KR20200024448A - Light-emitting optical system for applying light source having asymmetric luminescent region - Google Patents

Abstract

The present invention provides a light transmitting optical system of a LIDAR. Provided is the light transmitting optical system applied to a light source having an asymmetric light emitting region, which comprises: a laser diode which irradiates a laser; an aspherical cylinder lens installed in a path of the laser irradiated from the laser diode and having different focal lengths in horizontal and vertical directions of the laser; and a beam scanning mirror reflecting the laser passing through the aspherical cylinder lens and scanning in a one-dimensional or two-dimensional plane. According to the present invention, by constructing a lens having different focal lengths in the horizontal and vertical directions of the laser having an asymmetric light emitting region, the light efficiency is increased while increasing the resolution in a direction having a wide light emitting region.

Description

Light-emitting optical system for applying light source having asymmetric luminescent region

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission optical system, and more particularly, to a transmission optical system applied to a light source having an asymmetric emission region optimized for a laser diode used in a distance measuring device such as LIDAR (Light Detection And Ranging).

In general, LIDAR (Light Detection And Ranging) is an optical distance detection technology that can measure the distance by irradiating a laser to the target, and analyzing the light scattered by the target to return. Recently, many applications have been made to detect the surrounding situation during autonomous driving of automobiles.

The principle of measuring distance in LIDAR is a method of measuring the time of flight (TOF) of light and converting it to distance. The commonly used light source is a laser diode capable of pulse driving in the near infrared wavelength band. The higher the amplitude of the pulse of the laser diode and the shorter the pulse duration time, the higher the sensitivity of the signal.

In addition, the method of transmitting light to the LIDAR measurement area includes a method of transmitting light over a two-dimensional area and a method of scanning a small beam. The latter method is recommended for long distance measurements.

The two-dimensional scanning method can be implemented using a MEMS mirror or the like. In the case of using a MEMS mirror, the structure has a simple advantage and is widely employed. In order to increase the amount of light, a method of stacking a laser light emitting region in one direction and stacking it is common. In this case, the resolution of the LIDAR tends to decrease in a direction in which the emission area is wide. Especially when scanning light using a MEMS mirror, it is very difficult to increase the resolution while maintaining the light efficiency due to the limited mirror size.

1 is a view showing a general laser diode structure.

Referring to FIG. 1, in the general laser diode structure, the characteristics of the near field and the far field in the direction perpendicular to the active layer (active) and in the direction perpendicular to the active layer are very large. Although it is small, it can be seen as a point light source, but the horizontal direction is 2 ~ 200㎛, and the size for low power is small, but the high power is very large and it is difficult to see it as a point light source. In the case of the far field, the divergence in the vertical direction is larger, about 2 to 4 times larger in the horizontal direction (see FIG. 2).

3 is a view showing a transmission optical system of the LIDAR according to the prior art.

Referring to FIG. 3, the LIDAR transmission optical system 10 according to the related art includes a NIR (Near Infrared) laser diode 12 operated by an LD drive 11 and a light irradiated from the NIR laser diode 12. A collimator lens 13 installed in the path, a mirror 14 reflecting the light passing through the collimator lens 13 to a predetermined position, and a MEMS scanning the light reflected from the mirror 14 in two dimensions It may include a mirror (15).

However, this prior art uses a single collimator lens 13, whereby the resolution difference occurs by the difference in the size of the light emitting region of the NIR laser diode 12. For example, if the short side is 10 mu m and the long side is 200 mu m, the long side resolution is 20 times worse.

Therefore, in the prior art, it is necessary to develop the LIDAR transmission optical system to improve the resolution for a wide light emission area in the asymmetric light emission area.

In order to solve the problems of the prior art as described above, the present invention comprises a lens having a different focal length in the horizontal and vertical direction of the laser having an asymmetric light emitting area, while increasing the resolution of the direction having a wide light emitting area The purpose is to improve the light efficiency.

Other objects of the present invention will be readily understood through the following description of the embodiments.

In order to achieve the above object, according to an aspect of the present invention, in the transmission optical system of LIDAR, a laser diode for irradiating a laser; An aspherical cylinder lens installed in a path of a laser irradiated from the laser diode and having different focal lengths in horizontal and vertical directions of the laser; And a beam scanning mirror for reflecting the laser beam passing through the aspherical cylinder lens and scanning the laser beam in one or two dimensional planes.

The laser diode may have a short axis in a horizontal direction and a slow axis in a vertical direction.

The aspherical cylinder lens may be composed of first and second aspherical cylinder lenses having different focal lengths.

The aspherical cylinder lens may be formed of a single aspherical cylinder lens having both surfaces perpendicular to each other.

The beam scanning mirror may be formed of any one of a MEMS mirror, a polygon mirror, and a galvanometer scanner.

According to a transmission optical system applied to a light source having an asymmetric light emitting area according to the present invention, by forming a lens having a different focal length in the horizontal and vertical direction of the laser having an asymmetric light emitting area, the resolution of the direction having a wide light emitting area It also increases the light efficiency while increasing.

1 is a view showing a general laser diode structure.
2 is a view showing a far field pattern of a general laser diode.
3 is a block diagram showing a transmission optical system of the LIDAR according to the prior art.
4 is a block diagram showing a transmission optical system applied to a light source having an asymmetric light emitting area according to the first embodiment of the present invention.
FIG. 5 is a diagram illustrating a lamination structure of a laser diode in a transmission optical system applied to a light source having an asymmetric light emitting area according to the first embodiment of the present invention.
FIG. 6 is a diagram for describing a resolution in a transmission optical system applied to a light source having an asymmetric light emitting area according to the first embodiment of the present invention.
FIG. 7 is a diagram illustrating a light emitting region direction of a laser diode in a transmission optical system applied to a light source having an asymmetric light emitting region according to a first embodiment of the present invention.
FIG. 8 is a view showing the arrangement of two aspherical cylinder lenses in a transmission optical system applied to a light source having an asymmetric light emitting area according to the first embodiment of the present invention.
9 is a block diagram illustrating a transmission optical system applied to a light source having an asymmetric light emitting area according to a second embodiment of the present invention.
FIG. 10 is a view showing the arrangement of one aspherical cylinder lens in a transmission optical system applied to a light source having an asymmetric light emitting area according to the second embodiment of the present invention.

As the inventive concept allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to the specific embodiments, but should be understood in a way that includes all changes, equivalents, and substitutes included in the spirit and scope of the present invention, and may be modified in various other forms. It is to be understood that the scope of the present invention is not limited to the following examples.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, and like reference numerals denote the same or corresponding elements regardless of reference numerals, and redundant description thereof will be omitted.

4 is a block diagram illustrating a transmission optical system applied to a light source having an asymmetric light emitting area according to the first embodiment of the present invention.

Referring to FIG. 4, the transmission optical system 100 applied to a light source having an asymmetric light emitting area according to the first embodiment of the present invention is a transmission optical system of LIDAR (Light Detection And Ranging), and includes a laser diode 110 and an aspherical cylinder. The lens 120 and the beam scanning mirror 130 may be included.

In addition, the transmission optical system 100 applied to the light source having the asymmetric light emitting area according to the first embodiment of the present invention switches the path so that the laser beam passing through the aspherical cylinder lens 120 is irradiated to the beam scanning mirror 130. The reflective mirror 140 may be provided, and the laser is directed to the casing 150 in which the laser diode 110, the aspherical cylinder lens 120, the beam scanning mirror 130, and the reflective mirror 140 are accommodated. A window 151 for inspecting may be provided.

4 and 5, the laser diode 110 is installed to irradiate a laser, the operation is controlled by the laser diode driver 111 controlled by the control unit of the system. The laser diode 110 may be a NIR (Near Infrared) laser diode, for example, and may have a structure in which three or more layers are stacked, which may be applied to all the following embodiments. In addition, when the laser diode 110 is used as a vehicle LIDAR, a wavelength of 905 nm may be used, and may have a structure of three or more layers for high output. In this case, within about 10 μm (3) of the short axis (fast axis) Layer) and a slow axis, and may have a light emitting area of about 200 μm.

The aspherical cylinder lens 120 is installed in the path of the laser irradiated from the laser diode 110 and has different focal lengths in the horizontal and vertical directions of the laser. In the present embodiment, the aspherical cylinder lens 120 may include first and second aspherical cylinder lenses 121 and 122 having different focal lengths.

The beam scanning mirror 130 reflects the laser beam that has passed through the aspherical cylinder lens 120 to scan in one or two dimensional planes. The beam scanning mirror 130 may be made of any one of a MEMS mirror, a polygon mirror, and a galvanometer scanner, which may be applied to all the following embodiments. The MEMS mirror may be made of an analog type micromirror or an array of micromirrors by Micro-Electro-Mechanical Systems (MEMS). In addition, the polygon mirror may have a side surface having a predetermined number of light reflection surfaces, and installed to rotate about the polygon mirror axis. The galvanometer scanner also moves the reflecting mirror finely and quickly so that the laser is irradiated where it is desired.

Referring to FIG. 6, the resolution 2α of the transmission optical system 100 applied to a light source having an asymmetric light emitting area according to an embodiment of the present invention is as shown in Equation 1 below. It is determined by the size of the light emitting area (near field) and the focal length f of the lens to make the emitted light into parallel light.

EPD (entrance pupil diameter) shown in Table 1 below means the size of the beam coming out in parallel light.

Item unit level Perpendicular Entrance pupil diameter (EPD) mm 3.6 3.6 NA 0.3 0.3 Focal Length mm 6 6 Chip size mm 0.01 0.2 Resolution (perfect) ° 0.1 1.9

In the case of MEMS mirrors, larger mirror diameters are advantageous in terms of resolution and light efficiency, whereas fast scan frequency tends to be difficult due to slow scan frequency. The EPD should be set slightly smaller than the diameter of the MEMS mirror. To achieve light efficiency of 70-80% or more, the NA (numerical aperture) must be 0.3 or more. The relationship between NA, focal length f, and EPD is shown in Equation 2 below.

As shown in Table 1, using a conventional collimator lens having an EPD 3.6 and a focal length of 6 mm has a resolution of 1.9 degrees in the long direction. On the other hand, the shorter resolution is very good at 0.1 degrees. Since the horizontal side is more important than the vertical side, the resolution of the LIDAR used for autonomous driving for vehicles is as shown in FIG. 7, by turning the chip direction of the laser diode 110 by 90 degrees, so that the fast axis is horizontal and long. It is advantageous to arrange the slow axis in the vertical direction. Therefore, according to the above calculation, the resolution is 0.1 degrees horizontally and 1.9 degrees vertically. If the measurement range of LIDAR is far, the area of the vertical resolution of 1.8 degrees may become too large. As a way to minimize the loss of light efficiency and to make the vertical resolution more precise, the cylinder surface is aspheric as in this embodiment. Two cylinder lenses, that is, the first and second aspherical cylinder lenses 121 and 122 may be used. The sag equation of the aspherical cylinder can be written as in Equation 3 below.

It is better to keep the focal length of the aspherical cylinder in the horizontal direction so that NA is 0.3 or more. When the light emitting region of the laser diode 110 is arranged as shown in FIG. 7, as shown in FIG. 8, the first aspherical cylinder lens 121 directly in front of the laser diode 110 has the curvature XTO in the horizontal direction. do. The second placed aspherical cylinder lens 122 is rotated by 90 degrees with respect to the direction of laser travel, and thus has a curvature in the vertical direction YTO. When the focal length of the first aspherical cylinder lens 121 is 6 mm and the focal length EFY of the second aspherical cylinder lens 122 is 12 mm, the resolution is 0.1 degrees horizontal and 0.95 degrees vertically, so that the focal length EFY is 12 mm. The vertical resolution is doubled. Although the NA in the vertical direction decreases by 0.15 degrees, the far field pattern angle in this direction is small, so the influence is relatively small.

Table 2 and FIG. 8 below are examples of lens data by the transmission optical system 100 applied to a light source having an asymmetric light emitting area according to the first embodiment of the present invention. Table 3 below shows the resolution accordingly.

Surface Radius Thickness Glass
( Refractive index  @ 905nm) One Infinite 0.4 1.484249 2 Infinite 4.548618 Air 3 Infinite 1.8 1.52299 XTO X radius -3.13794 K -0.414415
A 0.545774E-03 B 0.383353E-04
C 0.183268E-05 D 0.168836E-06 4.818114 Air 5 Infinite 1.8 1.52299 YTO Y radius -6.27588 K -0.114259
A 0.222272E-03 B 0.405 145E-05
C 0.671294E-07 D 0.121207E-08 0 Air

Item unit level Perpendicular Entrance pupil diameter (EPD) mm 3.6 3.6 NA 0.3 0.15 Focal Length mm 6 12 Chip size mm 0.01 0.2 Resolution (perfect) ° 0.1 0.95

9 is a block diagram illustrating a transmission optical system applied to a light source having an asymmetric light emitting area according to a second embodiment of the present invention.

9, the transmission optical system 200 applied to a light source having an asymmetric light emitting area according to the second embodiment of the present invention is a transmission optical system of LIDAR, a laser diode 210 for irradiating a laser, and a laser diode ( Installed in the path of the laser irradiated from 210 and reflecting the laser beam passing through the aspherical cylinder lens 220 and the aspherical cylinder lens 220 having different focal lengths in the horizontal and vertical directions of the laser to reflect one or two dimensions. It can include a beam scanning mirror 230 to scan in the dimensional plane, the laser diode 210 can be maintained or adjusted the intensity of the laser by the laser diode driver 211 controlled by the control unit of the system, aspheric A reflection mirror 240 may be additionally provided to adjust a path so that the laser beam passing through the cylinder lens 220 is irradiated to the beam scanning mirror 230. It can be installed in the casing 250 having a window 251 irradiated with a light, and also the description of the configuration of this embodiment is transmitted to the light source having an asymmetric light emitting area according to the first embodiment of the present invention A description of the same configuration in the optical system 100 will be replaced.

In this embodiment, the aspherical cylinder lens 220 may be formed of a single aspherical cylinder lens orthogonal to both sides. This embodiment is implemented with a single aspherical cylinder lens 220 is shown in Figure 10 and Table 4 below.

Surface Radius Thickness Glass
( Refractive index  @ 905nm) One Infinite 0.4 1.484249 2 Infinite 5.730503 Air XTO X radius -3.13794 K -1.128837
A -0.478668E-02 B 0.343820E-03
C -0.249392E-04 D 0.119473E-05 9.137941 1.52299 YTO Y radius -6.27588 K -0.092991
A 0.209578E-03 B 0.341001E-05
C 0.179560E-06 D -0.699086E-08 4.818114 Air

According to the transmission optical system applied to the light source having an asymmetric light emitting area according to the present invention, by forming a lens having a different focal length in the horizontal and vertical direction of the laser having an asymmetric light emitting area, Increasing the resolution while increasing the light efficiency.

As described above with reference to the accompanying drawings, the present invention, of course, various modifications and variations can be made within the scope without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the claims below and equivalents thereof.

110,210: Laser Diode
111211: Laser Diode Driver
120220: Aspherical Cylinder Lens
130,230: Mirror for beam scanning
140,240: Reflective Mirror
150,250: Casing
151,251: Windows

Claims (5)

In the LIDAR transmission optical system,
A laser diode for irradiating a laser;
An aspherical cylinder lens installed in a path of a laser irradiated from the laser diode and having different focal lengths in horizontal and vertical directions of the laser; And
A beam scanning mirror for reflecting the laser beam passing through the aspherical cylinder lens and scanning it in a one-dimensional or two-dimensional plane;
Transmission optical system applied to a light source having an asymmetric light emitting region, including. The method according to claim 1,
The laser diode,
A light transmission optical system applied to a light source having an asymmetric light emitting region in which a short axis is horizontal and a slow axis is disposed in a vertical direction. The method according to claim 1,
The aspherical cylinder lens,
A light transmission optical system applied to a light source having an asymmetric light emitting area, comprising first and second aspherical cylinder lenses having different focal lengths. The method according to claim 1,
The aspherical cylinder lens,
A transmission optical system applied to a light source having an asymmetric light emitting area, consisting of a single aspherical cylinder lens having two surfaces perpendicular to each other. The method according to any one of claims 1 to 4,
The beam scanning mirror,
A transmission optical system applied to a light source having an asymmetric light emitting region, which is one of a MEMS mirror, a polygon mirror, and a galvanometer scanner.

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