Object detection device

Abstract

To enable high-speed and high-sensitivity position detection by using a spatial light phase modulation element in a light reception side in an object detection device for optically detecting an object by detecting reflection light of light applied to the object.SOLUTION: In an object detection device, a light reception section for receiving reflection light from an object in space and outputting a signal corresponding to a light reception result has an optical modulator including a spatial light phase modulation element capable of changing a relationship between an incidence direction and an emission direction of light by electrical control, a photodetector for outputting a signal according to received light, and an optical fiber for guiding light emitting from the optical modulator to the photodetector while one end is connected to the photodetector. A control section selectively allows light impinging on the photodetector from a specific incidence direction to impinge on the other end in the opposite side of the photodetector in the optical fiber by changing a relationship between an incidence direction and an emission direction with time, and at the same time changes a specific incidence direction with time.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to an object detection device that optically detects an object by irradiating light into space and detecting reflected light from the object.

Background Art

[0002] As a technique for detecting the distance and position of an object, there is a technique of irradiating light onto the object, receiving the reflected light from the object, and optically measuring the distance to the object and the shape of the object based on the information of the reflected light. For example, a technique using laser light called LiDAR (Light Detection And Ranging) is an example. The LiDAR technique is expected to be applied to, for example, obstacle detection in automobiles and robot control.

[0003] For example, in the technique described in Patent Document 1, the laser light beam is scanned by changing the direction of the emitted light from the laser light source over time by a MEMS (Micro Electro Mechanical Systems; micro electro mechanical system) phased array, and the light reflected from the object is received to detect the position to the object in a specific direction. Here, the MEMS phased array functions as a diffraction grating for an aggregate of a large number of arranged minute optical elements, and by driving each element individually and adjusting its position, the emission direction of the diffracted light can be electrically controlled. The MEMS phased array in this case functions as a programmable spatial light phase modulation element capable of electrically changing the diffraction direction of light.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In Patent Document 1, in addition to using a MEMS phased array for beam steering technology to change the emission direction of scanning light into space, it is also described that a MEMS phased array is used to identify the direction of light reflected from an object. That is, Patent Document 1 describes a configuration in which incident light from a distance is guided to a photodetector via a MEMS phased array. However, the specific configuration and operation are not described in detail.

[0006] For example, in order to enable high-speed and high-sensitivity position detection, it is conceivable to apply a balanced photodetector to light detection. However, in a balanced photodetector, generally, light input via an optical fiber is used. Patent Document 1 does not specifically describe such a combination with an optical fiber input type photodetector. In particular, when a position resolution is required for the photodetector, since such an optical fiber input type photodetector has not been put into practical use, a plurality of pairs of optical fibers and photodetectors are required, increasing the size and cost of the device.

[0007] As described above, in LiDAR technology, it cannot be said that there is sufficient technological accumulation regarding the specific configuration of the light receiving unit using a spatial light phase modulation element and its operation control.

[0008] This invention has been made in view of the above problems, and an object thereof is to provide a technique capable of high-speed and high-sensitivity position detection when a spatial light phase modulation element is used on the light receiving side in an object detection device that optically detects an object by detecting the reflected light of light irradiated on the object.

Means for Solving the Problems

[0009] The object detection device according to the present invention includes a light scanning unit that emits light and optically scans a space with the light, a light receiving unit that receives reflected light from an object in the space and outputs a signal according to the light receiving result, a processing unit that executes signal processing based on the signal to detect the object, and a control unit that controls the light receiving unit. Here, the light receiving unit includes an optical modulator including a spatial light phase modulation element whose relationship between the light incident direction and the light emission direction can be changed by electrical control, a photodetector that outputs the signal according to the received light, and an optical fiber having one end connected to the photodetector and guiding the light emitted from the optical modulator to the photodetector. Then, the control unit selectively makes the light incident from a specific incident direction on the optical modulator enter the other end of the optical fiber on the side opposite to the photodetector by changing the relationship between the incident direction and the emission direction over time, and changes the specific incident direction over time.

[0010] In the invention configured as described above, the light irradiated toward the space and reflected from an object in the space is transmitted from the optical modulator including the spatial light phase modulation element to the photodetector via the optical fiber. Specifically, one end of the optical fiber is connected to the photodetector, and the light from the optical modulator is incident on the other end of the optical fiber on the side opposite to the one end.

[0011] The optical modulator selectively guides the light from a specific incident direction determined by the control from the control unit among the incident light to the other end of the optical fiber. The spatial light phase modulation element included in the optical modulator can change the relationship between the light incident direction and the light emission direction according to the control from the control unit. Although light can be incident on the optical modulator from various directions, the optical modulator is controlled so that only the light from a specific incident direction among them enters the optical fiber. Since this specific incident direction changes over time, the light with different incident angles on the optical modulator sequentially enters the optical fiber. That is, the light incident on the optical modulator from different directions is sequentially received by the photodetector in a time-division manner.

[0012] At this time, even if the incident angle to the optical modulator varies variously, the optical path of the light traveling from the optical modulator to the other end of the optical fiber hardly changes. In other words, the light traveling toward the other end of the optical fiber enters the optical fiber from substantially a fixed direction regardless of the incident angle at which the light enters the optical modulator. When light enters the optical fiber from various directions, depending on the incident direction, the reflection at the end face may increase. This causes a decrease in the optical transmission efficiency. However, in the present invention, since the incident direction to the end face does not fluctuate, it is possible to efficiently guide the light emitted from the optical modulator to the photodetector via the optical fiber.

[0013] Therefore, light can be efficiently transmitted also in the combination with the photodetector connected to the optical fiber. As the spatial light phase modulation element, for example, those capable of high-speed switching on the order of 100 kHz have been put into practical use. By combining these, high-speed and highly sensitive object detection becomes possible.

[0014] Also, by using the spatial light phase modulation element, light from different directions can be sequentially incident on a single optical fiber. For this reason, it becomes possible to detect light from multiple directions by using one photodetector in a time-division manner, and the required number of photodetectors can be reduced and an increase in cost can be suppressed.

Effects of the Invention

[0015] As described above, according to the present invention, light incident from various directions is emitted in a fixed direction by an optical modulator having a spatial light phase modulation element, and an optical fiber is provided in that direction. For this reason, the incident direction of the light incident on the optical fiber can be made constant, and the light can be efficiently guided to the photodetector. As a result, in the present invention, high-speed and highly sensitive object detection becomes possible.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0017] FIG. 1 is a block diagram showing the schematic configuration of an embodiment of an object detection device according to the present invention. This object detection device 1 is a device that measures the distance to an object OB in space, its size, shape, and other properties (hereinafter, these may be collectively referred to as "spatial features") 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.

[0018] This object detection device 1 includes a transmission unit 20 that transmits a scanning light beam Ls to the object OB, a reception unit 60 that receives the light reflected by the object OB as a measurement light beam Lm, and a control unit 90 that controls the transmission unit 20 and the reception unit 60. In FIG. 1 and the following figures, dashed arrows indicate the optical paths of the light beams unless otherwise specified. However, the optical paths may be shown as solid lines as necessary.

[0019] The transmission unit 20 includes a laser light source 21 which is a wavelength-sweeping light source that continuously emits a laser light beam with a changing wavelength, and an optical modulator 22 which is a spatial light phase modulation element that performs phase modulation on the laser light beam emitted from the laser light source 21. A scanning light beam Ls subjected to phase modulation by the optical modulator 22 is transmitted to the object OB.

[0020] The reception unit 60 includes an optical modulator 61 which is a spatial light phase modulation element, a coherent light detector (hereinafter sometimes simply referred to as "light detector") 62, and an optical fiber 63 that connects them. The measurement light beam Lm reflected by the object OB is redirected by the optical modulator 61 and detected by the light detector 62 via the optical fiber 63. Although details will be described later, the reception unit 60 superimposes the reference light beam Lr received from the transmission unit 20 and the measurement light beam Lm reflected by the object OB to generate a composite wave, and detects this composite wave. This composite wave includes a beat generated by the interference between the measurement light beam Lm and the reference light beam Lr.

[0021] The control unit 90 includes a CPU (Central Processing Unit) 91. The CPU 91 realizes the following functional blocks to realize various operations described later by executing a control program stored in advance in a storage (not shown). The storage may be configured, for example, by a flash memory, a magnetic disk, or a combination thereof. The control unit 92 controls each part of the apparatus, specifically, the emission of the scanning light beam Ls and the reference light beam Lr from the laser light source 21, and the phase modulation by the optical modulators 22 and 61. Further, the processing unit 93 calculates the distance and direction to the object OB based on the beat included in the composite wave of the measurement light beam Lm and the reference light beam Lr detected by the light detector 62. At least a part of these functional blocks may be configured by hardware such as an FPGA (Field Programmable Gate Array).

[0022] The optical modulators 22 and 61 used in this object detection device 1 are, for example, the movable ribbon type MEMS (Micro Electro Mechanical Systems) phased array shown in FIG. 2. In this embodiment, the MEMS phased array is used as a programmable one-dimensional diffraction grating type optical element that diffracts incident light and emits it, and changes the emission direction over time. Hereinafter, the MEMS phased array may be referred to as a "diffractive optical element". As the diffractive optical element (Diffractive Optical Element; DOE), for example, the GLV (Grating Light Valve; "GLV" is a registered trademark of the company) element of Silicon Light Machines can be preferably applied.

[0023] FIG. 2 is a diagram schematically showing the structure of the MEMS phased array. FIG. 3 is a diagram for explaining the operation of the MEMS phased array. More specifically, FIG. 2(a) is a diagram schematically showing the schematic configuration of a diffractive optical element 40 which is a form of the MEMS phased array. FIG. 2(b) is a diagram showing the states that the diffractive optical element 40 can take. FIG. 3 is a diagram for explaining the operation of the MEMS phased array.

[0024] 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 at regular intervals in a direction parallel to the surface of a flat bottom electrode 43 while facing the surface on a substrate 41. In the movable ribbon 42, the upper surface thereof is a reflecting surface that reflects light, for example, by a metal coating. Each of the movable ribbons 42 is fixed at a certain interval with respect to the bottom electrode 43. That is, the distance between the movable ribbon 42 and the bottom electrode 43 is defined by a pair of post anchors 44 erected on the substrate 41 so as to sandwich the bottom electrode 43.

[0025] In the following description, in order to uniformly indicate directions, as shown in FIG. 2(a), XYZ orthogonal coordinates are set. Among the directions along the surface of the substrate 41, the arrangement direction of the plurality of movable ribbons 42 is the X direction, and the longitudinal direction of each movable ribbon 42 is the Y direction. Also, the direction perpendicular to the surface of the substrate 41 is the Z direction. Further, the arrangement pitch of the movable ribbons 42 in the X direction is represented by the symbol D.

[0026] The movable ribbon 42 is displaceable with respect to the bottom electrode 43. Specifically, as shown in FIG. 2(b), when a control voltage V is applied between the movable ribbon 42 and the bottom electrode 43, the movable ribbon 42 is deformed by electrostatic force and is displaced in the approaching / separating direction with respect to the bottom electrode 43, that is, in the Z direction, as shown by the solid line and the dotted line. The displacement amount 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 ribbon 42 from the drive circuit.

[0027] The control voltage V supplied from the drive circuit can be set individually for each movable ribbon 42. For this reason, the height of the 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 plurality of movable ribbons 42 are viewed macroscopically, various uneven patterns are realized due to the differences in the heights of the respective movable ribbons 42.

[0028] For example, as shown in FIG. 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 constitute a plane mirror. That is, when light (solid line arrow) is incident on the surface of the movable ribbon 42, the specularly reflected light (dashed line arrow) is emitted from the surface of the movable ribbon 42. That is, the surface of the diffractive optical element 40, which is an aggregate of the movable ribbons 42, acts as a plane mirror.

[0029] On the other hand, as shown in FIGS. 3(b) and 3(c), when a stepped uneven pattern is formed by slightly varying the surface height between adjacent movable ribbons 42, light reflected with a phase difference between the individual movable ribbons 42 interferes with each other to cause a diffraction phenomenon. For this reason, only diffracted light in a specific direction (indicated by the dashed arrow) is emitted from the diffractive optical element 40.

[0030] The diffraction angle θ is defined by the wavelength of light (hereinafter represented by the symbol λ), the pitch P of the uneven pattern, and the height difference H. In the example of FIG. 3(b), a stepped repeating pattern with five movable ribbons 42 as one unit is formed, and the pitch P of the pattern is 5D. Also, in the example of FIG. 3(c), a stepped repeating pattern with four movable ribbons 42 as one unit is formed, and the pitch P of the pattern is 4D.

[0031] These uneven patterns are variable by electrical control. By controlling the control voltage V applied to each movable ribbon 42 and changing the diffraction angle θ over time while forming a blazed pattern with a height difference H = (λ / 2) for the entire diffractive optical element 40, it is possible to continuously change the direction of the emitted light. Utilizing this, optical scanning can be realized. The diffraction angle θ at this time is given by the following equation using the wavelength and the repeating pitch P: θ = λ / P = λ / (n·D) … (Equation 1) Here, n is the number of movable ribbons 42 that make up one unit of the repeating pattern, corresponding to n = 5 in the example of FIG. 3(b) and n = 4 in the example of FIG. 3(c), respectively. Therefore, in reality, by specifying the value of n corresponding to the direction in which light is to be emitted and controlling each movable ribbon 42 so that a blazed pattern corresponding to this is formed, desired optical scanning is possible. Note that the value of n is not limited to an integer and can take continuous real values. The blazed pattern corresponding to the case where the value of n is other than an integer can be realized by discretizing the number of ribbons forming the stepped pattern or setting the displacement amount of the movable ribbon 42 corresponding to the end of each stepped pattern to a value greater than 0 and less than (λ / 2).

[0032] In this way, the diffractive optical element 40 realized by the MEMS phased array is a spatial light phase modulation element having a function of emitting (diffracting) incident light in different directions by using interference due to a phase difference, and the emission direction of light can be changed by electrical control. This can also be rephrased as that the relationship between the incident direction and the emission direction of light can be electrically controlled.

[0033] In this embodiment, the diffractive optical element (spatial light phase modulation element) 40 having the above-described structure and characteristics is used as the optical modulator 22 of the transmission unit 20 and the optical modulator 61 of the reception unit 60. Specifically, it is as follows.

[0034] FIG. 4 is a diagram for explaining the operation of the optical modulator in this embodiment. As shown in FIG. 4(a), the optical modulator (transmission-side optical modulator) 22 of the transmission unit 20 uses the function of changing the emission direction of light incident from a certain direction to emit the emission light from the laser light source 21 as a scanning light beam Ls in various directions.

[0035] Also, as shown in FIG. 4(b), the optical modulator (reception-side optical modulator) 61 of the reception unit 60 uses the function of emitting light incident from different directions in the same direction to guide the measurement light beam Lm that can be incident from various directions to the photodetector 62. More specifically, as shown in FIG. 4(b), one end of an optical fiber 63 is connected to the photodetector 62, and the emission light from the optical modulator 61 is incident on the other end on the opposite side.

[0036] The measurement light beam Lm generated by the scanning light being reflected by the object OB can be incident on the optical modulator 61 from various directions. By adjusting the diffraction pattern of the optical modulator 61, light incident from a specific direction can be selectively made to enter the optical fiber 63. By using this, it becomes possible to guide only the measurement light beam Lm corresponding to the scanning light beam Ls to the photodetector 62.

[0037] FIG. 5 is a diagram showing the configuration of the transmission unit and the reception unit in more detail. FIG. 5(a) shows the main configuration of the transmission unit 20. The transmission unit 20 is provided with a laser light source 21 which is a wavelength-sweeping light source. The laser light source 21 emits continuous laser light, but its output wavelength periodically changes within a predetermined range in response to a control command from the control unit 92. For example, by changing the control voltage for setting the output wavelength by the control unit 92 in a sawtooth wave shape, periodic wavelength sweeping can be realized.

[0038] The laser beam emitted from the laser light source 21 is branched at a predetermined ratio by a beam splitter 23, and a part of it is output as a reference light beam Lr. The other light beam is incident on the optical modulator 22 and is emitted as a scanning light beam Ls in various directions by the optical modulator 22. By changing the emission direction moment by moment in response to a control command from the control unit 92, optical scanning of the space by the scanning light beam Ls is realized.

[0039] An optical element, for example, a cylindrical lens 24, for stretching the beam spot shape in one axial direction may be further provided on the optical path of the measurement light beam Ls emitted from the optical modulator 22. Specifically, it is as follows. In the example of FIG. 5(a), the scanning light beam Ls changes its emission direction within a plane parallel to the paper surface by the optical modulator 22. Here, when a cylindrical lens 24 having power in the direction perpendicular to the paper surface is arranged, the scanning light beam Ls passing through the cylindrical lens 24 is emitted into the space as a line beam elongated in the direction perpendicular to the paper surface. That is, it becomes possible to perform light irradiation over a wide range in the major axis direction of the beam at once.

[0040] By combining with the change in the emission direction by the optical modulator 22 in the minor axis direction of the beam, that is, in the direction parallel to the paper surface, the space can be optically scanned two-dimensionally. For example, while illuminating the up and down directions at once with the line-shaped scanning light beam Ls formed by the cylindrical lens 24, the space can be scanned two-dimensionally by changing the emission direction over time by the optical modulator 22 in the horizontal direction intersecting this.

[0041] Figure 5(b) shows the main configuration of the receiving unit 60. The receiving unit 60 is provided with a band-pass filter 65 corresponding to the wavelength of the emitted light of the laser light source 21. The measurement light beam Lm reflected from the object OB corresponding to the scanning light beam Ls is incident on the optical modulator 61 through the band-pass filter 65.

[0042] Only a minute (for example, several μm in diameter) region at the center of the end of the optical fiber 63 can efficiently receive light from the outside. In order to converge light on this region, a condenser lens 66 is disposed in the optical path between the optical modulator 61 and the optical fiber 63. The light emitted from the optical modulator 61 is condensed by the condenser lens 66, and the converged light is incident on the end face of the optical fiber 63.

[0043] The optical fiber 63 forms an optical coupler 600 together with another optical fiber 64, and the converged light beam is incident on the end 631 of the optical fiber 63. The opposite end 632 of the optical fiber 63 is connected to the photodetector 62. A reference light beam Lr provided from the transmitting unit 20 is input to the end 641 of the other optical fiber 64 constituting the optical coupler 600.

[0044] Therefore, light corresponding to the measurement light beam Lm that has been interfered by the reference light beam Lr transmitted by the optical fiber 64 appears at the end 632 of the optical fiber 63. On the other hand, light corresponding to the reference light beam Lr that has been interfered by the measurement light beam Lm transmitted by the optical fiber 63 appears at the end 642 of the optical fiber 64. That is, light including the interference component (beat) between the measurement light beam Lm and the reference light beam Lr is output from the end 632 of the optical fiber 63 and the end 642 of the optical fiber 64.

[0045] The end portion 642 on the opposite side of the optical fiber 64 is connected to the optical detector 62. The optical detector 62 is a balanced detector having two optical input ports. That is, the optical detector 62 includes two optical input ports 621, 622, and two photodiodes 623, 624 are provided corresponding to each optical input port 621, 622. The light incident from the optical input port 621 is input to the photodiode 623, and the light incident from the optical input port 622 is input to the photodiode 624. The photodiodes 623, 624 generate currents (photoelectric currents) corresponding to the amount of received light, respectively.

[0046] Current-voltage (IV) conversion amplifiers 625, 626 are respectively connected to the photodiodes 623, 624, and their outputs are input to the differential amplifier 627. Therefore, a voltage signal corresponding to the difference in the output currents of the two photodiodes 623, 624 is output to the output terminal 629 of the optical detector 62.

[0047] The gain of one of the IV conversion amplifiers, for example, the IV conversion amplifier 626, is adjusted by the output voltage of the differential amplifier 627. Specifically, the output voltage of the differential amplifier 627 is applied to the IV conversion amplifier 626 via the integrator 628. The gain of the IV conversion amplifier 626 changes so as to cancel the DC component of the output voltage of the differential amplifier 627. Therefore, the DC balance between the two photodiodes 623, 624 is automatically maintained.

[0048] In this way, the optical detector 62, which is a balanced detector, automatically corrects the level difference between the two optical inputs and outputs an output signal corresponding to their difference. Since the two optical inputs are the measurement optical beam Lm and the reference optical beam Ls including the mutual interference component (beat), respectively, the output voltage of the optical detector 62 has a value corresponding to the magnitude of the beat generated between the measurement optical beam Lm and the reference optical beam Ls.

[0049] As a balanced detector, those that can be used up to the GHz band have been put into practical use. Also, by using differential output, the common-mode component between two inputs can be canceled to obtain a high signal-to-noise ratio (S / N ratio). Therefore, it is suitable for the light receiving unit of the object detection device 1 to detect the beat component between the measurement light and the reference light at high speed and with high sensitivity. The output voltage of the photodetector 62 is sent to the processing unit 93 of the control unit 90 as a signal representing the magnitude of the beat component. The processing unit 93 detects the object OB in the space where the scanning light beam Ls is reflected to generate the measurement light beam Lm from the detected beat component.

[0050] Note that the internal configuration of the balanced detector described here is an example, and there are also various circuit forms of balanced detectors that have been put into practical use other than this. For these as well, those having the function of outputting the difference between two optical inputs in the same manner as above can be used. Moreover, those having the function of automatically balancing the level difference between the two inputs as described above are more preferable.

[0051] Also, in the above description, in the transmission unit 20, the scanning light beam Ls and the reference light beam Lr are branched by the beam splitter 23, but the branching of the beam is not limited to this method and is arbitrary. For example, a configuration in which light is branched using an optical coupler may be used. Similarly, in the receiving unit 60, in the above embodiment, the measurement light beam Lm and the reference light beam Lr are mixed by the optical coupler 600, but the method of mixing light is not limited to this and is arbitrary.

[0052] In the transmission unit 20 and the receiving unit 60 configured as described above, by operating in cooperation with each other, they constitute the main part of the FMCW (Frequency Modulated Continuous Wave) LiDAR. Since the operating principle of the FMCW LiDAR is well-known, a detailed description is omitted here.

[0053] FIG. 6 is a diagram showing an example of cooperation between a laser light source and an optical modulator. FIG. 6(a) shows the temporal change in the wavelength of the continuous laser light emitted from the laser light source 21. When a sawtooth voltage is applied as a control signal, for example, from the control unit 92 to the laser light source 21 whose output wavelength can be changed by an externally applied control signal, the output wavelength periodically changes between a minimum value λmin and a maximum value λmax with a period T1 in response thereto.

[0054] In the optical modulator 21 of the transmission unit 20, the diffraction angle θ (FIG. 3) is changed over time by a control signal from the control unit 92 in synchronization with the change in the output wavelength of the laser light. Specifically, as shown in FIG. 6(b), after a period during which the diffraction angle θ is fixed continues for a certain time, the diffraction angle θ is changed stepwise at a minute angular interval Δθ. The change period T2 of the diffraction angle θ at this time is made the same as the change period T1 of the wavelength in the laser light source 21.

[0055] As a result, the scanning light beam Ls emitted from the transmission unit 20 has the following form. That is, the laser light emitted from the laser light source 21 is irradiated in the direction defined by the diffraction angle θ of the optical modulator 21. The output wavelength of the laser light changes over time from the minimum value λmin to λmax, and during this time the diffraction angle θ is maintained constant. Therefore, for one direction in space, laser light with a continuously changing wavelength is emitted, and then the emission direction is slightly changed, and the operation of emitting laser light with a changing wavelength is repeated. That is, each direction in space is optically scanned by the frequency-modulated continuous laser light.

[0056] On the other hand, in the receiving unit 60, an optical modulator 61 is used to select the direction from which the incident light is sent to the photodetector 62. Also in this case, as shown in Fig. 6(b), the diffraction angle θ is changed stepwise, and the change period is the same as the change period of the output wavelength of the laser light. For this reason, the receiving unit 60 operates to capture all the wavelength components of the measurement light beam Lm incident from one direction and then capture the measurement light beam Lm from another direction. In other words, while the wavelength of the scanning light beam Ls is being swept, each movable ribbon of the optical modulator 61 is substantially stationary. To achieve this, a diffractive optical element capable of high-speed operation is required.

[0057] In this way, by the cooperation of the transmitting unit 20 and the receiving unit 60, the object detection device 1 can irradiate light of various wavelength components in one direction in the space and receive the light of each wavelength component reflected from that direction. As is already known, the intensity of the beat component between the reflected light and the reference light in a coherent relationship represents information on the intensity of the reflected light from the object OB in that direction. Also, the wavelength at which the beat occurs has information regarding the distance to the object OB.

[0058] Therefore, by detecting the beat component between the measurement light beam Lm and the reference light beam Lr, the direction and distance of the object OB existing in the space can be obtained. By performing the detection in the same way in various directions, the spread of the region occupied by the object OB in the space, that is, the size and shape of the object OB can be obtained. Even when there are a plurality of objects OB in the space to be optically scanned, each can be detected.

[0059] Such detection becomes possible by the synchronous operation of the transmitting unit 20 and the receiving unit 60. For example, such synchronization can be realized by operating both the transmitting unit 20 and the receiving unit 60 based on the operation clock supplied from the control unit 92.

[0060] FIG. 7 is a diagram illustrating a method of capturing light from a scanning target space. As shown in the left diagram of FIG. 7(a), for example, as a method of receiving light from various directions within the scanning target region Rs in the space, it is conceivable that the optical modulator 61 sequentially causes light from each part within the vertically elongated strip-shaped region Rb to enter the optical fiber 63 in time series. As indicated by the dotted arrows, by sequentially changing the position of the strip-shaped region Rb in the horizontal direction, two-dimensional scanning becomes possible.

[0061] In this case, as shown in the right diagram, by periodically changing the diffraction angle in the vertical direction of the optical modulator 61, which is a one-dimensional diffraction grating, it is possible to individually detect light from each location in the vertical direction of the strip-shaped region Rb. Here, although the change in the diffraction angle is macroscopically represented by a saw-tooth graph that changes monotonically and continuously, microscopically, it changes in a step-like manner as shown in FIG. 6(b).

[0062] In combination with optical scanning by a linearly scanning light beam Ls extending in the vertical direction, a resolution in the horizontal direction is not necessarily required. This is because at a certain time in the scanning target region Rs, the scanning light beam Ls is irradiated only within one strip-shaped region. If it is known in which direction the scanning light beam Ls is emitted in the horizontal direction, it can be said that the received measurement light beam Lm enters from the same direction as the emission direction of the scanning light beam Ls in the horizontal direction.

[0063] For example, as shown by the dashed line in FIG. 7(a), when the scanning light beam Ls is irradiated toward the strip-shaped region Rb, it can be said that the measurement light beam Lm transmitted to the photodetector 62 is reflected light returning from the strip-shaped region Rb. Thus, in combination with optical scanning by a one-dimensional linear scanning light beam Ls, the optical modulator 61 on the receiving side only needs to have a position resolution in the major axis direction (the vertical direction in this example) of the scanning light beam Ls, and does not require a resolution in the minor axis direction (the horizontal direction in this example).

[0064] Note that as a programmable spatial light phase modulator based on the principle of a diffractive optical element, one capable of two-dimensionally controlling the light emission direction has also been realized. For example, PLV (Planar Light Valve; "PLV" is a registered trademark of Silicon Light Machines Corporation) enables two-dimensional light modulation by individually controlling pixels arranged in a two-dimensional matrix in the same manner as the movable ribbon 42 of the diffractive optical element 40 described above.

[0065] As shown in the left figure of Fig. 7(b), when such a two-dimensional light modulator 67 is used on the light receiving side, by changing the diffraction angles in the vertical and horizontal directions while synchronizing them with each other as shown in the right figure, it becomes possible to sequentially make the light from each direction within the scanning target region Rs incident on the optical fiber 63 in a time-division manner. In this case, the light receiving side alone has a two-dimensional position resolution. Therefore, regarding the scanning light beam, it may be scanning with a line beam as in Fig. 7(a), or it may be a mode of irradiating the entire scanning target region Rs with light all at once (so-called flash illumination).

[0066] Here, for the purpose of principle explanation, the cylindrical lens 24 provided on the transmission side and the condenser lens 66 provided on the reception side are exemplified, but various optical elements such as lenses and mirrors may be provided on the optical path in addition. Due to aberrations and the like of these optical elements, there may be a case where light cannot be appropriately converged onto the optical fiber 63. As a result, the light transmission efficiency to the photodetector 62 may decrease. In this embodiment, by correcting the blazed pattern realized by the light modulator 61, it is possible to correct the influence of such aberrations and surely converge the light onto the end of the optical fiber 63.

[0067] FIG. 8 is a diagram for explaining beam correction by an optical modulator. As shown in FIG. 8, the optical modulator 61 can be schematically represented as an assembly of minute reflection mirrors 61a. In the operation according to the above-described principle, as shown by the solid line in FIG. 8, a blazed pattern is configured such that light (broken line) incident on the optical modulator 61 as parallel light is emitted as parallel light in another direction. The light emitted as parallel light from the optical modulator 61 is condensed by a condenser lens 66 and directed toward an end portion 631 of an optical fiber 63.

[0068] Even if the distance between the condenser lens 66 and the optical fiber 63 is arranged to be the focal length Df of the condenser lens 66, due to the influence of aberration and the like of the condenser lens 66 and other optical elements as described above, the light does not necessarily converge on the end portion 631 of the optical fiber 63.

[0069] Therefore, the blazed pattern realized by the optical modulator 61 is partially changed so that the emitted light becomes non-parallel light with respect to the incident parallel light, as shown by the dotted line in FIG. 8. Specifically, the inclination of each reflection mirror 61a is not made uniform, and the inclination is varied depending on the position. Thereby, the parallel light becomes non-parallel emitted light and travels toward the condenser lens 66.

[0070] By doing so, the light emitted from the condenser lens 66 can be converged on the end portion 631 of the optical fiber 63. In other words, in consideration of the influence of aberration of optical elements on the optical path such as the condenser lens 66, the control pattern of the optical modulator 61 is determined so that the light converges on the end portion 631 of the optical fiber 63. Since the influence of aberration of each optical element can be evaluated in advance, such an operation can be realized by controlling the optical modulator 61 in consideration of that information. Thereby, the light transmission efficiency to the photodetector 62 is further improved, and highly sensitive detection becomes possible.

[0071] As described above, in this embodiment, in the object detection device 1 using LiDAR technology, in order to efficiently make the light that can be incident from various directions enter the photodetector 62, the light modulator 61, which is a spatial light phase modulation element, makes the light incident from various directions enter the optical fiber 63 connected to the photodetector 62. Regardless of the incident direction to the light modulator 61, since light enters the optical fiber 63 only from substantially the same direction, the influence of reflection at the end face of the optical fiber 63 can be suppressed, and light can be efficiently transmitted to the photodetector 62.

[0072] A wavelength-sweeping light source is used as the light source on the transmission side, and the continuous laser light whose wavelength changes periodically is used as the scanning light beam Ls. On the receiving side, the received measurement light beam Lm and the reference light beam Lr generated from the light source are mixed by an optical fiber coupler, and the beat component thereof is detected. Thereby, object detection based on the detection principle of FMCW LiDAR is performed.

[0073] A balanced detector is used as the photodetector 62 for detecting the beat component. By using a balanced detector, the beat component between the measurement light beam Lm and the reference light beam Lr can be detected at high speed and with high sensitivity. In particular, if a balanced detector having an automatic balance function for automatically correcting the difference in light amount between the two light inputs is used, the beat component can be accurately detected even when there is a difference in light amount between the measurement light beam Lm and the reference light beam Lr.

[0074] The object detection device 1 of this embodiment having these configurations can detect an object in space at high speed and with high sensitivity. Further, by combining a linear scanning light beam and a one-dimensional light modulator, or by using a two-dimensional light modulator, the emission direction of the measurement light beam Lm incident from various directions can be narrowed down to one direction and made to enter a single optical fiber 63. This means that object detection of the entire space can be performed by a single photodetector 62.

[0075] In a fiber optic input type photodetector capable of high-speed and high-sensitivity light detection, those having one-dimensional or two-dimensional position resolution have not been put into practical use. For this reason, when attempting to realize a light reception method equivalent to the prior art using a one-dimensional sensor or a two-dimensional sensor with a fiber optic input type photodetector, it becomes necessary to arrange a large number of optical fibers and photodetectors. Then, the device scale becomes large and the cost becomes high. On the other hand, in this embodiment, since light from various directions can be guided to a single photodetector, a compact device configuration can be achieved and an increase in cost can be suppressed.

[0076] Also, by making the diffraction angle by the optical modulator different depending on the position, it is possible to correct the aberration of the optical element on the optical path. In the optical modulator, various patterns (for example, a pattern imitating a Fresnel lens) can be realized by a control signal, and by using this function for aberration correction, the cost can be significantly reduced compared to the case where a correction optical element is provided. In this case, a pattern for correcting the aberration is superimposed on the pattern for guiding the incident light to the optical fiber 63.

[0077] As described above, in the object detection device 1 of this embodiment, the transmission unit 20 functions as the "light scanning unit" of the present invention, while the reception unit 60 functions as the "light receiving unit". Also, the control unit 92 and the processing unit 93 realized in the control unit 90 correspond to the "control unit" and the "processing unit" of the present invention, respectively. Further, in the reception unit 60, the optical modulator 61, the photodetector 62, and the optical fiber 63 function as the "optical modulator", the "photodetector", and the "optical fiber" of the present invention, respectively. And the end portion 632 of the optical fiber 63 corresponds to the "one end" of the present invention, while the other end portion 631 corresponds to the "other end" of the present invention.

[0078] In the above-described embodiment, an optical coupler 600 composed of two optical fibers 63 and 64 functions as the "optical coupler" of the present invention. Also, the condenser lens 66 in the above-described embodiment corresponds to the "lens" of the present invention. Further, in the aspect shown in FIG. 7(b) among the above-described embodiments, one of the horizontal direction and the vertical direction corresponds to the "first direction" of the present invention, and the other corresponds to the "second direction".

[0079] Note that the present invention is not limited to the above-described embodiments, and various modifications can be made other than those described above without departing from the spirit thereof. For example, the light source in the above-described embodiment is a wavelength-swept continuous laser light source. However, the configuration of the receiving unit 60 in the present embodiment is valid regardless of the type of the light source.

[0080] Also, in the above-described embodiment, an optical coupler is used to detect the beat component between the measurement light beam Lm and the reference light Lr. However, the technical idea of the present invention can be applied not only to the case where an optical coupler is used in this way, but also to the case where the light input to the photodetector is generally by an optical fiber.

[0081] As described above by exemplifying specific embodiments, in the object detection device according to the present invention, for example, a balanced detector can be applied as the photodetector. In this case, an optical fiber for guiding the light incident from the optical modulator and an optical fiber for guiding the reference light branched from the emitted light of the optical scanning unit can be connected to the two inputs of the balanced detector. According to such a configuration, it is possible to detect the difference between the light acquired from the space and the reference light with high sensitivity while removing the common mode component by the balanced detector, and to improve the S / N ratio of the signal.

[0082] In this case, two optical fibers may form an optical coupler. According to such a configuration, the light acquired from the space can be interfered with the reference light. In this case, the presence or absence of an object in the space can be determined by the presence or absence of the beat component, and by extracting the beat component, the distance to the object that reflects light in the space can be obtained.

[0083] Also, for example, the light scanning unit may be configured to perform light scanning by emitting continuous laser light whose output wavelength changes periodically. According to such a configuration, it is possible to perform object detection using the principle of so-called FMCW LiDAR. In that case, since light can be efficiently transmitted to a photodetector that takes an optical fiber as an input, high-speed and high-sensitivity object detection becomes possible.

[0084] In this case, for example, the control unit may be configured to change a specific incident direction at the same time interval as the change period of the output wavelength. According to such a configuration, since the incident direction of the received light can be fixed for one period of the wavelength change of the scanning light, the light from that direction can be received for each wavelength component. In FMCW LiDAR, information regarding the distance to the object is reflected in each wavelength component of the light reflected from the object. By receiving the light of various wavelength components without omission, it becomes possible to accurately detect the distance to the object.

[0085] Also, for example, the light scanning unit may be configured to perform light scanning by changing the emission direction of light over time, and the control unit may be configured to change a specific incident direction in synchronization with the change in the emission direction of light in the light scanning. According to such a configuration, it is possible to specify from which direction the reflected light received by the photodetector is incident based on the emission direction of light in the light scanning. Therefore, for example, as the optical modulator, it is possible to use one having a one-dimensional spatial light phase modulation element having a position resolution in one direction.

[0086] For example, the optical modulator may have a two-dimensional spatial light phase modulation element having a position resolution in each of a first direction and a second direction intersecting each other. According to such a configuration, light incident from various directions can be decomposed for each incident direction and made to enter the photodetector. Thereby, it becomes possible to individually detect the amount of received light from each direction, and from the detection results, it is possible to calculate the presence or absence, distance, etc. of an object in those directions.

[0087] For another example, when the light receiving unit has a lens that converges the light emitted from the optical modulator to the other end of the optical fiber in the optical path between the optical modulator and the other end of the optical fiber, the control unit may be configured to correct the aberration of the lens by adjusting the emission pattern from the optical modulator according to the characteristics of the lens. In an optical modulator using a spatial light phase modulation element, it is also possible to realize various light emission patterns, for example, an emission pattern imitating a Fresnel lens, by electrical control. Therefore, not only a blazed pattern that simply diffracts light in a certain direction, but also by partially correcting this according to the characteristics of the optical element on the optical path, it is possible to correct the aberration of the optical element, etc.

Industrial Applicability

[0088] This invention is suitable for various sensing technology fields, such as the detection of obstacles in the control of robots and vehicles.

Explanation of Signs

[0089] 1 Object detection device 20 Transmission unit (optical scanning unit) 60 Reception unit (light receiving unit) 66 Condensing lens (lens) 61 Optical modulator 61 62 Photodetector 63 Optical fiber 90 Control unit 92 Control section 93 Processing section 600 Optical coupler 631 (The other end of optical fiber 63) One end (of the optical fiber 63)

Claims

1. An optical scanning unit that emits light and optically scans a space with the light; A light receiving unit that receives reflected light from an object in the space and outputs a signal according to the light receiving result; A processing unit that executes signal processing based on the signal to detect the object; A control unit that controls the light receiving unit and includes: The light receiving unit includes an optical modulator including a spatial light phase modulation element whose relationship between the incident direction and the emission direction of light can be changed by electrical control, a photodetector that outputs the signal according to the received light, and an optical fiber having one end connected to the photodetector and guiding the light emitted from the optical modulator to the photodetector and has: The control unit selectively makes the light incident from a specific incident direction on the optical modulator incident on the other end of the optical fiber opposite to the photodetector by changing the relationship between the incident direction and the emission direction over time, and changes the specific incident direction over time, an object detection device.

2. The photodetector is a balanced detector, and the two inputs of the balanced detector are connected to the optical fiber that guides the light incident from the optical modulator and the optical fiber that guides the reference light branched from the emitted light of the optical scanning unit, the object detection device according to claim 1.

3. The object detection device according to claim 2, wherein the two optical fibers constitute an optical coupler.

4. The optical scanning unit emits continuous laser light whose output wavelength changes periodically to perform the optical scanning, the object detection device according to any one of claims 1 to 3.

5. The control unit changes the specific incident direction at the same time interval as the change period of the output wavelength, the object detection device according to claim 4.

6. The optical scanning unit performs the optical scanning by changing the emission direction of light over time, The control unit changes the specific incident direction in synchronization with the change in the emission direction of light in the optical scanning, the object detection device according to any one of claims 1 to 3.

7. The optical modulator has a one-dimensional spatial light phase modulation element having positional resolution in one direction, the object detection device according to claim 6.

8. The optical modulator has a two-dimensional spatial light phase modulation element having positional resolution in a first direction and a second direction that intersect each other, the object detection device according to any one of claims 1 to 3.

9. The light receiving unit has a lens that converges the light emitted from the optical modulator to the other end in the optical path between the optical modulator and the other end of the optical fiber. The object detection device according to any one of claims 1 to 4, wherein the control unit corrects the aberration of the lens by adjusting an emission pattern from the optical modulator according to characteristics of the lens.

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