JP7696215B2 - Light receiving element and measuring device - Google Patents

Description

The present invention relates to a light receiving element and a measuring device.

In distance measurement systems such as LiDAR (Light Detection and Ranging), a time-of-flight (TOF) method is known that measures the distance to an object by measuring the time between projecting a pulsed laser beam and receiving the reflected light. Distance measurement systems such as LiDAR also use laser beams to scan a wide range. For example, Patent Document 1 describes a distance measurement system that uses two-dimensional scanning with laser beams.

Special Publication No. 2021-500554

When installing a distance measurement system such as LiDAR on a vehicle, the light-emitting elements, light-receiving elements, and optical system that make up the distance measurement system must be placed in a small space. To place it in a small space, it is necessary to miniaturize the optical system by using small-diameter lenses and shortening the overall length of the lens assembly, but miniaturizing the optical system sacrifices optical performance. This could lead to a deterioration in the quality of the device, such as a decrease in object detection accuracy.

In view of the above, the present invention aims to provide a high-quality light receiving device.

To achieve the above object, the present invention provides, as one aspect, a light receiving device that includes a modification section that reflects light emitted from a light emitting element and reflected by an object twice and emits the light from an emission surface, and a light receiving element that has a detection surface that detects the light emitted from the modification section.

Other problems and solutions disclosed in this application will be made clear in the detailed description of the invention and the drawings.

The present invention provides a high-quality light receiving device.

FIG. 1 is an explanatory diagram of an example of a measuring device. FIG. 2 is an explanatory diagram of the mounting board 5 as viewed from the X direction. 3A is an explanatory diagram of two-dimensional scanning, FIG 3B is an explanatory diagram of two-dimensional scanning in a certain frame, and FIG 3C is an explanatory diagram of two-dimensional scanning by multiple channels. Fig. 4A is a top view of the optical receiver 20. Fig. 4B is a cross-sectional view of the optical receiver 20 taken along line BB in Fig. 4A. Fig. 4C is an exploded perspective view of the optical receiver 20. Fig. 4D is a cross-sectional view of the light-receiving element 21. Fig. 5A is a cross-sectional view of an example of the optical receiver 20. Fig. 5B is an exploded perspective view of the optical receiver 20. Fig. 6A is a horizontal cross-sectional view of an example of the optical receiver 20. Fig. 6B is an exploded perspective view of the optical receiver 20. Fig. 7A is an explanatory diagram of the manner in which light is collected by the light receiving optical system 32. Fig. 7B is an explanatory diagram of the light receiving window 23 and the light collecting spot in the light receiver 20 on the optical axis of the light receiving optical system 32. FIG. 8 is an explanatory diagram of an output signal from the optical receiver 20. As shown in FIG. FIG. 9 is an explanatory diagram of an example of a light detection device using the light receiving element of this embodiment. Fig. 10A is a diagram for explaining the position of the focused spot when the light receiving optical system 32 has a high NA value, Fig. 10B is a diagram for explaining the position of the focused spot when the light receiving optical system 32 has a low NA value, and Fig. 10C is a diagram for explaining the position of the focused spot when the light receiving optical system 32 has a low NA value and the prism 27 according to this embodiment is used. FIG. 11 is a cross-sectional view of a light receiving device according to a modified example.

The following describes the embodiment of the present invention with reference to the drawings. In the following description, the same or similar components may be designated by common reference numerals and duplicate descriptions may be omitted.

<About the measuring device>
FIG. 1 is an explanatory diagram of an example of a measuring device.

In the following description, the directions are defined as shown in FIG. 1. The direction along the optical axis (the rotational symmetry axis of the lens) of the light receiving optical system 32 (or the light projecting optical system 31) is defined as the Z direction. Note that the object 90 to be measured by the measuring device 1 is separated from the measuring device 1 in the Z direction. The direction perpendicular to the Z direction, in which the light projecting optical system 31 and the light receiving optical system 32 are aligned, is defined as the X direction. The direction perpendicular to the Z direction and the X direction is defined as the Y direction.

The measuring device 1 is a device for measuring the surface of an object 90. Specifically, the measuring device 1 emits laser light (Tx in FIG. 1) from a light-emitting element 10, detects the reflected light (Rx in FIG. 1) reflected from the surface of the object 90 by a light-receiver 20, and calculates the distance to the object 90 based on the detection result. The measuring device 1 includes a light-emitting element 10, a light-receiver 20, an optical system 30, and a controller 40. The measuring device 1 also includes a mounting board 5 having a plurality of light-emitting elements 10 and a plurality of light-receivers 20, and a driving device 45.

The light-emitting element 10 is an element that converts an electrical signal into an optical signal. For example, the light-emitting element 10 is an LD chip (LD: Laser Diode) and emits laser light. In this embodiment, the light-emitting element 10 emits pulsed light (Tx in FIG. 1) toward the surface of the object 90. The light-emitting element 10 in this embodiment is composed of an edge-emitting semiconductor laser, is surface-mounted on the mounting substrate 5, and emits laser light parallel to the substrate surface. Note that the light-emitting element 10 is not limited to an edge-emitting semiconductor laser, and the mounting method on the mounting substrate 5 is not limited to this.

The optical receiver 20 is a block that changes the direction of the optical signal from the light receiving optical system 32 and converts it into an electrical signal. The details of the optical receiver 20 will be described later, but it is configured to include a PD chip (photodiode). Optical receiver 20The optical receiver 20 is surface mounted on the mounting substrate 5. Note that the mounting method of the optical receiver 20 is not limited to this. Note that the mounting substrate 5 and the optical receiver 20 are an example of a light receiving device in the present invention.

The optical system 30 is an optical system that irradiates the light output from the light-emitting element 10 toward the object 90 and receives the reflected light from the object 90 in the light receiver 20. The light-emitting element 10 and the light receiver 20 are disposed in a conjugate position with respect to the optical system 30. The optical system 30 of this embodiment has a light-projecting optical system 31 and a light-receiving optical system 32.

The projection optical system 31 is an optical system for irradiating the light output from the light-emitting element 10 toward the object 90. The light-emitting element 10 is disposed within the focal plane of the projection optical system 31. The projection optical system 31 irradiates the object 90 with the laser light emitted from the light-emitting element 10 as collimated light. The collimated light is irradiated in a predetermined direction (predetermined angle) according to the positional relationship between the light-emitting element 10 and the projection optical system 31. The light-emitting element 10 irradiates the object 90 with light via the projection optical system 31. Each projection optical system 31 is composed of a lens group made up of multiple lenses (e.g., 5 to 7 lenses) (in FIG. 1, the lens group of the projection optical system 31 is shown simply).

The light receiving optical system 32 is an optical system for receiving the light reflected from the object 90 at the light receiver 20. The light receiver 20 is disposed within the focal plane of the light receiving optical system 32. The light receiving optical system 32 focuses the light reflected from the object 90 onto a predetermined light receiver 20. The light receiver 20 receives the light reflected from the object 90 via the light receiving optical system 32. Like the light projecting optical system 31, the light receiving optical system 32 is also composed of a lens group made up of multiple lenses (e.g., 5 to 7 lenses) (the lens group of the light receiving optical system 32 is shown simply in FIG. 1).

The light-projecting optical system 31 and the light-receiving optical system 32 are constructed as an integral unit, and their relative positions are fixed. Specifically, the light-projecting lens barrel that constitutes the light-projecting optical system 31 and the light-receiving lens barrel that constitutes the light-receiving optical system 32 are fixed to a common optical frame 33.

The controller 40 is a control unit that controls the measurement device 1. The controller 40 controls the emission of laser light from the light-emitting element 10. The controller 40 also calculates the distance to the object 90 based on the output signal of the light-receiver 20. Specifically, the controller 40 measures the distance to the object 90 by measuring the time from when the light-emitting element 10 emits pulsed laser light to when the light-receiver 20 receives the reflected light. That is, the controller 40 measures the distance to the object 90 by the TOF method (measures the Z coordinate of the surface of the object 90) by controlling the light-emitting element 10 and the light-receiver 20. In addition, the controller 40 can measure the X, Y, and Z coordinates of the surface of the object 90 by measuring the Z coordinate of the surface of the object 90 while scanning in the XY direction, utilizing the fact that the laser light is irradiated in a predetermined direction and the reflected light is received in a predetermined direction.

The controller 40 has a calculation device 41 and a storage device 42. The calculation device 41 is a calculation processing device such as a CPU or a GPU. The storage device 42 is a device that is composed of a main storage device and an auxiliary storage device and stores programs and data. When the calculation device 41 executes the program stored in the storage device 42, the calculation device 41 controls the emission of laser light from the light-emitting element 10 and calculates the distance to the object 90 based on the output signal of the light receiver 20. The calculation device 41 also calculates the X, Y, and Z coordinates of the surface of the object 90 based on the output signal of the light receiver 20. The calculation device 41 may store the acquired coordinate data in the storage device 42 or in an external storage device. The data of the X, Y, and Z coordinates of a large number of points on the surface of the object 90 becomes data indicating a three-dimensional image (point group: point cloud) of the surface of the object 90. The calculation device 41 may analyze the object 90 based on the three-dimensional image stored in the storage device 42 by the calculation device 41 executing a program stored in the storage device 42.

The mounting substrate 5 is a substrate on which multiple light-emitting elements 10 and multiple light-receivers 20 are mounted. A given light-receiver 20 is associated with a specific light-emitting element 10, and the detection position of a given light-receiver 20 is conjugate with the light-emitting position of the specific light-emitting element 10. In this embodiment, there are multiple pairs of light-emitting elements 10 and light-receivers 20, and the surface of the object 90 can be measured in multiple channels. The light-emitting element 10 emits laser light parallel to the substrate surface of the mounting substrate 5, and the light-receiver 20 receives light (reflected light) incident from a direction approximately parallel to the substrate surface of the mounting substrate 5.

As shown in FIG. 1, the mounting substrate 5 has five light-emitting elements 10 and five light-receivers 20. However, the number of light-emitting elements 10 and light-receivers 20 is not limited to this. On the mounting substrate 5, multiple light-emitting elements 10 are arranged at different positions in the X direction. Also, on the mounting substrate 5, multiple light-receivers 20 are arranged at different positions in the X direction.

As shown in FIG. 1, the mounting substrate 5 has a light-emitting curved portion 6 and a light-receiving curved portion 7.

The light-emitting side curved portion 6 is a portion having an arc-shaped edge. The light-emitting side curved portion 6 is a portion for arranging multiple light-emitting elements 10 so that they follow the curvature of the image plane of the light-projecting optical system 31. Multiple light-emitting elements 10 are arranged along the arc-shaped edge of the light-emitting side curved portion 6. This allows each light-emitting element 10 to be arranged at an appropriate position and angle relative to the light-projecting optical system 31, reducing the effects of the curvature of the image plane of the light-projecting optical system 31.

The light-receiving curved portion 7 is a portion having an arc-shaped edge, and is provided at a different position in the X direction from the light-emitting curved portion 6. The light-receiving curved portion 7 is a portion for arranging multiple light receivers 20 so that they follow the curvature of field of the light-receiving optical system 32. Multiple light receivers 20 are arranged along the arc-shaped edge of the light-receiving curved portion 7. This allows each light receiver 20 to be arranged at an appropriate position and angle relative to the light-receiving optical system 32, reducing the effects of the curvature of field of the light-receiving optical system 32.

However, the mounting substrate 5 does not necessarily have to have the light-emitting curved portion 6 or the light-receiving curved portion 7. In this case, multiple light-emitting elements 10 and multiple light-receiving devices 20 are arranged along the edge of the mounting substrate 5 perpendicular to the Z direction.

Figure 2 is an explanatory diagram of the mounting substrate 5 as viewed from the X direction. For the sake of explanation, the light-emitting curved portion 6 and the light-receiving curved portion 7 of the mounting substrate 5 are omitted, and the light-emitting element 10 and the light-receiver 20 are arranged along the edge of the mounting substrate 5 that is parallel to the X direction. For the sake of explanation, the inclination of the mounting substrate 5 is exaggerated in the illustration.

As shown in FIG. 2, the measuring device 1 has multiple mounting boards 5 (three mounting boards 5 in this example). The multiple mounting boards 5 are arranged at different positions in the Y direction. As shown in FIG. 1, each mounting board 5 has multiple (five here) light-emitting elements 10 and multiple light-receivers 20 arranged at different positions in the X direction. Therefore, a light-emitting element array is formed by arranging multiple (15 here) light-emitting elements 10 in the X and Y directions, and a light-receiving element array is formed by arranging multiple light-receivers 20 in the X and Y directions. Here, the surface of the object 90 is measured using 5 x 3 = 15 channels (five channels in the X direction and three channels in the Y direction).

The multiple mounting boards 5 are arranged at different angles with respect to the Z direction. Specifically, as shown in FIG. 2, the light-emitting element 10 of each mounting board 5 faces the light-projecting optical system 31, and the incident surface 27A (described later) of the light-receiver 20 of each mounting board 5 faces the light-receiving optical system 32, so that each mounting board 5 is arranged at a different angle with respect to the Z direction. As a result, the light-emitting element 10 and the light-receiver 20 are arranged at appropriate positions and angles with respect to the optical system 30, so that the effect of the curvature of field of the optical system 30 can be reduced. The light-emitting element 10 of each mounting board 5 is arranged to emit laser light parallel to the substrate surface of the mounting board 5. The light-receiver 20 of each mounting board 5 is arranged to receive light (reflected light) incident from a direction approximately parallel to the substrate surface of the mounting board 5. Since multiple (here, five) light-emitting elements 10 and multiple (here, five) light-receivers 20 are mounted on the same board, and since the light-projecting optical system 31 and the light-receiving optical system 32 are provided separately, even if the mounting board 5 is tilted in the Z direction (the direction of the optical axis of the optical system 30), each light-emitting element 10 and light-receiver 20 can be maintained in a conjugate positional relationship with respect to the optical system 30. Note that, if the mounting board 5 is provided with a light-emitting side curved portion 6 and a light-receiving side curved portion 7 as in this embodiment, even if the mounting board 5 is tilted, it is easy to arrange the multiple light-emitting elements so as to follow the curvature of field of the light-projecting optical system 31, and it is also easy to arrange the multiple light-receivers 20 so as to follow the curvature of field of the light-receiving optical system 32.

Note that multiple mounting substrates 5 may be arranged parallel to each other in the Z direction. However, if each mounting substrate 5 is arranged parallel to each other, it is necessary to make the positions and angles of the light emitting element 10 and the light receiver 20 different for each mounting substrate 5 so that the light emitting element 10 and the light receiver 20 are at appropriate positions and angles with respect to the optical system 30. In contrast, in this embodiment, the inclination of the mounting substrate 5 is made different, so that in each mounting substrate 5, the light emitting element 10 can be configured to emit laser light parallel to the mounting substrate 5, and the light receiver 20 can be configured to receive light (reflected light) incident from a direction approximately parallel to the mounting substrate 5. Therefore, in this embodiment, multiple light emitting elements 10 and multiple light receivers 20 can be arranged at appropriate positions and angles with respect to the optical system 30 at different positions in the X direction and Y direction with a simple configuration.

The multiple mounting boards 5 (three in this example) are fixed together, and their relative positions are fixed. Specifically, the multiple mounting boards 5 are fixed to a common board frame 8. However, as long as the relative positions of the multiple light-emitting elements 10 and the multiple light-receivers 20 can be fixed, the relative positions of the multiple light-emitting elements 10 and the multiple light-receivers 20 may be fixed by other methods. In addition, the measurement device 1 does not need to be equipped with multiple mounting boards 5.

The driving device 45 (see FIG. 1) is a device that moves the optical system 30 and the mounting substrate 5 (light-emitting element 10 and light-receiver 20) relatively in the XY directions. By the driving device 45 moving the optical system 30 and the mounting substrate 5 relatively in the XY directions, the positional relationship of the light-emitting element 10 with respect to the optical system 30 is changed, and the angle at which the laser light is irradiated is changed, thereby allowing the laser light to be scanned.

The driving device 45 moves at least one of the optical system 30 and the mounting board 5 (either the optical system 30 or the mounting board 5, or both the optical system 30 and the mounting board 5). The driving device 45 may move the optical system 30 in the XY direction relative to the mounting board 5, may move the optical system 30 in the XY direction relative to the mounting board 5, or may move the mounting board 5 in the Y direction (or X direction) while moving the optical system 30 in the X direction (or Y direction). In this embodiment, at least one of the optical frame 33 and the board frame 8 is supported by the housing 3 at a predetermined resonance frequency in the X direction and the Y direction, respectively, and the driving device 45 vibrates at least one of the optical system 30 and the mounting board 5 in the X direction and the Y direction at the respective resonance frequencies. The driving device 45 is, for example, configured by a voice coil motor, but is not limited thereto (for example, it may be configured by a piezoelectric element).

Figure 3A is an explanatory diagram of two-dimensional scanning. In this embodiment, by vibrating at least one of the optical system 30 and the mounting board 5 in the X direction and the Y direction at their respective resonant frequencies, the optical system 30 and the mounting board 5 (light-emitting element 10 or light-receiver 20) are relatively displaced in the XY direction along the Lissajous curve as shown in Figure 3A. The Lissajous curve is a graph of X = A sin (at + δ), Y = B sin (bt). Here, a and b are frequencies in the X direction and the Y direction, respectively, t is time, and δ is a phase difference. As already explained, since at least one of the optical frame 33 and the board frame 8 is supported in the X direction and the Y direction at a predetermined resonant frequency, respectively, a and b are known values. In addition, A and B become known values by the drive device 45 resonating the optical frame 33 or the board frame 8 with a predetermined amplitude, and δ becomes a known value based on the drive timing in the X direction and the Y direction by the drive device 45. Therefore, the controller 40 can calculate the position of the light emitting element 10 (or the light receiver 20) in the XY direction relative to the optical system 30 based on the time t. In other words, the controller 40 can calculate the direction in which the laser light is irradiated based on the time t. Note that instead of calculating the direction in which the laser light is irradiated based on the time t, the controller 40 may detect the relative positions in the XY direction between the optical frame 33 and the substrate frame 8 using a position detector (not shown), and calculate the direction in which the laser light is irradiated based on the detection result.

Figure 3B is an explanatory diagram of two-dimensional scanning in a certain frame. The controller 40 acquires one frame (one three-dimensional image of the object 90) at a predetermined time interval. For each measurement of one frame (one three-dimensional image), the X, Y, and Z coordinates of the surface of the object 90 are measured at multiple points on the Lissajous curve. This allows the coordinates to be measured with increased resolution. The same Lissajous curve may be repeated for each frame. In this case, the surface of the object 90 can be measured at the same position in each frame. On the other hand, the Lissajous curve may be shifted for each frame. In this case, the surface of the object 90 can be measured in the next frame so as to interpolate between the points measured in the previous frame.

Figure 3C is an explanatory diagram of two-dimensional scanning using multiple channels. As shown in the figure, in this embodiment, two-dimensional scanning is performed in a different range for each channel. This makes it possible to measure the surface of the object 90 over a wide range in the X and Y directions, achieving a wide FOV (field of view).

The two-dimensional scanning does not have to be performed along the Lissajous curve. For example, two-dimensional scanning may be performed by performing a line scan in the X direction (or Y direction) multiple times while shifting the line scan in the Y direction (or X direction). Also, one-dimensional scanning may be performed instead of two-dimensional scanning. Scanning may not be performed at all. If scanning is not performed, the measuring device 1 may not be equipped with the driving device 45. However, if scanning is not performed, the resolution of the point cloud will be reduced compared to this embodiment.

<About the receiver>
The optical receiver 20 according to this embodiment will be described.

Figure 4A is a top view of the optical receiver 20. The optical receiver 20 has a light receiving element 21 and a prism 27. Figure 4B is a cross-sectional view taken along line B-B in Figure 4A, and Figure 4C is an exploded perspective view of the optical receiver 20. Also, Figure 4D is a cross-sectional view of the light receiving element 21.

The light receiving element 21 is planarly mounted on the surface of the mounting substrate 5. In detail, the light receiving element 21 is fixed on the surface of the mounting substrate 5 so that the surface of the mounting substrate 5 and the surface of the light receiving element 21 that detects light (hereinafter referred to as the light receiving surface 21A) are approximately parallel. The light receiving element 21 has a light receiving window 23 that receives light on the light receiving surface 21A. The light receiving window 23 is a light receiving area provided on the light receiving surface 21A of the light receiving element 21. For example, when the light receiving element 21 is an avalanche photodiode (APD), the light receiving part 22 of the light receiving element 21 has a buffer layer, a light absorption layer, an intermediate layer, a multiplication layer, and a window layer on the substrate, and further has a light receiving area and a guard ring on the outer periphery of the light receiving area, and has electrodes 24 and 25 on the front and back surfaces of the substrate, respectively. In addition, a protective layer is also formed on the light receiving surface 21A of the light receiving element 21. Here, the light receiving window 23 corresponds to the inner region of the ring-shaped electrode 24 (the electrode on the light receiving surface 21A side; the electrode on the substrate surface side). The diameter of the light receiving window 23 is sometimes called the light receiving diameter. The size of the light receiving element 21 is several millimeters square (e.g., 5 mm square), while the light receiving diameter is, for example, 500 μm. However, the size of the light receiving element 21 and the light receiving diameter are not limited to this.

In FIG. 4D, for convenience, the height from the back surface of the light receiving element 21 to the surface of the light receiving window 23 provided in the center of the light receiving element 21 is drawn to be the highest, but in reality, a planarizing film, a protective film, etc. (not shown) are formed on the light receiving surface 21A side. Therefore, the height from the back surface of the light receiving element 21 to the light receiving surface 21A including the protective film, etc. is approximately the same throughout the light receiving element 21.

Prism 27 is a pentaprism fixed to light receiving element 21, and has the function of reflecting the incident light twice and changing the optical axis direction by 90 degrees before emitting it. Possible materials for prism 27 include optical glass, quartz, and resin, and an appropriate material is used depending on the required optical performance, usage conditions, design conditions, etc.

As shown in Figures 4 to 6, the prism 27 has a pentagonal cross section, two mutually orthogonal rectangular surfaces (referred to as the entrance surface 27A and the exit surface 27B), and rectangular reflecting surfaces 27C and 27D that are connected to the entrance surface 27A and the exit surface 27B, respectively.

As shown in FIG. 4B, the angle between rectangular reflecting surfaces 27C and 27D is 22.5 degrees. The cross-sectional dimensions of prism 27 are as shown in FIG. 4B, and the ratio of the length d of exit surface 27B in the normal direction of entrance surface 27A to the total length of prism 27 in the same direction is 1:1.41.

The incident surface 27A faces the light receiving optical system 32, and the reflected light collected by the light receiving optical system 32 is incident on the incident surface 27A. The exit surface 27B is fixed to the light receiving element 21 and faces the light receiving section 22. The area of the exit surface 27B is larger than that of the light receiving element 21.

The light incident on the entrance surface 27A is reflected twice by the reflecting surfaces 27D and 27C, changing the direction of the optical axis by 90 degrees, and is emitted from the exit surface 27B so as to be perpendicular to the exit surface 27B (Figure 4B).

An optical film can be attached or deposited on the incident surface 27A, the exit surface 27B, and the reflecting surfaces 27C and 27D. Examples of optical films include anti-reflection films, filters that absorb specific wavelengths, and reflecting mirrors. For example, by forming a reflecting mirror on either of the reflecting surfaces 27C and 27D, the reflectance can be increased. In addition, when an anti-reflection film is formed on either of the exit surface 27B and the reflecting surfaces 27C and 27D, the reflectance and transmittance of light on these surfaces can be adjusted. In this way, by forming an optical film on either of the incident surface 27A, the exit surface 27B, and the reflecting surfaces 27C and 27D, the required optical performance can be obtained.

The method of fixing the emission surface 27B to the light receiving element 21 is determined appropriately according to the material of the prism 27, the conditions of use, and the design conditions. Examples of bonding methods include bonding using low-melting-point glass, polymers, or films, anodic bonding, or direct bonding.

The exit surface 27B may be fixed to the light receiving element 21 via a resin film. In the example shown in Figs. 5A and 5B, a resin film 29 is sandwiched between the exit surface 27B and the light receiving element 21, and the exit surface 27B and the light receiving element 21 are fixed via the resin film 29. The resin film 29 may be, for example, an optical film. In this case, by passing the light emitted from the exit surface 27B through the resin film 29, it is possible to suppress the refraction and reflection of unnecessary light, or absorb specific wavelengths and adjust the transmittance, thereby obtaining the required optical performance.

A gap may be provided between the exit surface 27B and the light receiving element 21. In the example shown in Figs. 6A and 6B, the exit surface 27B is fixed to the light receiving element 21 via a mounting member 28. The mounting member 28 is provided along the periphery of the light receiving element 21, and a gap is formed between the exit surface 27B and the light receiving element 21 by the thickness of the mounting member 28. The gap between the exit surface 27B and the light receiving element 21 is used to obtain required optical performance, such as adjusting the position of the light receiving unit 22 and the focus of the light collected from the light receiving optical system 32. In addition, by adjusting the thickness of the mounting member 28, it is also possible to adjust the mounting angle or mounting position of the prism 27 with respect to the light receiving element 21.

Figure 7A is an explanatory diagram of how light is collected by the light receiving optical system 32. Figure 7B is an explanatory diagram of the light receiving window 23 and the light collecting spot in the light receiving element 21 on the optical axis of the light receiving optical system 32.

Since multiple light receivers 20 are arranged for one light receiving optical system 32, as shown in FIG. 7A, in addition to the light receiver 20 arranged on the optical axis of the light receiving optical system 32, there is a light receiver 20 arranged at a position off the optical axis. In FIG. 7A, only one light receiver 20 is drawn off the optical axis of the light receiving optical system 32, but there are multiple light receivers 20 off the optical axis of the light receiving optical system 32, and further, the way in which they are off the optical axis of the light receiving optical system 32 differs from one another. The reflected light emitted from the light receiving optical system 32 is focused on the light receiving surface 21A of the light receiving element 21 via the prism 27, forming a focused spot (FIG. 7B).

Figure 8 is an explanatory diagram of the output signal of the light receiving element 21. The upper graph in each diagram shows the current output from the light receiving unit 22. As already explained, in this embodiment, the light emitting element 10 emits pulsed light (Tx in Figure 1), so that a focused spot of pulsed reflected light (Rx in Figure 1) is irradiated onto the light receiving element 21. As the reflected light is irradiated onto the light receiving window 23, the light receiving unit 22 outputs a pulsed current (output signal) as shown in the graph in Figure 8.

The current output from the light receiving element 21 may be a positive current or a negative current. The light receiving unit 22 outputs a current (output signal) according to the light irradiated onto the light receiving window 23.

Based on the output signal, the controller 40 can determine the time t at which the pulsed reflected light is received. In other words, the controller 40 can measure the time from when the light-emitting element 10 emits a pulsed laser light until the light-receiving element 21 receives the reflected light, and can measure the distance to the object 90.

Figure 9 is an explanatory diagram of an example of a photodetector using the light receiving device of this embodiment. For example, the mounting board 5 described above is provided with a circuit for constituting the photodetector 50 shown in Figure 9.

The photodetector 50 has the above-mentioned photoreceiver 20 and a conversion unit 51. The conversion unit 51 is a circuit that converts the signal output from the photoreceiver 20 from a current to a voltage. The photodetector 50 has a conversion unit 51 for each photodetector 21. The conversion unit 51 shown in FIG. 9 is a circuit that converts the output signal output from the photoreceiver 22 from a current to a voltage. The conversion unit 51 is composed of a transimpedance amplifier (TIA).

The light detection device 50 has an analog-digital conversion circuit 52 (ADC). An analog-digital conversion circuit 52 (ADC) is provided for each conversion unit 51. Each analog-digital conversion circuit 52 converts the voltage (analog signal) output from the conversion unit 51 into a digital signal, and outputs the signal to the controller 40 (arithmetic unit 41). The controller 40 (arithmetic unit 41) obtains the time t at which the pulsed reflected light is received by comparing the voltage value of the output signal with a threshold value, calculates the time from when the pulsed laser light is emitted from the light-emitting element 10 until the light-receiving element 21 receives the reflected light, and calculates the distance to the object 90.

＜Effects＞
In the above embodiment, a prism 27 (corresponding to the modification portion in the present invention) is disclosed which reflects twice the optical axis direction of light irradiated from the light emitting element 10 and reflected by the object, and emits the light from the emission surface 27B, and a light receiving element 21 having a light receiving surface 21A (corresponding to the detection surface) which detects the light emitted from the prism 27.

By using the above configuration, the distance that the reflected light travels to reach the light receiving element 21 can be extended. In other words, the back focus distance of the light receiving optical system 32 is extended, and the numerical aperture (NA value) of the light receiving optical system 32 can be reduced.

A specific example is shown in Figure 10. When the light receiving optical system 32 has a short back focus and a large NA value (Figure 10A), the angular deviation of the reflected light relative to the optical axis of the light receiving optical system 32 significantly shifts the focused spot position, which may affect the detection performance of the light receiving element 21. On the other hand, when the light receiving optical system has a long back focus and a small NA value (Figure 10B), the effect of the angular deviation of the reflected light on the focused spot position can be reduced.

In this embodiment, an optical system with a long back focus and a low NA value can be obtained, so that the detection performance of reflected light by the light receiving element 21 is maintained even if the total length of the lens assembly of the light receiving optical system 32 is shortened or the lens diameter is reduced. In addition, because the optical path distance is extended using the prism 27, the design length from the light receiving optical system 32 to the light receiving element 21 can be shortened (Figure 10C). This makes it possible to miniaturize the light receiving optical system 32 and the measurement device 1.

In addition, the above configuration allows the photoreceiver 20 to be mounted on the mounting substrate 5. Therefore, there is no risk of the adhesion between the photoreceiver 21 and the mounting substrate 5 being lost, and a high-quality photoreceiver can be obtained.

The receiver 20 has a light receiving element 21 attached to the surface of the mounting substrate 5 and electrically connected. Therefore, there is no risk of the light receiving element 21 losing its adhesion to the mounting substrate 5, and a high-quality light receiving device can be obtained.

Prism 27 is a pentaprism. The receiver 20 has a simple structure using a pentaprism, making it possible to change the optical axis direction of the reflected light.

The area of the exit surface 27B is larger than the area of the light receiving surface 21A of the light receiving element 21. By making the prism 27 larger, the received light flux or amount of reflected light can be increased. The amount of light incident on the light receiving section 22 increases, improving the detection accuracy of the light receiving element 21.

The prism 27 may be provided with at least one of an anti-reflection film and a vapor deposition mirror. The prism 27 may face the light receiving surface 21A of the light receiving element 21 via a resin film. By providing the light receiver 20 with such an optical film, it is possible to obtain the desired optical performance, such as suppressing the refraction or reflection of unnecessary light, absorbing a specific wavelength, or adjusting the transmittance.

The receiver 20 may include a mounting member 28 that mounts the prism 27 to the light receiving element 21 while forming a gap between the light emitting surface 27B and the light receiving surface 21A. By forming a gap, it is possible to adjust the distance from the light receiving optical system 32 to the light receiving unit 22 and obtain the desired optical performance.

The light-emitting element 10 and the light-receiving element 21 are both surface-mounted and electrically connected to the mounting substrate 5. Therefore, there is no risk of the adhesion between the light-receiving element 21 and the mounting substrate 5 and between the light-emitting element 10 and the mounting substrate 5 being lost, and a high-quality light detection device 50 can be obtained.

<Modification>
In the above embodiment, the prism 27 is used as the change unit. The present invention is not limited to such a configuration. As an example, as shown in the modified example of FIG. 11, the optical axis direction of the reflected light may be changed using two or more mirrors 60, such as a pentagonal mirror instead of the prism 27. In addition, the conversion angle of the optical axis direction between the incident light and the outgoing light is not limited to 90 degrees. For example, the prism 27 may be a different type of prism from a pentagonal prism, or a mirror 60 may be used to set the change angle of the optical axis to an angle other than 90 degrees.

1 Measuring device, 3 Housing, 5 Mounting board,
6 light-emitting curved portion, 7 light-receiving curved portion,
8: Substrate frame; 10: Light-emitting element; 20: Light-receiver; 21: Light-receiving element; 22: Light-receiving section; 23: Light-receiving window; 24: Electrode; 25: Electrode; 27: Prism; 29: Resin film; 30: Optical system; 31: Light-projecting optical system;
32 Optical system for light reception, 33 Optical frame,
40 Controller, 41 Arithmetic unit, 42 Storage unit,
50 Photodetector, 51 Conversion unit,
52 Analog-to-digital conversion circuit,
90 Object

Claims (8)

A change unit that reflects light twice after it is irradiated from the light emitting element and reflected by an object, and emits the light from an exit surface;
a light receiving element having a detection surface for detecting light emitted from the change portion;
an attachment member that attaches the change portion to the light receiving element while forming only a gap constituted by air between the emission surface and the detection surface;
The attachment member is provided along the periphery of the light receiving element. The light receiving device according to claim 1, wherein the change portion is a pentaprism. The light receiving device according to claim 1 or 2, further comprising a substrate on whose surface the light receiving element is attached and which is electrically connected to the light receiving element. The light receiving device according to any one of claims 1 to 3, wherein the area of the emission surface is larger than the area of the detection surface. The light receiving device according to any one of claims 1 to 4, wherein the modification portion comprises at least one of an anti-reflection film and a vapor deposition mirror. The light receiving device according to any one of claims 1 to 5, wherein the emission surface and the detection surface face each other via a resin film. A light emitting element that irradiates light onto an object;
A modification unit that reflects the light reflected by the object twice and emits the light from an exit surface;
a light receiving element having a detection surface for detecting light emitted from the change portion;
an attachment member that attaches the change portion to the light receiving element while forming only a gap constituted by air between the emission surface and the detection surface;
The mounting member is provided along a peripheral portion of the light receiving element. The measurement device according to claim 7, further comprising a substrate on which the light-emitting element and the light-receiving element are attached and to which the light-emitting element and the light-receiving element are electrically connected.

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