WO2018168959A1

WO2018168959A1 - Laser radar device

Info

Publication number: WO2018168959A1
Application number: PCT/JP2018/010065
Authority: WO
Inventors: 琢也久志本; 任史河田; 渓江本; 野田　進
Original assignee: スタンレー電気株式会社; 国立大学法人京都大学
Priority date: 2017-03-17
Filing date: 2018-03-14
Publication date: 2018-09-20
Also published as: JP6789541B2; JP2018155628A

Abstract

[Problem] In a laser radar device mounted in a vehicle, to detect an object such as a preceding vehicle by performing scanning in a two-dimensional plane, without performing mechanical drive. [Solution] This laser radar device includes: a laser device which is a surface emitting laser device having multiple individual emission regions each with unique emission direction characteristics, wherein each of the individual emission regions has a laser structure including a photonic crystal structure, is capable of emitting two laser beams in symmetric directions relative to a normal to a light emitting surface, and the laser device includes a plurality of the individual emission regions of which an angle relative to the normal to the emission surface varies; a drive circuit which selectively drives the individual emission regions of the laser device in a time series manner and is capable of scanning a monitoring region in a two-dimensional plane; and a signal processing unit which detects reflected light from the monitoring region and calculates an azimuth of an object and the distance to the object.

Description

Laser radar device

The present invention relates to a laser radar device, and more particularly to a laser radar device provided with a photonic crystal.

Refer to FIG. 1A. The laser radar device 101 includes a signal transmission unit 102, a signal reception unit 103, and a signal processing unit 104. The signal transmission unit 102 includes a scanner driving unit 105, a scanner 106, and a laser diode 107. The laser diode 107 transmits infrared laser light based on the light emission command signal from the transmission pulse generation unit of the signal processing unit 104. The laser light is scanned by the scanner 106 driven by the scanner driving unit 105. The laser light is reflected by the object and becomes a reflected signal, which is received by the photodiode 108 in the signal receiving unit 103. The direction is detected based on the direction in which the light is reflected, and the distance is detected from the time from when the laser diode is emitted until it is received by the photodiode (for example, Patent Document 1). The mechanical drive that scans the laser light by changing the direction of the laser diode by the mechanical drive requires a drive mechanism and may cause a failure.

Refer to FIG. 1B. A photonic crystal laser 110 including an active layer 111, a first-period photonic crystal layer 121, and a second-period photonic crystal layer 122 includes a main beam and a main beam that travel in a direction perpendicular to the photonic crystal layer. On the other hand, it is possible to emit a sub-beam that travels in an inclined direction (for example, Patent Document 2). If scanning within the detection range is performed using two laser beams, the scanning speed can be increased.

Refer to FIG. 2A. In the active layer 115 and the plate-shaped slab 142, holes 141 are formed on the lattice points of the first rhomboid lattice and the second rhomboid lattice, the diagonal lines of which are parallel to each other and the lengths of only the diagonal lines are different. The photonic crystal surface-emitting laser 110 having the photonic crystal layer 114 formed with can emit tilted laser light in two symmetrical directions that form an angle θ with respect to the exit surface normal. When the length of the one diagonal line is made different depending on the position in the direction in which the one diagonal line extends, and the position of current injection is changed along the position, the inclined beam has a different exit angle (up to 45 degrees). Is emitted (for example, Patent Document 3). Here, a two-dimensional photonic crystal layer stacked on the active layer that generates light is considered.

Refer to FIG. 2B. The two-dimensional photonic crystal layer forms a resonant state of light of wavelength λ by forming a two-dimensional standing wave, and a different refractive index region is arranged at a lattice point that does not emit light to the outside. Different refractive index regions are arranged at lattice points having a reciprocal lattice vector in which the sum of the photonic crystal structure PCA for forming the optical resonance state and the wave vector corresponding to the wavelength λ in the reciprocal space is within a predetermined range. There has also been proposed a two-dimensional photonic crystal surface emitting laser that emits laser light in two symmetrical directions inclined from a direction perpendicular to the surface by including the photonic crystal structure PCB for light emission. In the configuration shown in the figure, the photonic crystal structure PCA for forming an optical resonance state is a square lattice having an inter-lattice distance (lattice constant) a in the x direction and the y direction, and the photonic crystal structure PCB for emitting light is an interstitial lattice in the y direction. The distance is a, and two adjacent grid points in the x direction are located at r1 * a and r2 * a in the x direction with respect to the x direction position of the grid point in the row adjacent in the y direction. It is an oblique grid. (For example, patent document 4).

The photonic crystal structure for forming the optical resonance state is composed of either a square lattice, a rectangular lattice, or a triangular lattice, and the photonic crystal structure for emitting light is an oblique lattice, a square lattice, a rectangular lattice, or a face-centered rectangular shape. It is disclosed that it is composed of either a lattice or a triangular lattice. In addition, the term used here has the meaning prescribed | regulated by the specification of patent document 4. FIG.

By changing the periodicity of the photonic crystal structure for emitting light, the traveling direction of the emitted laser light can be changed. It is taught that the emission direction of the tilted beam can be changed by defining a plurality of regions in the photonic crystal structure for light emission, changing the periodicity in each region, and switching the region for supplying current. ing.

JP 2004-28753 A (Patent No. 3659239) JP 2009-76900 (Patent No. 5070161) JP 2013-41948 (Patent No. 5794687) JP 2013-211152 A (Patent No. 6083703)

For example, in a laser radar device mounted on a vehicle, it is desired to perform scanning in a two-dimensional plane without performing mechanical driving to detect an object such as a preceding vehicle.

According to an embodiment of the present invention,
A surface-emitting laser device having a number of individual emission regions each having a unique emission direction characteristic, each of the individual emission regions having a laser structure including a photonic crystal structure, with respect to the normal of the emission surface A laser device including a plurality of individual emission regions capable of emitting two laser beams in symmetrical directions and changing an angle with respect to a normal line of the emission surface;
A drive circuit capable of selectively driving individual emission regions of the laser device in a time series and scanning a monitor region in a two-dimensional plane;
A signal processing unit that detects reflected light from the monitor region and calculates the direction of the object and the distance to the object;
A laser radar device is provided.

The direction of the emitted laser light can be changed by changing the periodicity of the photonic crystal. The individual emission areas selected in time series can perform pseudo-scanning.

FIG. 1A is a block diagram schematically showing the configuration of a laser radar device according to the prior art, and FIG. 1B is a cross-sectional view schematically showing the configuration of an example of a photonic crystal laser according to the prior art.
FIG. 2A is a perspective view schematically showing a configuration of a photonic crystal surface emitting laser device according to a prior application, and FIG. 2B is a photonic crystal structure for forming an optical resonance state and light output by continuous research of the photonic crystal surface emitting laser device. FIG. 3 is a plan view showing an example of a photonic crystal structure for use.
3A is a block diagram schematically illustrating the configuration of the laser radar device according to the embodiment, FIG. 3B is a plan view schematically illustrating the distribution of a large number of individual emission regions included in the laser device according to the embodiment, and FIG. 3C is an individual emission. FIG. 3D is a schematic diagram schematically showing the structure of lattice points of the photonic crystal layer constituting the laser device, and FIG. 3E is a schematic diagram showing two laser beams emitted from the laser device. 3F is an equation showing the relationship between the lattice constant a and coefficients r1 and r2 of the photonic crystal shown in FIG. 3C and the angles θ and φ of the laser beam shown in FIG. 3D, and FIG. FIGS. 3H and 3I show one of two laser beams reflected by the object OB, and the reflected light is reflected by two photodiodes PD1. , PD2 is a top view showing how light is received.
4A is a mathematical expression showing the relationship between the tilt angle θ and the coefficients r1 and r2 when φ = 0, FIG. 4B is a graph showing the change of the coefficient r1 = r2 when the tilt angle θ is changed, and FIG. 4C is the laser. FIG. 4D is a schematic top view showing an arrangement example of individual emission regions on the apparatus, and FIG. 4D is a photonic crystal change (DA), an emission laser beam change (DB), and an arrangement example of individual emission regions (DC) when axial rotation is included. ), A schematic top view showing the distribution (DD) of the emitted laser light when including a plurality of rotation angles.
FIG. 5A is a schematic top view showing a configuration in which the detection area is divided into a front area and a side area, and FIG. 5B is a timing chart showing a scanning process for continuously scanning the side area and the front area.

1 Laser radar device, 2 Laser device, 4 Drive circuit,
6 scanning calculation unit, 14 detection signal calculation unit, 16 distance calculation unit,
21 active layer, 23 photonic crystal layer, 25 first conductivity type region,
27 second conductivity type region, 28, 29 electrodes,
OB (detection) object, PD photodiode, LB laser beam,
IER individual emission area, a lattice constant, r1, r2 coefficient,
θ tilt angle, φ azimuth, x, y Cartesian coordinate axes,
FV field of view, FVD field of view.

For safe driving, vehicles traveling on the road need to pay attention to the preceding vehicle traveling ahead, pedestrians walking on the sidewalk, etc. In order to avoid inadvertent collisions and the like, it is desirable to detect objects on the road using a detection device and take measures when necessary. Laser radar devices are known as devices that meet such demands. In order to detect objects in the front area and the side area on the road using the laser light, the laser light is scanned in a predetermined area. In a vehicle where it is difficult to avoid mechanical vibration, temperature change, etc., it is desirable not to use a mechanical drive unit.

The light emitted from the photonic crystal laser device travels in a direction based on the periodic structure of the photonic crystal layer. When a large number of regions are defined in the photonic crystal layer and the periodic structure of each region is changed, it becomes possible to emit laser light whose traveling direction changes. If the predetermined area in the two-dimensional plane can be almost completely filled with a set of laser beams, it is considered that the predetermined area can be pseudo-scanned. A laser device having a large number of individual emission areas capable of emitting a large number of laser beams having different traveling directions is formed using a photonic crystal structure, and a plurality of reflected lights from an object in a predetermined area are formed. It is considered to detect with the light receiving element.

FIG. 3A schematically shows a configuration of a laser radar device according to the embodiment. The laser radar device 1 includes a laser device 2 having a large number of individual emission regions, a drive circuit 4 of the laser device 2, a scanning calculation unit 6 that generates a signal for controlling the drive circuit 4, and two photodiodes PD1, PD2, and so on. A detection signal calculation unit 14 that performs calculation based on the detection signals from the photodiodes PD1 and PD2 and the timing of laser light emission supplied from the drive circuit, the distance to the object OB that caused the reflected light based on the result, A distance direction calculation unit 16 that calculates the direction of the object is included. Laser light emitted from the laser device 2 is reflected by the object OB and detected by the photodiodes PD1 and PD2.

FIG. 3B shows a top view of the semiconductor laser device 2 having a large number of individual emission regions IER in the light emitting surface. In the figure, a large number of individual emission regions IER are arranged along the vertical y-axis direction and the horizontal x-axis direction. In order to supply a voltage to each individual emission region IER, a wiring is formed. As the semiconductor, when near-infrared light is used, a material containing GaAs such as GaAs, AlGaAs, InGaAs, or the like can be used.

FIG. 3C is a cross-sectional view schematically showing a structural example of the individual emission region IER. An active layer 21 and a photonic crystal layer 23 are disposed between a first conductivity type (for example, p-type) layer 25 and a second conductivity type (for example, n-type) layer 27. A second conductivity type side electrode 28 that is a common electrode is formed on the surface of the second conductivity type layer 27, and a first conductivity type side electrode 29 that supplies current to the individual emission region IER is formed on the surface of the first conductivity type layer 25. Is formed. The active layer 21 is formed, for example, with a multiple quantum well structure in which InGaAs is a well layer and GaAs is a barrier layer. The first and second conductivity type layers 25 and 27 can be made of, for example, AlGaAs. These materials can also be used for the photonic crystal layer. The electrode can be formed using, for example, a metal such as Au or a transparent electrode such as indium tin oxide (ITO). The shape of the electrode is not limited to this shape. What is necessary is just to be able to selectively apply a voltage to each individual emission region, such as a simple cross wiring or a combination of a common wiring and an active wiring.

FIG. 3D shows a design example of a photonic crystal according to the teaching of Patent Document 4. It is assumed that a photonic crystal 23 is formed by forming an optical resonance state forming lattice using a square lattice, forming a light emitting lattice using an oblique lattice, and superimposing them.

FIG. 3E shows an inclination angle θ with respect to the normal of the surface of the area of the two laser beams emitted from the individual emission areas IER of the laser apparatus 2 and an azimuth angle φ with respect to the x axis in the area surface.

FIG. 3F shows (Expression 1) representing the relationship between the coefficients r1 and r2, the tilt angle θ and the azimuth angle φ, and (Expression 2) representing the relationship between the lattice constant a and the wavelength λ (in vacuum). The effective refractive index n _eff is determined by the refractive index of the semiconductor active layer, the photonic crystal layer, or the like.

The inclination angle θ of the emitted light from the light emitting surface normal and the azimuth angle φ from the reference axis x in the light emitting surface are determined by the coefficients r1 and r2 in the light emitting grating. In other words, the coefficients r1 and r2 are selected so that a desired tilt image θ and azimuth angle φ are obtained. As shown in FIG. 3E, two laser beams are emitted in a symmetrical angular direction from the origin in the emission plane. When one beam scans the first quadrant, the other beam scans the third quadrant. When scanning a predetermined area in the field of view, if the center of the predetermined area is the origin and one beam scans, for example, the first and second quadrants, the other beam scans the third and fourth quadrants. An inclination angle θ and an azimuth angle φ required as a scanned region are determined, and coefficients r1 and r2 for realizing these are obtained.

FIG. 3G is a schematic top view showing the relationship between the section FVD in the field of view FV and the individual irradiation area IER in the laser device 2 when the field of view FV is scanned using the fixed laser device 2. A number of individual irradiation areas IER in the laser device 2 are set in correspondence with the section FVD defined in the field of view.

3H and 3I are schematic top views showing how the laser beam LB emitted from the laser device 2 is reflected by the object OB and detected by the photodiodes PD1 and PD2. By using two photodiodes, for example, it is possible to determine which of two laser beams is reflected by the laser beam. By tilting the light receiving surfaces of the two photodiodes, the traveling direction of the received light can be further confirmed. Based on the time difference from the light emission timing to the light reception timing, the distance from the laser radar device to the object can be obtained.

In the above-described example, the field of view is divided into a number of sections (for example, matrix-shaped sections), and an individual irradiation area including a photonic crystal layer using a common axis orientation that can irradiate each section with laser light is formed. The case where a laser device is used has been described. In this case, the coefficients r1 and r2 will change variously.

検討 Consider uniaxial scanning. In the case of scanning in a uniaxial direction parallel to the x-axis, the azimuth angle φ = 0. Assume that the inclination angle θ is changed to 0 degree, 10 degrees, 20 degrees, and 30 degrees. When the azimuth angle φ = 0, sin θ * sin φ = 0, and r1 = r2 from (Equation 1) in FIG. 3F.

FIG. 4A shows the case where φ = 0. r1 and r2 are expressed by the equations shown at the bottom.

FIG. 4B shows changes in the coefficients r1 and r2 when the inclination angle θ is changed. It can be seen that in order to change the tilt angle θ from 0 degree to 30 degrees in the photonic crystal, it is only necessary to increase r1 = r2 from 1 to about 1.2. Note that the maximum tilt angle is 45 degrees.

FIG. 4C shows (0, 0), (10, 0), (20, 0), (30, 0) as the angle pair (θ, φ) in the four individual irradiation areas in the laser device 2 in order. Indicates the case of setting. If these individual irradiation areas are formed, the projection of the laser light onto the light emitting surface is parallel to the x-axis, and laser light with an inclination angle of 0 degrees, 10 degrees, 20 degrees, and 30 degrees can be emitted. Here, four electrodes are used as an example, but this is only an example, and it is desirable to increase the number of divided electrodes with respect to the angle in order to improve controllability.

With the above settings, only laser light whose projection onto the light emitting surface of the laser light is parallel to the x-axis can be obtained. A predetermined area on the two-dimensional plane including the x-axis and the y-axis cannot be scanned. By the way, this conclusion is based on the premise that there is only one type of x-axis and y-axis. It is also possible to rotate the axis, and the plane can be covered by rotating the x axis around the origin.

FIG. 4D shows the case where the shaft is rotated. (DA) indicates a case where 90 ° rotation is performed. The x-axis direction before rotation corresponds to the y-axis direction after rotation, and the y-axis direction before rotation corresponds to the x-axis direction after rotation.

(DB) indicates the emitted light whose inclination angle changes along the y-axis direction by the rotated photonic crystal. Since the change in the x-axis direction is obtained from the individual emission region having the structure before the rotation, in combination, the inclination angles along the x-axis direction and the y-axis direction are obtained.

(DC) shows a case where an individual emission region that provides a change in inclination angle in the x-axis direction and a change in inclination angle in the y-axis direction is formed along the x-axis direction and the y-axis direction in the emission surface of the laser device 2. ing.

(DD) indicates a case where rotation other than 90 ° rotation is also used. In the illustrated configuration, two rotation axes are formed between the x-axis and the y-axis, the inter-axis angle in the vicinity of the x-axis is narrow, and the inter-axis angle increases as the y-axis is approached. The detection of the object considers the demand for higher accuracy near the road surface. It should be noted that an individual irradiation region in which the coefficient pair (r1, r2) is arbitrarily selected and an individual irradiation region on the premise that r1 = r2 can be mixed.

When performing vehicle object detection on the front area and the side area, the required conditions are different between the front area and the side area. It is conceivable to provide three sets of laser devices for the front and for both sides, but if it can be performed with one set, it will be effective for cost reduction. The front monitor object can be monitored with monitor light centered around 100 m, for example, and the side monitor object can be monitored with monitor light centered around 50 m, for example. Since the distance ahead is long, it is necessary to increase the intensity of the laser beam, and the time for the laser beam to reciprocate is long. On the other hand, since the distance is short at the side, the intensity of the emitted light can be reduced and the reflected light reaches The time until is short.

FIG. 5A is a schematic top view showing a state in which the monitor space of the laser radar device 1 is divided into a front region and a side region, and FIG. 5B is a time-division method for dividing the side region monitor and the front region monitor. The timing chart in the case of performing is shown. In the side area monitor, the emission frequency is set relatively high and the emission intensity is set relatively low, and in the front monitor, the emission frequency is set relatively low and the emission intensity is set relatively high.

As described above, the description has been given according to the embodiment. However, if necessary, the description is given in the column of the embodiment of Japanese Patent Laid-Open No. 2013-41948 (Patent No. 5794687) and Japanese Patent Laid-Open No. 2013-21542 (Patent No. 6083703). Can be taken in (can be
incorporated herein by reference). The material numerical values and the like in the above description are examples and are not limiting. Although described along the embodiment, a known equivalent or the like can be used. It will be apparent to those skilled in the art that other various modifications, improvements, combinations, and the like are possible.

Claims

A surface-emitting laser device having a number of individual emission regions each having a unique emission direction characteristic, each of the individual emission regions having a laser structure including a photonic crystal structure, with respect to the normal of the emission surface A laser device including a plurality of individual emission regions capable of emitting two laser beams in symmetrical directions and changing an angle with respect to a normal line of the emission surface;
A drive circuit capable of selectively driving individual emission regions of the laser device in a time series and scanning a monitor region in a two-dimensional plane;
A signal processing unit that detects reflected light from the monitor region and calculates the direction of the object and the distance to the object;
Including laser radar equipment.
The laser radar device according to claim 1, wherein the laser structure including the photonic crystal structure includes a photonic crystal layer parallel to the active layer.
The laser radar device according to claim 2, wherein the laser structure including the photonic crystal structure has a photonic crystal layer on both sides of the active layer.
2. The laser radar according to claim 1, wherein the signal processing unit includes a plurality of light receiving elements arranged at different positions, and the reflected light can determine which of two outgoing laser lights is reflected. apparatus.
2. The laser radar device according to claim 1, wherein the plurality of individual emission areas include a plurality of individual emission areas whose in-plane directions of projection with respect to a light emitting surface of an emission surface including two emission laser beams are the same direction.
2. The laser radar device according to claim 1, wherein the plurality of individual emission areas further include a plurality of individual emission areas in which a projection of an emission surface including two emission laser beams onto a light emitting surface changes an in-plane direction on the emission surface.
The photonic crystal structure forms a resonant state of light having a wavelength λ by forming a two-dimensional standing wave, and a different refractive index region is arranged at a lattice point having a periodicity that does not emit light to the outside. A different refractive index region is arranged at a lattice point having a reciprocal lattice vector whose sum of a photonic crystal structure for forming an optical resonance state and a wave vector corresponding to the wavelength λ in a reciprocal space is within a predetermined range. The laser radar device according to claim 1, further comprising a photonic crystal structure for emitting light.
The photonic crystal structure for forming an optical resonance state is composed of any one of a square lattice, a rectangular lattice, and a triangular lattice, and the photonic crystal structure for emitting light is an oblique lattice, a square lattice, a rectangular lattice, and a face center length. The laser radar device according to claim 7, wherein the laser radar device is configured by one of a rectangular lattice and a triangular lattice.
The laser radar device according to claim 8, wherein the photonic crystal structure for forming an optical resonance state is formed of a square lattice, and the photonic crystal structure for light emission is formed of an oblique lattice.
The square lattice has a lattice constant a between adjacent lattice points along the x-axis and the y-axis, the oblique lattice includes a lattice point sequence with an interval a in the y-axis direction, and the adjacent lattice point sequence in the x-axis direction. The laser radar device according to claim 9, comprising a plurality of individual emission regions that are separated from the k coordinate of the lattice point by r1a and r2a and have different coefficient pairs (r1, r2).
The square lattice has a lattice constant a between adjacent lattice points along the x-axis and the y-axis, the oblique lattice includes a lattice point sequence with an interval a in the y-axis direction, and the adjacent lattice point sequence in the x-axis direction. Is the same distance from the k coordinate of the grid point,
10. The laser radar according to claim 9, wherein the plurality of individual emission areas include a plurality of individual emission areas including a plurality of individual emission areas in which the in-plane directions of projection of the emission surface including the emission laser beam with respect to the light emitting surface are the same direction. apparatus.
The laser radar device according to claim 1, wherein the monitor area in the two-dimensional plane is divided into a plurality of areas, and the drive circuit drives the multiple individual emission areas under different conditions according to the division.
The laser radar device according to claim 1, wherein the multiple individual emission regions include GaAs and emit near-infrared light.
The laser radar device according to claim 1, wherein the multiple individual emission regions include those having a multiple quantum well structure.
The laser radar device according to claim 12, wherein the multiple quantum well structure includes an InGaAs well layer and a GaAs barrier layer.
2. The laser radar device according to claim 1, wherein the multiple individual emission regions include one region for a front region and two regions for side regions on both sides of the front region.
The multiple individual emission areas are time-divided to include a front area monitoring period and a side area monitoring period, and the emission intensity is set relatively high and the emission frequency is set relatively low in the front area monitoring period. The laser radar device according to claim 1, wherein the emission intensity is set to be relatively low and the emission frequency is set to be relatively high in the side region monitoring period.