JP2019045289A - Measurement device - Google Patents

Abstract

To provide a measurement device capable of obtaining information inside a scattering body by emitting light with a coherence length suitable for organism measurement.SOLUTION: The measurement device comprises: a light-emitting device 20 configured to emit light with a coherence length of 5 mm or more and 400 mm or less; and a light detection device for detecting light which is emitted from the light-emitting device and reflected by an object 4.SELECTED DRAWING: Figure 5

Description

  The present disclosure relates to a measurement device.

  Conventionally, as a method of obtaining information inside a scatterer such as a living body, a method of emitting coherent light to the scatterer and analyzing the returned scattered light is known (for example, Patent Documents 1 to 3).

US Pat. No. 5,807,264 Special table 2010-532699 gazette International Publication No. 2016/135818

Tokai University Press, Principles of Optics, p482 M. Born and others 14th Medical Near-Infrared Spectroscopy Study Group, p139-144, Prospects for Near-Infrared Biospectroscopy-1 Possibility of Wavelength Range of 1 μm, Ichiro Nishimura Ichiro Yamada and Guillaume Lopez, "Wearable sensing systems for healthcare monitoring", VLSI Technology (VLSIT), 2012 Symposium on. IEEE, 2012.

  The present disclosure provides a measurement device that emits light having a coherence length suitable for biological measurement and acquires information inside the scatterer.

  A measurement device according to one embodiment of the present disclosure detects a light emitting device that emits light having a coherence length of 5 mm or more and 400 mm or less, and scattered light that is emitted from the light emitting device and scattered inside the object. A photodetector.

  According to one aspect of the present disclosure, it is possible to obtain information inside the scatterer by emitting light having a coherence length suitable for biological measurement.

FIG. 1A is a diagram schematically illustrating a light detection system 100 according to a study example. FIG. 1B is a diagram illustrating a state of the scattered light 5 incident on one opening 9 a included in the photodetector 13. FIG. 2A is a cross-sectional view of the photodetector 13 in a plane along the direction in which light enters. FIG. 2B is a plan view of the photodetector 13 as viewed from the light incident side. FIG. 3 is a diagram illustrating a signal processing method of the photodetector 13. FIG. 4A is a cross-sectional view illustrating a positional relationship between incident light at four openings and three light receiving elements below the incident light in the study example. FIG. 4B is a diagram illustrating an analysis result regarding the relationship between the phase random coefficient a of the incident light and the detection signal. FIG. 5 is a diagram schematically illustrating a configuration example of the light emitting device 20 having a variable coherence length. FIG. 6 is a diagram schematically showing a general relationship between laser light output and drive current. FIG. 7 is a diagram schematically showing a change over time of the drive current input to the laser light source 2. FIG. 8 is a diagram illustrating an example of a measurement result of a change in the coherence length σ ₀ due to the drive current illustrated in FIG. FIG. 9 is a diagram illustrating a measurement result of the relationship between the coherence length and the variation in the phase difference in the case where the absorber exists inside the scatterer. FIG. 10 is a diagram schematically illustrating another configuration example of the light emitting device 20 having a variable coherence length. FIG. 11 is a diagram schematically illustrating still another configuration example of the light emitting device 20 having a variable coherence length. FIG. 12 is a diagram schematically illustrating a configuration example of the blood pressure measurement device 1000 according to the second embodiment and a blood pressure measurement method using the blood pressure measurement device 1000. 13 is a cross-sectional view of the configuration example of FIG. FIG. 14 is a diagram illustrating a measurement result of a variation in phase difference due to a pulse wave. FIG. 15 is a diagram schematically showing variations in phase difference due to pulse waves at position A (upper diagram) and position B (lower diagram). FIG. 16 is a block diagram illustrating a configuration example of the blood pressure measurement device 1000. FIG. 17 is a flowchart showing initialization steps of the blood pressure measurement method in blood pressure measurement apparatus 1000. FIG. 18 is a flowchart showing blood pressure measurement steps of the blood pressure measurement method in blood pressure measurement apparatus 1000. FIG. 19 is a block diagram illustrating another configuration example of the blood pressure measurement device 1000. FIG. 20 is a flowchart showing the coherence length initialization step of the blood pressure measurement method in blood pressure measurement apparatus 1000. FIG. 21 is a diagram schematically showing the lower surface of the blood pressure measurement device 1000. FIG. 22 shows a phase difference variation due to the pulse wave measured at position A (the lower diagram in FIG. 15) is shifted by the pulse wave propagation time, and a phase difference variation due to the pulse wave measured at position A (FIG. 15). It is a figure which shows typically having made it match | combine. FIG. 23 is a diagram illustrating a method for adjusting a detection time shift in the photodetector 13. FIG. 24 is a flowchart showing another example of the blood pressure measurement step of the blood pressure measurement method in blood pressure measurement apparatus 1000. FIG. 25A is a diagram schematically showing a configuration of a Michelson interferometer 200 which is a first conventional example shown in Non-Patent Document 1. FIG. FIG. 25B is a diagram schematically illustrating an example of a time change of an electric signal indicating the intensity of light detected by the light receiving element 36. FIG. 26 is a diagram for explaining the light interference phenomenon. FIG. 27A is a diagram schematically showing light having a wavelength spread of zero around the wavelength λ ₀ . FIG. 27B is a diagram schematically showing that the coherence length is infinite in the case of FIG. 27A. FIG. 27C is a diagram schematically showing light having a wavelength spread (full width at half maximum) of Δλ centered on the wavelength λ ₀ . FIG. 27D is a diagram schematically showing that the coherence length σ ₀ is λ ₀ ² / Δλ in the case of FIG. 27C. FIG. 27E is a diagram schematically showing that the light having the center wavelength λ ₀ and the wavelength spread Δλ can be replaced with the two lights 27 and 28 having the wavelengths λ ₀ −Δλ / 2 and λ ₀ + Δλ / 2. . FIG. 28A is a cross-sectional view schematically showing a light detection system 300 in the second conventional example. FIG. 28B is an explanatory diagram showing the relationship between the oscillation of the light source 42 and the detection signal from the light receiving element 50 in the light detection system 300 shown in FIG. 28A. FIG. 29 is a diagram showing temporal changes in the electrocardiogram (upper diagram) and the pulse wave (lower diagram). FIG. 30 is a diagram showing a measurement result of the relationship between blood pressure P and Young's modulus E.

  Prior to describing the embodiments of the present disclosure, the knowledge underlying the present disclosure will be described.

  The inventors of the present invention have found that the information inside the scatterer cannot be obtained accurately with the conventional technology.

  In the prior art, when a light is emitted to a scatterer such as a living body, a distributed feedback (DFB) laser diode or a Fabry-Perot (FP) laser diode is used. The DFB laser diode emits light having a relatively long coherence length (about 1 m to about 1 km). The FP laser diode emits light having a relatively short coherence length (about 1 mm or less).

  The coherence length of the light emitted from the DFB laser diode or the FP laser diode is too long or too short with respect to the optical path length to be measured inside the scatterer having a depth of 1 mm or more. Therefore, when these lights are used, there arises a problem that scattered light returning by backscattering is buried in noise, and information inside the scatterer cannot be obtained accurately. Therefore, a light source that emits light having a coherence length suitable for biological measurement has been demanded.

  The present inventors have found the above problems and have come up with a novel measuring apparatus for solving this problem.

  The present disclosure includes the measurement devices described in the following items.

[Item 1]
A light emitting device that emits light having a coherence length of 5 mm or more and 400 mm or less;
A photodetector that detects scattered light generated by being emitted from the light emitting device and scattered inside the object;
A measuring device comprising:

[Item 2]
The light detector detects the scattered light emitted from the surface of the object after being scattered within the object of 1 mm or more from the surface of the object.
Item 1. The measuring device according to Item 1.

[Item 3]
The light emitting device
A laser light source that emits light having a frequency width of 1 MHz to 100 MHz;
A control circuit for causing the laser light source to emit light having a coherence length of 5 mm to 400 mm by driving the laser light source at a frequency of 50 MHz to 500 MHz;
Comprising
Item 1. The measuring device according to Item 1.

[Item 4]
The photodetector is
A light-shielding film in which a plurality of light-transmitting regions and a plurality of light-shielding regions are alternately arranged in at least the first direction;
A light-receiving element that is arranged opposite to the light-shielding film and has a plurality of first light-receiving cells and a plurality of second light-receiving cells arranged on the imaging surface, wherein each of the plurality of first light-receiving cells is A light receiving element facing one of the plurality of light transmitting regions, and each of the plurality of second light receiving cells is opposed to one of the plurality of light shielding regions;
An optical coupling layer disposed between the light-shielding film and the light-receiving element, and when light having a predetermined wavelength is incident on the plurality of light-transmitting regions, a part of the light is directed in the first direction. An optical coupling layer that includes a propagating grating and transmits another part of the light incident on the plurality of light-transmitting regions;
Light incident on the position of each of the first and second light receiving cells by calculation using signals obtained from the plurality of first light receiving cells and signals obtained from the plurality of second light receiving cells. A signal processing circuit that outputs a signal indicating variation in the phase difference of
Having
Item 4. The measuring device according to any one of Items 1 to 3.

[Item 5]
The photodetector is an image sensor having a plurality of light receiving cells arranged two-dimensionally,
Each light receiving cell outputs a signal corresponding to the intensity of the received light.
Item 4. The measuring device according to any one of Items 1 to 3.

[Item 6]
The object is a living body, food, or concrete.
6. The measuring device according to any one of items 1 to 5.

  Below, a conventional method for measuring the coherence and phase of light and a conventional method for measuring blood pressure from the propagation speed of pulse waves (hereinafter referred to as “pulse wave propagation speed”) were examined in detail. The results will be explained.

  First, a conventional method for measuring the coherence and phase of light will be described.

  FIG. 25A is a diagram schematically showing a configuration of a Michelson interferometer 200 which is a first conventional example shown in Non-Patent Document 1. FIG. As shown in FIG. 25A, the light 31 emitted from the light source 30 is condensed by the first lens optical system 35 a to become parallel light 32. In the figure, only the optical axis is shown. Light 32a, which is a part of the parallel light 32, passes through the half mirror 33 and travels toward the first reflection mirror 34a. The light 32b reflected by the reflection mirror 34a is further reflected by the half mirror 33 and travels toward the second lens optical system 35b (light 32c). The light 32c passes through the second lens optical system 35b and enters the light receiving element 36 located on the focal plane of the lens optical system 35b (light 32d). On the other hand, the other part of the parallel light 32 is reflected by the half mirror 33 and travels toward the second reflecting mirror 34A (light 32A). The light 32B reflected by the reflecting mirror 34A travels toward the half mirror 33, passes through the half mirror 33, and travels toward the lens optical system 35b (light 32C). The light 32C passes through the lens optical system 35b and enters the light receiving element 36 in a form overlapping the light 32d (light 32D). The light receiving element 36 detects light generated by the interference between the light 32d and the light 32D. The second reflecting mirror 34A is configured to change its position along the normal direction (arrow A) of the reflecting surface. The relative phase of the light 32D with respect to the light 32d changes with the displacement of the second reflecting mirror 34A.

  FIG. 25B is a diagram schematically illustrating an example of a time change of an electric signal indicating the intensity of light detected by the light receiving element 36. FIG. 25B shows a method for evaluating the coherence and phase of light using the Michelson interferometer 200. The vertical axis in FIG. 25B indicates the intensity of the signal output from the light receiving element 36, and the horizontal axis indicates time. When the position of the reflection mirror 34A is changed with time, the signal intensity changes in a range from a to b as shown in FIG. 25B. Here, the value of (b−a) / (b + a) is called contrast in interference. The degree of coherence of the light 31 is defined by the contrast value.

  Even when the reflecting mirror 34A is fixed and the transparent subject 37 is disposed between the half mirror 33 and the reflecting mirror 34a, the same principle as when the position of the reflecting mirror 34A is changed is established. That is, the intensity difference according to the shape of the subject appears as a spatial distribution in the intensity of the signal output from the light receiving element 36 such as an image sensor, and so-called interference fringes are formed. By measuring the shape or interval of the interference fringes, the shape (or phase information) of the subject can be measured.

  In order to measure the spatial distribution of interference fringes at one time, the amount of light incident on each light receiving cell may be detected using the light receiving element 36 as an aggregate of a plurality of light receiving cells. Individual light receiving cells constituting an aggregate of a plurality of light receiving cells are also referred to as pixels.

FIG. 26 is a diagram for explaining the light interference phenomenon. FIG. 26 schematically shows a state at a certain time t ₀ of light emitted from the light source 30 and propagating in the Z direction. As shown in FIG. 26, a plurality of wave trains such as wave trains 37a and 37b are emitted from the light source 30 one after another. The wave length σ ₀ is called the coherence length. Within one wave train, the waves are continuous and the wavelength is uniform. If the wave trains are different, there is no phase correlation (phase δ ₀ for wave train 37a and phases δ ₁ and δ ₀ ≠ δ _{1 for} wave train 37b). If the wave train is different, the wavelength may also be different (wavelength λ ₀ for wave train 38a, wavelength λ ₁ , λ ₀ ≠ λ _{1 for} wave train 37b).

  First, a case will be described in which the position of the second reflecting mirror 34A is adjusted in the configuration shown in FIG. 25A so that the portion 37A ′ and the portion 37A of the wave train 37a in FIG. 26 interfere with each other. The wave in the portion 37A and the wave in the portion 37A 'have the same wavelength, and the phase difference between the waves is temporally stable (it does not change at a certain value). Therefore, the brightness of the light after interference (the magnitude of the amplitude of the interference light) is also temporally stable (a certain brightness is maintained). That is, as shown in the lower left diagram of FIG. 26, the interference light 39a appears bright (upper left in the lower left diagram) or dark depending on the amount of phase difference (displacement of the reflecting mirror 34A) (lower in the lower left diagram). ). This state is called coherent.

  Next, a case where the portion 37A of the wave train 37a and the portion 37B of the wave train 37b are caused to interfere with each other will be described. In this case, there is no guarantee that the wavelengths of the wave in the portion 37A and the wave in the portion 3B are equal, and the phase difference between these two waves also changes randomly in time. As a result, the brightness of the light after interference (the amplitude of the interference light) changes randomly in time. This change is, for example, the speed in femtosecond units. Therefore, as shown in the lower right diagram of FIG. 26, the interference light 39b repeats bright and dark at high speed, and the human eye can see only average brightness. This state is called incoherent. Laser light has a long wave length and a coherence length of several m to several hundred m, which is a typical example of coherent light. On the other hand, sunlight is a typical example of incoherent light having a short wave train and a coherence length of about 1 μm. When light is interfered with the configuration as shown in FIG. 25A, if light having a long coherence length such as laser light is used, the probability of interference within the same wave run increases. As a result, the contrast is improved and close to 1. On the other hand, when light having a short coherence length such as sunlight is used, the probability of interference between different wave trains increases. That is, the probability of interference between the same wave runs is reduced. As a result, the contrast decreases and approaches zero.

The relationship between the wavelength width (longitudinal mode width) and the coherence length of the light having the center wavelength λ ₀ will be described with reference to FIGS. 27A to 27E.

FIG. 27A is a diagram schematically showing light having a wavelength spread of zero around the wavelength λ ₀ . FIG. 27B is a diagram schematically showing that the coherence length is infinite in the case of FIG. 27A. FIG. 27C is a diagram schematically showing light having a wavelength spread (full width at half maximum) of Δλ centered on the wavelength λ ₀ . FIG. 27D is a diagram schematically showing that the coherence length σ ₀ is λ ₀ ² / Δλ in the case of FIG. 27C. The longitudinal mode width and the coherence length are in a Fourier transform relationship. This is called the Wiener Hinchin theorem. This theorem can be explained as follows.

FIG. 27E is a diagram schematically showing that the light having the center wavelength λ ₀ and the wavelength spread Δλ can be replaced with the two lights 27 and 28 having the wavelengths λ ₀ −Δλ / 2 and λ ₀ + Δλ / 2. . The period of twisting generated by the interference between the light 27 and the light 28 is λ ₀ ² / Δλ. The wavelength of the carrier wave is an average value λ ₀ of the wavelengths of the light 27 and the light 28. The vibration waveform of light is uniform and continuous within the period of rotation. On the other hand, when the period is crossed, the continuity of the vibration waveform of the light of the different period is lost, and the phase correlation is lost. That is, the period of turning λ ₀ ² / Δλ corresponds to the coherence length. Sunlight is incoherent because the wavelength width (longitudinal mode width) Δλ is large. When the center wavelength λ ₀ is 550 nm and the wavelength width Δλ is 300 nm, the coherence length σ ₀ is λ ₀ ² /Δλ=1.0 μm.

  Next, a light detection system disclosed in Non-Patent Document 2 will be described as a second conventional example. The light detection system disclosed in Non-Patent Document 2 measures the light intensity distribution for each light propagation distance.

FIG. 28A is a cross-sectional view schematically showing a light detection system 300 in the second conventional example. The light source 42 emits laser light. As shown in FIG. 28A, the object 44 is irradiated with light 43 having a wavelength λ ₀ emitted from the light source 42. As a result, the scattered light 45 a, 45 b, 45 c generated on or inside the subject 44 is collected by the lens optical system 47 and formed as an image 48 b on the image plane position of the lens optical system 47. A substantial object (a collection of object points) 48a exists on the object side of the lens corresponding to the image 48b. A light receiving element 50 is disposed at the image plane position. The light receiving element 50 is an aggregate of a plurality of light receiving cells (that is, pixels), and the amount of light incident on each pixel is detected. Light emission from the light source 42 is controlled by the controller 41. The amount of light detected by the light receiving element 50 is processed by the signal processing circuit 51 as a detection signal. The controller 41 and the signal processing circuit 51 are collectively controlled by the computer 52.

FIG. 28B is an explanatory diagram showing the relationship between the oscillation of the light source 42 and the detection signal from the light receiving element 50 in the light detection system 300 shown in FIG. 28A. The vertical axis in FIG. 28B represents the oscillation intensity of the light source 42 or the detection intensity of the light receiving element 50, and the horizontal axis represents the elapsed time. The light source 42 oscillates a pulse 43 a under the control of the controller 41. The light 43 by the pulse 43 a is scattered inside the subject 44 and received by the light receiving element 50 and detected as a signal 53. The time width of the detection signal 53 is wider than the time width of the original pulse 43a due to the influence of variations in optical path length due to scattering. The leading output 53 a of the detection signal 53 is a signal component by the light 45 a reflected from the surface of the subject 44. The output 53b between the times t _{0 and} t ₁ after the output 53a is a signal component of the light 45b that scatters inside the subject 44 and has a short scattering distance. The output 53c between the times t _{1 and} t ₂ after the output 53b is a signal component due to the light 45c having a long scattering distance. Under the control of the computer 52, the signal processing circuit 51 can time-divide the detection signal 53 and separate and detect the outputs of the signals 53a, 53b, and 53c. The light passes from the shallow side to the deep side of the subject in the order of outputs 53a, 53b, and 53c. Therefore, information with different depths can be separated and analyzed.

  According to the inventor's investigation, in order to measure the degree or phase of coherence (coherence) using the Michelson interferometer 200 which is the first conventional example, the reference light 32B from the reflection mirror 34A, 32C is required. This complicates the configuration. Further, since the interference optical path exists in a predetermined space, it is easily affected by changes in the surrounding environment (for example, air convection or vibration).

  On the other hand, according to the study by the inventor of the present application, the light detection system as the second conventional example has a limit in the time division width. Therefore, sufficient resolution in the depth direction cannot be ensured during measurement (diagnosis). For example, when the time division width is 300 ps, the depth resolution is about 90 mm. For this reason, the light detection system in the second conventional example is not suitable for diagnosis or examination of an object having a relatively small structure such as a living body.

  Next, before describing the embodiment of the present disclosure, a mode (study example) studied by the present inventors in order to solve the problems of the conventional example will be described.

(Examination example)
FIG. 1A is a schematic diagram of a light detection system 100 according to the present study example. The light detection system 100 includes a light source 2, a condenser lens 7, a light detector 13, a control circuit 1, and a signal processing circuit 14. The signal processing circuit 14 may be included in the photodetector 13.

  The light source 2 irradiates the subject 4 with light having a certain coherence length. For example, the light source 2 may be a laser light source that emits laser light that is representative of coherent light. The light source 2 may continuously emit light having a constant intensity, or may emit a single pulsed light. The wavelength of the light emitted from the light source 2 is arbitrary. However, when the subject 4 is a living body, the wavelength of the light source 2 can be set to, for example, approximately 650 nm or more and approximately 950 nm or less. This wavelength range is included in the wavelength range from red to near infrared. In this specification, not only visible light but also infrared rays and ultraviolet rays are included in the concept of “light”.

  The condensing lens 7 condenses the scattered light 5a and 5A generated on the surface or inside of the subject 4 by the light source 2 irradiating the subject 4 with light. The condensed light is imaged as an image 8 b at the image plane position of the lens optical system 7. A substantial object (collection of object points) 8a exists on the object side of the lens corresponding to the image 8b. In the example shown in FIG. 1A, the lens optical system 7 includes one lens. The lens optical system 7 may be an assembly of a plurality of lenses.

  The photodetector 13 is disposed at the image plane position of the condenser lens 7. The photodetector 13 detects the scattered lights 5a and 5A collected by the condenser lens 7. The detailed structure of the photodetector 13 will be described later.

  The signal processing circuit 14 performs arithmetic processing on the signal detected by the photodetector 13. The signal processing circuit 14 may be an image processing circuit such as a digital signal processor (DSP), for example.

  The control circuit 1 executes, for example, a program recorded in a memory, thereby detecting light by the photodetector 13, calculation processing by the signal processing circuit 14, light emission amount of the light source 2, lighting timing, continuous lighting time, light emission wavelength. Controlling at least one of the coherence length and the like. The control circuit 1 may be an integrated circuit such as a central processing unit (CPU) or a microcomputer (microcomputer). The control circuit 1 and the signal processing circuit 14 may be realized by a single integrated circuit.

  The light detection system 100 may include a display (not shown) that displays the result of the arithmetic processing performed by the signal processing circuit 14.

FIG. 1B shows a state of the scattered light 5 incident on one opening 9 a (“translucent region 9 a” described later) provided in the photodetector 13. The subject 4 is a scatterer. Rays propagating inside the object 4 is attenuated by the attenuation coefficient mu _a, repeats scattering by the scattering coefficient mu _s.

  FIG. 2A is a cross-sectional view of the photodetector 13 in a plane along the direction in which light enters. FIG. 2B is a plan view of the photodetector 13 as viewed from the light incident side. FIG. 2A is a plan view on the XY plane including a light shielding film 9 described later. FIG. 2A shows a cross section parallel to the XZ plane including a region surrounded by a broken line in FIG. 2B. As shown in FIG. 2B, the cross-sectional structure shown in FIG. 2A is taken as one unit structure, and the unit structures are periodically arranged in the XY plane. 2A and 2B show three orthogonal axes (X axis, Y axis, and Z axis) for convenience of explanation. Similar coordinate axes are used for other figures.

  The photodetector 13 includes the light receiving element 10, the optical coupling layer 12, and the light shielding film 9 in this order. In the example of FIG. 2A, these are stacked in the Z direction. In the example of FIG. 2A, a transparent substrate 9b and a band pass filter 9p are laminated in this order on the light shielding film 9. In the photodetector 13, a surface on which a plurality of pixels are arranged is referred to as an “imaging surface”.

  The light receiving element 10 includes a plurality of pixels (that is, light receiving cells) 10 a and 10 A in the in-plane direction (XY plane) of the light receiving element 10. The light receiving element 10 includes, from the light incident side, microlenses 11a and 11A, a transparent film 10c, a metal film 10d such as wiring, and a photosensitive portion formed of Si or an organic film. The photosensitive portions between the metal films 10d correspond to the pixels 10a and 10A. The plurality of microlenses (11a, 11A) are arranged so that one microlens faces one pixel (10a, 10A). Light collected by the microlenses 11a and 11A and entering the gap between the metal films 10d is detected by the pixels 10a and 10A.

The optical coupling layer 12 is disposed on the light receiving element 10, and in the direction perpendicular to the light receiving element 10 (Z-axis direction), the first transparent layer 12c, the second transparent layer 12b, and the third transparent layer 12a are arranged. Prepare in this order. The first transparent layer 12c and the third transparent layer 12a can be formed of, for example, SiO ₂ . The second transparent layer 12b can be formed of Ta ₂ O ₅ or the like, for example. The thickness t1 in the Z direction of the second transparent layer 12b is, for example, 0.34 μm. The thickness t2 in the Z direction of the first transparent layer 12c is, for example, 0.22 μm.

  The second transparent layer 12b has a higher refractive index than the first transparent layer 12c and the third transparent layer 12a. The optical coupling layer 12 may have a structure in which the high refractive index transparent layer 12b and the low refractive index transparent layer 12c are further repeated in this order. In FIG. 2A, a structure repeated six times in total is shown. The high refractive index transparent layer 12b is sandwiched between the low refractive index transparent layers 12c and 12a. Therefore, the high refractive index transparent layer 12b functions as a waveguide layer. A linear grating 12d having a pitch Λ is formed over the entire surface at the interface between the high refractive index transparent layer 12b and the low refractive index transparent layers 12c and 12a. The grating vector of the grating is parallel to the X axis in the in-plane direction (XY plane) of the optical coupling layer 12. The XZ cross-sectional shape of the grating 12d is sequentially transferred to the high refractive index transparent layer 12b and the low refractive index transparent layer 12c which are laminated. When the film formation of the transparent layers 12b and 12c has high directivity in the stacking direction, it is easy to maintain the shape transferability by making the XZ section of the grating S-shaped or V-shaped.

  The grating 12d may be provided at least in part of the high refractive index transparent layer 12b. Since the high refractive index transparent layer 12b includes the grating 12d, incident light can be coupled to light propagating through the high refractive index transparent layer 12b (waveguide light).

  The gap between the optical coupling layer 12 and the light receiving element 10 should be as narrow as possible. The optical coupling layer 12 and the light receiving element 10 may be in close contact with each other. A gap between the optical coupling layer 12 and the light receiving element 10 (including a space in which the microlenses 11a and 11A are arranged) may be filled with a transparent medium such as an adhesive. In the case of filling the transparent medium, in order to obtain the lens effect by the microlenses 11a and 11A, a material having a sufficiently higher refractive index than that of the transparent medium to be filled is used as a constituent material of the microlenses 11a and 11A.

  The translucent area 9a in FIG. 2A corresponds to the translucent areas 9a1, 9a2, 9a3, 9a4, etc. in FIG. 2B. The light shielding area 9A in FIG. 2A corresponds to the light shielding areas 9A1, 9A2, 9A3, 9A4, etc. in FIG. 2B. That is, the light shielding film 9 includes a plurality of light shielding regions 9A and a plurality of light transmitting regions 9a arranged in the in-plane direction (XY plane) of the light shielding film 9. The plurality of light shielding regions 9A are opposed to the plurality of second pixels 10A, respectively. The plurality of translucent regions 9a are opposed to the plurality of first pixels 10a, respectively. In this specification, an aggregate of the first pixels 10a may be referred to as a “first pixel group”, and an aggregate of the second pixels 10A may be referred to as a “second pixel group”.

  In the present disclosure, each of the plurality of first pixels 10a faces one of the plurality of light-transmissive regions 9a. Similarly, each of the plurality of second pixels 10A faces one of the plurality of light shielding regions 9A.

  Note that two or more first pixels 10a may face one light-transmitting region. Similarly, two or more second pixels 10A may face one light shielding region. The present disclosure includes such forms.

  In the example shown in FIG. 2B, the plurality of light shielding regions 9A (9A1 to 9A4) form a checker pattern. These light shielding regions 9A (9A1 to 9A4) may form a pattern other than the checker pattern.

The transparent substrate 9b is disposed on the light incident side of the light shielding film 9. The transparent substrate 9b can be formed of a material such as SiO ₂ . The band pass filter 9p is disposed on the light incident side of the transparent substrate 9b. The band pass filter 9p selectively transmits only the light in the vicinity of the wavelength λ ₀ among the incident light 5.

The light 5 incident on the photodetector 13 passes through the band-pass filter 9p and the transparent substrate 9b, and reaches the light-shielding region 9A where the reflective film is formed and the light-transmitting region 9a where the reflective film is removed as light 6A and 6a. The light 6A is blocked by the light blocking area 9A. The light 6 a passes through the light transmitting region 9 a and enters the optical coupling layer 12. The light 6a incident on the optical coupling layer 12 passes through the low refractive index transparent layer 12a and enters the high refractive index transparent layer 12b. A grating is formed on the upper and lower interfaces of the high refractive index transparent layer 12b. When the following expression (1) is satisfied, the guided light 6b is generated.

  Here, N is the effective refractive index of the guided light 6b. θ is an incident angle with respect to the normal line of the incident surface (XY plane). In FIG. 2A, light is incident perpendicular to the incident surface (θ = 0 °). In this case, the guided light 6b propagates in the X direction in the XY plane. That is, the light incident on the optical coupling layer 12 through the light transmitting region 9a is guided in the direction of the light shielding region 9A adjacent to the X direction.

The light component that passes through the high refractive index transparent layer 12b and enters the lower layer is incident on all the high refractive index transparent layers 12b on the lower layer side. As a result, the guided light 6c is generated under the same conditions as in the expression (1). Although guided light is generated in all the high refractive index transparent layers 12b, FIG. 2A shows only guided light generated in two layers as a representative. Similarly, the guided light 6c generated on the lower layer side propagates in the X direction in the XY plane. The guided light beams 6b and 6c propagate while emitting light in the vertical direction at an angle θ (θ = 0 ^{o in} the example of FIG. 2A) with respect to the normal line of the waveguide surface (XY plane). The components 6B1 and 6C1 of the radiated light 6B2 are reflected directly by the light shielding region 9A immediately below the light shielding region 9A, and become light 6B2 traveling downward along the normal line of the reflective surface (XY surface). . The lights 6B1, 6C1, and 6B2 satisfy the formula (1) with respect to the high refractive index transparent layer 12b. Accordingly, part of the light becomes the guided light 6b and 6c again. The guided lights 6b and 6c also generate new emitted lights 6B1 and 6C1. These processes are repeated. As a whole, immediately below the light-transmitting region 9a, a component that has not become guided light passes through the optical coupling layer 12 and enters the microlens 11a as transmitted light 6d. As a result, the component that has not become guided light is detected by the first pixel 10a. In practice, the component finally radiated after waveguiding is also added to the component that has not become guided light. However, in this specification, such a component is also treated as a component that has not become guided light. Immediately below the region 9A, the component that has become the guided light is emitted, and enters the microlens 11A as the emitted light 6D. As a result, the component that has become the guided light is detected by the second pixel 10A.

  The light transmitting region 9a corresponds to the opening shown in FIG. 1B. Through the light-transmitting region 9a, the light is branched into a detector directly below and a detector on the left and right (that is, adjacent to the X direction), and is detected respectively.

  Assume that the detected light amounts at the first pixels facing the translucent regions 9a1, 9a2, 9a3, and 9a4 shown in FIG. 2B are q1, q2, q3, and q4, respectively. The detected light amounts at the second pixels facing the light shielding regions 9A1, 9A2, 9A3, and 9A4 shown in FIG. 2B are Q1, Q2, Q3, and Q4, respectively. q1 to q4 represent the detected light amounts of light that has not become guided light. Q1 to Q4 represent the detected light amount of the light that has become the guided light. In the first pixel 10a immediately below the light-transmitting region 9a1, the amount of light that has been guided light is not detected. On the other hand, the amount of light that has not become guided light is not detected in the second pixel 10A immediately below the light shielding region 9A2. Here, the detection light quantity Q0 = (Q1 + Q2) / 2 of the light that has become the guided light is defined at the detection position immediately below the light transmitting region 9a1. Alternatively, Q0 = (Q1 + Q2 + Q3 + Q4) / 4 may be defined. Similarly, a detection light quantity q0 = (q1 + q2) / 2 of light that has not become guided light at the detection position immediately below the light shielding region 9A2 is defined. Alternatively, q0 = (q1 + q2 + q3 + q4) / 4 may be defined. In other words, in a certain region (light-shielding region or light-transmitting region), an average value of the amount of light detected at a detection position immediately below a region (pixel) adjacent to the region in the X direction and / or the Y direction is defined.

  By applying this definition to all regions, the detection amount of light that has not become waveguide light and the detection of light that has become waveguide light in all detection regions (that is, all pixels) constituting the light receiving element 10. The amount of light can be defined.

  The signal processing circuit 14 uses the detected light amount of the light that has not been changed to the guided light and the detected light amount of the light that has become the guided light, based on the above definition, to distribute the degree of coherence. An arithmetic process such as generating an optical distribution image indicating the above is performed. The signal processing circuit 14 generates an optical distribution image by assigning to each pixel a value obtained by calculating for each pixel the value of the ratio of these two detected light amounts or the value of the ratio of each light amount to the sum of these light amounts. .

FIG. 3 is a diagram illustrating a signal processing method of the photodetector 13. In FIG. 3, eight light receiving cells (10A, 10a, etc.) are arranged along the grating lattice vector. The light receiving cells 10A and 10a face the light shielding region 9A and the light transmitting region 9a, respectively. The signals detected by the eight detectors _{p 0, k-4, p} 1, k-3, p 0, k-2, p 1, k-1, p 0, k, p 1, k + 1, p 0 _{, K + 2} , p _{1, k + 3} . For example, the average value (p _{1, k-1} + p _{1, k + 1} ) / 2 of the signals (p _{1, k-1} and p _{1, k + 1} ) on the left and right of p _{0, k} is used as the interpolation value p _{1, k.} Define (see interpolation formula in FIG. 3). Similarly, an average value (p _{0, k-2} + p _{0, k} ) / 2 is _obtained from the signals (p _{0, k-2} and p _{0, k} ) on the left and right _{sides of} p _{1, k-1} , and an interpolation value p _{0 is obtained. , K−1} . From the detection value p _{0, k} and the interpolation value p _{1, k} , the P0 modulation degree p _{0, k} / (p _{0, k} + p _{1, k} ) or the P1 modulation degree p _{1, k} / (p _{0, k} + p _{1, k} ) is calculated. In the study example, these modulation degrees are used as detection signals.

FIG. 4A is a cross-sectional view illustrating a positional relationship between incident light at four openings and three light receiving elements below the incident light in the study example. Lights having different phases are incident on the four openings. Where ω is the angular frequency of light (ω = 2πc / λ ₀ , c is the speed of light), t is time, r1, r2, r3, r4 are random functions (functions that take random values between 0 and 1), a is a random coefficient (amplitude of a random value).

  FIG. 4B is an analysis result showing the relationship between the phase random coefficient a of the incident light and the detection signal. The light receiving cell immediately below the light shielding part in the middle of the four openings is 10A, and the light receiving cells immediately below the light transmitting part on both sides are 10a and 10a '. The detected light amounts are P1, P0, and P0 ', respectively. The detection signal is defined by 2P1 / (P0 + P0 '). A rhombus mark represents TE mode incidence (S-polarized light), a square mark represents TM mode incidence (P-polarized light), and a triangular mark represents TEM mode incidence (random polarized light, circularly polarized light, or polarized light in a 45 degree direction). When attention is focused on TE mode incidence and TEM mode incidence, the detection signal decreases as the coefficient a increases. a = 0 corresponds to the case where the phases are coherent and aligned. a = 1 corresponds to incoherent. Therefore, the degree of coherence of incident light or the variation in phase difference of incident light can be known from the magnitude of the detection signal. Similarly, the phase difference of incident light can be measured.

  The signal processing circuit 14 may be included in the photodetector 13. In that case, the photodetector 13 includes a light shielding film 9, a light receiving element 10, an optical coupling layer 12, and a signal processing circuit 14. In the light shielding film 9, a plurality of light transmitting regions 9a and a plurality of light shielding regions 9A are alternately arranged in at least the X direction. The light receiving element 10 includes a plurality of light receiving cells 10a and a plurality of light receiving cells 10A that are arranged to face the light shielding film 9 and are arranged on the imaging surface. Each of the plurality of light receiving cells 10a faces one of the plurality of light transmitting regions. Each of the plurality of light receiving cells 10A faces one of the plurality of light shielding regions. The optical coupling layer 12 includes a grating that is disposed between the light shielding film 9 and the light receiving element 10 and propagates a part of the light in the X direction when light having a predetermined wavelength is incident on the plurality of light transmitting regions 9a. The other part of the light incident on the plurality of light transmitting regions 9A is transmitted. The signal processing circuit 14 calculates the phase difference of the light incident on the positions of the light receiving cells 10a and 10A by calculation using the signals obtained from the light receiving cells 10a and the signals obtained from the light receiving cells 10A. A signal indicating the variation of the output is output.

  A detailed description of the photodetector 13 is disclosed in US Patent Application Publication No. 2016/360967 and US Patent Application Publication No. 2017/023410. The entire disclosure of US Patent Application Publication No. 2016/360967 and US Patent Application Publication No. 2017/023410 are incorporated herein by reference.

  Next, a conventional method for measuring blood pressure from pulse wave propagation speed will be described with reference mainly to Non-Patent Document 3.

  First, the pulse wave will be described. A pulse wave is a bulge of a blood vessel, and is a progression of the bulge and a temporal variation of the bulge at a certain position. The temporal fluctuation of the bulge is called a pulse. The normal pulse at rest of an adult is about 60 to 100 times per minute.

  A method for measuring a pulse wave velocity using an electrocardiograph and a pulse wave measuring machine will be described.

  FIG. 29 is a diagram showing temporal changes in the electrocardiogram (upper diagram) and the pulse wave (lower diagram). The electrocardiogram is measured by an electrocardiograph. The pulse wave is measured by a pulse wave measuring device, for example, on an arm or a leg. The time from the peak value of the R wave of the electrocardiogram to the minimum value of the pulse wave corresponds to the pulse wave transit time (PWTT). A pulse wave velocity (PWV) can be obtained by dividing the distance from the heart to the arm or leg by the pulse wave propagation time. When the heart motion is not used, the pulse wave velocity can be obtained by measuring the pulse wave at the arm and the leg. The pulse wave propagation speed corresponds to the traveling speed of the pulse wave, and in most cases is 5 to 15 m / second. Pulse wave propagation is different from blood propagation.

  Next, the relationship between pulse wave propagation speed and blood pressure will be described. Blood pressure is also called intravascular pressure.

Ｅは、血管の硬さを表すヤング率、または、より正確にはフープ応力である。ｈは血管壁厚であり、Ｄは血管内径であり、ρは血液粘度である。脈波伝搬速度は、ヤング率Ｅ、血管壁厚ｈ、血管内径Ｄ、および血液粘度ρに依存する。血液粘度は、個人による変動要因の他、（１）赤血球数の増加、（２）血漿蛋白濃度の上昇、および（３）血液水分量の減少によって高くなる。しかし、血液粘度の変動は、脈波伝搬速度にそれほど大きな影響を与えないと考えられている。 Equation (2) below represents the relationship between the pulse wave velocity and the stiffness of the blood vessel.

E is a Young's modulus representing the hardness of a blood vessel, or more precisely, a hoop stress. h is the vessel wall thickness, D is the vessel inner diameter, and ρ is the blood viscosity. The pulse wave velocity depends on Young's modulus E, vessel wall thickness h, vessel inner diameter D, and blood viscosity ρ. In addition to factors that vary from individual to individual, blood viscosity increases due to (1) an increase in red blood cell count, (2) an increase in plasma protein concentration, and (3) a decrease in blood water content. However, it is considered that fluctuations in blood viscosity do not significantly affect the pulse wave propagation speed.

ΔＰは血圧の変化量であり、ΔＲは血管内径の変化量である。原理的には、ヤング率Ｅは、血圧の変化量と血管内径の変化量との比により得られる。 The following formula (3) represents the relationship between blood vessel hardness and blood pressure.

ΔP is the amount of change in blood pressure, and ΔR is the amount of change in blood vessel inner diameter. In principle, the Young's modulus E is obtained by the ratio between the change amount of the blood pressure and the change amount of the blood vessel inner diameter.

  FIG. 30 is a diagram showing a measurement result of the relationship between blood pressure P and Young's modulus E. A circle indicates a normal case, and a triangle indicates a case of hypertension. In any case, the Young's modulus E can be approximated as an exponential function of the blood pressure P.

αは血管特性を示す係数であり、Ｅ_０はある血圧Ｐ_０におけるヤング率である。式（３）は、式（４）に簡単化される。 The following formula (4) represents an approximate relational expression between the blood pressure P and the Young's modulus E.

α is a coefficient indicating blood vessel characteristics, and E ₀ is a Young's modulus at a certain blood pressure P ₀ . Equation (3) is simplified to Equation (4).

βは、上記の複数のパラメータに依存する係数である。式（５）から、ＰＷＶの２乗の対数が血圧Ｐに比例することわかる。 By substituting equation (4) into equation (2), the following equation (5) is obtained.

β is a coefficient depending on the plurality of parameters. From equation (5), it can be seen that the logarithm of the square of PWV is proportional to blood pressure P.

  The above approximation is only an example, and various approximations exist as shown in other papers. However, in order to obtain the blood pressure P from PWV, it is necessary to know parameters α and β depending on the individual before measurement.

  In the following, exemplary embodiments of the present disclosure will be described.

(Embodiment 1)
The measuring device in the present embodiment includes a light emitting device and a photodetector. The light emitting device emits light having a coherence length of 5 mm to 400 mm. The photodetector detects light emitted from the light emitting device and reflected by the object. The object is, for example, a scatterer such as a living body.

  FIG. 5 is a diagram schematically illustrating a configuration example of the light emitting device 20 having a variable coherence length. The light emitting device 20 includes a laser light source 2 and a control circuit 1. The laser light source 2 emits light having a frequency width of 1 MHz to 100 MHz. The light emitting device 20 emits light having a coherence length of 5 mm or more and 400 mm or less by driving the laser light source 2 at a frequency of 50 MHz or more and 500 MHz or less by the control circuit 1. The control circuit 1 may drive the laser light source 2 using the high frequency drive power supply 16. The laser light source 2 is, for example, a DFB laser diode. A part of the light emitted from the light emitting device 20 enters the depth of 1 mm or more from the surface of the scatterer 4, is scattered inside the scatterer 4, and then is emitted from the surface of the scatterer 4.

  FIG. 6 is a diagram schematically showing a general relationship between laser light output and drive current. When the drive current exceeds the oscillation threshold, laser light is output. In the example of FIG. 6, the optical output corresponding to the high-frequency driving current is emitted with temporal changes. The waveform of the drive current is a sine wave. The waveform may be a rectangular wave, a triangular wave, a sawtooth wave, or a combination thereof.

FIG. 7 is a diagram schematically showing a change over time of the drive current input to the laser light source 2. The high frequency driving power supply 16 can set the upper limit current value I _max and the lower limit current value I _min of the rectangular current and the duty ratio of the upper limit current and the lower limit current. For example, when the laser light source 2 is driven by a rectangular current having a frequency of 100 MHz and a duty ratio of 1: 1, the drive time of the upper limit current may be set to t _max = 5 ns, and the drive time of the lower limit current may be set to t _min = 5 ns. At that time, the period is T _M = t _max + t _min = 10 ns, and the frequency is f _M = 1 / T _M = 100 MHz.

  Next, the principle of adjusting the coherence length by the drive current will be described.

The electric field of the light output from the laser light source 2 is represented by, for example, E (t) = A (t) cos (2πf ₀ t + θ ₀ ). A (t) (> 0) is the amplitude of the electric field. f ₀ is the frequency of light emitted from the laser light source 2 by a constant drive current. The light output emitted from the laser light source 2 is proportional to the square of A (t). The spectrum of the light output emitted from the laser light source 2 is proportional to the square of the absolute value of the Fourier transform of E (t).

When A (t) is constant, the light output spectrum obtained from E (t) has a peak only at the frequency of f = f ₀ . That is, when the light output is constant, the frequency width of the light output from the laser light source 2 is zero. Actually, even if the driving current is constant, the light emitted from the laser light source 2 has a narrow frequency width.

Meanwhile, A (t) is the period T _M and duty ratio of 1: it is assumed that a square wave of 1. In this case, A (t) = A ₀ + A ₁ cos (2πf _M t + θ _M ) + A ₃ cos (6πf _M t + θ _M ) + A ₅ cos (10πf _M t + θ _M ) +... . A (t) _has no 2f M, an even multiple of the frequency component of _{f M} such 4f _M and 6f _M.

For _{example, cos (2πf M t + θ} M) cos (2πf 0 t + θ 0) = (1/2) [cos {2π (f 0 + f M) t + (θ 0 + θ M)} + cos {2π (f 0 -f M) As can be seen from t + (θ ₀ −θ _M )}], the frequency f = f ₀ changes to f = f ₀ ± f _M due to cos (2πf _M t + θ _M ).

Therefore, when A (t) is the above-described rectangular wave, the spectrum of the optical output obtained from E (t) is f = f ₀ , f ₀ ± f _M , f ₀ ± 3 f _M and f ₀ ± 5 f _M Have multiple peaks at such frequencies. The plurality of peaks decrease with distance from f = f ₀ . If a curve smoothly connecting the vertices of the peaks is drawn, it can be seen that the spectrum of the light output spreads around f = f ₀ . The full width at half maximum obtained from the curve is defined as a frequency width Δf. The frequency width Δf increases as the difference between the upper limit and the lower limit of the rectangular wave increases.

The center frequency f ₀ and the frequency width Δf correspond to λ ₀ and Δλ in FIG. 27C, respectively (λ ₀ = c / f ₀ , Δλ to cΔf / f ₀ ² ). Therefore, the coherence length σ ₀ = λ ₀ ² / Δλ can be adjusted by modulating the light output emitted from the laser light source 2 by the drive current.

FIG. 8 is a diagram illustrating an example of a measurement result of a change in the coherence length σ ₀ due to the drive current illustrated in the example of FIG. The horizontal axis represents the lower limit current value I _min , and the vertical axis represents the coherence length σ ₀ . The upper limit current value is I _max = 150 mA, the duty ratio is 1: 1, and the frequency is 100 MHz. As the laser light source 2, a DFB laser diode having a maximum frequency width of 10 MHz is used. In the example of FIG. 8, when the lower limit current value I _min changes from 0 mA to 100 mA, the coherence length σ ₀ varies widely from 40 mm to 680 mm.

The coherence length σ ₀ in continuous wave oscillation of the light source is 150 m, which is very long. A coherence length σ _{0 of 5} to 400 mm can be covered by controlling the upper limit current value and lower limit current value, frequency, and duty ratio of the drive current input to the light source.

  In the configuration example of FIG. 5, the information inside the scatterer 4 is expressed as variations in the optical path length of the scattered light. This variation can be detected by the photodetector as a variation in phase difference. By comparing the detected variation in the phase difference with a simulation predicted in advance, it can be seen whether the scattered light has moved in the same manner as the simulation. However, the coherence length of the light source should be set appropriately. If the coherence length is too long, phase information for all optical path lengths is detected. Such phase information becomes noise information when obtaining phase information at a desired depth. On the other hand, if the coherence length is too short, phase information for an optical path length longer than the coherence length cannot be obtained. For this reason, it is desirable to appropriately adjust the coherence length of the light source.

  As a specific method of obtaining the phase difference variation, there is a method of calculating the phase difference from the image detected by the photodetector 13 shown in the example of FIG. 2A and obtaining the phase difference variation. In addition, when obtaining the dispersion | variation in a phase difference from a speckle, you may use the general image sensor which has several light receiving cells arranged in two dimensions instead of the photodetector. Each light receiving cell outputs a signal corresponding to the amount of light received. A variation in phase difference can be obtained from the contrast of the signal output from the image sensor. For example, the standard deviation of signals output from a plurality of light receiving cells included in a certain area may be used as a variation in phase difference.

  FIG. 9 is a diagram showing a measurement result of the relationship between the coherence length and the variation in phase difference when an absorber is present inside the scatterer 4 (see FIG. 5). The variation in the phase difference was calculated from the contrast of the image. The absorption coefficient and scattering coefficient of the scatterer are almost the same as the absorption coefficient and scattering coefficient of the living body, respectively. It can be seen that the variation in the detected phase difference changes by scanning the coherence length. If the phase difference variation is 0.001 or more, an error in obtaining the phase difference variation can be ignored. From this condition, it can be seen that the optimum range of the coherence length is 5 mm or more and 400 mm or less. From other experiments, it was found that measurement can be performed in other living body parts if the coherence length is within the range. This range is greatly different from the range of coherence length (0.1 mm to 1 mm) suitable for the measurement inside the living body, which is conventionally known. The target object as the scatterer is not limited to a living body, and may be food, concrete, or the like. In the case of food, foreign matter in the food can be detected, and in the case of concrete, which is the material of the building, deterioration of the concrete can be inspected.

  In addition to the example of FIG. 5, the following configuration may be used as the light emitting device 20 having a variable coherence length.

  FIG. 10 is a diagram schematically illustrating another configuration example of the light emitting device 20 having a variable coherence length.

  The light emitting device 20 includes a laser light source 2, a prism 17 or a diffraction grating, and a diaphragm 18. The laser light source 2 is, for example, an FP laser diode, and emits light having a coherence length of 1 mm or less. The light emitting device 20 emits light having a coherence length of 5 mm or more and 400 mm or less by passing a part of the light emitted from the laser light source 2 and spatially dispersed by the prism 17 or the diffraction grating using the diaphragm 18. Exit.

  In the example of FIG. 10, the coherence length of the light emitted from the laser light source 2 is converted into a longer coherence length. The refractive index of the prism 17 varies depending on the frequency. Therefore, the refraction angle of the light incident on the prism 17 differs depending on each frequency. As a result, the light emitted from the prism 17 is spatially dispersed. The dispersed light has different frequencies in the spatial width direction of the light. When a part of the dispersed light is passed using the diaphragm 18, a part of the frequency width of the light emitted from the laser light source 2 is obtained. That is, the frequency width of the light that has passed through the diaphragm 18 is narrower than the frequency width of the light emitted from the laser light source 2. This increases the coherence length.

  FIG. 11 is a diagram schematically illustrating still another configuration example of the light emitting device 20 having a variable coherence length.

  The light emitting device 20 includes a laser light source 2 and an intensity modulator 19. The laser light source 2 is a DFB laser diode, for example, and emits light having a coherence length of 1 m or more. The intensity modulator 19 modulates the intensity of the light emitted from the laser light source 2. The light emitting device 20 emits light having a coherence length of 5 mm or more and 400 mm or less by modulating the intensity of light emitted from the laser light source 2 using the intensity modulator 19 at a frequency of 1 to 40 GHz.

  In the example of FIG. 11, the coherence length of the light emitted from the laser light source 2 is converted to a shorter coherence length. The light emitted from the laser light source 2 has a narrow frequency width. The intensity of the emitted light, that is, the light output, is modulated by the intensity modulator 19 from, for example, constant (lower left diagram) to a rectangle (lower right diagram). As a result, the frequency width of the modulated light is wider than the frequency width of the light emitted from the laser light source 2. This shortens the coherence length. In the example of FIG. 5, the light directly modulated from the laser light source 2 is emitted, and in the example of FIG. 11, the light emitted from the laser light source 2 is modulated by the intensity modulator 19.

(Embodiment 2)
FIG. 12 is a diagram schematically illustrating a configuration example of the blood pressure measurement device 1000 according to the present embodiment and a blood pressure measurement method using the blood pressure measurement device 1000.

  The blood pressure measurement device 1000 according to the present embodiment is a device that measures blood pressure in the test unit 4 and includes a light emitting device 20a, a light emitting device 20b, a photodetector 13, a storage device (not shown), and a not shown device. And an arithmetic circuit.

  The photodetector 13 detects the reflected light that is emitted from the light emitting device 20a and reflected from the position A in the test portion 4, and outputs a signal corresponding to the amount of the reflected light. Similarly, the photodetector 13 detects the reflected light emitted from the light emitting device 20b and reflected from the position B in the test portion 4, and outputs a signal corresponding to the amount of the reflected light.

  The storage device stores parameters necessary for calculating blood pressure.

  The arithmetic circuit calculates the propagation time of the pulse wave propagating between the position A and the position B from the comparison of the time changes of the two signals. The arithmetic circuit further calculates the blood pressure in the test unit 4 by calculation using the parameters, the propagation time, and the distance between the position A and the position B.

  Each of the two signals indicates a variation in the phase difference of the reflected light.

  In the example of FIG. 12, the blood pressure measurement device 1000 is a wearable terminal. When the wearable terminal is a wristwatch type, the radial artery may be used as the test part 4 or other arteries / veins may be used. The frame speed of the photodetector 13 or the image sensor may be 1000 fps or more, and preferably 2000 fps or more. It is also desirable to have a global shutter function. In the present embodiment, the frame rate of the photodetector 13 is 2000 fps.

  13 is a cross-sectional view of the configuration example of FIG. The interval between the two light emitting devices 20a and 20b is 23 mm. The radial artery is located at a depth of 4 mm from the surface. The radial artery is 2 mm wide. The radial artery swells several percent due to the propagation of the pulse wave. Thereby, the dispersion | variation in the phase difference of the detected light changes.

  A case is assumed in which a wearable terminal including two light emitting devices 20a and 20b having a variable coherence length and a photodetector 13 is attached to an arm. In this case, the lower surface of the wearable terminal and the surface of the arm may not be in direct contact.

  The light emitting device 20a emits light having an appropriate coherence length. The photodetector 13 detects light reflected from the position A in a region near the light emitting device 20a on the light receiving surface of the photodetector 13. Similarly, the light emitting device 20b emits light having an appropriate coherence length. The photodetector 13 detects light reflected from the position B in a region near the light emitting device 20b on the light receiving surface of the photodetector 13. Here, a coherence length of 10 mm is set.

  The pulse wave can be measured from the phase difference variation obtained by the photodetector 13. The pulse wave can be measured even when the artery is located at a depth of 1 mm or more from the surface.

  FIG. 14 is a diagram illustrating a measurement result of a variation in phase difference due to a pulse wave. The horizontal axis is time, and the vertical axis is variation in phase difference. It can be seen that the pulse wave is about once per second. The variation in the phase difference due to the pulse wave is measured, for example, at an interval of 2000 fps or more, that is, 0.5 ms or less. Hereinafter, the phase variation due to the pulse wave may be referred to as “pulse wave data”.

  FIG. 15 is a diagram schematically showing the variation in the phase difference due to the pulse wave at position A (upper figure) and position B (lower figure). In order to facilitate the comparison, the interval between the measurement points (circles) and the deviation of the pulse wave are larger than actual. The timing at which light is emitted from the light emitting device 20a and the reflected light from the position A is detected is not the same as the timing at which light is emitted from the light emitting device 20b and the reflected light from the position B is detected. For this reason, the detection times of the two pulse waves are shifted. This distinguishes between the reflected light from the position A and the reflected light from the position B when light is emitted simultaneously from the light emitting device 20a and the light emitting device 20b and the reflected light from the position A and the position B is detected simultaneously. Because it is difficult.

  The difference between the interval between the two light emitting devices 20a and 20b and the interval between the position A and the position B where the pulse wave is measured can be calculated by simulation such as FDTD. In the present embodiment, the linear distance between the position A and the position B is about 20 mm.

  At position A and position B, almost the same two pulse waves are obtained. The linear distance between the position A and the position B may be 10 cm or less. The two pulse waves are shifted by the pulse wave propagation time PWTT. The pulse wave propagation velocity PWV is calculated by dividing the distance between the two positions by the pulse wave propagation time PWTT.

The following equation (6) represents a calculation method of the pulse wave propagation velocity PWV.

  However, in order to obtain the blood pressure from the pulse wave velocity, it is necessary to know the parameters α and β in the equation (5) before measuring the blood pressure.

  Next, the configuration of the blood pressure measurement device 1000 will be described more specifically.

  FIG. 16 is a block diagram of a configuration example of the blood pressure measurement device 1000.

  The blood pressure measurement device 1000 includes an image acquisition unit 1100, an arithmetic circuit 1200, a storage device 1300, and a display device 1400.

  The image acquisition unit 1100 has an illumination function and an imaging function.

  The arithmetic circuit 1200 transfers the obtained image group to the storage device 1300 and calculates blood pressure from the storage device 1300. The storage device 1300 stores initial value parameter data 131, position A pulse wave data 132, position B pulse wave data 133, image data 134, and the like. Display device 1400 outputs blood pressure data.

  The image acquisition unit 1100 includes a lighting device 111 and an image acquisition unit 112.

  The illumination device 111 includes two light emitting devices 20a and 20b having a fixed coherence length. The image acquisition unit 112 includes a photodetector 13 or an image sensor that detects variations in phase difference.

  The arithmetic circuit 1200 includes an illumination condition adjustment unit 121, an image information acquisition unit 122, a blood vessel thickness calculation unit 123, a pulse wave data comparison unit 124, an input interface 125, a parameter calculation unit 126, and a blood pressure value calculation unit. 127 and an output interface 128.

  The illumination condition adjustment unit 121 controls the coherence length of the illumination device 111 to oscillate the laser. The image information acquisition unit 122 acquires an image by controlling the photodetector 13 or the image sensor, and stores the acquired image data 134 in the storage device 1300. The blood vessel thickness calculator 123 calculates the thickness of the blood vessel from the image data 134 and stores the pulse wave data in the storage device. The thickness of the blood vessel depends on the variation in the detected light phase difference. As the blood vessel thickness increases, the phase difference variation also increases, and as the blood vessel thickness decreases, the phase difference variation also decreases. The pulse wave data comparison unit 124 compares the pulse wave data at two positions in the storage device 1300 to calculate the pulse wave propagation time. The input interface 125 inputs blood pressure data at the time of initialization. The parameter calculation unit 126 calculates parameters from the input blood pressure and pulse wave propagation time, and stores the parameter data 131 in the storage device 1300. The blood pressure value calculation unit 127 calculates blood pressure from the pulse wave propagation time and the parameter data 131 and outputs the blood pressure to the output interface 128. The output interface 128 outputs data to the display device 1400.

  The storage device 1300 includes parameter data 131, pulse wave data 132 at position A, pulse wave data 133 at position B, and image data 134.

  The parameter data 131 contains parameters necessary for calculating blood pressure. The pulse wave data 132 at the position A contains the pulse wave data measured at the position A. The pulse wave data at position B contains the pulse wave data measured at position B. The image data 134 stores the obtained image.

  The display device 1400 displays the output blood pressure value and the like. Note that the display device 1400 does not need to be disposed inside the blood pressure measurement device 1000 and may have an external display function such as a smartphone.

  Next, initialization and image acquisition operations of the blood pressure measurement device 1000 in the above embodiment will be described. The blood pressure measurement method in the blood pressure measurement device 1000 is divided into an initialization step and a blood pressure measurement step.

<Initialization step>
The arithmetic circuit 1200 executes the following initialization steps.

  FIG. 17 is a flowchart showing initialization steps of the blood pressure measurement method in blood pressure measurement apparatus 1000.

  In the initialization step, in order to execute initialization of parameters α and β necessary for blood pressure measurement, a general blood pressure measurement device is attached to one arm, and the blood pressure measurement device 1000 of the present embodiment is attached to the other arm. The

  The arithmetic circuit 1200 measures blood pressure with a general blood pressure measuring device (step S101). The arithmetic circuit 1200 inputs the maximum blood pressure displayed on the general blood pressure measurement device to the blood pressure measurement device 1000 of the present embodiment through the input interface 125 (step S102). The arithmetic circuit 1200 measures the pulse wave velocity such as 30 seconds before and after the maximum blood pressure is input (step S103). The pulse wave velocity is, for example, the median value of the measured values. The arithmetic circuit 1200 determines whether the systolic blood pressure is stable (step S104). The arithmetic circuit 1200 repeats steps S101 to S103, for example, at one minute intervals until the systolic blood pressure is stabilized. By repeating steps S101 to S103, a plurality of pairs of systolic blood pressure and pulse wave velocity are obtained. The arithmetic circuit 1200 uses the parameter arithmetic unit 126 to calculate the parameters α and β from the plurality of pairs using the least square method (step S105). The arithmetic circuit 1200 stores the calculated parameters α and β in the storage device 1300 (step S106). The initialization is thus completed.

  In summary, the arithmetic circuit 1200 calculates the parameters α and β by calculation using the blood pressure obtained by another blood pressure measurement device and the pulse wave propagation velocity before measuring the blood pressure. As described above, the pulse wave propagation velocity is obtained by dividing the distance between the position A and the position B by the pulse wave propagation time.

  It is desirable to execute the initialization step until the subject's own highest blood pressure is obtained by exercise as active as possible, and until the highest blood pressure is stabilized. The initialization step is preferably performed periodically, for example, once a month.

<Blood pressure measurement step>
The arithmetic circuit 1200 executes the following blood pressure measurement steps.

  FIG. 18 is a flowchart showing blood pressure measurement steps of the blood pressure measurement method in blood pressure measurement apparatus 1000.

  The arithmetic circuit 1200 instructs blood pressure measurement (step S201). The arithmetic circuit 1200 adjusts the light emitting devices 20a and 20b to oscillate light having a predetermined coherence length by the illumination condition adjusting unit 121, and causes the light emitting devices 20a and 20b to perform laser oscillation (step S202). The arithmetic circuit 1200 uses the image information acquisition unit 122 to acquire the returned scattered light image, and stores the acquired image in the storage device 1300 (step S203). The arithmetic circuit 1200 calculates two pulse wave data at the position A and the position B by the blood vessel thickness calculation unit 123, and stores the calculated two pulse wave data in the storage device 1300 (step S204). The arithmetic circuit 1200 uses the pulse wave data comparison unit 124 to compare the two pulse wave data (step S205). The arithmetic circuit 1200 calculates and outputs the blood pressure by the blood pressure value calculator 127 (step S206).

  The blood pressure measurement step can be measured at an arbitrary timing as long as the blood pressure measurement device 1000 of this embodiment is mounted. If the blood pressure measuring device 1000 of this embodiment is always worn, blood pressure can be constantly measured.

(Modification 1)
Next, initialization of the coherence length will be described as a modification. Hereinafter, differences from the above-described configuration will be described.

  FIG. 19 is a block diagram of another configuration example of the blood pressure measurement device 1000. Differences from the block diagram of FIG. 16 will be described.

  In the image acquisition unit 1100, the illumination device 111 includes two light emitting devices 20a and 20b having variable coherence lengths. The arithmetic circuit 1200 causes the illumination condition adjustment unit 121 to adjust the coherence length of the illumination device 111 to oscillate the laser. The arithmetic circuit 1200 determines the optimal coherence length by exchanging data between the illumination condition adjustment unit 121 and the pulse wave data comparison unit 124.

  By adjusting the coherence length appropriate for blood pressure measurement, it is possible to accurately measure the variation in the phase difference shown in the example of FIG. Therefore, it is desirable to initialize the coherence length.

  The step of initializing the coherence length is a step for optimizing blood pressure measurement in consideration of measurement conditions. The measurement conditions depend on differences in individual skin and blood vessel thickness, as well as the wearing state of the blood pressure measurement device 1000 of the present embodiment.

  The arithmetic circuit 1200 scans the coherence length and sets an optimal coherence length. The difference between the minimum and maximum of the pulse wave data is defined as the pulse wave peak. The arithmetic circuit 1200 adjusts the coherence length so that the pulse wave peak is maximized.

  Next, the initialization step and the blood pressure measurement step will be described.

<Initialization step>
The arithmetic circuit 1200 executes the following initialization step of the coherence length in addition to the initialization step shown in the example of FIG.

  FIG. 20 is a flowchart showing the coherence length initialization step of the blood pressure measurement method in blood pressure measurement apparatus 1000.

The arithmetic circuit 1200 sets the coherence length of at least one of the two light emitting devices 20a and 20b to L ₀ = 5 mm by the illumination condition adjusting unit 121, and measures pulse wave data of at least one of the position A and the position B. The coherence length is set to L ₁ = L ₀ + ΔL (step S301). ΔL is a scanning step and can be arbitrarily set. Here, ΔL = 5 mm. The arithmetic circuit 1200 sets the coherence length to L ₁ (= 10 mm) and measures pulse wave data (step S302). The arithmetic circuit 1200 compares the two pulse wave peaks of L ₀ and L ₁ and determines whether or not the pulse wave peak of L ₁ is lower than the pulse wave peak of L ₀ (step S303). If the pulse wave peak of L ₁ is higher than the pulse wave peak of L ₀ , the arithmetic circuit 1200 updates L ₀ to L ₁ and L ₁ to L ₁ + ΔL (step S304). Thereafter, the arithmetic circuit 1200 executes steps S302 and S303. Arithmetic circuit 1200, the pulse wave peak of _{L 1} until lower than the pulse wave peak of _{L 0,} repeats steps S304, S302 and S303. Arithmetic circuit 1200, the pulse wave peak of _{L 1} is is lower than the pulse wave peak of _{L 0,} the pulse wave data comparator 124, and calculates the _{L 0} as the best coherence length (step S305). The arithmetic circuit 1200 stores the optimal coherence length as the parameter data 131 in the storage device 1300 (step S306).

  In summary, the arithmetic circuit 1200 sequentially changes the coherence length of the light emitted from at least one of the light emitting devices 20a and 20b before measuring the blood pressure, and changes in time of at least one of the pulse wave data at the position A and the position B. The coherence length light that maximizes the peak is determined. Thereafter, when the blood pressure is measured, the arithmetic circuit 1200 causes the two light emitting devices 20a and 20b to emit light having the determined coherence length.

<Blood pressure measurement step>
The arithmetic circuit 1200 executes the blood pressure measurement step shown in the example of FIG.

(Modification 2)
Next, as a modification, a difference in detection time between two pulse waves will be described. Hereinafter, differences from the above-described configuration will be described.

  By adjusting the difference between the detection times of the two pulse waves, the pulse wave propagation time can be obtained with high accuracy. As a result, blood pressure measurement accuracy is improved.

FIG. 21 is a diagram schematically showing the lower surface of the blood pressure measurement device 1000. C ₁ -C ₂ in the example of FIG. 21 corresponds to C ₁ -C ₂ in FIG. In the example of FIG. 21, the photodetector 13 is arranged in the middle of the two light emitting devices 20a and 20b, and measures the variation in the phase difference due to the pulse wave. The light receiving surface of the photodetector 13 is divided into two regions 13a and 13b. The photodetector 13 detects light incident on each of the two regions 13a and 13b by dividing the time using a global shutter. The frame rate in each of the two regions 13a and 13b is preferably about 1000 fps or more. In this embodiment, the frame rate is 1000 fps.

  Assuming that light incident on each of the two regions 13a and 13b is detected at the same timing, the two pulse wave data are different at the positions A and B. Therefore, when calculating the pulse wave propagation time, it is necessary to check how much the two pulse wave data match. For example, by shifting the time of one pulse wave data and searching for the time when the sum of the errors of the two pulse wave data at each data point is minimized, or the time when the correlation function of the two pulse wave data is maximized There is a way to search. However, the resolution of such methods depends on the data point spacing. A high frame rate is required to increase the resolution. However, such highly accurate measurement is generally difficult.

  Therefore, it suffices to adjust a shift in detection time of light incident on each of the two regions 13a and 13b. By adjusting the difference in detection time, the pulse wave data measured at the two positions can be made to coincide with each other with high accuracy.

  FIG. 22 shows a phase difference variation due to the pulse wave measured at the position B (lower diagram in FIG. 14) shifted by the pulse wave propagation time, and a phase difference variation due to the pulse wave measured at the position A (FIG. 14). It is a figure which shows typically having made it match | combine. By matching the two pulse wave data, a time difference between both output values of the two pulse wave data is obtained.

  FIG. 23 is a diagram illustrating a method for adjusting a detection time shift in the photodetector 13. As shown in the upper diagram of FIG. 23, the time difference between the two output values when the pulse wave data matches is represented by subtracting the pulse wave propagation time from the shift in detection time. By adjusting the deviation of the detection time, the time difference between the two outputs can be made zero. As shown in the lower part of FIG. 23, if the detection time shift coincides with the pulse wave propagation time, the pulse wave propagation time can be measured with high accuracy.

  Further, as shown in the region surrounded by a circle in FIG. 22, the operation time of the photodetector can be reduced by measuring at 1000 fps, that is, at an interval of 1 ms only when measuring the peak of the pulse wave. Thereby, the consumption can be reduced. Low consumption is an important factor in mobile devices such as wearable terminals.

  Next, the initialization step and the blood pressure measurement step will be described.

<Initialization step>
The arithmetic circuit 1200 executes the initial step in the example of FIG. 17 or the initialization step in the examples of FIGS.

<Blood pressure measurement step>
The arithmetic circuit 1200 executes the following blood pressure measurement steps.

  FIG. 24 is another flowchart showing the blood pressure measurement steps of the blood pressure measurement method in blood pressure measurement apparatus 1000.

  The arithmetic circuit 1200 instructs blood pressure measurement (step S401). The arithmetic circuit 1200 adjusts the light emitting devices 20a and 20b so that the illumination condition adjusting unit 121 oscillates the light having the coherence length determined by the pulse wave data comparing unit 124, and causes the light emitting devices 20a and 20b to perform laser oscillation ( Step S402). The arithmetic circuit 1200 uses the image information acquisition unit 122 to acquire the two scattered light images returned with a given shift in detection time, and stores the acquired images in the storage device 1300 (step S403). The arithmetic circuit 1200 calculates the two pulse wave data at the position A and the position B by the blood vessel thickness calculation unit 123, and stores the calculated two pulse wave data in the storage device 1300 (step S404). The arithmetic circuit 1200 causes the pulse wave data comparison unit 124 to match the two pulse wave data with each other (step S405). The arithmetic circuit 1200 determines whether the output values of the two pulse wave data match (step S406). If the output values do not match, the arithmetic circuit 1200 changes the shift in detection time (step S407). The arithmetic circuit 1200 repeats steps S407 and S403 to 406 until the output values match. The arithmetic circuit 1200 calculates and outputs the blood pressure by the blood pressure value calculator 127 using the difference in detection time when the output values match as the pulse wave propagation time (step S406).

  In summary, the arithmetic circuit 1200 sequentially changes the detection time lag between the reflected light from the position A and the reflected light from the position B in the photodetector 13, thereby changing the time change of the pulse wave data at the position A. And a shift in detection time at which the time change of pulse wave data at position B coincides. The arithmetic circuit 1200 sets the determined detection time shift as the pulse wave propagation time.

  The blood pressure measurement step can be measured at an arbitrary timing as long as the blood pressure measurement device 1000 of this embodiment is mounted. If the blood pressure measuring device 1000 of this embodiment is always worn, blood pressure can be constantly measured. In the initial state, the given detection time lag may be 0 msec or may be a lag in the previous measurement.

  The present disclosure also includes a computer program that defines the operation executed by the arithmetic circuit 1200. Such a computer program is stored in a recording medium such as a memory in the blood pressure measurement apparatus 1000, and causes the arithmetic circuit 1200 to execute the above-described operation.

  Blood pressure can be easily measured at all times, and prevention of myocardium and cerebral infarction and hypertension can be measured.

DESCRIPTION OF SYMBOLS 100 Photodetection system 1 Control circuit 2 Light source 3 Outgoing light 4 Subject, to-be-tested part 5, 5a, 5A Scattered light 7 Condensing lens 8a Virtual object (collection of object points)
8b Image surface position image 9 Light-shielding film 9a Aperture, light-transmitting area 9A Light-shielding area 10 Photodetection layer 10a, 10A Light-receiving cell 11a, 11A Microlens 13 Photodetector 13a, 13b Area 14 Signal processing circuit 16 High frequency drive power supply 17 Prism 18 Aperture 19 Intensity modulator 20, 20a, 20b Light emitting device 1000 Blood pressure measurement device 1100 Image acquisition unit 1200 Arithmetic circuit 1300 Storage device 1400 Display device

Claims (6)

A light emitting device that emits light having a coherence length of 5 mm or more and 400 mm or less;
A photodetector that detects scattered light generated by being emitted from the light emitting device and scattered inside the object;
A measuring device comprising: The light detector detects the scattered light emitted from the surface of the object after being scattered within the object of 1 mm or more from the surface of the object.
The measuring device according to claim 1. The light emitting device
A laser light source that emits light having a frequency width of 1 MHz to 100 MHz;
A control circuit for causing the laser light source to emit light having a coherence length of 5 mm to 400 mm by driving the laser light source at a frequency of 50 MHz to 500 MHz;
Comprising
The measuring device according to claim 1 or 2. The photodetector is
A light-shielding film in which a plurality of light-transmitting regions and a plurality of light-shielding regions are alternately arranged in at least the first direction;
A light-receiving element that is arranged opposite to the light-shielding film and has a plurality of first light-receiving cells and a plurality of second light-receiving cells arranged on the imaging surface, wherein each of the plurality of first light-receiving cells is A light receiving element facing one of the plurality of light transmitting regions, and each of the plurality of second light receiving cells is opposed to one of the plurality of light shielding regions;
An optical coupling layer disposed between the light-shielding film and the light-receiving element, and when light having a predetermined wavelength is incident on the plurality of light-transmitting regions, a part of the light is directed in the first direction. An optical coupling layer that includes a propagating grating and transmits another part of the light incident on the plurality of light-transmitting regions;
Light incident on the position of each of the first and second light receiving cells by calculation using signals obtained from the plurality of first light receiving cells and signals obtained from the plurality of second light receiving cells. A signal processing circuit that outputs a signal indicating variation in the phase difference of
Having
The measuring device according to claim 1. The photodetector is an image sensor having a plurality of light receiving cells arranged two-dimensionally,
Each light receiving cell outputs a signal corresponding to the intensity of the received light.
The measuring device according to claim 1. The object is a living body, food, or concrete.
The measuring device according to claim 1.

Images