WO2020036014A1

WO2020036014A1 - Light detection device and light detection system

Info

Publication number: WO2020036014A1
Application number: PCT/JP2019/026871
Authority: WO
Inventors: 青児西脇; 鳴海　建治
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2018-08-13
Filing date: 2019-07-05
Publication date: 2020-02-20
Also published as: JP2021179310A

Abstract

A light detection device according to one embodiment of the present disclosure is provided with: a light blocking film that comprises a plurality of light transmitting regions and a plurality of light blocking regions, which are alternately arranged in a first direction and in a second direction that intersects with the first direction; a light detector that has an imaging surface and comprises a plurality of first light detection cells and a plurality of second light detection cells, which are arranged on the imaging surface; and a light coupling layer which is positioned between the light blocking film and the light detector, and which comprises a grating that causes some of light to propagate in the first direction and in the second direction when light is incident on the plurality of light transmitting regions.

Description

Photodetector and photodetection system

The present disclosure relates to a light detection device and a light detection system.

Light is an electromagnetic wave and is characterized by optical properties such as polarization or coherence in addition to wavelength or intensity. For example, Patent Literature 1 discloses a light detection device that utilizes light coherence among optical characteristics.

Patent No. 6044862

The present disclosure provides a photodetector capable of measuring the degree or phase of coherence of transmitted light, reflected light, and / or scattered light from an object without using a complicated optical system.

The light detection device according to one aspect of the present embodiment includes a light-shielding device including a plurality of light-transmitting regions and a plurality of light-shielding regions alternately arranged in a first direction and a second direction intersecting the first direction. A photodetector having a film, an imaging surface, and a plurality of first light detection cells and a plurality of second light detection cells arranged on the imaging surface; A grating that propagates a part of the light in the first direction and the second direction when incident; and a light coupling layer located between the light shielding film and the photodetector. .

According to the light detection device according to an aspect of the present disclosure, it is possible to measure the degree of coherence or phase of transmitted light, reflected light, and / or scattered light from an object without a complicated optical system. it can.

FIG. 1 is a diagram schematically illustrating an example of a light detection system according to the present embodiment. FIG. 2A is a diagram schematically illustrating an object and propagation of scattered light incident on one translucent region in the example of the photodetector according to the present embodiment. FIG. 2B is a perspective view schematically showing propagation of light incident on one light-transmitting region in the example of the photodetector in the present embodiment. FIG. 2C is a plan view schematically illustrating an example of the photodetector according to the present embodiment when viewed from the light incident side. FIG. 3A is a diagram schematically illustrating an arrangement of detection signals corresponding to each of the plurality of light-transmitting regions and the plurality of light-shielding regions. FIG. 3B is a diagram illustrating a flow up to generation of a modulation degree signal in a region surrounded by a thick line illustrated in FIG. 3A. FIG. 4A is a perspective view schematically showing propagation of light incident on one translucent region in a modification of the photodetector in the present embodiment. FIG. 4B is a plan view schematically showing a first modified example of the photodetector according to the present embodiment when viewed from the light incident side. FIG. 4C is a plan view schematically illustrating a second modified example of the photodetector according to the present embodiment when viewed from the light incident side. FIG. 5A is a diagram schematically illustrating a conventional light detection system. FIG. 5B is a diagram schematically showing an object, a condensing lens, and propagation of scattered light incident on one light-transmitting region in a conventional light detection device. FIG. 6A is a cross-sectional view schematically illustrating a conventional photodetector. FIG. 6B is a plan view schematically showing a conventional photodetector. FIG. 7A is a cross-sectional view schematically illustrating an optical configuration when a target is a phase step plate. FIG. 7B is a diagram illustrating an observation image of the TE mode when light having a long coherence length of 1 m or more is incident. FIG. 7C is a diagram illustrating an observation image of the TM mode when light having a long coherence length of 1 m or more is incident. FIG. 7D is a diagram illustrating an observation image of the TE mode when light having a short coherence length of about 30 μm is incident. FIG. 7E is a diagram showing a TM mode observation image when light having a short coherence length of about 30 μm is incident. FIG. 8 shows a phase difference d obtained by measuring phase steps having various depths and a modulation degree signal P ₁ / (P ₁ + P ₀ ) when light having a long coherence length of 1 m or more is incident. FIG.

(History leading to one embodiment of the present disclosure)
Hereinafter, the principle of the conventional photodetector will be described.

FIG. 5A is a diagram schematically showing a conventional photodetection system 200. The light detection system 200 includes the light source 2, the condenser lens 7, the light detection device 13, the control circuit 1, and the arithmetic circuit 14.

(4) The light source 2 irradiates the object 4 with light 3 having a constant coherence length. The light source 2 is, for example, a laser device that emits light having a relatively long coherence length or an LED device that emits light having a short coherence length. The light source 2 may continuously emit light having a constant intensity, or may emit pulsed light. The wavelength of the light 3 emitted from the light source 2 is arbitrary. When the object 4 is a living body, the wavelength of the light source 2 can be set to, for example, about 650 nm or more and about 950 nm or less. This wavelength range is included in the wavelength range from red to near infrared rays. In this specification, the term “light” is used not only for visible light but also for infrared light.

The condensing lens 7 condenses the scattered light 5a and the scattered light 5A generated on the surface of the object 4 or in the object 4 by the light 3 emitted from the light source 2. Here, scattered light is used in a broad sense including transmitted light or reflected light. The condensed light is formed as an image 8b on the image plane position of the condenser lens 7. A substantial object 8a exists on the object 4 side of the condenser lens 7 corresponding to the image 8b. The object 8a is a collection of object points.

The photodetector 13 is disposed at the image plane position of the condenser lens 7. The light detecting device 13 detects the scattered light 5a and the scattered light 5A collected by the collecting lens 7. Details of the structure of the light detection device 13 will be described later.

The arithmetic circuit 14 performs arithmetic processing on the signal detected by the light detection device 13. The arithmetic circuit 14 may be an image processing circuit such as a digital signal processor (DSP).

The control circuit 1 executes, for example, a program recorded in a memory to detect light by the photodetector 13, perform arithmetic processing by the arithmetic circuit 14, the amount of light emitted from the light source 2, the lighting timing, the continuous lighting time, or the emission wavelength. Alternatively, the coherence length is controlled. The control circuit 1 can be an integrated circuit such as a central processing unit (CPU) or a microcomputer, for example. The control circuit 1 and the arithmetic circuit 14 may be realized by one integrated circuit.

The light detection system 200 may include a display (not shown) that displays the result of the arithmetic processing performed by the arithmetic circuit 14.

FIG. 5B is a diagram schematically showing the object 4, the condenser lens 7, and the propagation of the light 5 incident on one translucent area 9a in the conventional photodetector 13. In FIG. 5B, the light transmitting region 9a corresponds to an opening. In the example shown in FIG. 5B, an example of propagation of light 3, light 5, light 5s, light 6a, guided light 6b, transmitted light 6d, and emitted light 6D, which will be described later, is indicated by arrows. In practice, the distribution of the light 3 spreads in a direction perpendicular to the propagation direction. In the example illustrated in FIG. 5B, the region hatched by the horizontal line passes through the stop 7 c among the light scattered within the target object 4 and emitted from the positions L and R when the target object 4 is irradiated with the light 3. Represents light incident on the photodetector 13. Actually, light that exits from a position other than the position L and the position R of the object 4 and passes through the aperture 7c and enters the photodetector 13 is also omitted, but is omitted. In addition, there is light incident on the photodetector 13 from the translucent region 9a other than the above, but is omitted. In the following figures, an example of light propagation is indicated by an arrow.

The object 4 is a scatterer. Light rays propagating inside the object 4 repeat scattering inside. The condenser lens 7 includes a front lens 7a, a stop 7c, and a rear lens 7b. The condenser lens 7 forms a double telecentric lens or an image telecentric lens. In the case of both telecentric lenses, only the light along the optical axis of the lens out of the light scattered on the object 4 becomes the light 5 that passes through the aperture 7c and enters the photodetector 13. The light 5s, which is stray light shifted from the optical axis, is blocked by the stop 7c. The light 5 is perpendicularly incident on one light-transmitting region 9 a of the light detection device 13.

6A and 6B are a cross-sectional view and a plan view, respectively, schematically showing the conventional photodetector 13. 6A and 6B show three orthogonal X, Y, and Z axes for convenience of description. The same applies to other figures. As used herein, "X direction" means both the same direction as the X direction and the opposite direction. The same applies to the Y direction and the Z direction. FIG. 6A is a cross-sectional view of the photodetector 13 in the XZ plane along the direction in which light is incident. The cross-sectional view includes a region surrounded by a broken line shown in FIG. 6B. FIG. 6B is a plan view in the XY plane of the light detection device 13 when viewed from the light incident side. The plan view includes a light-shielding film described later. With the cross-sectional structure shown in FIG. 6A as one unit structure, the unit structures are periodically arranged in the XY plane.

The photodetector 13 includes the photodetector 10, the optical coupling layer 12, and the light shielding film 9 in this order. In the example shown in FIG. 6A, these are stacked in the Z direction. In the example shown in FIG. 6A, a transparent substrate 9b and a bandpass filter 9p are arranged on the light shielding film 9 in this order.

The photodetector 10 includes a plurality of first photodetection cells 10a and a plurality of second photodetection cells 10A arranged on an imaging plane parallel to the XY plane. The photodetector 10 includes a plurality of first microlenses 11a and a plurality of second microlenses 11A arranged in an XY plane, a transparent film 10c, a metal film 10d such as a wiring, and the like. , Si or an organic film. Each of the plurality of photosensitive units is arranged between two adjacent metal films 10d in the X direction or the Y direction. The plurality of photosensitive units correspond to the plurality of first light detection cells 10a and the plurality of second light detection cells 10A. Each of the plurality of first microlenses 11a is arranged so as to face one of the plurality of first photodetection cells 10a. Each of the plurality of second microlenses 11A is disposed so as to face one of the plurality of second photodetection cells 10A. Light collected by each of the plurality of first microlenses 11a and incident on the gap between two adjacent metal films 10d is detected by one of the plurality of first light detection cells 10a. Light condensed by each of the plurality of second microlenses 11A and incident on a gap between two adjacent metal films 10d is detected by one of the plurality of second photodetection cells 10A.

The optical coupling layer 12 is located between the light shielding film 9 and the photodetector 10. The optical coupling layer 12 is disposed on the photodetector 10. The optical coupling layer 12 includes a low-refractive-index transparent layer 12c, a high-refractive-index transparent layer 12b, and a low-refractive-index transparent layer 12a in this order in a direction perpendicular to the surface of the photodetector 10. The high refractive index transparent layer 12b is on the low refractive index transparent layer 12c. The low refractive index transparent layer 12a is on the high refractive index transparent layer 12b. The low-refractive-index transparent layer 12c and the low-refractive-index transparent layer 12a are formed of, for example, SiO ₂ . The high refractive index transparent layer 12b is formed of, for example, Ta ₂ O ₅ . The high refractive index transparent layer 12b has a higher refractive index than the low refractive index transparent layer 12c and the low refractive index 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 the example shown in FIG. 6A, a structure repeated six times in total is shown. The high refractive index transparent layer 12b is sandwiched between the low refractive index transparent layer 12c and the low refractive index transparent layer 12a. Therefore, the high refractive index transparent layer 12b functions as a waveguide layer. A grating 12d having a pitch Λ is formed over the entire surface between the high refractive index transparent layer 12b and the low refractive index transparent layer 12c and / or between the high refractive index transparent layer 12b and the low refractive index transparent layer 12a. You. The grating vector of the grating 12d is parallel to the X direction in the XY plane of the optical coupling layer 12. The shape of the cross section of the grating 12d in the XZ plane is sequentially transferred to the laminated high-refractive-index transparent layer 12b and low-refractive-index transparent layer 12c. The high refractive index transparent layer 12b and the low refractive index transparent layer 12c may have high directivity in the stacking direction. At this time, by making the shape of the cross section of the grating 12d in the XZ plane into an S-shape or a V-shape, the transferability of the shape is easily maintained.

The grating 12d is formed on at least a part of the high-refractive-index transparent layer 12b. The incident light can be coupled to the guided light propagating through the high refractive index transparent layer 12b by the grating 12d. The incident light is guided in the optical coupling layer 12 by the grating 12d along the direction of the lattice vector having the pitch Λ.

隙間 The gap between the optical coupling layer 12 and the photodetector 10 may be, for example, as narrow as possible or may be in close contact. The gap and the space between the first micro lens 11a and the second micro lens 11A may be filled with a transparent medium such as an adhesive. When a transparent medium is filled, the first microlenses 11a and the second microlenses 11A have a refractive index sufficiently larger than that of the filled transparent medium in order to obtain a lens effect.

(4) The light shielding film 9 includes a plurality of light shielding regions 9A and a plurality of light transmitting regions 9a in the XY plane. The plurality of light-shielding regions 9A and the plurality of light-transmitting regions 9a are alternately arranged in the X direction and the Y direction. In the example shown in FIG. 6A, the plurality of light shielding regions 9A and the plurality of light transmitting regions 9a are formed by patterning a metal reflection film formed on a transparent substrate 9b described later. The metal reflection film is formed of, for example, Al. The light transmitting area 9a shown in FIG. 6A corresponds to, for example, the light transmitting areas 9a1, 9a2, 9a3, and 9a4 shown in FIG. 6B. The light shielding area 9A shown in FIG. 6A corresponds to, for example, the light shielding areas 9A1, 9A2, 9A3, and 9A4 shown in FIG. 6B. Each of the plurality of light shielding regions 9A faces one of the plurality of second light detection cells 10A. Each of the plurality of light transmitting regions 9a faces one of the plurality of first light detection cells 10a. In the example shown in FIG. 6B, the plurality of light shielding regions 9A form a checker pattern. The plurality of light-shielding regions 9A may be formed in a pattern other than the checker pattern, for example, may be formed in a stripe pattern.

In the present embodiment, each of the plurality of light-shielding regions 9A faces one of the plurality of second photodetection cells 10A, and each of the plurality of light-transmitting regions 9a corresponds to one of the plurality of first photodetection cells 10a. However, the present invention is not limited to such a configuration. For example, when light transmitted through the light shielding film 9 and the light coupling layer 12 is condensed on the photodetector 10 by a lens, each of the light shielding regions 9A faces one of the plurality of second light detection cells 10A. The invention is not limited thereto, and each of the plurality of light transmitting regions 9a does not necessarily face one of the plurality of first light detection cells 10a. Light emitted from immediately below each of the light shielding regions 9A is detected by one of the plurality of second light detection cells 10A, and light emitted from immediately below each of the plurality of light transmitting regions 9a is detected by a plurality of first light detection cells. A plurality of light-transmitting regions, a plurality of light-shielding regions, a plurality of first light-detecting cells, a plurality of second light-detecting cells, and optical systems around these are arranged so as to be detected by one of the cells 10a. It may be.

The transparent substrate 9b is disposed on the light incident side of the light shielding film 9. Transparent substrate 9b is formed of a material such as SiO _2. The bandpass filter 9p is arranged on the light incident side of the transparent substrate 9b. The bandpass filter 9p selectively transmits only light near the wavelength λ of the light 5.

The light 5 passes through the band-pass filter 9p and the transparent substrate 9b to reach 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 light 6a, respectively. The light 6A is blocked by the light blocking region 9A. The light 6a transmits through the light transmitting region 9a and enters the optical coupling layer 12. Light 6a incident on the optical coupling layer 12 is incident on the high refractive index transparent layer 12b via the low refractive index transparent layer 12a. A grating 12d is formed on the upper and lower interfaces of the high refractive index transparent layer 12b. If 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 the incident angle of the guided light 6b with reference to the normal to the XY plane that is the incident surface. λ is the wavelength of the guided light 6b. Λ is the grating pitch of the grating 12d. In the example shown in FIG. 6A, light is incident perpendicular to the incident surface. Therefore, θ = 0. In this case, the guided light 6b propagates in the XY plane in the X direction.

(4) The component that passes through the high refractive index transparent layer 12b and enters the lower layer also enters all the lower layer high refractive index transparent layers 12b. As a result, the guided light 6c is generated under the same conditions as in the equation (1). Thus, guided light is generated in all the high refractive index transparent layers 12b. In FIG. 6A, guided light generated in the two layers is representatively shown. Similarly to the guided light 6b, the guided light 6c propagates in the XY plane in the X direction. The guided light 6b and the guided light 6c propagate while emitting light in the vertical direction at an angle θ with reference to the normal to the XY plane that is the waveguide surface. In the example shown in FIG. 6A, θ = 0. Of the emitted light 6B1 and the emitted light 6C1, the component toward the upper reflective film side is reflected by the reflective film of the light-shielding region 9A immediately below the light-shielding region 9A, and is lowered along the normal line of the XY plane as the reflective surface. It becomes light 6B2 toward. The emitted light 6B1, the emitted light 6C1, and the light 6B2 satisfy Expression (1) in the high refractive index transparent layer 12b. Therefore, part of the emitted light 6B1, the emitted light 6C1, and the light 6B2 becomes the guided light 6b and the guided light 6c again. The guided light 6b and the guided light 6c newly generate radiation light 6B1 and radiation light 6C1, respectively. In this way, a similar process is repeated. As a whole, immediately below the light-transmitting region 9a, a component that did not become guided light is transmitted through the optical coupling layer 12, enters the first microlens 11a as transmitted light 6d, and is transmitted by the first light detection cell 10a. Is detected. Actually, some components are finally radiated after guided, but here, they are classified as components that did not become guided light. Immediately below the light-shielding region 9A, the component that has become the guided light is emitted, enters the second microlens 11A as emitted light 6D, and is detected by the second light detection cell 10A.

The incident light is branched into the light detection cell immediately below and the right and left light detection cells through the light transmitting region 9a. Light branched to the optical detection cell and the left and right optical detecting cell immediately below, as shown in Figure 5B, are detected as a signal P ₀ and the signal P _1.

４Suppose that four light detection cells respectively facing the light transmitting regions 9a1 to 9a4 detect the light amounts of q1 to q4, respectively. Similarly, it is assumed that four light detection cells respectively opposing the light shielding area 9A1 to the light shielding area 9A4 detect the light amounts of Q1 to Q4, respectively. q1 to q4 are detected light amounts of light that did not become guided light. Q1 to Q4 are the detected light amounts of the light that has become the guided light. In the light detection cell immediately below the light transmitting region 9a1, the light amount of the light that has become the guided light is not detected. In the light detection cell immediately below the light-shielding region 9A2, the amount of light that did not become guided light is not detected. Here, the detected light amount of the light that has become the guided light at the detection position immediately below the light transmitting region 9a1 is defined as Q0 = (Q1 + Q2 + Q3 + Q4) / 4 or Q0 = (Q1 + Q2) / 2. Similarly, the detected light amount of the light that did not become the guided light at the detection position immediately below the light shielding region 9A2 is defined as q0 = (q1 + q2 + q3 + q4) / 4 or q0 = (q1 + q2) / 2. That is, the amount of light detected in a region including the light-shielding region 9A or the light-transmitting region 9a is defined as an average value of the amount of light detected at a detection position immediately below a region adjacent to the region in the X direction and / or the Y direction. Is done. By applying this definition to all the regions, in all the first photodetection cells 10a and the second photodetection cells 10A included in the photodetector 10, the detected light amount of the light that did not become the guided light, The detected light amount of the light that has become the guided light can be defined.

The arithmetic circuit 14 performs, for example, the following first to third arithmetic processing. In the first arithmetic processing, the detected light amounts of the light that did not become the guided light and the detected light amounts of the light that became the guided light in all the light detection cells included in the photodetector 10 are defined as described above. You. In the second arithmetic processing, the value of these ratios or the value of the ratio of each light amount based on the sum of these light amounts is calculated for each photodetection cell. In the third arithmetic processing, an image is generated by assigning the calculated value of the ratio to a pixel corresponding to each light detection cell. The average value, the standard deviation value of the detection values within a certain area, or the calculated value obtained by combining them, reflects the distribution of optical constants such as the refractive index, absorption coefficient, or scattering coefficient inside the object 4. . Therefore, information inside the object 4 can be detected using the coherence length of light emitted from the light source 2 as a parameter.

FIG. 7A is a cross-sectional view schematically illustrating an optical configuration when the object 4 is the phase step plate 16. The optical configuration is a step image detection system. In the example shown in FIG. 7A, the linearly polarized light emitted from the light source 2 is converted into parallel light by the collimator lens 18. The polarization direction of the parallel light is adjusted by the half-wave plate 15. The parallel light whose polarization direction has been adjusted passes through the phase plate 16 having a step-like step. The transmitted light becomes light 5 enlarged or reduced by the telecentric lens 7. The light 5 is vertically incident on the photodetector 13 formed on the transparent substrate 9b. In the example shown in FIG. 7A, an image immediately after passing through the light coupling layer 12 in the light detection device 13 is observed by the microscope 17 instead of the light detector 10.

FIGS. 7B and 7C are views showing observation images of the TE mode and the TM mode when light having a long coherence length of 1 m or more is incident, respectively. FIGS. 7D and 7E are views showing observation images of the TE mode and the TM mode when light having a short coherence length of about 30 μm is incident, respectively. In the examples shown in FIGS. 7B and 7D, the excitation condition of the guided light in the TE mode is satisfied. In the TE mode, the polarization direction of the light 5 is parallel to the Y direction. In the example shown in FIGS. 7C and 7E, the condition for exciting the guided light in the TM mode is satisfied. In the TM mode, the polarization direction of the light 5 is parallel to the X direction.

In the examples shown in FIGS. 7B to 7E, the observed image is processed by the relational expression of the detected light quantity q0 = (q1 + q2) / 2. In the example shown in FIGS. 7B to 7E, the grating vector of the grating 12d is parallel to the X direction. In the examples shown in FIGS. 7B to 7E, the positions corresponding to the phase steps are indicated by broken lines. At a position where a phase difference exists along the Y direction, the observation image becomes dark due to a decrease in the detected light amount, and a dark line is formed. The Y direction is a direction orthogonal to the grating vector of the grating 12d.

In the example shown in FIG. 7C, unlike the example shown in FIG. 7B, the dark line of the observed image spreads in the X direction, and the relationship between the dark line and the step position becomes unclear. The reason why the width of the dark line is increased as shown in FIG. 7C is as follows. The radiation loss coefficient of the guided light in the TM mode is smaller than the radiation loss coefficient of the guided light in the TE mode, and is about 1/3 to 1/4. Therefore, the guided light of the TM mode can propagate a long distance without being radiated. Thus, the guided light propagates across a plurality of pixels. As a result, crosstalk of the detection signal between pixels increases. When the coherence length of the light emitted from the light source 2 is reduced, guided light that enters and propagates at a distant position is less likely to interfere with guided light that enters near the detection position. Thereby, light interference is limited to only guided light incident near the detection position. As a result, crosstalk of the detection signal between pixels is reduced. Therefore, as shown in FIGS. 7D and 7E, the dark line becomes thinner, and the observed image becomes clearer. As described above, the conventional photodetector 13 can clearly detect the phase difference image of the phase difference plate 16.

FIG. 8 shows a phase difference d and a modulation degree signal P ₁ / (P ₁ + P) obtained by measuring phase steps 16 having various depths when light having a long coherence length of 1 m or more is incident. ₀₎ is a diagram showing the relationship between. A stepped quartz glass plate was used for the phase difference plate 16. A solid line and a broken line represent theoretical values of the TE mode and the TM mode, respectively. Circles and triangles represent experimental values in the TE mode and the TM mode, respectively. As shown in FIG. 8, it can be seen that the modulation degree signal P ₁ / (P ₁ + P ₀ ) changes sinusoidally according to the phase step amount d. Therefore, by measuring the modulation degree signal P ₁ / (P ₁ + P ₀ ), information on the phase difference of the object 4 can be obtained.

Next, the reason why the radiation loss coefficient of the guided light in the TM mode is smaller than the radiation loss coefficient of the guided light in the TE mode will be described. At the interface between the high-refractive-index transparent layer 12b and the low-refractive-index transparent layer 12a and the interface between the high-refractive-index transparent layer 12b and the low-refractive-index transparent layer 12c shown in FIG. 6A, the TM mode guided light is a P-wave. , TE-mode guided light is an S-wave. The high refractive index transparent layer 12b corresponds to a core, and the low refractive index transparent layer 12a and the low refractive index transparent layer 12c correspond to a clad. The guided light of the TM mode as the P wave is more easily transmitted through the waveguide interface than the guided light of the TE mode as the S wave, and the evanescent component, which is the amount of penetration into the clad side, is increased. Thus, in the TM mode, the overlap between the evanescent light and the region where the refractive index is modulated by the grating 12d is reduced, and as a result, the radiation loss coefficient of the guided light in the TM mode is reduced. Therefore, the guided distance of the guided light in the TM mode is longer than the guided distance of the guided light in the TE mode.

ＢAs shown in FIGS. 7B and 7C, the light and dark patterns of the observed image are clearer in the TE mode than in the TM mode. In the TE mode, since the guided distance of the guided light is short, the coherence (that is, the influence on the detection signal) of the guided light that enters at a position separated by two or more pixels and propagates to the position of the detection pixel is not affected by the adjacent pixels. It becomes smaller than the coherence due to the guided light that enters and propagates to the detection pixel position. As a result, crosstalk of the detection signal between pixels is reduced. Therefore, the bright and dark pattern of the observed image is clearer in the TE mode than in the TM mode.

(4) When the coherence length of the light emitted from the light source 2 is reduced, the coherence of the light decreases. Accordingly, the coherence (that is, the effect on the detection signal) of the guided light that is incident at two or more pixels apart and propagates to the detection pixel position is changed by the guided light that is incident on the adjacent pixel and propagates to the detection pixel position. It becomes smaller than coherence. As a result, crosstalk of the detection signal between pixels is reduced. Therefore, as shown in FIG. 7E, even in the TM mode, the bright and dark pattern of the observed image becomes clear.

As described above, in the conventional photodetector, when the coherence length of the guided light is long, the bright and dark pattern of the observed image in the TM mode becomes unclear as shown in FIG. 7C. Further, in the conventional photodetector, as shown in FIGS. 7B to 7E, a phase step along the X direction parallel to the grating vector of the grating is not detected. In these respects, the conventional photodetector has room for improvement.

Based on the above study, the present inventors have conceived of a photodetector described in the following items.

[Item 1]
The light detection device according to item 1 of the present disclosure is a light shielding film including a plurality of light transmitting regions and a plurality of light shielding regions alternately arranged in a first direction and a second direction intersecting the first direction. A photodetector having an imaging surface and including a plurality of first photodetection cells and a plurality of second photodetection cells arranged on the imaging surface; and light incident on the plurality of translucent regions. And a light coupling layer located between the light shielding film and the photodetector, the grating including a grating for transmitting a part of the light in the first direction and the second direction.

[Item 2]
In the photodetection device according to item 1, each of the plurality of first photodetection cells corresponds to one of the plurality of translucent regions, and each of the plurality of second photodetection cells is It may correspond to one of the plurality of light shielding regions.

[Item 3]
2. The photodetector according to item 1, wherein the optical coupling layer includes a first dielectric layer, a second dielectric layer on the first dielectric layer, and a second dielectric layer on the second dielectric layer. 3, wherein the refractive index of the second dielectric layer is higher than the refractive index of the first dielectric layer and the refractive index of the third dielectric layer. It may be arranged between the first dielectric layer and the second dielectric layer.

[Item 4]
2. The photodetector according to item 1, wherein the optical coupling layer includes a first dielectric layer, a second dielectric layer on the first dielectric layer, and a second dielectric layer on the second dielectric layer. 3, wherein the refractive index of the second dielectric layer is higher than the refractive index of the first dielectric layer and the refractive index of the third dielectric layer. It may be arranged between the second dielectric layer and the third dielectric layer.

[Item 5]
2. The photodetector according to item 1, wherein the optical coupling layer includes a first dielectric layer, a second dielectric layer on the first dielectric layer, and a second dielectric layer on the second dielectric layer. 3, wherein the refractive index of the second dielectric layer is higher than the refractive index of the first dielectric layer and the refractive index of the third dielectric layer. It may be arranged between a first dielectric layer and the second dielectric layer, and between the second dielectric layer and the third dielectric layer.

[Item 6]
6. The photodetector according to any one of items 1 to 5, wherein the grating has a concentric circle or a concentric polygonal shape in a plan view.

[Item 7]
The light detection system according to Item 7 of the present disclosure includes the light detection device according to any one of Items 1 to 6, a plurality of first signals obtained from the plurality of first light detection cells, Based on the plurality of second signals obtained from the second light detection cells, the coherence of light incident on each of the positions of the plurality of first light detection cells and the plurality of second light detection cells is determined. And an arithmetic circuit for generating and outputting the signal shown.

[Item 8]
In the optical detection system of claim 7, the signals obtained from each of the plurality of first light detection cell is P _0, the signals obtained from each of the plurality of second light detection cell is P _1, Of the plurality of second light detection cells, a first light detection cell obtained from a second light detection cell adjacent in the same direction as the first direction around each of the plurality of first light detection cells. A signal, a second signal obtained from a second light detection cell adjacent in a direction opposite to the first direction, and a third signal obtained from a second light detection cell adjacent in the same direction as the second direction. And the average value of a fourth signal obtained from a second light detection cell adjacent in the direction opposite to the second direction is P ₁ ′, and among the plurality of first light detection cells, Around the plurality of second light detection cells, in the same direction as the first direction. A fifth signal obtained from the contacting first light detection cell, a sixth signal obtained from the first light detection cell adjacent in the direction opposite to the first direction, in the same direction as the second direction; The average value of the seventh signal obtained from the adjacent first light detection cell and the average value of the eighth signal obtained from the first light detection cell adjacent in the direction opposite to the second direction is P ₀ ′. When performing the above, the arithmetic circuit converts the signal obtained by the operation of P ₁ ′ / (P ₀ + P ₁ ′) or P ₁ ′ / P ₀ into the light incident on each of the plurality of first light detection cells. A signal that is generated as a signal indicating coherence, and a signal obtained by an operation of P ₁ / (P ₀ ′ + P ₁ ) or P ₁ / P ₀ ′ is converted into a coherence of light incident on each of the plurality of second photodetection cells. May be generated as a signal indicating

(4) In the photodetector described in the above item, the light propagates so as to diffuse around the light input position in the waveguide plane. With such propagation, the amount of guided light decreases in inverse proportion to the propagation distance. Accordingly, the coherence (that is, the influence on the detection signal) of the guided light that is incident at a position separated by two or more pixels and propagates to the detection pixel position also decreases in inverse proportion to the propagation distance. Further, the crosstalk of the detection signal between pixels is reduced. Therefore, even in the case of TM mode guided light having a long guided distance, crosstalk of a detection signal between pixels is reduced. From the above, it is considered that the phase difference image can be sharpened regardless of the shape of the phase step, such as the interval between the step positions, using any light source.

実施 Each of the embodiments described below shows a comprehensive or specific example. Numerical values, shapes, materials, constituent elements, arrangement positions of constituent elements, and the like shown in the following embodiments are merely examples, and do not limit the present disclosure. In addition, among the components in the following embodiments, components not described in the independent claims indicating the highest concept are described as arbitrary components.

In this disclosure, all or a part of a circuit, a unit, a device, a member, or a part, or all or a part of a functional block in a block diagram is a semiconductor device, a semiconductor integrated circuit (IC), or an LSI (large scale integration). It may be performed by one or more electronic circuits, including: The LSI or IC may be integrated on one chip, or may be configured by combining a plurality of chips. For example, functional blocks other than the storage element may be integrated on one chip. Here, the term is referred to as an LSI or an IC, but the term is changed depending on the degree of integration, and may be referred to as a system LSI, a VLSI (very large scale integration), or a ULSI (ultra large scale integration). A Field Programmable Gate Array (FPGA), which is programmed after the manufacture of the LSI, or a reconfigurable logic device capable of reconfiguring a bonding relationship inside the LSI or setting up a circuit section inside the LSI can also be used for the same purpose.

Furthermore, all or some of the functions or operations of the circuits, units, devices, members or units can be executed by software processing. In this case, the software is recorded on one or more non-transitory recording media such as a ROM, an optical disk, a hard disk drive, etc., and is specified by the software when the software is executed by a processor. The functions performed are performed by a processor and peripheral devices. The system or apparatus may include one or more non-transitory storage media on which the software is recorded, a processor, and any required hardware devices, such as an interface.

Hereinafter, the present embodiment will be specifically described with reference to the drawings.

(Embodiment)
In the present embodiment, the configuration is the same as that of the above-described conventional photodetector except that the shape of the grating 12d is different. Therefore, elements common to the examples shown in FIGS. 5A to 6B are assigned the same numbers, and detailed descriptions thereof are omitted.

FIG. 1 is a diagram schematically illustrating an example of a light detection system 100 according to the present embodiment. The light detection system 100 includes a light source 2, a light detection device 13, a control circuit 1, and an arithmetic circuit 14.

(4) The light source 2 irradiates the object 4 with light having a constant coherence length. At this time, scattered light 5a and scattered light 5A are generated on the surface of the object 4 or within the object 4. Of the scattered light 5a and the scattered light 5A, a component perpendicular to the incident surface of the light detection device 13 becomes the light 5 incident on the light detection device 13. A substantial object 8a exists on the object 4 side corresponding to the image 8b formed by the light 5. The object 8a is a collection of object points.

構成 The configuration of the photodetector 13 is the same as the configuration of the above-described conventional photodetector. That is, the light detection device 13 includes the light detector 10, the light coupling layer 12, and the light shielding film 9 in this order. As described in FIG. 6A, the optical coupling layer 12 is disposed on the photodetector 10. The optical coupling layer 12 includes a low-refractive-index transparent layer 12c, a high-refractive-index transparent layer 12b, and a low-refractive-index transparent layer 12a in this order in a direction perpendicular to the surface of the photodetector 10. All other configurations are the same as the example shown in FIG. 6A. Therefore, detailed description is omitted.

FIG. 2A is a diagram schematically showing the object 4 and the propagation of light 6a incident on one translucent area 9a in the example of the photodetector 13 in the present embodiment. FIG. 2B is a perspective view schematically showing propagation of light incident on one light transmitting region 9a in the example of the photodetecting device 13 in the present embodiment. FIG. 2C is a plan view schematically illustrating an example of the light detection device 13 in the present embodiment when viewed from the light incident side.

In the example shown in FIG. 2A, a part of the light scattered in the object 4 becomes the light 5 that is incident perpendicularly to the light detection device 13. The light 5 is incident as light 6A in the light-shielding region 9A on which the reflective film is formed, and is incident as light 6a in the light-transmitting region 9a from which the reflective film is removed. The light 6A is blocked by the light blocking region 9A. The light 6a transmits through the light transmitting region 9a and enters the optical coupling layer 12. Light 6a incident on the optical coupling layer 12 is incident on the high refractive index transparent layer 12b via the low refractive index transparent layer 12a. A grating 12d is formed on the upper and lower interfaces of the high refractive index transparent layer 12b. As shown in FIGS. 2B and 2C, the grating 12d in the present embodiment has a concentric shape centered on the center of each of the plurality of light-transmitting regions 9a and each of the plurality of light-shielding regions 9A. If the pitch の of the grating 12d satisfies the formula (1), a part of the incident light 6a generates the guided light 6b, and the rest is transmitted as the transmitted light 6d. In other words, when light having a predetermined wavelength is incident on the plurality of light transmitting regions 9a, the grating 12d propagates a part of the light in the X direction and the Y direction. In the present embodiment, the light 6a is perpendicularly incident on the incident surface. Therefore, θ = 0. The guided light 6b propagates in all directions from the center of the light transmitting region 9a toward the outer periphery. The propagation length is short because the propagation is spread in the plane. Therefore, regardless of the coherence length of the light emitted from the light source 2, the crosstalk of the detection signal between pixels is small. Further, since the propagation is in all directions, the phase difference in the X direction and the Y direction can be simultaneously detected regardless of the shape of the phase step. Immediately below the light shielding region 9A, a part of the guided light 6b is emitted. The part of the guided light 6b overlaps with the reflection of the light-shielding region 9A on the reflection film to become the emitted light 6D. All other operations are the same as in the example shown in FIGS. 6A and 6B. Therefore, detailed description is omitted.

Next, the arithmetic processing of the arithmetic circuit 14 will be described.

The arithmetic circuit 14 outputs a signal indicating the coherence or phase coherence of the light incident on each of the positions of the plurality of first photodetecting cells 10a and the plurality of second photodetecting cells 10A by the arithmetic processing. In the arithmetic processing, a plurality of signals obtained from the plurality of first light detection cells 10a and a plurality of signals obtained from the plurality of second light detection cells 10A are used.

FIG. 3A is a diagram schematically illustrating an arrangement of detection signals corresponding to each of the plurality of light-transmitting regions 9a and the plurality of light-shielding regions 9A. P ₀ denotes the amount of light detected by the first light detecting cell 10a immediately below the light-transmitting region 9a. P ₁ represents the amount of light detected by the second light detecting cell 10A immediately below the light-shielding region 9A. In other words, P ₀ is a raw signal obtained from each of the plurality of first light detection cells 10a, and P ₁ is a raw signal obtained from each of the plurality of second light detection cells 10A. . Raw signal means a signal as detected. P ₀ and P ₁ are arranged in the order of indices i and j on the XY plane. Based on the following equation (2), from the four raw signal P ₁ adjacent to the X and Y directions shown in FIG. 3A, the interpolation signal P _'1 corresponding to right under the light-transmitting region 9a in their center Generated.

P ′ ₁ is from four second light detection cells 10A adjacent in the X and Y directions around each of the plurality of first light detection cells 10a among the plurality of second light detection cells 10A. It is the average value of the four raw signals obtained.

Similarly, based on the following equation (3), as shown in FIG. 3A, four raw signal P ₀ adjacent to X and Y directions, the interpolation corresponding to the right under the light-shielding region 9A in their center signal P _'0 is generated.

P ₀ ′ is from four first light detection cells 10 a adjacent in the X direction and the Y direction around each of the plurality of second light detection cells 10 A among the plurality of first light detection cells 10 a. It is the average value of the four raw signals obtained.

FIG. 3B is a diagram illustrating a flow up to generation of a modulation factor signal in a region surrounded by the thick line shown in FIG. 3A.

By the interpolation of the expression (2), the raw signal P ₀ and the interpolation signal P ′ ₁ are generated immediately below all the translucent regions 9 a. The arithmetic circuit 14 uses the modulation degree signal obtained by the arithmetic operation of P ′ ₁ / (P ₀ + P ′ ₁ ) to indicate the coherence or phase coherence of the light incident on each of the plurality of first photodetection cells 10 a. Generate as a signal. The modulation degree signal may be obtained by calculating P ′ ₁ / P ₀ .

Similarly, by interpolation of Equation (3), the raw signal P ₁ and the interpolation signal P _'0 directly below all of the light shielding region 9A is generated. The arithmetic circuit 14 converts the modulation degree signal obtained by the calculation of P ₁ / (P ₀ ′ + P ₁ ) into a signal indicating the coherence or phase coherence of the light incident on each of the plurality of second photodetection cells 10A. Generate as The modulation signal _may be obtained by calculation of _P 1 / _P _'0.

こと By using the shape of the grating 12d in the present embodiment, the guided light 6b propagates in the X direction and the Y direction and interferes in the structures in the respective directions. By using the calculation method shown in FIG. 3B, the phase difference images of the object 4 in two directions can be detected. This makes it possible to detect a phase difference image of the object 4 having a phase step having an arbitrary shape. Furthermore, since the guided light 6b propagates in a plane, the crosstalk of the detection signal between pixels can be reduced regardless of the coherence length of the light emitted from the light source 2. Therefore, a clear phase difference image can be detected regardless of the shape of the phase step.

Next, a modified example of the photodetector 13 according to the present embodiment will be described.

FIG. 4A is a perspective view schematically showing propagation of light 6a incident on one translucent region 9a in a first modification of the photodetector 13 in the present embodiment. FIG. 4B is a plan view schematically showing a first modified example of the light detection device 13 in the present embodiment when viewed from the light incident side.

4A and 4B, the grating 12d in the present embodiment has a concentric square shape centered on the center of each of the plurality of light-transmitting regions 9a and each of the plurality of light-shielding regions 9A. If the pitch の of the grating 12d satisfies the expression (1), a part of the light 6a generates a guided light 6b. In the photodetector 13 according to the present embodiment, light is incident perpendicularly to the incident surface. Therefore, θ = 0. The guided light 6b propagates in all directions from the center of the light transmitting region 9a toward the outer periphery. The propagation length is short because the propagation is spread in the plane. Therefore, regardless of the coherence length of the light emitted from the light source 2, the crosstalk of the detection signal between pixels is small. Immediately below the light shielding region 9A, a part of the guided light 6b is emitted. The part of the guided light 6b overlaps with the reflection of the light-shielding region 9A on the reflection film to become the emitted light 6D. All other operations are the same as in the example shown in FIGS. 6A and 6B. Therefore, detailed description is omitted.

4A and 4B, similarly to the examples shown in FIGS. 2B and 2C, the guided light 6b propagates in the X direction and the Y direction and interferes in the structures in the respective directions. Therefore, a phase difference image of the object 4 can be detected in two directions. This makes it possible to detect a phase difference image of the object 4 having a phase step having an arbitrary shape. Furthermore, since the guided light 6b propagates in a plane, the crosstalk of a detection signal between pixels can be reduced regardless of the coherence length of the light source 2. Therefore, a clear phase difference image can be detected regardless of the shape of the phase step.

In the example shown in FIGS. 4A and 4B, the grating 12d has a concentric square shape, but may have another concentric shape, for example, a hexagonal or octagonal shape.

FIG. 4C is a plan view schematically showing a second modified example of the photodetector 13 according to the present embodiment when viewed from the light incident side. In the example shown in FIG. 4C, the grating 12d in the present embodiment has a concentric octagonal shape centered on the center of each of the plurality of light-transmitting regions 9a and each of the plurality of light-shielding regions 9A. Also in the example shown in FIG. 4C, a clear phase difference image can be detected regardless of the shape of the phase step.

The light detection device according to an aspect of the present disclosure can detect the state of coherence or phase of transmitted light, reflected light, and / or scattered light from an object as distribution information in a plane. The light detection device can be used, for example, for measuring biological information such as cerebral blood flow. In addition, for example, by combining light intensity distribution information, a time division detection method, and a light source with a variable coherence length, information inside the object can be analyzed with high accuracy and high resolution. In particular, a new evaluation axis of the state or phase of coherence is added to the imaging technique which has been limited to the analysis of the light intensity distribution, and multifunctionality can be provided to the imaging technique.

Reference Signs List 100 light detection system 1 control circuit 2

light source

3, 5, 5s, 6a, 6A light 4

object

5a, 5A scattered light 6b, 6c guided light 6d transmitted light 6D radiation light 7 condenser lens 8a object 8b image 9 light-shielding film 9a Light transmitting area 9A Light shielding area 10 Photodetector 12 Optical coupling layer 12d Grating 13 Photodetector 14 Operation circuit

Claims

A light-shielding film including a plurality of light-transmitting regions and a plurality of light-shielding regions alternately arranged in a first direction and a second direction intersecting the first direction;
A photodetector having an imaging surface and including a plurality of first photodetection cells and a plurality of second photodetection cells arranged on the imaging surface;
A grating that propagates part of the light in the first direction and the second direction when light enters the plurality of light-transmitting regions, between the light-shielding film and the photodetector; An optical coupling layer located thereon;
Comprising,
Photodetector.
Each of the plurality of first light detection cells corresponds to one of the plurality of light transmitting regions,
Each of the plurality of second light detection cells corresponds to one of the plurality of light-shielding regions,
The light detection device according to claim 1.
The optical coupling layer includes a first dielectric layer, a second dielectric layer on the first dielectric layer, and a third dielectric layer on the second dielectric layer;
The refractive index of the second dielectric layer is higher than the refractive index of the first dielectric layer and the refractive index of the third dielectric layer,
The grating is disposed between the first dielectric layer and the second dielectric layer;
The light detection device according to claim 1.
The optical coupling layer includes a first dielectric layer, a second dielectric layer on the first dielectric layer, and a third dielectric layer on the second dielectric layer;
The refractive index of the second dielectric layer is higher than the refractive index of the first dielectric layer and the refractive index of the third dielectric layer,
The grating is disposed between the second dielectric layer and the third dielectric layer;
The light detection device according to claim 1.
The optical coupling layer includes a first dielectric layer, a second dielectric layer on the first dielectric layer, and a third dielectric layer on the second dielectric layer;
The refractive index of the second dielectric layer is higher than the refractive index of the first dielectric layer and the refractive index of the third dielectric layer,
The grating is disposed between the first dielectric layer and the second dielectric layer and between the second dielectric layer and the third dielectric layer.
The light detection device according to claim 1.
In a plan view, the grating has a concentric circle or concentric polygonal shape,
The photodetector according to claim 1.
A light detection device according to any one of claims 1 to 6,
The plurality of first lights are detected based on a plurality of first signals obtained from the plurality of first light detection cells and a plurality of second signals obtained from the plurality of second light detection cells. An arithmetic circuit that generates and outputs a signal indicating coherence of light incident on the detection cell and the position of each of the plurality of second light detection cells;
Comprising,
Light detection system.
A signal obtained from each of the plurality of first light detection cells is P 0 ,
The signals obtained from each of the plurality of second light detection cell is P 1,
Of the plurality of second light detection cells, with each of the plurality of first light detection cells as a center,
A first signal obtained from a second light detection cell adjacent in the same direction as the first direction;
A second signal obtained from a second light detection cell adjacent in a direction opposite to the first direction;
A third signal obtained from a second light detection cell adjacent in the same direction as the second direction, and a fourth signal obtained from a second light detection cell adjacent in a direction opposite to the second direction. Let the average value of the signal be P 1 ′,
Of the plurality of first light detection cells, with the plurality of second light detection cells as the center,
A fifth signal obtained from a first light detection cell adjacent in the same direction as the first direction;
A sixth signal obtained from a first light detection cell adjacent in a direction opposite to the first direction;
A seventh signal obtained from a first light detection cell adjacent in the same direction as the second direction, and an eighth signal obtained from a first light detection cell adjacent in a direction opposite to the second direction. When the average value of the signal is P 0 ′,
The arithmetic circuit,
A signal obtained by calculating P 1 ′ / (P 0 + P 1 ′) or P 1 ′ / P 0 is generated as a signal indicating coherence of light incident on each of the plurality of first light detection cells,
Generating a signal obtained by calculating P 1 / (P 0 ′ + P 1 ) or P 1 / P 0 ′ as a signal indicating coherence of light incident on each of the plurality of second photodetection cells;
The light detection system according to claim 7.