EP3574345A1

EP3574345A1 - Optical assembly and a lidar device having an optical assembly of this type

Info

Publication number: EP3574345A1
Application number: EP18700996.4A
Authority: EP
Inventors: Stefanie Mayer; Annette Frederiksen; Tobias Graf
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2017-01-25
Filing date: 2018-01-15
Publication date: 2019-12-04
Also published as: JP2020505620A; WO2018137950A1; US10914839B2; DE102017201127A1; CN110249239A; US20190346569A1; KR102548146B1; KR20190105087A

Abstract

The invention relates to an optical assembly for receiving light waves, comprising a receiver optic for focusing at least one incoming light wave onto a surface of a detector for detecting the at least one light wave, wherein at least one diffractive optical element is arranged with a planar extension between the receiver optic and the detector, and wherein the at least one diffractive optical element has a surface with a surface structure with at least one optical function. The invention also relates to a LIDAR device having an optical assembly of this type.

Description

Description title

Optical arrangement and a LIDAR device with such an optical arrangement

The invention relates to an optical arrangement for receiving light waves and to a LIDAR device having such an optical arrangement,

State of the art

There are different concepts for LIDAR (Light Detection And Ranging) devices, One possibility is the use of so-called "macro scanners", where a rotating macro mirror, for example, has a diameter of a few centimeters, which can also produce a light beam with a diameter A large beam diameter has particular advantages in terms of eye safety, since a pupil diameter of 7 mm assumed in the standards (IEC 60825-1) can capture only a fraction of the beam Larger beam diameter more robust against disturbances, such as rain or dust Another possibility is the use of "micro-scanners". In this case, small mirrors with a diameter of the order of a few millimeters are used, which are produced in MEMS (Micro-Electro Mechanical Systems) technology and are mounted swingably or rotatably in one or two axes in order to realize beam deflection. Advantageous here are the small size and the absence of macroscopically moved elements, Small

However, mirror diameters have a detrimental effect on eye safety and susceptibility to interference. Furthermore, it is difficult to operate these micro mirror-based systems such that a same optical path can be used for the transmission and reception path. Here, the micromirror, depending on the size of the receiving aperture greatly restrict, which not enough photons can be collected for optimal illumination of a detector.

In current systems with complex receiving optics, a large-area detector must be used. This is necessary so that the signal-to-noise behavior of the detector is so low that even objects at greater distances can still be reliably detected. However, the size of the area of the detector has a direct influence on the manufacturing cost of the device.

Disclosure of the invention

The object underlying the invention can be seen to provide an optical device and a LIDAR device with such an arrangement, which allow a use of a smaller detector surface.

This object is achieved by means of the subject matter of the independent claims. Advantageous embodiments of the invention are the subject of each dependent subclaims.

According to one aspect of the invention, there is provided an optical device for receiving lightwaves, having receiving optics for focusing at least one incoming lightwave on a surface of a detector for detecting the at least one lightwave, wherein at least one diffractive optical element having a planar extension between the receiving optics and the detector is arranged and the at least one diffractive optical element has a surface with a surface structure having at least one optical function.

By doing so, an arrangement for receiving light waves having a diffractive optical element can be provided. By virtue of this measure, an incident light wave can be deflected and focused onto a detector by diffraction or diffraction in such a way that the area of the detector can be made smaller than an optical arrangement which consists only of lens elements. The diffractive optical element in this case has a lattice constant or pixels with a pixel size. Each lattice constant or Each pixel focuses and directs the light of the total angle of incidence of the optical arrangement by diffraction in at least one direction. The optical arrangement can be used, for example, in a LIDAR device for receiving a reflected light wave. Further areas of application may be, for example, removal and speedometers. An incoming light wave can in this case have any wavelength in the visible or invisible spectrum. Possible wavelengths of the light wave may be, for example, when using laser beams in the range of 150 nm to δθθμηη. The diffractive optical element may for example be a diffraction grating, which may be embodied as a transmission grating. Such a diffraction grating may in this case be a laminar grid or, for example, a wire grid with a lattice constant or with a pixel size which is adapted to the wavelength of the light wave and the detector. The optical function of the diffractive optical element may be, for example, to focus or to focus the light wave by diffraction. Furthermore, as a possible optical functions also a spreading of the light wave to a plurality of areas of the detector or to a plurality of detectors, correction of aberrations or selective transmission based on the wavelength of the light wave or an angle of incidence of the light wave conceivable.

According to one embodiment, the diffractive optical element of the optical arrangement is designed as a hologram for deflecting or focusing a light wave. It should be noted that the diffractive optical element with its applications includes holograms. Holograms can thus be regarded as special applications of diffractive optical elements. A hologram or a holographic optical element can be manufactured technically simple and inexpensive. For example, photolithographic techniques can be used to fabricate the hologram. Alternatively, a holographic printer can make the hologram. For example, the printer may assign a different optical function to each pixel of the hologram.

In another embodiment, the diffractive optical element is implemented as a volume hologram for deflecting or focusing a light wave. As a result, the diffractive optical element can have a particularly high diffraction efficiency. In particular, the volume hologram be executed here as a phase hologram. The volume hologram may have constant or variable angle and / or wavelength selectivity. As a result, the volume element can suppress stray light or interference reflexes and have additional filter functions. The measure of

Selectivity of the angles of incidence and / or the wavelengths and / or the

Filter function can be controlled by material parameters such as thickness and refractive index of the holographic layer or the volume hologram.

According to a further embodiment, the detector has a plurality of detector cells which are distributed uniformly or non-uniformly along the surface of the detector. Here, the detector may be constructed as an array or a matrix of a plurality of sensors or detector cells, which allow to detect an incident light wave location-dependent. The sensors may be, for example, CCD, CMOS, APD or SPAD sensors.

According to a further embodiment, the receiving optics focuses incoming light waves via at least one lens element on the at least one diffractive optical element. As a result, the diffractive optical element can be irradiated in accordance with the angle of incidence so that the efficiency of the device can be improved.

In a preferred embodiment, the diffractive optical element has a flat or uneven surface. In this case, the surface may have, for example, a surface structure. Preferably, the diffractive optical element may be implemented as a volume hologram having a flat or uneven surface. As a further possibility, the volume hologram can have at least one uneven surface due to a curved shape. The surface structure is preferably in the range of nano, micro or millimeters. When using an uneven surface with, for example, a curvature, a diffraction behavior of the diffractive optical element can be additionally influenced. As a result, the diffractive optical element can be adapted to different configurations.

Alternatively, the diffractive optical element can also be provided on both sides with a surface structure. In this case, the respective surface can optionally be flat or uneven. According to a preferred embodiment, the optical function varies along the surface of the diffractive optical element. As a result, for example, different gliding constants or pixel sizes may be present at one edge of the surface of the diffractive optical element than in a central region of the surface. Thus, the light waves in the edge region can be influenced differently than in a central region of the surface of the diffractive optical element. In a further embodiment, the surface of the diffractive optical element has at least two superimposed optical functions.

As a result, the diffractive optical element can simultaneously have a plurality of optical functions. This can be next to the diversion and

Focusing, for example, realize filter functions. Consequently, by the design of the diffractive optical element also

Aberrations are corrected.

According to a further embodiment, the diffractive optical element has an optical function which is dependent on a wavelength of the at least one light wave

Permeability of the diffractive optical element can be adjusted so that only light waves with a defined wavelength can pass through the diffractive optical element. In addition, the optical function can be adjusted in such a way that the light wave is deflected differently or focused differently depending on the location. For example, a

Deflection of the light wave in an edge region of the diffractive optical element stronger and in a central region, for example in the region of an optical axis of the diffractive optical element, are made weaker. Furthermore, this can also be an additional

Filter effect can be achieved.

In one embodiment, each detector cell is to be illuminated by at least two pixels of the diffractive optical element. As a result, in applications with low immunity requirements, assuming a poorer signal-to-noise behavior, multiple light waves can occur

Hologram pixels are each focused on a detector cell. This will Each detector cell exposed particularly strong and can be made smaller or read faster. Alternatively, the detector itself may be made smaller. In this case, the detector cells can remain the same or be made larger,

According to another aspect of the invention, there is provided a LIDAR apparatus for transmitting and receiving at least one lightwave having at least one rotatable or pivotable lightwave source and an optical assembly.

By using an optical arrangement according to an aspect of the invention in a LIDAR apparatus for transmitting and receiving

Light waves, a diffractive optical element is used with at least one optical function. By virtue of this measure, an incident light wave can be deflected and focused onto a detector by diffraction or diffraction, so that the area of the detector can be smaller than an optical arrangement which consists only of element elements. By using smaller detectors and reducing lenses in the beam path of the optical assembly, the manufacturing cost of the LIDAR device can be reduced.

In one embodiment, the optical assembly is synchronously rotatable or pivotable with the at least one lightwave source. As a result, for example, the beam path for the transmission of a light wave through the light wave source and the reception of a reflected light wave can be shared by the optical arrangement. The rotation or pivoting can alternatively be done by variable deflection of the light wave.

For example, a deflecting mirror can rotate or pivot.

This embodiment is technically easy to implement.

The following are based on highly simplified schematic

Representations preferred embodiments of the invention explained in more detail. Show here

Fig. 1 is a schematic representation of an optical arrangement according to

a first embodiment, 2 shows a schematic illustration of an optical arrangement according to a second exemplary embodiment.

Fig. 3 is a schematic representation of an optical arrangement according to

a third embodiment,

Fig. 4 is a schematic representation of a LIDAR device with a

Optical arrangement according to the first embodiment

In the figures, the same constructive elements each have the same reference numerals,

FIG. 1 shows a schematic representation of an optical arrangement 1 according to a first exemplary embodiment. In particular, a beam path 2 in edge regions of the optical arrangement 1 is indicated, which defines an incident angle β / 2. Thus, an incoming light wave at the angle of incidence β / 2 can be deflected or focused via a receiving optical system 4 onto a diffractive optical element 6 and then onto a detector 8. The receiving optics 4 is designed here in the form of a convex converging lens.

Alternatively, the receiving optics 4 may also comprise a group or a system of convex and / or concave lenses, which, in addition to concentrating the light wave, also counteract aberrations such as aberrations or astigmatism. The diffractive optical element 6 according to the exemplary embodiment is a hologram or a holographic optical element 6, which is arranged at a distance 10 from the receiving optical system 4. The distance 10 is selected such that when an incoming light wave, the diffractive optical element 6 is completely illuminated or illuminated. The diffractive optical element 6 includes focusing as an optical function and diffracts the incoming light wave to strike the detector 8. The detector 8 has a rectangular shape and consists of a plurality of detector cells 18. The hologram 6 has a plurality of hologram pixels 16 in which the optical function is stored. The optical function is stored here in each hologram pixel 16 and in this embodiment is the same in each hologram pixel 16. Alternatively, the optical function may vary locally along an extent of the hologram 6. Thus, for example, the incident light wave can be local in

Depending on the optical function of the illuminated hologram pixels 16 deflected in different directions or with different focal lengths be focused. The distances 10, 12 between the receiving optics 4, the hologram 6 and the detector 8, and the hologram pixels 18 and the size of the detector cells 18 are adapted to each other and a wavelength of the light wave. Here, each hologram pixel 16 is associated with a detector cell 18 and the number of detector cells 18 corresponds to the nxn

Hologram pixels 16. A reduction of an area of the detector 8 by an interposition of a hologram 6 results from the ratio:

Size_hologram_pixel = n * size_detector_cell

This results in a reduction of the area of the detector 16 by

Using the hologram 16;

The size of the detector cells 18 can be increased hereby _» so

Deviations from the defined wavelength of the light wave can be taken into account, for example, by wavelength shifts caused by temperature changes or batch deviations or manufacturing surges.

FIG. 2 shows a schematic representation of an optical arrangement 1 according to a second exemplary embodiment. In contrast to the first exemplary embodiment of the optical arrangement 1, here the hologram 6 has locally varying optical functions. The hologram 6 is divided into two areas, each of which directs the incoming light wave to the entire area of the detector 8. As a result, the detector cells 18 can be illuminated with a double light intensity, so that the detector cells 18 can be made smaller. Thus, the area of the detector 8 can be downsized. For the sake of clarity, only the deflected beams 20 of one half of the

Hologram 6 shown.

With worse signal-to-noise behavior, this configuration is particularly suitable for applications that are unproblematic in terms of interference. Examples include indoor applications or applications with low Range. Alternatively, variants are possible in which three or more hologram pixels 16 illuminate a detector cell 18.

FIG. 3 shows a schematic representation of an optical arrangement 1 according to a third exemplary embodiment. In contrast to the first and second embodiments in this case no receiving optics 4 is used. Rather, the hologram 6 or the diffractive optical element 6 has a

parabolic curvature on and is thus contrary to the previous one

Embodiments not executed in the form of a flat Fliehe. The optical function of the hologram pixels 16 here varies along the local extent of the hologram 6, so that the at least one light wave is focused on the detector 8.

FIG. 4 shows a schematic representation of a UDAR device 24 with an optical arrangement 1 according to the first exemplary embodiment. The LIDAR device 24 has a lightwave source 26, here a laser for emitting coherent lightwaves. The entire device 24 is designed pivotable according to the embodiment, whereby a certain angle on objects 28 and their speed can be sampled. For the determination of the speed, a change of a transit time measurement over the distance to the object 28 can be carried out and from this the speed can be calculated. In particular, the optical serves

Arrangement 1 as a receiving arrangement for receiving reflected

Light waves 32. If, for example, a light wave 30 generated by the laser 26 strikes an object 28 or obstacle 28, then the light wave 30 is partially reflected. The reflected light wave 32 can thus reach the receiving optics 4. The receiving optics 4 focuses the light wave 32 on the hologram 6. The hologram 6 can in turn correct optical errors and forward the light wave 32 to the detector so that the reflected light wave 32 can be optimally detected. From the difference in the transit times of the generated light wave 30 and the reflected light wave 32, the distance and, in the case of a large number of measurements, the speed and the contour of the object 28 can be determined.

Claims

claims

1. Optical arrangement (1) for receiving light waves, with a

Receiving optics (4) for focusing at least one incoming light wave (32) on a surface of a detector (8) for detecting the at least one light wave (32), characterized in that at least one diffractive optical element (6) with a planar extension between the

Receiving optics (4) and the detector (8) is arranged, wherein the at least one diffractive optical element (6) has a surface with a

Having a surface structure with at least one optical function,

2. An optical arrangement according to claim 1, wherein the diffractive optical element (6) is designed as a hologram for deflecting or focusing a light wave (32).

3. Optical arrangement according to one of claims 1 or 2, wherein the diffractive optical element (6) as a volume hologram for deflecting or

Focusing a light wave (32) is performed.

4. An optical arrangement according to one of claims 1 to 3, wherein the detector (8) has a plurality of detector cells (18) which are distributed uniformly or non-uniformly along the surface of the detector (8).

5. An optical arrangement according to one of claims 1 to 4, wherein the

Receiving optics (4) incoming light waves (32) via at least one

Lens element focused on the at least one diffractive optical element (6).

6. An optical arrangement according to one of claims 1 to 3, wherein the diffractive optical element (6) has a flat or uneven surface with a

Surface structure along the surface has.

7. An optical arrangement according to any one of claims 1 to 6, wherein the optical function varies along the surface of the diffractive optical element (8).

8. Optical arrangement according to one of claims 1 to 7, wherein the Oberfliche the diffractive optical element (6) has at least two superimposed optical functions.

9. An optical arrangement according to one of claims 1 to 8, wherein the diffractive optical element (6) has an optical function which is dependent on a wavelength of the at least one light wave (32)

10. An optical arrangement according to one of claims 1 to 9, wherein at least two pixels (16) of the diffractive optical element (6) are focused on each detector cell (18).

1 1. LIDAR device (24) for transmitting and receiving at least one light wave (30, 32) with at least one rotatable or pivotable

Lightwave source (26) and with an optical arrangement (1) according to one of the preceding claims.

12. LIDAR device according to claim 1 1, wherein the optical arrangement (1) with the at least one Lichtwellenqueile (26) is synchronously rotatable or pivotable.