Optical scanning device and ranging device

Abstract

This optical scanning device and this ranging device comprising same are provided with: a light source unit including a vertical-cavity surface-emitting laser as a pulsed light source; a scanning unit that includes a diffraction grating optical element allowing for a diffraction angle to be modified electrically, the optical element causing a direction of emission of incident light incident from the light source unit to change over time to scan with the emitted light in a predetermined scanning direction; and a filter unit that is arranged on an optical path of the incident light or emitted light and limits a spectrum width of light transmitting therethrough. As regards the technology for detecting reflected light of light with which an object was irradiated and optically measuring the distance to the object, the invention makes it possible to prevent decrease in resolution caused by spreading of the light source spectrum.

Description

Optical scanning device and distance measuring device

[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 realizing the same.

[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, the shape of the object, and so on based on the information from the reflected light. One example is a technology using laser light called LiDAR (Light Detection and Ranging). LiDAR technology is expected to be applied to obstacle detection in automobiles, robot control, and so on.

[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 using a MEMS (Micro Electro Mechanical Systems) phased array to scan the laser light. Then, the position of the object in a specific direction is detected by receiving the light reflected from the object. Here, the MEMS phased array functions as a collection of many arranged microscopic optical elements as a diffraction grating, and by individually driving each element and adjusting its position, the emission direction of the diffracted light can be electrically controlled.

[0004] Special Publication No. 2022-545543

[0005] When optical scanning is performed using a diffraction grating-type optical element as described above, the effect of the spectral width of the light on the diffraction angle can become a problem. In other words, since the magnitude of the diffraction angle depends, in principle, on the wavelength of the incident light, a wide spectral width of the incident light results in a large divergence of the output light irradiated onto the target. This leads to a decrease in detection resolution. However, the above-mentioned prior art 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 a 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 from light irradiated onto the object, and in an optical scanning device that can be used therewith.

[0007] One aspect of the optical scanning device of the present invention comprises a light source unit including a vertical cavity surface emitting laser, a scanning unit including a diffraction grating type optical element whose diffraction angle can be electrically changed, wherein the optical element changes the direction of the light emitted from the light source over time to scan the light, and a filter unit arranged 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 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 perpendicular to the device substrate surface, and since multiple light emitting elements can be arranged closely to each other, it is possible to realize a high-output surface light source having a light-emitting surface of any shape. For this reason, a VCSEL is suitable as the light source for the above-mentioned distance measuring device, which requires both high output and a short pulse width.

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

[0010] As will be described later, the upper limit of the spectral width required for a light source is determined by the device specifications, specifically the required light irradiation range (field of view) and resolution. In the present invention, narrow-band light that satisfies both the required field of view and resolution is realized by placing a filter section on the optical path of the emitted light. Therefore, such a narrow spectral width does not need to be achieved by the VCSEL alone. This makes it easier to achieve the required specifications and ensures the necessary narrow-band light. This makes it possible to configure an optical scanning device that can simultaneously achieve the required field of view and resolution.

[0011] In addition, a distance measuring device according to one aspect of the present invention includes an optical scanning device having the above-described 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 as described above, the optical inspection device configured as described above is used as the light irradiation means for scanning the object, which makes it possible to suppress the broadening of the light source spectrum due to diffraction and to measure the distance to the object with excellent resolution.

[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 minimize the broadening of the light source spectrum due to diffraction. Also, in a distance measuring device that detects reflected light from an object to optically measure the distance to the object, it is possible to measure the distance to the object while preventing a decrease in resolution due to the broadening of the light source spectrum.

[0014] The above and other objects and novel features of the present invention will become more fully apparent from the following detailed description taken in conjunction with the accompanying drawings, which are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0015] 1 is a block diagram showing a schematic configuration of an embodiment of a distance measuring device according to the present invention; FIG. 2 is a diagram showing a schematic structure of a MEMS phased array; FIG. 3 is a diagram showing a schematic structure of a MEMS phased array; FIG. 4 is a diagram explaining the operation of a MEMS phased array; FIG. 5 is a diagram explaining the operation of a MEMS phased array; FIG. 6 is a diagram showing the relationship between the spectrum of incident light and the diffraction direction; FIG. 7 is a diagram showing the relationship between the spectrum of incident light and the diffraction direction; FIG. 8 is a diagram showing a schematic configuration of an optical scanning unit and the path of light; FIG. 9 is a diagram showing a schematic configuration of an optical scanning unit and the path of light; FIG. 10 is a diagram showing a schematic configuration of an optical scanning unit and the path of light; FIG. 11 is a diagram explaining restrictions on the light source size;

[0016] 1 is a block diagram showing the schematic configuration of an embodiment of a distance measuring device according to the present invention. This 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 vehicles.

[0017] 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 a similar concept can be applied to this embodiment. Therefore, only a brief description of the distance measuring principle and device configuration will be given here.

[0018] 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 Lr when the scanning light Ls is reflected by 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 Lr.

[0019] In the optical scanning unit 100, 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, reflected light Lr from the object OBJ is incident on a 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.

[0020] The control unit 300 calculates the distance to the object OBJ using time-of-flight (ToF) technology based on the signal input from the photodetector 70. Specifically, the time difference detection unit 80 detects the time difference between when pulsed light is emitted from the laser light source 10 and when the corresponding reflected light Lr is received, and the calculation unit 90 calculates the distance to the object OBJ from the calculated time difference. The scanning light Ls is scanned toward a space within a predetermined angular range, and the distance to objects in each direction is determined by detecting the reflected light Lr from each direction within the space. The size, shape, and distance from the distance measuring device 1 of the object OBJ can then be estimated from this information. For this purpose, the control unit 300 may include a central processing unit (CPU), memory (RAM), storage, and the like.

[0021] A vertical-cavity surface-emitting laser (VCSEL) is used as the laser light source 10. As described above, VCSELs are capable of outputting light with high optical intensity and a narrow spectral width, making them suitable as light sources for this technology. More specifically, a large number of optical output elements can be closely arranged to obtain high output power. Furthermore, these optical output elements can be formed from monolithic semiconductors, resulting in small variations in the emission wavelength and a narrow spectral width. Furthermore, by arranging the optical output elements, it is possible to set various shapes of the light-emitting surface, which can be regarded as a surface light source of essentially finite size. The operating principles and structure of such VCSELs are well known, and therefore will not be described here.

[0022] 2A and 2B are diagrams schematically illustrating the structure of a MEMS phased array. Also, FIGS. 3A to 3C are diagrams illustrating the operation of the MEMS phased array. In this embodiment, the MEMS phased array 40 is used as a programmable one-dimensional diffraction grating optical element that diffracts incident light and outputs the light, and changes the output direction over time through electrical control. 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 used.

[0023] FIG. 2A is a diagram schematically illustrating the configuration of a diffractive optical element 40. FIG. 2B is a diagram illustrating possible states of the diffractive optical element 40. As shown in FIG. 2A , the diffractive optical element 40 has a general 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 of a flat bottom electrode 43 while facing the surface. The upper surfaces of the movable ribbons 42 are formed as reflective surfaces that reflect light, for example, by a metal coating. Each of the movable ribbons 42 is fixed at a regular interval relative to the bottom electrode 43. That is, the distance between the movable ribbons 42 and the bottom electrode 43 is determined by a pair of post anchors 44 that are erected on the substrate 41 so as to sandwich the bottom electrode 43 therebetween.

[0024] To uniformly indicate directions in the following description, an XYZ Cartesian coordinate system is set as shown in Figure 2A. Of the directions along the surface of the substrate 41, the arrangement direction of the 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 the substrate 41 is defined as the Z direction. The arrangement pitch of the movable ribbons 42 in the X direction is represented by the symbol D.

[0025] The movable ribbons 42 are displaceable relative to the bottom electrode 43. Specifically, as shown in FIG. 2B , 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, i.e., 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 this drive circuit.

[0026] The control voltage V applied from the drive circuit can be set individually for each movable ribbon 42. Therefore, the height of each movable ribbon 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 can be realized depending on the differences in the height of each movable ribbon 42.

[0027] 3A , when the surface height of all the movable ribbons 42 is the same, the surfaces of those movable ribbons 42 collectively form a plane mirror. That is, when light (solid arrow) is incident on the surface of the movable ribbon 42, specularly reflected light (dashed arrow) is emitted from the surface of the movable ribbon 42. In other words, the surface of the diffractive optical element 40, which is an assembly of the movable ribbons 42, acts as a plane mirror.

[0028] 3B and 3C , 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 diffractive optical element 40.

[0029] The diffraction angle θ is determined by the wavelength of light (hereinafter represented by the symbol λ), the pitch P of the concave-convex pattern, and the height difference H. In the example of FIG. 3B, a stepped, repeated 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. 3C, a stepped, repeated pattern is formed with four movable ribbons 42 as one unit, and the pitch P of the pattern is 4D.

[0030] These concave and convex patterns are variable through electrical control. By controlling the control voltage V applied to each movable ribbon 42 and varying the diffraction angle θ over time while forming a blazed pattern with a height difference H = (λ / 2) across the entire diffractive optical element 40, the direction of the emitted light can be varied from moment to moment. This can be used to achieve optical scanning. The diffraction angle θ can be expressed using the wavelength and the repeat pitch P as follows: θ = λ / P = λ / (n·D) ... (Equation 1). Here, n is the number of movable ribbons 42 that make up one unit of the repeat pattern. The example in FIG. 3B corresponds to n = 5, and the example in FIG. 3C corresponds to n = 4. Therefore, in practice, desired optical scanning can be achieved by specifying the value of n corresponding to the desired direction of light emission and controlling each movable ribbon 42 to form a corresponding blazed pattern. The value of n is not limited to an integer and can take on a continuous real value. A blazed pattern corresponding to the case where the value of n is 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 ribbon 42 at the end of each stepped pattern to a value greater than 0 and less than (λ / 2).

[0031] 4A and 4B are diagrams illustrating the relationship between the spectrum of incident light and the diffraction direction. As shown in FIG. 4A, consider the case where incident light Li on diffractive optical element 40 has a certain spectral width Δλ. Since the diffraction angle θ is wavelength-dependent in principle, as shown in FIG. 4B, output light Lo from diffractive optical element 40 propagates while spreading with a certain spread angle Δθ. If the spread angle Δθ is large, the spot size when incident on a distant object OBJ will increase, resulting in a decrease in resolution in position detection. Because the position resolution in distance measurement is thus determined by the magnitude of the spread angle Δθ, the spread angle Δθ that determines the resolution is sometimes referred to as the "angular resolution."

[0032] As the diffraction angle θ increases, the value of the angular resolution Δθ also increases, and further, 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, the appropriate minimum value of n is about 4. When the diffraction angle θ at this time is represented by the symbol θmax, the following equation holds: θmax=λ / (4D) ... (Equation 2).

[0033] Here, if the magnification of the projection optical system 50 is represented by the symbol M and the field of view angle (described later) indicating the range to be measured for distance is represented by the symbol FOV, the required magnification M can be expressed by the following equation: M=FOV / θmax (Equation 3) Although a detailed explanation will be omitted, the relationship between the spectral width Δλ and the divergence angle Δθ of the incident light Li is expressed by the following equation: Δθ=Δλ·M / (4D)=Δλ·FOV / λ (Equation 4)

[0034] Therefore, based on the field of view FOV and angular resolution Δθ that are specified as specifications of the distance measuring device 1, the spectral width Δλ required for the light source can be expressed by the following equation: Δλ<Δθ·λ / FOV (Equation 5) For example, when the field of view FOV=90 ​​degrees, angular resolution Δθ=0.1 degrees, and wavelength λ=905 nm, which are performance generally required for an in-vehicle distance measuring device, are substituted into (Equation 5), Δλ≈1.0 nm is obtained.

[0035] Although a VCSEL as the laser light source 10 can achieve a relatively narrow spectral width, it is more reliable to limit the spectral width by providing a filter on the optical path in order to satisfy the condition of (Equation 5) above. Therefore, in this embodiment, a 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 for the scanning light Ls. To achieve this, the passband width of the bandpass filter 20 is 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.

[0036] 5A, 5B, and 6 are diagrams showing the general configuration of the optical scanning unit and the path of light. More specifically, FIGS. 5A and 5B are diagrams 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 while 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 added as appropriate.

[0037] 5A 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. Here, the bandpass filter 20 is provided between the laser light source 10 and the illumination optical system 30, but the location of the bandpass filter 20 is not limited thereto. In other words, the bandpass filter 20 may be provided at any position on the optical path of the light that is emitted from the laser light source 10 and irradiated onto the object OBJ as the scanning light Ls.

[0038] As can be seen by referring to FIGS. 5A 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.

[0039] Specifically, the laser light source 10 has a light-emitting surface with a flat light intensity distribution that is relatively wide in the XZ plane parallel to the lamp axis direction and the ribbon arrangement direction, and narrower in the YZ plane parallel to the lamp axis direction and perpendicular to the ribbon arrangement direction. In other words, the spot shape of the incident light Li crossing the XY plane is a flat shape that is long in the X direction and short in the Y 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 this axis extends is referred to as the "lamp axis direction." More specifically, the "lamp axis" refers to an axis that passes through the optical center, which can be considered as the effective center point of the light-emitting surface of the laser light source 10, and is perpendicular to the light-emitting surface.

[0040] The illumination optical system 30 includes a cylindrical lens 31 that has no power in the major axis direction of the laser light having a flat spot shape but has power in the minor axis direction, and an imaging lens 32. Here, the "major axis" refers to the axis along the longitudinal direction of the flattened laser light spot in a plane perpendicular to the lamp axis, and the "minor axis" refers to the axis perpendicular to the major axis in the plane. The imaging lens 32 has power in both the major axis direction and the minor axis direction and is, for example, a spherical lens. In this case, the major axis direction is a direction perpendicular to the lamp axis direction of the laser light and included in the XZ plane that includes the ribbon arrangement direction. The minor axis direction is a direction perpendicular to the lamp axis direction and the major axis direction of the laser light.

[0041] 5A, light emitted from a laser light source 10 having a relatively large light emission range in the major axis direction is not converged by a cylindrical lens 31, but is emitted as approximately parallel light by an imaging lens 32 and is incident on 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 a projection optical system 50. The projection optical system 50 is a teleconverter that reduces the spot size of the incident light before emitting it, while widening the exit angle compared to the incident angle.

[0042] Therefore, as shown in Figures 5A and 5B, the scanning light Ls emitted from the projection optical system 50 has a reduced spot size in the XZ plane compared to the light Lo incident from the diffractive optical element 40, and the emission direction changed by the diffractive optical element 40 is expanded.

[0043] 6 , in which the optical path is projected onto the XY plane, in the short axis direction, light emitted from a relatively narrow light-emitting range of the laser light source 10 is collimated by the cylindrical lens 31 and then focused onto 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 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 passing light is anisotropic.

[0044] Therefore, the light Lo emitted from the diffractive optical element 40 spreads before entering the projection optical system 50. Because the projection optical system 50 is a teleconverter, the angle of inclination of the emitted light is larger than that of the incident light Lo. From the above, when a virtual image plane S is considered behind the projection optical system 50, the image of the light source is formed on the image plane S in the shape of a band 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.

[0045] 7 is a diagram schematically illustrating optical scanning according to this embodiment. A strip-shaped region Rb, which is collectively irradiated with light emitted from the optical scanning unit 100, is sequentially moved in a direction intersecting the longitudinal direction by the operation of the diffractive optical element 40. This achieves optical scanning of the scanning region Rs in the surrounding space. At this time, the angle at which the strip-shaped region Rb is viewed from the optical scanning unit 100 is the field of view FOV.

[0046] 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.

[0047] For example, when a Fabry-Perot semiconductor laser is used as the light source, the far-field pattern on the major axis side of the light intensity distribution is Gaussian. Therefore, as long as the major axis direction and the ribbon arrangement direction are used in the same plane, it can be said that the size of the light source does not need to be taken into consideration when designing the optical system.

[0048] On the other hand, when the light source is a VCSEL having a light-emitting surface of a certain size as in this embodiment, 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 does not decrease.

[0049] 8 is a diagram illustrating limitations on light source size. Consider an illumination optical system 30 with a focal length f, and a surface light source with an object height h disposed at a position conjugate with the reflecting surface of the diffractive optical element 40. Considering this, the divergence angle Δθ of light emitted from an imaging optical system 50 with a magnification M can be expressed by the following equation: Δθ / 2=M·(h / 2) / f (Equation 6). By modifying this, the maximum allowable value of the object height h of the light source for the required angular resolution Δθ can be expressed by the following equation: h=f·Δθ / M (Equation 7), which is the condition required for the object height h of the light source.

[0050] This is a condition required for the light source size when a VCSEL is used as the light source, independent of the condition required for the spectral width Δλ in (Equation 5). In this embodiment, 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.

[0051] For example, in a system where the typical values ​​are focal length f = 50 mm, M = 4, and Δθ = 0.1 degrees = (0.1π / 180) rad, from (Equation 7), h ≈ 22 μm, that is, it is necessary to use a light source size of 22 μm or less.

[0052] As described above, the distance measuring device 1 of this embodiment uses a vertical cavity surface emitting laser (VCSEL) as the light source and a MEMS phased array as the beam steering device. A VCSEL provides a relatively high output and a narrow spectral width, and its manufacturing costs can be kept relatively low, making it suitable as the light source for the distance measuring device 1. Furthermore, by using a MEMS phased array as the beam steering device and driving it by electrical control, it is possible to scan a wide spatial range at high speed.

[0053] Thus, the combination of a VCSEL and a MEMS phased array is suitable for configuring an optical scanning mechanism in a distance measuring device. However, simply combining them is not enough; 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.

[0054] 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. Furthermore, the control unit 300 has the functions of both 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. Furthermore, 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.

[0055] The present invention is not limited to the above-described embodiment, and various modifications other than those described above are possible without departing from the spirit of the present invention. For example, the above-described embodiment is one embodiment of a "distance measuring device" of the present invention, but its main feature is the optical scanning unit 100, which is one embodiment of an "optical scanning device." Therefore, the optical scanning unit 100 of the above embodiment can be implemented alone as the "optical scanning device" of the present invention. In this case, its use is not limited to the above-described distance measuring device. In other words, the "optical scanning device" of the present invention can be applied to various technical fields for scanning space with light to detect the presence, position, shape, surface condition, etc. of an object, or as an illumination light source for imaging, etc.

[0056] Furthermore, 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, the cross-sectional shape of the light incident on the MEMS phased array 40 can also be shaped using other optical elements, so 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.

[0057] Furthermore, the optical scanning unit 100 of the above embodiment is provided with an illumination optical system 30 that is an anamorphic optical system and a projection optical system 50 that is a teleconverter. These structures are not limited to those described above, and may be replaced with those having equivalent functions as appropriate. Furthermore, the present invention can also be implemented with a configuration in which at least one of these components is omitted.

[0058] For example, when the VCSEL serving 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. Furthermore, a teleconverter serving as the projection optical system 50 is advantageous in that it allows for the construction of a compact optical scanning device with a wide scanning angle. However, if there are no restrictions on the device size, it may be omitted or replaced with an optical system having other functions.

[0059] As described above with reference to specific embodiments, in the optical scanning device according to the present invention, for example, the scanning unit may include a one-dimensional optical diffraction grating-type optical element that changes the emission direction of the emitted light in a plane parallel to the incident 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 with a configuration that performs scanning in a direction perpendicular to the scanning direction, two-dimensional optical scanning becomes possible.

[0060] More specifically, for example, the optical element may have a plurality of movable ribbons, each of which has a reflective surface that reflects incident light and is electrically driven independently of one another, each of which has a strip shape extending in a first direction, and the plurality of movable ribbons may be arranged at regular intervals in a direction perpendicular to the first direction. Such an optical element is a type of optical element known as a MEMS phased array, and various blazed patterns can be realized by controlling the displacement amount of each movable ribbon, thereby enabling high-speed and precise control of the output direction of light.

[0061] Alternatively, for example, the light source unit may be configured to cause incident light having a flat light intensity distribution that is long in a second direction and short in a direction perpendicular to the second direction in a plane perpendicular to the lamp axis direction to be incident on 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 second direction. Here, the "lamp axis direction" refers to the direction of an axis that passes through the optical center, which is the effective center point of the light-emitting surface of the light source unit, which can be considered a surface light source of finite size, and is perpendicular to the light-emitting surface. For example, the light source unit may have an anamorphic optical system that shapes the light emitted from a vertical-cavity surface-emitting laser to achieve an appropriate light intensity distribution. This configuration allows the light intensity in the scanning direction to be increased.

[0062] Furthermore, for example, a teleconverter may be further provided in the optical path of the outgoing light from the scanning unit, which emits light with a spot size smaller than that of the incident light and an exit angle larger than the incident angle of the incident light. With this configuration, the angular amplitude of the scanning light can be expanded by the teleconverter, making it possible to ensure a wide scanning angle with a small device.

[0063] In this case, the size of the light-emitting surface may be set so that the object height h of the light-emitting surface of the light source unit satisfies the following equation: h < f Δθ / M, where λ is the central wavelength of the light emitted by the light source unit, M is the magnification of the teleconverter, and Δθ is the angle at which the required resolution is expressed in degrees. Alternatively, for example, where λ is the central wavelength of the light emitted by the light source unit, FOV is the spread angle of the light emitted from the scanning unit, and Δθ is the angle at which the required resolution is expressed in degrees, the filter unit may limit the spectral width Δλ of the light passing through it so that the spectral width Δλ satisfies the following equation: Δλ < (Δθ λ) / FOV. An optical scanning device configured to satisfy these conditions can reliably achieve the angular resolution Δθ required of the device.

[0064] While the invention has been described with reference to specific embodiments, this description is not intended to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as other embodiments of the invention, will become apparent to those skilled in the art upon reference to the description of the invention. It is therefore contemplated that the appended claims will cover such modifications or embodiments within the true scope of the invention.

[0065] The present invention is suitable for various sensing technology fields, such as detecting obstacles in controlling robots and vehicles.

[0066] REFERENCE SIGNS LIST 1 Range finding device 10 Laser light source (light source section) 20 Bandpass filter (filter section) 30 Illumination optical system (anamorphic optical system) 40 MEMS phased array (diffractive optical element, scanning section) 42 Movable ribbon 50 Projection optical system (teleconverter) 100 Optical scanning unit (optical scanning device) 200 Detection unit (light receiving section) 300 Control unit (scanning control section, distance detection section)

Claims

1. An optical scanning device comprising: a light source section including a vertical cavity surface emitting laser as a pulsed light source; a scanning section including a diffraction grating type optical element whose diffraction angle can be electrically changed, the optical element changing over time the emission direction of incident light from the light source section, thereby scanning the emitted light in a predetermined scanning direction; and a filter section disposed on the optical path of the incident light or the emitted light, for limiting the spectral width of the light passing through.

2. The optical scanning device according to claim 1, wherein the scanning section has an 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 scanning device described in claim 2, wherein the optical element has a plurality of movable ribbons, each of which has a reflective surface that reflects the incident light and is electrically driven independently of one another, each of the movable ribbons being strip-shaped extending in a first direction, and the plurality of movable ribbons being arranged at regular intervals in a direction perpendicular to the first direction.

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

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

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

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

8. The optical scanning device of claim 1, wherein the filter unit limits the spectral width Δλ of the passing light so that the spectral width satisfies the following equation: Δλ<(Δθ·λ) / FOV, where λ is the central wavelength of the light emitted from the light source unit, FOV is the spread angle of the light emitted from the scanning unit, and Δθ is the required resolution expressed in degrees.

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

Images