of a sensor according to another embodiment of the present invention. [Figure 11] Figure 11 shows the fluorescence state within the diamond element. [Figure 12] Figure 12 is a perspective view showing the tip of a double-clad fiber and a diamond element of a sensor according to another embodiment of the present invention. [Figure 13] Figure 13 is a cross-sectional view showing the tip of a double-clad fiber and an element of a sensor according to another embodiment of the present invention. [Figure 14] Figure 14 is a cross-sectional view showing the tip of a double-clad fiber and an element of a sensor according to another embodiment of the present invention. [Figure 15] Figure 15 is a cross-sectional view showing the tip of a double-clad fiber and an element of a sensor according to another embodiment of the present invention. [Figure 16] Figure 16 is a cross-sectional view showing the tip of a double-clad fiber and an element of a sensor according to another embodiment of the present invention. [Figure 17] Figure 17 is a cross-sectional view showing the tip of a double-clad fiber and an element of a sensor according to another embodiment of the present invention. [Figure 18] Figure 18 is a perspective view showing a diamond element according to another embodiment of the present invention. [Figure 19] Figure 19 is a cross-sectional view showing the tip of a double-clad fiber and an element of a sensor according to another embodiment of the present invention. [Figure 20] Figure 20 is a cross-sectional view showing the tip of a double-clad fiber and an element of a sensor according to another embodiment of the present invention. [Figure 21]Figure 21 is a cross-sectional view showing the tip of a double-clad fiber and an element of a sensor according to another embodiment of the present invention. [Figure 22] Figure 22 is a cross-sectional view showing the tip of a double-clad fiber and an element of a sensor according to another embodiment of the present invention. [Modes for carrying out the invention]

[0011] The present invention will be described below in accordance with preferred embodiments. However, the present invention is not limited to the embodiments shown below, and can be modified as appropriate without departing from the spirit of the invention. Furthermore, in the embodiments shown below, some components are not illustrated or described; however, details of the omitted technologies can be appropriately applied from publicly known or well-known technologies, to the extent that they do not contradict the content described below.

[0012] Figure 1 is a schematic diagram of a sensor 1 according to one embodiment of the present invention. As shown in this figure, the sensor 1 comprises a diamond element 2, a light source 3, an optical sensor 4, a control and calculation processing unit 5, a microwave irradiator 6, a magnetic field generator 7, and an optical fiber 10.

[0013] The diamond element 2 has an NV center. The light source 3 emits excitation light GL, which is green light. The photosensor 4 detects the optical signal generated due to the electron spin resonance of the NV center. The control and processing unit 5 processes the optical signal detected by the photosensor 4 and controls the entire sensor 1. The microwave irradiator 6 irradiates the diamond element 2 with a tunable frequency microwave. The magnetic field generator 7 generates a DC magnetic field around the diamond element 2. The optical fiber 10 propagates the excitation light GL from the light source 3 to the diamond element 2 and the red fluorescence RL (described later) from the diamond element 2 to the photosensor 4.

[0014] Sensor 1, configured as described above, irradiates the NV center with excitation light GL and simultaneously irradiates the NV center with microwaves while sweeping the frequency, and measures the magnetic field strength, electric field strength, temperature, etc. of the object to be measured using the principle of photodetection magnetic resonance.

[0015] The optical fiber 10 comprises a double-clad fiber 10D and a double-clad fiber coupler 10E. The double-clad fiber coupler 10E comprises mutually fused double-clad fibers 10F and multimode fiber 10G, and connection ports 10H, 10I, and 10J.

[0016] Connection port 10H is provided at one end of the double-clad fiber 10F, and connection port 10I is provided at the other end of the double-clad fiber 10F. The multimode fiber 10G branches off from the double-clad fiber 10F, and connection port 10J is provided at one end (tip) of the multimode fiber 10G.

[0017] A light source 3 is connected to connection port 10H, for example, via an optical system such as a lens. One end of a double-clad fiber 10D is connected to connection port 10I, and the other end of a double-clad fiber 10F is connected to one end of the double-clad fiber 10D via connection port 10I. Furthermore, a light sensor 4 is connected to connection port 10J.

[0018] Double-clad fiber 10D, 10F comprises a core 10A, a first cladding layer 10B, and a second cladding layer 10C. In double-clad fiber 10D, 10F, the outer cladding of the core 10A has a two-layer structure, with the inner cladding being the first cladding layer 10B and the outer cladding layer being the second cladding layer 10C.

[0019] The core 10A of double-clad fiber 10D and the core 10A of double-clad fiber 10F are connected via connection port 10I. Furthermore, the first cladding 10B of double-clad fiber 10D and the first cladding 10B of double-clad fiber 10F are connected via connection port 10I. Additionally, the second cladding 10C of double-clad fiber 10D and the second cladding 10C of double-clad fiber 10F are connected via connection port 10I.

[0020] Here, the light source 3 is positioned opposite the end face of the core 10A of the double-clad fiber 10F via an optical system such as a lens, and emits excitation light GL toward the core 10A of the double-clad fiber 10F. Due to the properties of the double-clad fiber, the excitation light GL is not emitted from the core 10A of the double-clad fibers 10D and 10F, but propagates to the tip of the core 10A of the double-clad fiber 10D. Furthermore, a diamond element 2 is in contact with the tip surface of the core 10A of the double-clad fiber 10D, and the excitation light GL is incident from the core 10A to the NV center of the diamond element 2.

[0021] On the other hand, the diamond element 2 is in contact with the leading edge of the first cladding 10B of the double-clad fiber 10D, and the red fluorescence RL emitted from the NV center of the diamond element 2 is incident on the first cladding 10B of the double-clad fiber 10D. The fluorescence RL incident on the first cladding 10B of the double-clad fiber 10D propagates through the first cladding 10B of the double-clad fibers 10D and 10F to reach the multimode fiber 10G.

[0022] The multimode fiber 10G comprises a core 10K and an outer cladding 10L surrounding the core 10K. The core 10K branches off from the first cladding 10B of the double-cladded fiber 10F.

[0023] The light sensor 4 is positioned opposite the leading edge of the core 10K of the multimode fiber 10G, and receives the fluorescent RL that has propagated to the leading edge of the core 10K of the multimode fiber 10G.

[0024] Figure 2 schematically shows the structure of a diamond element 2 having an NV center. As shown in this figure, an NV center is a composite impurity defect consisting of a nitrogen (N) atom that has entered a carbon substitution position in the diamond lattice and a vacancy (V) where an adjacent carbon atom has been removed. This NV center is in a neutral charge state NV 0 NV captures one electron from- Therefore, the magnetic quantum number m S It forms an electron spin triplet state of -1, 0, and +1. The diamond quantum sensor uses this electron spin triplet state to measure magnetic fields, electric fields, temperature, strain, etc.

[0025] Figure 3 is a diagram illustrating the principle of a diamond quantum sensor that measures magnetic field strength and other parameters using the principle of photodetection magnetic resonance, equipped with a diamond element 2 having an NV center. As shown in Figures 2 and 3, the NV center emits red fluorescence RL when irradiated with green excitation light GL. The brightness of this fluorescence RL is determined by the ground state of the NV center (electron spin magnetic quantum number m). S While the excitation is large when the electron spin is excited from a state where =0, the NV center is at an energy level where electron spin resonance occurs (magnetic quantum number m of electron spin). S The excitation level becomes smaller when the excitation is performed from a state of ±1.

[0026] Here, when the magnetic field strength is 0, if microwaves (MW) at the resonance frequency (approximately 2.8 GHz) are irradiated onto the NV center, the NV center will reach an energy level (m) where electron spin resonance (ESR) occurs. S The transition occurs to (±1). Some of the electrons photoexcited from this level return to the ground state via a non-radiative transition and do not contribute to emission. Therefore, as described above, when the NV center is excited from a level where electron spin resonance occurs, the brightness of the fluorescent RL decreases.

[0027] Figure 4 is a graph showing the relationship between the frequency of the microwave MW and the magnetic field strength B, and the luminance depletion points of the fluorescent RL during frequency sweep of the microwave MW. As shown in this graph, when the magnetic field strength B is 0, there is only one luminance depletion point for the fluorescent RL. However, when the magnetic field strength B is a value greater than 0, B1, B2, B3 (B3>B2>B1>0), there are two luminance depletion points for the fluorescent RL. Here, the frequency split Δf (=f2-f1) of the microwave MW corresponding to the two luminance depletion points of the fluorescent RL increases in proportion to the magnetic field strength B.

[0028] Figure 5 is a cross-sectional view showing a double-clad fiber 10D. As shown in this figure, in the double-clad fiber 10D, a first cladding 10B is arranged on the outside of the core 10A, and a second cladding 10C is arranged on the outside of the first cladding 10B. The second cladding 10C is covered with a coating material (not shown). The double-clad fiber 10F (see Figure 1) has a similar configuration.

[0029] Core 10A has a low NA (e.g., 0.11-0.13, where NA is the numerical aperture) and a small cross-sectional area (e.g., a diameter of 10 μm or less). On the other hand, the first cladding 10B has a higher NA (e.g., around 0.5) and a larger cross-sectional area (e.g., a diameter of several tens to several hundred μm) compared to core 10A. The second cladding 10C is formed of, for example, a low refractive index polymer in order to increase the NA of the first cladding 10B.

[0030] Figure 6 shows the state in which the excitation light GL is incident on the diamond element 2 from the tip surface of the double-clad fiber 10D. As shown in this figure, the diamond element 2 is formed in a rectangular parallelepiped shape and has an upper surface 2A, a lower surface 2B, and a side surface 2C. The upper surface 2A is the plane to which the tip surface of the double-clad fiber 10D abuts, and is the incident surface on which the excitation light GL is incident. The lower surface 2B is a plane parallel to the upper surface 2A. The side surface 2C is a circumferential surface that connects the periphery of the upper surface 2A and the periphery of the lower surface 2B, and is rectangular in plan view.

[0031] The areas of the upper surface 2A and the lower surface 2B are greater than the cross-sectional area of ​​the core 10A. Also, the length of one side of the upper surface 2A and the lower surface 2B is greater than the diameter of the first cladding 10B. The center of the core 10A coincides with the centers of the upper surface 2A and the lower surface 2B, and the tip surface of the core 10A abuts against the center of the upper surface 2A. Also, the center of the first cladding 10B coincides with the centers of the upper surface 2A and the lower surface 2B, and the entire tip surface of the first cladding 10B abuts against the upper surface 2A.

[0032] As described above, since the NA of the core 10A is as low as about 0.11 to 0.13 (about 0.1), the emission angle of the excitation light GL from the end face of the core 10A is suppressed to be small, and the excitation light GL with a high energy density is irradiated onto a narrow area of the diamond element 2. Further, the path of the excitation light GL is single-mode. Therefore, even when the sensor 1 is mounted on a moving body or an object where other vibrations may occur, modal noise such as that in a multi-mode does not occur.

[0033] The NA of the core 10A is about 0.1, while the refractive index of the diamond element 2 is 2.42 (about 2.4). Therefore, the excitation light GL directly incident from the core 10A to the diamond element 2 has a divergence angle of about 2.4° within the diamond element 2.

[0034] FIG. 7 is a diagram showing a state in which fluorescence RL is radiated from a portion (hereinafter referred to as an excitation portion) 2D of the diamond element 2 excited by the excitation light GL. As shown in this figure, the fluorescence RL is radiated omnidirectionally from the excitation portion 2D of the diamond element 2.

[0035] FIG. 8 is a diagram showing the state of fluorescence RL within the diamond element 2. As shown in this figure, a part of the fluorescence RL radiated from the excitation portion 2D exits into the air from the lower surface 2B and the side surface 2C. Specifically, assuming that the refractive index of the diamond element 2 is about 2.4 and the refractive index of air is 1.0, according to Snell's law (see the following equation (1)), the fluorescence RL is radiated into the air when θ dia < 24.4°. On the other hand, the fluorescence RL is reflected at an angle θ dia > 24.4° at the interface between the diamond element 2 and air at a reflection angle θ ref (= θ dia ) and undergoes total reflection. n1 × sin θ dia = n2 × sin θ air …(1) However, n1 is the refractive index of the diamond element 2, n2 is the refractive index of air, θ dia is the incident angle, and θ air is the exit angle.

[0036] Figure 9 is a cross-sectional view showing the state in which a portion of the fluorescence RL emitted from the excited portion 2D of the diamond element 2 is focused onto the first cladding 10B. As shown in this figure, a portion of the fluorescence RL emitted from the excited portion 2D is reflected from the bottom surface 2B or the side surface 2C and directed toward the top surface 2A.

[0037] Here, due to the relatively large NA of the first cladding 10B, the range of incident angles of the fluorescent RL at the interface between the diamond element 2 and the first cladding 10B is widened. Specifically, assuming that the refractive index of the diamond element 2 is approximately 2.4 and the NA of the first cladding 10B is 0.5, the fluorescent RL propagates to the first cladding 10B when the incident angle at the interface between the diamond element 2 and the first cladding 10B is 11.9° or less. Furthermore, coupled with the fact that the diameter of the first cladding 10B is large compared to the diameter of the core of the single-mode fiber, the range of incident angles of the fluorescent RL into the double-cladding fiber 10D is relatively widened, and the focusing efficiency of the fluorescent RL into the optical fiber 10 (see Figure 1) is relatively high.

[0038] As described above, in the sensor 1 of this embodiment, the core 10A of the double-clad fibers 10F, 10D propagates the excitation light GL emitted from the light source 3 to the diamond element 2. As a result, similar to the case where a single-mode fiber is used, the generation of modal noise can be suppressed and fluctuations in the light intensity of the excitation light GL can be reduced, leading to improved sensor performance.

[0039] On the other hand, in the sensor 1 of this embodiment, the first cladding 10B of the double-clad fibers 10D, 10F propagates the fluorescent RL emitted from the NV center of the diamond element 2 toward the photosensor 4. As a result, the fluorescent RL emitted from the NV center can be collected with high collection efficiency, similar to when a multimode fiber is used, and the sensitivity of the sensor 1 can be improved.

[0040] Furthermore, in the sensor 1 of this embodiment, a double-clad fiber coupler 10E is connected to the double-clad fiber 10D. This double-clad fiber coupler 10E includes a double-clad fiber 10F connected to the double-clad fiber 10D, and a multimode fiber 10G branching off from the double-clad fiber 10F. The core 10A of the double-clad fiber 10F propagates the excitation light GL emitted from the light source 3 to the core 10A of the double-clad fiber 10D. In addition, fluorescence RL propagates from the first cladding 10B of the double-clad fiber 10D to the first cladding 10B of the double-clad fiber 10F.

[0041] Here, the core 10K of the multimode fiber 10G propagates the fluorescent RL from the first cladding 10B of the double-cladded fiber 10F to the optical sensor 4. As a result, the fluorescent RL, which has been collected with high collection efficiency by the first cladding 10B of the double-cladded fiber 10D, can be detected by the optical sensor 4, realizing a highly sensitive sensor 1.

[0042] Furthermore, in the sensor 1 of this embodiment, the microwave irradiator 6 (see Figure 1) irradiates the NV center of the diamond element 2 with microwaves MW. As a result, the excitation light GL is irradiated onto the NV center, and the microwaves are irradiated onto the NV center while sweeping the frequency, and the sensor 1 is realized that measures the magnetic field strength, electric field strength, temperature, etc. of the object to be measured using the principle of photodetection magnetic resonance.

[0043] Furthermore, in the sensor 1 of this embodiment, the magnetic field generator 7 (see Figure 1) generates a DC magnetic field around the NV center of the diamond element 2 and adjusts the DC magnetic field. This realizes a sensor 1 in which the offset of the magnetic field sensor can be adjusted.

[0044] Figure 10 is a perspective view showing the tip of the double-clad fiber 10D and the diamond element 20 of a sensor according to another embodiment of the present invention. Components similar to those in the above-described embodiments are denoted by the same reference numerals, and the descriptions of the above-described embodiments will be used accordingly.

[0045] As shown in Figure 10, the diamond element 20 of this embodiment is formed in the shape of a truncated square pyramid and comprises an upper surface 20A, a lower surface 20B, and a side surface 20C. The upper surface 20A is a square-shaped plane to which the tip surface of the double-clad fiber 10D abuts, and is the incident surface to which the excitation light GL is incident. The lower surface 20B is a square-shaped plane parallel to the upper surface 20A, similar in shape to the upper surface 20A, and relatively smaller in area. The side surface 20C is a circumferential surface that connects the periphery of the upper surface 20A and the periphery of the lower surface 20B.

[0046] The area of ​​the upper surface 20A is larger than the cross-sectional area of ​​the core 10A. Also, the length of one side of the upper surface 20A is larger than the diameter of the first cladding 10B. The center of the core 10A coincides with the centers of the upper surface 20A and the lower surface 20B, and the tip surface of the core 10A abuts against the center of the upper surface 20A. Also, the center of the first cladding 10B coincides with the centers of the upper surface 20A and the lower surface 20B, and the entire tip surface of the first cladding 10B abuts against the upper surface 20A.

[0047] Here, the side surface 20C is an inclined surface that slopes outward from the center of the diamond element 20, from the bottom surface 20B to the top surface 20A. In other words, the side surface 20C is inclined such that the cross-sectional area of ​​the diamond element 20 gradually increases from the bottom surface 20B to the top surface 20A.

[0048] Figure 11 shows the state of fluorescence RL within the diamond element 20. As shown in this figure, a portion of the fluorescence RL emitted from the excited portion is reflected by the bottom surface 20B and the side surface 20C. As in the embodiment described above, assuming that the refractive index of the diamond element 20 is 2.42 (approximately 2.4) and the refractive index of air is 1.0, the fluorescence RL is θ dia Total internal reflection occurs at the interface between the diamond element 20 and the air when the angle is >24.4°. On the other hand, the fluorescent RL is θ dia It is emitted into the air when the temperature is <24.4°.

[0049] Here, the side surface 20C is inclined outward from the center of the diamond element 20, from the bottom surface 20B towards the top surface 20A. As a result, compared to the case where the side surface 20C is vertical, the angle of incidence of the fluorescent RL reflected from the bottom surface 20B to the side surface 20C is larger, and the proportion of fluorescent RL that is reflected toward the first cladding 10B without being emitted into the air at the interface between the side surface 20C and the air is increased.

[0050] Furthermore, compared to the case where the side surface 20C is vertical, the incident angle θ of the fluorescence RL at the interface between the diamond element 20 and the first cladding 10B is different. dia_clad By satisfying these conditions, the proportion of fluorescent RL incident on the first cladding 10B increases. For example, assuming that the refractive index of the diamond element 20 is approximately 2.4 and the NA of the first cladding 10B is 0.5, the incident angle θ of the fluorescent RL at the interface between the diamond element 20 and the first cladding 10B is... dia_clad The condition is θ dia_clad The result is <11.9°.

[0051] As described above, according to this embodiment, in addition to the fact that the diameter of the first cladding 10B is larger than the diameter of the core of the single-mode fiber, the proportion of the fluorescent RL reflected within the diamond element 20 toward the first cladding 10B and the incident angle θ of the fluorescent RL are also present. dia_clad The proportion of conditions that are met increases. As a result, the fluorescent RL emitted from the NV center can be focused with high concentration efficiency.

[0052] Figure 12 is a perspective view showing the tip of the double-clad fiber 10D and the diamond element 30 of a sensor according to another embodiment of the present invention. Components similar to those in the above-described embodiments are denoted by the same reference numerals, and the descriptions of the above-described embodiments will be used accordingly.

[0053] As shown in Figure 12, the diamond element 30 of this embodiment is formed in a frustoconical shape and comprises an upper surface 30A, a lower surface 30B, and a side surface 30C. The upper surface 30A is a circular plane to which the tip surface of the double-clad fiber 10D abuts, and is the incident surface to which the excitation light GL is incident. The lower surface 30B is a circular plane parallel to the upper surface 30A, is similar in shape to the upper surface 30A, and has a relatively smaller area. The side surface 30C is a circumferential surface that connects the periphery of the upper surface 30A and the periphery of the lower surface 30B.

[0054] The area of ​​the upper surface 30A is larger than the cross-sectional area of ​​the core 10A. Also, the diameter of the upper surface 30A is larger than the diameter of the first cladding 10B. The center of the core 10A coincides with the centers of the upper surface 30A and the lower surface 30B, and the tip surface of the core 10A abuts against the center of the upper surface 30A. Also, the center of the first cladding 10B coincides with the centers of the upper surface 30A and the lower surface 30B, and the entire tip surface of the first cladding 10B abuts against the upper surface 30A.

[0055] Here, the side surface 30C is an inclined surface that slopes from the center side to the outer circumference side of the diamond element 30, from the bottom surface 30B side to the top surface 30A side. In other words, the side surface 30C is inclined such that the cross-sectional area of ​​the diamond element 30 gradually increases from the bottom surface 30B side to the top surface 30A side.

[0056] According to this embodiment with the above configuration, the diameter of the first cladding 10B is larger than the diameter of the core of the single-mode fiber, and the proportion of the fluorescent RL reflected within the diamond element 30 toward the first cladding 10B, and the incident angle θ of the fluorescent RL are also large. dia_clad The proportion of conditions that are met increases. As a result, the fluorescent RL emitted from the NV center can be focused with high concentration efficiency.

[0057] Figure 13 is a cross-sectional view showing the tip of the double-clad fiber 10D and the element 40 of a sensor according to another embodiment of the present invention. Components similar to those in the above-described embodiment are denoted by the same reference numerals, and the descriptions of the above-described embodiment will be used accordingly.

[0058] As shown in Figure 13, the element 40 of this embodiment comprises a diamond element 40D having an NV center and a substitute element 40S made of a material with the same refractive index as the diamond element 40D. The diamond element 40D is rectangular or disc-shaped and has an upper surface 40A that contacts the tip surface of the double-clad fiber 10D.

[0059] On the other hand, the substitute element 40S is frustum-pyramidal or frustum-cone in shape and comprises a lower surface 40B and an inclined surface 40C. The lower surface of the diamond element 40D and the upper surface of the substitute element 40S are the same shape and dimensions and are joined to each other.

[0060] Here, the inclined surface 40C is inclined outward from the center of the element 40, from the lower surface 40B towards the diamond element 40D. In other words, the inclined surface 40C is inclined such that the cross-sectional area of ​​the substitute element 40S gradually increases from the lower surface 40B towards the diamond element 40D.

[0061] According to this embodiment with the configuration described above, the diameter of the first cladding 10B is larger than the diameter of the core of the single-mode fiber, and the proportion of the fluorescent RL reflected within the element 40 toward the first cladding 10B, and the incident angle θ of the fluorescent RL are also large. dia_clad The proportion of conditions that are met increases. As a result, the fluorescent RL emitted from the NV center can be focused with high concentration efficiency.

[0062] Furthermore, by forming an inclined surface 40C on the alternative element 40S made of a diamond substitute material, the inclined surface 40C can be formed more easily and at a lower cost compared to forming an inclined surface on an element made of diamond.

[0063] Figure 14 is a cross-sectional view showing the tip of the double-clad fiber 10D and the element 50 of a sensor according to another embodiment of the present invention. Components similar to those in the above-described embodiment are denoted by the same reference numerals, and the descriptions of the above-described embodiment will be used accordingly.

[0064] As shown in Figure 14, the element 50 of this embodiment comprises a diamond element 50D having an NV center and a substitute element 50S made of a material with the same refractive index as the diamond element 50D. The diamond element 50D is rectangular or disc-shaped, and its upper surface 50D abuts the tip surface of the double-clad fiber 10D. A It is equipped with.

[0065] On the other hand, the alternative element 50S is frustum square or frustum cone shaped, and its upper surface 50S contacts the tip surface of the double-clad fiber 10D. A It comprises a bottom surface 50B and a side surface 50C. The top surface 50S of the replacement element 50S A A recess is formed therein into which the diamond element 50D is fitted. A and the upper surface 50S of the replacement element 50S A This means it is flush with the surface and is in contact with the tip surface of the double-clad fiber 10D.

[0066] Here, side 50C is connected to top 50S from the bottom 50B side. A The element 50 is inclined outward from the center towards the side. In other words, the side surface 50C is inclined outward from the bottom surface 50B towards the top surface 50S. A The element 50 is tilted such that its cross-sectional area gradually increases towards the side.

[0067] According to this embodiment with the configuration described above, the diameter of the first cladding 10B is larger than the diameter of the core of the single-mode fiber, and the proportion of the fluorescent RL reflected within the element 50 toward the first cladding 10B, and the incident angle θ of the fluorescent RL are also large. dia_clad The proportion of conditions that are met increases. As a result, the fluorescent RL emitted from the NV center can be focused with high concentration efficiency.

[0068] Furthermore, by forming a side surface 50C on the alternative element 50S made of a diamond substitute material, the side surface 50C can be formed more easily and at a lower cost compared to forming an inclined surface on an element made of diamond.

[0069] Figure 15 is a cross-sectional view showing the tip of the double-clad fiber 10D and the element 60 of a sensor according to another embodiment of the present invention. Components similar to those in the above-described embodiment are denoted by the same reference numerals, and the descriptions of the above-described embodiment will be used accordingly.

[0070] As shown in Figure 15, the element 60 of this embodiment comprises a diamond element 60D having an NV center and a substitute element 60S made of a material with the same refractive index as the diamond element 60D. The diamond element 60D is rectangular or disc-shaped, and its upper surface 60D abuts the tip surface of the double-clad fiber 10D. A It also includes a lower surface 60B.

[0071] On the other hand, the alternative element 60S is frustum square or frustum cone shaped, and its upper surface 60S contacts the tip surface of the double-clad fiber 10D. A The substitute element 60S has a through hole into which the diamond element 60D is fitted. A and the upper surface 60S of the replacement element 60S A This means it is flush with the surface and is in contact with the tip surface of the double-clad fiber 10D.

[0072] Here, side 60C is connected to top 60S from the bottom 60B side. A The element 60 is inclined outward from the center towards the side. In other words, the side surface 60C is inclined outward from the bottom surface 60B towards the top surface 60S. A The element 60 is tilted such that its cross-sectional area gradually increases towards the side.

[0073] According to this embodiment with the configuration described above, the diameter of the first cladding 10B is larger than the diameter of the core of the single-mode fiber, and the proportion of the fluorescent RL reflected within the element 60 toward the first cladding 10B, and the incident angle θ of the fluorescent RL are also large. dia_clad The proportion of conditions that are met increases. As a result, the fluorescent RL emitted from the NV center can be focused with high concentration efficiency.

[0074] Furthermore, by forming a side surface 60C on the alternative element 60S made of a diamond substitute material, the side surface 60C can be formed more easily and at lower cost compared to forming an inclined surface on an element made of diamond.

[0075] Figure 16 is a cross-sectional view showing the tip of the double-clad fiber 10D and the element 70 of a sensor according to another embodiment of the present invention. Components similar to those in the above-described embodiment are denoted by the same reference numerals, and the descriptions of the above-described embodiment will be used accordingly.

[0076] As shown in Figure 16, the element 70 of this embodiment comprises a diamond element 70D having an NV center and a substitute element 70S made of a material with the same refractive index as the diamond element 70D. The diamond element 70D is disc-shaped and has an upper surface 70A that contacts the tip surface of the double-clad fiber 10D.

[0077] On the other hand, the substitute element 70S has a spherical cutout shape (a shape in which a part of a sphere has been cut off) and is equipped with a spherical inclined surface 70C. The lower surface of the diamond element 70D and the upper surface of the substitute element 70S are the same shape and dimensions and are joined to each other.

[0078] Here, the inclined surface 70C slopes from the apex side of the replacement element 70S toward the upper surface 70A, and from the center side of the replacement element 70S toward the outer circumference. In other words, the inclined surface 70C is inclined such that the cross-sectional area of ​​the replacement element 70S gradually increases from the apex side of the replacement element 70S toward the upper surface 70A.

[0079] According to this embodiment with the configuration described above, the diameter of the first cladding 10B is larger than the diameter of the core of the single-mode fiber, and the proportion of the fluorescent RL reflected within the element 70 toward the first cladding 10B, and the incident angle θ of the fluorescent RL are also large. dia_clad The proportion of conditions that are met increases. As a result, the fluorescent RL emitted from the NV center can be focused with high concentration efficiency.

[0080] Furthermore, by forming an inclined surface 70C on the alternative element 70S made of a diamond substitute material, the inclined surface 70C can be formed more easily and at a lower cost compared to forming an inclined surface on an element made of diamond.

[0081] Figure 17 is a cross-sectional view showing the tip of the double-clad fiber 10D and the diamond element 20' of a sensor according to another embodiment of the present invention. Components similar to those in the above-described embodiments are denoted by the same reference numerals, and the descriptions of the above-described embodiments will be used accordingly.

[0082] As shown in Figure 17, the diamond element 20' of this embodiment has a configuration in which a conductive reflective film 20R is formed on the lower surface 20B and side surface 20C of the diamond element 20 shown in Figure 10 by vapor deposition or the like. Examples of materials for the reflective film 20R include aluminum, silver, copper, and gold.

[0083] Figure 18 is a perspective view showing the diamond element 20' of this embodiment. As shown in Figures 17 and 18, the central part of the lower surface 20B of the diamond element 20' is irradiated with excitation light GL. Therefore, from the viewpoint of suppressing the reflection of the excitation light GL, a light-transmitting portion 20E without a reflective film 20R is formed in the central part of the lower surface 20B of the diamond element 20'.

[0084] Here, the insulating portion 20F is formed spanning the lower surface 20B and the side surface 20C, and a portion of the conductive reflective film 20R is insulated by the insulating portion 20F. The microwave irradiator 6 is connected to the conductive reflective film 20R via power supply lines PL1 and PL2. Specifically, one end and the other end of the reflective film 20R are in close proximity via the insulating portion 20F, with power supply line PL1 connected to one end of the reflective film 20R and power supply line PL2 connected to the other end of the reflective film 20R.

[0085] In other words, in this embodiment, high-frequency power is supplied to the reflective film 20R from the microwave irradiator 6 via feed lines PL1 and PL2, thereby causing the reflective film 20R to function as an antenna for irradiating microwaves MW necessary for photodetection magnetic resonance. Here, the reflective film 20R has a light-transmitting portion 20E formed therein to allow excitation light GL to pass through, so that the entire reflective film 20R is shaped to form a loop antenna.

[0086] With the diamond element 20' of this embodiment having the configuration described above, the amount of fluorescent RL transmitted through the lower surface 20B and the side surface 20C can be reduced, and the amount of fluorescent RL incident on the first cladding 10B of the double-cladded fiber 10D can be increased. In addition, because a light-transmitting portion 20E is formed in the reflective film 20R, the amount of excitation light GL returning to the double-cladded fiber 10D can be suppressed.

[0087] Furthermore, by enabling the conductive reflective film 20R to function as a loop antenna, the separate loop antenna that would normally be required becomes unnecessary, thus enabling miniaturization and simplification of the sensor 1. In particular, the effect of miniaturization and simplification of the sensor 1 is even greater when the loop antenna is integrated with the diamond element 20'.

[0088] Figure 19 is a cross-sectional view showing the tip of the double-clad fiber 10D and the element 40' of a sensor according to another embodiment of the present invention. Components similar to those in the above-described embodiments are denoted by the same reference numerals, and the descriptions of the above-described embodiments will be used accordingly.

[0089] As shown in Figure 19, the element 40' of this embodiment has a configuration in which a conductive reflective film 40R is formed on the lower surface 40B and inclined surface 40C of the element 40 shown in Figure 13 by vapor deposition or the like. In addition, a light-transmitting portion 40E without the reflective film 40R is formed in the central part of the lower surface 40B of the element 40', from the viewpoint of suppressing the reflection of excitation light GL.

[0090] Furthermore, an insulating portion (not shown) is formed spanning the lower surface 40B and the inclined surface 40C, and a portion of the conductive reflective film 40R is insulated by the insulating portion. In addition, a microwave irradiator 6 is connected to the conductive reflective film 40R via a pair of power supply lines PL1 and PL2. Specifically, one end and the other end of the reflective film 40R are close together via the insulating portion, with power supply line PL1 connected to one end of the reflective film 40R and power supply line PL2 connected to the other end of the reflective film 40R.

[0091] In this embodiment, similar to the embodiment described above, high-frequency power is supplied to the reflective film 40R from the microwave irradiator 6 via feed lines PL1 and PL2, thereby causing the reflective film 40R to function as an antenna for irradiating microwaves MW necessary for photodetection magnetic resonance. Here, the reflective film 40R has a light-transmitting portion 40E formed therein to allow excitation light GL to pass through, so that the entire reflective film 40R is shaped to form a loop antenna.

[0092] With the element 40' of this embodiment having the above configuration, the amount of fluorescent RL transmitted through the lower surface 40B and the inclined surface 40C can be reduced, and the amount of fluorescent RL incident on the first cladding 10B of the double-cladded fiber 10D can be increased. In addition, because the light-transmitting portion 40E is formed on the reflective film 40R, the amount of excitation light GL returning to the double-cladded fiber 10D can be suppressed.

[0093] Furthermore, by enabling the conductive reflective film 40R to function as a loop antenna, the separate loop antenna that would normally be required becomes unnecessary, thus enabling miniaturization and simplification of sensor 1. In particular, the effect of miniaturization and simplification of sensor 1 is even greater when the loop antenna is integrated with element 40'.

[0094] Figure 20 is a cross-sectional view showing the tip of the double-clad fiber 10D and the element 50' of a sensor according to another embodiment of the present invention. Components similar to those in the above-described embodiment are denoted by the same reference numerals, and the descriptions of the above-described embodiment will be used accordingly.

[0095] As shown in Figure 20, the element 50' of this embodiment has a configuration in which a conductive reflective film 50R is formed on the lower surface 50B and side surface 50C of the element 50 shown in Figure 14 by vapor deposition or the like. In addition, a light-transmitting portion 50E without the reflective film 50R is formed in the central part of the lower surface 50B of the element 50', from the viewpoint of suppressing the reflection of excitation light GL.

[0096] Furthermore, an insulating portion (not shown) is formed spanning the lower surface 50B and the side surface 50C, and a portion of the conductive reflective film 50R is insulated by the insulating portion. In addition, a microwave irradiator 6 is connected to the conductive reflective film 50R via a pair of power supply lines PL1 and PL2. Specifically, one end and the other end of the reflective film 50R are close together via the insulating portion, with power supply line PL1 connected to one end of the reflective film 50R and power supply line PL2 connected to the other end of the reflective film 50R.

[0097] In this embodiment, similar to the embodiment described above, high-frequency power is supplied to the reflective film 50R from the microwave irradiator 6 via feed lines PL1 and PL2, thereby causing the reflective film 50R to function as an antenna for irradiating microwaves MW necessary for photodetection magnetic resonance. Here, the reflective film 50R has a light-transmitting portion 50E formed therein to allow excitation light GL to pass through, so that the entire reflective film 50R is shaped to form a loop antenna.

[0098] With the element 50' of this embodiment having the above configuration, the amount of fluorescent RL transmitted through the lower surface 50B and the side surface 50C can be reduced, and the amount of fluorescent RL incident on the first cladding 10B of the double-cladded fiber 10D can be increased. In addition, because the light-transmitting portion 50E is formed on the reflective film 50R, the amount of excitation light GL returning to the double-cladded fiber 10D can be suppressed.

[0099] Furthermore, by enabling the conductive reflective film 50R to function as a loop antenna, the separate loop antenna that would normally be required becomes unnecessary, thus enabling miniaturization and simplification of sensor 1. In particular, the effect of miniaturization and simplification of sensor 1 is even greater when the loop antenna is integrated with element 50'.

[0100] Figure 21 is a cross-sectional view showing the tip of the double-clad fiber 10D and the element 60' of a sensor according to another embodiment of the present invention. Components similar to those in the above-described embodiment are denoted by the same reference numerals, and the descriptions of the above-described embodiment will be used accordingly.

[0101] As shown in Figure 21, the element 60' of this embodiment has a configuration in which a conductive reflective film 60R is formed on the lower surface 60B and side surface 60C of the element 60 shown in Figure 15 by vapor deposition or the like. In addition, a light-transmitting portion 60E without the reflective film 60R is formed in the central part of the lower surface 60B of the element 60', from the viewpoint of suppressing the reflection of excitation light GL.

[0102] Furthermore, an insulating portion (not shown) is formed spanning the lower surface 60B and the side surface 60C, and a portion of the conductive reflective film 60R is insulated by the insulating portion. In addition, a microwave irradiator 6 is connected to the conductive reflective film 60R via a pair of power supply lines PL1 and PL2. Specifically, one end and the other end of the reflective film 60R are close together via the insulating portion, with power supply line PL1 connected to one end of the reflective film 60R and power supply line PL2 connected to the other end of the reflective film 60R.

[0103] In this embodiment, similar to the embodiment described above, high-frequency power is supplied to the reflective film 60R from the microwave irradiator 6 via feed lines PL1 and PL2, thereby causing the reflective film 60R to function as an antenna for irradiating microwaves MW necessary for photodetection magnetic resonance. Here, the reflective film 60R has a light-transmitting portion 60E formed therein to allow excitation light GL to pass through, so that the entire reflective film 60R is shaped to form a loop antenna.

[0104] With the element 60' of this embodiment having the above configuration, the amount of fluorescent RL transmitted through the lower surface 60B and the side surface 60C can be reduced, and the amount of fluorescent RL incident on the first cladding 10B of the double-cladded fiber 10D can be increased. Furthermore, because a light-transmitting portion 60E is formed in the reflective film 60R, the amount of excitation light GL returning to the double-cladded fiber 10D can be suppressed.

[0105] Furthermore, by enabling the conductive reflective film 60R to function as a loop antenna, the separate loop antenna that would normally be required becomes unnecessary, thus enabling miniaturization and simplification of sensor 1. In particular, the effect of miniaturization and simplification of sensor 1 is even greater when the loop antenna is integrated with element 60'.

[0106] Figure 22 is a cross-sectional view showing the tip of the double-clad fiber 10D and the element 70' of a sensor according to another embodiment of the present invention. Components similar to those in the above-described embodiments are denoted by the same reference numerals, and the descriptions of the above-described embodiments will be used accordingly.

[0107] As shown in Figure 22, the element 70' of this embodiment has a configuration in which a conductive reflective film 70R is formed on the spherical inclined surface 70C of the element 70 shown in Figure 16 by vapor deposition or the like. In addition, a light-transmitting portion 70E without the reflective film 70R is formed in the central part of the inclined surface 70C of the element 70', from the viewpoint of suppressing the reflection of excitation light GL.

[0108] Furthermore, an insulating portion (not shown) is formed on the inclined surface 70C, and a portion of the conductive reflective film 70R is insulated by the insulating portion. The microwave irradiator 6 is connected to the conductive reflective film 70R via a pair of power supply lines PL1 and PL2. Specifically, one end and the other end of the reflective film 70R are close together via the insulating portion, with power supply line PL1 connected to one end of the reflective film 70R and power supply line PL2 connected to the other end of the reflective film 70R.

[0109] In this embodiment, similar to the embodiment described above, high-frequency power is supplied to the reflective film 70R from the microwave irradiator 6 via feed lines PL1 and PL2, thereby causing the reflective film 70R to function as an antenna for irradiating microwaves MW necessary for photodetection magnetic resonance. Here, the reflective film 70R has a light-transmitting portion 70E formed therein to allow excitation light GL to pass through, so that the entire reflective film 70R is shaped to form a loop antenna.

[0110] With the element 70' of this embodiment having the configuration described above, the amount of fluorescent RL transmitted through the inclined surface 70C can be reduced, and the amount of fluorescent RL incident on the first cladding 10B of the double-cladded fiber 10D can be increased. Furthermore, because a light-transmitting portion 70E is formed in the reflective film 70R, the amount of excitation light GL returning to the double-cladded fiber 10D can be suppressed.

[0111] Furthermore, by enabling the conductive reflective film 70R to function as a loop antenna, the separate loop antenna that would normally be required becomes unnecessary, thus enabling miniaturization and simplification of sensor 1. In particular, the effect of miniaturization and simplification of sensor 1 is even greater when the loop antenna is integrated with element 70'.

[0112] Although the present invention has been described above based on embodiments, the present invention is not limited to the above embodiments, and modifications may be made, or publicly known or well-known technologies may be combined as appropriate, without departing from the spirit of the present invention.

[0113] For example, in this embodiment, the element having a color center to be excited is a diamond element having an NV center, but this element may be other, such as a diamond element having a SnV color center made of tin (Sn) and vacancies, a diamond element having a SiV color center made of silicon (Si) and vacancies, or a diamond element having a GeV color center made of germanium (Ge) and vacancies.

[0114] Furthermore, although this embodiment focuses on a photodetection magnetic resonance sensor 1 equipped with a microwave irradiator 6, the present invention can also be applied to fluorescent temperature sensors and the like that generate a temperature signal by receiving fluorescence emitted from a fluorescent material excited by excitation light. [Explanation of Symbols]

[0115] 1: Sensor 2: Diamond element (element) 3:Light source 4: Light sensor (light receiving part) 6: Microwave irradiator (microwave irradiation unit, power supply) 10A: Core 10B: First cladding 10C: Second cladding 10D, 10F: Double-clad fiber 10G: Multimode fiber 20,20': Diamond element (element) 20A: Top surface (first surface) 20C: Side (second surface, inclined surface) 20R: Reflective film 30: Diamond element (element) 30A: Top surface (first surface) 30C: Side (second surface, inclined surface) 40,40': Element 40A:Top surface (first surface) 40C: Inclined surface (second surface) 40D: Diamond element (main part) 40R: Reflective film 40S: Replacement element (sub-part) 50,50': element 50s A ,50D A :Top surface (1st surface) 50C: Side (second surface, inclined surface) 50D: Diamond element (main part) 50R: Reflective film 50S: Replacement element (sub-part) 60,60': element 60s A ,60DA :Top surface (1st surface) 60C: Side (second surface, inclined surface) 60D: Diamond element (main part) 60R: Reflective film 60S: Replacement element (sub-part) 70,70': element 70A:Top surface (first surface) 70C: Inclined surface (second surface 70D: Diamond element (main part) 70R: Reflective film 70S: Replacement element (sub-part) GL: Excitation light RL: Fluorescent MW: Microwave n1: refractive index

Claims

1. An element having a color center that emits fluorescence upon irradiation with excitation light, A light source that emits the aforementioned excitation light, A light-receiving unit that receives the aforementioned fluorescence, A double-clad fiber having a core that propagates the excitation light emitted from the light source to the element, a first cladding disposed outside the core that propagates the fluorescence emitted from the color center toward the light receiving section, and a second cladding disposed outside the first cladding. A sensor equipped with the following features.

2. The sensor according to claim 1, further comprising a multimode fiber that branches off from the double-clad fiber and propagates the fluorescence to the light-receiving unit.

3. The sensor according to claim 1 or 2, further comprising a microwave irradiation unit for irradiating the element with microwaves.

4. The aforementioned device, The first surface is the surface to which the end face of the double-clad fiber abuts, The second surface is a circumferential surface that is connected to the periphery of the first surface. Equipped with, The sensor according to claim 1 or 2, wherein the second surface is an inclined surface that slopes outward from the center side of the element toward the first surface.

5. The aforementioned device, The main part having the aforementioned color center, The sub-part is formed of a material with the same refractive index as the main part, is integrated with the main part, and includes the inclined surface. The sensor according to claim 4, comprising:

6. The aforementioned device, The first surface to which the end face of the double-clad fiber abuts, The second surface is a circumferential surface that is connected to the periphery of the first surface. Equipped with, The sensor according to claim 1 or 2, wherein the second surface is covered with a reflective film that reflects the fluorescence.

7. The element is provided with a microwave irradiation unit that irradiates the element with microwaves, The aforementioned reflective film is formed of a conductive material, and a portion of it in the circumferential direction is insulated, thereby forming a loop coil. The sensor according to claim 6, wherein the microwave irradiation unit supplies a high-frequency current to the reflective film.

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