Ranging device

Abstract

The present disclosure improves the utilization efficiency of light beams in a ToF-type ranging device. The ranging device comprises: an image-forming optical system; a light-receiving element that includes a first microlens array; a light-emitting element that includes a second microlens array and emits linearly polarized pulsed light through the second microlens array; a polarization beam splitter that is disposed in the image-forming optical system, projects light emitted from the light-emitting element onto a measurement object, and includes a partial reflection surface for guiding the light from the measurement object to the light-receiving element; and a calculation part that calculates the distance from the measurement object to the light-receiving element by using a signal that is outputted by the light-receiving element upon reception of the light emitted from the light-emitting element and reflected by the measurement object. The partial reflection surface is arranged such that the angle formed by the central optical axis of the image-forming optical system and the normal line of the partial reflection surface is greater than 0° and less than 90°. The light-receiving element and the light-emitting element are separately arranged, on a side where the light from the measurement object is reflected by the partial reflection surface and on a side where the light penetrates, at positions where the distance between the partial reflection surface and the light-receiving element is substantially the same as the distance between the partial reflection surface and the light-emitting element, and conjugation is achieved for the measurement object via the image-forming optical system.

Description

distance measuring device

[0001] This disclosure relates to a distance measuring device that uses light to measure distance.

[0002] A distance measuring device is known that measures the distance to an object by irradiating the object with a light pulse and measuring the time-of-flight (ToF), which is the time it takes from irradiating the object until the reflected light from the object is received.

[0003] Patent documents 1 and 2 disclose devices that perform distance measurement using the Time of Flight (TF) method.

[0004] In this type of Time-of-Flight (TOF) distance measuring device, pulsed laser light can be used to project light onto the subject. When humans are also considered as subjects, the intensity of the projected laser light must meet eye-safe conditions, and there is an upper limit to the intensity of the laser light that can be projected. Since the intensity of reflected light from the subject decreases with distance, projecting pulsed light of sufficient intensity onto the subject within the range that meets eye-safe conditions is effective for high-sensitivity distance measurement in order to extend the measurable distance.

[0005] Furthermore, the attenuation of light emitted from a light source within the measuring device due to various losses within the device before it is emitted from the optical system means that more energy is required to project pulsed light of a predetermined intensity onto the subject. Therefore, it is desirable to suppress light loss within the measuring device.

[0006] Patent No. 7234171 Publication Special Publication No. 2021-518560

[0007] However, in the technology disclosed in Patent Document 1, when light is projected, the light emitted from the light source in the measuring device is split by a partial reflector. One of the split parts is projected onto the subject, but the other part is lost within the device without being projected onto the subject. Therefore, there is room for improvement in the efficiency of light utilization.

[0008] Furthermore, while Patent Document 2 mentions the use of polarized light sources and polarized beam splitters, the efficiency of light utilization is still not sufficiently high.

[0009] This disclosure was made in view of the above-mentioned problems, and aims to improve the efficiency of light utilization in a Time-of-Flight (ToF) type distance measuring device.

[0010] The distance measuring device according to this disclosure includes an imaging optical system, a photodetector having a first microlens array, a light-emitting element having a second microlens array and emitting linearly polarized pulsed light through the second microlens array, a polarization beam splitter disposed in the imaging optical system and having a partial reflective surface that projects the light emitted from the light-emitting element onto the object to be measured and guides the light from the object to be measured to the photodetector, and a signal output by the photodetector when it receives the light emitted from the light-emitting element and reflected by the object to be measured, which is used to determine the distance from the object to be measured. The system comprises a calculation means for calculating the distance to the light-receiving element, wherein the partial reflective surface is arranged such that the angle between the central optical axis of the imaging optical system and the normal to the partial reflective surface is greater than 0° and less than 90°, and the light-receiving element and the light-emitting element are arranged separately on the side where light from the object to be measured is reflected by the partial reflective surface and the side where light is transmitted, such that the distance between the partial reflective surface and the light-receiving element is substantially the same as the distance between the partial reflective surface and the light-emitting element, and are arranged in a position conjugate to the object to be measured via the imaging optical system.

[0011] This disclosure makes it possible to improve the efficiency of light utilization in Time-of-Flight (Tof) distance measuring devices. Other features and advantages of the technical ideas derived from this disclosure will become clear from the following description with reference to the attached drawings. In the attached drawings, the same or similar components are given the same reference numeral.

[0012] The attached drawings are included in the specification and constitute a part thereof, illustrating embodiments in this disclosure and used to explain the technical ideas derived from this disclosure together with their descriptions. Block diagram showing the configuration of a distance measuring device relating to the first embodiment of this disclosure. Schematic diagram illustrating the overall configuration of the distance measuring device. Schematic diagram illustrating the configuration of the light-emitting element array. Schematic diagram illustrating the configuration of the light-receiving element array. Schematic diagram showing an afocal optical system. Schematic diagram illustrating the appearance of the focused image on the subject and on the light-receiving element array. Schematic diagram illustrating the appearance of the focused image on the subject and on the light-receiving element array. Schematic diagram illustrating the appearance of the focused image on the subject and on the light-receiving element array. Schematic diagram illustrating the appearance of the focused image on the subject and on the light-receiving element array. Schematic diagram illustrating the light-emitting unit. Schematic diagram illustrating the measurement unit. Block diagram illustrating the configuration of the pixels. Schematic diagram illustrating the configuration of the TDC array. Block diagram illustrating the configuration of the oscillator. Schematic diagram showing the state of the buffer when the oscillator is reset. Schematic diagram showing the state of the buffer when the oscillator is reset. Timing chart showing the operation of the light-emitting element and light-receiving element. Timing chart showing the operation of the light-emitting element and light-receiving element. A schematic diagram illustrating the configuration of the oscillation adjustment voltage generation circuit. A schematic diagram illustrating the function of the polarizing beam splitter included in the optical system. A schematic diagram illustrating the function of the polarizing beam splitter included in the optical system. A schematic diagram illustrating the function of the polarizing beam splitter included in the optical system. A schematic diagram illustrating the function of the polarizing beam splitter and quarter-wave plate included in the optical system. A schematic diagram illustrating the function of the polarizing beam splitter included in the optical system. A schematic diagram illustrating the arrangement of the quarter-wave plate included in the optical system and the related drive control of the distance measuring device. A schematic diagram illustrating the arrangement of the quarter-wave plate included in the optical system and the related drive control of the distance measuring device. A flowchart illustrating the distance measuring operation. A flowchart illustrating the distance measuring operation. A schematic diagram illustrating the optical system in the second embodiment.

[0013] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the scope of the claims. While the embodiments describe multiple features, not all of these features are necessary, and the features may be combined in any way. Furthermore, in the attached drawings, identical or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0014] (First Embodiment) Hereinafter, a first embodiment of the distance measuring device of the present disclosure will be described in detail with reference to the attached drawings.

[0015] <Overall Configuration of the Distance Measuring Device> Figure 1 is a schematic block diagram showing the configuration of the distance measuring device 100 according to the first embodiment of the present disclosure. Solid lines connecting each block indicate signal exchange, dashed lines indicate illumination light projected onto the subject (the object to be measured for distance), and dashed lines indicate reflected light from the subject.

[0016] The distance measuring device 100 is comprised of a light projection unit 110, a measurement unit 120, an imaging lens 130 which is an imaging optical system, an overall control unit 140, and a polarizing beam splitter 150.

[0017] The light projection unit 110 is configured to include a light source unit 113 having a light-emitting element array 111 in which light-emitting elements 111a are arranged in a two-dimensional array, a light-emitting element drive unit 112, and a light source control unit 114.

[0018] The measurement unit 120 is comprised of a photodetector array 121 in which photodetectors are arranged in a two-dimensional array, a TDC (Time-to-Digital Converter) array section 122, a signal processing section 123, a measurement control section 124, and a row selection circuit 125.

[0019] The overall control unit 140 is equipped with a CPU and controls the entire range measuring device 100 by executing a control program stored in the memory 141.

[0020] The polarizing beam splitter 150 has a half-mirror (partially reflective surface) 151 that transmits specific polarizations and reflects specific polarizations. When a specific linearly polarized light is incident at a Brewster angle, this half-mirror 151 has the property of transmitting this specific linearly polarized light and reflecting linearly polarized light in a direction perpendicular to this specific linearly polarized light.

[0021] Furthermore, it is desirable to place a bandpass filter on the photodetector array 121 that transmits light of wavelengths including the wavelength emitted by the light-emitting element array 111 and reflects and absorbs light of other wavelengths. The bandpass filter can be made of, for example, a dielectric multilayer film, but is not limited to this.

[0022] Each light-emitting element 111a of the light-emitting element array 111 emits pulsed light, which is projected into space via the imaging lens 130. The pulsed light emitted from each separate light-emitting element 111a is projected into a different field of view in space. The projected light is irradiated onto a subject, and a portion of the light reflected by the subject is received by the photodetector array 121 via the imaging lens 130. The time from when the light-emitting element 111a emits light until it is received by the photodetector array 121 is the time of flight (ToF), and this time is measured by the TDC array unit 122. However, a single measurement cannot eliminate noise components such as ambient light and dark counts, and the distance measurement error becomes large due to the influence of noise in the measurement circuit. Therefore, the time measurement from emission to reception is repeated, and the signal processing unit 123 creates a histogram of the measurement results to remove noise components and average the measurement results. By substituting the time of flight ToF obtained in this way into the following equation (1), the distance L to the subject can be determined with high accuracy. Here, c is the speed of light.

[0023] L = ToF × c / 2 … (1) <Light-emitting and light-receiving optical system> Figure 2 is a schematic diagram illustrating the overall configuration of the distance measuring device 100.

[0024] In Figure 2, the dashed line AOB represents the central optical axis of the imaging lens 130. The subject (not shown) is located on side A, and the dashed line AOB connects the subject, the polarizing beam splitter 150, and the photodetector array 121. On the other hand, the dashed line AOC represents the central optical axis of the optical system connecting the subject, the polarizing beam splitter 150, and the light-emitting element array 111.

[0025] Here, the light-receiving element array 121 and the light-emitting element array 111, which are positioned at different spatial locations, are arranged to be conjugate with respect to the subject via the imaging lens 130. Specifically, the light-receiving element array 121 and the light-emitting element array 111 are positioned separately on the side where light from the subject is reflected by the polarizing beam splitter 150 and the side where it is transmitted. Therefore, the distance L1 (OB distance) between the polarizing beam splitter 150 and the light-receiving surface M of the light-receiving element array 121 and the distance L2 (OC distance) between the polarizing beam splitter 150 and the light-emitting element array 111 are designed to be substantially equidistant (L1 = L2). As shown in Figure 2, the x, y, and z axes are defined as being orthogonal to each other. The y axis is parallel to the optical axis AO, and the z axis is parallel to the optical axis OC. The light-receiving surface M of the light-receiving element array 121 is orthogonal to the y axis.

[0026] Figure 3 is a side view illustrating the schematic configuration of the light-emitting element array 111. In this embodiment, the light-emitting element array 111 has light-emitting elements 330 formed in a two-dimensional array on a gallium arsenide (GaAs) semiconductor substrate 320. Microlenses 340 are arranged in a two-dimensional array above each light-emitting element 330, thereby forming a microlens array. Each microlens 340 collimates (makes the divergence angle close to 0°) or suppresses divergence of light from the corresponding light-emitting element 330.

[0027] In the light-emitting element array 111, a surface-emitting laser VCSEL (Vertical Cavity Surface Emitting Laser) with an oscillation center wavelength of approximately 800 nm is used as the light-emitting unit 330. By using light with a wavelength outside the visible light wavelength band used for imaging, it becomes easy to distinguish between the distance measurement signal and the imaging signal using the ToF method. The light-emitting unit 330 is not limited to the above configuration; for example, a stripe-type laser, light-emitting diode (LED), quantum dot element, or organic EL element can also be used. Since the light emitted from many minute light-emitting elements, including the surface-emitting laser, is diffuse light, the diffusion of the light emitted from the light-emitting unit 330 is suppressed by the microlens 340. The light-emitting unit of the light-emitting element array 111 may be a single light source, but a microlens array is necessary.

[0028] When the distance measuring device 100 of this embodiment is used in combination with an imaging device such as a camera, it is particularly necessary to project light with high efficiency while taking into account manufacturing variations in the light-emitting parts 330, etc., of the light-emitting element array 111. To this end, it is desirable to set the light projection area to be slightly inside the subject area corresponding to the imaging angle of view of the imaging device. In other words, it is desirable to set the light projection area from the light-emitting element array 111 to be narrower than the subject area corresponding to the imaging angle of view. In the description of this embodiment, the expressions "same" and "match" are not to be interpreted strictly, but rather include a certain range in which intentional deviations and assembly errors are permitted as long as the desired performance is obtained.

[0029] Figure 4 shows a schematic configuration of the photodetector array 121. Each photodetector 121a in the photodetector array 121 is configured with a light-receiving section 430 and a microlens 440 provided on a silicon (Si) substrate 420. The array period of the photodetector array 121 is, for example, 60 micrometers. It is also preferable to set the array period of the photodetector array 121 to be equal to the array period of the light-emitting element array 111 in Figure 3, and to set the focal length of the microlens 440 of the photodetector array 121 to be equal to the focal length of the microlens 340 of the light-emitting element array. However, the configuration is not limited to this. For example, an optical configuration in which n × m light-receiving sections 430 in Figure 4 correspond to and receive light from one light-emitting section 330 in Figure 3, or a configuration in which the focal lengths of the microlens 340 of the light-emitting element array and the microlens 440 of the photodetector array are different is also possible.

[0030] It is also preferable from the viewpoint of improving the signal-to-noise ratio to place a pinhole array (not shown) in close proximity to the microlens 440 of the photodetector array 121. The pinhole diameter is preferably approximately equal to the size of the image of the aperture diameter of the VCEL formed on the surface of the photodetector array 121, for example, when the light-emitting element array 111 is a VCSEL array.

[0031] It is also preferable to place a narrowband bandpass filter in the light-receiving element array 121. From the viewpoint of improving the signal-to-noise ratio, it is preferable to use a narrowband bandpass filter to transmit only the light of the wavelength emitted by the light-emitting element array 111 to the light-receiving unit 430, and to prevent light of other wavelengths from reaching the light-receiving unit 430. The transmission wavelength bandwidth of the bandpass filter is, for example, about 20 nm, which includes the emission wavelength of the laser. The bandpass filter may be placed on the microlens 440 of the light-receiving element 121a, or it may be built into the light-receiving unit closer to the microlens 440. Alternatively, it may be placed near the polarizing beam splitter 150 or before or after the imaging lens 130, as long as it is on the optical path on the light-receiving side.

[0032] The imaging lens 130, which is an image-side telecentric optical system, preferably forms an afocal system with the microlens array (microlens 340) of the light-emitting element array 111. Therefore, using FIG. 5, the state of the projected image after the light emitted from the light-emitting element 111a of the light-emitting element array 111 passes through the imaging lens (image-side telecentric lens) 130 in the case of an afocal system will be described.

[0033] The microlens 340 and the imaging lens 130 constitute an afocal system. For this reason, when projected from the imaging lens 130, it is projected at an angle corresponding to the image height (the positional relationship between the microlens 340 and the imaging lens 130) and is projected in parallel. Therefore, the width db (thickness in three dimensions) of the projected light is projected with the same width (thickness in three dimensions) at any distance on the subject side as seen from the imaging lens 130 (independent of the distance to the subject). However, if the light-emitting diameter on the microlens 340 is p (when p is larger than the pitch of the microlens, p is limited by the pitch of the microlens), the focal length of the microlens 340 is fM, and the focal length of the imaging lens 130 is fL, the width db of the projected light is expressed by the following formula (2). However, when the width db of the projected light is larger than the pupil diameter of the imaging lens 130, the width db of the projected light is limited by the pupil diameter.

[0034] db = p·fL / fM …(2) Here, although the configuration omits the collimating lens, when the spread of the light emitted from the light-emitting element 111 is large, a collimating lens may be inserted between the light-emitting unit 330 and the microlens 340 for collimation.

[0035] Next, referring to FIGS. 6A to 6C, the state of the projected light described in FIG. 5 as seen on the subject will be described. FIGS. 6A to 6C are diagrams showing the state in which the projected light is projected onto the subject (object) 601. In FIGS. 6A to 6C, the projected light is projected as a projected image 602 onto the subject 601. The projected image size db in FIGS. 6A to 6C and the width db of the projected light in FIG. 5 are equal to each other. The subject 601 is shown as FIGS. 6A, 6B, and 6C in order from the closest to the imaging lens 130.

[0036] As shown in FIGS. 6A to 6C, as the distance from the imaging lens 130 increases, the projection light interval increases, but the projection image size db does not change. That is, the interval of the projection light (projection light interval) irradiated to the subject 601 through the imaging lens 130 changes according to the distance to the subject 601. On the other hand, the width of each of the plurality of projection lights (projection image size db) does not change according to the distance to the subject 601.

[0037] Since the light emitted from a certain light emitting element 111a forms a projection image 602 on the light receiving element array 121, as shown in FIG. 6D, it is possible to cause light reception only by a specific light receiving element 121a in the light receiving element array 121. That is, it is possible to make the light emitting element 111a and the light receiving element 121a in FIG. 5 correspond to each other one-to-one. For this reason, it is possible to cause only a part of the plurality of light emitting elements 111a to emit light, and to drive only the light receiving element 121a corresponding to the light emitting element 111a that has emitted light among the plurality of light receiving elements 121a. For example, it is possible to drive the corresponding light emitting element 111a and the light receiving element 121a sequentially. As a result, one TDC can be shared by the plurality of light receiving elements 121a, and the pixel size can be reduced, which is effective for increasing the resolution.

[0038] <Projection unit> FIG. 7 is a schematic diagram showing the configuration of the light source unit 113 and the light source control unit 114 that constitute the projection unit 110 in the present embodiment.

[0039] The light emitting element array 111 is configured such that VCSELs are arranged in a two-dimensional array as the light emitting elements 111a on a substrate. The light emitting element array 111 also has a microlens array. Further, the light emitting element driving unit 112 is formed by arranging light emitting element row driving circuits 702 in a one-dimensional array.

[0040] The light-emitting element 111a is not limited to VCSELs, but is preferably one that can be integrated in a one-dimensional or two-dimensional array, such as an end-face emitting laser or an LED (light-emitting diode). When an end-face emitting laser is used instead of a VCSEL array as the light-emitting element 111a, a laser bar arranged in one dimension on a substrate, or a laser bar stack which is stacked to form a two-dimensional light-emitting element array, can be used. When an LED is used as the light-emitting element, one in which LEDs are arranged in a two-dimensional array on a substrate can be used.

[0041] In the distance measuring system of this embodiment, it is preferable to set the emission wavelength of the light-emitting element 111a to the near-infrared band in order to suppress the influence of ambient light. However, it is not limited to this. VCSELs are manufactured using semiconductor processes, and when the emission wavelength is set to the near-infrared band, GaAs-based semiconductor materials can be mainly used as the semiconductor material. In this case, the dielectric multilayer film that forms the DBR (distributed reflection) mirror constituting the VCSEL can be made of two thin films made of materials with different refractive indices that are alternately and periodically stacked (GaAs / AlGaAs). The emission wavelength can be changed by adjusting the combination of elements and composition of the compound semiconductor.

[0042] Furthermore, the VCSELs forming the VCSEL array are equipped with electrodes for injecting current and holes into the active layer. These electrodes are shared in the row direction and connected to light-emitting element row driving circuits 702 located in each row. By operating only a specific light-emitting element row driving circuit 702 among the light-emitting element driving circuits 112, current is injected only into the VCSELs belonging to a specific row, making it possible to cause the light-emitting elements in that specific row to emit light. Additionally, by controlling the driving current of the VCSELs, it is possible to emit arbitrary pulsed light or modulated light.

[0043] Furthermore, the light source used in this embodiment is a light source that generates linearly polarized light. For this purpose, the light source itself may be a light source that generates linearly polarized light, or the light emitted from the light source may be converted into light with a desired polarization component by a polarizer or the like before it is incident on the polarizing beam splitter.

[0044] <Measurement Unit> [Light-receiving element array, row selection circuit] Figure 8 is a schematic diagram showing the configuration of the measurement unit 120 in this embodiment.

[0045] The measurement unit 120 includes a photodetector array 121 in which pixels 801 equipped with photodetectors 430 are arranged in a two-dimensional array, a TDC array section 122, a signal processing section 123, and a measurement control section 124. In addition, it includes a row selection circuit 125 for activating only specific rows, a row selection pulse wiring 803 that outputs the output signal of the row selection circuit 125 to the pixels 801, and a pixel output line 804 that outputs the output signal of the pixels to the TDC array section 122.

[0046] Figure 9 is a block diagram showing the schematic configuration of a pixel 801 in this embodiment. The pixel 801 comprises a SPAD element 901 which is a light-receiving element, a load transistor 902, an inverter 903, a pixel output circuit 904, a row selection pulse wiring 803, and a pixel output line 804. The SPAD element 901 has a light-receiving region and an avalanche region.

[0047] When light is incident on the SPAD element 901, it is photoelectrically converted in the light-receiving region, generating electrons and holes. The positively charged holes are discharged through the anode electrode Vbd. The negatively charged electrons are transported as signal charges to the avalanche region by an electric field set to decrease in potential toward the avalanche region within the light-receiving region. The signal charges that reach the avalanche region undergo avalanche breakdown due to the strong electric field in the avalanche region, generating an avalanche current.

[0048] When no avalanche current is flowing, the voltage of the anode electrode Vbd is set so that a reverse bias greater than the breakdown voltage is applied to the avalanche region of the SPAD element 901. At this time, since there is no current flowing through the load transistor 902, the cathode potential Vc is close to the power supply voltage Vdd, and the inverter output signal is "0".

[0049] When a photon arrives, an avalanche current is generated in the SPAD element 901, causing the voltage Vc to drop and the output of the inverter 903 to invert. In other words, the inverter output changes from "0" to "1".

[0050] As the potential of Vc decreases, the reverse bias applied to the SPAD element 901 decreases, and the generation of avalanche current stops when the reverse bias falls below the breakdown voltage.

[0051] Subsequently, a hole current flows from Vdd to Vc through the load transistor 902, causing the cathode potential Vc to rise and the inverter output to return from "1" to "0," returning to the state before the arrival of the photon.

[0052] Furthermore, in pixels 801 where the row selection pulse wiring 803 is turned on, the output of the inverter 903 is controlled to be output to the pixel output line 804. Conversely, in pixels 801 where the row selection pulse wiring 803 is turned off, the inverter output is controlled to be disconnected from the pixel output line 804. As a result, it is possible to detect only the light incident on a specific row selected by the row selection circuit 125.

[0053] In this way, the light detection at the pixels belonging to the row selected by the row selection circuit 125 can be output to the TDC array unit 122 as a low-latency digital signal.

[0054] [TDC Array Section] In the TDC (Time-to-Digital Converter) array section 122, the time from the time the light source unit 111 emits light until the pixel output signal changes from "0" to "1" is measured as the ToF time.

[0055] Figure 10 is a schematic diagram of the TDC array unit 122. The TDC array unit 122 has TDCs 1001 arranged for the number of pixels in the horizontal direction of the pixel array, and can simultaneously measure the pixel output of one row. The TDC 1001 includes an oscillator 1011, an oscillation count circuit 1021, and a synchronous clock count circuit 1031. The count result from the synchronous clock count circuit 1031 is the upper bit, the internal signal of the oscillator 1011 is the lower bit, and the count result from the oscillation count circuit 1021 is the bit in between. In other words, the synchronous clock count circuit 1031 measures roughly, the internal signal of the oscillator 1011 measures finely, and the oscillation count circuit 1021 measures in between. Alternatively, each may be configured to have redundant bits.

[0056] Figure 11 is a schematic diagram of the oscillator 1011 of the TDC 1001. The oscillator 1011 includes an oscillation start / stop signal generation circuit 1140, buffers 1111 to 1118, an oscillation switch 1130, and a delay adjustment current source 1120. The buffers 1111 to 1118 and the oscillation switch 1130 are connected alternately in a loop configuration of eight stages.

[0057] Figures 12A and 12B are tables showing the output signals of buffers 1111 to 1118 and the internal signal of oscillator 1011 at the time of reset, and the output signals of buffers 1111 to 1118 and the internal signal of oscillator 1011 after a certain period of time has elapsed since the oscillation switch 1130 was turned on. At the time of reset, the outputs of buffers 1111 to 1117 are "0", and the output of buffer 1118 is "1". After the oscillation switch 1130 is turned on and a delay time of one buffer stage tbuff has elapsed, the outputs of buffers 1112 to 1118, which have matching input / output, do not change. Only the output of buffer 1111, which does not have matching input / output, changes from "0" to "1" (the signal advances by one stage). Furthermore, after a delay time equivalent to one buffer stage, tbuff, has elapsed (after 2 x tbuff), the outputs of buffers 1111 and 1113-1118, which have matching input / output, remain unchanged, while only the output of buffer 1112, which does not have matching input / output, changes from "0" to "1" (the signal advances by one stage).

[0058] In this way, with each buffer stage delay time tbuff, the output of one buffer whose input / output is not matched changes sequentially. After the oscillation switch 1130 is turned on, after 8 × tbuff, the outputs of all buffers change (the signal completes one cycle), and 16 (2 4 After ) × tbuff, all buffers change further (signal cycles twice) and return to their original state. Thereafter, the same operation is repeated every 16 × tbuuf time. In this way, time measurement is performed with a time resolution of tbuff. Furthermore, this time resolution tbuff is 1 / (2) of the synchronous clock by the oscillation adjustment voltage generation circuit 1041 described later. 7 It is adjusted to be such that...

[0059] Furthermore, the output of the oscillator 1011, which is the output of the buffer 1118, is input to the oscillation count circuit 1021. The oscillation count circuit 1021 counts the rising edges of the output of the oscillator 1011, thereby achieving a time resolution of 16 (2 4 Time measurement will be performed using ) × tbuff.

[0060] Figure 13 shows the timing from when a light-emitting element 111a belonging to a specific row of the light-emitting element array 111 emits light, until the SPAD element 901 receives the reflected light and the counting operation of the TDC 1001 is completed. It also shows the changes in the SPAD cathode potential Vc, pixel output signal, synchronous clock, synchronous clock count circuit, oscillator start / stop signal generation circuit output, oscillator output, and oscillator count circuit.

[0061] The SPAD cathode potential Vc is an analog voltage, with the upper side of the page indicating a higher voltage. The synchronous clock, the oscillator start / stop signal generation circuit output, and the oscillator output are digital signals, with the upper side of the page indicating the ON state and the lower side indicating the OFF state. The synchronous clock count circuit output and the oscillation count circuit output are digital values, shown as decimal numbers. Figure 14 is an enlarged view of Figure 13 from time T1303 to time T1305, showing the oscillator start / stop signal generation circuit output, oscillator output, oscillation count circuit output, and the internal signals of oscillator 1011. The internal signals of oscillator 1011 are digital values, shown as decimal numbers.

[0062] Using Figures 13 and 14, we will explain the operation of measuring the time from the light emission time T1301 of a light-emitting element 111a belonging to a specific row of the light-emitting element array 111 to the time T1303 when the pixel receives a photon, using TDC 1001.

[0063] At a time T1301, which is synchronized with the rising edge time of the synchronization clock supplied via the overall control unit 140, a specific light-emitting element row drive circuit 702 is driven so that a light-emitting element 111a belonging to a specific row of the light-emitting element array 111 lights up. The synchronization clock count circuit 1031 starts counting the rising edge of the synchronization clock from the time when the light-emitting element 111a lights up.

[0064] At time T1303, photons reflected from the subject are received by pixel 801, causing the SPAD cathode potential Vc to drop and the pixel output signal to change from "0" to "1". Upon receiving the pixel output signal as "1", the output of the oscillation start / stop signal generation circuit 1140 changes from "0" to "1", and the oscillation switch 1130 turns on. When the oscillation switch 1130 turns on, the oscillation operation begins, and a signal loop starts inside the oscillator 1011 as shown in Figures 12A, 12B, and 14. Every two loops of the signal inside the oscillator 1011, a rising edge appears at the output of the oscillator 1011, and the oscillation count circuit 1021 measures its number. Also at time T1303, the synchronous clock count circuit 1031 stops counting and holds the value.

[0065] After the oscillator 1011 is turned on, the timing when the synchronous clock first rises is time T1305. In response to the rising of the synchronous clock, the output of the oscillation start / stop signal generation circuit 1140 becomes "0", and the oscillation switch 1130 turns off. At the timing when the oscillation switch 1130 becomes "0", the oscillation ends, and the internal signal of the oscillator 1011 is held as it is. Also, since the oscillation stops, the counting of the oscillation count circuit 1031 also stops.

[0066] By doing so, the count result DGclk of the synchronous clock count circuit 1031 is the value obtained by counting the time from time T1301 to time T1302 with 2 7 × the time of tbuff. Also, the count result DROclk of the oscillation count circuit 1021 is the value obtained by counting the time from time T1303 to time T1304 with 2 4 × the time of tbuff. Furthermore, the internal signal DROin of the oscillator 1011 is the value obtained by counting the time from time T1304 to time T1305 with the time of tbuff. After performing the following processing on these signals, they are output to the signal processing unit 123, and one TDC operation is completed.

[0067] The count result DROclk of the oscillation count circuit 1021 and DROin of the oscillator 1011 are added together by the following formula (2).

[0068] DRO = 2 4 × DROclk + DROin …(2) DRO is the value obtained by counting the time from time T1303 to time T1305 with tbuff, and the time from time T1302 to time T1305 is the period of the synchronous clock and is 2 7 × tbuff. Therefore, as shown in the following formula (3), by subtracting DRO from the period of the synchronous clock and adding it to DGclk, the value DToF obtained by counting the flight time of light (the time from time T1301 to time T1303) with tbuff is obtained.

[0069] DToF = 2 7 × DGclk + (2 7 -DRO) = 2 7 × DGclk + (27 -2 4 ×DROCLK-DROin) …(3) The delay time tbuff for one buffer stage varies due to process factors such as transistor manufacturing tolerances, fluctuations in the voltage applied to TDC1001, and temperature, so an oscillation adjustment voltage generation circuit 1041 is provided for each TDC.

[0070] The oscillation adjustment voltage generation circuit 1041 has the configuration shown in Figure 15, and consists of a dummy oscillator 1501 and 1 / (2 3 It is equipped with a periodic oscillator 1502 and a phase comparator 1503. The dummy oscillator 1501 is the same oscillator as the oscillator 1011 mounted on the TDC 1001.

[0071] The output of the dummy oscillator 1501 is 1 / (2 3 ) is input to a period of 1502 minutes. 1 / (2 3 ) A period of 1502 is half the input clock frequency. 3 This circuit outputs a clock signal with double the clock frequency. Phase comparator 1503 has a synchronous clock and 1 / (2 3 The output of a period of 1502 is input. And the frequency of the synchronous clock is 1 / (2 3 The frequency of the output signal of the period 1502 is compared, and if the frequency of the synchronous clock is higher, the output voltage is increased, and if the frequency of the synchronous clock is lower, the output voltage is decreased. The output voltage of the phase comparator is input to the delay adjustment current source 1120 of the oscillator 1011, so that the oscillation frequency of the oscillator 1011 is 2 times that of the synchronous clock. 3 The voltage is adjusted to three times the original voltage.

[0072] Thus, the oscillation frequency is determined based on the synchronous clock frequency. Therefore, by generating the synchronous clock using an external IC that can output a constant frequency regardless of process / voltage / temperature changes, frequency variations due to process / voltage / temperature changes can be suppressed.

[0073] For example, by inputting a 160MHz clock to the synchronous clock frequency, the oscillation frequency becomes 8 (2) of the synchronous clock frequency. 3This results in a frequency of 1.28 GHz, which is double the original frequency. The delay time tbuff, which is the time resolution for one buffer stage, becomes 48.8 ps.

[0074] <Beam Splitter> Figure 16A is a schematic diagram showing cross-sections of the polarizing beam splitter 150, light-emitting element array 111, photodetector array 121, and imaging lens 130.

[0075] The light-emitting element array 111 and the light-receiving element array 121 are in a conjugate relationship via the half-mirror 151 of the polarizing beam splitter 150, and each light-emitting element 111a and each light-receiving element 121a are also in a conjugate relationship. In Figure 16A, both the light-emitting element array 111 and the light-receiving element array 121 are shown with 8 rows, but the number of rows is not limited to this. Also, although the light-emitting elements 111a and light-receiving elements 121a are configured to be in a one-to-one conjugate relationship, this is not limited to this, and the number of light-receiving elements may be n × n times the number of light-emitting elements, so that one light-emitting element is in a conjugate relationship with n × n light-receiving elements. Alternatively, the light-emitting elements 111a and light-receiving elements 121a are not necessarily limited to being in a conjugate relationship. In this explanation, the row numbers of the light-emitting element array 111 are assigned in ascending order from small to large Yv in Figure 16A, and the row numbers of the light-receiving element array 121 are assigned in ascending order from small to large Y in Figure 16A. Furthermore, the light-emitting element array and the light-receiving element array with the same row number are in a conjugate relationship.

[0076] In this embodiment, the polarizing beam splitter is cube-shaped and designed with an incident angle of 45 degrees. The half-mirror 151 of the polarizing beam splitter is positioned at a 45-degree angle to the optical axis of the imaging lens 130. Light from the light-emitting element array 111 is incident at a 90-degree angle to the optical axis and reflected at a right angle, thereby projecting light onto the subject along the optical axis. However, the shape of the polarizing beam splitter usable in this disclosure is not limited to cube shape. For example, a plate shape may also be used. In the case of a plate shape, the end face of the polarizing beam splitter does not directly face the central optical axis of the imaging optical system or the optical path of light emitted from the light source, making it preferable because reflected light from the end face of the polarizing beam splitter is less likely to return to the photodetector 121a or light-emitting element 111a.

[0077] Figure 16B shows the optical path of light when the light-emitting element in row 1 of the light-emitting element array 111 emits light. The light ray 1610 emitted from the light-emitting element array 111 is reflected by the half mirror 151 and becomes the light ray 1611 that illuminates the subject. We have explained the first row so far, but the same applies to the other rows.

[0078] The polarization component of the light ray 1610 emitted from the light-emitting element array 111 is assumed to be perpendicular to the plane of the paper in the figure (indicated by black circles on the light ray in the figure). By emitting light from the light source with a polarization component that has high reflectivity in the polarizing beam splitter 150, most of the light from the light source is projected toward the subject, resulting in high light utilization efficiency, which is preferable.

[0079] Furthermore, as shown in Figure 16C, it is preferable from the viewpoint of removing stray light that an anti-reflective film 1620 be formed on the surface of the polarizing beam splitter 150 that faces the surface into which light is incident from the light-emitting element array 111 (the surface into which light is emitted). The anti-reflective structure can be achieved by an anti-reflective film or a reflected light suppression structure composed of a dielectric multilayer film or microstructure, or by the arrangement of light-absorbing materials.

[0080] <Quarter Wave Plate> In the distance measuring device 100 of this embodiment, the optical system when a quarter wave plate is included will be explained with reference to Figure 17.

[0081] The quarter-wave plate 1731 is configured such that it transmits linearly polarized light from a light source and converts it into circularly polarized light. Specifically, the high-speed axis and low-speed axis of the quarter-wave plate 1731 are positioned at a 45-degree angle to the linearly polarized light from the light source. Birefringent crystals are used for the quarter-wave plate 1731. Because birefringent crystals have different refractive indices for each optical axis, when the incident polarization component has polarization components in multiple optical axis directions, the phase advance differs for each polarization component. Here, the optical axis in which the phase advances relatively is called the high-speed axis, and the optical axis in which the phase lags relatively is called the low-speed axis.

[0082] When the light illuminating the subject is made circularly polarized 1711 using the quarter-wave plate 1731, the reflected light from the subject is also circularly polarized, provided the subject surface is relatively smooth. After the circularly polarized reflected light from the subject passes through the quarter-wave plate, the polarization of the reflected light from the subject is converted to linearly polarized light perpendicular to the original illumination light, as shown in Figure 17. Therefore, the reflected light 1712 from the subject that enters the polarizing beam splitter 150 passes through the polarizing beam splitter 150 and is received by the photodetector array 121.

[0083] Furthermore, if the surface of the subject is rough and the reflected light is diffusely reflected, the polarization component of the reflected light becomes an unpolarized state with various polarization components mixed together, and the original polarization state is not preserved. In this case, when the reflected light 1812 from the surface of the subject is unpolarized, as shown in Figure 18, even without a quarter-wave plate, light with approximately half the intensity is transmitted through the polarizing beam splitter 150 and received by the photodetector array 121.

[0084] When using a quarter-wave plate in combination with an imaging optical system, it is necessary to appropriately control the drive of the light-receiving system for each placement position. This will be explained using Figures 19A and 19C.

[0085] First, Figure 19A shows the configuration of the optical system when the quarter-wave plate 1731 is positioned closer to the object than the object-side focal point 170 of the imaging lens 130. In this configuration, the light emitted from the light source that is reflected by the output end face of the polarizing beam splitter 150 or the surface of the optical components constituting the optical system 130, and returns without passing through the quarter-wave plate 1731, retains its polarization in the direction perpendicular to the plane of the paper in the figure. Therefore, when it returns to the polarizing beam splitter 150, it is reflected by the half-mirror 151 and returns to the light-emitting element array 111. Consequently, there is a low possibility that light that returns without hitting the subject will be received by the photo-receiving element array 121, which is preferable.

[0086] Furthermore, in such an optical system, when measuring the time to flight (ToF) from when light is emitted from the light-emitting element array 111 until it is reflected by the subject and received by the photodetector array 121, the following considerations can be made. That is, the ToF of the reflected light from the subject is longer than the ToF that would be obtained if the light from the light source were reflected by the quarter-wave plate 1731, slightly transmitted through the polarizing beam splitter, and received by the photodetector 121. Thus, it is also preferable to consider that the reflected light from the subject is present if the ToF is longer than a predetermined time. By performing such calculations, it is possible to suppress erroneous distance measurement due to stray light in the optical system. The quarter-wave plate 1731 can be inserted into or removed from the central optical axis of the imaging lens 130 by the quarter-wave plate driving mechanism 180.

[0087] Next, Figure 19B shows the configuration of the optical system when the quarter-wave plate 1731 is located at the same position as the object-side focal point 170 of the imaging lens 130, or when it is located closer to the photodetector 121 than the object-side focal point 170 and closer to the object than the imaging lens 130. In this configuration as well, similar to Figure 19A, the light emitted from the light source that is reflected by the emission-side end face of the polarizing beam splitter 150 or the surface of the optical components constituting the optical system 130 and returns without passing through the quarter-wave plate retains its polarization in the direction perpendicular to the plane of the paper in the figure. Therefore, when it returns to the polarizing beam splitter 150, it is reflected by the half-mirror 151 and returns to the light-emitting element array 111. Consequently, there is a low possibility that light that returns without hitting the subject will be received by the photodetector array 121, which is preferable.

[0088] Furthermore, in such an optical system, when measuring the time (ToF) from when light is emitted from the light-emitting element array 111 until it is reflected by the subject and received by the photodetector array 121, the following can be considered. That is, the ToF of the reflected light from the subject is longer than the ToF that would be obtained if the light from the light source were reflected by some object at the object-side focal point 170 of the imaging lens 130, slightly transmitted through the polarizing beam splitter, and received by the photodetector. Thus, it is also preferable to consider that the light is reflected from the subject if the ToF is longer than a predetermined time, and to calculate distance information from the subject using only that ToF.

[0089] The distance image of the subject, obtained from light reflected closer to the imaging lens 130 than the object-side focal point 170, is inverted vertically and horizontally compared to the distance image of an object located further from the imaging lens 130 than the object-side focal point 170. Therefore, it is undesirable for distance information closer to and farther from the object-side focal point 170 to be mixed in the distance image information acquired at a certain angle of view. Accordingly, as described above, it is preferable to perform distance measurement calculations using only ToF information, which is considered to be light from an object located further than the object-side focal point 170. Furthermore, similar to the configuration in Figure 19A, it is possible to suppress erroneous distance measurement due to stray light in the optical system. In addition, placing the quarter-wave plate at the object-side focal point is preferable because it allows for the smallest possible diameter of the quarter-wave plate.

[0090] Although the imaging lens 130 has been described as having an object-side focal point closer to the object than the frontmost lens of the imaging lens 130, this is not always the case. There are also cases where the object-side focal point of the imaging lens 130 is not closer to the object than the frontmost lens. In such cases, it is preferable to perform drive control assuming that the quarter-wave plate is located closer to the object than the position of the object-side focal point 170 of the imaging lens 130, as in the case of Figure 19A.

[0091] Finally, Figure 19C shows the configuration of the optical system when the quarter-wave plate 1731 is placed between the polarizing beam splitter 150 and the imaging lens 130. In this configuration, the light emitted from the light source that is reflected from the exit-side end face of the polarizing beam splitter 150 and returns without passing through the quarter-wave plate retains its polarization perpendicular to the plane of the paper in the figure. Therefore, when it returns to the polarizing beam splitter 150, it is reflected by the half-mirror 151 and returns to the light-emitting element array 111. Consequently, the possibility of it being received by the light-receiving element array 121 is low, making this configuration preferable. On the other hand, the reflected light from each optical element within the imaging lens 130 has its polarization rotated 90 degrees at the quarter-wave plate 1731, resulting in linear polarization. Therefore, the possibility of it being reflected by the polarizing beam splitter 150 and returning to the light-emitting element array 111 is reduced. Consequently, this optical arrangement is particularly suitable in situations where damage to the light-emitting element array 111 due to reflected light is a concern.

[0092] Furthermore, in such an optical system, when measuring the time (ToF) from when light is emitted from the light-emitting element array 111 until it is reflected by the subject and received by the photodetector array 121, the following can be considered. That is, the ToF of the reflected light from the subject is longer than the ToF that would be obtained if the light from the light source were reflected by some object at the object-side focal point 170 of the imaging lens 130, slightly transmitted through the polarizing beam splitter, and received by the photodetector. Thus, it is also preferable to consider that the light is reflected from the subject if the ToF is longer than a predetermined time, and to calculate distance information from the subject using only that ToF.

[0093] Furthermore, if it is assumed that there is no object to be measured at such close range, the time to flight (ToF) from when light is emitted from the light-emitting element array 111 until it is reflected by the object and received by the photodetector array 121 can be considered as follows: That is, the ToF of the reflected light from the object is longer than the ToF that would be obtained if the light from the light source were reflected at the outermost surface of the optical element closest to the object on the imaging lens 130, slightly transmitted through the polarizing beam splitter, and received by the photodetector. Thus, it is also preferable to consider that the reflected light is from the object if the ToF is longer than a predetermined time, and to calculate the distance information from the object using only that ToF.

[0094] Furthermore, in any optical configuration, placing the aperture at the object-side focal point of the imaging optical system is preferable for improving the signal-to-noise ratio of the measurement.

[0095] <Distance Measurement Sequence> Figures 20A and 20B are flowcharts showing the flow of distance measurement operations in the distance measuring device of this embodiment. The distance measurement operation for acquiring three-dimensional distance information will be explained using Figures 20A and 20B. Note that the flowcharts in Figures 20A and 20B are realized by the overall control unit 140, which has a CPU, executing a control program stored in the memory 141.

[0096] First, in step S2001, the overall control unit 140 resets the row counter j and sets it to 1.

[0097] In step S2002, the overall control unit 140 selects a row corresponding to the row counter using the row selection circuit 125, and sets it so that the pixel signal of the corresponding row is output to the TDC array unit 122 via the output line 804.

[0098] In step S2003, the overall control unit 140 resets the histogram circuits, which are arranged in the same number as the TDC 1001 within the signal processing unit 123, and resets the measurement counter i.

[0099] In step S2004, the overall control unit 140 operates the light-emitting element row drive circuit 702 for the row corresponding to the row counter j, causing the light-emitting element 111a belonging to the corresponding row to emit a short pulse of light.

[0100] In step S2005, the overall control unit 140 determines whether the time since the light emission is less than or equal to Tmax, which is the time corresponding to the longest distance measurement distance. If the time since the light emission is less than or equal to Tmax, the process proceeds to step S2006; otherwise, the process proceeds to step S2009.

[0101] In step S2006, the overall control unit 140 determines whether the pixel output has become "1". If the pixel output has become "1", the process proceeds to step S2007; otherwise, steps S2005 and S2006 are repeated. During this waiting period between repetitions, the light reflected back from the subject is incident on the photodetector 121a (pixel 801), which is conjugate to the light-emitting element 111a. When the pixel output signal becomes "1" due to the reception of light, the process proceeds to step S2007.

[0102] In step S2007, the overall control unit 140 measures the time since the light was emitted using TDC 1001.

[0103] In step S2008, the overall control unit 140 stores the time measurement result from TDC 1001 into a histogram and returns to the standby state.

[0104] In step S2009, the overall control unit 140 increments the light emission count counter i by 1.

[0105] In step S2010, the overall control unit 140 determines whether the flash count counter i is greater than the pre-set flash count Ntotal. If the flash count counter i is less than or equal to the flash count Ntotal, the process returns to step S2004 and repeats steps S2004 to S2010. If the flash count counter i is greater than the flash count Ntotal, the process proceeds to step S2011.

[0106] In step S2011, the overall control unit 140 performs histogram processing to calculate distance measurement results such as distance, signal strength, and ambient light intensity from the histogram obtained from the measurement results of TDC 1001.

[0107] In step S2012, the overall control unit 140 outputs the distance measurement result calculated in step S2011 from the measurement unit. From step S2002 to step S2012, the distance measurement for one line is completed and the distance measurement result is output.

[0108] In step S2013, the overall control unit 140 increments the row counter j by 1.

[0109] In step S2014, it is determined whether the row counter j is greater than the number of rows Nrow (in the case of Figure 16A-16C, Nrow = 8). If the row counter j is less than or equal to the set number Nrow, the process returns to step S2002 and the distance measurement for the next row is performed. If the row counter j is greater than the set number Nrow (i.e., the distance measurement for all rows is completed), the measurement ends.

[0110] By doing so, it is possible to obtain distance measurement results in the form of a two-dimensional array, similar to image information.

[0111] As described above, in this embodiment, the light-emitting element array 111 is made to emit light at different times for each row, and only the light-emitting elements of the row emitting light within the light-emitting element array 111 and the conjugate light-receiving elements via a half-mirror are enabled. This makes it possible to improve the utilization efficiency of light rays in a Time-of-Flight (ToF) type distance measuring device.

[0112] Furthermore, in this embodiment, linearly polarized light is emitted from the light-emitting element, and most of that light is reflected back towards the subject by a polarizing beam splitter. In addition, because a quarter-wave plate is placed on the subject side, the reflected light from the subject becomes linearly polarized in a direction perpendicular to the initial linear polarization, and most of it passes through the polarizing beam splitter and is received by the photodetector. This improves the efficiency of light ray utilization.

[0113] (Second Embodiment) In this second embodiment, the polarization state of the light-emitting element array 2111 and the arrangement angle of the polarizing beam splitter 2150 differ from those of the first embodiment. Even with an optical system that does not have a quarter-wave plate, it is possible to detect reflected light from the subject and measure the distance.

[0114] In the following, we will omit explanations of parts that are the same as in the first embodiment and focus on explaining the differences from the first embodiment.

[0115] In Figure 21, the polarization state of the light-emitting element array 2111 is linearly polarized. However, its polarization component is not composed entirely of components perpendicular to the plane of the paper in the figure (Xv axis direction), but rather a portion of it, for example 10% of the light intensity, has a polarization component in the plane of the paper in the figure (Yv axis direction).

[0116] The polarizing beam splitter 2150 is a cube-shaped beam splitter designed for 45-degree incidence, and is an element that selectively has a high reflectivity for the polarization component perpendicular to the plane of the paper in the figure when incident at 45 degrees. Here, as shown in Figure 21, the polarizing beam splitter 2150 is positioned such that the angle 2164 between the normal 2152 of its half mirror 2151 and the optical axis 2163 is slightly shifted from 45 degrees within the plane of the paper in the figure (within the YvZv plane). For example, the half mirror 2151 is positioned such that the angle between the optical axis 2163 and the normal 2152 of the half mirror 2151 is greater than 0° and less than 90°. In this state, the incidence angle of the light from the light-emitting element array 2111 is adjusted so that the light from the light-emitting element array 2111 is reflected by the half mirror 2151 of the polarizing beam splitter 2150 and directed toward the imaging lens 2130 parallel to the optical axis 2163.

[0117] Therefore, the angle of incidence of the light 2160 from the light-emitting element array 2111 incident on the polarizing beam splitter 2150 is deviated from 45 degrees when it makes contact with the normal to the half mirror 2151. As a result, the polarization component of the incident light from the light-emitting element array 2111 in the Xv axis direction in the figure is not completely reflected, but a small portion is transmitted. On the other hand, a portion of the polarization component in the Yv axis direction in the figure is also reflected in the direction of the optical axis 2163. Therefore, the subject is illuminated with both the polarization component in the X axis direction and the polarization component in the Y axis direction in the figure.

[0118] When the surface of the subject is rough, the reflection of the incident light 2161 from the subject surface is diffuse reflection, so the reflected light becomes unpolarized. However, when the surface of the subject is relatively smooth, the polarization state of the irradiated light is almost preserved in the reflected light from the subject. Therefore, the reflected light 2162 from the subject that returns to the polarizing beam splitter 2150 also contains a polarization component that has high transmittance in the polarizing beam splitter (i.e., the polarization component in the Y-axis direction in the figure). As a result, even if the surface of the subject is relatively smooth, it is possible to detect the reflected light from the subject in the photodetector array 2121.

[0119] (Other Embodiments) The present invention can also be realized by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (for example, an ASIC) that implements one or more functions.

[0120] The disclosures herein include the following distance measuring devices:

[0121] (Item 1) The imaging optical system comprises: an imaging optical system; a photodetector having a first microlens array; a light-emitting element having a second microlens array and emitting linearly polarized pulsed light through the second microlens array; a polarizing beam splitter disposed in the imaging optical system and projecting light emitted from the light-emitting element onto an object to be measured, and having a partial reflective surface that guides light from the object to be measured to the photodetector; and a calculation means that calculates the distance from the object to be measured to the photodetector using a signal output by the photodetector when it receives light emitted from the light-emitting element and reflected by the object to be measured, wherein the partial reflective surface is arranged such that the angle between the central optical axis of the imaging optical system and the normal to the partial reflective surface is greater than 0° and less than 90°. The distance measuring device is characterized in that the light-receiving element and the light-emitting element are arranged separately on the side where light from the object to be measured is reflected by the partial reflective surface and the side where light is transmitted, such that the distance between the partial reflective surface and the light-receiving element is substantially the same as the distance between the partial reflective surface and the light-emitting element, and are arranged in positions conjugate to the object to be measured via the imaging optical system.

[0122] (Item 2) The imaging optical system comprises: an imaging optical system; a photodetector having a first microlens array; a light-emitting element having a second microlens array and emitting linearly polarized pulsed light through the second microlens array; a polarizing beam splitter disposed in the imaging optical system and projecting light emitted from the light-emitting element onto an object to be measured, and having a partial reflective surface that guides light from the object to be measured to the photodetector; and a calculation means that calculates the distance from the object to be measured to the photodetector using a signal output by the photodetector when it receives light emitted from the light-emitting element and reflected by the object to be measured, wherein the partial reflective surface is arranged such that the angle between the central optical axis of the imaging optical system and the normal to the partial reflective surface is greater than 0° and less than 90°, and the photodetector and the light-emitting element are positioned such that the distance between the partial reflective surface and the photodetector is substantially the same as the distance between the partial reflective surface and the light-emitting element, on the side where light from the object to be measured is reflected by the partial reflective surface and the side where light is transmitted, respectively. The distance measuring device is characterized in that the imaging optical system is a telecentric optical system, and the imaging optical system and the first microlens array form an afocal system.

[0123] (Item 3) The distance measuring device according to Item 1 or 2, characterized in that the linearly polarized light emitted from the light-emitting element is linearly polarized light that is orthogonal to the linearly polarized light that satisfies the Brewster angle at the partial reflective surface.

[0124] (Item 4) The distance measuring device according to any one of Items 1 to 3, characterized in that the light from the light-emitting element includes a polarization component that satisfies the Brewster angle and a polarization component perpendicular thereto when incident on the partial reflective surface at a predetermined incident angle, the angle of the partial reflective surface is set to reflect the light from the light-emitting element and guide it to the imaging optical system, and the light from the light-emitting element is incident on the partial reflective surface at an angle in which neither of its polarization components satisfies the Brewster angle.

[0125] (Item 5) The distance measuring device according to Item 1 or 2, characterized in that the shape of the polarizing beam splitter is plate-shaped.

[0126] (Item 6) The distance measuring device according to Item 1 or 2, characterized in that the polarizing beam splitter is cube-shaped, and an anti-reflective coating or anti-reflective structure is formed on the surface through which light from the light-emitting element passes through the partial reflective surface and is emitted to the outside of the polarizing beam splitter.

[0127] (Item 7) The distance measuring device according to Item 1 or 2, characterized in that a quarter-wave plate with respect to the wavelength of light of the light-emitting element is arranged on the central optical axis of the imaging optical system.

[0128] (Item 8) The distance measuring device according to Item 7, characterized in that the high-speed axis and the low-speed axis of the quarter-wave plate are arranged at an angle such that they convert the linearly polarized light from the light-emitting element into circularly polarized light.

[0129] (Item 9) The distance measuring device according to Item 7, further comprising a mechanism for inserting or removing the quarter-wave plate with respect to the central optical axis of the imaging optical system.

[0130] (Item 10) The distance measuring device according to Item 7, characterized in that the quarter-wave plate is located on the central optical axis of the imaging optical system and is positioned on the object side of the imaging optical system.

[0131] (Item 11) The distance measuring device according to Item 10, characterized in that the quarter-wave plate is located on the central optical axis of the imaging optical system and is positioned at the focal point on the object side of the imaging optical system, or closer to the imaging optical system than the focal point.

[0132] (Item 12) The distance measuring device according to Item 7, characterized in that the quarter-wave plate is positioned between the partial reflective surface and the imaging optical system.

[0133] (Item 13) The distance measuring device according to Item 10, characterized in that the quarter-wave plate is positioned on the central optical axis of the imaging optical system and closer to the object than the imaging optical system, and the distance to the object to be measured is calculated using light received by the photodetector at a time later than the time when light emitted from the light-emitting element is reflected by the quarter-wave plate, returned to the imaging optical system, and reaches the photodetector.

[0134] (Item 14) The distance measuring device according to Item 10, characterized in that the quarter-wave plate is positioned on the central optical axis of the imaging optical system, on the object side of the imaging optical system, and closer to the imaging optical system than the object-side focal point of the imaging optical system, and the distance to the object to be measured is calculated using light received by the photodetector at a time later than the time when light emitted from the light-emitting element is reflected from the object-side focal point, returned to the imaging optical system, and reaches the photodetector.

[0135] (Item 15) The distance measuring device according to Item 12, characterized in that the quarter-wave plate is positioned on the central optical axis of the imaging optical system and between the partial reflective surface and the imaging optical system, and the distance to the object to be measured is calculated using light received by the photodetector at a time later than the time when light emitted from the light-emitting element is reflected from the object-side focal position of the imaging optical system, returned to the imaging optical system, and reaches the photodetector.

[0136] (Item 16) The distance measuring device according to Item 12, characterized in that the quarter-wave plate is positioned on the central optical axis of the imaging optical system and between the partial reflective surface and the imaging optical system, and the distance to the object to be measured is calculated using light received by the photodetector at a time later than the time when light emitted from the light-emitting element is reflected by the surface of the lens on the object side of the imaging optical system, returned to the partial reflective surface, and reaches the photodetector.

[0137] The technical ideas derived from this disclosure are not limited to the exemplary embodiments disclosed, but are intended to encompass various modifications of the exemplary embodiments, or substitutions with equivalent structures or functions. The scope of the following claims should be interpreted in the broadest way to encompass all such modifications and equivalent structures and functions.

[0138] This application claims priority based on Japanese Patent Application No. 2025-016997, filed on February 4, 2025, and all of its contents are incorporated herein by reference.

Claims

1. The imaging optical system comprises: an imaging optical system; a photodetector having a first microlens array; a light-emitting element having a second microlens array and emitting linearly polarized pulsed light through the second microlens array; a polarizing beam splitter disposed in the imaging optical system and projecting light emitted from the light-emitting element onto an object to be measured, and having a partial reflective surface that guides light from the object to be measured to the photodetector; and a calculation means that calculates the distance from the object to be measured to the photodetector using a signal output by the photodetector when it receives light emitted from the light-emitting element and reflected by the object to be measured, wherein the partial reflective surface is arranged such that the angle between the central optical axis of the imaging optical system and the normal to the partial reflective surface is greater than 0° and less than 90°. The distance measuring device is characterized in that the light-receiving element and the light-emitting element are arranged separately on the side where light from the object to be measured is reflected by the partial reflective surface and the side where light is transmitted, such that the distance between the partial reflective surface and the light-receiving element is substantially the same as the distance between the partial reflective surface and the light-emitting element, and are arranged in positions conjugate to the object to be measured via the imaging optical system.

2. The imaging optical system comprises: an imaging optical system; a photodetector having a first microlens array; a light-emitting element having a second microlens array and emitting linearly polarized pulsed light through the second microlens array; a polarizing beam splitter disposed in the imaging optical system and projecting light emitted from the light-emitting element onto an object to be measured, and having a partial reflective surface that guides light from the object to be measured to the photodetector; and a calculation means for calculating the distance from the object to be measured to the photodetector using a signal output by the photodetector when it receives light emitted from the light-emitting element and reflected by the object to be measured, wherein the partial reflective surface is arranged such that the angle between the central optical axis of the imaging optical system and the normal to the partial reflective surface is greater than 0° and less than 90°, and the photodetector and the light-emitting element are positioned such that the distance between the partial reflective surface and the photodetector is substantially the same as the distance between the partial reflective surface and the light-emitting element, on the side where light from the object to be measured is reflected by the partial reflective surface and the side where light is transmitted, respectively. The distance measuring device is characterized in that the imaging optical system is a telecentric optical system, and the imaging optical system and the first microlens array form an afocal system.

3. The distance measuring device according to claim 1 or 2, characterized in that the linearly polarized light emitted from the light-emitting element is linearly polarized light that is orthogonal to the linearly polarized light that satisfies the Brewster angle at the partial reflective surface.

4. The distance measuring device according to claim 1 or 2, characterized in that the light from the light-emitting element includes a polarization component that satisfies the Brewster angle and a polarization component perpendicular thereto when incident on the partial reflective surface at a predetermined incident angle, the angle of the partial reflective surface is set to reflect the light from the light-emitting element and guide it to the imaging optical system, and the light from the light-emitting element is incident on the partial reflective surface at an angle in which neither of its polarization components satisfies the Brewster angle.

5. The distance measuring device according to claim 1 or 2, characterized in that the shape of the polarizing beam splitter is plate-shaped.

6. The distance measuring device according to claim 1 or 2, characterized in that the polarizing beam splitter has a cube shape, and an anti-reflective coating or anti-reflective structure is formed on the surface through which light from the light-emitting element passes through the partially reflective surface and is emitted to the outside of the polarizing beam splitter.

7. The distance measuring device according to claim 1 or 2, characterized in that a quarter-wave plate with respect to the wavelength of light of the light-emitting element is arranged on the central optical axis of the imaging optical system.

8. The distance measuring device according to claim 7, characterized in that the high-speed axis and the low-speed axis of the quarter-wave plate are arranged at an angle such that they convert linearly polarized light from the light-emitting element into circularly polarized light.

9. The distance measuring device according to claim 7, further comprising a mechanism for inserting or removing the quarter-wave plate with respect to the central optical axis of the imaging optical system.

10. The distance measuring device according to claim 7, characterized in that the quarter-wave plate is located on the central optical axis of the imaging optical system and is positioned on the object side of the imaging optical system.

11. The distance measuring device according to claim 10, characterized in that the quarter-wave plate is located on the central optical axis of the imaging optical system and is positioned at the focal point on the object side of the imaging optical system, or closer to the imaging optical system than the focal point.

12. The distance measuring device according to claim 7, characterized in that the quarter-wave plate is disposed between the partial reflective surface and the imaging optical system.

13. The distance measuring device according to claim 10, characterized in that the quarter-wave plate is positioned on the central optical axis of the imaging optical system and closer to the object than the imaging optical system, and the distance to the object to be measured is calculated using light received by the photodetector at a time later than the time when light emitted from the light-emitting element is reflected by the quarter-wave plate, returned to the imaging optical system, and reaches the photodetector.

14. The distance measuring device according to claim 10, characterized in that the quarter-wave plate is positioned on the central optical axis of the imaging optical system, on the object side of the imaging optical system, and closer to the imaging optical system than the object-side focal point of the imaging optical system, and the distance to the object to be measured is calculated using light received by the photodetector at a time later than the time when light emitted from the light-emitting element is reflected from the object-side focal point, returned to the imaging optical system, and reaches the photodetector.

15. The distance measuring device according to claim 12, characterized in that the quarter-wave plate is positioned on the central optical axis of the imaging optical system and between the partial reflective surface and the imaging optical system, and the distance to the object to be measured is calculated using light received by the photodetector at a time later than the time when light emitted from the light-emitting element is reflected from the object-side focal point of the imaging optical system, returned to the imaging optical system, and reaches the photodetector.

16. The distance measuring device according to 12, characterized in that the quarter-wave plate is positioned on the central optical axis of the imaging optical system, between the partial reflective surface and the imaging optical system, and the distance to the object to be measured is calculated using light received by the photodetector at a time later than the time when light emitted from the light-emitting element is reflected by the surface of the lens on the object side of the imaging optical system, returned to the partial reflective surface, and reaches the photodetector.

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