Distance imaging device

Abstract

This suppresses multipath errors and improves the accuracy of distance measurement. [Solution] The distance image capturing device comprises a light source that emits light pulses, an image sensor having a pixel array in which a plurality of pixels having photoelectric conversion elements that generate an electric charge corresponding to the incident light are arranged, a diffusion unit that diffuses the light pulses emitted from the light source and has at least a first quarter-wave plate which is a quarter-wave plate that converts linearly polarized light based on the light pulses emitted from the light source into circularly polarized light, a focusing unit that images the reflected light from the subject, which is the circularly polarized light pulses converted by the diffusion unit, onto the image sensor and has at least a second quarter-wave plate which is a quarter-wave plate that converts the reflected light, which is circularly polarized, into linearly polarized light, and a distance image processing unit that calculates the distance to the subject based on the output of the image sensor for the reflected light, which is circularly polarized in the opposite direction to the circularly polarized light converted by the first quarter-wave plate.

Description

Technical Field

[0001] The present invention relates to a distance image capturing device.

Background Art

[0002] A time-of-flight (TOF) distance image capturing device that measures the distance between a measuring instrument and an object based on the flight time of light in space (measurement space) by utilizing the fact that the speed of light is known has been realized (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the TOF distance image capturing device as described above, a multipath may occur where the irradiated light is reflected by an object other than the target object before reaching the target object or after reaching it. In such a case, in a conventional distance image capturing device, due to the multipath, the flight time of light changes, and a distance longer than the actual distance to the target object may be measured, and it may not be possible to accurately measure the distance. The distance error caused by this multipath is referred to as a multipath error.

[0005] The present invention has been made to solve the above problems, and an object thereof is to provide a distance image capturing device capable of suppressing multipath errors and improving the measurement accuracy of distance.

Means for Solving the Problems

[0006] To solve the above problems, one aspect of the present invention is a distance image imaging device comprising: a light source that emits light pulses; an image sensor having a pixel array in which a plurality of pixels having photoelectric conversion elements that generate an electric charge corresponding to the incident light; a diffusion unit that diffuses the light pulses emitted from the light source, and having at least a first quarter-wave plate which is a quarter-wave plate that converts linearly polarized light based on the light pulses emitted from the light source into circularly polarized light; a focusing unit that images the reflected light from the subject, which is the circularly polarized light pulses converted by the diffusion unit, onto the image sensor, and having at least a second quarter-wave plate which is a quarter-wave plate that converts the reflected light, which is circularly polarized, into linearly polarized light; and a distance image processing unit that calculates the distance to the subject based on the output of the image sensor for the reflected light, which is circularly polarized in the opposite direction to the circularly polarized light converted by the first quarter-wave plate. [Effects of the Invention]

[0007] According to the present invention, multipath errors can be suppressed and the accuracy of distance measurement can be improved. [Brief explanation of the drawing]

[0008] [Figure 1] This is a block diagram showing an example of a distance image acquisition device according to the first embodiment. [Figure 2] This is a block diagram showing an example of a distance image sensor in the first embodiment. [Figure 3] This is a block diagram showing an example of a pixel in the first embodiment. [Figure 4] This figure shows an example of a combination of a linear polarizer and a quarter-wave plate in the first embodiment. [Figure 5] This is the first figure showing an example of the operation of a distance image acquisition device according to the first embodiment. [Figure 6] The second figure shows an example of the operation of the distance image acquisition device according to the first embodiment. [Figure 7] This figure illustrates an example of the process for removing reflected light from multipath imaging devices according to the first embodiment. [Figure 8] This figure shows a modified example of the combination of a linear polarizer and a quarter-wave plate in the first embodiment. [Figure 9] This figure illustrates the process of removing multipath reflected light in a modified example of the distance image acquisition device according to the first embodiment. [Figure 10] This block diagram shows an example of a distance image acquisition device according to a second embodiment. [Modes for carrying out the invention]

[0009] A distance image acquisition device according to one embodiment of the present invention will be described below with reference to the drawings.

[0010] [First Embodiment] Figure 1 is a block diagram showing an example of a distance image acquisition device 1 according to the first embodiment. As shown in Figure 1, the distance image acquisition device 1 comprises a light source unit 2, a light receiving unit 3, and a distance image processing unit 4. Figure 1 also shows the subject OB, which is the object whose distance is to be measured using the distance image acquisition device 1.

[0011] The light source unit 2, in accordance with control from the distance image processing unit 4, irradiates the space of the object to be photographed, where the object OB whose distance is to be measured by the distance image acquisition device 1 is located, with an optical pulse PO. The light source unit 2 is, for example, a surface-emitting semiconductor laser module such as a vertical cavity surface-emitting laser (VCSEL). The light source unit 2 emits circularly polarized optical pulse PO. The light source unit 2 also comprises a light source device 21 and a diffusion unit 22.

[0012] The light source device 21 (an example of a light source) is a light source that emits laser light in the near-infrared wavelength band (for example, a wavelength band of 850 nm to 940 nm) which becomes a light pulse PO irradiated onto the subject OB. The light source device 21 is, for example, a semiconductor laser light-emitting element. The light source device 21 emits pulsed laser light in response to control from the measurement control unit 43.

[0013] The diffusing unit 22 is an optical component (optical member) that diffuses the laser light in the near-infrared wavelength band emitted by the light source device 21 over the area of the surface that irradiates the subject OB. The diffusing unit 22 is an optical member that diffuses the light pulse PO emitted from the light source device 21, and at least includes a first quarter-wave plate (quarter-wave plate 222) that converts the linearly polarized light based on the light pulse PO emitted by the light source device 21 into circularly polarized light. Specifically, the diffusing unit 22 includes a linear polarizer 221 and a quarter-wave plate 222 (first quarter-wave plate).

[0014] The linear polarizer 221 is, for example, a linear polarizing plate, a linear polarization filter, etc., and converts the light pulse PO emitted by the light source device 21 into linearly polarized light. The quarter-wave plate 222 (first quarter-wave plate) converts the linearly polarized light pulse PO emitted by the linear polarizer 221 into a circularly polarized light pulse PO and irradiates the subject OB. Details of the combination of the linear polarizer 221 and the quarter-wave plate 222 will be described later.

[0015] The light receiving unit 3 receives the reflected light RL of the light pulse PO reflected by the subject OB, which is the object to be measured for distance in the distance image capturing device 1, and outputs a pixel signal corresponding to the received reflected light RL. Note that the light receiving unit 3 according to the present embodiment utilizes the characteristics of circular polarization to receive the reflected light RL that returns through the direct path and excludes the reflected light RL that returns through the multi-path. The light receiving unit 3 includes a condensing unit 31 and a distance image sensor 32.

[0016] The condensing unit 31 forms an image of the reflected light RL of the circularly polarized light pulse PO converted by the diffusing unit 22 and reflected by the subject on the distance image sensor 32. The condensing unit 31 allows the reflected light RL of the circular polarization that rotates in the opposite direction to the circular polarization converted by the quarter-wave plate 222 to pass through as the reflected light RL of the direct path and form an image on the distance image sensor 32. Also, the condensing unit 31 absorbs and does not allow the reflected light RL of the circular polarization that rotates in the same direction as the circular polarization converted by the quarter-wave plate 222 to pass through as the reflected light RL of the multi-path.

[0017] The light condensing unit 31 includes at least a second quarter-wave plate (quarter-wave plate 311) which is a quarter-wave plate that converts the reflected light RL which is circularly polarized light into linearly polarized light. The light condensing unit 31 includes a quarter-wave plate 311, a linear polarizer 312, and a lens 313.

[0018] The quarter-wave plate 311 (second quarter-wave plate) converts the circularly polarized reflected light RL into linearly polarized light and allows it to pass through. The linear polarizer 312 is, for example, a linear polarizing plate, a linear polarization filter, etc., and passes or blocks the linearly polarized reflected light RL converted by the quarter-wave plate 311 according to the polarization direction. The linear polarizer 312 blocks the reflected light RL when the linear direction of the linearly polarized reflected light RL and the direction of the absorption axis coincide, and allows the linearly polarized reflected light RL to pass through when the linear direction of the linearly polarized reflected light RL and the direction of the absorption axis do not coincide (for example, are orthogonal).

[0019] Note that the quarter-wave plate 311 and the linear polarizer 312 are configured to allow the reflected light RL in the direct path to pass through and not allow the reflected light RL in the multi-path to pass through. Details of the combination of the quarter-wave plate 311 and the linear polarizer 312 will be described later.

[0020] The lens 313 is an optical lens that guides the incident reflected light RL to the distance image sensor 32 after passing through the quarter-wave plate 311 and the linear polarizer 312. The lens 313 emits the incident reflected light RL toward the distance image sensor 32 side and causes it to be received (incident) by the pixel 321 provided in the light receiving region of the distance image sensor 32.

[0021] The distance image sensor 32 (an example of a distance image capturing element) is a capturing element used in the distance image capturing device 1. The distance image sensor 32 includes a plurality of pixels 321 in a two-dimensional light receiving region and a pixel driving circuit 322 that controls each of the pixels 321.

[0022] Pixel 321 is provided with one photoelectric conversion element (for example, a photoelectric conversion element PD described later), a plurality of charge storage units corresponding to this one photoelectric conversion element (for example, charge storage units CS (CS1 to CS4) described later), and a component that distributes charge to each charge storage unit.

[0023] The pixel driving circuit 322 conducts the transfer transistor G (described later) to each of the charge storage units CS (CS1 to CS4) at a predetermined storage timing synchronized with the irradiation of the light pulse PO, thereby distributing and storing the charge. Details of the distance image sensor 32, which includes pixels 321 and a pixel driving circuit 322, will be described later with reference to Figure 2.

[0024] The distance image sensor 32 distributes the charge generated by the photoelectric conversion element to its respective charge storage units in accordance with the control from the measurement control unit 43. The distance image sensor 32 also outputs a pixel signal corresponding to the amount of charge distributed to the charge storage units. The distance image sensor 32 has multiple pixels 321 arranged in a two-dimensional matrix, and outputs a pixel signal for one frame corresponding to each pixel 321.

[0025] Now, with reference to Figure 2, the detailed configuration of the distance image sensor 32 will be described. Figure 2 is a block diagram showing an example of the distance image sensor 32 in this embodiment.

[0026] As shown in Figure 2, the distance image sensor 32 includes, for example, a light-receiving area 320 on which multiple pixels 321 are arranged, and a pixel driving circuit 322. The pixel driving circuit 322 also includes a vertical scanning circuit 323 with distribution operation, a horizontal scanning circuit 324, a pixel signal processing circuit 325, and a control circuit 326.

[0027] The light-receiving region 320 is a region in which multiple pixels 321 are arranged, and Figure 2 shows an example in which they are arranged in a two-dimensional matrix with 8 rows and 8 columns. The light-receiving region 320 is a pixel array in which multiple pixels 321 are arranged.

[0028] Multiple pixels 321 are arranged in a two-dimensional matrix and accumulate charge corresponding to the amount of light received. The detailed configuration of pixels 321 will be described later with reference to Figure 3.

[0029] The control circuit 326 comprehensively controls the distance image sensor 32. For example, the control circuit 326 controls the operation of the components of the distance image sensor 32 in response to instructions from the measurement control unit 43 of the distance image processing unit 4. In addition, the control of the components of the distance image sensor 32 may be directly performed by the measurement control unit 43, in which case the control circuit 326 can be omitted.

[0030] The vertical scanning circuit 323 controls the pixels 321 arranged in the light-receiving area 320 row by row in response to control from the control circuit 326. The vertical scanning circuit 323 causes the pixel signal processing circuit 325 to output a voltage signal corresponding to the amount of charge accumulated in each of the charge storage units CS of the pixels 321. In this case, the vertical scanning circuit 323 distributes and stores the charge converted by the photoelectric conversion element in each of the charge storage units CS of the pixels 321.

[0031] The pixel signal processing circuit 325 performs predetermined signal processing (for example, noise suppression processing or A / D conversion processing) on ​​the voltage signals output from the pixels 321 of each row, in response to control from the control circuit 326.

[0032] The horizontal scanning circuit 324 is a circuit that sequentially outputs the signals output from the pixel signal processing circuit 325 in a time series, in response to control from the control circuit 326. As a result, pixel signals corresponding to the amount of charge accumulated for one frame are sequentially output to the distance image processing unit 4. In the following description, it is assumed that the pixel signal processing circuit 325 performs A / D conversion processing and that the pixel signals are digital signals.

[0033] Next, with reference to Figure 3, the configuration of the pixels 321 arranged within the light-receiving area 320 of the distance image sensor 32 will be described.

[0034] Figure 3 is a block diagram showing an example of a pixel 321 in this embodiment. Note that the pixel 321 shown in Figure 3 is an example configuration equipped with four pixel signal readout units RU (RU1 to RU4).

[0035] As shown in Figure 3, the pixel 321 comprises one photoelectric conversion element PD, a charge emission transistor GD, and four pixel signal readout units RU (RU1 to RU4) that output voltage signals from their corresponding output terminals O (O1 to O4). Each of the pixel signal readout units RU comprises a transfer transistor G, a floating diffusion FD, a capacitor C (charge storage capacitance), a reset transistor RT, a source follower transistor SF, and a selection transistor SL. The floating diffusion FD and capacitor C constitute a charge storage unit CS.

[0036] The transfer transistor G, reset transistor RT, source follower transistor SF, and selection transistor SL are all NMOS (N-channel Metal Oxide Semiconductor) transistors.

[0037] The transfer transistors G (G1 to G4) transfer charge from the photoelectric conversion element PD to the respective charge storage units CS (CS1 to CS4). The reset transistors RT (RT1~RT4) correspond to each of the charge storage units CS (CS1~CS4) and reset the charge storage units CS to a predetermined reset potential supplied from the power line VRD.

[0038] The source follower transistors SF (SF1~SF4) correspond to the charge storage units CS (CS1~CS4), and convert the charge stored in the charge storage units CS into an electrical signal. The selection transistors SL (SL1~SL4) select the readout of the electrical signal from pixel 321. The charge discharge transistor GD discharges charge from the photoelectric conversion element PD.

[0039] In the pixel 321 shown in Figure 3, the pixel signal readout unit RU1, which outputs a voltage signal from the output terminal O1, comprises a transfer transistor G1, a floating diffusion transistor FD1, a capacitor C1, a reset transistor RT1, a source follower transistor SF1, and a selection transistor SL1. In the pixel signal readout unit RU1, the floating diffusion transistor FD1 and the capacitor C1 constitute a charge storage unit CS1. Pixel signal readout units RU2 to RU4 have a similar configuration.

[0040] The photoelectric conversion element (PD) is an embedded photodiode that converts incident light into electricity to generate an electric charge corresponding to the incident light, and stores the generated charge. In this embodiment, the incident light is introduced from the space being measured.

[0041] In pixel 321, the photoelectric conversion element PD converts incident light into electricity to generate charge, which is then distributed to each of the four charge storage units CS (CS1 to CS4). The voltage signals corresponding to the amount of charge distributed are then output to the pixel signal processing circuit 325.

[0042] Furthermore, the configuration of pixels arranged in the distance image sensor 32 is not limited to the configuration with four pixel signal readout units RU (RU1 to RU4) as shown in Figure 3, but may also be a configuration in which the pixel signal readout unit RU has two or more pixel signal readout units RU.

[0043] Furthermore, in driving the pixel 321, an optical pulse PO is irradiated at irradiation time To, and the reflected light RL is received by the distance image sensor 32 after a delay time Td. The pixel driving circuit 322, under the control of the measurement control unit 43, synchronizes with the irradiation of the optical pulse PO according to the frame period and distributes the charge generated in the photoelectric conversion element PD to the transfer transistors G (G1, G2, G3, G4) by supplying accumulation drive signals TX1 to TX4 at their respective timings, thereby accumulating the charge in the charge accumulation units CS1, CS2, CS3, and CS4 in that order.

[0044] Furthermore, the pixel driving circuit 322 controls the reset transistor RT and the selection transistor SL respectively with the driving signals RST and SEL, converts the charge stored in the charge storage unit CS into an electrical signal using the source follower transistor SF, and outputs the generated electrical signal to the distance calculation unit 42 via the output terminal O.

[0045] Furthermore, the pixel driving circuit 322, under the control of the measurement control unit 43, turns on the charge discharge transistor GD in response to the driving signal RSTD, and discharges the charge generated in the photoelectric conversion element PD by flowing it to the power supply VDD (erasing the charge).

[0046] Returning to the explanation of Figure 1, the distance image processing unit 4 controls the distance image acquisition device 1 and calculates the distance to the subject OB. Based on the amount of charge accumulated in each of the charge storage units CS, the distance image processing unit 4 measures the distance to the subject OB in the measurement space as the measurement distance. Furthermore, the distance image processing unit 4 includes a timing control unit 41, a distance calculation unit 42, and a measurement control unit 43.

[0047] The timing control unit 41 controls the timing of outputting various control signals required for measurement, in accordance with the control of the measurement control unit 43. These various control signals include, for example, a signal to control the irradiation of the light pulse PO, a signal to distribute and store reflected light RL in multiple charge storage units CS, and a signal to control the number of storage cycles per frame. The number of storage cycles is the number of times the process of distributing and storing charge in the charge storage units CS is repeated, and is a preset number of distribution cycles in the frame period. The exposure time is the product of this number of storage cycles and the time width (storage time width) for storing charge in each charge storage unit CS per charge distribution and storage cycle.

[0048] The distance calculation unit 42 outputs distance information calculated based on the pixel signals output from the distance image sensor 32, determining the distance to the subject OB. The distance calculation unit 42 calculates the delay time from the irradiation of the light pulse PO to the reception of the reflected light RL based on the amount of charge accumulated in the multiple charge storage units CS. The distance calculation unit 42 calculates the distance to the subject OB according to the calculated delay time.

[0049] The distance calculation unit 42 calculates the delay time Td using the following equation (1), by utilizing the fact that the amount of charge corresponding to the reflected light RL component is distributed and accumulated in the two charge storage units CS in a ratio corresponding to the delay time Td until the reflected light RL is incident on the distance image capturing device 1. The distance calculation unit 42 calculates the round-trip distance to the subject OB by multiplying the delay time Td obtained in equation (1) by the speed of light (velocity). Then, the distance calculation unit 42 determines the distance to the subject OB by dividing the round-trip distance calculated above by 1 / 2. Note that equation (1) assumes that the amount of charge corresponding to the ambient light component (ambient light component) is accumulated in the charge storage unit CS1, and the amount of charge corresponding to the reflected light RL component is distributed and accumulated in the charge storage units CS2 and CS3.

[0050] Td=To×(Q3-Q1) / (Q2+Q3-2×Q1) …(1) However, To is the period during which the optical pulse PO was irradiated. Q1 is the amount of charge stored in the charge storage unit CS1. Q2 is the amount of charge stored in the charge storage unit CS2. Q3 is the amount of charge stored in the charge storage unit CS3.

[0051] Note that the example shown in equation (1) is an example where the amount of charge in the reflected light RL is distributed and stored in the charge storage units CS2 and CS3, with the amount of charge corresponding to the reflected light RL component being distributed. Therefore, although there are slight differences when the charge is stored in charge storage units CS1 and CS2, or charge storage units CS3 and CS4, the basic method for calculating the delay time Td from the ratio of the amounts of charge stored in the two charge storage units CS remains the same.

[0052] In this configuration, the distance image acquisition device 1 receives reflected light RL from the light pulse PO in the near-infrared wavelength band that the light source unit 2 irradiates onto the subject OB, and the light receiving unit 3 receives the reflected light RL from the subject OB. The distance image processing unit 4 then outputs distance information (distance image) that measures the distance to the subject OB.

[0053] Next, with reference to Figure 4, the combination of linear polarizers (221, 312) and quarter-wave plates (222, 311) in this embodiment will be described. Figure 4 shows an example of a combination of linear polarizers (221, 312) and quarter-wave plates (222, 311) in this embodiment.

[0054] In Figure 4, the direction of propagation of the light pulse PO or reflected light RL is defined as the X-axis, the horizontal direction (horizontal axis of the paper) as the Y-axis, and the vertical direction (vertical axis of the paper) as the Z-axis.

[0055] Figure 4(a) shows the orientation of the linear polarizer 211. The linear polarizer 211 is positioned so that the absorption axis of linearly polarized light is in the horizontal direction (Y-axis direction). When the light pulse PO emitted by the light source device 21 passes through the linear polarizer 211, the light that oscillates horizontally (Y-axis direction) (Y component) is attenuated, and the light that oscillates vertically (Z-axis direction) (Z component) passes through. Therefore, the linear polarizer 211 emits the Z component of linearly polarized light pulse PO to the quarter-wave plate 222.

[0056] Figure 4(b) shows the orientation of the quarter-wave plate 222. The quarter-wave plate 222 is positioned such that its delay axis for shifting by 1 / 4 wavelength (1 / 4 phase) is at a 45-degree angle to the horizontal direction (Y-axis direction). In other words, the quarter-wave plate 222 converts the linearly polarized light pulse PO of the Z component emitted by the linear polarizer 211 into a clockwise (right-rotating) rotationally polarized light pulse PO and radiates it onto the subject OB.

[0057] Figure 4(c) shows the orientation of the quarter-wave plate 311. Similar to the quarter-wave plate 222, the quarter-wave plate 311 is positioned so that its delay axis is at a 45-degree angle to the horizontal direction (Y-axis direction). That is, when the quarter-wave plate 311 receives counterclockwise (left-rotating) rotational polarization as the reflected light RL in the direct path, it emits reflected light RL with linear polarization of the Z component. Also, when the quarter-wave plate 311 receives clockwise (right-rotating) rotational polarization as the reflected light RL in the multi-path, it emits reflected light RL with linear polarization of the Y component.

[0058] The difference between the reflected light RL of a direct path and the reflected light RL of a multipath path will be explained later with reference to Figures 5 and 6.

[0059] Furthermore, Figure 4(d) shows the orientation of the linear polarizer 312. Similar to the linear polarizer 211, the linear polarizer 312 is positioned so that the absorption axis of linearly polarized light is in the horizontal direction (Y-axis direction). When reflected light RL passes through the linear polarizer 312, the light that oscillates horizontally (Y-axis direction) (Y component) is attenuated, and the light that oscillates vertically (Z-axis direction) (Z component) passes through.

[0060] Therefore, in the case of reflected light RL from a direct path, the linear polarizer 312 emits the reflected light RL of linear polarization of the Z component through the lens 313 to the light-receiving area 320 of the distance image sensor 32.

[0061] Furthermore, in the case of multipath reflected light RL, the linear polarizer 312 blocks the reflected light RL of the linear polarization of the Y component, as the quarter-wave plate 311 emits the reflected light RL of the linear polarization of the Y component.

[0062] As shown in Figure 4, in this example of the embodiment, the linear polarizer 211 and the quarter-wave plate 222 are arranged such that the absorption axis of the linear polarizer 211 and the delay axis of the quarter-wave plate 222 are at a 45-degree angle. In addition, the quarter-wave plate 311 and the linear polarizer 312 are arranged such that the delay axis of the quarter-wave plate 311 and the absorption axis of the linear polarizer 312 are at a 45-degree angle.

[0063] Furthermore, the linear polarizers 211 and 312 are positioned such that the absorption axis of the linear polarizer 211 coincides with the absorption axis of the linear polarizer 312. Also, the quarter-wave plates 222 and 311 are positioned such that the delay axis of the quarter-wave plate 222 coincides with the delay axis of the quarter-wave plate 311.

[0064] Next, the operation of the distance image acquisition device 1 according to this embodiment will be described with reference to Figures 5 and 6. Figure 5 is a first diagram showing an example of the operation of the distance image acquisition device 1 according to this embodiment. In Figure 5, path DP1 represents a direct path where the light pulse PO is directly reflected back from the subject OB. In this case, the right-handed circularly polarized light pulse PO emitted from the depth image acquisition device 1 reverses its direction of rotation when reflected by the subject OB, and returns as left-handed circularly polarized reflected light RL (see path DP1). That is, in the case of the direct path (path DP1), the depth image acquisition device 1 receives left-handed circularly polarized reflected light RL.

[0065] Furthermore, path MP1 represents a multipath reflection of the light pulse PO from the subject OB and other objects. In this case, the right-handed circularly polarized light pulse PO emitted from the depth image acquisition device 1 reverses its direction of rotation when reflected by other objects, becoming left-handed circularly polarized reflected light RL. Then, when reflected by the subject OB, its direction of rotation reverses again, returning as right-handed circularly polarized reflected light RL (see path MP1). In other words, in the case of a multipath (path MP1), the depth image acquisition device 1 receives right-handed circularly polarized reflected light RL.

[0066] Figure 6 is a second diagram showing an example of the operation of the distance image acquisition device 1 according to this embodiment. In Figure 6, path DP2 represents the direct path. In this case, the right-handed circularly polarized (right-rotating circularly polarized) light pulse PO emitted from the depth image acquisition device 1 reverses its rotation direction when reflected by the subject OB, and returns as left-handed circularly polarized (left-rotating circularly polarized) reflected light RL (see path DP2). That is, in the case of the direct path (path DP2), the depth image acquisition device 1 receives left-handed circularly polarized (left-rotating circularly polarized) reflected light RL.

[0067] Furthermore, path MP2 indicates multipath. In this case, the right-handed circularly polarized (right-rotating circularly polarized) light pulse PO emitted from the depth image acquisition device 1 reverses its direction of rotation when reflected by another object, becoming left-handed circularly polarized (left-rotating circularly polarized) reflected light RL. Then, when reflected by subject OB, its direction of rotation reverses again, returning as right-handed circularly polarized (right-rotating circularly polarized) reflected light RL (see path MP2). In other words, in the case of multipath (path MP2), the depth image acquisition device 1 receives right-handed circularly polarized (right-rotating circularly polarized) reflected light RL.

[0068] Next, with reference to Figure 7, the process for removing the reflected light RL of the multipath reflection image acquisition device 1 according to this embodiment will be described. Figure 7 illustrates an example of the multipath reflected light RL removal process of the distance image acquisition device 1 according to this embodiment.

[0069] Figure 7(a) shows the characteristics of the linearly polarized light pulse PO emitted by the linear polarizer 211. The linear polarizer 211 emits a linearly polarized light pulse PO that contains only the Z component. Figure 7(b) also shows the characteristics of the circularly polarized light pulse PO emitted by the quarter-wave plate 222. The linear polarizer 211 emits a right-handed circularly polarized light pulse PO.

[0070] Furthermore, Figure 7(c) shows the characteristics of the reflected light RL reflected from the subject OB. The right-handed circularly polarized light pulse PO emitted by the linear polarizer 211 is reflected from the subject OB, and the direction of rotation is reversed, resulting in the left-handed circularly polarized reflected light RL.

[0071] Furthermore, Figure 7(d) shows the characteristics of the linearly polarized light pulse PO emitted by the quarter-wave plate 311 in the direct path case. In the direct path case, the quarter-wave plate 311 receives left-handed circularly polarized reflected light RL and emits linearly polarized reflected light RL containing only the Z component.

[0072] Furthermore, Figure 7(e) shows the characteristics of the linearly polarized reflected light RL emitted by the linear polarizer 312 in the case of a direct path. In the case of a direct path, the linear polarizer 312 receives linearly polarized reflected light RL containing only the Z component and emits linearly polarized reflected light RL containing only the Z component.

[0073] Furthermore, Figure 7(f) shows the characteristics of the reflected light RL in the case of multipath reflection, where the light is reflected by another object after being reflected by the subject OB. The reflected light RL, which is inverted at the subject OB and becomes counterclockwise circularly polarized, is reflected again by another object, and the direction of rotation is reversed, resulting in reflected light RL that is clockwise circularly polarized.

[0074] Furthermore, Figure 7(g) shows the characteristics of the linearly polarized light pulse PO emitted by the quarter-wave plate 311 in the case of multipath. In the case of multipath, the quarter-wave plate 311 receives the reflected light RL which is right-handed circularly polarized and emits the reflected light RL which is linearly polarized and contains only the Y component.

[0075] Furthermore, Figure 7(h) shows the characteristics of the reflected linearly polarized light RL emitted by the linear polarizer 312 in the case of multipath. In the case of multipath, the linear polarizer 312 receives the reflected linearly polarized light RL containing only the Y component. However, since the Y component is the same as the absorption axis, it absorbs the reflected light RL and does not emit it. In other words, in the case of multipath, the linear polarizer 312 removes the reflected light RL without allowing it to pass through.

[0076] Thus, in the distance image acquisition device 1 according to this embodiment, the multipath reflected light RL is removed by the light-collecting unit 31, and only the direct path reflected light RL is received by the distance image sensor 32.

[0077] Next, a modified example of the distance image acquisition device 1 according to this embodiment will be described with reference to Figures 8 and 9. In this modified example, the linear polarizer 211, linear polarizer 312, quarter-wave plate 222, and quarter-wave plate 311 are arranged such that the absorption axis of the linear polarizer 211 and the absorption axis of the linear polarizer 312 are orthogonal, and the delay axis of the quarter-wave plate 222 and the delay axis of the quarter-wave plate 311 are orthogonal.

[0078] Figure 8 shows a modified example of the combination of linear polarizers (221, 312) and quarter-wave plates (222, 311) in this embodiment.

[0079] In Figure 8, the direction of propagation of the light pulse PO or reflected light RL is defined as the X-axis, the horizontal direction (horizontal axis of the paper) as the Y-axis, and the vertical direction (vertical axis of the paper) as the Z-axis.

[0080] Figure 8(a) shows the orientation of the linear polarizer 211. The linear polarizer 211 is positioned so that the absorption axis of linearly polarized light is in the horizontal direction (Y-axis direction). When the light pulse PO emitted by the light source device 21 passes through the linear polarizer 211, the light that oscillates horizontally (Y-axis direction) (Y component) is attenuated, and the light that oscillates vertically (Z-axis direction) (Z component) passes through. Therefore, the linear polarizer 211 emits the Z component of linearly polarized light pulse PO to the quarter-wave plate 222.

[0081] Figure 8(b) shows the orientation of the quarter-wave plate 222. The quarter-wave plate 222 is positioned such that its delay axis for shifting by 1 / 4 wavelength (1 / 4 phase) is at a 45-degree angle to the horizontal direction (Y-axis direction). In other words, the quarter-wave plate 222 converts the linearly polarized light pulse PO of the Z component emitted by the linear polarizer 211 into a clockwise (right-rotating) rotationally polarized light pulse PO and radiates it onto the subject OB.

[0082] Figure 8(c) shows the orientation of the quarter-wave plate 311. The quarter-wave plate 311 is positioned so that its delay axis is perpendicular to that of the quarter-wave plate 222, and the delay axis is positioned at -45 degrees (135 degrees) with respect to the horizontal direction (Y-axis direction). That is, when the quarter-wave plate 311 receives counterclockwise (left-rotating) rotational polarization as the reflected light RL in the direct path, it emits reflected light RL of linear polarization of the Y component. Also, when the quarter-wave plate 311 receives clockwise (right-rotating) rotational polarization as the reflected light RL in the multi-path, it emits reflected light RL of linear polarization of the Z component.

[0083] Furthermore, Figure 8(d) shows the orientation of the linear polarizer 312. The linear polarizer 312 is positioned so that its absorption axis is perpendicular to that of the linear polarizer 211, and so that the absorption axis of linearly polarized light is in the vertical direction (Z-axis direction). When reflected light RL passes through the linear polarizer 312, the light that oscillates horizontally (Y-axis direction) (Y component) is attenuated, and the light that oscillates horizontally (Y-axis direction) (Y component) passes through.

[0084] Therefore, in the case of reflected light RL from a direct path, the linear polarizer 312 emits the reflected light RL of linear polarization of the Y component through the lens 313 to the light-receiving area 320 of the distance image sensor 32.

[0085] Furthermore, in the case of multipath reflected light RL, the linear polarizer 312 blocks the reflected light RL of the linear polarization of the Z component, as the quarter-wave plate 311 emits the reflected light RL of the linear polarization of the Z component.

[0086] As shown in Figure 8, in the modified embodiment of this embodiment, the linear polarizer 211 and the quarter-wave plate 222 are arranged such that the absorption axis of the linear polarizer 211 and the delay axis of the quarter-wave plate 222 are at a 45-degree angle. In addition, the quarter-wave plate 311 and the linear polarizer 312 are arranged such that the delay axis of the quarter-wave plate 311 and the absorption axis of the linear polarizer 312 are at a 45-degree angle.

[0087] Furthermore, the linear polarizers 211 and 312 are positioned such that the absorption axis of the linear polarizer 211 and the absorption axis of the linear polarizer 312 are orthogonal to each other. Additionally, the quarter-wave plates 222 and 311 are positioned such that the delay axis of the quarter-wave plate 222 and the delay axis of the quarter-wave plate 311 are orthogonal to each other.

[0088] Figure 9 illustrates an example of the removal process of multipath reflected light RL in the distance image acquisition device 1, based on a modified example shown in Figure 8.

[0089] Figure 9(a) shows the characteristics of the linearly polarized light pulse PO emitted by the linear polarizer 211. The linear polarizer 211 emits a linearly polarized light pulse PO that contains only the Z component. Figure 9(b) also shows the characteristics of the circularly polarized light pulse PO emitted by the quarter-wave plate 222. The linear polarizer 211 emits a right-handed circularly polarized light pulse PO.

[0090] Furthermore, Figure 9(c) shows the characteristics of the reflected light RL reflected from the subject OB. The right-handed circularly polarized light pulse PO emitted by the linear polarizer 211 is reflected from the subject OB, and the direction of rotation is reversed, resulting in the left-handed circularly polarized reflected light RL.

[0091] Furthermore, Figure 9(d) shows the characteristics of the linearly polarized light pulse PO emitted by the quarter-wave plate 311 in the direct path case. In the direct path case, the quarter-wave plate 311 receives left-handed circularly polarized reflected light RL and emits linearly polarized reflected light RL containing only the Y component.

[0092] Furthermore, Figure 9(e) shows the characteristics of the linearly polarized reflected light RL emitted by the linear polarizer 312 in the case of a direct path. In the case of a direct path, the linear polarizer 312 receives linearly polarized reflected light RL containing only the Y component and emits linearly polarized reflected light RL containing only the Y component.

[0093] Furthermore, Figure 9(f) shows the characteristics of the reflected light RL in the case of multipath reflection, where the light is reflected by another object after being reflected by the subject OB. The reflected light RL, which is inverted at the subject OB and becomes left-handed circularly polarized, is reflected again by another object, and the direction of rotation is reversed, resulting in right-handed circularly polarized reflected light RL.

[0094] Furthermore, Figure 9(g) shows the characteristics of the linearly polarized light pulse PO emitted by the quarter-wave plate 311 in the case of multipath. In the case of multipath, the quarter-wave plate 311 receives the reflected light RL which is right-handed circularly polarized and emits the reflected light RL which is linearly polarized and contains only the Z component.

[0095] Furthermore, Figure 9(h) shows the characteristics of the reflected linearly polarized light RL emitted by the linear polarizer 312 in the case of multipath. In the case of multipath, the linear polarizer 312 receives the reflected linearly polarized light RL containing only the Z component. However, since the Z component is the same as the absorption axis, it absorbs the reflected light RL and does not emit it. In other words, in the case of multipath, the linear polarizer 312 removes the reflected light RL without allowing it to pass through.

[0096] Thus, in the distance image acquisition device 1 according to this embodiment, the multipath reflected light RL is removed by the light-collecting unit 31, and only the direct path reflected light RL is received by the distance image sensor 32.

[0097] As described above, the distance image imaging device 1 according to this embodiment comprises a light source device 21 (light source), a distance image sensor 32 (image sensor), a diffusion unit 22, a light concentrating unit 31, and a distance image processing unit 4. The light source device 21 (light source) emits light pulses PO. The distance image sensor 32 (image sensor) comprises a pixel array (light receiving area 320) in which a plurality of pixels 321 having photoelectric conversion elements PD that generate charge according to incident light are arranged. The diffusion unit 22 is a diffusion unit 22 that diffuses the light pulses PO emitted from the light source device 21, and comprises at least a first quarter-wave plate (quarter-wave plate 222) which is a quarter-wave plate that converts linearly polarized light based on the light pulses PO emitted from the light source device 21 into circularly polarized light. The light-gathering unit 31 is a light-gathering unit 31 that focuses the reflected light RL, which is reflected from the subject OB by the circularly polarized light pulse PO converted by the diffusion unit 22, onto the distance image sensor 32, and has at least a second quarter-wave plate (quarter-wave plate 311) which is a quarter-wave plate that converts the reflected light, which is circularly polarized, into linearly polarized light. The distance image processing unit 4 calculates the distance to the subject OB based on the output of the distance image sensor 32 for the reflected light RL, which is circularly polarized in the opposite rotation to the circularly polarized light converted by the quarter-wave plate 222.

[0098] As a result, in the distance image imaging device 1 according to this embodiment, the circularly polarized light pulse PO converted by the quarter-wave plate 222 and the reflected circularly polarized light RL rotating in the opposite direction become a direct path, and the reflected circularly polarized light RL in the same direction as the circularly polarized light pulse PO becomes a multipath, so the multipath reflected light RL can be eliminated. The distance image imaging device 1 according to this embodiment can accurately calculate the distance to the subject OB in the direct path by calculating the distance to the subject OB based on the output of the distance image sensor 32 for the reflected circularly polarized light RL rotating in the opposite direction, which is a direct path. Therefore, the distance image imaging device 1 according to this embodiment can suppress multipath errors and improve the accuracy of distance measurement.

[0099] Furthermore, in this embodiment, the diffusion unit 22 includes a quarter-wave plate 222 (first quarter-wave plate) and a linear polarizer 221 that converts the optical pulse PO into linearly polarized light. As a result, the distance image acquisition device 1 according to this embodiment can easily generate circularly polarized light pulses PO in the diffusion section 22 by combining the quarter-wave plate 222 (first quarter-wave plate) and the linear polarizer 221.

[0100] Furthermore, in this embodiment, the light-gathering unit 31 includes a quarter-wave plate 311 (a second quarter-wave plate) and a linear polarizer 312 that emits linearly polarized light RL of the reflected light RL that has passed through the quarter-wave plate 311.

[0101] As a result, the distance image acquisition device 1 according to this embodiment, by combining a quarter-wave plate 311 (second quarter-wave plate) and a linear polarizer 312, can easily remove multi-path reflected light RL at the light-gathering unit 31 and focus the direct-path reflected light RL onto the distance image sensor 32.

[0102] Furthermore, the distance image acquisition device 1 according to this embodiment can appropriately remove light other than the direct path, such as ambient light (corresponding to noise), using the light-collecting unit 31, thereby improving the accuracy of distance measurement.

[0103] Furthermore, in this embodiment, the quarter-wave plate 222 and the quarter-wave plate 311 are arranged so that their delay axes for the quarter-phase difference are orthogonal, and the absorption axis of the linear polarizer 221 in the diffusion section 22 and the absorption axis of the linear polarizer 312 in the light-gathering section 31 are orthogonal (see Figure 8).

[0104] As a result, the distance image acquisition device 1 according to this embodiment can easily remove multipath reflected light RL and focus the direct path reflected light RL onto the distance image sensor 32 by appropriately arranging the quarter-wave plate 222 and quarter-wave plate 311 and the linear polarizer 221 and linear polarizer 312.

[0105] Furthermore, in this embodiment, the quarter-wave plate 222 and the quarter-wave plate 311 are arranged so that their delay axes of the quarter-phase difference coincide, and the absorption axis of the linear polarizer 221 in the diffusion section 22 coincides with the absorption axis of the linear polarizer 312 in the light-gathering section 31 (see Figure 4).

[0106] As a result, the distance image acquisition device 1 according to this embodiment can easily remove multipath reflected light RL and focus the direct path reflected light RL onto the distance image sensor 32 by appropriately arranging the quarter-wave plate 222 and quarter-wave plate 311 and the linear polarizer 221 and linear polarizer 312.

[0107] Furthermore, in this embodiment, the distance image sensor 32 includes a pixel 321 having a photoelectric conversion element PD and a plurality of charge storage units CS for accumulating charge, and a pixel driving circuit 322 that distributes and accumulates charge in each of the charge storage units CS in the pixel 321 at a predetermined timing synchronized with the emission of an optical pulse PO. The distance image processing unit 4 determines the measurement distance to the subject OB based on the amount of charge accumulated in each of the charge storage units CS.

[0108] As a result, the distance image acquisition device 1 according to this embodiment distributes and accumulates charge in multiple charge storage units CS, and uses the amount of charge accumulated in each charge storage unit CS to determine the measurement distance to the subject OB, thereby enabling more accurate measurement of the measurement distance.

[0109] Next, with reference to the drawings, a distance image acquisition device 1a according to a second embodiment will be described.

[0110] [Second Embodiment] Figure 10 is a block diagram showing an example of a distance image acquisition device 1a according to the second embodiment. In this embodiment, a modified example in which the light source device 21a, which will be described later, emits linearly polarized light pulses PO will be explained.

[0111] As shown in Figure 10, the distance image acquisition device 1a comprises a light source unit 2a, a light receiving unit 3, and a distance image processing unit 4. In Figure 10, components identical to those in the first embodiment shown in Figure 1 are given the same reference numerals, and their descriptions are omitted.

[0112] The light source unit 2a, in accordance with the control from the distance image processing unit 4, irradiates the space of the object to be photographed, where the object OB whose distance is to be measured by the distance image acquisition device 1a is located, with light pulses PO. The light source unit 2a emits circularly polarized light pulses PO, similar to the first embodiment. The light source unit 2a also includes a light source device 21a and a diffusion unit 22a.

[0113] The light source device 21a has a function equivalent to the linear polarizer 211 of the first embodiment and emits linearly polarized light pulses PO.

[0114] The diffusion section 22a includes a quarter-wave plate 222 (first quarter-wave plate) and does not include a linear polarizer 221. The quarter-wave plate 222 converts the linearly polarized light pulse PO emitted by the light source device 21a into a circularly polarized light pulse PO and irradiates the subject OB with it.

[0115] The absorption axis of linearly polarized light from the light source device 21a and the delay axis of the quarter-wave plate 222 are the same as in the first embodiment. Furthermore, in this embodiment, the configuration other than the light source unit 2a is the same as in the first embodiment, so its description is omitted here.

[0116] As described above, the distance image imaging device 1a according to this embodiment comprises a light source device 21a, a diffusion unit 22a, a light concentrator 31, and a distance image processing unit 4. The light source device 21a emits linearly polarized light pulses PO. The diffusion unit 22a converts the linearly polarized light pulses PO emitted by the light source device 21a into circularly polarized light. The light concentrator 31 has at least a quarter-wave plate 311 that converts circularly polarized reflected light into linearly polarized light. The distance image processing unit 4 calculates the distance to the subject based on the output of the distance image sensor 32 for the reflected light which is circularly polarized in the opposite direction to the circular polarization converted by the quarter-wave plate 222.

[0117] As a result, the distance image acquisition device 1a according to this embodiment achieves the same effects as the first embodiment, suppressing multipath errors and improving the accuracy of distance measurement. Furthermore, by having the light source device 21a emit linearly polarized light pulses PO, the configuration of the diffusion unit 22a can be simplified.

[0118] It should be noted that the present invention is not limited to the embodiments described above, and can be modified without departing from the spirit of the invention. For example, in each of the embodiments described above, the light-gathering unit 31 was described as comprising a quarter-wave plate 311, a linear polarizer 312, and a lens 313, but it is not limited to this. For example, the lens 313 may be made of a metalens and configured to substitute for some or all of the functions of the quarter-wave plate 311 and the linear polarizer 312. That is, at least a part of the light-gathering unit 31 may be made of a metalens.

[0119] In other words, the light-gathering section 31 may be composed of a metalens in at least a portion of it. As a result, the distance image acquisition device 1(1a) can simplify the configuration of the light-gathering unit 31 (for example, by reducing the size in the thickness direction using a metalens).

[0120] Similarly, the diffusion section 22 may be configured to employ a metalens to substitute for some or all of the functions of the linear polarizer 221 and the quarter-wave plate 223. In other words, the diffusion section 22 (22a) may be composed of a metalens in at least a portion of it. As a result, the distance image acquisition device 1(1a) can simplify the configuration of the diffusion section 22 (for example, by reducing the size in the thickness direction using a metalens).

[0121] Furthermore, in each of the above embodiments, the linear polarizer 221 and the quarter-wave plate 223 may be replaced with other configurations such as a circular polarizing filter that combines two functions. Similarly, the quarter-wave plate 311 and the linear polarizer 312 may be replaced with other configurations such as a circular polarizing filter that combines two functions.

[0122] Furthermore, in each of the above embodiments, the arrangement and combination of the linear polarizer 221 and quarter-wave plate 223, and the quarter-wave plate 311 and linear polarizer 312 are not limited to the configurations shown in Figures 4 and 8 above. Other configurations are also acceptable as long as the light-gathering unit 31 removes (suppresses) the multi-path reflected light RL.

[0123] Furthermore, although the above embodiments describe an example in which the pixel 321 is equipped with multiple (for example, four) charge storage units CS, the invention is not limited to this, and the distance to the subject may be calculated using other methods that do not use multiple (for example, four) charge storage units CS.

[0124] Furthermore, although the above embodiment describes an example in which the distance image processing unit 4 is located inside the distance image capturing device 1, the invention is not limited to this, and the distance image processing unit 4 may be located outside the distance image capturing device 1.

[0125] Furthermore, in each of the embodiments described above, the photoelectric conversion element PD was described as an embedded photodiode that converts incident light photoelectrically to generate charge and stores the generated charge, but it is not limited to this, and the structure of the photoelectric conversion element PD can be arbitrary. The photoelectric conversion element PD may be, for example, a PN photodiode with a structure in which a P-type semiconductor and an N-type semiconductor are joined, or a PIN photodiode with a structure in which an I-type semiconductor is sandwiched between a P-type semiconductor and an N-type semiconductor. Moreover, the photoelectric conversion element PD is not limited to a photodiode, but may be, for example, a photogate type photoelectric conversion element.

[0126] Furthermore, each component of the distance image acquisition device 1(1a) described above has a computer system inside. The processing in each component of the distance image acquisition device 1(1a) described above may be performed by recording a program for realizing the functions of each component of the distance image acquisition device 1(1a) onto a computer-readable recording medium, loading the program recorded on this recording medium into the computer system, and executing it. Here, "loading the program recorded on the recording medium into the computer system and executing it" includes installing the program into the computer system. Here, "computer system" includes hardware such as the OS and peripheral devices.

[0127] Furthermore, "computer system" may include multiple computer devices connected via a network, including communication lines such as the Internet, WAN, LAN, and dedicated lines. "Computer-readable recording medium" refers to portable media such as flexible disks, magneto-optical disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into computer systems. Thus, the recording medium storing the program may be a non-transient recording medium such as a CD-ROM.

[0128] Furthermore, the recording medium also includes internal or external recording media accessible from the distribution server for distributing the program. The program may be divided into multiple parts, downloaded at different times, and then combined in each configuration of the distance image acquisition device 1(1a), and different distribution servers may distribute each of the divided programs. Additionally, "computer-readable recording media" includes volatile memory (RAM) within computer systems that act as servers or clients when a program is transmitted over a network, which retains the program for a certain period of time. Moreover, the program may be intended to implement only a part of the functions described above. Furthermore, the program may be a so-called differential file (differential program) that can implement the functions described above in combination with a program already recorded in the computer system.

[0129] Furthermore, some or all of the above-mentioned functions may be implemented as integrated circuits such as LSIs (Large Scale Integrations). Each of the above-mentioned functions may be implemented as an individual processor, or some or all of them may be integrated into a single processor. In addition, the method of implementing integrated circuits is not limited to LSIs; they may also be implemented using dedicated circuits or general-purpose processors. Furthermore, if advances in semiconductor technology lead to the emergence of integrated circuit technologies that can replace LSIs, integrated circuits using such technologies may be used. [Explanation of Symbols]

[0130] 1, 1a... Distance image acquisition device 2, 2a...Light source section 3...Light receiving section 4… Distance image processing unit 21, 21a...Light source device 22, 22a... Diffusion section 31... Light-gathering section 32... Distance image sensor 41... Timing control unit 42...Distance calculation section 43...Measurement Control Unit 221, 312… Linear polarizers 222, 311…1 / 4 wavelength plate 313... Lens 320…Light receiving area 321... pixels 322...Pixel driving circuit 323…Vertical scanning circuit 324... Horizontal scanning circuit 325...Pixel signal processing circuit 326...Control circuit C, C1, C2, C3, C4... Capacitors CG, CG1, CG2, CG3, CG4... Common gate CS, CS1, CS2, CS3, CS4...Charge storage section FD, FD1, FD2, FD3, FD4… Floating Diffusion G, G1, G2, G3, G4… Transfer transistors GD, GD1, GD2... Charge Emission Transistors OB…Subject PD…Photoelectric converter PO... Light pulse RL…Reflected light RT, RT1, RT2, RT3, RT4… Reset transistors SF, SF1, SF2, SF3, SF4… Source follower transistors SL, SL1, SL2, SL3, SL4… Selective transistors

Claims

1. A light source that emits light pulses, An image sensor comprising a pixel array in which multiple pixels are arranged, each having a photoelectric conversion element that generates an electric charge corresponding to incident light, A diffusion unit for diffusing the light pulses emitted from the light source, the diffusion unit having at least a first quarter-wave plate which is a quarter-wave plate that converts linearly polarized light pulses emitted from the light source into circularly polarized light, A light-gathering unit that focuses the reflected light, which is reflected by the subject from the circularly polarized light pulse converted by the diffusion unit, onto the image sensor, the light-gathering unit having at least a second quarter-wave plate which is a quarter-wave plate that converts the circularly polarized reflected light into linearly polarized light, A distance image processing unit calculates the distance to the subject based on the output of the image sensor for the reflected light, which is circularly polarized in the opposite direction to the circularly polarized light converted by the first quarter-wave plate. A distance image acquisition device equipped with the following features.

2. The aforementioned diffusion section is The first quarter-wave plate and, A linear polarizer that converts the aforementioned light pulse into linearly polarized light, A distance image capturing device according to claim 1, comprising:

3. The aforementioned light-gathering unit is The second quarter-wave plate and, A linear polarizer that emits linearly polarized light of the reflected light that has passed through the second quarter-wave plate and The distance image capturing device according to claim 2, comprising:

4. The first quarter-wave plate and the second quarter-wave plate are arranged such that their delay axes for the quarter-phase difference are orthogonal to each other. The absorption axis of the linear polarizer in the diffusion section and the absorption axis of the linear polarizer in the light-gathering section are arranged to be perpendicular to each other. The distance image acquisition device according to claim 3.

5. The first quarter-wave plate and the second quarter-wave plate are arranged such that their delay axes for the quarter-phase difference coincide. The absorption axis of the linear polarizer in the diffusion section and the absorption axis of the linear polarizer in the light-gathering section are arranged to coincide. The distance image acquisition device according to claim 3.

6. The light source emits the light pulses which are linearly polarized. The distance image acquisition device according to claim 1.

7. The diffusion section is composed of at least a portion of a metalens. The distance image acquisition device according to claim 1.

8. The light-gathering section is composed of at least a portion of a metalens. The distance image acquisition device according to claim 1.

9. The aforementioned imaging sensor is The photoelectric conversion element and the pixel having a plurality of charge storage units for accumulating the charge, and the pixel driving circuit which distributes and stores the charge in each of the charge storage units in the pixel at a predetermined timing synchronized with the emission of the light pulse, The distance image processing unit determines the measurement distance to the subject based on the amount of charge accumulated in each of the charge storage units. A distance image capturing apparatus according to any one of claims 1 to 8.

Images