Measuring equipment

Abstract

This measurement device comprises: a first light source that emits first emission light; a second light source that emits second emission light; a diffusion plate; a mirror that converges the first emission light and the second emission light to cause the same to enter one region of the diffusion plate, by changing the propagation direction of at least one selected from between the first emission light and the second emission light; an optical detector that detects first reflection light generated from a target object and originating from the first emission light that has been diffused by the diffusion plate, and second reflection light generated from the target object and originating from the second emission light that has been diffused by the diffusion plate; and a processing circuit that generates and outputs information pertaining to the target object on the basis of the results of detecting the first reflection light and the second reflection light, by the optical detector. The distance between a first emission light light-spot which is formed in the one region of the diffusion plate and a second emission light light-spot which is formed in the one region of the diffusion plate is shorter than the distance between the first light source and the second light source.

Description

[Technical Field]

[0001] The present disclosure relates to a measurement device. [Background technology]

[0002] There are technologies that acquire internal information of an object, such as a living body, by irradiating the object with light and detecting the light that has passed through the object. For example, Patent Document 1 discloses a device that acquires internal information of the object by removing noise caused by surface reflection components of light from the object. Patent Document 2 discloses a device that detects pulse waves from images acquired using a camera. These technologies achieve non-contact biometric measurement by using a measuring device such as a camera. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-202328 [Patent Document 2] International Publication No. 2016 / 006027 [Patent Document 3] Japanese Patent Application Publication No. 4-189349 [Patent Document 4] Japanese Patent Application Publication No. 11-164826 Summary of the Invention [Problem to be solved by the invention]

[0004] In a measurement device that acquires internal information of an object in a non-contact manner, if the object or the measurement device moves during measurement, an error occurs in the acquired signal.

[0005] The present disclosure provides a measurement technique that makes it possible to reduce signal errors that occur when movement occurs in the object or measurement device during measurement. [Means for solving the problem]

[0006] A measurement device according to one aspect of the present disclosure includes a first light source that emits a first output light, a second light source that emits a second output light, a diffuser, a mirror that changes the propagation direction of at least one selected from the group consisting of the first output light and the second output light to converge and make the first output light and the second output light incident on a region of the diffuser, a photodetector that detects a first reflected light generated from an object due to the first output light diffused by the diffuser and a second reflected light generated from the object due to the second output light diffused by the diffuser, and a processing circuit that generates and outputs information about the object based on a detection result of the first reflected light and the second reflected light by the photodetector. A distance between a light spot of the first output light formed on the region of the diffuser and a light spot of the second output light formed on the region of the diffuser is shorter than a distance between the first light source and the second light source.

[0007] A measuring device according to another aspect of the present disclosure includes a first light-emitting device including a first light source that emits a first emitted light, a second light source adjacent to the first light source that emits a second emitted light, and a first submount that supports the first light source and the second light source; a diffuser plate arranged on the optical path of the first emitted light and the second emitted light; a photodetector that detects first reflected light generated from an object due to the first emitted light diffused by the diffuser plate and second reflected light generated from the object due to the second emitted light diffused by the diffuser plate; and a processing circuit that generates and outputs information about the object based on the detection results of the first reflected light and the second reflected light by the photodetector.

[0008] According to yet another aspect of the present disclosure, there is provided a measurement device comprising: a light source; a diffuser disposed on an optical path of light emitted from the light source; a photodetector configured to detect reflected light from an object due to the emitted light diffused by the diffuser; and a processing circuit configured to generate and output information about the object based on a detection result of the reflected light by the photodetector. The processing circuit estimates a distance from the photodetector to at least one measurement point on the object based on the detection result of the photodetector, estimates a position of the at least one measurement point based on the distance estimated by the processing circuit, estimates an angle of incidence of the emitted light at the at least one measurement point based on the position estimated by the processing circuit, corrects a signal indicating the detection result based on the angle of incidence estimated by the processing circuit and previously generated calibration data defining a relationship between the angle of incidence of the emitted light on the object and the reflectance of the emitted light on the object, and generates information about the object based on the signal corrected by the processing circuit.

[0009] A method according to yet another aspect of the present disclosure includes performing the operations of emitting light from a light source toward an object or a calibration plate having optical properties similar to those of the living body to measure the reflectance of at least one measurement point on the object or the plate, and estimating the angle of incidence of the light at the at least one measurement point multiple times while changing the distance between the object or the plate and the light source, and generating calibration data that specifies the relationship between the angle of incidence of the light at the at least one measurement point and the reflectance.

[0010] A general or specific aspect of the present disclosure may be realized as a system, an apparatus, a method, an integrated circuit, a computer program, or a recording medium such as a computer-readable recording disk, or as any combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a recording medium. The computer-readable recording medium may include a non-volatile recording medium such as a CD-ROM (Compact Disc-Read Only Memory). An apparatus may be composed of one or more devices. When an apparatus is composed of two or more devices, the two or more devices may be located in a single device or may be located separately in two or more separate devices. In this specification and claims, the term "apparatus" may refer not only to a single device but also to a system consisting of multiple devices. [Effects of the Invention]

[0011] According to the technology of the present disclosure, it is possible to reduce signal errors that occur when movement occurs in the object or the measurement device during measurement. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram schematically illustrating a measurement device according to an exemplary embodiment of the present disclosure. [Figure 2] FIG. 2 is a diagram illustrating an example of the configuration of a photodetector. [Figure 3A] FIG. 3A is a diagram schematically illustrating an example of the temporal change of the surface reflection component I1 and the internal scattering component I2 contained in the reflected light pulse when the light pulse Ip has an impulse waveform. [Figure 3B] FIG. 3B is a diagram schematically illustrating an example of the temporal change of the surface reflection component I1 and the internal scattering component I2 contained in the reflected light pulse when the light pulse Ip has a rectangular waveform. [Figure 4] FIG. 4 is a flowchart showing an outline of the operation of the control circuit to control the first light source, the second light source, and the photodetector. [Figure 5A]FIG. 5A is a diagram showing an example of the configuration of a diffuser plate, a plurality of light sources, and an optical system. [Figure 5B] FIG. 5B is a diagram showing an example of the illuminance distribution in the region indicated by the dashed line in FIG. 5A. [Figure 5C] FIG. 5C is a diagram schematically illustrating an example of two adjacent light spots formed in one area of ​​the diffuser plate. [Figure 5D] FIG. 5D is a graph showing the relationship between the tilt angle of the human forehead as the measurement target and the allowable distance between two light spots of different wavelengths on a diffuser plate. [Figure 6] FIG. 6 is a diagram showing another example of the configuration of the light source, the optical system, and the diffuser plate. [Figure 7] FIG. 7 is a diagram showing an example of a light emitting device in which a plurality of light emitting elements are aggregated and arranged in one package. [Figure 8] FIG. 8 is a diagram showing still another example of the configuration of the light emitting device. [Figure 9] FIG. 9 is a diagram schematically showing how light diffused by a diffusion plate enters a measurement target portion. [Figure 10] FIG. 10 is a graph showing the incidence angle dependency of the diffuse reflectance of the measurement target portion in the configuration of FIG. [Figure 11] FIG. 11 is a flowchart illustrating an example of a method for generating calibration data. [Figure 12] FIG. 12 is a flowchart showing an example of a signal correction method using calibration data executed during measurement. [Figure 13] FIG. 13 is a diagram showing another example of the configuration of the diffuser plate, the plurality of light sources, and the optical system. DETAILED DESCRIPTION OF THE INVENTION

[0013] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component arrangement and connection configurations, steps, and step orders shown in the following embodiments are merely examples and are not intended to limit the technology of the present disclosure. Among the components in the following embodiments, components that are not described in the independent claims that represent the highest concepts are described as optional components. Each figure is a schematic diagram and is not necessarily an exact illustration. Furthermore, in each figure, substantially identical or similar components are assigned the same reference numerals. Duplicate descriptions may be omitted or simplified.

[0014] In this disclosure, all or part of a circuit, unit, device, component, or part, or all or part of a functional block in a block diagram, may be implemented by one or more electronic circuits, including, for example, a semiconductor device, a semiconductor integrated circuit (IC), or an LSI (large scale integration). An LSI or IC may be integrated on a single chip or may be configured by combining multiple chips. For example, functional blocks other than memory elements may be integrated on a single chip. While the terms LSI and IC are used here, the term may be changed depending on the degree of integration, and may be referred to as a system LSI, a VLSI (very large scale integration), or an ULSI (ultra large scale integration). A field programmable gate array (FPGA), which is programmable after LSI fabrication, or a reconfigurable logic device, which can reconfigure connections within an LSI or set up circuit partitions within an LSI, may also be used for the same purpose.

[0015] Furthermore, all or part of the functions or operations of a circuit, unit, device, component, or section can be implemented by software processing. In this case, the software is recorded on one or more non-transitory recording media such as ROMs, optical disks, hard disk drives, etc., and when the software is executed by a processor, the functions specified in the software are performed by the processor and peripheral devices. A system or device may include one or more non-transitory recording media on which software is recorded, a processor, and necessary hardware devices, such as interfaces.

[0016] First, an overview of the embodiment of the present disclosure will be described.

[0017] A measurement device according to one aspect of the present disclosure includes a first light source, a second light source, a diffuser, a mirror, a photodetector, and a processing circuit. The first light source emits a first output light. The second light source emits a second output light. The mirror changes the propagation direction of at least one selected from the group consisting of the first output light and the second output light, thereby concentrating the first output light and the second output light and making them incident on a region of the diffuser. The photodetector detects a first reflected light generated from an object due to the first output light diffused by the diffuser, and a second reflected light generated from the object due to the second output light diffused by the diffuser. The processing circuit generates and outputs information about the object based on a detection result of the first reflected light and the second reflected light by the photodetector. The distance between the optical spot of the first output light formed in the one region of the diffuser plate and the optical spot of the second output light formed in the one region of the diffuser plate is shorter than the distance between the first light source and the second light source.

[0018] The photodetector may detect the first reflected light and the second reflected light individually, or may detect light generated by overlapping the first reflected light and the second reflected light, or reflected light generated due to overlapping the first outgoing light and the second outgoing light. The "detection result of the first reflected light and the second reflected light" may include a result indicated by a signal generated by the photodetector detecting each of the first reflected light and the second reflected light, or a detection result indicated by a signal generated by the photodetector detecting reflected light generated due to overlapping the first outgoing light and the second outgoing light, or light generated due to overlapping the first reflected light and the second reflected light.

[0019] "The distance between the light spot of the first emitted light and the light spot of the second emitted light" refers to the distance between the center or center of gravity of the light spot of the first emitted light and the center or center of gravity of the light spot of the second emitted light. "The distance between the first light source and the second light source" refers to the distance between the center of the first light source and the center of the second light source. Thus, in this specification, the distance between two adjacent light spots or two light sources refers to the distance between the centers or centers of gravity.

[0020] According to the above configuration, by disposing one or more mirrors, the first output light emitted from the first light source and the second output light emitted from the second light source are concentrated and incident on a relatively narrow area of ​​the diffuser plate. Therefore, the diffused light resulting from the first output light and the diffused light resulting from the second output light are incident on the measured portion of the object at approximately the same angle of incidence. Therefore, even if the relative positions of the measured portion and the measuring device change due to movement of the object or the measuring device, changes in the illuminance or reflectance on the measured portion can be made independent of the difference in light intensity or uneven illuminance between the light sources. As a result, correction, i.e., calibration, of the signal acquired by the photodetector can be easily performed.

[0021] A measurement device according to another aspect of the present disclosure includes a first light-emitting device, a diffuser, a photodetector, and a processing circuit. The first light-emitting device includes a first light source that emits a first output light, a second light source adjacent to the first light source that emits a second output light, and a first submount that supports the first light source and the second light source. The diffuser is disposed on the optical paths of the first output light and the second output light. The photodetector detects first reflected light generated from an object due to the first output light diffused by the diffuser, and second reflected light generated from the object due to the second output light diffused by the diffuser. The processing circuit generates and outputs information about the object based on the detection results of the first reflected light and the second reflected light by the photodetector.

[0022] According to the above configuration, the first light source and the second light source are disposed on the same submount. The first light source and the second light source are integrated into a single package. Even with this configuration, the first emitted light from the first light source and the second emitted light from the second light source are integrated and incident on a relatively small area of ​​the diffuser plate. Therefore, the same effects as those of the above-described embodiment can be obtained.

[0023] The distance between the center of the light spot of the first output light and the center of the light spot of the second output light on the diffuser plate may be, for example, 5 mm or less. In this specification, if the distance between two adjacent light spots is 5 mm or less, it is interpreted that their positions are substantially the same. The distance between the centers of these light spots may be 2 mm or less.

[0024] Here, the widths of the light spot of the first output light and the light spot of the second output light on the diffuser plate in the major axis direction are defined as w1 and w2, respectively. The distance between the light spot of the first output light and the second light spot can be shorter than w1 and w2, for example. The light sources and optical systems may be arranged so that the first output light and the second output light at least partially overlap when they enter the diffuser plate.

[0025] The measurement device may further include a first collimator lens disposed on the optical path between the first light source and the diffuser plate, and a second collimator lens disposed on the optical path between the second light source and the diffuser plate. By disposing a collimator lens on the optical path between each light source and the diffuser plate, each emitted light can be converted into parallel light. This allows the parallel light to be concentrated and incident on a single area of ​​the diffuser plate. As a result, the influence of intensity differences between the light sources on illuminance fluctuations on the measurement target due to movement of the object or the measurement device can be further reduced.

[0026] The angle of incidence of the first output light incident on the diffuser plate may be the same as the angle of incidence of the second output light incident on the diffuser plate. That is, the light sources and optical systems may be arranged so that the first output light and the second output light are incident on the diffuser plate at the same angle of incidence. This configuration can further reduce the influence of intensity differences between light sources on illuminance fluctuations on the measured part due to movement of the object or measurement device. Here, "the same angle of incidence" means that the angles of incidence are substantially the same, but does not necessarily mean that the angles of incidence are strictly the same.

[0027] The diffuser plate may have, for example, multiple recesses or multiple protrusions on its surface, which diffuses incident light rays randomly in various directions, thereby suppressing uneven illuminance on the measurement target.

[0028] The wavelength of the first emitted light may be, for example, not less than 650 nm and not more than 805 nm. The wavelength of the second emitted light may be, for example, not less than 805 nm and not more than 950 nm. These wavelengths are suitable for measuring the concentrations of oxygenated hemoglobin and deoxygenated hemoglobin in blood inside a living body, as will be described later.

[0029] The wavelength of the first emitted light may be the same as the wavelength of the second emitted light. Here, the two wavelengths being "the same" means that they are substantially the same, not necessarily strictly the same. By emitting light of the same wavelength from multiple light sources, the light of that wavelength can be enhanced. Therefore, even if the light output of each light source is small, for example, the lack of light output can be compensated for.

[0030] The measurement device may further include a control circuit that controls the first light source, the second light source, and the photodetector. The first reflected light and the second reflected light may be pulsed light. The control circuit may cause the first light source to emit the first emitted light, the second light source to emit the second emitted light, the photodetector to detect a first component of the first reflected light during a first falling period, which is a period from the start to the end of a decrease in the intensity of the first reflected light, and the photodetector to detect a second component of the second reflected light during a second falling period, which is a period from the start to the end of a decrease in the intensity of the second reflected light. The processing circuit may generate information about the object based on the intensities of the first and second components of the first and second reflected light detected by the photodetector. With this configuration, for example, if the object is a living organism, information about blood flow in a relatively deep part of the living organism can be obtained as biological information.

[0031] The measurement device may further include a third light source that emits a third outgoing light. The photodetector may further detect a third reflected light generated from the object due to the third outgoing light diffused by the diffuser. The processing circuit may generate and output the information based on a detection result of the first reflected light, the second reflected light, and the third reflected light by the photodetector.

[0032] The photodetector may detect the first reflected light, the second reflected light, and the third reflected light individually, or may detect light resulting from the overlap of the first reflected light, the second reflected light, and the third reflected light, or reflected light resulting from the overlap of the first output light, the second output light, and the third output light. The term "the first reflected light, the second reflected light, and the third reflected light" may refer to a result indicated by a signal generated by the photodetector detecting the first reflected light, the second reflected light, and the third reflected light, respectively, or a detection result indicated by a signal generated by the photodetector detecting reflected light resulting from the overlap of the first output light, the second output light, and the third output light, or light resulting from the overlap of the first reflected light, the second reflected light, and the third reflected light. The wavelength of the third output light may be the same as or different from the wavelengths of the first output light and the second output light.

[0033] According to the above configuration, by adding a third light source, it becomes possible to further increase the amount of light and obtain even more information.

[0034] The first light emitting device may further include a third light source that emits a third output light, a fourth light source that emits a fourth output light, a second submount that supports the third light source and the fourth light source, and a housing that houses the first light source, the second light source, the third light source, and the fourth light source. The photodetector may further detect third reflected light generated from the object due to the third output light diffused by the diffuser plate, and fourth reflected light generated from the object due to the fourth output light diffused by the diffuser plate. The processing circuit may generate and output the information based on detection results of the first reflected light, the second reflected light, the third reflected light, and the fourth reflected light by the photodetector. The first light source, the second light source, the third light source, and the fourth light source may be housed as a single package within the housing.

[0035] The photodetector may detect the first reflected light, the second reflected light, the third reflected light, and the fourth reflected light individually, or may detect light resulting from the overlap of the first reflected light, the second reflected light, the third reflected light, and the fourth reflected light, or reflected light resulting from the overlap of the first outgoing light, the second outgoing light, the third outgoing light, and the fourth outgoing light. "The first reflected light, the second reflected light, the third reflected light, and the fourth reflected light" may include a result indicated by a signal generated by the photodetector detecting each of the first reflected light, the second reflected light, the third reflected light, and the fourth reflected light, or a detection result indicated by a signal generated by the photodetector detecting reflected light resulting from the overlap of the first outgoing light, the second outgoing light, the third outgoing light, and the fourth outgoing light, or light resulting from the overlap of the first reflected light, the second reflected light, the third reflected light, and the fourth reflected light.

[0036] According to the above configuration, by adding a fourth light source, it is possible to further increase the amount of light and obtain even more information. Furthermore, because the four light sources are integrated into one package, it is easy to concentrate the light emitted from the four light sources into a small area on the diffuser plate and make it incident thereon.

[0037] The processing circuit may estimate a distance from the photodetector to at least one measurement point on the object based on the detection result by the photodetector, estimate a position of the at least one measurement point based on the distance from the photodetector to the at least one measurement point on the object estimated by the processing circuit, estimate a first angle of incidence of the first outgoing light to the at least one measurement point and a second angle of incidence of the second outgoing light to the at least one measurement point based on the position estimated by the processing circuit, correct a signal indicating the detection result based on the first angle of incidence estimated by the processing circuit, the second angle of incidence estimated by the processing circuit, and pre-generated calibration data that defines the relationship between the angle of incidence of light on the object and the reflectivity of the light on the object, and generate the information based on the signal corrected by the processing circuit.

[0038] According to the above configuration, the signal output from the photodetector can be appropriately corrected based on the calibration data generated in advance, and more accurate information about the target object can be generated based on the corrected signal.

[0039] The object may be a living body, and the information may include, for example, at least one piece of information selected from the group consisting of blood flow, oxygen saturation, pulse rate, and blood pressure of the living body. The information may include information indicating cerebral blood flow of the living body.

[0040] The measurement device may further include a second light-emitting device including a third light source that emits a third output light, a fourth light source adjacent to the third light source that emits a fourth output light, and a second submount that supports the third light source and the fourth light source, and a mirror that concentrates and incidents the first output light, the second output light, the third output light, and the fourth output light on one area of ​​the diffuser plate by changing the propagation direction of at least one selected from the group consisting of the output light from the first light-emitting device and the output light from the second light-emitting device.

[0041] According to yet another aspect of the present disclosure, there is provided a measurement device comprising: a light source; a diffuser disposed on an optical path of light emitted from the light source; a photodetector configured to detect reflected light from an object due to the emitted light diffused by the diffuser; and a processing circuit configured to generate and output information about the object based on a detection result of the reflected light by the photodetector. The processing circuit estimates a distance from the photodetector to at least one measurement point on the object based on the detection result of the photodetector, estimates a position of the at least one measurement point based on the distance estimated by the processing circuit, estimates an angle of incidence of the emitted light at the at least one measurement point based on the position estimated by the processing circuit, corrects a signal indicating the detection result based on the angle of incidence estimated by the processing circuit and previously generated calibration data defining a relationship between the angle of incidence of the emitted light on the object and the reflectance of the emitted light on the object, and generates the information based on the signal corrected by the processing circuit.

[0042] According to the above configuration, the signal output from the photodetector can be appropriately corrected based on the calibration data generated in advance, and more accurate information about the object can be generated based on the corrected signal. Note that in the above aspect, it is not necessary to use multiple light sources. When multiple light sources are used, the signal correction may be performed for each light source or for each wavelength used.

[0043] A method according to yet another aspect of the present disclosure includes: performing an operation of emitting light from a light source toward an object or a calibration plate having optical properties similar to those of the object to measure the reflectance of at least one measurement point on the object or the plate; and performing an operation of estimating the angle of incidence of the light at the at least one measurement point multiple times while changing the distance between the object or the plate and the light source; and generating calibration data that specifies the relationship between the angle of incidence of the light at the at least one measurement point and the reflectance.

[0044] This method makes it possible to efficiently generate calibration data that is referenced when correcting signals from the aforementioned measurement device.

[0045] Hereinafter, more specific embodiments of the present disclosure will be described with reference to the drawings.

[0046] (Embodiment) [1. Measurement equipment configuration] FIG. 1 is a schematic diagram illustrating a measurement device 100 according to an exemplary embodiment of the present disclosure. The measurement device 100 according to this embodiment irradiates a target portion 10 of a measurement object with light and detects light reflected from the target portion 10 to non-contactly acquire internal information of the target portion 10. The measurement object may be, for example, a living body such as a human. The target portion 10 may be, for example, an exposed part of the skin, such as the human head, particularly the forehead. The internal information may be, for example, information reflecting the state of human brain activity. Depending on the application, the target portion 10 may be an object other than a living body. For example, the target may be a scattering object such as a liquid, gas, or food. In the following description, unless otherwise specified, the target portion 10 is assumed to be the human forehead.

[0047] The measurement device 100 in this embodiment includes a first light source 20a, a second light source 20b, a photodetector 30, an electronic circuit 40, and a diffuser 70. The electronic circuit 40 includes a signal processing circuit 50 and a control circuit 60. In the following description, the first light source 20a and the second light source 20b may be referred to indistinguishably as the "light source 20." The first light source 20a and the second light source 20b emit light pulses to illuminate the measurement target 10. The photodetector 30 detects a portion of the reflected light pulse reflected by the measurement target 10 and outputs a signal indicating its intensity. The signal processing circuit 50 processes the signal output from the photodetector 30 to generate and output a signal indicating the internal state of the measurement target 10. The control circuit 60 controls the first light source 20a, the second light source 20b, the photodetector 30, and the signal processing circuit 50. 1, the measurement device 100 may include an optical system including one or more mirrors or one or more collimator lenses between the light source 20 and the diffuser plate 70. The specific configuration of the optical system will be described later.

[0048] Each component of the measurement device 100 will be described below.

[0049] 1-1. First Light Source 20a and Second Light Source 20b The first light source 20a emits a first light pulse I p1 First light pulse Ip1 The second light source 20b emits a second light pulse I for irradiating the measurement target 10. p2 The second light pulse I is emitted. p2 has a second wavelength longer than the first wavelength. In the example shown in FIG. 1, the number of first light sources 20a is one, but it may be multiple. The same applies to the number of second light sources 20b. By providing multiple light sources that emit light of the same wavelength, the intensity of the irradiated light can be increased. Depending on the application, it is not necessary to use both the first light source 20a and the second light source 20b, and only one of them may be used. In that case, two or more first light sources 20a or two or more second light sources 20b are arranged.

[0050] In the following description, the first light pulse I p1 and the second light pulse I p2 Without distinction, we call them "light pulses I" p " Light Pulse I p includes a rising portion and a falling portion. The rising portion is p The falling part is the part of the optical pulse I from when its intensity starts to increase until it stops increasing. p This is the portion of the signal that begins to decrease in intensity and ends when the decrease is complete.

[0051] The first light source 20a includes a first light-emitting element 22a that emits light with an intensity corresponding to an injected first current and a first adjustment circuit 24a that adjusts the first current. The second light source 20b includes a second light-emitting element 22b that emits light with an intensity corresponding to an injected second current and a second adjustment circuit 24b that adjusts the second current. In the following description, the first light-emitting element 22a and the second light-emitting element 22b may be referred to as "light-emitting element 22" without distinction. The first adjustment circuit 24a and the second adjustment circuit 24b may be referred to as "adjustment circuits" without distinction. The first light-emitting element 22a and the second light-emitting element 22b may include, for example, a laser diode that emits laser light. The first adjustment circuit 24a and the second adjustment circuit 24b may include, for example, a field-effect transistor (FET) including a gallium nitride (GaN) semiconductor with high electrical responsiveness.

[0052] Light pulse I arriving at the measured part 10 p A portion of this light becomes a surface reflection component I1 that is reflected on the surface of the measurement target 10, and another portion becomes an internal scattering component I2 that is reflected or scattered once or multiple times inside the measurement target 10. The surface reflection component I1 includes three components: a direct reflection component, a diffuse reflection component, and a scattered reflection component. The direct reflection component is a reflection component whose angle of incidence and reflection angle are equal. The diffuse reflection component is a component that is diffused and reflected by the unevenness of the surface. The scattered reflection component is a component that is scattered and reflected by internal tissue near the surface. If the measurement target 10 is the user's forehead, the scattered reflection component is a component that is scattered and reflected inside the epidermis. In the following, the surface reflection component I1 that is reflected on the surface of the measurement target 10 will be described as including these three components. Furthermore, the internal scattering component I2 will be described as not including a component that is scattered and reflected by internal tissue near the surface. The surface reflection component I1 and the internal scattering component I2 change direction as they are reflected or scattered, and some of them reach the photodetector 30 as reflected light pulses. The surface reflection component I1 may include surface information about the subject, such as blood flow information on the face or scalp. The internal scattering component I2 may include internal information about the subject, such as cerebral blood flow information. Therefore, by detecting the surface reflection component I1, surface information about the subject, such as blood flow information on the face or scalp, can be obtained. Furthermore, by detecting the internal scattering component I2, internal information about the subject, such as cerebral blood flow information, can be obtained.

[0053] First light pulse I p1 The first wavelength and the second light pulse I p2The second wavelength may be any wavelength within the wavelength range of 650 nm to 950 nm, for example. This wavelength range is included in the red to near-infrared wavelength range. This wavelength range is known as the "biological window" and is relatively less absorbed by water and skin in living organisms. When detecting a living organism, using light within this wavelength range can improve detection sensitivity. When detecting changes in blood flow in a user's brain, the light used is believed to be absorbed primarily by oxygenated hemoglobin (HbO2) and deoxygenated hemoglobin (Hb). Generally, changes in blood flow cause changes in the concentrations of oxygenated hemoglobin and deoxygenated hemoglobin. This change also changes the degree of light absorption. Therefore, as blood flow changes, the amount of detected light also changes over time.

[0054] Oxygenated hemoglobin and deoxygenated hemoglobin have different wavelength dependences of light absorption. When the wavelength is 650 nm or longer and shorter than 805 nm, the light absorption coefficient of deoxygenated hemoglobin is larger than that of oxygenated hemoglobin. At a wavelength of 805 nm, the light absorption coefficients of deoxygenated hemoglobin and oxygenated hemoglobin are approximately the same. When the wavelength is longer than 805 nm and shorter than 950 nm, the light absorption coefficient of oxygenated hemoglobin is larger than that of deoxygenated hemoglobin.

[0055] Therefore, the first light pulse I p1 The first wavelength of the second light pulse I is set to a value greater than or equal to 650 nm and less than 805 nm. p2 The second wavelength of the first light pulse I can be set to a value between 805 nm and 950 nm. p1 and the second light pulse I p2 By irradiating the measurement part 10 with two light pulses having different wavelengths, the concentrations of oxygenated hemoglobin and deoxygenated hemoglobin contained in the blood inside the measurement part 10 can be determined by processing described below. By irradiating the measurement part 10 with two light pulses having different wavelengths, more detailed internal information about the measurement part 10 can be obtained.

[0056] In this embodiment, the first light source 20a and the second light source 20b may be designed taking into consideration the impact on the user's retina. For example, the first light source 20a and the second light source 20b may be designed to satisfy Class 1 of the laser safety standards established in various countries. When Class 1 is satisfied, the measurement target 10 is irradiated with light of such low illuminance that the accessible emission limit (AEL) is below 1 mW. Note that the first light source 20a and the second light source 20b themselves do not need to satisfy Class 1. For example, the Class 1 laser safety standard may be satisfied by installing a diffuser 70 or an ND filter in front of the first light source 20a and the second light source 20b to diffuse or attenuate the light.

[0057] [1-2. Photodetector 30] The photodetector 30 detects the first light pulse I p1 The photodetector 30 outputs a first signal 56a corresponding to the intensity of at least a part of the component of the first reflected light pulse generated by the second light pulse I being reflected by the measured portion 10. p2 The photodetector 30 outputs a second signal 56b corresponding to the intensity of at least a portion of the component of the second reflected light pulse generated when the first reflected light pulse and the second reflected light pulse are reflected by the measured portion 10. When the photodetector 30 detects at least a portion of the components of the falling periods of the first reflected light pulse and the second reflected light pulse, information about the blood flow inside the measured portion 10 can be obtained. On the other hand, when the photodetector 30 detects at least a portion of the components of the rising periods of the first reflected light pulse and the second reflected light pulse, information about the blood flow on the surface of the measured portion 10 can be obtained. This detection operation of the photodetector 30 is controlled by the control circuit 60. The falling period of the first reflected light pulse or the second reflected light pulse is the period from the start to the end of the decrease in intensity of the first reflected light pulse or the second reflected light pulse. The rising period of the first reflected light pulse or the second reflected light pulse is the period from the start to the end of the increase in intensity of the first reflected light pulse or the second reflected light pulse.

[0058] The measurement apparatus 100 may include two photodetectors 30. One of the two photodetectors 30 may detect at least a portion of the component of the falling period of the first reflected light pulse and output a first signal 56a, and the other may detect at least a portion of the component of the falling period of the second reflected light pulse and output a second signal 56b. That is, the number of photodetectors 30 in this embodiment is not limited to one, and may be two or more.

[0059] The photodetector 30 may include a plurality of photoelectric conversion elements 32 and a plurality of charge accumulation units 34. Specifically, the photodetector 30 may include a plurality of photodetection cells arranged two-dimensionally. Such a photodetector 30 can simultaneously acquire two-dimensional information of the measurement target 10. In this specification, the photodetector cells are also referred to as "pixels." The photodetector 30 may be any imaging element, such as a CCD image sensor or a CMOS image sensor. More generally, the photodetector 30 includes at least one photoelectric conversion element 32 and at least one charge accumulation unit 34.

[0060] The photodetector 30 may include an electronic shutter. The electronic shutter is a circuit that controls the timing of imaging. The electronic shutter controls the period of one signal accumulation, during which received light is converted into an effective electrical signal and accumulated, and the period during which signal accumulation is stopped. The signal accumulation period is also referred to as the "exposure period." In the following description, the width of the exposure period is also referred to as the "shutter width." The time from the end of one exposure period to the start of the next exposure period is also referred to as the "non-exposure period."

[0061] The photodetector 30 uses an electronic shutter to adjust the exposure and non-exposure periods to subnanoseconds, for example, in the range of 30 ps to 1 ns. A TOF (Time of Flight) camera, which is designed to measure distance, detects all light emitted from a light source and reflected by a subject. For this reason, the shutter width of a TOF camera must be larger than the pulse width of the light. In contrast, the measurement device 100 of this embodiment does not need to have the shutter width larger than the pulse width. The shutter width can be set to a value between 1 ns and 30 ns, for example. The measurement device 100 of this embodiment can reduce the shutter width, thereby reducing the influence of dark current contained in the detection signal.

[0062] The photodetector 30 may include a plurality of pixels arranged two-dimensionally on an imaging surface. Each pixel may include a photoelectric conversion element such as a photodiode and one or more charge storage units.

[0063] FIG. 2 illustrates an example of the configuration of the photodetector 30. In FIG. 2, the area enclosed by the dashed-dotted line corresponds to one pixel 201. The pixel 201 includes one photodiode (not shown). While FIG. 2 shows only four pixels arranged in two rows and two columns, many more pixels may be arranged in practice. The pixel 201 includes a first floating diffusion layer 204, a second floating diffusion layer 205, a third floating diffusion layer 206, and a fourth floating diffusion layer 207. Signals accumulated in the first floating diffusion layer 204 to the fourth floating diffusion layer 207 are treated as if they were four pixel signals in a typical CMOS image sensor and output from the photodetector 30. In the example illustrated in FIG. 2, the pixel 201 includes four floating diffusion layers. However, depending on the application, the number of floating diffusion layers may be three or less, or five or more. The number of floating diffusion layers included in the pixel 201 depends on the number of signals to be accumulated simultaneously.

[0064] Each pixel 201 has four signal detection circuits. Each signal detection circuit includes a source follower transistor 309, a row selection transistor 308, and a reset transistor 310. Each transistor is, for example, but not limited to, a field-effect transistor formed on a semiconductor substrate. As shown in the figure, one of the input terminal and output terminal of the source follower transistor 309 is connected to one of the input terminal and output terminal of the row selection transistor 308. The one of the input terminal and output terminal of the source follower transistor 309 is typically the source. The one of the input terminal and output terminal of the row selection transistor 308 is typically the drain. The gate, which is the control terminal of the source follower transistor 309, is connected to the photodiode. Signal charges, such as holes or electrons, generated by the photodiode are accumulated in a floating diffusion layer, which is a charge storage region between the photodiode and the source follower transistor 309.

[0065] Although not shown in FIG. 2 , the first floating diffusion layer 204 to the fourth floating diffusion layer 207 are connected to a photodiode. A switch may be provided between the photodiode and each of the first floating diffusion layer 204 to the fourth floating diffusion layer 207. This switch switches the conduction state between the photodiode and each of the first floating diffusion layer 204 to the fourth floating diffusion layer 207 in response to a signal accumulation pulse from the control circuit 60. This controls the start and stop of accumulation of signal charge in each of the first floating diffusion layer 204 to the fourth floating diffusion layer 207. The electronic shutter in this embodiment has a mechanism for such exposure control.

[0066] The signal charges accumulated in the first floating diffusion layer 204 to the fourth floating diffusion layer 207 are read out when the row selection circuit 302 turns on the gate of the row selection transistor 308. At this time, the current flowing from the source follower power supply 305 to the source follower transistor 309 and the source follower load 306 is amplified according to the signal potential of the first floating diffusion layer 204 to the fourth floating diffusion layer 207. An analog signal resulting from this current read out from the vertical signal line 304 is converted into digital signal data by an analog-to-digital (AD) conversion circuit 307 connected to each column. This digital signal data is read out column by column by the column selection circuit 303 and output from the photodetector 30. After reading out one row, the row selection circuit 302 and the column selection circuit 303 read out the signal charges in the floating diffusion layers of all rows in the same manner. After reading out all the signal charges, the control circuit 60 resets all the floating diffusion layers by turning on the gate of the reset transistor 310. This completes the imaging of one frame. By repeating the same high-speed imaging of frames, the photodetector 30 completes the imaging of a series of frames.

[0067] In this embodiment, an example of a CMOS-type photodetector 30 has been described, but the photodetector 30 may be another type of imaging element. The photodetector 30 may be, for example, a CCD-type, a single-photon counting element, or an amplification-type image sensor such as an EMCCD or ICCD. When a single-pixel sensor is used, the measurement point is one, but high-speed detection is possible.

[0068] [1-3.Electronic circuit 40] The signal processing circuit 50 included in the electronic circuit 40 processes the signal output from the photodetector 30. The signal processing circuit 50 generates and outputs a signal indicating the internal state of the measured portion 10 based on the first signal 56a and the second signal 56b output from the photodetector 30. Here, the first optical pulse I p1 The wavelength of the second light pulse I is equal to or greater than 650 nm and less than 805 nm. p2The wavelength of the signal 56a is between 850 nm and 950 nm. In this case, the amount of change in the concentrations of HbO2 and Hb in the blood from their initial values ​​can be determined by solving a predetermined simultaneous equation using the first signal 56a and the second signal 56b. The simultaneous equation is expressed, for example, by the following equations (1) and (2).

number

number

[0069] ΔHbO2 and ΔHb represent the change in the concentrations of HbO2 and Hb in the blood from their initial values, respectively. 750 OXY and ε 750 deOXY and ε are the molar extinction coefficients of HbO2 and Hb at a wavelength of 750 nm, respectively. 850 OXY and ε 850 deOXY and represent the molar extinction coefficients of HbO2 and Hb at a wavelength of 850 nm, respectively. 750 ini and I 750 now and I represent the detected intensities at the initial time point and the measurement time point at a wavelength of 750 nm, respectively. 850 ini and I 850 now and represent the detected intensity at the initial time point and the measurement time point, respectively, for a wavelength of 850 nm. In this example, the brain is assumed to be inactive at the initial time point and to be active at the time of detection.

[0070] The signal processing circuit 50 can be realized, for example, by a digital signal processor (DSP), a programmable logic device (PLD) such as a field programmable gate array (FPGA), or a combination of a central processing unit (CPU) or a graphics processing unit (GPU) and a computer program.

[0071] The control circuit 60 included in the electronic circuit 40 controls the first adjustment circuit 24a and the second adjustment circuit 24b to generate a light pulse I from the first light-emitting element 22a and the second light-emitting element 22b. p The control circuit 60 controls the first light source 20a and the second light source 20b to emit the light pulse I p The control circuit 60 adjusts the time difference between the emission timing of the first light source 20a and the second light source 20b and the shutter timing of the photodetector 30. In this specification, this time difference is sometimes referred to as a "phase difference." The "emission timing" of the first light source 20a and the second light source 20b is the timing at which the light pulses emitted from the first light source 20a and the second light source 20b start to rise. The "shutter timing" is the timing at which exposure starts. The control circuit 60 may adjust the phase difference by changing the emission timing, or may adjust the phase difference by changing the shutter timing.

[0072] The control circuit 60 may be configured to remove an offset component from the signal detected by each pixel of the photodetector 30. The offset component is a signal component due to ambient light such as sunlight or fluorescent light, or disturbance light. The offset component due to ambient light or disturbance light can be estimated by detecting a signal using the photodetector 30 in a state where the first light source 20a and the second light source 20b are turned off and no light is emitted from the first light source 20a and the second light source 20b.

[0073] The control circuit 60 may be, for example, a combination of a processor and memory, or an integrated circuit such as a microcontroller having a built-in processor and memory. The control circuit 60 adjusts, for example, the emission timing and the shutter timing, and causes the signal processing circuit 50 to process signals, for example, by the processor executing a program recorded in the memory.

[0074] The signal processing circuit 50 and the control circuit 60 may be integrated into a single circuit or may be separate individual circuits. The signal processing circuit 50 may be a component of an external device, such as a server, located in a remote location. In this case, the external device, such as the server, transmits and receives data to and from the light source 20, the photodetector 30, and the control circuit 60 via wireless or wired communication.

[0075] [1-4.Other] The measurement device 100 may be equipped with an imaging optical system that forms a two-dimensional image of the measured part 10 on the light receiving surface of the photodetector 30. The optical axis of the imaging optical system is approximately perpendicular to the light receiving surface of the photodetector 30. The imaging optical system may include a zoom lens. When the position of the zoom lens changes, the magnification ratio of the two-dimensional image of the measured part 10 changes, and the resolution of the two-dimensional image on the photodetector 30 changes. Therefore, even if the distance to the measured part 10 is long, it is possible to enlarge the desired measurement area and observe it in detail.

[0076] The measurement device 100 may include a bandpass filter between the measurement target 10 and the photodetector 30 that passes only light in the wavelength bands emitted by the first light source 20a and the second light source 20b, or light in the vicinity thereof. This reduces the influence of disturbance components such as ambient light. The bandpass filter may be configured, for example, with a multilayer film filter or an absorption filter. Taking into account band shifts due to temperature changes of the first light source 20a and the second light source 20b and oblique incidence on the filter, the bandwidth of the bandpass filter may be approximately 20 nm or more and 100 nm or less.

[0077] The measurement device 100 may include polarizing plates between the measured part 10 and the first light source 20a and the second light source 20b, and between the measured part 10 and the photodetector 30. In this case, the polarization directions of the polarizing plates arranged on the first light source 20a and the second light source 20b side and the polarizing plate arranged on the photodetector 30 side may be in a crossed Nicol relationship. The arrangement of these two polarizing plates can prevent the specular reflection component of the surface reflection component I1 of the measured part 10, i.e., the component whose angle of incidence and reflection angle are the same, from reaching the photodetector 30. In other words, the amount of light of the surface reflection component I1 reaching the photodetector 30 can be reduced.

[0078] [2. Signal detection operation] Next, an example of the operation of detecting a biological signal will be described with reference to Figures 3A to 4. Here, a specific example of a method for detecting the internal scattering component I2 will be described.

[0079] Figure 3A shows the light pulse I p 3B is a diagram showing an example of the time variation of the surface reflection component I1 and the internal scattering component I2 contained in the reflected light pulse when the light pulse I has an impulse waveform. p 1A and 1B are diagrams each showing an example of temporal changes in the surface reflection component I1 and the internal scattering component I2 contained in the reflected light pulse when the reflected light pulse I1 has a rectangular waveform. In each diagram, the diagram on the left shows the light pulse I1 emitted from the first light source 20a and the second light source 20b. p 3A and 3B show examples of the waveform of the surface reflection component I1 and the internal scattering component I2 contained in the reflected light pulse, and the diagram on the right shows examples of the waveform of the surface reflection component I1 and the internal scattering component I2 contained in the reflected light pulse. Although the internal scattering component I2 is actually weak, the intensity of the internal scattering component I2 is exaggerated in the diagrams.

[0080] As shown in Figure 3A, light pulse I p has an impulse waveform, the surface reflection component I1 is p The internal scattering component I2 has an impulse response waveform that is delayed more than the surface reflection component I1 because the internal scattering component I2 corresponds to a combination of light rays that have passed through various paths within the measured part 10.

[0081] As shown in Figure 3B, light pulse I p has a rectangular waveform, the surface reflection component I1 is p The internal scattering component I2 has a waveform similar to that of the optical pulse I1, and the internal scattering component I2 has a waveform in which multiple impulse response waveforms are superimposed. p We confirmed that the amount of internally scattered light component I2 detected by the photodetector 30 can be amplified compared to when the reflected light pulse has an impulse waveform. By initiating the electronic shutter at the falling edge of the reflected light pulse, the internally scattered light component I2 can be effectively detected. The area enclosed by the dashed line on the right side of Figure 3B represents an example of the shutter-open period during which the electronic shutter of the photodetector 30 is open. Compared to using a femtosecond laser with a pulse width on the order of femtoseconds (fs) or a picosecond laser with a pulse width on the order of picoseconds (ps), a rectangular pulse with a pulse width on the order of 1 ns to 10 ns allows the first light source 20a and the second light source 20b to be driven at a lower voltage. This allows for the measurement device 100 to be made smaller and at a lower cost.

[0082] Conventionally, streak cameras have been used to distinguish and detect information such as the light absorption coefficient or light scattering coefficient at different locations in the depth direction inside a living organism. For example, Patent Document 3 discloses an example of such a streak camera. In order to measure with a desired spatial resolution, streak cameras use ultrashort light pulses with a pulse width of femtoseconds or picoseconds. In contrast, this embodiment can distinguish and detect the surface reflection component I1 and the internal scattering component I2. Therefore, the light pulses emitted from the first light source 20a and the second light source 20b do not need to be ultrashort light pulses, and the pulse width can be selected arbitrarily.

[0083] When irradiating a human head with light to obtain information on cerebral blood flow, the amount of light of the internally scattered component I2 can be an extremely small value, about one thousandth to one tens of thousandsth of the amount of light of the surface-reflected component I1. Furthermore, considering the safety standards for lasers, the amount of light that can be irradiated becomes extremely small. Therefore, it becomes very difficult to detect the internally scattered component I2. Even in this case, the first light source 20a and the second light source 20b emit light pulses I with a relatively large pulse width. p By emitting the light beam, it is possible to increase the accumulated amount of the internally scattered component I2, which is accompanied by a time delay. This increases the amount of detected light and improves the signal-to-noise ratio.

[0084] The first light source 20a and the second light source 20b emit light pulses I having a pulse width of, for example, 3 ns or more. p Alternatively, the first light source 20a and the second light source 20b can emit a light pulse I having a pulse width of 5 ns or more, or even 10 ns or more. p On the other hand, if the pulse width is too large, the amount of unused light increases and is wasted, so the first light source 20a and the second light source 20b may emit a light pulse I with a pulse width of, for example, 50 ns or less. p Alternatively, the first light source 20a and the second light source 20b may be controlled to emit a light pulse I having a pulse width of 30 ns or less, or even 20 ns or less. p If the pulse width of the rectangular pulse is several nanoseconds to several tens of nanoseconds, the first light source 20a and the second light source 20b can be driven at a low voltage. This allows the measurement device 100 to be made smaller and at a lower cost.

[0085] The irradiation patterns of the first light source 20a and the second light source 20b may be, for example, a pattern with a uniform intensity distribution within the irradiation area. In this respect, the measurement device 100 of this embodiment differs from, for example, the conventional device disclosed in Patent Document 4. In the device disclosed in Patent Document 4, the detector and the light source are separated by approximately 3 cm, and the surface reflection component is spatially separated from the internal scattering component. This necessitates discrete light irradiation. In contrast, in this embodiment, the surface reflection component I1 can be temporally separated and reduced from the internal scattering component I2. This allows the use of a light source with an irradiation pattern with a uniform intensity distribution. An irradiation pattern with a uniform intensity distribution can be formed by diffusing the light emitted from the first light source 20a and the second light source 20b with a diffuser 70.

[0086] Unlike the conventional technology, this embodiment can detect the internal scattering component I2 even directly below the irradiation point of the measured part 10. By irradiating the measured part 10 with light over a spatially wide range, the measurement resolution can also be improved.

[0087] 4 is a flowchart showing an outline of the operation of the control circuit 60 to control the first light source 20a, the second light source 20b, and the photodetector 30. The control circuit 60 performs the operation generally shown in FIG. 4 to cause the photodetector 30 to detect at least a portion of the components of the falling periods of the first reflected light pulse and the second reflected light pulse.

[0088] In step S101, the control circuit 60 controls the first light source 20a to emit a first light pulse I for a predetermined time. p1At this time, the electronic shutter of the photodetector 30 is in a state where exposure is stopped. The control circuit 60 controls the electronic shutter to stop exposure until the period during which the surface-reflected component I1 of the first reflected light pulse reaches the photodetector 30 is completed. Next, in step S102, the control circuit 60 controls the electronic shutter to start exposure at the timing when the internally scattered component I2 of the first reflected light pulse reaches the photodetector 30, thereby causing the electronic shutter to start accumulating a first signal charge. After a predetermined time has elapsed, in step S103, the control circuit 60 controls the electronic shutter to stop exposure, thereby causing the electronic shutter to stop accumulating the first signal charge. Through steps S102 and S103, a signal charge is accumulated in one of the first to fourth floating diffusion layers 204 to 207 shown in FIG. 2. This signal charge is referred to as a "first signal charge."

[0089] In step S104, the control circuit 60 controls the second light source 20b to emit the second light pulse I for a predetermined time. p2 At this time, the electronic shutter of the photodetector 30 is in a state where exposure is stopped. The control circuit 60 controls the electronic shutter to stop exposure until the period during which the surface-reflected component I1 of the second reflected light pulse reaches the photodetector 30 is completed. Next, in step S105, the control circuit 60 controls the electronic shutter to start exposure at the timing when the internally scattered component I2 of the second reflected light pulse reaches the photodetector 30, thereby causing the electronic shutter to start accumulating a second signal charge. After a predetermined time has elapsed, in step S106, the control circuit 60 controls the electronic shutter to stop exposure, thereby causing the electronic shutter to stop accumulating the second signal charge. Through steps S105 and S106, signal charge is accumulated in another floating diffusion layer among the first floating diffusion layer 204 to the fourth floating diffusion layer 207 shown in FIG. 2. This signal charge is referred to as a "second signal charge."

[0090] Subsequently, in step S107, the control circuit 60 determines whether the number of times the signal accumulation has been executed has reached a predetermined number. If the determination in step S107 is No, steps S101 to S106 are repeated until the determination is Yes.

[0091] If the determination in step S107 is Yes, the process proceeds to step S108. In step S108, the control circuit 60 causes the photodetector 30 to generate and output a first signal 56a and a second signal 56b based on the first signal charge and the second signal charge, respectively.

[0092] In this way, the control circuit 60 controls the first light source 20a to emit the first light pulse I p1 The control circuit 60 executes a first operation of causing the second light source 20b to emit the second light pulse I and causing the photodetector 30 to detect at least a part of the component of the falling edge period of the first reflected light pulse. p2 and executes a second operation in which the control circuit 60 emits the reflected light pulse and causes the photodetector 30 to detect at least a portion of the falling edge of the second reflected light pulse. The control circuit 60 repeats a series of operations including the first operation and the second operation a predetermined number of times. Alternatively, the control circuit 60 may repeat the first operation a predetermined number of times, and then repeat the second operation a predetermined number of times. The order of the first operation and the second operation may also be reversed.

[0093] The operation shown in Figure 4 enables highly sensitive detection of the internally scattered component I2. When irradiating a human head with light to acquire information such as cerebral blood flow, the internal light attenuation rate is extremely large. For example, the emitted light may attenuate to approximately one millionth of the incident light. As a result, a single pulse of light may not be enough to detect the internally scattered component I2. Irradiation under Class 1 laser safety standards requires particularly weak light. Therefore, in the example shown in Figure 4, the first light source 20a and the second light source 20b emit multiple light pulses, and the photodetector 30 also exposes multiple times using an electronic shutter in response. This operation allows the detection signals to be integrated, improving sensitivity. Note that multiple light emission and exposure are not required and are performed as needed.

[0094] In the example of FIG. 4, the internal scattering component I2 is detected, but the surface scattering component I1 may also be detected. Alternatively, both the surface scattering component I1 and the internal scattering component I2 may be detected. In this case, a step of accumulating signal charges based on the surface scattering component I1 of the first reflected light pulse is added between steps S101 and S102, and a step of accumulating signal charges based on the surface scattering component I1 of the second reflected light pulse is added between steps S104 and S105. These signal charges are accumulated in the remaining two floating diffusion layers of the first floating diffusion layer 204 to the fourth floating diffusion layer 207 shown in FIG. 2. By detecting the surface scattering component I1, it is possible to obtain information indicating, for example, facial appearance or the state of scalp blood flow.

[0095] In the above example, two light sources emitting light of different wavelengths are used, but multiple light sources emitting light of the same wavelength may also be used. If the light output of each light source is small, the lack of light output can be compensated for by providing multiple light sources emitting light of the same wavelength. Here, "the same wavelength" does not have to be strictly the same, and the wavelengths may be slightly different.

[0096] [3. Light concentration on the diffuser 70] Next, an example of a configuration for concentrating light on the diffusion plate 70 will be described with reference to FIGS. 5A and 5B.

[0097] FIG. 5A illustrates an example configuration of a diffuser 70, multiple light sources, and an optical system. The measurement device 100 in this example includes two first light sources 20a that emit light at a first wavelength and two second light sources 20b that emit light at a second wavelength. The first wavelength is, for example, within a range of 650 nm to 805 nm, and the second wavelength is, for example, within a range of 805 nm to 950 nm. The optical system includes multiple mirrors 80 and multiple collimator lenses 25. The multiple mirrors 80 concentrate the first emitted light from the first light source 20a and the second emitted light from the second light source 20b onto one region of the diffuser 70 and direct the collected light thereto. The multiple collimator lenses 25 convert the light emitted from the first light source 20a or the second light source 20b into parallel light.

[0098] In the case of non-contact measurement at a distance, as in this embodiment, a high-power light source is required to ensure sufficient intensity of the diffused light. Therefore, in the example of Fig. 5A, multiple first light sources 20a that emit light of the same first wavelength and multiple second light sources 20b that emit light of the same second wavelength are provided.

[0099] A plurality of collimator lenses 25 are provided corresponding to the plurality of light sources 20, respectively. Each collimator lens 25 collimates the light emitted from the corresponding first light source 20a or second light source 20b. A plurality of mirrors 80 are arranged on the optical path between the corresponding first light source 20a or second light source 20b and the diffuser plate 70. These mirrors 80 reflect the light beams collimated by the collimator lenses 25 and change the propagation direction of the light beams. The collimator lenses 25 and the mirrors 80 enable the light beams from the first light source 20a and the second light source 20b to be concentrated on the diffuser plate 70. This allows the distance between the center of the light spot of the first emitted light and the center of the light spot of the second emitted light formed on the diffuser plate 70 to be shorter than the distance between the center of the first light source 20a and the center of the second light source 20b.

[0100] Normally, due to restrictions on the package size of the light source, the spacing between light beams from multiple light sources cannot be made shorter than the spacing between the light sources. In contrast, in this embodiment, an optical system including a collimator lens 25 and a mirror 80 makes it possible to make the spacing between light beams shorter than the spacing between the light sources. For example, the spacing between light beams on the diffuser plate 70 can be made half or less of the spacing between the light sources. By concentrating the light beams in one area on the diffuser plate 70 using the optical system, light can be irradiated from that area toward the measured portion 10.

[0101] In this embodiment, the light beams from the multiple first light sources 20a and the multiple second light sources 20b are emitted from approximately the same point on the diffuser plate 70. Therefore, the incident angles of light incident on the measurement target 10 are approximately the same for all light sources, and the difference in incident angles between the light sources is reduced. Therefore, even if the relative positions of the measurement target 10 and the measurement device 100 change due to body movement or movement of the measurement device 100, changes in the illuminance or reflectance on the measurement target 10 can be prevented from depending on the difference in light intensity or unevenness between the light sources. This facilitates correction, i.e., calibration, of the signal acquired by the photodetector 30. This effect is particularly pronounced when the measurement target 10 has a curved surface. The illuminance on the measurement target 10 increases as the incident angle of light approaches perpendicularity. Unlike the example in FIG. 5A, when light is irradiated onto the measurement target 10 from two distant points on the diffuser plate 70, the light from the point closest to perpendicular incidence has a greater effect on the illuminance on the measurement target 10. Therefore, when the positional relationship between the measured unit 10 and the two points changes due to body movement or movement of the measurement device 100, the angular difference of the light from the two points incident on the measured unit 10 changes. In this case, the contribution of each light component from the two distant points on the diffuser plate 70 changes, causing a complex change in the illuminance on the measured unit 10. In contrast, as shown in FIG. 5A , by concentrating the light beams from the multiple first light sources 20a and the multiple second light sources 20b in one area on the diffuser plate 70, it is possible to reduce the influence of the intensity difference between the light sources on the illuminance fluctuation on the measured unit 10 that occurs due to body movement or movement of the measurement device 100.

[0102] The diffuser 70 has multiple recesses or protrusions on its surface, which randomly diffuse incident light in various directions. Therefore, the diffuser 70 has the function of eliminating uneven illuminance on the measurement target 10. The diffuser 70 can be formed, for example, by a microlens array. In addition to the diffuser 70 of the type that refracts and transmits light internally as shown in the example of FIG. 5A, a diffuser that reflects and diffuses light may also be used. A reflective diffuser also has microscopic irregularities on its reflective surface, which diffuses reflected light in random directions.

[0103] Although it is possible to use a lens instead of the diffuser plate 70 to diffuse the light, a lens projects the illuminance distribution of light from the light source as is, which tends to result in illuminance unevenness remaining on the measured unit 10. Therefore, when multiple light sources are used, if the intensity of one of the multiple light sources decreases, the two-dimensional illuminance distribution on the measured unit 10 itself changes, which can result in a deviation from the calibration data. In contrast, when the diffuser plate 70 is used as in this embodiment, although the overall intensity fluctuates due to a change in the intensity of some of the multiple light sources, a stable two-dimensional illuminance distribution according to the characteristics of the diffuser plate 70 can be obtained. Therefore, it is possible to reduce the deviation from the calibration data regarding the two-dimensional distribution.

[0104] In the optical system of this embodiment, ray bundles from the multiple first light sources 20a and the multiple second light sources 20b are incident on the diffuser plate 70 in a substantially parallel manner. If the ray bundles are not incident on the diffuser plate 70 in a parallel manner, the light emitted from the diffuser plate 70 is diffused, but the illuminance distribution tends to depend on the incident direction. In other words, the illuminance distribution tends to remain depending on the incident angle on the diffuser plate 70. In this embodiment, the collimator lens 25 is provided not only to concentrate the ray bundles but also to make the ray bundles incident on the diffuser plate 70 in a parallel manner. This uniformly reduces the influence of uneven illuminance distributions of the light sources. Furthermore, even if there is a difference in intensity between the emitted light beams of the multiple light sources, the influence of the difference in intensity between the light sources on the illuminance distribution on the surface of the measurement unit 10 is less pronounced than when the ray bundles are not incident on the diffuser plate 70 in a parallel manner. In other words, the light from each light source is diffused from substantially the same area with a substantially identical overlapping distribution. In particular, when the relative intensity difference between the light sources fluctuates over time, the two-dimensional illuminance distribution on the surface of the measurement target 10 is likely to fluctuate unless the angles of incidence on the diffuser 70 are matched. In this case, deviations from the pre-stored calibration data for the illuminance distribution occur. However, when the incident light is collimated, the time fluctuations in the two-dimensional relative distribution of illuminance after it leaves the diffuser 70 are suppressed, and errors in the illuminance distribution correction can be reduced.

[0105] In this embodiment, each collimator lens 25 is disposed immediately after the light-emitting element 22 of each of the plurality of first light sources 20a and the plurality of second light sources 20b. This allows the emitted light to be collimated before being reflected by the mirror 80. This configuration makes it possible to narrow the width of the ray bundle from each light source. This allows the ray bundles from the plurality of light sources to be concentrated at a higher density.

[0106] The shape of the reflective surface of the mirror 80 can be any shape, such as square or rectangular. When high-power semiconductor lasers are used as the multiple first light sources 20a and the multiple second light sources 20b, the radiation direction of the light rays emitted from the light-emitting element 22 tends to expand in a direction perpendicular to the contact surface of the submount. Therefore, the cross-section of the collimated light beam becomes elliptical. Therefore, the vertical and horizontal lengths of the reflective surface of each mirror 80 may be adjusted to match the elliptical shape. By using mirrors 80 with rectangular reflective surfaces whose vertical and horizontal lengths are appropriately adjusted, it is easier to arrange the mirrors 80 closer to each other than when the reflective surface is square, and the light beam can be concentrated more densely on the diffuser 70. Alternatively, instead of using mirrors 80 with flat reflective surfaces, free-form mirrors may be used. By curved reflective surfaces of the mirror 80 in accordance with the radiation angle of the light from the light source, the reflected light beams can be collimated, thereby eliminating the need for the collimator lens 25. Furthermore, by matching the radii of curvature of the curved surfaces to the vertical and horizontal focal lengths of the light emitted from the light source, the light beams can be more precisely collimated.

[0107] One possible method for concentrating light emitted from the plurality of first light sources 20a and the plurality of second light sources 20b to one location on the diffuser plate 70 is to use optical fibers. However, in a configuration in which optical fibers are used to concentrate light, there is a risk that the parallelism of the light incident on the diffuser plate 70 may be significantly reduced. For this reason, in this embodiment, light concentration is achieved by an optical system including a plurality of collimator lenses 25 and a plurality of mirrors 80, rather than by optical fibers.

[0108] The number of each of the first light sources 20a and the second light sources 20b is not limited to two, but may be one, or three or more. The more the number of each of the first light sources 20a and the second light sources 20b is increased, the more the intensity of the emitted light can be increased. Note that only one of the first light source 20a and the second light source 20b may be provided. In this case, multiple light sources that emit light of the same wavelength are provided.

[0109] In this embodiment, the light beams emitted from the first light source 20a and the second light source 20b are concentrated in a relatively narrow area on the diffuser plate 70 by the collimator lens 25 and the mirror 80. This makes it easier for the illuminance distribution on the measurement target 10 to coincide relatively easily between the two wavelengths. FIG. 5B is a diagram showing an example of the illuminance distribution at the position indicated by the dashed line in FIG. 5A. In FIG. 5B, I 20a shows an example of the illuminance distribution of light from the first light source 20a, and I 20b shows an example of the illuminance distribution of light from the second light source 20b. In this embodiment, because light of two wavelengths is emitted from approximately the same point on the diffuser plate 70, the illuminance ratio between the two wavelengths is always constant on the measured unit 10 even if the relative positions of the measured unit 10 and the measuring device 100 change. For example, even when light is incident on the side of the measured unit 10, the angle of incidence of the light beam on the side is approximately equal for the two wavelengths. Therefore, the reflectance is more likely to match for the two wavelengths than when the incident positions of the light beams of the two wavelengths on the diffuser plate 70 are far apart. In this embodiment, when body movement or movement of the measuring device 100 occurs, the detection signals of the two wavelengths fluctuate synchronously. Therefore, signal noise associated with body movement or movement of the measuring device 100 can be stably eliminated.

[0110] Now, with reference to FIG. 5C, the light concentrated on the diffuser plate 70 will be described in more detail.

[0111] 5C is a diagram schematically illustrating an example of two adjacent light spots 151 and 152 among four light spots formed in one region of the diffuser plate 70. The light spots 151 and 152 are each formed by projecting two light beams emitted from two adjacent light sources among the multiple light sources onto the diffuser plate 70. The distance d between these light spots 151 and 152 is shorter than the distance between the two adjacent light sources, and can be, for example, 5 mm or less. In this specification, if the distance d between two adjacent light spots is 5 mm or less, their positions are considered to be substantially the same.

[0112] The steeper the inclination angle of the measurement target 10, the more sensitive the change in illuminance or reflectance on the measurement target 10 due to body movement becomes. That is, in order to perform a measurement with higher accuracy, the steeper the inclination angle of the measurement target 10, the smaller the tolerable difference between the angle of incidence of light incident on the measurement target 10 from the first light source 20a and the angle of incidence of light incident on the measurement target 10 from the second light source 20b becomes. Since the difference in the angle of incidence between the two light sources depends on the distance d between the light spots 151 and 152 on the diffuser, it is desirable to set d appropriately.

[0113] Figure 5D is a graph showing the results of a simulation of the relationship between the tilt angle of a human forehead and the tolerance M of the distance d between two light spots of different wavelengths on a diffuser plate when the human forehead is used as the measurement target. The tolerance M represents the distance d between the light spots at which the difference in the rate of change of the detection signal caused by the first emitted light and the second emitted light can be suppressed to 0.5% before and after a human rotates 10° horizontally. In other words, if the distance d between the two light spots is smaller than the tolerance M, the difference in the rate of change of the detection signal can be suppressed to 0.5% or less. This makes the signal detection error caused by the difference in the rate of change of the detection signal smaller than the fluctuation of the cerebral blood flow detection signal, enabling more accurate detection of the cerebral blood flow signal. Note that the graph in Figure 5D shows the results of a simulation in which the tolerance M was calculated assuming that the detection signal attenuates as cos Θ, depending on the incident angle Θ when the emitted light enters the measurement target.

[0114] Based on MRI structural images, the average forehead tilt angle for Westerners is approximately 37° near area 46 of the working memory region of the frontal lobe. Figure 5D shows that when the forehead tilt angle is 37°, the tolerance M is 5 mm. Therefore, if the distance d between the light spots is 5 mm or less, even if a person moves, the error caused by the difference in the rate of change of the detection signal between the two light sources before and after the movement can be prevented from exceeding the fluctuation of the cerebral blood flow detection signal. This enables highly accurate cerebral blood flow measurement.

[0115] The distance d between these light spots may be 2 mm or less. The shapes of the light spots 151 and 152 are typically elliptical. The widths of the light spots 151 and 152 in the major axis direction are w1 and w2, respectively. In the illustrated example, the distance d between the two light spots 151 and 152 is shorter than w1 and w2. The two light spots 151 and 152 have an overlapping portion 153. As in this example, the optical system can be configured so that the emitted light from multiple light sources partially overlaps and enters the diffuser plate 70. With such a configuration, diffused light from multiple emitted light beams can be irradiated from substantially the same point on the diffuser plate 70.

[0116] The configurations of the first light source 20a, the second light source 20b, the optical system, and the diffuser plate 70 are not limited to the above configurations and can be modified in various ways. Other configuration examples will be described below.

[0117] FIG. 6 illustrates another exemplary configuration of the light source 20, the optical system, and the diffuser 70. The optical system in this example includes multiple collimator lenses 25, multiple first mirrors 80, and a second mirror 81. In this example, multiple light sources 20 are aligned in one direction. Multiple mirrors 80 are arranged corresponding to the multiple light sources 20, respectively. The second mirror 81 further reflects the light beams reflected by each first mirror 80 and causes them to enter the diffuser 70. The distance between the mirror 80 and the light source 20 varies for each light source 20. This prevents interference between the paths of the light beams from multiple light sources 20, enables the light beams from multiple light sources 20 to be aggregated, and enhances illuminance. Furthermore, the second mirror 81 reflects multiple light beams together, thereby reducing the number of components in the optical system and lowering costs.

[0118] In the above embodiment, an optical system including multiple mirrors 80 is provided to collect light from multiple light sources 20 and make it incident on the diffuser plate 70. However, light collection may be achieved without using such an optical system. For example, a light emitting device in which multiple light sources are collected in a single package may be used. Even when such a light emitting device is used, the light emitted from the multiple light sources can be collected and made incident on one location on the diffuser plate 70.

[0119] FIG. 7 illustrates an example of a light-emitting device 120 in which multiple light-emitting elements 22 are aggregated and arranged in a single package. In this example, the multiple light-emitting elements 22 are closely aligned in one direction. Each light-emitting element 22 may be, for example, a semiconductor laser element. These light-emitting elements 22 are mounted on the same submount and aggregated in a single package. No mirror is provided to change the path of light emitted from each light-emitting element 22. This configuration allows the light-emitting points in the package to be close to each other. Even in this configuration, multiple collimator lenses 25 are disposed between the diffuser plate 70 and the multiple light-emitting elements 22 to cause parallel light to enter the diffuser plate 70. The collimator lenses 25 are disposed corresponding to each light-emitting element 22. This allows the light emitted from each light-emitting element 22 to be collimated, thereby reducing the cross-sectional area of ​​the ray bundle.

[0120] The submount is, for example, a member that supports the first light-emitting element 22a and the second light-emitting element 22b. By supporting them with the same member, the first light-emitting element 22a and the second light-emitting element 22b can be placed close to each other. This allows the optical axes of the first light source 20a and the second light source 20b to be brought closer to each other, and the distance between the light spot 151 of the first emitted light and the light spot 152 of the second emitted light on the diffuser plate 70 can be reduced. Therefore, the first emitted light and the second emitted light are emitted from approximately the same point on the diffuser plate 70, which has the effect of suppressing the difference in the angle of incidence of the light incident on the measured unit 10.

[0121] The submount may also be a heat-dissipating material. For example, if a semiconductor laser is used as the light-emitting element 22, heat may cause a deterioration in the light-emitting characteristics of the semiconductor laser. The heat-dissipating submount can prevent the heat-induced deterioration of the light-emitting characteristics of the semiconductor laser. The submount may be a material with good thermal conductivity, such as a ceramic material such as AlN (aluminum nitride) or Al2O3 (aluminum oxide), a Cu-AlN-Cu (copper / aluminum nitride / copper) multilayer structure material in which copper is laminated on aluminum nitride, a metal composite material such as Cu-W (copper / tungsten), or Cu-Diamond (copper / diamond). In this case, heat generated by the first light source 20a and the second light source 20b can be more efficiently dissipated. The submount is not limited to the above examples, and may also be a flat plate, a heat-sealing material, or a surface-mount substrate.

[0122] The first light-emitting element 22a and the second light-emitting element 22b may be formed on a single laser chip or a single semiconductor crystal, which allows the two light-emitting elements to be closer to each other and more significantly reduces the difference in the angle of incidence of light incident on the measurement portion 10.

[0123] However, if there are too many light-emitting points, there is a risk that the characteristics of the falling portion of the pulse waveform will deteriorate if a time difference occurs between the light-emitting pulses from the multiple light-emitting elements 22. For this reason, the output power per light-emitting element 22 may be maximized and the number of light-emitting elements 22 may be minimized. For example, the number of light-emitting elements 22 in one light source package may be 10 or less, or may be 5 or less.

[0124] FIG. 8 illustrates yet another exemplary configuration of the light-emitting device 120. The measurement device 100 in this example includes four light-emitting device 120 packages mounted on a substrate 26. The four light-emitting devices 120 are arranged in a matrix. Two light-emitting devices 120 are aligned in each of the X and Y directions shown in FIG. 8. Each light-emitting device 120 may be, for example, a semiconductor laser package. Each light-emitting device 120 includes a first light-emitting element 22a and a second light-emitting element 22b, a submount 23 supporting the first light-emitting element 22a and the second light-emitting element 22b, and a housing 27 accommodating them. The first light-emitting element 22a emits light of a first wavelength, and the second light-emitting element 22b emits light of a second wavelength. The mounting of adjacent light-emitting devices 120 on the substrate 26 is inverted by 180 degrees in both the X and Y directions. With this arrangement, the difference in illuminance distribution of light emitted from the first light-emitting element 22a and the second light-emitting element 22b between adjacent light-emitting devices 120 is canceled out, making it easier for the illuminance distribution to match between the two wavelengths at the measured portion 10. Note that the number of light-emitting devices 120 is not limited to four and may be any number.

[0125] Each first light-emitting element 22a is electrically connected to a first adjustment circuit 24a that adjusts a first current and emits light with an intensity corresponding to the injected first current. Similarly, each second light-emitting element 22b is electrically connected to a second adjustment circuit 24b that adjusts a second current and emits light with an intensity corresponding to the injected second current. By providing the first adjustment circuit 24a and the second adjustment circuit 24b in this manner, the first light-emitting element 22a and the second light-emitting element 22b on the same submount can be appropriately driven according to the measurement content. Specifically, by alternately injecting a first current from the first adjustment circuit 24a and injecting a second current from the second adjustment circuit 24b, it is possible to alternately emit light from the first light-emitting element 22a and the second light-emitting element 22b on the same submount. When simultaneously emitting light beams with different wavelengths and performing a measurement, the light beams with different wavelengths are detected by the photodetector 30 as a sum value, which presents a problem in that it is difficult to distinguish between measurement results corresponding to each wavelength. By performing the above-mentioned control using the first adjustment circuit and the second adjustment circuit and alternately emitting the first emitted light and the second emitted light, it is possible to achieve the effect of making it possible to obtain the measurement results of each of the two wavelength light components separately in a time-division manner without mixing them.

[0126] As described above, by controlling the first light-emitting element 22a and the second light-emitting element 22b on the same submount using the first adjustment circuit 24a and the second adjustment circuit 24b, it is possible to more significantly suppress the difference in the angle of incidence of light incident on the measured portion 10, and further to obtain the measurement results of each of the light components of the two wavelengths without mixing them.

[0127] [4. Signal Calibration] Next, an example of a method for calibrating the signal detected by the photodetector 30 will be described with reference to FIGS.

[0128] In this embodiment, calibration data defining the relationship between the angle of incidence of light on the measurement target 10 and the reflectance is generated prior to measurement. During measurement, the signal processing circuit 50 corrects the signal acquired from the photodetector 30 by referring to the previously generated calibration data. This allows stable biosignals to be acquired even when body movement or movement of the measurement device 100 occurs. To calibrate the signal, the measurement device 100 has a function for performing distance measurement using TOF. Distance measurement is performed, for example, by the signal processing circuit 50 based on the detection results of light emitted from either the first light source 20a or the second light source 20b. The TOF method may be indirect TOF or direct TOF.

[0129] FIG. 9 is a diagram schematically showing how light diffused by a diffuser plate 70 enters the measured portion 10. The arrows in the diagram represent the distribution of surface normal vectors in the measured portion 10. In the example of FIG. 9, three light sources 20 are aligned in one direction, and the light emitted from the three light sources 20 is concentrated by multiple mirrors 80 and enters the diffuser plate 70. A photodetector 30 and a lens 90 are disposed near the diffuser plate 70. The lens 90 collects the light from the measured portion 10 and forms an image on the light-receiving surface of the photodetector 30.

[0130] FIG. 10 is a graph showing the incidence angle dependency of the diffuse reflectance of the measurement portion 10 in the configuration of FIG. 9. In this embodiment, calibration data showing the incidence angle characteristics of the diffuse reflectance as shown in FIG. 10 is generated in advance and recorded on a recording medium. During measurement, the signal is corrected using the pre-recorded calibration data. The diffuse reflectance exhibits different values ​​depending on the surface roughness of the measurement portion 10. Therefore, data showing the incidence angle dependency of the diffuse reflectance may be obtained as calibration data for each user.

[0131] The calibration data in this embodiment may be table or function data that defines the relationship between the incident angle of a light beam on the measurement target 10 and the diffuse reflectance corresponding to that incident angle. The incident angle can be determined, for example, using TOF ranging. The measurement device 100 can determine the distance distribution of the measurement target 10 using TOF ranging with optical pulses and convert the distance distribution into a three-dimensional coordinate distribution. The surface normal vector of each measurement point can then be calculated from the three-dimensional coordinate distribution. The incident angle of the light beam incident on each measurement point can be determined from the calculated surface normal vector, the three-dimensional coordinates of the light beam's emission point on the diffuser 70, and the three-dimensional coordinates of each measurement point on the measurement target 10. In the measurement device 100 of this embodiment, light from multiple light sources 20 is concentrated at one point on the diffuser 70, and the light is incident on the measurement target 10 from that point. Therefore, the incident angle can be uniquely determined for each measurement point on the measurement target 10. Therefore, it is possible to obtain data showing the incidence angle dependency of diffuse reflectance from a single image of the measured portion 10. This allows calibration data to be obtained in a short time without imposing a burden on the user. By plotting the relationship between this incidence angle and the detection signal value at each measurement point and interpolating the values ​​between the plotted points, a table or function showing the incidence angle dependency of diffuse reflectance can be obtained.

[0132] TOF ranging and signal detection can be performed by the same measurement device 100. This makes it possible to suppress pixel position shift, parallax, and occlusion, and to accurately calculate the angle of incidence.

[0133] 9, the measurement device 100 includes a lens 90 disposed opposite the photodetector 30. The lens 90 forms an image of the light reflected from the measured portion 10 on the light receiving surface of the photodetector 30. This allows the photodetector 30 to acquire information about the two-dimensional intensity distribution of the light reflected from the measured portion 10.

[0134] 9, the lens 90 can be disposed close to the diffuser plate 70. Such an arrangement reduces the difference between the angle of the light ray incident on the measurement target 10 from the diffuser plate 70 and the angle of the light ray emerging from the measurement target 10 toward the lens 90, making it possible to stably acquire data in a table showing the dependency of diffuse reflectance on the angle of incidence.

[0135] The distance between the center of the concentrated light beams on the diffuser plate 70 and the center of the lens 90 can be set to, for example, 30 mm or less, in one example 20 mm or less, and in yet another example 10 mm or less.

[0136] The measuring device 100 may emit continuous wave (CW) light instead of pulsed light to acquire information on the measured part 10. By using CW waves, the measuring device 100 can also be used to acquire other vital information such as oxygen saturation, pulse rate, or blood pressure. In this case, too, concentrating multiple beams of light on the diffuser 70 is effective for stable measurement that eliminates body movement components.

[0137] Next, an example of a method for generating calibration data and an example of a method for correcting a signal using the calibration data will be described with reference to FIGS.

[0138] 11 is a flowchart showing an example of a method for generating calibration data. In this example, a calibration plate having optical characteristics similar to those of the measured part 10 of the measurement subject is prepared in advance. As the calibration data, an illuminance correction table is created that associates the illuminance or reflectance of each measurement point on the measured part 10 with the angle of incidence.

[0139] First, in step S201, the calibration plate is moved along the optical axis and positioned at a predetermined position. This movement can be performed automatically or manually. In step S202, the light source 20 of the measurement device 100 irradiates the calibration plate with light, and the illuminance distribution or reflectance distribution on the plate is measured by the photodetector 30. Next, in step S203, the signal processing circuit 50 calculates the distance from the photodetector 303 to each measurement point on the calibration plate, the three-dimensional coordinates of each measurement point, and the angle of incidence at each measurement point. The three-dimensional coordinates of each measurement point can be calculated based on the distance to the measurement point measured by TOF ranging and the position of the measurement point in the image. The angle of incidence is calculated from the three-dimensional coordinates of the measurement point and the three-dimensional coordinates of the light emission point on the diffuser 70. In step S204, the control circuit 60 determines whether a predetermined number of measurements have been completed. If the predetermined number of measurements has not been completed, the process returns to step S201, and the calibration plate is moved a predetermined distance in the optical axis direction. Steps S201 to S204 are repeated until it is determined in step S204 that the predetermined number of measurements has been completed. Once the predetermined number of measurements has been completed, the process proceeds to step S205. In step S205, the signal processing circuit 50 creates an illuminance correction table that associates the reflectance of each measurement point measured in step S202 with the angle of incidence of each measurement point calculated in step S203. The illuminance correction table can be generated under multiple conditions with different distances between the calibration plate and the measurement device 100.

[0140] If the measurement device 100 includes a plurality of light sources that emit light of different wavelengths, the operation of FIG. 11 can be performed for each light source to create an illuminance correction table.

[0141] By using this method, calibration data for correcting the detection signal output from the photodetector 30 during measurement can be effectively generated.

[0142] Instead of using the calibration plate, the measurement target portion 10 of the subject may be used to generate calibration data in the same manner as above.

[0143] As described above, the calibration data generating method of this embodiment includes the steps of: emitting light from a light source toward a measurement object or a calibration plate having optical properties similar to those of the object to measure the reflectance of one or more measurement points on the object or plate; and estimating the angle of incidence of the light at the one or more measurement points, the steps being performed multiple times while changing the distance between the object or plate and the light source; and generating calibration data that defines the relationship between the angle of incidence of the light and the reflectance for the one or more measurement points. By using such a method, calibration data can be generated efficiently.

[0144] FIG. 12 is a flowchart showing an example of a signal correction method using calibration data executed during measurement. In this example, first, in step S301, light is irradiated from the light source 20 onto the measured unit 10, and the reflected light is detected by the photodetector 30. In the following step S302, the signal processing circuit 50 calculates the distance from the photodetector 30 to each measurement point on the measured unit 10, the three-dimensional coordinates of each measurement point, and the angle of incidence at each measurement point. Next, in step S303, the signal processing circuit 50 refers to a pre-generated illuminance correction table to determine a signal correction value based on the three-dimensional coordinates and the angle of incidence, and corrects the value of the signal generated by the photodetector 30. The correction is performed, for example, by multiplying the signal value by the reciprocal of the reflectance shown in FIG. 10. The signal processing circuit 50 generates information indicating the internal state of the object based on the corrected signal.

[0145] As described above, the signal processing circuit 50 in this embodiment estimates the distance to one or more measurement points on the object based on the detection results from the photodetector 30, estimates the position of one or more measurement points based on the estimated distance, estimates the angle of incidence of the emitted light to one or more measurement points based on the estimated position, corrects a signal indicating the detection result of the reflected light based on the estimated angle of incidence and pre-generated calibration data that defines the relationship between the angle of incidence and reflectance, and generates information about the object based on the corrected signal. This operation allows the signal to be appropriately corrected even if the measured unit 10 or the measuring device 100 moves.

[0146] (Variation) FIG. 13 is a diagram showing another example configuration of the measurement device 100. The measurement device 100 in this example includes a light-emitting device 120a, a light-emitting device 120b, a diffuser 70, multiple mirrors 80, and multiple collimator lenses 25. The light-emitting device 120a and the light-emitting device 120b may be, for example, semiconductor laser packages. The light-emitting device 120a includes a first light-emitting element 22a and a second light-emitting element 22b, and a submount 23 that supports the first light-emitting element 22a and the second light-emitting element 22b. The light-emitting device 120b includes a third light-emitting element 22c and a fourth light-emitting element 22d, and a submount 23 that supports the third light-emitting element 22c and the fourth light-emitting element 22d. The first emitted light emitted from the first light-emitting element 22a and the third emitted light emitted from the third light-emitting element 22c have, for example, a first wavelength. The second output light emitted from the second light-emitting element 22b and the fourth output light emitted from the fourth light-emitting element 22d have, for example, a second wavelength. The multiple mirrors 80 collect the first output light, the second output light, and the third output light and the fourth output light and direct them to one region of the diffuser plate 70. When any two light spots are selected from a group consisting of light spots of the first output light, the second output light, the third output light, and the fourth output light, the distance between the selected two light spots is shorter than the distance between the light-emitting elements corresponding to the selected light spots. For example, the distance between the light spot of the first output light and the light spot of the third output light formed in one region of the diffuser plate 70 is shorter than the distance between the first light-emitting element and the third light-emitting element. The distance between the light spot of the first output light and the light spot of the fourth output light formed in one region of the diffuser plate 70 is shorter than the distance between the first light-emitting element and the fourth light-emitting element. The distance between the light spot of the second output light and the light spot of the third output light formed in one region of the diffuser plate 70 is shorter than the distance between the second light-emitting element and the third light-emitting element. The distance between the light spot of the second output light and the light spot of the fourth output light formed in one region of the diffuser plate 70 is shorter than the distance between the second light-emitting element and the fourth light-emitting element.

[0147] As described above, in this configuration example, a plurality of light-emitting devices 120, each including a plurality of light-emitting elements, are mounted on the measurement device 100. This increases the amount of light irradiated onto the measurement target 10, thereby improving the signal-to-noise ratio of the signal observed by the photodetector 30. Furthermore, by using a plurality of mirrors to concentrate and direct the light from the light-emitting devices 120a and 120b onto one area of ​​the diffuser 70, it is possible to prevent errors resulting from differences in the rate of change of the detection signals between the two light sources, the light-emitting devices 120a and 120b, before and after body movement from exceeding the amount of fluctuation in the detection signal of cerebral blood flow.

[0148] The number of mirrors does not need to be multiple. For example, no mirror may be disposed on the optical paths of the first and second emitted lights, and a mirror may be disposed on the optical paths of the third and fourth emitted lights, so that the emitted lights are concentrated and incident on one region of the diffuser plate 70. Furthermore, the light emitting devices 120a and 120b may be housed in a single housing.

[0149] In the above embodiments, examples have been described in which information about blood flow in a living organism is generated. The technology of the present disclosure is not limited to biometric measurements and can be used to measure the internal state of various substances. For example, the technology of the present disclosure can be applied to measuring the state of fruits, vegetables, meat, fish, or cooked foods. More specifically, information such as the degree of internal decay of fresh food, processed food, or cooked foods, or the degree of internal baking or heating of food (e.g., cake sponge batter or frozen food) in a microwave oven, can be generated. Furthermore, by using the trunk, stem, or leaves of a plant as the target, information such as the state of internal growth can be generated. In these application examples, light of two or more wavelengths may be used, rather than just one wavelength. When light of multiple wavelengths is used, wavelengths with different absorption coefficients are selected. One of the wavelengths can be used as a reference wavelength, and the internal state can be estimated based on the relative light absorption of the other wavelengths. [Industrial Applicability]

[0150] The measurement device disclosed herein can stably detect information indicating the internal state of an object even when the object or the measurement device moves. Therefore, the technology disclosed herein is useful in a wide range of fields, such as non-contact cerebral blood flow measurement, vital signs sensing, authentication, and food inspection. [Explanation of symbols]

[0151] 10. Measured part 20a 1st light source 20b 2nd light source 22a First light-emitting element 22b Second light-emitting element 23 Submount 24a 1st adjustment circuit 24b 2nd adjustment circuit 25 Collimator lens 26 PCB 27 Case 30 Photodetector 32 Photoelectric conversion element 34 Charge storage section 40 Electronic circuits 50 Signal processing circuit 60 Control circuit 70 Diffuser 80 Mirror 90 Lens 100 Measuring Equipment 120 Light-emitting device 201 pixels 204 First floating diffusion layer 205 Second floating diffusion layer 206 Third floating diffusion layer 207 4th floating diffusion layer 302 Row selection circuit 303 Column Selection Circuit 304 vertical signal line 305 Source Follower Power Supply 306 Source Follower Load 307 Analog-to-Digital Conversion Circuit 308 Row select transistor 309 Source Follower Transistor 310 Reset transistor

Claims

1. a first light source that emits a first emission light; a second light source that emits a second emission light at a timing different from a timing at which the first light source emits the first emission light; A diffusion plate; a mirror that changes a propagation direction of at least one selected from the group consisting of the first outgoing light and the second outgoing light, thereby concentrating the first outgoing light and the second outgoing light and making them incident on one region of the diffusion plate; a photodetector that detects first reflected light generated from an object due to the first outgoing light diffused by the diffuser plate, and detects second reflected light generated from the object due to the second outgoing light diffused by the diffuser plate at a timing different from the detection timing of the first reflected light; a processing circuit that generates and outputs information about the object based on a detection result of the first reflected light and the second reflected light by the photodetector; Equipped with a distance between a light spot of the first emitted light formed in the one region of the diffuser plate and a light spot of the second emitted light formed in the one region of the diffuser plate is shorter than a distance between the first light source and the second light source; Measuring equipment.

2. a first light emitting device including: a first light source that emits a first emitted light; a second light source that is adjacent to the first light source and emits a second emitted light at a timing different from a timing at which the first light source emits the first emitted light; and a first submount that supports the first light source and the second light source; a diffusion plate disposed on an optical path of the first emitted light and the second emitted light; a photodetector that detects first reflected light generated from an object due to the first outgoing light diffused by the diffuser plate, and detects second reflected light generated from the object due to the second outgoing light diffused by the diffuser plate at a timing different from the detection timing of the first reflected light; a processing circuit that generates and outputs information about the object based on a detection result of the first reflected light and the second reflected light by the photodetector; Equipped with Measuring equipment.

3. The photodetector is an image sensor that outputs an image signal as the detection result, The processing circuitry estimating a distance from the photodetector to at least one measurement point on the object based on the image signal; correcting the image signal based on information indicating a position corresponding to the at least one measurement point in the image signal and the distance; The measuring device according to claim 1 or 2.

4. a distance between a center of a light spot of the first emitted light and a center of a light spot of the second emitted light on the diffusion plate is 5 mm or less; The measuring device according to any one of claims 1 to 3.

5. the first output light and the second output light are incident on the diffusion plate while at least partially overlapping each other; The measuring device according to any one of claims 1 to 4.

6. a first collimator lens disposed on an optical path between the first light source and the diffuser; a second collimator lens disposed on an optical path between the second light source and the diffuser; Further provided with The measuring device according to any one of claims 1 to 5.

7. an incident angle of the first output light incident on the diffuser plate is the same as an incident angle of the second output light incident on the diffuser plate; The measuring device according to any one of claims 1 to 6.

8. The diffusion plate has a plurality of recesses or a plurality of protrusions on its surface. The measuring device according to any one of claims 1 to 7.

9. the wavelength of the first emitted light is equal to or greater than 650 nm and less than 805 nm; The wavelength of the second emitted light is not less than 805 nm and not more than 950 nm. The measuring device according to any one of claims 1 to 8.

10. The wavelength of the first emitted light is the same as the wavelength of the second emitted light. The measuring device according to any one of claims 1 to 8.

11. a control circuit that controls the first light source, the second light source, and the photodetector; the first reflected light and the second reflected light are pulsed lights, The control circuit causing the first light source to emit the first emitted light; causing the second light source to emit the second emitted light; causing the photodetector to detect a first component of the first reflected light in a first falling period, which is a period from the start to the end of a decrease in intensity of the first reflected light; causing the photodetector to detect a second component of the second reflected light during a second falling period, which is a period from the start to the end of the decrease in intensity of the second reflected light; the processing circuit generates the information based on an intensity of the first component of the first reflected light and an intensity of the second component of the second reflected light detected by the photodetector. The measuring device according to any one of claims 1 to 10.

12. further comprising a third light source that emits a third emission light; the photodetector further detects third reflected light generated from the object due to the third emitted light diffused by the diffuser plate; the processing circuit generates and outputs the information based on detection results of the first reflected light, the second reflected light, and the third reflected light by the photodetector. The measuring device according to any one of claims 1 to 11.

13. the first light-emitting device, a third light source that emits a third emission light; a fourth light source that emits a fourth output light; a second submount supporting the third light source and the fourth light source; a housing that houses the first light source, the second light source, the third light source, and the fourth light source; Furthermore, the photodetector further detects third reflected light generated from the object due to the third outgoing light diffused by the diffuser plate, and fourth reflected light generated from the object due to the fourth outgoing light diffused by the diffuser plate; the processing circuit generates and outputs the information based on detection results of the first reflected light, the second reflected light, the third reflected light, and the fourth reflected light by the photodetector. The measurement device according to claim 2 .

14. The processing circuitry estimating a distance from the photodetector to at least one measurement point on the object based on the detection result by the photodetector; estimating a position of the at least one measurement point based on the distance from the light detector to the at least one measurement point on the object estimated by the processing circuitry; estimating a first angle of incidence of the first output light at the at least one measurement point and a second angle of incidence of the second output light at the at least one measurement point based on the position estimated by the processing circuit; correcting a signal indicating the detection result based on the first angle of incidence estimated by the processing circuit, the second angle of incidence estimated by the processing circuit, and calibration data generated in advance that defines a relationship between an angle of incidence of light on the object and a reflectance of the light on the object; generating the information based on the signal corrected by the processing circuit; The measuring device according to any one of claims 1 to 13.

15. the object is a living body, The information includes at least one piece of information selected from the group consisting of blood flow, oxygen saturation, pulse rate, and blood pressure. The measuring device according to any one of claims 1 to 14.

16. the object is a living body, The information includes information indicating cerebral blood flow of the living body. The measuring device according to any one of claims 1 to 14.

17. a second light emitting device including a third light source that emits a third output light, a fourth light source that is adjacent to the third light source and emits a fourth output light, and a second submount that supports the third light source and the fourth light source; a mirror that changes a propagation direction of at least one light selected from the group consisting of light emitted from the first light-emitting device and light emitted from the second light-emitting device, thereby concentrating the first emitted light, the second emitted light, the third emitted light, and the fourth emitted light and making them incident on one region of the diffusion plate, The measurement device according to claim 2 .

18. A first light source that emits a first emitted light; a second light source that emits a second emitted light; A diffusion plate; a mirror that changes a propagation direction of at least one selected from the group consisting of the first outgoing light and the second outgoing light, thereby concentrating the first outgoing light and the second outgoing light and making them incident on one region of the diffusion plate; a photodetector that detects first reflected light generated from an object due to the first outgoing light diffused by the diffuser plate and second reflected light generated from the object due to the second outgoing light diffused by the diffuser plate; a processing circuit that generates and outputs information about the object based on a detection result of the first reflected light and the second reflected light by the photodetector; Equipped with a distance between a light spot of the first emitted light formed in the one region of the diffusion plate and a light spot of the second emitted light formed in the one region of the diffusion plate is shorter than a distance between the first light source and the second light source; The wavelength of the first emitted light is the same as the wavelength of the second emitted light. Measuring equipment.

19. A first light emitting device including a first light source that emits a first emitted light, a second light source adjacent to the first light source that emits a second emitted light, and a first submount that supports the first light source and the second light source; a diffusion plate disposed on an optical path of the first emitted light and the second emitted light; a photodetector that detects first reflected light generated from an object due to the first outgoing light diffused by the diffuser plate and second reflected light generated from the object due to the second outgoing light diffused by the diffuser plate; a processing circuit that generates and outputs information about the object based on a detection result of the first reflected light and the second reflected light by the photodetector; Equipped with The wavelength of the first emitted light is the same as the wavelength of the second emitted light. Measuring equipment.

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