Patent Description:
Sensors that use NV centers of diamonds have been known. In a case of using the NV center of a diamond in combination with a microscope, a configuration as shown in <FIG> is adopted, for example. That is, an LED <NUM> disposed on a substrate <NUM> emits green light for exciting the NV center of a diamond <NUM>. The emitted light passes through an SPF (Short Pass Filter) <NUM>, and subsequently enters diamond <NUM> disposed on a substrate <NUM>. Accordingly, electrons at the NV center are brought into an excited state. When the excited electrons return to the original ground state, red fluorescent light is emitted from diamond <NUM>. The fluorescent light is collected by a lens <NUM>, passes through an LPF (Long Pass Filter) <NUM>, and subsequently, is detected by a photodiode <NUM> disposed on a substrate <NUM>. Diamond <NUM> is irradiated by microwaves generated by an external device (not shown). Accordingly, a resonant state with a state in a different spin state is achieved, and excitation is made, and thus the intensity of the red fluorescent light from diamond <NUM> is changed. The change is detected by photodiode <NUM>. Lens <NUM> may have a lens structure of a high-performance optical microscope, or have a simple lens configuration.

Patent Literature <NUM> described below discloses a scanning probe microscope that uses the NV center of a diamond (i.e., a frequency modulation atomic force microscope (FM-AFM)). Patent Literature <NUM> described below discloses a magnetic field detection device that uses the NV center of a diamond. Non Patent Literature <NUM> described below discloses a compact magnetic field detection device that includes a lens. <NPL>, relates to a hyperfine level structure in nitrogen-vacancy centers near the ground-state anticrossing. <NPL>, relates to high-resolution magnetic field imaging with a nitrogen-vacancy diamond sensor integrated with a photonic-crystal fiber. <NPL> relates to subnanotesla magnetometry with a fiber-coupled diamond sensor. <NPL> relates to enhancing fluorescence excitation and collection from the nitrogen-vacancy center in diamond through a micro-concave mirror. <CIT> relates to gemstones based on HD-NV diamonds and discloses a sensor unit containing two optical waveguides for excitation light and fluorescent light, respectively.

A diamond sensor unit according to an aspect of the present invention is according to claim <NUM>.

A diamond sensor system according to another aspect of the present invention is according to claim <NUM>.

In a case of using a sensor for high-voltage equipment, such as power equipment, a light emitting element and a light receiving element are possibly damaged owing to a high voltage and high current instantaneously caused by electrical discharge and strong electromagnetic waves generated accordingly. The configuration disclosed in Patent Literature <NUM> cannot be adopted for the sensor used in a high-voltage environment.

Patent Literature <NUM> discloses that a light emitting element and a light receiving element are disposed to be separated from a diamond and a microwave emission coil. Unfortunately, excitation light and emitted fluorescent light are transmitted as parallel light in the air, and the light is diffused. There is thus a limitation on the distance of separation. In particular, the signal intensity of fluorescent light is low, which causes a problem.

Consequently, the present invention has an object to provide a diamond sensor unit and a diamond sensor system that can accurately detect a magnetic field and the like even remotely, without being damaged even in a high-voltage environment.

According to the present invention, the diamond sensor unit and the diamond sensor system can be provided that can accurately measure a magnetic field, an electric field and the like even remotely, without being damaged even in a high-voltage environment.

The details of embodiments of the present invention are described. At least parts of the embodiments described below may be freely combined within the scope of the claims.

A diamond sensor unit according to a first aspect of the present invention is according to claim <NUM>. Accordingly, the magnetic field, the electric field and the like can be accurately measured even remotely without damage even in a high-voltage environment.

The sensor part can include a light collecting element that collects the excitation light and the radiated light, and the light collecting element can be disposed between the diamond and the optical waveguide. Accordingly, the losses of the excitation light and the radiated light are reduced, and the detection accuracy can be improved.

The light collecting element may be a spherical lens formed on a silicon oxide basis or a Fresnel lens formed on a silicon oxide basis, and the optical waveguide may be an optical fiber having a core diameter of <NUM> or more and <NUM> or less. Accordingly, the excitation light and the radiated light can be efficiently transmitted, and the detection accuracy can be improved. Furthermore, laser light can be relatively easily introduced to a desired position, and the diffusion at the output end of the optical fiber can be suppressed.

The optical waveguide may be disposed via at least an inside of a piece of insulating glass. Accordingly, even in case electrical discharge or the like occurs in a high-voltage environment where the sensor part is disposed, the detection part and the like can be prevented from being damaged.

In a reference example, the optical waveguide may include one medium that transmits the excitation light and the radiated light, and a fluorescent light reflection filter, an LPF, or a dichroic mirror that separates the excitation light and the radiated light from each other may be included within a predetermined distance from one end positioned more remote from the diamond between both ends of the optical waveguide. Accordingly, in comparison with a case where media for respectively transmitting the excitation light and the radiated light are provided, the number of components can be reduced, which can achieve a simple configuration.

The optical waveguide includes a first optical waveguide that transmits the excitation light, and a second optical waveguide that transmits the radiated light, one end of the first optical waveguide is disposed closer to the diamond than another end of the first optical waveguide, one end of the second optical waveguide is disposed closer to the diamond than another end of the second optical waveguide, and a fluorescent light reflection filter, an LPF, or a dichroic mirror that separates the excitation light and the radiated light from each other is included within a predetermined distance from each of the one end of the first optical waveguide and the one end of the second optical waveguide. Accordingly, in comparison with a case of transmitting the excitation light and the radiated light together through one medium, the excitation light and the radiated light can be transmitted respectively in suitable forms, which can improve the detection accuracy.

The first optical waveguide may include a first optical fiber, the second optical waveguide may include a second optical fiber, and a core diameter of the second optical fiber may be larger than a core diameter of the first optical fiber. Accordingly, the excitation light and the radiated light can be transmitted in forms suitable for the respective wavelengths, and the detection accuracy can be improved.

The core diameter of the first optical fiber may be <NUM> or more and <NUM> or less, and the core diameter of the second optical fiber may be <NUM> or more and <NUM> or less. Accordingly, the excitation light and the radiated light can be transmitted using the optical fibers having the core diameters suitable for the respective wavelengths. Thus, optical fibers having unnecessarily large diameters are not used, which can reduce the cost.

The diamond may have at least a plurality of flat surfaces, the excitation light may enter a first flat surface among the plurality of flat surfaces, and the detection part may detect the radiated light emitted from a second flat surface that is other than the first flat surface among the plurality of flat surfaces. This negates the need of a member that separates the excitation light and the radiated light from each other (e.g., a fluorescent light reflection filter, an LPF, or a dichroic mirror). Accordingly, the cost can be reduced.

(The sensor part that includes the diamond may be entirely formed of an electrical insulating member. Accordingly, even in case electrical discharge or the like occurs in a high-voltage environment where the sensor part is disposed, the sensor part can be hindered from being damaged.

The diamond may be disposed on a transmission line that transmits microwaves or millimeter waves, and the sensor part may function as a magnetic sensor. Accordingly, the NV center of the diamond can be accurately irradiated with microwaves or millimeter waves.

The transmission line may include a main wiring disposed on a rectangular printed board having each side of <NUM> or less, and the diamond may be disposed at one end of the main wiring. Accordingly, the NV center of the diamond can be irradiated with microwaves.

A spin coherence time of the diamond may be less than <NUM>µsec. Accordingly, the NV center promptly returns from the excited state to the original state. Consequently, the AC magnetic field, electric field and the like can be efficiently detected. In particular, the pulsatingly changing magnetic field, electric field and the like can be detected.

A total hydrogen concentration in the diamond may be <NUM> ppm or less. Accordingly, the spin coherence time T2 of the diamond can be reduced, and the NV center can promptly return from the excited state to the original state. Consequently, the AC magnetic field, electric field and the like can be efficiently detected.

Each of NVH- concentration, CH concentration and CH<NUM> concentration in the diamond may be less than <NUM> ppm. Accordingly, the spin coherence time T2 of the diamond can be reduced, and the NV center can promptly return from the excited state to the original state. Consequently, the pulsatingly changing magnetic field, electric field and the like are included, and the AC magnetic field, electric field and the like can be efficiently detected.

A diamond sensor system according to a second aspect of the present invention is according to claim <NUM>. Accordingly, the magnetic field, the electric field and the like can be accurately measured even remotely without damage even in a high-voltage environment.

In the following embodiments, the same components are respectively assigned with the same reference numerals. Their names and functions are also the same. Consequently, the detail description about them is not repeated.

Referring to <FIG>, a diamond sensor unit <NUM> according to a reference example includes an excitation light generation part <NUM>, a fluorescent light reflection filter <NUM>, an optical waveguide <NUM>, a sensor part <NUM>, an LPF <NUM>, and a light receiving part <NUM>. An electromagnetic wave generating part <NUM>, and a control part <NUM> are disposed outside of the diamond sensor unit <NUM>.

Control part <NUM> includes a CPU (Central Processing Unit), and a storage part (neither is shown). After-mentioned processes performed by control part <NUM> are achieved by the CPU reading programs preliminarily stored in the storage part, and executing the programs.

Excitation light generation part <NUM> includes a light emitting element <NUM>, and a light collecting element <NUM>. Under control by control part <NUM>, light emitting element <NUM> generates excitation light for exciting a diamond NV- center described later (hereinafter abbreviated as the NV center). For example, control part <NUM> supplies light emitting element <NUM> with a voltage for causing light emitting element <NUM> to emit light at predetermined timing. The excitation light is green light (i.e., with a wavelength of about <NUM> to <NUM>). Preferably, the excitation light is laser light. Preferably, light emitting element <NUM> is a semiconductor laser (e.g., the wavelength is <NUM>, which is of the radiated light). Light collecting element <NUM> collects the excitation light output from light emitting element <NUM>. Light collecting element <NUM> is for inputting the excitation light output from light emitting element <NUM> in a diffused manner, as much as possible, into an after-mentioned light incident end of optical waveguide <NUM>. Preferably, light collecting element <NUM> outputs parallel light collected in a smaller range than the size of the light incident end of optical waveguide <NUM> (for example, in a case of using an optical fiber, its core diameter (i.e., the diameter of the core)).

Fluorescent light reflection filter <NUM> is an element for separating the excitation light having entered from light collecting element <NUM>, and light having been radiated from an after-mentioned diamond (i.e., fluorescent light) from each other. For example, fluorescent light reflection filter <NUM> is a short-pass filter that allows light having a wavelength of a predetermined wavelength or less to travel while cutting light having a wavelength longer than the predetermined wavelength (i.e., reflection), or a bandpass filter that allows light within a predetermined wavelength range to travel while cutting light out of the predetermined wavelength range (i.e., reflection). In general, the excitation light has a shorter wavelength than the fluorescent light does. Accordingly, such a configuration is preferable. Preferably, fluorescent light reflection filter <NUM> is a dichroic mirror having such a function.

Optical waveguide <NUM> includes a medium that transmits light, and bi-directionally transmits light. That is, excitation light having entered one end disposed closer to excitation light generation part <NUM> is transmitted to the other end disposed closer to sensor part <NUM>. Meanwhile, radiated light (i.e., fluorescent light) from a diamond element <NUM> having entered the other end is transmitted to the one end. Optical waveguide <NUM> is, for example, an optical fiber. To increase the energy density of the excitation light to be transmitted, it is preferable that the core diameter of the optical fiber be smaller as much as possible. On the other hand, if the core diameter is too small, the efficiency of entrance of light radiated from a light source (i.e., the light emitting element) in a diffused manner into the optical fiber is reduced. Consequently, there is an appropriate core diameter. For example, the core diameter of the optical fiber is about <NUM> or less and <NUM> or more. For example, in a case where the core diameter is larger than <NUM>, it is difficult to increase the energy density of the excitation light even if a lens is used. Accordingly, initialization of the spin of the NV center takes time. Thus, the sensor has a slow response speed. To solve this, a laser having a higher output is required, which makes trade-offs in portability and stability. On the other hand, if the core diameter is smaller than <NUM>, the incident efficiency into the optical fiber is degraded, and light source size of the corresponding laser diode becomes too small. Accordingly, a failure due to catastrophic optical damage (COD) is readily caused. Furthermore, the laser diode having sufficient output as excitation light is limited to an expensive one. Actual use thus becomes difficult.

Sensor part <NUM> includes a light collecting element <NUM>, diamond element <NUM>, and an electromagnetic wave irradiation part <NUM>. Diamond element <NUM> includes the NV center. Light collecting element <NUM> is disposed in contact with diamond element <NUM>. Light collecting element <NUM> converges the excitation light output from optical waveguide <NUM>, and irradiates diamond element <NUM> with the light. An electromagnetic wave irradiation part <NUM> irradiates diamond element <NUM> with electromagnetic waves (e.g., microwaves). Electromagnetic wave irradiation part <NUM> is, for example, a coil formed to include an electrical conductor. The electromagnetic waves are supplied from electromagnetic wave generating part <NUM> outside of diamond sensor unit <NUM> to electromagnetic wave irradiation part <NUM>. The irradiation of diamond element <NUM> with the excitation light and the electromagnetic waves is controlled by control part <NUM>, and is performed at timing as shown in <FIG>, for example. That is, control part <NUM> controls light emitting element <NUM> so as to output excitation light at predetermined timing for a predetermined time (e.g., a time period t1). Control part <NUM> controls electromagnetic wave generating part <NUM> so as to output electromagnetic waves at predetermined timing for a predetermined time (e.g., a time period t2). A pulse sequence in time period t2 may be an appropriate one in accordance with the diamond to be used (for example, the degree of bearing alignment of a plurality of NV centers), an observed signal (i.e., a signal affected by the spin state at the NV center) and the like. Accordingly, the electromagnetic waves are temporally and spatially combined with the excitation light, and diamond element <NUM> is irradiated with them. As described later, control part <NUM> captures, at predetermined timing (e.g., in a time period t3), an output signal of a light detection part <NUM> that is to be input, and stores the signal in the storage part.

The NV center has a structure where a carbon (C) atom in a diamond crystal is replaced with a nitrogen (N) atom, a carbon atom that should be adjacently present is absent (i.e., a hole (V)). The NV center transitions from the ground state to the excited state by green light having a wavelength of about <NUM> to <NUM> (e.g., laser light of <NUM>), and emits red light having a wavelength of about <NUM> to <NUM> (e.g., fluorescent light of <NUM>) and returns to the ground state. In a state where one electron is captured (i.e., NV-), the NV center forms a spin-triplet state with magnetic quantum numbers ms of -<NUM>, <NUM>, and +<NUM>, and possible presence of a magnetic field separates the energy level in a state of ms = ±<NUM> in accordance with the magnetic field intensity (i.e., Zeeman splitting). The NV center is irradiated with microwaves of about <NUM>, a state of ms = <NUM> is caused to transition to a state of ms = ±<NUM> (i.e., electron spin resonance), subsequently irradiated with green light, and excitation is caused. Thus, the transition returning to the ground state includes transition without radiation of light (i.e., fluorescent light). Accordingly, the intensity of radiated light to be observed decreases. Consequently, in the ESR (Electron Spin Resonance) spectrum, a valley (i.e., falling of the signal) is observed. By control part <NUM> controlling light emitting element <NUM> and electromagnetic wave generating part <NUM> as described above, a spectrum as shown in <FIG> is measured, for example. The observed Δf depends on the magnetic field intensity at the position of diamond element <NUM>.

As for specific measurement of the spectrum, the measurement is performed as follows. That is, light radiated form diamond element <NUM> in a diffused manner (i.e., fluorescent light) is collected by light collecting element <NUM>, and enters, as parallel light, the other end of optical waveguide <NUM>. The light input into optical waveguide <NUM> (i.e., fluorescent light) is transmitted through optical waveguide <NUM>, and is output from the one end of optical waveguide <NUM>. The light output from the one end of optical waveguide <NUM> (i.e., fluorescent light) is reflected by fluorescent light reflection filter <NUM>, passes through LPF <NUM>, is collected by a light collecting element <NUM>, and is emitted to light detection part <NUM>. Accordingly, the light having a frequency in accordance with the magnetic field at the position where diamond element <NUM> is disposed is detected by light detection part <NUM>. Light detection part <NUM> generates an electric signal in accordance with the incident light, and outputs the signal. Light detection part <NUM> is, for example, a photodiode. The output signal of light detection part <NUM> is obtained by control part <NUM>.

LPF <NUM> is a long-pass filter, allows light having a wavelength that is a predetermined wavelength or more to pass while cutting light having wavelengths shorter than the predetermined wavelength (e.g., reflection). The radiated light from diamond element <NUM> is red light, which passes through LPF <NUM>. However, since the excitation light has a shorter wavelength than the red light, the excitation light does not pass through LPF <NUM>. Thus, the excitation light radiated from light emitting element <NUM> is prevented from being detected by light detection part <NUM>, from serving as noise, and from reducing the detection sensitivity of the radiated light (i.e., fluorescent light) from diamond element <NUM>.

As described above, control part <NUM> irradiates diamond element <NUM> with excitation light, and sweeps the frequency of electromagnetic waves in a predetermined range and irradiates diamond element <NUM> with the light, thus allowing the light (e.g., fluorescent light) radiated from diamond element <NUM> to be obtained as the electric signal output from light detection part <NUM>. Based on observed Δf (i.e., the value depending on the magnetic field intensity at the position of diamond element <NUM>), the magnetic field intensity at the position of diamond element <NUM> can be calculated. That is, diamond sensor unit <NUM> functions as a magnetic sensor. Note that diamond sensor unit <NUM> can be used as a sensor for detecting not only the magnetic field (i.e., magnetic field) but also physical quantities related to the magnetic field, e.g., the magnetization, electric field, voltage, current, temperature, pressure, etc..

In a case where an optical fiber is adopted as optical waveguide <NUM>, diamond element <NUM>, which is the main part of the sensor, and light collecting element <NUM> are formed of an electrical insulator, and occurrence of damage due to electrical discharge or the like can be suppressed accordingly, even with sensor part <NUM> and the other end of optical waveguide <NUM> being installed in a high-voltage facility or the like. Consequently, the magnetic field and the like can be safely measured in a high-voltage environment by diamond sensor unit <NUM>. Furthermore, excitation light generation part <NUM> and light receiving part <NUM> can be disposed remotely from the high-voltage environment, via optical waveguide <NUM>. The magnetic field and the like can be remotely measured by diamond sensor unit <NUM>. Sensor part <NUM> includes light collecting element <NUM> disposed between diamond element <NUM> and optical waveguide <NUM>. Accordingly, the losses of the excitation light and the radiated light can be reduced, and the detection accuracy can be improved. Fluorescent light reflection filter <NUM>, which separates the excitation light and the radiated light from each other, is provided, and transmission of the excitation light and the radiated light can be performed through a single medium (e.g., optical waveguide <NUM>). Accordingly, as described later, in comparison with a case where two media for respectively transmitting the excitation light and the radiated light are provided, the number of components can be reduced, which can achieve a simple configuration.

In the first embodiment, the light (i.e., the excitation light and the radiated light) is bi-directionally transmitted using single optical waveguide <NUM>. In a second embodiment, optical waveguides for respectively transmitting the excitation light for and the radiated light from a diamond element <NUM> are used. Referring to <FIG>, a diamond sensor unit <NUM> according to the second embodiment of the present invention includes an excitation light generation part <NUM>, a first optical waveguide <NUM>, a light collecting element <NUM>, a fluorescent light reflection filter <NUM>, a sensor part <NUM>, an LPF <NUM>, a light collecting element <NUM>, a second optical waveguide <NUM>, and a light receiving part <NUM>. Similar to the first embodiment, an electromagnetic wave generating part <NUM>, and a control part <NUM> are disposed outside of the diamond sensor unit <NUM>.

Excitation light generation part <NUM> includes a light emitting element <NUM>, and a light collecting element <NUM>. Sensor part <NUM> includes a light collecting element <NUM>, diamond element <NUM>, and an electromagnetic wave irradiation part <NUM>. Light receiving part <NUM> includes a light detection part <NUM>. Light emitting element <NUM>, light collecting element <NUM>, fluorescent light reflection filter <NUM>, light collecting element <NUM>, diamond element <NUM>, electromagnetic wave irradiation part <NUM>, LPF <NUM>, and light detection part <NUM> respectively correspond to light emitting element <NUM>, light collecting element <NUM>, fluorescent light reflection filter <NUM>, light collecting element <NUM>, diamond element <NUM>, electromagnetic wave irradiation part <NUM>, LPF <NUM>, and light detection part <NUM> shown in <FIG>, and similarly function. Consequently, these are briefly described.

Similar to the first embodiment, under control by control part <NUM>, light emitting element <NUM> generates excitation light for exciting the diamond NV center. For example, control part <NUM> supplies, at predetermined timing, light emitting element <NUM> with a voltage for causing light emitting element <NUM> to emit light. The excitation light is green light. Preferably, the excitation light is laser light. Preferably, light emitting element <NUM> is a semiconductor laser. Light collecting element <NUM> collects the excitation light output from light emitting element <NUM> in a diffused manner, and inputs the light into a light incident end of first optical waveguide <NUM>.

First optical waveguide <NUM> includes a medium for transmitting light. Unlike optical waveguide <NUM> shown in <FIG>, first optical waveguide <NUM> transmits the excitation light but does not transmit the radiated light from diamond element <NUM>. That is, the excitation light incident on one end (i.e., an incident end) of first optical waveguide <NUM> disposed closer to excitation light generation part <NUM> is transmitted to the other end (i.e., an output end) disposed closer to sensor part <NUM>, and is output. First optical waveguide <NUM> is, for example, an optical fiber. The excitation light output from first optical waveguide <NUM> in a diffused manner is collected by light collecting element <NUM>, and enters, as parallel light, fluorescent light reflection filter <NUM>.

Fluorescent light reflection filter <NUM> is an element for separating the excitation light having entered from light collecting element <NUM>, and light having been radiated from diamond element <NUM> (i.e., fluorescent light) from each other. Fluorescent light reflection filter <NUM> may be a dichroic mirror.

Light collecting element <NUM> converges the excitation light having passed through fluorescent light reflection filter <NUM> and entered, and irradiates diamond element <NUM> with the light. Light collecting element <NUM> is disposed in contact with diamond element <NUM>. Diamond element <NUM> includes an NV center. Electromagnetic wave irradiation part <NUM> irradiates diamond element <NUM> with electromagnetic waves (e.g., microwaves). Electromagnetic wave irradiation part <NUM> is, for example, a coil. Electromagnetic waves are supplied from electromagnetic wave generating part <NUM> to electromagnetic wave irradiation part <NUM>. The irradiation of diamond element <NUM> with the excitation light and the electromagnetic waves is controlled by control part <NUM>, and is controlled at timing as shown in <FIG>, for example. Accordingly, as described above, red light (i.e., fluorescent light) is radiated from diamond element <NUM>.

The light radiated from diamond element <NUM> in a diffused manner (i.e., red fluorescent light) is collected by light collecting element <NUM> as parallel light, and is incident on fluorescent light reflection filter <NUM>. The light (i.e., red fluorescent light) incident on fluorescent light reflection filter <NUM> is reflected by fluorescent light reflection filter <NUM>, and enters LPF <NUM>. The radiated light (i.e., red fluorescent light) from diamond element <NUM> that is incident on LPF <NUM> passes through LPF <NUM>, is collected by light collecting element <NUM>, and enters one end (i.e., an incident end) of second optical waveguide <NUM>. LPF <NUM> prevents the excitation light radiated from light emitting element <NUM> from being detected by light detection part <NUM>, from serving as noise, and from reducing the detection sensitivity of the radiated light (i.e., fluorescent light) from diamond element <NUM>.

Second optical waveguide <NUM> includes a medium for transmitting light. Second optical waveguide <NUM> transmits the light (i.e., the radiated light from diamond element <NUM>) entering one end (i.e., an incident end) from light collecting element <NUM>, to the other end (i.e., an output end) disposed closer to light receiving part <NUM>. Light output from second optical waveguide <NUM> is detected by light detection part <NUM>. Light detection part <NUM> is, for example, a photodiode. The output signal of light detection part <NUM> is obtained by control part <NUM>.

As described above, similar to the first embodiment, control part <NUM> irradiates diamond element <NUM> with excitation light, and sweeps the frequency of electromagnetic waves in a predetermined range and irradiates diamond element <NUM> with the light, thus allowing the light (e.g., fluorescent light) radiated from diamond element <NUM> to be obtained as the electric signal output from light detection part <NUM>. Consequently, diamond sensor unit <NUM> functions as a magnetic sensor. Diamond sensor unit <NUM> can be used as a sensor for detecting not only the magnetic field but also physical quantities related to the magnetic field, e.g., the magnetization, electric field, voltage, current, temperature, pressure, etc..

In a case where the optical fibers are adopted as the two optical waveguides, diamond element <NUM>, which is the main part of the sensor, and light collecting element <NUM> are formed of an electrical insulator, and occurrence of damage due to electrical discharge or the like can be suppressed accordingly. Consequently, the magnetic field and the like can be safely measured in a high-voltage environment by diamond sensor unit <NUM>. Furthermore, excitation light generation part <NUM> and light receiving part <NUM> can be disposed remoted from high-voltage environment via first optical waveguide <NUM> and second optical waveguide <NUM>. The magnetic field and the like can be remotely measured by diamond sensor unit <NUM>. Sensor part <NUM> includes light collecting element <NUM> disposed between diamond element <NUM>, and first optical waveguide <NUM> and second optical waveguide <NUM>. Accordingly, the losses of the excitation light and the radiated light can be reduced, and the detection accuracy can be improved.

Through use of the two optical waveguides (i.e., first optical waveguide <NUM> and second optical waveguide <NUM>), the excitation light and the radiated light from diamond element <NUM> that have wavelengths different from each other can be appropriately transmitted. That is, through use of the optical fibers having core diameters in accordance with the wavelengths, the respectively suitable light collecting optical systems (i.e., light collecting element <NUM>, light collecting element <NUM>, light collecting element <NUM>, and light collecting element <NUM>) can be designed, the light transmission efficiency can be improved, and the measurement accuracy can be improved. In the case of using the optical fibers as the optical waveguides, it is preferable that the core diameter of the optical fiber (i.e., second optical waveguide <NUM>) for transmitting the radiated light from the diamond be larger than the core diameter of the optical fiber (i.e., first optical waveguide <NUM>) for transmitting the excitation light.

As described above, to increase the energy density of the excitation light, it is preferable that the core diameter of the optical fiber used for transmitting the excitation light preferably be small. However, if the core diameter is too small, a loss occurs when light enters the optical fiber from the light source. Consequently, there is an appropriate degree of the core diameter. Preferably, the core diameter of first optical waveguide <NUM> is <NUM> or more and <NUM> or less. On the other hand, preferably, the core diameter of the optical fiber for transmitting the radiated light from diamond element <NUM> is large as much as possible. Note that if the core diameter is too large, the cost increases. Preferably, the core diameter of second optical waveguide <NUM> is <NUM> or more and <NUM> or less. Note that also in this case, if the core diameter of second optical waveguide <NUM> is smaller than the core diameter of first optical waveguide <NUM>, the fluorescent light caused by the excitation light is not sufficiently collected, and the loss of drive power increases. Consequently, the core diameter of second optical waveguide <NUM> is preferably equal to or larger than the core diameter of first optical waveguide <NUM>, and more preferably larger than the core diameter of first optical waveguide <NUM>. For example, if the core diameter of first optical waveguide <NUM> is <NUM>, the core diameter of second optical waveguide <NUM> is preferably <NUM> or more, is more preferably <NUM> or more, and is further preferably <NUM> or more. If the core diameter of first optical waveguide <NUM> is <NUM>, the core diameter of second optical waveguide <NUM> that is <NUM> is more preferable than that of <NUM> ; <NUM> or more is more preferable, and <NUM> or more is further preferable. For example, if the core diameter of first optical waveguide <NUM> is <NUM>, the core diameter of second optical waveguide <NUM> is preferably <NUM> or more, is more preferably <NUM> or more, is further preferably <NUM> or more, and is still further preferably <NUM> or more. In every case, if the core diameter is larger than <NUM>, inconveniences, such as resistance to bending the optical fiber, and the accompanying cost, occur. As described above, if the core diameter of first optical waveguide <NUM> is in a range from <NUM> or more and <NUM> or less, the preferable condition described above holds.

In the second embodiment, the excitation light and the radiated light from diamond element <NUM> are separated from each other using fluorescent light reflection filter <NUM> and LPF <NUM>. However, there is no limitation to this. The excitation light and the radiated light from diamond element <NUM> may be separated from each other using the excitation light reflection filter having the function of LPF.

Referring to <FIG>, a diamond sensor unit <NUM> according to a first modification separates the excitation light from light emitting element <NUM>, and the radiated light from diamond element <NUM> from each other, using an excitation light reflection filter <NUM> having the function of LPF. Diamond sensor unit <NUM> is diamond sensor unit <NUM> (see <FIG>) where fluorescent light reflection filter <NUM> and LPF <NUM> are replaced with an excitation light reflection filter <NUM> having the function of LPF, and the path of occurrence and transmission of excitation light, and the path of transmission and detection of radiated light from diamond element <NUM> are replaced with each other. Excitation light reflection filter <NUM> having the function of LPF is a long-pass filter, and is also an excitation light reflection filter. In <FIG>, configuration elements assigned with the same symbols as in <FIG> represent the same elements in <FIG>. Consequently, redundant description about them is not repeated.

The excitation light caused by light emitting element <NUM> is collected by light collecting element <NUM>, and enters one end of first optical waveguide <NUM>. The excitation light is transmitted through first optical waveguide <NUM>, is output from the other end of first optical waveguide <NUM>, is collected by light collecting element <NUM> as parallel light, which enters excitation light reflection filter <NUM> having the function of LPF. Since the excitation light is green light, the light is reflected by excitation light reflection filter <NUM> having the function of LPF, and enters light collecting element <NUM>.

On the other hand, the radiated light from diamond element <NUM> is collected by light collecting element <NUM> as parallel light, which enters excitation light reflection filter <NUM> having the function of LPF. The radiated light (i.e., red fluorescent light) from diamond element <NUM> passes through excitation light reflection filter <NUM> having the function of LPF, is collected by light collecting element <NUM>, enters second optical waveguide <NUM>, is transmitted through second optical waveguide <NUM> to light receiving part <NUM>, and is detected by light receiving part <NUM>. Consequently, similar to diamond sensor unit <NUM> in the second embodiment, diamond sensor unit <NUM> functions as a sensor that detects the magnetic field and the like.

The case where the excitation light is incident on one surface of the diamond element including the NV center, and the radiated light from the same surface is measured has been described above. However, there is no limitation to this. In a case where the diamond element including the NV center has a plurality of flat surfaces, a surface irradiated with the excitation light, and a surface where the radiated light is measured may be different from each other. The flat surface means one flat surface having a predetermined area or more. Here, the flat surface of the diamond element including the NV center means one flat surface having an area larger than a circle having a diameter of about <NUM>.

Referring to <FIG>, diamond sensor unit <NUM> according to a second modification detects light radiated from a surface different from a surface through which the excitation light has entered a diamond element <NUM>. Diamond sensor unit <NUM> is diamond sensor unit <NUM> shown in <FIG> in which sensor part <NUM> is replaced with sensor part <NUM> and from which light collecting element <NUM>, fluorescent light reflection filter <NUM>, and light collecting element <NUM> are removed. In <FIG>, configuration elements assigned with the same symbols as in <FIG> represent the same elements in <FIG>. Redundant description about them is not repeated.

Sensor part <NUM> includes diamond element <NUM>, a light collecting element <NUM>, a light collecting element <NUM>, and electromagnetic wave irradiation part <NUM>. Diamond element <NUM> includes the NV center, and has a plurality of flat surfaces. Diamond element <NUM> is formed to be a rectangular parallelepiped, for example. Light collecting element <NUM> is disposed in contact with one flat surface (hereinafter called a first flat surface) of diamond element <NUM>. Light collecting element <NUM> is disposed in contact with a flat surface (hereinafter called a second flat surface) of diamond element <NUM> that is different from the first flat surface.

The excitation light transmitted from first optical waveguide <NUM> enters light collecting element <NUM>, is collected by light collecting element <NUM>, and is irradiated to the first flat surface of diamond element <NUM>. As described above, diamond element <NUM> is irradiated with the excitation light and irradiated with electromagnetic waves (e.g., microwaves) from electromagnetic wave irradiation part <NUM> at predetermined timing, thus allowing diamond element <NUM> to radiate light. The radiated light is radiated in all the directions. Light (i.e., red fluorescent light) emitted from the second flat surface of diamond element <NUM> is collected by light collecting element <NUM> as parallel light, enters LPF <NUM>, passes through LPF <NUM>, and enters one end of second optical waveguide <NUM>. Subsequently, the light (i.e., red fluorescent light) radiated from the second flat surface of diamond element <NUM> is transmitted through second optical waveguide <NUM> to light detection part <NUM>, and is detected by light detection part <NUM>. Consequently, similar to diamond sensor unit <NUM> in the second embodiment, diamond sensor unit <NUM> functions as a sensor that detects the magnetic field and the like.

As described above, by adopting the configuration where the radiated light is detected from the surface (i.e., the second flat surface) different from the surface (i.e., the first flat surface) irradiated with the excitation light, the number of light collecting elements can be reduced, and the elements (e.g., the fluorescent light reflection filter etc.) for separating the excitation light from the radiated light from the diamond element can be omitted. Consequently, the diamond sensor unit can have a simpler configuration, and the cost can be reduced.

The case where diamond element <NUM> is formed to be a rectangular parallelepiped, and the first flat surface and the second flat surface are two surfaces forming an angle of <NUM> degrees has been described above. However, there is no limitation to this. In the case where diamond element <NUM> is formed to have a rectangular parallelepiped, a flat surface parallel with the first flat surface may be the second flat surface for collecting the radiated light that is a detection target. Diamond element <NUM> is only required to have at least two flat surfaces. There is no limitation to the hexahedron. Any shape may be adopted as that of diamond element <NUM>.

The case where the diamond element including the NV center is irradiated with electromagnetic waves (e.g., microwaves) has been described above. However, there is no limitation to this. As disclosed in NPL <NUM>, the diamond element including the NV center functions as a magnetic sensor even without irradiation with electromagnetic waves.

Referring to <FIG>, a diamond sensor unit <NUM> according to a third modification is diamond sensor unit <NUM> shown in <FIG> where electromagnetic wave irradiation part <NUM> is removed. That is, a sensor part <NUM> includes light collecting element <NUM>, and diamond element <NUM>, but does not include the electromagnetic wave irradiation part (e.g., a coil or the like). Similar to diamond sensor unit <NUM> (see <FIG>), diamond sensor unit <NUM> allows diamond element <NUM> to be irradiated with the excitation light (i.e., green light) output from light emitting element <NUM>. Accordingly, the NV center of diamond element <NUM> is excited, radiates light (i.e., red fluorescent light), and returns to the original state. Consequently, by measuring the radiated light, diamond sensor unit <NUM> functions as a magnetic sensor.

The measurement principle using microwaves is as described above. Through use of the difference between the intensity of the fluorescent light from the ground level and the intensity of the fluorescent light from the excited level achieved by microwave resonance absorption, the resonant level can be quantified by the frequency of microwaves, and the change in magnetic field can be measured based on the change in resonant level. On the other hand, the measurement principle used here uses the change in fluorescent light intensity even in a case of emitting no microwave. That is, the change of the electron at the ground level due to the effect of the magnetic field, and the change of the fluorescent light intensity in a manner correlated with the magnetic field are used.

Consequently, diamond sensor unit <NUM> functions as a sensor that detects the magnetic field etc. Sensor part <NUM> does not include a conductive member, such as a coil, and is entirely made of an electrical insulating member. Consequently, sensor part <NUM> is not damaged due to electrical discharge or the like even in a case of being installed in a high-voltage facility. As a result, the magnetic field and the like can be safely measured in a high-voltage environment by diamond sensor unit <NUM>.

The configuration that causes the diamond element including the NV center to function as a magnetic sensor without irradiation with electromagnetic waves is not limited to that shown in <FIG>. Referring to <FIG>, a diamond sensor unit <NUM> according to a fourth modification is diamond sensor unit <NUM> shown in <FIG> from which light collecting element <NUM> and electromagnetic wave irradiation part <NUM> are removed. That is, a sensor part <NUM> includes diamond element <NUM>, but includes neither the light collecting element nor the electromagnetic wave irradiation part. Diamond element <NUM> is disposed in contact with an end of optical waveguide <NUM>.

Similar to diamond sensor unit <NUM> (see <FIG>), when diamond sensor unit <NUM> irradiates diamond element <NUM> with the excitation light (i.e., green light) output from light emitting element <NUM>, the NV center of diamond element <NUM> is excited and radiates light (i.e., red fluorescent light), and the state is returned to the original state. Consequently, by measuring the radiated light, diamond sensor unit <NUM> functions as a magnetic sensor. The method of measuring the magnetic field is similar to that in the third modification.

Consequently, diamond sensor unit <NUM> functions as a sensor that detects the magnetic field etc. Sensor part <NUM> does not include a conductive member, such as a coil, and is entirely made of an electrical insulating member. Consequently, sensor part <NUM> is not damaged by electrical discharge or the like even in a case of being installed in a high-voltage facility, and can safely measure the magnetic field and the like in the high-voltage environment.

In the third modification and the fourth modification, the excitation light and the radiated light are transmitted through the single optical waveguide. Two optical waveguides may be used to transmit the excitation light and the radiated light, respectively. Referring to <FIG>, a diamond sensor unit <NUM> according to a fifth modification is diamond sensor unit <NUM> shown in <FIG> where electromagnetic wave irradiation part <NUM> is removed. That is, a sensor part <NUM> includes light collecting element <NUM>, and diamond element <NUM>, but does not include the electromagnetic wave irradiation part (e.g., a coil or the like). Similar to diamond sensor unit <NUM> (see <FIG>), when diamond sensor unit <NUM> irradiates diamond element <NUM> with the excitation light (i.e., green light) output from light emitting element <NUM>, the NV center of diamond element <NUM> is excited and radiates light (i.e., red fluorescent light), and the state is returned to the original state. Consequently, by measuring the radiated light, diamond sensor unit <NUM> functions as a magnetic sensor. The method of measuring the magnetic field measurement is similar to that in the third modification.

Note that in each of diamond sensor unit <NUM> shown in <FIG>, and diamond sensor unit <NUM> shown in <FIG>, electromagnetic wave irradiation part <NUM> may be removed. Also in this case, the magnetic field can be measured without irradiation with electromagnetic waves.

The case where the diamond element including the NV center is used as the diamond sensor unit has been described above. However, there is no limitation to this. The diamond element is only required to have a color center with electron spin. The color center with electron spin is a center that forms a spin-triplet state, and emits light by excitation. The NV center is a typical example. Furthermore, it has been known that a color center with electron spin is present also at a silicon-hole center (i.e., Si-V center), germanium- hole center (i.e., Ge-V center), and tin-hole center (i.e., Sn-V center). Consequently, a diamond sensor unit may be configured using a diamond element including any of them instead of the diamond element including the NV center.

Note that depending on the level of the color center, the wavelengths of the excitation light and the radiated light (i.e., fluorescent light), and the frequency of electromagnetic waves causing resonance excitation vary. Among them, the NV center is preferable in terms of the wavelength of light and the frequency of microwaves. In the cases of the Si-V center, Ge-V center, and Sn-V center, millimeter waves (e.g., <NUM> to <NUM>) or submillimeter waves (e.g., <NUM> to <NUM> THz) that have frequencies higher than the frequency of microwaves (e.g., <NUM> to <NUM>) are used as electromagnetic waves with which irradiation is performed. For example, in the case of Si-V center, millimeter waves at about <NUM> can be used. In the case of Sn-V center, submillimeter waves at about <NUM> can be used.

Preferably, the excitation light is laser light. It is preferable that the generation device be a semiconductor laser in terms of reduction in size. A detector for the radiated light from the diamond element may be of a vacuum tube type. However, a semiconductor detection device is preferable in terms of reduction in size.

Preferably, the optical waveguide has a two-or-more-layered coaxial structure that includes a core portion through which light passes, and a portion that is made of a material having an refractive index different from that of the core portion and is formed around the core. The core portion is not necessarily made in a form densely filled with a medium for transmitting light. Since the space itself can transmit light, the core may be hollow. Preferably, the optical waveguide is an optical fiber having a core diameter of <NUM> or more and <NUM> or less. This is because through use of the optical fiber, laser light can be relatively easily introduced to a desired position, and the diffusion at the output end of the optical fiber can be suppressed.

The light collecting element is only required to be formed of a material having a function of collecting light. For example, the element may be a lens formed of a silicon-oxide-based material (e.g., glass; an additive other than silicon oxide may be contained), or a material having a diffractive function. Preferably, the light collecting element is a lens that allows light to pass and uses a refractive phenomenon. A spherical lens, a hemispherical lens, and a Fresnel lens are preferable. In particular, in terms of the relationship between the refractive index and the spherical shape, a lens having a focal point of parallel light on a spherical surface is more preferable. This is because through use of such a lens, adjustment of the optical focal point and the optical axis becomes significantly simple, and the amount of light can be utilized as much as possible. Preferably, the lens made of a silicon-oxide-based material is in direct contact with the diamond. This is because without contact, a failure of incapability of appropriately collecting light occurs. Furthermore, this is because with a strong impact, the distance from the diamond to the lens is sometimes changed, and light cannot appropriately be collected in such a case. More preferably, the lens made of a silicon-oxide-based material is in direct contact also with the optical fiber. This is because the loss during collection of fluorescent light into the optical fiber decreases, and is unlikely to cause a change in distance due to an impact.

Preferably, in a case where the sensor part is disposed in a high-voltage environment, the optical waveguide (e.g., the optical fiber) for transmitting the excitation light and the radiated light from the diamond is disposed through insulating glass. Accordingly, the excitation light generation part and the light receiving part can be insulated from a high voltage, the devices used in the excitation light generation part and the light receiving part can be protected.

The electromagnetic wave irradiation part is not limited to a coil-shaped one, and may be linear electric wiring as described later. In this case, the diamond element may be disposed on the surface or an end of the transmission path (e.g., the conductive member) for transmitting electromagnetic waves (e.g., microwaves or millimeter waves). Accordingly, the NV center of the diamond can be accurately irradiated with electromagnetic waves.

Preferably, in a case of detecting temporal change in varying magnetic field and the like with respect to AC power using the diamond sensor unit described above, the NV center of the diamond element is excited and subsequently returns from the light radiating state to the original state (i.e., the state before excitation). To achieve this, it is preferable that spin coherence time T2 of the diamond element be short. Preferably, for example, spin coherence time T2 of the diamond element is less than <NUM>µsec. Note that the detection sensitivity is proportional to (T2)-<NUM>/<NUM>. Accordingly, the smaller T2 is, the lower the detection sensitivity is. Consequently, when abrupt change in magnetic field variation is detected, for example, when pulse shape variation in magnetic field is detected, it is conceivable that spin coherence time T2 of the diamond element is made short as much as possible at the expense of the detection sensitivity.

Preferably, to reduce the spin coherence time, the diamond element contains impurities. In consideration of the fact that the smaller T2 is, the lower the detection sensitivity is, for example, it is preferable that the total hydrogen concentration in the diamond is higher than <NUM> ppm, and <NUM> ppm or less. Preferably, all the NVH-concentration, CH concentration and CH<NUM> concentration in the diamond are higher than <NUM> ppm, and <NUM> ppm or less. Here, the concentration (ppm unit) represents the ratio of the number of atoms.

Hereinafter, according to an Example, the effectiveness of the present invention is described. <FIG> shows the Example of the configuration shown in <FIG>. In <FIG>, components corresponding to the configuration elements shown in <FIG> are respectively assigned with symbols identical to those in <FIG>.

Step-index multimode optical fibers are used as first optical waveguide <NUM> and second optical waveguide <NUM>. First optical waveguide <NUM> has a core diameter of <NUM>, and an NA (i.e., numerical aperture) of <NUM>. Second optical waveguide <NUM> has a core diameter of <NUM>, and an NA of <NUM>. A rectangular parallelepiped diamond of <NUM> × <NUM> × <NUM> is used as diamond element <NUM>. A spherical lens having a diameter of <NUM> is used as light collecting element <NUM>. Light collecting element <NUM> is brought into contact with a surface (i.e., a flat surface of <NUM> × <NUM>) of diamond element <NUM> and is fixed. In the optical system for transmitting the excitation light, a triangular prism <NUM> is disposed in addition to light collecting element <NUM> and fluorescent light reflection filter <NUM>, thus configuring a collimating optical system. Thus, adjustment is performed so that the excitation light can enter the center of light collecting element <NUM>.

The coplanar line shown in <FIG> is used as electromagnetic wave irradiation part <NUM>. A U-shape is cut out from copper foil <NUM> formed on a surface of a glass epoxy substrate <NUM> with each side of about <NUM>, thus forming, at the center, electromagnetic wave irradiation part <NUM> that is the main wiring having a width of <NUM>. Diamond element <NUM> is fixed with silver paste at one end (i.e., a region indicated by a chain-line ellipse in <FIG>) of electromagnetic wave irradiation part <NUM>. Accordingly, the NV center of diamond element <NUM> can be accurately irradiated with microwaves. The other end of electromagnetic wave irradiation part <NUM> (i.e., the end where no diamond element <NUM> is disposed) is in contact with a connector <NUM> in <FIG>.

The microwaves are generated by a remotely provided microwave generation device, are transmitted in the air, and received by an antenna <NUM> (see <FIG>). To radiate microwaves into the air, a horn antenna (gain of <NUM> dB) is used. A patch antenna (a frequency of <NUM>, and a maximum gain of about <NUM> dBi) shown in <FIG> is used as antenna <NUM>. The patch antenna includes substrates <NUM> and <NUM>, and a connector <NUM> for outputting a received signal. Substrates <NUM> and <NUM> are arranged at an interval H (H = <NUM> (mm)) with spacers <NUM> at four corners. Each of substrates <NUM> and <NUM> is a substrate made of a glass epoxy resin (e.g., FR4), and has a thickness of <NUM>, and has a flat surface that is a square (the length L of one side is <NUM>). Four conductive members <NUM> are arranged on a surface of substrate <NUM> that does not face substrate <NUM>. A conductive member is disposed on the entire surface of substrate <NUM> (hereinafter called the ground surface) that faces substrate <NUM>. Four conductive members <NUM> are connected to a signal line of connector <NUM> in parallel. The ground surface of substrate <NUM> is connected to a shield (i.e., ground) of connector <NUM>. Microwaves received by antenna <NUM> are transmitted to connector <NUM> through a transmission path (i.e., a coaxial cable), and are irradiated to diamond element <NUM> from electromagnetic wave irradiation part <NUM>.

A PIN-AMP (i.e., a photodiode IC including a linear current amplifier circuit) is used as light detection part <NUM>. The PIN-AMP used here has a photodiode sensitivity wavelength range of <NUM> to <NUM> and a maximum sensitivity wavelength of <NUM>, and amplifies the photocurrent generated by the photodiode by <NUM> times, and outputs the amplified signal.

Light collecting element <NUM>, diamond element <NUM>, and electromagnetic wave irradiation part <NUM>, which constitute the sensor part, are disposed adjacent to electrical wiring <NUM>. An alternating current (<NUM> or <NUM>, and <NUM> A) is caused to flow through electrical wiring <NUM>. The thus caused varying magnetic field is adopted as a detection target. The maximum value of the magnetic field formed at the sensor part by the alternating current is about <NUM>µT. The power of microwaves radiated from the horn antenna is made constant (<NUM> dBm (= <NUM> W)), the distance D between the sensor part and the horn antenna that radiates microwaves is changed, and measurement is performed. The results are shown in <FIG> and <FIG>.

<FIG> show the signals detected by the PIN-AMP in a state where a <NUM> alternating current (<NUM> A) is caused to flow through electrical wiring <NUM>. <FIG> show measurement results with D = <NUM> (m), D = <NUM> (m), and D = <NUM> (m), respectively. In each of them, a scale on the ordinate axis indicates <NUM> mV, and a scale on the abscissa axis indicates <NUM>. <FIG> shows the signal detected by the PIN-AMP in a state where a <NUM> alternating current (<NUM> A) is caused to flow through electrical wiring <NUM>, and D = <NUM> (m). A unit scale on the ordinate axis indicates <NUM> mV, and a unit scale on the abscissa axis indicates <NUM>.

As can be seen in <FIG> and <FIG>, the detected signal decreases with increase in distance D of microwave radiation. However, even when relatively weak microwaves of about <NUM> W were radiated from a position apart from the sensor part by about <NUM>, the change in magnetic field formed by the alternating current were sufficiently detected. The detection signals shown in <FIG> vary at the AC frequency of <NUM>. The detection signal shown in <FIG> varies at the AC frequency of <NUM>. While the microwaves are attenuated depending on the distance, the power of microwaves to be radiated, the gain of radiation antenna, the gain of reception antenna and the like may be adjusted in consideration of the detection limit (i.e., the lower limit value of the power) of the adopted light detection part, and the radiation distance.

In the above description, the coplanar line is formed on the substrate with each side of about <NUM>. Alternatively, a rectangular substrate with each side of about <NUM> or less.

As shown in the third modification to the fifth modification (see <FIG>), the magnetic field can be detected even without irradiation of the diamond element with electromagnetic waves (e.g., microwaves etc.). For example, as shown in <FIG>, the diamond sensor unit may be configured by removing the elements for irradiation with microwaves (i.e., electromagnetic wave irradiation part <NUM>, antenna <NUM>, connector <NUM>, etc.) from the configuration of Example shown in <FIG>. Also in this case, the varying magnetic field generated by the alternating current caused to flow through electrical wiring <NUM> can be detected.

Light collecting element <NUM> was disposed apart from the surface of diamond element <NUM> by <NUM> and thus was made contactless, and the other conditions were the same as the experiment conditions with D = <NUM> described above, i.e., the experiment conditions with which the signal in <FIG> was observed, and the experiment was performed. As a result, the signal intensity became less than <NUM>/<NUM> of the detection limit, and the observation was unsuccessful. It is conceivable that the density of excitation light decreased, and the fluorescent light intensity was not concentrated, and the signal intensity became less than <NUM>/<NUM>. Note that the signal intensity means the difference between the maximum value and the minimum value of the values on the ordinate axis in <FIG> obtained by averaging the noise portion.

The core diameter of first optical waveguide <NUM> was <NUM>, and the core diameter of second optical waveguide <NUM> was changed to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, and the experiment was performed. The other conditions were made the same as the aforementioned experiment conditions with D = <NUM>, i.e., the experiment conditions with which the signal in <FIG> was observed. As a result, the signal intensity (i.e., fluorescent light intensity) was less than <NUM> times of the signal intensity in <FIG> as a reference value (e.g., one), was <NUM> times, <NUM> times, <NUM> times, <NUM> times, <NUM> times, and twice. That is, except the case where the core diameter of second optical waveguide <NUM> was <NUM>, the signals were successfully detected. As the core diameter of second optical waveguide <NUM> increased, the detection signal increased accordingly. Note that in the case where the core diameter of second optical waveguide <NUM> was <NUM> was not successfully accommodated in a compact experiment system. As a result of similar experiments performed for the other modifications using first optical waveguide <NUM> and second optical waveguide <NUM>, ratios substantially similar to those described above about the detected signal intensity were obtained.

Claim 1:
A diamond sensor unit (<NUM>), comprising:
a sensor part (<NUM>) that includes a diamond having a color center with electron spin;
an irradiation part that irradiates the diamond with excitation light;
a detection part that detects radiated light from the color center of the diamond; and
an optical waveguide that transmits the excitation light and the radiated light, wherein:
the optical waveguide includes a first optical waveguide (<NUM>) that transmits the excitation light, and a second optical waveguide (<NUM>) that transmits the radiated light,
one end of the first optical waveguide (<NUM>) is disposed closer to the diamond than another end of the first optical waveguide (<NUM>),
one end of the second optical waveguide (<NUM>) is disposed closer to the diamond than another end of the second optical waveguide (<NUM>), and
a fluorescent light reflection filter (<NUM>), a long-pass filter LPF (<NUM>), or a dichroic mirror that separates the excitation light and the radiated light from each other is included within a predetermined distance from each of the one end of the first optical waveguide (<NUM>) and the one end of the second optical waveguide (<NUM>).