Light beam deflecting device and light projecting and receiving device

Abstract

This light beam deflecting device comprises: a planar optical waveguide circuit (3) that branches light from a wavelength variable semiconductor laser (1) into a first number of light beams that is the same as the number of divided areas in a first direction, selects an emission position in the first direction of the branched light and emits the branched light such that the light beams are simultaneously emitted to the position of one pixel in the corresponding areas; a dispersion element (5) for deflecting the first number of light beams from the circuit (3) at an angle corresponding to the wavelength of the light in a plane parallel to a second direction orthogonal to the first direction; an optical system (6) for converting the first number of light beams from the element (5) so as to be parallel to the axis of the optical system; and an optical system (7) for deflecting the first number of light beams from the optical system (6) to irradiate a target space.

Description

Light beam deflection device and light projecting / receiving device

[0001] The present invention relates to a light beam deflector that irradiates a target space with light and performs beam scanning in horizontal and vertical directions, and to a light projecting and receiving device that integrates a light beam deflector and a light receiving device.

[0002] Light detection and ranging (LiDAR) is a well-known technology that uses laser light to measure the distance to an object and its shape based on information from the reflected light. LiDAR methods include the direct time of flight (dTOF) method, which measures the round-trip time of a light pulse, and the frequency modulated continuous wave (FMCW) method, which continuously emits laser light while changing its frequency and measures the frequency shift of the light returned from the object.

[0003] Because dTOF has a relatively simple configuration, it has been integrated into a single chip and modularized, and is widely used in automobiles, platform gates, industrial robots, etc. However, dTOF requires a filter to remove the effects of sunlight, etc., and cannot distinguish whether the received pulse is its own or that of another source, which poses the problem of interference with other LiDARs.

[0004] On the other hand, FMCW has limited practical application due to its complex configuration, but it is attracting attention as a high-precision LiDAR for applications such as autonomous driving, because it is not affected by sunlight or other LiDARs and does not require filters.

[0005] In LiDAR, deflection of a light beam irradiated onto an object is required to obtain a 3D image of the object (see Patent Document 1, Patent Document 2, and Non-Patent Document 1). FIG. 8 is a diagram showing the configuration of the light beam deflection device disclosed in Patent Document 1. This light beam deflection device includes a dispersive element 1000 arranged to direct light from a wavelength-tunable laser (not shown) in one of first directions (e.g., along the x-axis in FIG. 8), and dispersive elements 1001-1, 1001-2, ..., 1001-M arranged to direct the light received from the dispersive element 1000 in one of second directions depending on the position at which the light is incident. 1002 in FIG. 8 denotes a screen onto which light from dispersive elements 1001-1 to 1001-M is irradiated.

[0006] Each of the first directions corresponds to a possible optical path, and in turn a wavelength channel, of the light 1003 exiting the dispersive element 1000. For example, as shown in FIG. 8, optical path 1003a corresponds to wavelength channel λ １ and the optical path 1003b corresponds to the wavelength channel λ Ｎ The dispersive element 1000 may comprise, for example, one or more diffraction gratings. The angular spread of the light 1003 depends on the range of wavelength channels and the dispersive properties of the dispersive element 1000. In one example, the dispersive element 1000 has a grating period of 1000-1100 lines / mm, achieving a deviation of 5-10 degrees.

[0007] Each of the M dispersion elements 1001-1, 1001-2, ..., 1001-M corresponding to the M wavelength bands is made of a variable line spacing diffraction grating whose grating period changes continuously from the first end to the second end. As shown in Figure 8, the second direction is aligned along a plane based on each wavelength band. For example, the wavelength channel {λ １ , λ ２ , ..., λ ｋ} is deflected by dispersive element 1001-1 in a direction aligned along the leftmost plane 1004-1 corresponding to the first of M wavelength bands. Similarly, although not shown, light in wavelength channel {λ ｋ＋１ , λ ｋ＋２, ..., λ ２ｋ} is deflected by dispersive element 1001-2 toward a direction aligned along a plane corresponding to the second of the M wavelength bands. Ｎ－ｋ＋１ , λ Ｎ－ｋ＋２ , ..., λ Ｎ} is deflected by dispersive element 1001-M towards a direction aligned along rightmost plane 1004-M corresponding to the Mth of the M wavelength bands.

[0008] 9 is a diagram showing the configuration of an optical beam deflector disclosed in Patent Document 2. This optical beam deflector includes a wavelength tunable laser 2000 that outputs light selected from N wavelength channels grouped into M non-adjacent wavelength channel groups, an optical interleaver 2001 that routes the light from the wavelength tunable laser 2000 from a first port 2002 to one of second ports 2003-1, 2003-2, ..., 2003-M, and dispersive element arrays 2004-1, 2004-2, ..., 2004-M that are arranged to receive the routed light from one of the second ports 2003-1, 2003-2, ..., 2003-M, respectively. Reference numeral 2005 in FIG. 9 denotes a screen onto which light from the dispersive element arrays 2004-1, 2004-2, ..., 2004-M is irradiated.

[0009] The N wavelength channels each have a center wavelength λ １ , λ ２ , ..., λ Ν and the M groups of interleaved wavelength channels are denoted by {λ １ , λ Μ＋１ , ..., λ Ν－Μ＋１}, {λ ２ , λ Μ＋２ , ..., λ Ν－Μ＋２}, ..., {λ Μ , λ ２Μ , ..., λ Ν}. The tunable laser 2000 may have a 100 nm wavelength tunable range, such as from about 1527 nm to about 1567 nm (or about 5000 GHz at 1550 nm), tunable from 0.0004 nm to 0.008 nm in steps (or from about 50 MHz to 1 GHz at 1550 nm in steps). For example, if the tunable laser 2000 is wavelength tunable over 40 nm, there are a total of about 5000 steps (i.e., N=5000).

[0010] The optical interleaver 2001 is composed of one or more Mach-Zehnder interferometers (MZIs) or one or more arrayed waveguide gratings (AWGs). In one use case, the free spectral range (FSR) of the optical interleaver 2001 is designed to be 10 GHz or less. In another use case, the FSR is designed to be 5 GHz or less. In yet another use case, the FSR is designed to be 1 GHz or less.

[0011] All of the above light beam deflection devices relate to two-dimensional light beam deflection technology for LiDAR using a wavelength-tunable laser. Each light beam deflection device provides two-dimensional light beam deflection technology in the horizontal and vertical directions using a wavelength-tunable laser of approximately 30 to 40 nm, which was developed for optical communications. Table 1 shows an example of target specifications for automotive LiDAR.

[0012]

[0013] The specifications for automotive LiDAR require a horizontal resolution of 512 pixels, a vertical resolution of 128 pixels, and a frame rate of approximately 10 to 20 Hz. The time required to allocate to one pixel (the time required to process each pixel sequentially) is determined by the frame rate and spatial resolution. When measuring a total of 65,536 pixels (512 horizontal pixels and 128 vertical pixels) at a frame rate of 20 Hz (50 ms period), the time allocated to one pixel is 0.76 μs, as shown in Table 1.

[0014] However, as shown in Table 1, if the maximum distance measurement is 300 m, the round-trip time of light returning from 300 m away is 2 μs, which is longer than the 0.76 μs assigned to one pixel. Therefore, to achieve a frame rate of 20 Hz, it is necessary to divide the target space into areas and process each area simultaneously. In reality, the time required is the sum of the time to send and receive the optical signal for measurement in addition to the round-trip propagation delay time of light.

[0015] For example, Figure 10 shows a case where 5 μs is required for both transmitting and receiving an optical signal when using FMCW as the LiDAR method. In Figure 10, 800 is the transmitted signal, 801 is the received signal, 802 is the up-chirp period during which the optical frequency of the transmitted signal increases, 803 is the down-chirp period during which the optical frequency of the transmitted signal decreases, and 804 is the optical frequency chirp width. Comparing the sum of the FMCW sweep time and the optical round-trip propagation delay time (5 μs × 2 + 2 μs = 12 μs) with the 0.76 μs allocated to one pixel (12 / 0.76 ≒ 15.8), this setting requires simultaneous measurement of at least 16 areas.

[0016] In other words, the wavelength tuning range of approximately 30 to 40 nm shown in the prior art cannot achieve the above-mentioned resolution point and frame rate, and an extremely wide wavelength tuning range is required to achieve this. However, a wavelength tunable semiconductor laser with such a wide wavelength tuning range cannot be realized with a single semiconductor laser chip that is small and low-cost and suitable for in-vehicle installation. Non-Patent Document 1 experimentally demonstrates one form of two-dimensional beam steering using the wavelength tuning means disclosed in Patent Document 2, but the resolution point is limited to 69 pixels horizontally and 47 pixels vertically with a wavelength tuning range of 100 nm using a measuring instrument.

[0017] Patent No. 7125582 Publication Special Publication No. 2020-532714

[0018] ZHI LI, et al., “Solid-state FMCW LiDAR with two-dimensional spectral scanning using a virtually imaged phased array”, Optics Express, Vol. 29, No. 11, pp. 16547-16562, 2021

[0019] The present invention has been made to solve the above-mentioned problems, and aims to provide a light beam deflection device and a light projector / receiver that can achieve a larger number of horizontal and vertical resolution points and a higher frame rate than conventional devices.

[0020] The optical beam deflection device of the present invention is characterized by comprising: a wavelength-tunable light source; a planar optical waveguide circuit that branches light emitted from the wavelength-tunable light source into a first number of light beams equal to the number of areas divided in a first direction of a target space, and selects and emits the branched light beams from emission positions in the first direction so that each of the light beams is simultaneously irradiated onto a pixel position in a corresponding area; a dispersive element that deflects each of the first number of light beams emitted from the planar optical waveguide circuit at an angle corresponding to the wavelength of the light in a plane parallel to a second direction orthogonal to the first direction; a first optical system that converts the first number of light beams emitted from the dispersive element so that the light beams are parallel to an axis of the optical system and emits the first number of light beams; and a second optical system that deflects each of the first number of light beams emitted from the first optical system and irradiates the target space.

[0021] According to the present invention, by providing a wavelength-tunable light source, a planar optical waveguide circuit, a dispersive element, and first and second optical systems, it is possible to simultaneously scan each area divided in a first direction of a target space in a second direction. As a result, the present invention can achieve a larger number of horizontal and vertical resolution points and a higher frame rate than conventional methods, and can satisfy the horizontal and vertical resolution points and frame rate specifications required for, for example, automotive LiDAR.

[0022] FIG. 1 is a diagram showing the configuration of an optical beam deflector according to a first embodiment of the present invention. FIG. 2 is a diagram showing the detailed configuration of the optical beam deflector according to the first embodiment of the present invention. FIG. 3 is a cross-sectional view of the optical beam deflector according to the first embodiment of the present invention, taken along horizontal and vertical planes. FIG. 4 is a flowchart explaining the operation of the optical beam deflector according to the first embodiment of the present invention. FIG. 5 is a diagram showing a virtual screen for showing the spatial distribution of a beam irradiated into a target space. FIG. 6 is a diagram showing the configuration of a light projecting and receiving device according to a second embodiment of the present invention. FIG. 7 is a block diagram showing an example configuration of a computer that realizes the optical beam deflectors according to the first and second embodiments of the present invention. FIG. 8 is a diagram showing the configuration of a conventional optical beam deflector. FIG. 9 is a diagram showing another configuration of a conventional optical beam deflector. FIG. 10 is a diagram showing frequency changes of a transmission signal and a reception signal in an FMCW system.

[0023] [First embodiment] An embodiment of the present invention will now be described with reference to the drawings. Fig. 1 is a diagram showing the configuration of a light beam deflector according to a first embodiment of the present invention. the optical beam deflection device includes a wavelength-tunable semiconductor laser 1 (wavelength-tunable light source); an optical amplifier 2 that amplifies the light emitted from the wavelength-tunable semiconductor laser 1; a planar optical waveguide circuit 3 that branches the light amplified by the optical amplifier 2 into a first number of light beams equal to the number of areas divided in the vertical direction (Y direction in FIG. 1) of a target space and selects and emits the branched light beams from vertical emission positions such that each of the branched light beams is simultaneously irradiated onto the position of one pixel in a corresponding area; a focal plane lens 4 that converts each of the first number of light beams emitted from the planar optical waveguide circuit 3 into parallel light and deflects it at the same time; a dispersive element 5 that deflects each of the first number of light beams emitted from the focal plane lens 4 at an angle in a horizontal plane according to the wavelength of the light; an optical system 6 that converts the first number of light beams emitted from the dispersive element 5 so that they are parallel to the axis of the optical system and emits them; an optical system 7 that deflects each of the first number of light beams emitted from the optical system 6 and irradiates the target space; and a control unit 8 that controls the wavelength tuning by the wavelength-tunable semiconductor laser 1 and the selection of the emission position by the planar optical waveguide circuit 3. Reference numeral 12 in FIG. 1 denotes a screen onto which light from the light beam deflector is irradiated.

[0024] Figure 2 is a diagram showing the detailed configuration of the light beam deflector shown in Figure 1. The wavelength-tunable semiconductor laser 1 has a wavelength tunable range of 30 to 40 nm. An example of the wavelength-tunable semiconductor laser 1 is an RTF (Reflection-type Transversal Filter)-LD (Laser Diode). The RTF-LD allows wavelength control using voltage, so it can switch wavelengths faster than other wavelength-tunable lasers.

[0025] The optical amplifier 2 amplifies the laser light emitted from the wavelength tunable semiconductor laser 1. An example of the optical amplifier 2 is a polarization-maintaining EDFA (Erbium-Doped Fiber Amplifier).

[0026] As shown in FIG. 2 , the planar lightwave circuit 3 includes an optical waveguide 30 that guides the light amplified by the optical amplifier 2, a 1×16 optical splitter 31 that splits the light from the optical waveguide 30 into 16 (first number) light beams, 16 optical waveguides 32-1 to 32-16 that respectively guide the light beams split by the optical splitter 31, 16 1×8 optical switches 33-1 to 33-16 that have a second number (eight in this embodiment) of output ports equal to the number of pixels in the vertical direction in each divided area of ​​the target space and that selectively output the light beam split by the 1×16 optical splitter 31 to any one of the eight output ports, and 128 optical waveguides 34-1 to 34-128 that respectively guide the light beams output from the output ports of the 1×8 optical switches 33-1 to 33-16.

[0027] The optical waveguides 34-1 to 34-128 are arranged in the vertical direction, the number of which is equal to the first number (16 in this embodiment) multiplied by the second number (8 in this embodiment), so as to guide the light output from the output ports of the 1×8 optical switches 33-1 to 33-16 and emit it from the end face of the planar optical waveguide circuit 3. The spacing between the optical waveguides 34-1 to 34-128 at the end face of the planar optical waveguide circuit 3 is, for example, 10 to 20 μm.

[0028] With the above configuration, the planar optical waveguide circuit 3 splits the light amplified by the optical amplifier 2 into a first number of beams and selects vertical output positions of the split beams so that each beam is simultaneously irradiated onto a pixel in a corresponding area. In this embodiment, the vertical resolution point of 128 pixels is assumed to be divided into 16 areas, so the first number is 16, and the number of branches of the 1×16 optical splitter 31, the number of optical waveguides 32-1 to 32-16, and the number of 1×8 optical switches 33-1 to 33-16 are all 16. Furthermore, since the number of vertical pixels in each divided area of ​​the target space is 8, the second number is 8, and the number of output ports of the 1×8 optical switches 33-1 to 33-16 is 8. An example of the 1×8 optical switches 33-1 to 33-16 is a Mach-Zehnder interferometer optical switch.

[0029] The focal plane lens (focal plane collimating lens) 4 converts each of the first number of light beams emitted from the planar optical waveguide circuit 3 into parallel light beams, and at the same time, deflects these parallel light beams so that they pass through the focal point of the focal plane lens 4 on the target space side.

[0030] The dispersive element 5 deflects each of the first number of light beams emitted from the focal plane lens 4 in the horizontal plane at an angle corresponding to the wavelength of the light. An example of the dispersive element 5 is a diffraction grating. Furthermore, in this embodiment, a plurality of transmissive diffraction gratings are arranged along the traveling direction of the light.

[0031] The optical system 6 converts the first number of light beams output from the dispersive element 5 so that they are parallel to the axis of the optical system 6 and outputs them. The angle of the light incident on the optical system 6 changes due to wavelength tuning by the tunable semiconductor laser 1, switching of the output position by the planar optical waveguide circuit 3, deflection by the focal plane lens 4, and deflection by the dispersive element 5, but the light incident on the optical system 6 is output in a direction parallel to the axis of the optical system 6. An example of the optical system 6 is a telecentric fθ lens. A telecentric fθ lens is made by precisely processing and combining multiple lenses.

[0032] The optical system 7 deflects the first number of light beams incident parallel to the axes of the optical systems 6 and 7 so that they pass through the focal point on the target space side of the optical system 7, and irradiates the target space with the deflected light. The deflection angle of the light can be increased by using the optical system 7. An example of the optical system 7 is a convex lens formed by precisely processing and combining multiple lenses.

[0033] The main design parameters of the optical beam deflector will be explained. Fig. 3(A) is a cross-sectional view of the optical beam deflector taken along a horizontal plane, and Fig. 3(B) is a cross-sectional view of the optical beam deflector taken along a vertical plane. In Fig. 3(A), θ １ is the angle at which the emitted light from the dispersion element 5 spreads in the horizontal plane, and θ ２ is the angle at which the emitted light from the optical system 7 spreads in the horizontal plane, and f ０ is the focal length of the focal plane lens 4, f １ is the focal length of the optical system 6, f ２ is the focal length of the optical system 7, h １ is the maximum image height in the horizontal direction (X direction in FIG. 1) of the light emitted from the optical system 6 (the distance from the position of the light beam at the edge of the light emitted from the optical system 6 to the optical axis of the optical system 6), and h ２ is the maximum image height in the vertical direction of the light emitted from the optical system 6.

[0034] In Figures 3(A) and 3(B), 60 indicates the rightmost light in the horizontal direction (e.g., light with the shortest wavelength) among the light emitted from optical system 6, 61 indicates the leftmost light in the horizontal direction (e.g., light with the longest wavelength) among the light emitted from optical system 6, 62 indicates the uppermost light in the vertical direction among the light emitted from optical system 6 (e.g., light emitted from optical waveguide 34-128), and 63 indicates the lowermost light in the vertical direction among the light emitted from optical system 6 (e.g., light emitted from optical waveguide 34-1).

[0035] The horizontal positions of the exit ends of the optical waveguides 34-1 to 34-128 of the planar optical waveguide circuit 3 coincide with the horizontal position of the axis (L in FIGS. 3A and 3B) of the lens system (the focal plane lens 4, the dispersion element 5, and the optical systems 6 and 7). The vertical spacing between the exit ends of the optical waveguides 34-1 to 34-128 is set equal to the maximum horizontal image height h of the light emitted from the optical system 6. １ and the maximum image height h in the vertical direction ２ The ratio of１ :h ２ = 512:128).

[0036] As described above, the dispersive element 5 is composed of multiple transmission diffraction gratings arranged along the light propagation direction. The grooves of each diffraction grating are formed in the vertical direction. This allows the dispersive element 5 to deflect incident light in a horizontal plane at an angle corresponding to its wavelength. The dispersive element 5 is arranged so that the position on the axis L of the exit surface of the final diffraction grating coincides with the position on the axis L of the focal point of the lens 4 on the target space side. Note that when multiple diffraction gratings are used, the exit position of the light shifts for each wavelength of light, along with the angle of the light, so an optical design that takes this position shift into account is required.

[0037] The maximum image height h in the horizontal direction of the light emitted from the optical system 6 １ and the focal length f of the optical system 6 １ and the angle θ at which the emitted light from the dispersion element 5 spreads in the horizontal plane. １ The relationship is expressed as in equation (1).

[0038]

[0039] Maximum image height h １ and the focal length f of the optical system 7 ２ and the angle θ at which the emitted light from the optical system 7 spreads in the horizontal plane. ２ The relationship between these is expressed as equation (2).

[0040]

[0041] Equation (3) is obtained from equations (1) and (2).

[0042]

[0043] FIG. 4 is a flowchart illustrating the operation of the optical beam deflector. The control unit 8 outputs control signals to the 1×8 optical switches 33-1 to 33-16, respectively, to set the 1×8 optical switches 33-1 to 33-16 (step S100 in FIG. 4). In the beam scanning of the first line, the 1×8 optical switches 33-1 to 33-16 are set so that the optical beam is directed to the uppermost pixel position in each of the 16 vertically divided areas. In the example of FIGS. 2 and 3B, the 1×8 optical switches 33-1 to 33-16 are set so that light is emitted from the optical waveguides 34-1, 34-9, 34-17, ..., 34-121.

[0044] Next, the control unit 8 changes the wavelength of the laser light emitted from the wavelength-tunable semiconductor laser 1 by changing the voltage supplied to the wavelength-tunable semiconductor laser 1 (step S101 in FIG. 4). FIG. 5 shows a virtual screen 12 for showing the spatial distribution of the beam irradiated in the target space. As described above, in this embodiment, the 128 vertical resolution pixels in the target space are divided into 16 areas A1 to A16. The number of vertical pixels in each of the areas A1 to A16 is 8. In FIG. 5, a pixel with horizontal number x (x is 1 to 512), vertical number y (y is 1 to 8) in each of the areas A1 to A16, and area number n (n is 1 to 16) is represented by P(x, y, n).

[0045] The 16 light beams emitted from the optical waveguides 34-1, 34-9, 34-17, ..., 34-121 pass through the focal plane lens 4, the dispersive element 5, and the optical systems 6 and 7, and are irradiated onto the uppermost pixel (pixel with y number equal to 1) in each of the areas A1 to A16 in the target space. Furthermore, the controller 8 continuously changes the wavelength of the laser light from the shortest wavelength to the longest wavelength, and the dispersive element 5 changes the deflection angle of the light in the horizontal plane. As a result, the irradiation position of the light beam moves from the rightmost pixel (pixel with x number equal to 1) to the leftmost pixel (pixel with x number equal to 512) in the horizontal direction, thereby performing one-line beam scanning.

[0046] After beam scanning of the first line is completed, the control unit 8 switches the output ports selected by the 1×8 optical switches 33-1 to 33-16, thereby switching the optical waveguides 34 (34-1 to 34-128) from which light of the planar optical waveguide circuit 3 is emitted (step S102 in FIG. 4). For beam scanning of the second line, the 1×8 optical switches 33-1 to 33-16 are set so that the light beam is irradiated onto the second pixel from the top (pixel with y number 2) in each of the areas A1 to A16 in the target space. Although not shown in FIG. 2, the 1×8 optical switches 33-1 to 33-16 are set so that light is emitted from the optical waveguides 34-2, 34-10, 34-18, ..., 34-122. The control unit 8 performs beam scanning of the second line by processing in step S101.

[0047] After beam scanning of the second line is completed, the control unit 8 switches the output ports selected by the 1×8 optical switches 33-1 to 33-16 (step S102). For beam scanning of the third line, the 1×8 optical switches 33-1 to 33-16 are set so that the light beam is irradiated onto the third pixel from the top (the pixel with y number 3) in each of the areas A1 to A16 in the target space. Although not shown in FIG. 2, the 1×8 optical switches 33-1 to 33-16 are set so that light is emitted from the optical waveguides 34-3, 34-11, 34-19, ..., 34-123. The control unit 8 performs beam scanning of the third line by the processing of step S101.

[0048] Similarly, beam scanning of the fourth to seventh lines is sequentially performed. After beam scanning of the seventh line is completed, the control unit 8 switches the output ports selected by the 1×8 optical switches 33-1 to 33-16 (step S102). For beam scanning of the eighth line, the 1×8 optical switches 33-1 to 33-16 are set so that the light beam is irradiated onto the position of the lowest pixel (pixel with y number 8) in each of the areas A1 to A16 in the target space. In the example of FIGS. 2 and 3B, the 1×8 optical switches 33-1 to 33-16 are set so that light is emitted from the optical waveguides 34-8, 34-16, 34-24, ..., 34-128. The control unit 8 performs beam scanning of the eighth line by processing in step S101.

[0049] When the beam scanning of the eighth line is completed, scanning of all areas is completed (YES in step S103 in FIG. 4). As described above, in this embodiment, by simultaneously performing horizontal beam scanning of each area divided vertically, simultaneous measurement of 16 areas is possible, and the horizontal and vertical resolution points and frame rate required for automotive LiDAR can be achieved. When this embodiment is applied to automotive LiDAR, continuous measurement is required, so the process of FIG. 4 can be performed repeatedly. Furthermore, in this embodiment, while using different deflection means for horizontal beam deflection and vertical beam deflection, the horizontal and vertical deflection optical systems can be integrated into one.

[0050] Table 2 shows specific numerical examples when the FMCW method is used as the LiDAR method.

[0051]

[0052] Here, the wavelength switching time of the tunable semiconductor laser 1 is 1 μs, and the switching time of the 1×8 optical switches 33-1 to 33-16 is 100 μs. As explained above, horizontal beam deflection, which requires high-speed sweeping, is performed by wavelength tuning, and vertical beam deflection is performed by switching the 1×8 optical switches 33-1 to 33-16. In the vertical direction, the space onto which the light beam is irradiated is divided into 16 areas, and horizontal beam scanning is performed simultaneously on each of the 16 divided areas. Each area has eight lines.

[0053] The FMCW up-chirp period and down-chirp period are each 5 μs. If the maximum ranging distance is 300 m, the round-trip propagation time (round-trip time) of light returning from 300 m away is 2 μs. Since a total of 13 μs is used per pixel, consisting of the FMCW sweep time (5 μs × 2), the round-trip time of 2 μs, and the wavelength switching time of 1 μs, the time required for beam scanning of one horizontal line of 512 pixels is 6656.7 μs. The time required for vertical beam scanning is 100 μs × 8 = 800 μs. Therefore, the total time required to measure the target space is 6656.7 × 8 + 800 = 54048 μs ≒ 54 ms, and the achievable frame rate is 18.5 Hz. From the above, it can be seen that the configuration of this embodiment can meet the automotive LiDAR specifications shown in Table 1.

[0054] In the first embodiment, a light beam deflector applied to, for example, LiDAR was described. However, in LiDAR, it is necessary to receive light returning from the target space. In this embodiment, the configuration of a light projecting and receiving device in which a light beam deflector and a light receiving device are integrated is shown in FIG.

[0055] The light projecting and receiving device uses a planar optical waveguide circuit 3a instead of the planar optical waveguide circuit 3 of the first embodiment, and adds 16 photodetectors 9-1 to 9-16, 16 photodetectors 10-1 to 10-16, and 16 transimpedance amplifiers (TIAs) 11-1 to 11-16. The configuration after the focal plane lens 4 is the same as in the first embodiment, so it is not shown in Figure 6.

[0056] The planar lightwave circuit 3a includes an optical waveguide 30, a 1×16 optical splitter 31, optical waveguides 32-1 to 32-16, 1×8 optical switches 33-1 to 33-16, optical waveguides 34-1 to 34-128, sixteen 10:1 optical splitters 35-1 to 35-16 that split the light from the optical waveguides 32-1 to 32-16 into two lights at a splitting ratio of 10:1, and a second port that splits the light input from the 10:1 optical splitters 35-1 to 35-16 into two lights at a splitting ratio of 10:1. and outputs light input to the second port to a third port; sixteen 3 dB couplers 36-1 to 36-16, which combine the light output from the third ports of the 3 dB couplers 36-1 to 36-16 and the light output from the second output ports of the 10:1 optical splitters 35-1 to 35-16 at an equal ratio, split the light into two equal parts, and output the combined light; and sixteen 3 dB couplers 37-1 to 37-16, which combine the light output from the third ports of the 3 dB couplers 36-1 to 36-16 and the light output from the second output ports of the 10:1 optical splitters 35-1 to 35-16 at an equal ratio, split the light into two equal parts, and output the combined light; 16 optical waveguides 38-1 to 38-16 connecting the first output ports of the 10:1 optical splitters 35-1 to 35-16 and the first ports of the 3 dB couplers 36-1 to 36-16; 16 optical waveguides 39-1 to 39-16 connecting the second output ports of the 10:1 optical splitters 35-1 to 35-16 and the second ports of the 3 dB couplers 37-1 to 37-16; and 16 optical waveguides 40-1 to 40-4 connecting the second ports of the 3 dB couplers 36-1 to 36-16 and the input ports of the 1×8 optical switches 33-1 to 33-16. 0-16, sixteen optical waveguides 41-1 to 41-16 connecting the third ports of the 3 dB couplers 36-1 to 36-16 and the first ports of the 3 dB couplers 37-1 to 37-16, sixteen optical waveguides 42-1 to 42-16 for guiding the light output from the third ports of the 3 dB couplers 37-1 to 37-16, and sixteen optical waveguides 43-1 to 43-16 for guiding the light output from the fourth ports of the 3 dB couplers 37-1 to 37-16.

[0057] The light (probe light) split by 1x16 optical splitter 31 and guided by optical waveguides 32-1 to 32-16 is then split into two by 10:1 optical splitters 35-1 to 35-16 at a branching ratio of 10 for the output light intensity of the first port and 1 for the output light intensity of the second port. The probe light output from the first ports of 10:1 optical splitters 35-1 to 35-16 is guided by optical waveguides 38-1 to 38-16, input to first ports of 3 dB couplers 36-1 to 36-16, and output from second ports of 3 dB couplers 36-1 to 36-16. On the other hand, the light (reference light) output from the second ports of the 10:1 optical splitters 35-1 to 35-16 is guided by the optical waveguides 39-1 to 39-16 and input to the second ports of the 3 dB couplers 37-1 to 37-16.

[0058] The probe light output from the second port of the 3 dB couplers 36-1 to 36-16 is guided by the optical waveguides 40-1 to 40-16 and input to the 1 × 8 optical switches 33-1 to 33-16. Thereafter, the probe light is irradiated into the target space by the configuration after the focal plane lens 4 described in the first embodiment.

[0059] On the other hand, the return light reflected by an object present in the target space and returning from the target space travels the opposite path to the probe light, i.e., passes through the optical system 7, the optical system 6, the dispersive element 5, and the focal plane lens 4, and enters the exit end of the same optical waveguide as the source of the probe light, among the optical waveguides 34-1 to 34-128 of the planar optical waveguide circuit 3.

[0060] A prerequisite of this embodiment is that the 1×8 optical switches 33-1 to 33-16 are kept selected until the return light returns to the optical waveguide 34 (34-1 to 34-128) that emitted the probe light, but in the example values ​​shown in Table 2, the time required for one pixel is calculated taking into account the round-trip time of light of 2 μs. Therefore, even if the control unit 8 keeps the 1×8 optical switches 33-1 to 33-16 selected until the return light returns to the optical waveguide 34 (34-1 to 34-128) that emitted the probe light, the total time required to measure the target space is the same as in the first embodiment.

[0061] The return light is input from the optical waveguides 34-1 to 34-128 to the 1×8 optical switches 33-1 to 33-16 and output from the input ports of the 1×8 optical switches 33-1 to 33-16. The return light is then guided by the optical waveguides 40-1 to 40-16, input to the second ports of the 3 dB couplers 36-1 to 36-16, and output from the third ports of the 3 dB couplers 36-1 to 36-16.

[0062] The 3 dB couplers 37-1 to 37-16 combine the return light guided by the optical waveguides 41-1 to 41-16 and input to the first port with the reference light guided by the optical waveguides 39-1 to 39-16 and input to the second port in equal proportions, divide the combined light into two equal parts, and output the resulting light to the third and fourth ports. The light output from the third ports of the 3 dB couplers 37-1 to 37-16 is guided by the optical waveguides 42-1 to 42-16, and the light output from the fourth ports of the 3 dB couplers 37-1 to 37-16 is guided by the optical waveguides 43-1 to 43-16.

[0063] The photodetectors 9-1 to 9-16 convert the light emitted from the optical waveguides 42-1 to 42-16 into an electrical signal. The photodetectors 10-1 to 10-16 convert the light emitted from the optical waveguides 43-1 to 43-16 into an electrical signal. The TIAs 11-1 to 11-16 amplify the differences in the output signals from the photodetectors 9-1 to 9-16 and 10-1 to 10-16 that receive the light emitted from the optical waveguides 42-1 to 42-16 and 43-1 to 43-16 connected to the same 3 dB couplers 37-1 to 37-16. In this way, the received signal can be obtained.

[0064] In the first embodiment, it is assumed that the light beam deflector and the light receiving device are provided separately. On the other hand, in this embodiment, the light beam deflector and the light receiving device are integrated, but the total time required to measure the target space is the same as in the first embodiment, and this embodiment also satisfies the specifications of the automotive LiDAR shown in Table 1.

[0065] Note that the configuration after the TIAs 11-1 to 11-16 is not an essential component of the present invention, and is therefore omitted from Fig. 6. An example of the use of the received signals obtained by the TIAs 11-1 to 11-16 is LiDAR, but the application of the present invention is not limited to LiDAR.

[0066] In the first and second embodiments, the vertical direction is the first direction and the horizontal direction perpendicular to the vertical direction is the second direction, but the vertical and horizontal directions may be interchanged. That is, vertical beam deflection may be performed by wavelength tuning, and horizontal beam deflection may be performed by switching the 1×8 optical switches 33-1 to 33-16.

[0067] The control unit 8 described in the first and second embodiments can be realized by a computer equipped with a CPU (Central Processing Unit), a storage device, and an interface, and a program that controls these hardware resources. An example of the configuration of this computer is shown in FIG.

[0068] The computer includes a CPU 200, a storage device 201, and an interface device (I / F) 202. The I / F 202 is connected to a circuit that supplies voltage to the wavelength tunable semiconductor laser 1, a circuit that supplies control signals to the 1×8 optical switches 33-1 to 33-16, and the like. In such a computer, a program for implementing the method of the present invention is stored in the storage device 201. The CPU 200 executes the processes described in the first and second embodiments in accordance with the program stored in the storage device 201.

[0069] Some or all of the above embodiments can be described as, but are not limited to, the following supplementary notes.

[0070] (Supplementary Note 1) An optical beam deflection device of the present invention includes a wavelength-tunable light source; a planar optical waveguide circuit that branches light emitted from the wavelength-tunable light source into a first number of light beams equal to the number of areas divided in a first direction of a target space, and selects and emits the branched light beams from emission positions in the first direction so that each of the light beams is simultaneously irradiated onto a pixel position in a corresponding area; a dispersive element that deflects each of the first number of light beams emitted from the planar optical waveguide circuit at an angle corresponding to the wavelength of the light in a plane parallel to a second direction orthogonal to the first direction; a first optical system that converts the first number of light beams emitted from the dispersive element so that the light beams are parallel to an axis of the optical system and emits the first number of light beams; and a second optical system that deflects each of the first number of light beams emitted from the first optical system and irradiates the target space.

[0071] (Supplementary Note 2) The light beam deflection device described in Supplementary Note 1 further includes a control unit that controls wavelength tuning by the tunable light source and selection of emission position by the planar optical waveguide circuit, and the control unit repeatedly performs scanning in the second direction to simultaneously move the first number of light beams irradiated from the second optical system to the target space in the second direction by changing the wavelength of the light emitted from the tunable light source to change the deflection angle of the light in a plane parallel to the second direction, and after completing scanning of a line in the second direction, repeatedly performs scanning in the first direction to simultaneously move the first number of light beams irradiated to the target space in the first direction by changing the emission position of the light emitted from the planar optical waveguide circuit to change the deflection angle of the light in a plane parallel to the first direction.

[0072] (Supplementary Note 3) In the optical beam deflector described in Supplementary Note 1, the planar optical waveguide circuit comprises: an optical splitter that splits the light emitted from the wavelength-tunable light source into the first number of light beams; the first number of optical switches that have a second number of output ports equal to the number of pixels in the first direction in each divided area of ​​the target space and selectively output the light split by the optical splitter to any one of the second number of output ports; and optical waveguides, the number of which is equal to the first number multiplied by the second number, that are arranged along the first direction so as to guide the light output from each output port of the first number of optical switches and output it from an end face of the planar optical waveguide circuit.

[0073] (Supplementary Note 4) The optical beam deflection device described in Supplementary Note 1 further includes a focal plane lens inserted between the planar optical waveguide circuit and the dispersive element, and the focal plane lens converts each of the first number of light beams emitted from the planar optical waveguide circuit into parallel light beams, and at the same time, deflects the parallel light beams so that they pass through a focus of the focal plane lens on the target space side.

[0074] (Supplementary Note 5) In the light beam deflector according to Supplementary Note 1, the dispersive element comprises a plurality of diffraction gratings arranged along the light traveling direction.

[0075] (Supplementary Note 6) In the light beam deflector according to Supplementary Note 1, the first optical system is composed of a telecentric fθ lens.

[0076] (Supplementary Note 7) In the light beam deflector according to Supplementary Note 1, the second optical system is made up of a convex lens.

[0077] (Supplementary Note 8) A light projecting and receiving device of the present invention includes the optical beam deflector according to Supplementary Note 1, the first number of first photodetectors that convert incident light into an electric signal, the first number of second photodetectors that convert incident light into an electric signal, and the first number of transimpedance amplifiers that calculate a difference between output signals of the first and second photodetectors, and the planar lightwave circuit includes a first optical splitter that splits light emitted from the wavelength-tunable light source into the first number of light beams, and the first number of second optical splitters that split each of the light beams split by the first optical splitter into two. the first number of first couplers that output one of the lights split by the second optical splitter from a first port to a second port and output the light input to the second port to a third port; the first number of optical switches that have a second number of output ports equal to the number of pixels in the first direction in each divided area of ​​the target space and that selectively output the light output from the second port of the first coupler to any one of the second number of output ports; and a planar optical waveguide circuit that guides the light output from each output port of the first number of optical switches. a first number of second couplers that combine the light output from the third port of the first coupler and the other light split by the second optical splitter, split the light into two equal parts, and output the combined light; a first number of second optical waveguides that guide the light output from one output port of the second coupler and output it from a second end face of a planar optical waveguide circuit; and a second number of second optical waveguides that guide the light output from the other output port of the second coupler and output it from a second end face of a planar optical waveguide circuit. the first number of return light beams returning from the target space pass through the second optical system, the first optical system, and the dispersive element and are incident on the exit ends of the first optical waveguides of the planar optical waveguide circuit; the first coupler is output from an input port of the optical switch and outputs the return light input to the second port to the third port; the first photodetector converts the light output from the second optical waveguides into an electrical signal; and the second photodetector converts the light output from the third optical waveguides into an electrical signal;The transimpedance amplifier determines the difference between output signals from the first and second photodetectors that receive light emitted from the second and third optical waveguides connected to the same second coupler.

[0078] The present invention can be applied to light deflection technology required for LiDAR and the like.

[0079] 1...Tunable wavelength semiconductor laser, 2...Optical amplifier, 3, 3a...Planar optical waveguide circuit, 4...Focal plane lens, 5...Dispersion element, 6, 7...Optical system, 8...Control unit, 9-1 to 9-16, 10-1 to 10-16...Photodetector, 11-1 to 11-16...TIA, 30, 32-1 to 32-16, 34-1 to 34-128, 38-1 to 38-16, 39-1 to 39 -16, 40-1 to 40-16, 41-1 to 41-16, 42-1 to 42-16, 43-1 to 43-16...optical waveguide, 31...1x16 optical splitter, 33-1 to 33-16...1x8 optical switch, 35-1 to 35-16...10:1 optical splitter 35-1 to 35-16, 36-1 to 36-16, 37-1 to 37-16...3dB coupler.

Claims

1. A light beam deflection device comprising: a wavelength-tunable light source; a planar optical waveguide circuit that branches the light emitted from the wavelength-tunable light source into a first number of light beams equal to the number of areas divided in a first direction of a target space, and selects and emits the branched light from emission positions in the first direction so that each of these light beams is simultaneously irradiated onto the position of one pixel in a corresponding area; a dispersive element that deflects each of the first number of light beams emitted from the planar optical waveguide circuit at an angle corresponding to the wavelength of the light in a plane parallel to a second direction that is orthogonal to the first direction; a first optical system that converts the first number of light beams emitted from the dispersive element so that they are parallel to the axis of the optical system and emits them; and a second optical system that deflects each of the first number of light beams emitted from the first optical system and irradiates the target space.

2. An optical beam deflection device according to claim 1, further comprising a control unit that controls wavelength tuning by said wavelength-tunable light source and selection of emission position by said planar optical waveguide circuit, wherein said control unit repeatedly performs scanning in the second direction to simultaneously move said first number of light beams irradiated from said second optical system to said target space in said second direction by changing the wavelength of light emitted from said wavelength-tunable light source to change the deflection angle of light in a plane parallel to said second direction, and scanning in the first direction to simultaneously move said first number of light beams irradiated to said target space in said first direction by changing the emission position of light emitted from said planar optical waveguide circuit to change the deflection angle of light in a plane parallel to said first direction after scanning of a line in the second direction is completed.

3. An optical beam deflector according to claim 1, wherein the planar optical waveguide circuit comprises: an optical splitter that splits the light emitted from the wavelength-tunable light source into the first number of light beams; the first number of optical switches that have a second number of output ports equal to the number of pixels in the first direction in each divided area of ​​the target space and that selectively output the light split by the optical splitter to one of the second number of output ports; and optical waveguides that number equal to the first number multiplied by the second number and are arranged along the first direction so as to guide the light output from each output port of the first number of optical switches and emit it from an end face of the planar optical waveguide circuit.

4. An optical beam deflection device according to claim 1, further comprising a focal plane lens inserted between said planar optical waveguide circuit and said dispersive element, said focal plane lens converting each of said first number of light beams emitted from said planar optical waveguide circuit into parallel light beams and at the same time deflecting said parallel light beams so that they pass through a focus of said focal plane lens on the target space side.

5. An optical beam deflector according to claim 1, wherein said dispersive element comprises a plurality of diffraction gratings arranged along the direction in which the light travels.

6. An optical beam deflector according to claim 1, wherein said first optical system comprises a telecentric fθ lens.

7. A light beam deflector according to claim 1, wherein said second optical system comprises a convex lens.

8. An optical beam deflector according to claim 1, comprising: the first number of first photodetectors that convert incident light into an electrical signal; the first number of second photodetectors that convert incident light into an electrical signal; and the first number of transimpedance amplifiers that determine the difference between the output signals of the first and second photodetectors, wherein the planar optical waveguide circuit comprises: a first optical splitter that splits the light emitted from the tunable light source into the first number of light; the first number of second optical splitters that split each of the light split by the first optical splitter into two; the first number of first couplers that output one of the light split by the second optical splitter from a first port to a second port and output the light input to the second port to a third port; and the first number of optical switches that have a second number of output ports equal to the number of pixels in the first direction in each divided area of ​​the target space, and that selectively output the light output from the second port of the first coupler to any one of the second number of output ports. the first number of first optical waveguides multiplied by the second number are arranged along the first direction so as to guide light output from each output port of the first number of optical switches and output it from a first end face of a planar optical waveguide circuit; the first number of second couplers that merge the light output from a third port of the first coupler and the other light split by the second optical splitter, divide the light into two equal parts, and output the merged light; the first number of second optical waveguides that guide the light output from one output port of the second coupler and output it from the second end face of the planar optical waveguide circuit; and the first number of third optical waveguides that guide the light output from the other output port of the second coupler and output it from the second end face of the planar optical waveguide circuit, wherein the first number of returning light beams returning from the target space pass through the second optical system, the first optical system, and the dispersive element and are incident on the output ends of the first optical waveguides of the planar optical waveguide circuit, the first coupler outputs the return light, which is output from the input port of the optical switch and input to the second port, to the third port; the first photodetector converts the light output from the second optical waveguide into an electrical signal;a second photodetector that converts the light emitted from the third optical waveguide into an electrical signal, and the transimpedance amplifier that determines a difference between output signals from the first and second photodetectors that receive the light emitted from the second and third optical waveguides that are connected to the same second coupler.

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