Optical scanning device and ranging device

Abstract

To prevent deterioration in resolution caused by the spread of a light source spectrum in a technology of optically measuring a distance to an object by detecting reflection light of light radiated to the object.SOLUTION: An optical scanning device and a ranging device including the same include: a light source part which includes a vertical resonator type surface light emitting laser as a pulse light source; a scanning part which includes a diffraction grating type optical element which can electrically change a diffraction angle, in which the optical element changes the emission direction of the incident light that enters from the light source part with time, and which scans the emission light in a predetermined scan direction; and a filter part placed on an optical path of the incident light or emission light, for restricting the spectral width of the passing light.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a distance measuring device that irradiates an object with light and detects reflected light to optically measure the distance to the object, and to an optical scanning device for implementing the same. [Background technology]

[0002] One technology for detecting the distance to an object and its position involves irradiating the object with light, receiving the light reflected from the object, and optically measuring the distance to the object and the shape of the object based on the information from the reflected light. One example is a technology that uses laser light called LiDAR (Light Detection And Ranging). LiDAR technology is expected to be applied to obstacle detection in automobiles and robot control, for example.

[0003] For example, in the technology described in Patent Document 1, the direction of light emitted from a laser light source is changed over time by a MEMS (Micro Electro Mechanical Systems) phased array to scan the laser light, and the position of the object in a specific direction is detected by receiving the light reflected from the object. Here, the MEMS phased array is a collection of many arranged microscopic optical elements that function as a diffraction grating, and each element is individually driven to adjust its position, making it possible to electrically control the emission direction of the diffracted light. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2022-545543 Summary of the Invention [Problem to be solved by the invention]

[0005] When implementing optical scanning using the above-mentioned diffraction grating type optical element, the effect of the spectral width of light on the diffraction angle can be a problem. In other words, since the size of the diffraction angle depends in principle on the wavelength of the incident light, if the spectral width of the incident light is wide, the divergence of the emitted light irradiated to the target object increases, which leads to a decrease in the resolution in detection. However, the above-mentioned conventional technology does not mention a specific solution to this problem, and it can be said that there is still room for improvement in this regard.

[0006] The present invention has been made in consideration of the above-mentioned problems, and aims to provide technology that can prevent a decrease in resolution caused by the broadening of the light source spectrum in a distance measuring device that optically measures the distance to an object by detecting reflected light of light irradiated onto the object, and in an optical scanning device applicable thereto. [Means for solving the problem]

[0007] One aspect of the optical scanning device of the present invention comprises a light source section including a vertical cavity surface emitting laser, a scanning section including a diffraction grating type optical element whose diffraction angle can be electrically changed, the optical element changing the direction of the light emitted from the light source over time to scan the light, and a filter section disposed on the optical path of the light to limit the spectral width of the light.

[0008] In the invention configured as described above, a vertical cavity surface emitting laser (hereinafter sometimes abbreviated as "VCSEL") is used as the light source of the optical scanning device. A VCSEL is a laser light emitting element that emits laser light in a direction perpendicular to the device substrate surface, and since it is possible to arrange a plurality of light emitting elements close to each other, it is possible to realize a high-output surface light source having a light output surface of any shape. For this reason, it is suitable as a light source for the above-mentioned distance measuring device, which requires both high output and a short pulse width.

[0009] In addition, while more common laser light sources, such as Fabry-Perot lasers, have a spectral width of typically about 10 nanometers, VCSELs can achieve a narrower spectral width, for example, about 1 nanometer, which can suppress the degradation of resolution caused by the wavelength dependence of the diffraction angle.

[0010] As described later, the upper limit of the spectral width required for the light source is determined by the specifications of the device, specifically, the required light irradiation range (viewing angle) and resolution. In the present invention, a filter section is disposed on the optical path of the emitted light to realize narrowband light that achieves both the required viewing angle and resolution. Therefore, it is not necessary to realize such a narrow spectral width by the VCSEL alone. This makes it easier to achieve the required specifications, and the required narrowband light can be reliably achieved. This makes it possible to configure an optical scanning device that can achieve both the required viewing angle and resolution.

[0011] In addition, a distance measuring device according to one embodiment of the present invention includes an optical scanning device having the above-mentioned configuration, a scanning control unit that controls the optical element to perform optical scanning, a light receiving unit that receives reflected light reflected by an object, and a distance detection unit that detects the distance to the object based on information about the reflected light received by the light receiving unit.

[0012] In the invention configured in this manner, the optical inspection device configured as described above is used as a light irradiation means for scanning an object, so that it is possible to suppress the spread of the light source spectrum due to diffraction and perform distance measurement of the object with excellent resolution. Effect of the Invention

[0013] As described above, according to the present invention, in an optical scanning device that irradiates an object with light for scanning, it is possible to suppress the spread of the light source spectrum caused by diffraction to a small extent. Also, in a distance measuring device that detects reflected light from an object and optically measures the distance to the object, it is possible to measure the distance to the object while preventing a decrease in resolution caused by the spread of the light source spectrum. [Brief description of the drawings]

[0014] [Figure 1] 1 is a block diagram showing a schematic configuration of an embodiment of a distance measuring device according to the present invention; [Diagram 2] FIG. 1 is a diagram illustrating a schematic structure of a MEMS phased array. [Diagram 3] FIG. 1 is a diagram illustrating the operation of a MEMS phased array. [Figure 4] FIG. 2 is a diagram showing the relationship between the spectrum of incident light and the diffraction direction. [Diagram 5] 2 is a diagram showing a schematic configuration of an optical scanning unit and a path of light; FIG. [Figure 6] 2 is a diagram showing a schematic configuration of an optical scanning unit and a path of light; FIG. [Figure 7] FIG. 2 is a diagram illustrating optical scanning according to this embodiment. [Figure 8] FIG. 1 is a diagram illustrating limitations on a light source size. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] 1 is a block diagram showing a schematic configuration of an embodiment of a distance measuring device according to the present invention. The distance measuring device 1 is a device that measures the distance to an object OBJ using LiDAR (Light Detection And Ranging) technology, and is applicable to various measurement and control fields, such as robot control and obstacle detection in a vehicle.

[0016] In this distance measuring device 1, a MEMS (Micro Electro Mechanical Systems) phased array is used for beam steering to optically scan the object OBJ. The operating principle and basic configuration of a distance measuring device using beam steering by a MEMS phased array are described in Patent Document 1, and the same idea can be applied to this embodiment. Therefore, the distance measuring principle and device configuration will be only briefly described here.

[0017] The distance measuring device 1 mainly comprises an optical scanning unit 100 that irradiates an object OBJ with laser pulse light as coherent scanning light Ls, a detection unit 200 that detects reflected light Ls from the object OBJ, and a control unit 300 that controls the operation of each part of the device and calculates the distance to the object OBJ from the detected reflected light Ls.

[0018] In the optical scanning unit 100, the laser pulse light emitted from the laser light source 10 is shaped into a predetermined spectrum and spot shape by a bandpass filter (BPF) 20 and an illumination optical system 30. Then, the light steered by the MEMS phased array 40 is irradiated onto the object OBJ as scanning light Ls via a projection optical system 50. In the detection unit 200, the reflected light Lr from the object OBJ is incident on the photodetector 70 via a bandpass filter (BPF) 60. The photodetector 70 generates a signal including information indicating the distance from the object OBJ from the received light, and outputs the signal to the control unit 300.

[0019] The control unit 300 calculates the distance to the object OBJ using ToF (Time of Flight) technology based on the signal input from the photodetector 70. Specifically, the time difference detection unit 80 detects the time difference between when the pulsed light is emitted from the laser light source 10 and when the corresponding reflected light Ls is received, and the calculation unit 90 calculates the distance to the object OBJ from the obtained time difference. The scanning light Ls is scanned toward a space within a predetermined angle range, and the distance to an object in each direction is obtained by detecting the reflected light Lr from each direction in the space. Then, it is possible to estimate the size, shape, distance from the distance measuring device 1, etc. of the object OBJ from the information. For this purpose, the control unit 300 can be equipped with a CPU (Central Processing Unit), memory (RAM), storage, etc.

[0020] A vertical cavity surface emitting laser (VCSEL) is used as the laser light source 10. As described above, the VCSEL can output light having high optical intensity and narrow spectral width, and is suitable as a light source in this technology. More specifically, since a large number of optical output elements can be arranged in close proximity, high output can be obtained, and since these optical output elements can be formed of a monolithic semiconductor, the variation in the emission wavelength is small and a narrow spectral width can be obtained. In addition, depending on the arrangement of the optical output elements, the shape of the light emitting surface that can be regarded as a surface light source of a finite size can be set in various ways. The operating principle and structure of such a VCSEL are publicly known, so a description thereof will be omitted here.

[0021] FIG. 2 is a diagram showing a schematic structure of a MEMS phased array. FIG. 3 is a diagram explaining the operation of the MEMS phased array. In this embodiment, the MEMS phased array 40 is used as a programmable one-dimensional diffraction grating type optical element that diffracts incident light and outputs it, and changes the output direction over time. Hereinafter, the MEMS phased array may be referred to as a "diffractive optical element." As the diffractive optical element (DOE) 40, for example, a GLV (Grating Light Valve; "GLV" is a registered trademark of Silicon Light Machines) element can be suitably applied.

[0022] FIG. 2(a) is a diagram showing a schematic configuration of the diffractive optical element 40. FIG. 2(b) is a diagram showing possible states of the diffractive optical element 40. As shown in FIG. 2(a), the diffractive optical element 40 has a schematic configuration in which a plurality of movable ribbons 42 are arranged on a substrate 41 at regular intervals in a direction parallel to the surface while facing the surface of a flat bottom electrode 43. The upper surface of the movable ribbons 42 is a reflective surface that reflects light, for example, by metal coating. Each of the movable ribbons 42 is fixed to the bottom electrode 43 at a regular interval. That is, the distance between the movable ribbons 42 and the bottom electrode 43 is determined by a pair of post anchors 44 erected on the substrate 41 so as to sandwich the bottom electrode 43.

[0023] In order to indicate directions uniformly in the following description, an XYZ Cartesian coordinate system is set as shown in Fig. 2(a). Among the directions along the surface of substrate 41, the arrangement direction of multiple movable ribbons 42 is defined as the X direction, and the longitudinal direction of each movable ribbon 42 is defined as the Y direction. The direction perpendicular to the surface of substrate 41 is defined as the Z direction. The arrangement pitch of movable ribbons 42 in the X direction is represented by the symbol D.

[0024] The movable ribbons 42 are displaceable relative to the bottom electrode 43. Specifically, as shown in Fig. 2(b), when a control voltage V is applied between the movable ribbons 42 and the bottom electrode 43, the movable ribbons 42 are deformed by electrostatic force and displaced in the direction toward or away from the bottom electrode 43, that is, in the Z direction, as shown by the solid and dotted lines. The amount of displacement of the movable electrode 42 depends on the magnitude of the control voltage V. The control unit 90 is provided with a drive circuit (CMOS driver) (not shown), and the control voltage V is applied to the movable ribbons 42 from the drive circuit.

[0025] The control voltage V applied from the drive circuit can be set individually for each movable ribbon 42. Therefore, the height of the movable ribbons 42 in the Z direction can be individually controlled by the magnitude of the control voltage V. Therefore, when the surfaces of the multiple movable ribbons 42 are viewed macroscopically, various uneven patterns are realized due to differences in the height of each movable ribbon 42.

[0026] 3(a), when the surface heights of all the movable ribbons 42 are the same, the surfaces of those movable ribbons 42 as a whole form a plane mirror. That is, when light (solid arrow) is incident on the surface of the movable ribbon 42, the specularly reflected light (dashed arrow) is emitted from the surface of the movable ribbon 42. That is, the surface of the diffractive optical element 40, which is an assembly of the movable ribbons 42, acts as a plane mirror.

[0027] 3(b) and 3(c), when the surface heights of adjacent movable ribbons 42 are made slightly different to form a stepped uneven pattern, light reflected with a phase difference between the individual movable ribbons 42 interferes with each other, causing a diffraction phenomenon. As a result, only diffracted light in a specific direction (indicated by the dashed arrow) is emitted from the diffractive optical element 40.

[0028] The diffraction angle θ is determined by the wavelength of light (hereinafter, represented by the symbol λ) and the pitch P and height difference H of the concave-convex pattern. In the example of Fig. 3(b), a stepped repeating pattern is formed with five movable ribbons 42 as one unit, and the pitch P of the pattern is 5D. In the example of Fig. 3(c), a stepped repeating pattern is formed with four movable ribbons 42 as one unit, and the pitch P of the pattern is 4D.

[0029] These concave and convex patterns are variable through electrical control. By controlling the control voltage V applied to each movable ribbon 42 and forming a blazed pattern with a height difference H=(λ / 2) across the entire diffractive optical element 40 while varying the diffraction angle θ over time, it is possible to change the direction of the emitted light from moment to moment. This can be utilized to achieve optical scanning. The diffraction angle θ at this time is calculated using the wavelength and the repetition pitch P in the following formula: θ=λ / P=λ / (n D) … (Equation 1) Here, n is the number of movable ribbons 42 constituting one unit of the repeating pattern, and the example of FIG. 3(b) corresponds to n=5, and the example of FIG. 3(c) corresponds to n=4. Therefore, in reality, the desired optical scanning is possible by specifying the value of n corresponding to the direction in which light is desired to be emitted and controlling each movable ribbon 42 so that a blazed pattern corresponding to this is formed. Note that the value of n is not limited to an integer, and can take a continuous real value. A blazed pattern corresponding to a value of n other than an integer can be realized by making the number of ribbons forming the stepped pattern discrete, or by setting the displacement amount of the movable ribbons 42 that contact the end of each stepped pattern to a value greater than 0 and less than (λ / 2).

[0030] FIG. 4 is a diagram showing the relationship between the spectrum of incident light and the diffraction direction. As shown in FIG. 4(a), when the incident light Li to the diffractive optical element 40 has a certain spectral width Δλ, the diffraction angle θ has wavelength dependency in principle, so that the emitted light Lo from the diffractive optical element 40 advances while spreading with a certain spread angle Δθ, as shown in FIG. 4(b). If the spread angle Δθ is large at this time, the spot size when the light is incident on the object OBJ located at a distant position becomes large, and the resolution in position detection decreases. In this way, since the position resolution in distance measurement is determined by the magnitude of the spread angle Δθ, the spread angle Δθ that determines the resolution is sometimes called the "angular resolution".

[0031] As the diffraction angle θ is increased, the angular resolution Δθ also increases, and the diffraction efficiency also decreases, so it is not preferable to make the value of n in (Equation 1) too small. According to the knowledge of the present inventors, a minimum value of n of about 4 is appropriate. If the diffraction angle θ at this time is represented by the symbol θmax, then the following equation is obtained: θmax=λ / (4D) … (Equation 2) holds true.

[0032] Here, if the magnification of the projection optical system 50 is represented by the symbol M and the field of view (described later) indicating the range to be measured for distance is represented by the symbol FOV, the necessary magnification M is expressed by the following formula: M=FOV / θmax … (Equation 3) Although a detailed explanation is omitted, the relationship between the spectral width Δλ and the divergence angle Δθ of the incident light Li can be expressed by the following formula: Δθ=Δλ·M / (4D)=Δλ·FOV / λ … (Formula 4) It is expressed by:

[0033] Therefore, based on the field of view FOV and the angular resolution Δθ defined as the specifications of the distance measuring device 1, the spectral width Δλ required for the light source is expressed by the following formula: Δλ<Δθ λ / FOV … (Equation 5) For example, if the field of view FOV = 90[deg], angular resolution Δθ = 0.1[deg], and wavelength λ = 905[nm], which are the performance generally required for an in-vehicle distance measuring device, are substituted into (Equation 5), then Δλ ≒ 1.0[nm] is obtained.

[0034] Although the VCSEL as the laser light source 10 can realize a relatively narrow spectral width, it is more reliable to provide a filter on the optical path to limit the spectral width in order to satisfy the condition of the above-mentioned (Equation 5). Therefore, in this embodiment, the bandpass filter 20 is provided on the optical path to further limit the spectral width, thereby ensuring that the condition of (Equation 5) is satisfied in the scanning light Ls. To achieve this, the passband width of the bandpass filter 20 may be set narrower than the spectral width of the light source. The configuration of the optical scanning unit 100 will be described in more detail below.

[0035] 5 and 6 are diagrams showing the schematic configuration of the optical scanning unit and the path of light. More specifically, Fig. 5 is a diagram showing the optical scanning unit 100 as viewed in the Y direction, and Fig. 6 is a diagram showing the optical scanning unit 100 as viewed in the X direction. Note that, although optical elements necessary for explaining the principle are shown here, in the actual optical scanning unit 100, in addition to those shown here, optical elements for folding back the optical path or shaping the light spot shape may be appropriately added.

[0036] 5(a) and 6, the optical scanning unit 100 mainly comprises a laser light source 10 which is a VCSEL, a bandpass filter 20, an illumination optical system 30, a diffractive optical element 40, and a projection optical system 50. Note that, although the bandpass filter 20 is provided between the laser light source 10 and the illumination optical system 30 here, its location is not limited thereto. In other words, it is sufficient that the bandpass filter 20 is provided at any position on the optical path of the light emitted from the laser light source 10 and irradiated to the object OBJ as the scanning light Ls.

[0037] As can be seen with reference to Figures 5(a) and 6, the incident light Li incident on the diffractive optical element 40, which is a MEMS phased array, is a substantially parallel light in the X direction, which is the ribbon arrangement direction, and is a converged pulsed light beam in the Y direction, which is the ribbon longitudinal direction.

[0038] Specifically, the laser light source 10 has a light emitting surface with a relatively wide light intensity distribution in the XZ plane parallel to the lamp axis direction and the ribbon arrangement direction, and a narrower flattened light intensity distribution in the YZ plane parallel to the lamp axis direction and perpendicular to the ribbon arrangement direction. In this specification, the effective central axis of the light emitted from the laser light source 10 is referred to as the "lamp axis", and the direction in which it extends is referred to as the "lamp axis direction". More specifically, the "lamp axis" refers to an axis that passes through the optical center that can be regarded as the effective central point of the light emitting surface of the laser light source 10 and is perpendicular to the light emitting surface.

[0039] The illumination optical system 30 includes a cylindrical lens 31 that has no power in the long axis direction of the laser light having a flat spot shape, but has power in the short axis direction, and an imaging lens 32. Here, the "long axis" refers to an axis along the longitudinal direction of the laser light spot that spreads flat in a plane perpendicular to the lamp axis, and the "short axis" refers to an axis perpendicular to the long axis in the plane. The imaging lens 32 has power in both the long axis direction and the short axis direction, and is, for example, a spherical lens. In this case, the long axis direction is a direction that is perpendicular to the lamp axis direction of the laser light and is included in the XZ plane including the ribbon arrangement direction. The short axis direction is a direction perpendicular to the lamp axis direction and the long axis direction of the laser light.

[0040] 5(a), light emitted from a laser light source 10 having a relatively large light emission range in the long axis direction is not converged by a cylindrical lens 31, but is emitted as substantially parallel light by an imaging lens 32 and enters a diffractive optical element 40 as incident light Li. Light Lo emitted from the diffractive optical element 40 is emitted as scanning light Ls via an imaging optical system 50. The imaging optical system 50 is a teleconverter that reduces the spot size of the incident light and emits it at a larger angle of emission than the incident angle.

[0041] Therefore, as shown in Figures 5(a) and 5(b), the scanning light Ls emitted from the imaging optical system 50 has a reduced spot size in the XZ plane compared to the light Lo incident on the diffractive optical element 40, and the emission direction changed by the diffractive optical element 40 is expanded.

[0042] 6 in which the optical path is projected onto the XY plane, in the short axis direction, the light emitted from a relatively narrow light-emitting range of the laser light source 10 is collimated by the cylindrical lens 31, and is further converged on the surface of the diffractive optical element 40 by the imaging lens 32. To make this possible, the laser light source 10 and the diffractive optical element 40 are disposed so as to have a mutually conjugate positional relationship with respect to the illumination optical system 30. In this way, the illumination optical system 30 is a so-called anamorphic optical system in which the power it exerts on the passing light is anisotropic.

[0043] Therefore, the light Lo emitted from the diffractive optical element 40 enters the imaging optical system 50 while expanding. Because the imaging optical system 50 is a teleconverter, the inclination angle of the emitted light is larger than that of the incident light Lo. From the above, when a virtual image surface S is considered behind the imaging optical system 50, the image of the light source is formed on the image surface S in a band shape that is narrow in the direction parallel to the ribbon arrangement direction and wide in the direction perpendicular to this. Light is irradiated all at once onto this band-shaped area.

[0044] Fig. 7 is a diagram showing optical scanning according to this embodiment. The strip-shaped area Rb, which is collectively irradiated with the light emitted from the optical scanning unit 100, is moved sequentially in a direction intersecting with the longitudinal direction by the operation of the diffractive optical element 40. This realizes optical scanning of the scanning area Rs in the surrounding space. At this time, the angle at which the strip-shaped area Rb is viewed from the optical scanning unit 100 is the field of view FOV described above.

[0045] The light Lr reflected by an object in the scanning region Rs and returning from the strip region Rb is received by the photodetector 70 via the bandpass filter 60 of the detection unit 200. The control unit 300 detects the time difference between the scanning light Ls and the reflected light Lr, and measures the distance to the object from the result.

[0046] When a Fabry-Perot type semiconductor laser is used as the light source, the far-field pattern on the long axis side in the light intensity distribution is Gaussian. Therefore, as long as the long axis direction and the ribbon arrangement direction are used in the same plane, it is not necessary to consider the size of the light source in the design of the optical system.

[0047] On the other hand, when the light source is a VCSEL having a light-emitting surface of a certain size, even if the incident light Li is arranged to be converged on the diffractive optical element 40 as shown in Fig. 6, the image of the light source will have a certain size on the diffractive optical element 40. This acts to limit the resolution in distance measurement. Therefore, it is desirable to set the size of the light source so that the resolution is not reduced.

[0048] 8 is a diagram for explaining limitations on the light source size. Consider that a surface light source with an object height h is placed at a position conjugate with the reflecting surface of the diffractive optical element 40 for an illumination optical system 30 with a focal length f. Considering this, the spread angle Δθ of light emitted from an imaging optical system 50 with a magnification M is expressed by the following equation: Δθ / 2=M·(h / 2) / f … (Equation 6) By modifying this, the condition required for the object height h of the light source is that the maximum value of the object height h of the light source allowed for the required angular resolution Δθ is expressed by the following formula: h=f Δθ / M … (Equation 7) It can be expressed as follows:

[0049] This is a requirement for the light source size when using a VCSEL as a light source, independent of the requirement for the spectral width Δλ in (Equation 5). By using the optical scanning unit 100 designed to satisfy both (Equation 5) and (Equation 7), it is possible to realize a distance measuring device 1 having the required angular resolution Δθ in this embodiment.

[0050] For example, in a system with typical values ​​of focal length f = 50 mm, M = 4, and Δθ = 0.1 degrees = (0.1π / 180) rad, from (Equation 7), h ≒ 22 μm, meaning that a light source size of 22 μm or less must be used.

[0051] As described above, in the distance measuring device 1 of this embodiment, a vertical cavity surface emitting laser (VCSEL) is used as the light source, and a MEMS phased array is used as the beam steering device. The VCSEL provides a relatively high output and a narrow spectral width, and the manufacturing cost can be kept relatively low, making it suitable as the light source for the distance measuring device 1. In addition, by using a MEMS phased array as the beam steering device and driving it by electrical control, a wide spatial range can be scanned at high speed.

[0052] In this way, the combination of a VCSEL and a MEMS phased array is suitable for configuring an optical scanning mechanism in a distance measuring device. However, it is not enough to simply combine them; by applying a design concept that takes into account the above-mentioned conditions, it is possible to configure an optical scanning device and a distance measuring device that meet the required performance.

[0053] As described above, in the distance measuring device 1 of this embodiment, the optical scanning unit 100 functions as the "optical scanning device" of the present invention, and the detection unit 200 functions as the "light receiving section" of the present invention. The control unit 300 also functions as the "scanning control section" and the "distance detection section" of the present invention. The diffractive optical element 40, which is a MEMS phased array, functions as the "scanning section" of the present invention. The laser light source 10 and the illumination optical system 30 function as the "light source section" of the present invention, and the bandpass filter 20 functions as the "filter section" of the present invention.

[0054] The present invention is not limited to the above-mentioned embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the above-mentioned embodiment is an embodiment of the "distance measuring device" of the present invention, but its main feature is the optical scanning unit 100, which is an embodiment of the "optical scanning device". Therefore, the optical scanning unit 100 of the above-mentioned embodiment can be implemented alone as the "optical scanning device" of the present invention. In this case, the application is not limited to the above-mentioned distance measuring device. In other words, the "optical scanning device" of the present invention can be applied to various technical fields for scanning a space with light to detect the presence, position, shape, surface condition, etc. of an object, or as an illumination light source for imaging.

[0055] In addition, since the laser light source 10 in the above embodiment is a VCSEL, any shape of the light-emitting surface can be realized. Therefore, in the above embodiment, a flat light-emitting surface shape suitable for incidence on the MEMS phased array 40, which is a one-dimensional diffraction grating type optical element, can be adopted. However, since the cross-sectional shape of the light to be incident on the MEMS phased array 40 can be shaped using other optical elements, the shape of the light-emitting surface is not limited to the above. For example, a larger number of light-emitting elements may be arranged to achieve higher output.

[0056] In addition, the optical scanning unit 100 of the above embodiment is provided with an illumination optical system 30 which is an anamorphic optical system, and a projection optical system 50 which is a teleconverter. These structures are not limited to those described above, and may be replaced with those having equivalent functions as appropriate. The present invention may also be implemented with a configuration in which at least one of these is omitted.

[0057] For example, when the VCSEL as the laser light source 10 is configured to emit a line light beam with a cross-sectional shape that is long in one direction and sufficiently short in the other direction, the illumination optical system does not necessarily have to have anamorphic characteristics. Also, the teleconverter as the projection optical system 50 is advantageous in that it allows a compact optical scanning device with a wide scanning angle to be configured, but if there is no limit to the size of the device, it can be omitted or replaced with an optical system having other functions.

[0058] As described above by way of example of specific embodiments, in the optical scanning device according to the present invention, for example, the scanning unit may have a one-dimensional optical diffraction grating type optical element that changes the emission direction of the emitted light in a plane parallel to the incidence direction of the incident light. With such a configuration, the emission direction of the light can be scanned one-dimensionally. Furthermore, by combining this configuration with a light source unit that extends in a direction perpendicular to the scanning direction, or by combining this configuration with a configuration that performs scanning in a direction perpendicular to the scanning direction, two-dimensional optical scanning becomes possible.

[0059] More specifically, for example, the optical element may have a plurality of movable ribbons, each of which is provided with a reflective surface that reflects incident light and is electrically driven independently of each other, each of which is a strip extending in one direction, and the plurality of movable ribbons may be arranged at regular intervals in a direction perpendicular to the one direction. Such an optical element is called a MEMS phased array, and various blazed patterns can be realized by controlling the displacement amount of each movable ribbon, making it possible to control the light emission direction at high speed and precision.

[0060] Also, for example, the light source unit may be configured to cause incident light having a flat light intensity distribution that is long in one direction and short in a direction orthogonal to the one direction in a plane orthogonal to the lamp axis direction to enter the optical element, and the scanning unit may be configured to change the emission direction of the emitted light in a plane parallel to the one direction. Here, the "lamp axis direction" means the direction of an axis passing through the optical center, which is the effective center point, of the light emitting surface of the light source unit that can be regarded as a surface light source of finite size and perpendicular to the light emitting surface. For example, the light source unit can be configured to have an anamorphic optical system that shapes the light emitted from a vertical cavity surface emitting laser to generate light having an appropriate light intensity distribution. According to such a configuration, the light intensity in the light scanning direction can be increased.

[0061] Also, for example, a teleconverter that emits light having a smaller spot size than the incident light and a larger emission angle than the incident angle of the light may be further provided in the optical path of the emitted light emitted from the scanning unit. According to such a configuration, the angular amplitude of the scanning light can be expanded by the teleconverter, so that a wide scanning angle can be ensured with a small-sized device.

[0062] In this case, when the central wavelength of the light emitted from the light source unit is λ, the magnification of the teleconverter is M, and the required resolution expressed as an angle is Δθ, for example, the object height h of the light emitting surface of the light source unit may be determined so as to satisfy the following formula: h < f·Δθ / M. Alternatively, for example, when the central wavelength of the light emitted from the light source unit is λ, the divergence angle of the light emitted from the scanning unit is FOV, and the required resolution expressed as an angle is Δθ, the filter unit may be configured to limit the spectral width such that the spectral width Δλ of the transmitted light satisfies the following formula: Δλ < (Δθ·λ) / FOV. In the optical scanning device configured to satisfy these conditions, it is possible to reliably achieve the angular resolution Δθ required for the device.

Industrial Applicability

[0063] This invention is suitable for various sensing technology fields such as obstacle detection in the control of robots and vehicles, for example. [Explanation of symbols]

[0064] 1 Ranging device 10 Laser light source (light source section) 20 Bandpass filter (filter section) 30 Lighting optical system (anamorphic optical system) 40 MEMS phased array (diffractive optical element, scanning unit) 42 Movable Ribbon 50 Projection optical system (teleconverter) 100 Optical scanning unit (optical scanning device) 200 Detection unit (light receiving part) 300 Control unit (scanning control unit, distance detection unit)

Claims

1. a light source unit including a vertical cavity surface emitting laser as a pulse light source; a scanning unit including a diffraction grating type optical element capable of electrically changing a diffraction angle, the optical element changing an emission direction of the incident light from the light source unit over time, and scanning the emitted light in a predetermined scanning direction; a filter section that is disposed on an optical path of the incident light or the outgoing light and limits a spectral width of the light passing therethrough; An optical scanning device comprising:

2. The optical scanning device according to claim 1 , wherein the scanning section has the optical element of a one-dimensional optical diffraction grating type that changes the emission direction of the outgoing light within a plane parallel to the incident direction of the incident light.

3. the optical element includes a plurality of movable ribbons each having a reflecting surface for reflecting the incident light and electrically driven independently of one another; 3. The optical scanning device according to claim 2, wherein each of the movable ribbons is in the form of a strip extending in one direction, and a plurality of the movable ribbons are arranged at regular intervals in a direction perpendicular to the one direction.

4. The light source unit causes the incident light having a flat light intensity distribution that is long in one direction and short in a direction perpendicular to the one direction in a plane perpendicular to the lamp axis direction to be incident on the optical element, The optical scanning device according to claim 1 , wherein the scanning section changes an emission direction of the emitted light within a plane parallel to the one direction.

5. The optical scanning device according to claim 4 , wherein the light source section has an anamorphic optical system that shapes the light emitted from the vertical cavity surface emitting laser to generate light having the light intensity distribution.

6. 2. The optical scanning device according to claim 1, further comprising a teleconverter in an optical path of the outgoing light emitted from the scanning unit, the teleconverter emitting light having a spot size smaller than that of the incoming light and an exit angle larger than an incident angle of the incoming light.

7. When the central wavelength of the light emitted by the light source unit is λ, the magnification of the teleconverter is M, and the required resolution expressed in degrees is Δθ, the object height h of the light emitting surface of the light source unit is expressed by the following formula: h<f·Δθ / M The optical scanning device according to claim 6 , wherein the size of the light emitting surface is determined so as to satisfy the following:

8. When the central wavelength of the light emitted from the light source unit is λ, the spread angle of the light emitted from the scanning unit is FOV, and the required resolution expressed in degrees is Δθ, The filter section has a spectral width Δλ of light passing therethrough that satisfies the following formula: Δλ<(Δθ・λ) / FOV The optical scanning device according to claim 1 , wherein the spectral width is limited so as to satisfy the following:

9. An optical scanning device according to any one of claims 1 to 8, A scanning control unit that controls the optical element to perform optical scanning; A light receiving unit that receives light reflected by an object; a distance detection unit that detects the distance to the object based on information about the reflected light received by the light receiving unit; A distance measuring device comprising:

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