JP2019045247A - Measuring device - Google Patents

Abstract

A surface scattering component of light from a scatterer is suppressed even when disturbance light is present. A measuring device acquires information indicating a state in the living body by detecting light that has passed through the living body. The measuring device is disposed on a path of a light source that emits linearly polarized light, surface scattered light that is emitted from the light source and scattered on the surface of the living body, and internal scattered light that is scattered inside the living body. A quarter-wave plate, and an optical element that is arranged on a path of light that has passed through the quarter-wave plate and separates the light into first linearly polarized light and second linearly polarized light whose polarization directions are orthogonal to each other; And a first photodetector for detecting the first linearly polarized light and a second photodetector for detecting the second linearly polarized light. [Selection] Figure 7

Description

  The present disclosure relates to a measurement device that acquires internal information of a scatterer such as a living body.

  In the fields of biological measurement and material analysis, a method is used in which light is irradiated to an object and internal information of the object is acquired from information of light transmitted through the inside of the object. In such a method, it is required to be able to obtain scatterer internal information with high image quality, eg high contrast.

  As an example, a method for analyzing the activity state of blood has been developed by acquiring information on blood flow in living tissue such as the brain. In particular, a method for acquiring and analyzing information on cerebral blood flow using light such as near-infrared light or red light is called optical topography, and research is being conducted (for example, Non-Patent Document 1).

A problem in optical topography is surface scattering of light generated on the surface of a scatterer such as a living body. The surface scattered light has an intensity on the order of 10 ⁴ to 10 ⁶ times that of the internally scattered light returning through the inside of the scatterer. Therefore, there is a problem that the signal component of the internally scattered light to be acquired is buried in the signal component of the surface scattered light and the S / N becomes low. Therefore, there has been proposed a technique for removing the influence of surface scattered light by using an optical system in which two polarizers are disposed in a cross nicol arrangement (crossed nicol arrangement) between a light source and a light detector (for example, Patent Document 1).

Special table 2002-529713

Tomohiro Suto et al. "Multichannel Near-Infrared Spectroscopy in Depression and Schizophrenia: Cognitive Brain Activation Study", Biological psychiatry 55.5 (2004), pp 501-511. Valury V. Tuchin "Polarized light interaction with tissues", J. Biomed. Opt. 21 (7), 071114 (2016) Minami et al., "High-power THz wave generation in plasma induced by polarization adjusted by two-color laser pulses", App. Phys. Lett. 102, 041105 (2013) Kemp et al., "Security applications of teraherts technology", Terahertz for Military and Security Applications, R. Jennifer Hwu, Dwight L. Woolard, Editors, Proceedings of SPIE Vol. 5070 (2003)

  In the configuration of the conventional cross nicol arrangement, when disturbance light such as sunlight exists in the measurement environment, the light scattered on the surface of the object can not be sufficiently removed.

  The present disclosure provides a technique capable of suppressing surface scattering components of light from an object even in the presence of ambient light.

  The measuring device according to an aspect of the present disclosure acquires information indicating the in-vivo state by detecting light that has passed through the inside of the in-vivo. The measuring device includes a light source emitting linearly polarized light, surface scattered light emitted from the light source and scattered on the surface of the living body, and disposed on a path of internally scattered light scattered inside the living body 1 A quarter-wave plate, an optical element disposed on a path of light passing through the quarter-wave plate and separating the light into first linearly polarized light and second linearly polarized light whose polarization directions are orthogonal to each other; A first light detector for detecting the first linear polarization; and a second light detector for detecting the second linear polarization.

  The above general or specific aspects may be realized by a system, a method, an integrated circuit, a computer program, or a recording medium. Alternatively, the present invention may be realized by any combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a storage medium.

  According to an aspect of the present disclosure, even when disturbance light is present, internal information of an object can be acquired with a relatively high S / N.

FIG. 1 is a view schematically showing a general measurement device provided with a light source for irradiating light to a scatterer such as a living body and a light detector for detecting light scattered by the scatterer. FIG. 2 is a schematic view showing an example of an apparatus for removing the influence of surface scattered light by using a polarizer in a cross nicol arrangement. FIG. 3 is a view schematically showing the state of scattering of incident light in a cell which is the minimum unit scatterer in the inside of a living body. FIG. 4A is a view schematically showing how linearly polarized incident light passes through a quarter wave plate and a Wollaston prism. FIG. 4B is a view schematically showing the intensities of S-polarization and P-polarization detected in the example of FIG. 4A. FIG. 4C is a view schematically showing how incident light that is not linearly polarized passes through the quarter wavelength plate and the Wollaston prism. FIG. 4D is a view schematically showing the intensities of S-polarization and P-polarization detected in the example of FIG. 4C. FIG. 5 is a diagram for explaining the principle of light detection in the embodiment of the present disclosure. FIG. 6 is a view showing the time waveform (a) of the terahertz wave disclosed in Non-Patent Document 4 and its Fourier transform (b). FIG. 7 is a view schematically showing the configuration of the measurement device in the first embodiment. FIG. 8A is a diagram showing another configuration example of the first embodiment. FIG. 8B is a diagram showing a configuration example of the two light detectors 140A and 140B and the arithmetic circuit 160 shown in FIG. 8A. FIG. 9 is a view schematically showing a configuration of the measuring device 100 in the second embodiment. FIG. 10A is a view schematically showing a cross section of each light detector in the third embodiment. FIG. 10B is a plan view of the photodetector as viewed from the light incident side. FIG. 11 is a diagram illustrating an example of a signal processing method of the light detector 140. As illustrated in FIG. FIG. 12A is a cross-sectional view showing the positional relationship between incident light at four openings and three light detection cells located thereunder in the third embodiment. FIG. 12B is a diagram showing analysis results regarding the relationship between the random coefficient a of the phase of incident light and the detection signal. FIG. 13 shows an example in which the measurement device is used as a wearable terminal. FIG. 14 is a view showing an optical element replacing a lens. FIG. 15 is a diagram showing a configuration example of the measuring device 100 provided with the face plate 190. As shown in FIG. FIG. 16 is a diagram showing a configuration example of the measuring device 100 provided with the band pass filter 150. As shown in FIG.

  Before describing the embodiments of the present disclosure, first, surface scattering and diffuse backscattering in a scatterer will be described. Next, how to obtain ellipticity and elliptically polarized light with high accuracy will be described. Thereafter, embodiments of the present disclosure will be described.

  FIG. 1 is a view schematically showing a general measuring device provided with a light source 110 for irradiating light to a scatterer such as a living body and a light detector 140 for detecting light scattered by the scatterer.

  The light irradiated to the surface of the scatterer is either scattered at the surface or penetrates into the interior of the scatterer. The light path differs depending on whether it is scattered at the surface or penetrates inside. The manner of scattering varies depending on the size of the scattering particles. In a general scatterer such as a living body, Mie scattering occurs. Me backscattering occurs at the surface. Diffuse backscattering occurs inside the scatterer. Thus, when light is incident on the scatterer, surface scattering or diffuse backscattering occurs. In the present specification, light scattered near the surface of the scatterer is referred to as “surface scattered light”, and light scattered inside the scatterer is referred to as “internal scattered light”.

In general, surface scattered light has higher intensity than internal scattered light. The intensity of light emerging from the surface by diffuse backscattering depends on the path of the scattered light inside the scatterer. The longer the light path, the lower the intensity. The degree of attenuation inside the scatterer depends on the type of scatterer in question. For example, in the case of acquiring information about a depth of about 10 mm from the surface using an apparatus for observing the inside of a living body using near-infrared light, the light intensity is about 10 ^-6 to 10 ^-4 descend.

  From this, in order to acquire information inside the scatterer such as a living body, it is necessary to remove the influence of surface scattered light having high intensity. For that purpose, for example, Patent Document 1 discloses a configuration in which surface scattered light is removed using, for example, a polarizer in a cross nicol arrangement.

  FIG. 2 is a schematic view showing an example of an apparatus for removing the influence of surface scattered light by using a polarizer in a cross nicol arrangement. This device comprises two polarizers 170A, 170B whose polarization transmission axes are orthogonal to each other. The polarizer 170A is disposed on the light path from the light source 110 to the scatterer. The polarizer 170 B is disposed on the light path from the scatterer to the light detector 140. The polarizer 170A transmits only a linearly polarized component that is S-polarized light to the surface of the scatterer. The polarizer 170B transmits only a linearly polarized component that is P-polarized with respect to the surface of the scattered light. Here, S-polarization is polarization in which the electric field oscillates perpendicularly to the reflection surface, and P-polarization is polarization in which the electric field oscillates in parallel to the reflection surface.

  In general, scattering near the surface of the scatterer does not change the polarization state. However, in the scattering inside the scatterer, the longer the light path, the more the polarization state is disturbed and the proportion of elliptically polarized light increases. Elliptically polarized light can be said to be an overlapping state of various linear polarization states such as S-polarization and P-polarization. For this reason, a part of the light scattered and scattered inside the scatterer can pass through the polarizer 170B. On the other hand, light scattered near the surface can not pass through the polarizer 170B because it is S-polarized light. With such a configuration, it is possible to remove the influence of very strong surface scattered light that is noise, and obtain a signal of internally scattered light with high S / N.

  FIG. 3 is a view schematically showing a state of scattering of incident light in a cell which is a scatterer of the minimum unit in the inside of a living body as an example. There are many cells in the living body. Since the refractive index of each cell is different from that of its surroundings, light reflection and refraction occur on the surface (interface) of each cell. The light that has invaded into the living body repeats reflection and refraction at many cells. In the process, the polarization state changes.

  When light is incident on the cell surface from the outside of the cell and reflected, the change in phase differs depending on whether the light is S-polarized or P-polarized with respect to the interface. Similarly, when light is incident on the interface from inside the cell and reflected, the change in phase differs depending on whether the light is S-polarized or P-polarized with respect to the interface. The manner of this change depends on the refractive index of the particle and the external medium, as well as the angle of incidence on the interface. The frequent occurrence of reflection with such phase change in the living body disturbs the polarization state of the internally scattered light. When light passes through the interface, no change in phase occurs.

  In this way, generally, linearly polarized light also changes to elliptically polarized light inside a scatterer such as a living body. Furthermore, the more scattered, the more random the ellipticity of the ellipticity occurs. Generally, when light scattered inside a living body is detected, almost completely random polarization is detected. For example, according to Non-Patent Document 2, it is known that general normal tissues become approximately elliptically polarized light except for special conditions such as a tumor.

  Next, how to determine the ellipticity of elliptically polarized light with high accuracy will be described.

Ｅｘ０は電場のｘ成分の最大値を示している。Ｅｙ０は電場のｙ成分の最大値を示している。ωは光の角周波数を示している。δｔはＥｘとＥｙとの間の位相のずれを示している。δｔ＝０，πであれば、この光は直線偏光である。δｔ≠０,πであれば、この光は円偏光または楕円偏光である。 The x component of the electric field of a certain light traveling in the z direction in vacuum is Ex, and the y component is Ey. Here, x, y and z represent directions orthogonal to one another. Ex and Ey are represented by the following equation 1:

Ex0 indicates the maximum value of the x component of the electric field. Ey0 indicates the maximum value of the y component of the electric field. ω indicates the angular frequency of light. δt indicates the phase shift between Ex and Ey. If δt = 0, π, this light is linearly polarized. If δt ≠ 0, π, this light is circularly polarized or elliptically polarized.

  FIG. 4A is a view schematically showing an optical configuration in a measurement device which the present inventors are examining. In this measurement apparatus, a quarter wavelength plate (also referred to as a λ / 4 phase plate) 120 and two orthogonally polarized light (including circularly polarized light) or non-polarized light on the path of light returned from the object An optical element 130 for converting light into linearly polarized light is disposed. For the optical element 130, for example, a polarization element using birefringence, such as a Wollaston prism or a lotion prism, may be used.

  The present inventors considered that the configuration as shown in FIG. 4A can remove the linearly polarized light component of the light returned from the object and effectively obtain only the component of the internally scattered light. This measurement apparatus converts linearly polarized light into elliptically polarized light using a quarter-wave plate 120, and further separates elliptically polarized light into two orthogonal linear polarized lights using an optical element 130 such as a Wollaston prism.

  In the following description, an example in which a Wollaston prism is used as the optical element 130 will be described. Similarly to the optical element 130, the Wollaston prism is denoted by the reference numeral "130" and is described as "Wollaston prism 130". The Wollaston prism 130 is a type of polarizing beam splitter. The Wollaston prism 130 separates the incident light into S-polarization and P-polarization.

  When linearly polarized light passes through the quarter wave plate 120, it changes to elliptically polarized light (including circularly polarized light). Thereafter, when passing through the Wollaston prism 130 whose axis is inclined 45 ° with respect to the axis of the quarter-wave plate 120, the elliptically polarized light is separated into two S-polarized light and P-polarized light. At this time, the intensities of S-polarization and P-polarization become equal.

The linearly polarized light incident on the quarter-wave plate 120 is expressed by the following equation 2.

The light passing through the quarter-wave plate 120 is represented by the following equation 3.

Rewriting these equations with the ξ 軸 axis, which is the xy axis rotated 45 ° around the z axis, is rewritten into the following formula 4.

  FIG. 4B schematically shows the intensities of S-polarization and P-polarization to be detected. As shown in FIG. 4B, the intensity of S-polarization matches the intensity of P-polarization.

  On the other hand, FIG. 4C schematically shows an example in the case where incident light which is not linearly polarized light passes through the quarter wavelength plate 120 and the Wollaston prism 130. When the non-linearly polarized incident light passes through the quarter-wave plate 120, it changes into elliptically polarized light although it differs from that before incidence. Thereafter, when the light passes through the Wollaston prism 130 whose axis is inclined 45 ° with respect to the axis of the quarter-wave plate 120, the elliptically polarized light is split into two types of linear polarized light of S polarized light and P polarized light. The intensity of S polarized light and P polarized light at this time are different.

Elliptically polarized light incident on the quarter-wave plate 120 is expressed by the following equation 5.

In this case, the light passing through the quarter wavelength plate 120 is represented by the following equation 6.

Rewriting these equations with the ξ 軸 axis, which is rotated 45 ° around the x-y axis, can be rewritten as the following equation 7.

  FIG. 4D schematically shows the intensities of S polarized light and P polarized light detected in this case. As shown in FIG. 4D, the intensity of S-polarization and the intensity of P-polarization do not match.

  From the above, it can be seen that the component of linearly polarized light scattered on the surface can be removed by detecting the two linearly polarized light separated by the optical element 130 such as the Wollaston prism and taking the difference between the two signals. Further, as described later, according to such a configuration, the influence of disturbance light can be suppressed.

  FIG. 5 is a diagram for explaining the principle of light detection in the embodiment of the present disclosure. FIG. 5 schematically shows an optical configuration of a measuring apparatus that detects the state inside the living body using the light source 110 that emits stronger detection light (for example, laser light) in the presence of disturbance light. . This measuring device detects the difference in intensity between two linearly polarized light (S-polarized light and P-polarized light) separated by the optical element 130.

  Since the light returned from the living body includes surface scattered light and internally scattered light as described above, it is desirable to distinguish between them when acquiring information inside the living body. Furthermore, it is desirable to remove the effects of ambient light.

  Generally, ambient light is random linearly polarized light. For this reason, as described above, the information of the linearly polarized light disappears at the time of measuring the intensity difference of the finally detected S polarized light and P polarized light. As a result, it is possible to obtain only diffuse backscattering information having in vivo information.

  Table 1 shows the incident intensity, the incident polarization, and the emission intensity of the surface scattering component and the internal scattering component, the emission polarization, and the presence or absence of the final output of the light from the light source 110 and the disturbance light, respectively. If the light from the light source 110 is, for example, a laser beam stronger than the disturbance light, it is understood that the finally obtained output is such that the contribution of the light from the light source 110 is larger than the contribution of the disturbance light. Therefore, according to the above configuration, information inside the living body can be detected.

  The configuration using a quarter-wave plate and an optical element such as a Wollaston prism can also be used, for example, for detecting terahertz waves (for example, Non-Patent Documents 3 and 4). For example, there is a terahertz wave detection method called time-resolved measurement. In this method, the time waveform of the terahertz wave is acquired by performing measurement a plurality of times for each minute time. The measurement of each minute time is performed by injecting the probe light of the linear polarization of the ultrashort pulse simultaneously with the terahertz wave to an electro-optical (EO) crystal such as GaP or ZnTe. When a terahertz wave is incident on the EO crystal, birefringence occurs according to the electric field strength due to the Pockels effect. The amount of birefringence increases as the electric field strength of the terahertz wave increases. When linearly polarized probe light passes through the birefringence EO crystal, it changes to elliptically polarized light. The electric field strength of the terahertz wave can be measured by measuring the ellipticity using a measurement optical system including optical elements such as a 1⁄4 wavelength plate and a Wollaston prism. This measurement is performed a plurality of times every minute time while gradually shifting the overlapping time of the terahertz wave and the probe light.

Here, for reference, FIG. 2 disclosed in Non-Patent Document 4 is cited as FIG. FIG. 6 shows the time waveform (a) of the terahertz wave disclosed in Non-Patent Document 4 and its Fourier transform (b). The waveform in FIG. 6A is obtained from the measurement of each minute time. In fact, since the ellipticity of elliptically polarized light at each measurement point, that is, the ratio of the minor axis b to the major axis a (b / a) is measured, the ellipticity to be detected is in the range of -1 or more and 1 or less. It is in. The portion with the highest intensity in the frequency waveform shown in FIG. 9B indicates the signal component (S) that is in the elliptical polarization state. The lowest intensity portion in the frequency waveform indicates the noise component (N) in the portion where there is no signal, that is, the state of almost linear polarization. It is understood that this S / N ratio is a high value of five digits or more. That is, it can be seen that this optical configuration has the ability to measure the ellipticity of elliptically polarized light of at least 10 ^-5 times the intensity of the noise component.

From this, it can be understood that the information in the living body can be detected by the configuration of the embodiment of the present disclosure. According to Non-Patent Document 2, the ellipticity of elliptically polarized light of backward diffused scattered light measured in most living bodies is about 1/2, and the intensity is about 10 ^-6 to 10 ^-4 times that of surface scattered light. is there. Therefore, it is understood that it is feasible to separate surface scattered light and backward diffused scattered light according to the configuration of the embodiment of the present disclosure, and to detect only backward diffused scattered light in a scatterer such as a living body.

  In the configuration of FIG. 5, even if the signal acquired in the state where the light source 110 is turned off is subtracted from the signal acquired in the state where light is emitted from the light source 110, the influence of background disturbance light is eliminated. Good. In such a configuration, light source 110 may not emit light of higher intensity than ambient light. If necessary, a wavelength filter or a band pass filter that selectively transmits only light of a wavelength emitted from the light source 110 may be disposed at any position between the object and the light detector.

First Embodiment
Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In addition, detailed description more than necessary may be omitted. For example, detailed description of already well-known matters and redundant description of substantially the same configuration may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. The inventors provide the attached drawings and the following description so that those skilled in the art can fully understand the present disclosure. They are not intended to limit the claimed subject matter by these. In the present specification, components having similar functions are given the same reference numerals.

  FIG. 7 is a view schematically showing a configuration of a measurement device in the first exemplary embodiment of the present disclosure. The measuring device 100 acquires information indicating the activity state in the living body by detecting the light that has passed through the living body. The living body may be a skin-covered site, such as the human forehead, arms, legs, etc.

  The measuring apparatus 100 includes a light source 110, a quarter wavelength plate 120, a Wollaston prism 130, a first light detector 140A, a second light detector 140B, and an arithmetic circuit 160.

  The light source 110 emits linearly polarized light. The light source 110 may be, for example, a light source that emits light of a certain coherence length. For example, light source 110 may be a laser light source that emits laser light that is representative of coherent light. The light source 110 may emit light of constant intensity continuously or may emit single pulse light. The wavelength of light emitted by the light source 110 is arbitrary. However, when using a living body as a measurement target, the wavelength of the light source 110 may be set to, for example, about 650 nm or more and about 950 nm or less. This wavelength range is included in the red to near infrared wavelength range. In the present specification, not only visible light but also infrared light and ultraviolet light are included in the concept of "light".

  The quarter-wave plate 120 is disposed on a path of surface scattered light emitted from the light source 110 and scattered on the surface of the living body, and internally scattered light scattered inside the living body.

  The Wollaston prism 130 is disposed on the path of the light passing through the quarter-wave plate 120, and separates the light into first linearly polarized light and second linearly polarized light whose polarization directions are orthogonal to each other. Instead of the Wollaston prism 130, another polarizing optical element having the same function may be used. Such other optical elements include, for example, lotion prisms, Glan laser prisms, Nomarski prisms, polarization splitters, Savart plates and the like.

  The first light detector 140A is disposed at a position where the first linearly polarized light is incident. The first light detector 140A detects a first linear polarization and outputs a first signal. The second light detector 140B is disposed at a position where the second linearly polarized light is incident. The second light detector 140B detects the second linearly polarized light and outputs a second signal.

  The arithmetic circuit 160 performs in-vivo state by processing including a difference operation between the first signal output from the first light detector 140A and the second signal output from the second light detector. Generate and output the signal shown. In the present embodiment, the arithmetic circuit 160 outputs the difference signal between the first signal and the second signal as a signal of light scattered and scattered inside the living body. The arithmetic circuit 160 may generate information such as the state of blood, for example, blood pressure, pulse, hemoglobin concentration, etc., by arithmetic operation using the difference signal. The arithmetic circuit 160 may be an element outside the measuring device 100.

  FIG. 8A is a diagram showing another configuration example of the present embodiment. The measuring apparatus 100 in this example includes three lenses 170A and a galvano mirror 180 in addition to the components shown in FIG. The light emitted from the light source 110 enters the living body. The light emitted from the surface and the inside is collected by the lens 170 A and guided to the quarter wavelength plate 120 by the galvano mirror 180. The light transmitted through the quarter wave plate 120 is separated into two linearly polarized light (S polarized light and P polarized light) by the Wollaston prism 130. The S-polarization is collected by the lens 170B and detected by the first light detector 140A. P-polarized light is collected by a lens 170C and detected by a second light detector 140B.

  FIG. 8B is a diagram showing a configuration example of the two light detectors 140A and 140B and the arithmetic circuit 160 shown in FIG. 8A. In the present embodiment, each of the first light detector 140A and the second light detector 140B includes a photodiode (PD). The arithmetic circuit 160 outputs a signal indicating the difference between the first signal output from the photodiode in the first photodetector 140A and the second signal output from the photodiode in the second photodetector 140B. Do. The arithmetic circuit 160 shown in FIG. 8B includes an amplifier for amplifying the difference signal. The difference in voltage generated by each photodiode can be accurately measured by being input to the amplifier. With such a configuration, it is possible to output differential signals in an analog manner. By observing this output, it is possible to acquire a signal only inside the living body.

  In this embodiment, sample scanning can be performed by using the galvano mirror 180 (or galvano scanner) shown in FIG. 8A. Therefore, by acquiring data while synchronizing the signal obtained from the arithmetic circuit 160 with the operation of the galvano mirror 180, it is possible to obtain information of a two-dimensional image or the like.

  The arithmetic circuit 160 is not limited to the circuit shown in FIG. 8B, and may be, for example, a signal processing circuit such as a digital signal processor (DSP) or a microcontroller. The arithmetic circuit 160 controls the operation of the light source 110 and other components such as the galvano mirror 180 in addition to the above-described arithmetic operation. The measuring device 100 may include a display for displaying the result of the arithmetic processing of the arithmetic circuit 160.

Second Embodiment
Next, an exemplary second embodiment of the present disclosure will be described. Hereinafter, only differences from the first embodiment will be described.

  FIG. 9 schematically shows the configuration of the measuring device 100 in the second embodiment. The difference from the first embodiment is that the image sensor is used as the photodetectors 140A and 140B instead of PD in the first embodiment, and the galvano mirror 180 is omitted. The arithmetic circuit 160 can obtain internal information of a living body as two-dimensional data by calculating the difference between data obtained by the two light detectors 140A and 140B, which are image sensors.

  Thus, in the present embodiment, each of the light detectors 140A, 140B includes an image sensor. The arithmetic circuit 160 outputs a first signal output from at least one pixel of the image sensor in the first photodetector 140A and a first signal output from at least one pixel of the image sensor in the second photodetector 140B. The difference with the signal of 2 is calculated for each pixel. Thereby, the arithmetic circuit 160 can generate two-dimensional data indicating internal information of the living body.

Third Embodiment
Next, an exemplary third embodiment of the present disclosure will be described. Hereinafter, only differences from the first and second embodiments will be described.

  In the present embodiment, each of the light detectors 140A, 140B can detect the degree of coherence of the incident light. In the following description, in the case where the light detectors 140A and 140B are described without distinction, they are referred to as "light detectors 140".

  In each of the light detectors 140A and 140B in the present embodiment, 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 a first direction, and a light detection layer facing the light shielding film And a light coupling layer between the light shielding film and the light detection layer. The light detection layer has a plurality of first light detection cells respectively facing the plurality of light transmitting regions, and a plurality of second light detection cells respectively facing the plurality of light shielding regions. The light coupling layer has at least a laminated first transparent layer, a second transparent layer, and a third transparent layer in this order. The second transparent layer has a grating for propagating light in the first direction, and has a higher refractive index than the first and third transparent layers. The arithmetic circuit 160 outputs, for each of the light detectors 140A and 140B, a plurality of signals output from the plurality of first light detection cells and a plurality of signals output from the plurality of second light detection cells. Based on the signal, a signal is generated that indicates the coherence of light that has entered each of the light-transmissive regions and the light-shielded regions. The arithmetic circuit 160 generates a signal indicating the difference between the signal indicating the coherence of the light generated for the first light detector 140A and the signal indicating the coherence of the light generated for the second light detector 140B. Output.

  FIG. 10A is a view schematically showing a cross section of the light detector 140 in a plane along the light incident direction. FIG. 10B is a plan view of the light detector 140 as viewed from the side on which light is incident, more specifically, a plan view in an XY plane including a light shielding film 9 described later. FIG. 10A shows a cross section parallel to the XZ plane including the region surrounded by the broken line in FIG. 10B. As shown in FIG. 10B, with the cross-sectional structure shown in FIG. 10A as one unit structure, the unit structures are periodically arranged in the XY plane. In FIG. 10A and FIG. 10B, for convenience of explanation, three orthogonal axes (X axis, Y axis, Z axis) are shown. Similar coordinate axes are used in the following figures.

  The light detector 140 includes the light detection layer 10, the light coupling layer 12, and the light shielding film 9 in this order. In the example of FIG. 10A, these are stacked in the Z direction. A transparent substrate 9 b and a band pass filter 9 p are provided in this order on the light shielding film 9.

  The light detection layer 10 includes a plurality of light detection cells 10 a and 10 A in the in-plane direction (in the XY plane) of the light detection layer 10. The light detection cell may be referred to as a "pixel". The light detection layer 10 includes, from the side on which light is incident, microlenses 11a and 11A, a transparent film 10c, a metal film 10d such as a wiring, and a photosensitive portion formed of Si or an organic film. The photosensitive portions between the metal films 10d correspond to the light detection cells 10a and 10A. The microlenses 11a and 11A are disposed to face the light detection cells 10a and 10A, respectively. The light collected by the microlenses 11a and 11A and incident on the gap between the metal films 10d is detected by the light detection cells 10a and 10A.

The light coupling layer 12 is disposed on the light detection layer 10, and the first transparent layer 12c, the second transparent layer 12b, and the third transparent layer are disposed in the direction perpendicular to the surface of the light detection layer 10 (Z axis direction). 12a is provided in this order. The first transparent layer 12c and the third transparent layer 12a can be formed of, for example, SiO ₂ or the like. The second transparent layer 12b can be formed of, for example, Ta ₂ O ₅ or the like. 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 light coupling layer 12 may have a structure in which the high refractive index transparent layer 12 b and the low refractive index transparent layer 12 c are further repeated in this order as shown in FIG. 10A. FIG. 10A shows the structure repeated a total of six times. 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 of 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, 12a. The grating vector of the grating is parallel to the X axis in the in-plane direction (XY plane) of the light coupling layer 12. The XZ cross-sectional shape of the grating 12d is sequentially transferred also to the high refractive index transparent layer 12b and the low refractive index transparent layer 12c to be stacked. When the film formation of the transparent layers 12b and 12c has high directivity in the stacking direction, the transferability of the shape can be easily maintained by making the XZ cross 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. When the high refractive index transparent layer 12b includes the grating 12d, incident light can be coupled to light (referred to as waveguide light) propagating through the high refractive index transparent layer 12b.

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

  The light transmitting region 9 a in FIG. 10A corresponds to the light transmitting regions 9 a 1, 9 a 2, 9 a 3, 9 a 4 and the like in FIG. 10B. The light shielding area 9A in FIG. 10A corresponds to the light shielding areas 9A1, 9A2, 9A3, 9A4 and the like in FIG. 10B. That is, the light shielding film 9 has a plurality of light shielding regions 9A and a plurality of light transmitting regions 9a arranged in the in-plane direction (in the XY plane) of the light shielding film 9. The plurality of light shielding regions 9A respectively face the plurality of second light detection cells 10A. The plurality of light transmitting regions 9a respectively face the plurality of first light detection cells 10a. In this specification, the assembly of the first photodetection cells 10a may be referred to as "first photodetection cell group", and the assembly of the second photodetection cells 10A may be referred to as "second photodetection cell group". is there.

  In the present embodiment, each of the plurality of first light detection cells 10a is opposed to one of the plurality of light transmitting regions 9a. Similarly, each of the plurality of second light detection cells 10A is opposed to one of the plurality of light blocking regions 9A. Note that two or more first light detection cells 10a may be opposed to one light transmission region. Similarly, two or more second light detection cells 10A may be opposed to one light shielding area. The present disclosure also includes such forms.

  In the example shown in FIG. 10B, the plurality of light shielding regions 9A (9A1 to 9A4) form a checkered pattern. These light shielding regions 9A (9A1 to 9A4) may form a pattern other than the checkered pattern.

  The transparent substrate 9 b is disposed on the light incident side of the light shielding film 9. The transparent substrate 9b can be formed of, for example, a material such as SiO2. The band pass filter 9p is disposed on the light incident side of the transparent substrate 9b. The band pass filter 9 p selectively transmits only the light in the vicinity of the wavelength λ 0 emitted from the light source 110 among the incident light 5.

The light 5 incident on the light detector 140 passes through the band pass filter 9p and the transparent substrate 9b to reach the light blocking area 9A where the reflective film is formed and the light transmissive area 9a where the reflective film is removed as the light 6A, 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 light coupling layer 12. The light 6a incident on the light 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 at the upper and lower interfaces of the high refractive index transparent layer 12b. When the following equation (1) is satisfied, guided light 6 b is generated.
sin θ = N−λ0 / Λ (1)

  Here, N is the effective refractive index of the guided light 6b. θ is an incident angle with respect to the normal to the incident surface (XY surface). In FIG. 10A, light is vertically incident on the incident surface (θ = 0 o). In this case, the guided light 6 b propagates in the X direction in the XY plane. That is, the light incident on the light coupling layer 12 through the light transmitting region 9a is guided in the direction of the light shielding region 9A adjacent in the X direction.

  A component of light transmitted through the high refractive index transparent layer 12b and incident on 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 the equation (1). Although the guided light is generated in all the high refractive index transparent layers 12b, FIG. 10A shows only the guided light generated in the two layers. 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. 10A) with respect to the normal to the waveguide surface (XY surface). In the emitted light 6B1 and 6C1, the component directed upward (reflection film side) immediately below the light shielding area 9A is reflected by the light shielding area 9A, and becomes light 6B2 going downward along the normal to the reflection surface (XY plane) . The lights 6B1, 6C1 and 6B2 satisfy the formula (1) with respect to the high refractive index transparent layer 12b. Therefore, part of the light is guided light 6b and 6c again. The guided lights 6b and 6c also generate new radiations 6B1 and 6C1. These processes are repeated. As a whole, the component which has not been guided light passes through the light coupling layer 12 immediately below the light transmitting region 9a, and enters the microlens 11a as the transmitted light 6d. As a result, the component that did not become guided light is detected by the first light detection cell 10a. In fact, the component finally emitted after the wave guide also adds to the component which did not become the wave guide light. However, in this specification, such a component is also treated as a component that did not become guided light. Immediately below the region 9A, the component that has become guided light is emitted and enters the micro lens 11A as a radiation 6D. As a result, the component that has become guided light is detected by the second light detection cell 10A.

  Through the light transmitting region 9a, light is branched to the detector immediately below and the detectors on the left and right (that is, adjacent to the X direction), and detected.

  The detection light amounts in the first light detection cells facing the light transmitting regions 9a1, 9a2, 9a3 and 9a4 shown in FIG. 10B are denoted by q1, q2, q3 and q4, respectively. The detection light amounts of the second light detection cells facing the light shielding regions 9A1, 9A2, 9A3 and 9A4 shown in FIG. 10B are denoted as Q1, Q2, Q3 and Q4, respectively. q1 to q4 represent the detected light amounts of the light which did not become guided light. Q <b> 1 to Q <b> 4 represent detected light amounts of the light which has become guided light. In the first light detection cell 10a immediately below the light transmitting region 9a1, the light amount of the light which has become guided light is not detected. On the other hand, the second light detection cell 10A immediately below the light shielding area 9A2 does not detect the light quantity of the light which did not become guided light. Here, the detection light quantity Q0 = (Q1 + Q2) / 2 of the light which has become 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, the detection light quantity q0 = (q1 + q2) / 2 of the light which did not become guided light is defined at the detection position immediately below the light shielding area 9A2. Alternatively, q0 = (q1 + q2 + q3 + q4) / 4) may be defined. That is, in a certain area (a light shielding area or a light transmitting area), an average value of light amounts detected at detection positions immediately below pixels adjacent to the area in the X direction and / or Y direction is defined.

  By applying this definition to all the regions, it is possible to define the detected light quantity of the light which did not become guided light and the detected light quantity of the light which became guided light in all the pixels constituting the light detection layer 10.

  Based on the above definition, the arithmetic circuit 160 uses the detected amount of light of the light that did not become guided light and the detected amount of light that becomes light that is guided to calculate the distribution of the degree of coherence. Calculation processing such as generating an optical distribution image shown is performed. The arithmetic circuit 160 generates an optical distribution image by assigning the value calculated for each pixel to the value of the ratio of the two detected light amounts (or the value of the ratio of each light amount to the sum of these light amounts). be able to.

FIG. 11 shows an example of the signal processing method of the light detector 140. In FIG. 11, eight light detection cells (10A, 10a, etc.) are arranged along the grating vector of the grating. The light detection cells 10A and 10a face the light shielding area 9A and the light transmitting area 9a, respectively. The signals detected by the eight light detection cells are p _{0, k -4} , p _{1, k -3} , p _{0, k -2} , p _{1, k -1} , p _{0, k} , p _{1, k + 1} , p _{It is} assumed that _{0, k + 2} and p1 _{, k + 3} . For example, from the signals p _{1, k-1} and p _{1, k + 1 on} the left and right of p _{0, k} , the average value (p _{1, k-1} + p _{1, k + 1} ) / 2 is defined as the interpolation value p _{1, k} . Similarly, from the signals p _{0, k -2} and p _{0, k on} the left and right of p _{1, k -1,} the mean value (p _{0, k -2} + p _{0, k} ) / 2 is interpolated value p _{0, k} Defined as _-1 . From the detected value _{p 0, k} and the interpolation value _{p 1, k,} P0 modulation _{p 0, k / (p 0} , k + p 1, k) or P1 modulation factor _{p 1, k / (p 0} , k + p 1, _k ) is calculated. These modulation degrees can be used as detection signals.

  FIG. 12A is a cross-sectional view showing the positional relationship between incident light at four openings and three light detection cells located thereunder in the present embodiment. Light having different phases randomly enters the four apertures. In FIG. 12A, ω is the angular frequency of light (ω = 2πc / λ0, c is the speed of light), t is time, r1, r2, r3, r4 are random functions, and a is a random coefficient. The random functions r1, r2, r3 and r4 are functions taking random values between 0 and 1. The random coefficient a is the amplitude of the random value.

  FIG. 12B is a diagram showing analysis results regarding the relationship between the random coefficient a of the phase of incident light and the detection signal. A detector immediately below the light shielding portion located in the middle of the four openings is denoted by 10A, and light detection cells immediately below the light transmitting portions respectively located at both sides thereof are denoted by 10a and 10a '. Let their detected light amounts be P1, P0 and P0 ', respectively. The detection signal is defined by 2P1 / (P0 + P0 '). The rhombic marks indicate TE mode incidence (S polarized light), the square marks indicate TM mode incident (P polarized light), and the triangular marks indicate TEM mode incident (randomly polarized light or circularly polarized light or polarized light in the 45-degree direction). Focusing on TE mode incidence and TEM mode incidence, the detection signal decreases as the coefficient a increases. a = 0 corresponds to the case of coherent and in phase alignment. a = 1 corresponds to incoherence. Therefore, the degree of coherence (randomness of the phase) of the incident light can be known from the magnitude of the detection signal. Similarly, the difference in the phase of incident light can also be measured.

  A detailed description of the light detector 140 is disclosed in U.S. Patent Application Publication 2016/360967 and U.S. Patent Application Publication 2017/023410. The entire disclosure content of US Patent Application Publication No. 2016/360967 and US Patent Application Publication No. 2017/023410 is incorporated herein by reference.

  The measuring apparatus 100 in this embodiment is the same configuration as the configuration shown in FIG. However, the light detectors 140A and 140B are not general image sensors, and have the above-described structure. The arithmetic circuit 160 can acquire information inside the living body as two-dimensional data by obtaining the difference between the data obtained from the two light detectors 140A and 140B.

(Other embodiments)
FIG. 13 shows an example in which the measurement device in any of the above embodiments is used for a wearable terminal. On the living body side of the wearable terminal, the light source 110 and the photodetectors 140A and 140B and the like in any of the above embodiments are disposed. Such a device can measure blood pressure or blood glucose level.

  FIG. 14 shows an optical member instead of a lens for simplifying the optical configuration in each of the above embodiments. The optical member has a first surface and a second surface, and can transfer an optical image incident on the first surface to the second surface. As the optical member, an element generally called a face plate can be used. The face plate is produced, for example, by setting a large number of thin drawn glass fibers with an optical resin having light absorbing properties. By adjusting the refractive index of the glass fiber and the refractive index of the optical resin, only light incident at an arbitrary incident angle can be received. By using a face plate, it is possible to transfer an image at a fixed distance without using a lens. By using this, it becomes easy to mount the optical configuration of each of the above-described embodiments in a casing such as a thin wearable terminal.

  FIG. 15 shows a configuration example of a measuring device 100 provided with a face plate 190. The measuring device 100 includes a face plate 190 on the path of light incident on the light detectors 140A and 140B from a living body. The position of the face plate 190 is not limited to the position shown in FIG.

  In each of the above embodiments, the arithmetic circuit 160 is obtained from the light detectors 140A and 140B in the state where light is emitted from the light source 110 and the signals obtained from the light detectors 140A and 140B in the state where light is not emitted from the light source 110. The influence of disturbance light included in the signal indicating the in-vivo state may be reduced based on the difference from the signal to be transmitted.

  The measuring apparatus 100 has a band pass filter for selectively transmitting light in a first wavelength range, which is a wavelength range of light emitted from the light source 110, on a path of light incident on the light detectors 140A and 140B from a living body. You may provide further. For example, as shown in FIG. 16, a band pass filter 150 may be disposed between an object such as a living body and the quarter wavelength plate 120. By disposing the band pass filter 150, it is possible to remove light of wavelengths other than the wavelength range of the light emitted by the light source 110, so that detection with higher accuracy is possible.

  In each of the above embodiments, the individual optical elements may be replaced with other optical elements having similar effects. Devices configured with such replacement are also within the scope of the present disclosure.

  The present disclosure can be used for scattered light measurement applications such as so-called optical tomography. For example, it can be used for a wearable terminal or the like equipped with a living body measurement function.

9 light shielding film 10 light detection layer 12 light coupling layer 100 measurement device 110 light source 120 quarter wavelength plate 130 optical element (Wollaston prism)
140A First photodetector 140B Second photodetector 150 Band pass filter 160 Arithmetic circuit 170A, 170B, 170C Lens 180 Galvano mirror 190 face plate

Claims (8)

A measuring apparatus for acquiring information indicating a state in the living body by detecting light having passed through the living body,
A light source emitting linearly polarized light;
Surface scattered light emitted from the light source and scattered on the surface of the living body, and a quarter-wave plate disposed on a path of internally scattered light scattered inside the living body;
An optical element disposed on a path of light passing through the quarter-wave plate to separate the light into first linearly polarized light and second linearly polarized light whose polarization directions are orthogonal to each other;
A first light detector for detecting the first linearly polarized light;
A second light detector for detecting the second linearly polarized light;
Measuring device equipped with   The signal indicating the in-vivo state is processed by processing including a difference operation between the first signal output from the first photodetector and the second signal output from the second photodetector. The measurement device according to claim 1, further comprising an arithmetic circuit that generates and outputs. Each of the first light detector and the second light detector includes a photodiode.
The first signal is output from the photodiode in the first photodetector,
The second signal is output from the photodiode in the second photodetector,
The arithmetic circuit outputs a signal indicating a difference between the first signal and the second signal.
The measuring device according to claim 2. Each of the first and second light detectors includes an image sensor,
The arithmetic circuit is configured to output a first signal output from at least one pixel of the image sensor in the first light detector and at least one pixel of the image sensor in the second light detector. Output a signal indicating the difference from the second signal,
The measuring device according to claim 2. Each of the first and second photodetectors
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 a first direction;
A plurality of first light detection cells, each of which is a light detection layer facing the light shielding film, and a plurality of second light detection cells, which respectively face the plurality of light shielding regions. A light detection layer having
A light coupling layer between the light shielding film and the light detection layer, comprising at least a first transparent layer, a second transparent layer, and a third transparent layer stacked in this order; An optical coupling layer having a grating for propagating light in the first direction and having a higher refractive index than the first and third transparent layers;
Equipped with
The arithmetic circuit is
For each of the first and second photodetectors, a plurality of signals respectively output from the plurality of first light detection cells, and a plurality of signals respectively output from the plurality of second light detection cells To generate a signal indicating the coherence of light incident on each light-transmissive region and the position of each light-shielded region,
Generating and outputting a signal indicating the difference between the signal indicating the coherence of the light generated for the first photodetector and the signal indicating the coherence of the light generated for the second photodetector;
The measuring device according to claim 2.   The arithmetic circuit detects signals obtained from the first and second photodetectors in a state in which the light is not emitted from the light source, and detects the first and second light in a state in which the light is emitted from the light source The measuring apparatus according to any one of claims 2 to 5, wherein the influence of disturbance light included in the signal indicating the in-vivo state is reduced based on the difference between the signal and the signal obtained from the device. The light source emits light in a first wavelength range,
And a band pass filter for selectively transmitting light in the first wavelength range on a path of light incident on the first and second light detectors from the living body.
The measuring device according to any one of claims 1 to 6.   A first surface and a second surface are provided on paths of light incident on the first and second light detectors from the living body, and an optical image incident on the first surface is the second optical image. The measuring device according to any one of claims 1 to 7, further comprising an optical member to be transferred to the surface of the sheet.

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