EP3155449A1

EP3155449A1 - Vehicle lidar system

Info

Publication number: EP3155449A1
Application number: EP15727593.4A
Authority: EP
Inventors: Heiko Ridderbusch
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2014-06-11
Filing date: 2015-05-26
Publication date: 2017-04-19
Also published as: DE102014211073A1; CN106461784A; US20170090034A1; JP2017525940A; KR20170010064A; US10386488B2; WO2015189024A1

Abstract

The invention relates to a vehicle lidar system (101) comprising: • a solid-state laser (103) with a brightness of at least 100 kW/(mm ²sr), which is designed to emit laser pulses with a wavelength of at least 900 nm and a maximum power per laser pulse of at least 50 W, • at least one displaceably mounted mirror (105) for deflecting the laser pulses towards objects to be detected (111), and • a receiver (113) for detecting the laser pulses reflected by the objects.

Description

Description title

Vehicle lidar system

The invention relates to a vehicle lidar system and to a use of the vehicle lidar system.

State of the art

From the published patent application DE 10 2007 004 609 A1 is a laser and

Optical system known for use in vehicle-based lidar systems. The system includes a semiconductor laser array and a suitable lens or other optical system. The system is operated in a way to replace lidar laser systems employing mechanically rotated or shifted reflective optics.

Disclosure of the invention

The object underlying the invention can be seen to provide a vehicle lidar system.

The object underlying the invention may further be seen to indicate a use of the vehicle lidar system.

These objects are achieved by means of the subject matter of the independent claims. Advantageous embodiments of the invention are the subject of each dependent subclaims.

In one aspect, there is provided a vehicle lidar system comprising: a solid-state laser with a brilliance of at least 100 kW / (mm ² sr), which is designed to emit laser pulses having a wavelength of at least 900 nm, preferably of at least 1000 nm, and a maximum power per laser pulse of at least 50 W,

at least one deflectably arranged mirror for deflecting the laser pulses in the direction of objects to be detected,

a receiver for detecting the laser pulses reflected from the objects.

In another aspect, the vehicle lidar system is used to detect objects around a vehicle. In particular, a transit time measurement of the laser pulses is carried out by means of the vehicle lidar system, so that advantageously a distance measurement can be detected

Objects can be performed.

In another aspect, a vehicle including the vehicle lidar system is provided.

By using the solid-state laser with the above properties for the vehicle lidar system, the technical advantage in particular that within an eye safety directive according to DIN 60825 a high range of up to, for example, 200 m and a high resolution of, for example, <0.3 °, preferably <0.15 ° are possible. Furthermore, at wavelengths greater than 900 nm, in particular greater than 1000 nm, the

As a rule, the burden on the human eye is no longer so great due to the laser radiation, so that an eye-safe laser class 1 can be achieved advantageously even at higher pulse powers and energies, which in turn increases the range of the system. Furthermore, at wavelengths greater than 900 nm, preferably greater than 1000 nm, an intensity of the solar radiation is reduced by a factor of approximately 2, so that a signal-to-noise ratio of the vehicle lidar system becomes better. This is in comparison to known laser systems for lidar systems, for example edge emitters, which emit at a wavelength of 850 nm to 950 nm. The provision of the deflectable mirror in particular has the technical advantage that an illuminating surface or a region which can be illuminated by means of the laser pulses, in which the objects can be detected, can not be deflected by the mirror and / or a mirror, for example more depends on a specific beam size of the solid-state laser. Accordingly, the

Solid state laser can be sized smaller. In particular, a

Beam diameter of the laser radiation are smaller dimensions. Furthermore, the solid-state laser can be installed at any position in the vehicle. Because the deflection of the emitted laser pulses in the direction of objects to be detected is effected by means of the mirror. That is, an installation location of the solid-state laser in the vehicle is independent of the desired area to be illuminated in the vicinity of the vehicle.

According to one embodiment, it is provided that the solid-state laser has a brilliance of at least 1 MW / (mm ² sr). The brilliance of the solid-state laser is preferably between 100 kW / (mm ² sr) and 1 MW7 (mm ² sr). In general, a higher brilliance advantageously means a higher one

Detection range of the vehicle lidar system. This means that advantageously objects can be detected or detected at distances from the solid state laser of up to 200 m and more. The brilliance can be referred to in particular as a beam quality. The brilliance in optics and in laser technology usually describes the bundling of a beam of electromagnetic radiation, here the laser beam.

According to one embodiment, it is provided that a maximum power per laser pulse is between 50 W and 100 W. Again, higher maximum power means greater range. A maximum performance per

Laser pulse means that even laser pulses with a lower power can be emitted. The maximum possible power per laser pulse is 50 W, 100 W or a value between 50 W or 100 W.

According to a further embodiment, it is provided that the laser pulses have a duration of <100 ns, preferably of <50 ns, in particular of <10 ns, for example of <1 ns, in particular between 2 ns and 20 ns, preferably between 2 ns and 4 ns, for example 2.2 ns. Typically, smaller pulse durations provide improved accuracy or resolution in terms of range finding. According to one embodiment, it is provided that the solid-state laser is electrically and / or optically pumpable or excitable. This means that the solid-state laser is or will be electrically or optically pumped or excited.

In another embodiment, it is provided that the solid-state laser is designed as a vertical resonator surface-emitting laser. Such a

Vertical cavity surface emitting laser is commonly referred to as a vertical cavity surface emitting laser. The corresponding abbreviation is: VCSEL. By providing such a vertical emitter, the abovementioned beam quality or brilliance can advantageously be effected in a particularly simple manner in comparison to known edge emitters. This especially in ranges of the vehicle Lidar system of> 50 m, in particular up to 200 m in the aforementioned resolution of

for example, 1 x 1 m ² at 200 m. A further advantage is that such a vertical emitter, in contrast to the known edge emitter is more robust.

For example, a VCSEL can not be destroyed by an overcurrent and thus to high pulse power at a Auskoppelfacette. Rather, a VCSEL shows at most a thermal roll-over. Such a thermal roll-over does not lead to destruction and is advantageously reversible. Furthermore, a VCSEL on wafer level scale can be produced and tested, so that

Manufacturing costs are scalable, in particular similar to high-power LEDs are scalable. In a thermal roll-over, the laser material is hotter, thereby reducing the efficiency, with the result that it is even hotter. From a certain reduction of Wrkungsgrades the laser goes out. LED and vertical emitter radiate the power upwards. During production, the radiation properties can also be tested if the entire wafer has not yet been singulated. In contrast, a beaming

Edge emitter to the side and testing is therefore not possible. It is therefore necessary to isolate (cut) the wafer to test the laser. Therefore, a vertical emitter can be tested if it is still arranged on the wafer, ie before singulation. Because he radiates upwards. Furthermore, it is advantageously particularly easy to generate or generate short pulses of <1 ns pulse rise time with such vertical emitters. This in particular at a higher duty cycle compared to known edge emitters. Duty Cycle (duty cycle) is the ratio between "in operation, ie on" and "not in operation, that is off". In one embodiment, a duty cycle of the

Solid state laser between 1% to 2%. Known edge emitters for lidar applications are nowadays able to produce only less than 1% or less (eg OSRAM SPL PL90_3 with a duty factor of up to 0.1%).

Furthermore, by means of such a vertical emitter, the inventive brilliance or beam quality at output wavelengths (ie wavelength of the laser pulses) of greater than 900 nm, in particular greater than 1000 nm can be achieved, preferably at 1050 nm to 1100 nm.

In the context of the present invention, a solid-state laser in particular comprises a laser-active material which is incorporated in a crystal lattice or other material. Examples of such solid-state lasers are: Neodymium or Ytterbium-doped yttrium aluminum garnet (Nd: YAG, Yb: YAG). Furthermore, according to other embodiments, the solid-state laser may also be a semiconductor laser. For example, the semiconductor laser may be an aluminum gallium arsenide laser. This emits laser radiation having a wavelength of up to 1100 nm. For example, a semiconductor laser may comprise an indium or a phosphate-doped laser-active material. Such a semiconductor laser emits laser radiation in the wavelength range of> 1000 nm.

In a further embodiment it is provided that the mirror can be deflected in two different directions. As a result, in particular, the technical advantage is achieved that a footprint or the illuminable area can be spanned by these two directions, within which objects can be detected. In particular, the two are

Directions perpendicular to each other. Preferably, only a mirror is provided, which is deflectable in two different directions. According to another embodiment, it is provided that two mirrors are provided which are each deflectable in a different direction. This means that each of the mirrors can be deflected in each case in a different direction. Again, a footprint or a

illuminated area within which the objects can be detected. Since two mirrors are provided here, which can be deflected independently of each other in different directions, a particularly fast detection or detection of objects is made possible. Again, the two directions are preferably aligned perpendicular to each other. Preferably only two mirrors are provided.

Preferably, the two mirrors are each deflectable exclusively in one direction, wherein these two directions are different, in particular aligned perpendicular to each other.

In one embodiment, a plurality of mirrors are provided

in particular the same or, for example, are formed differently.

Embodiments with regard to a plurality of mirrors result analogously from embodiments with regard to a mirror and vice versa. Explanations, features and descriptions in connection with a mirror apply analogously to multiple mirrors and vice versa. This means that when using the singular for mirrors always the plural should be read and vice versa.

In one embodiment, it is provided that the mirror can be deflected magnetically and / or piezoelectrically. By such a magnetic and / or piezoelectric deflectability is a particularly good accuracy and

Speed given in the deflection.

According to one embodiment, it is provided that a diameter of the mirror is greater than or equal to 1 mm, in particular greater than or equal to 3 mm, for example equal to 3.5 mm, for example between 1 mm and 8 mm, in particular between 3 mm and 5 mm. The larger the mirror, the less large is the requirement on the laser (for example the brilliance). The larger the mirror, the more light can be transported via the mirror (with a constant value of brilliance). In another embodiment, it is provided that the mirror can be deflected over at least one angle of 20 °, in particular 30 °.

In particular, it is provided that the mirror is deflectable relative to a center position over at least +/- 10 °, preferably +/- 15 °. The deflectability of the mirror usually corresponds to the illuminable area by means of

Laser radiation. That is, the greater the deflectability, the larger the area that can be illuminated.

In another embodiment it is provided that the mirror a

Has reflectivity of at least 80%, in particular of at least 90%, preferably of at least 95%, in particular of at least 99%. The higher the reflectivity of the mirror, the higher the efficiency of the vehicle lidar system is usually higher. Losses of laser radiation can thus be minimized in an advantageous manner. The reflectivity relates in particular to the laser wavelength, ie to the wavelength of

Laser pulses. That is, the above reflectivities are preferably achieved at least at the laser wavelength.

Such a reflectivity can be effected, for example, by the mirror being coated according to one embodiment, that is to say having a coating, in particular an optical coating. Such a coating may be, for example, a metal coating. In particular, to form such a coating, metal may be vapor-deposited on a mirror substrate. The mirror is in particular coated with a metal, that is to say it has a metal layer, in particular a vapor-deposited metal layer. A metal may be, for example, gold, silver, aluminum. For example, a

Combination of the above-mentioned metals are vapor-deposited on the mirror substrate. That is, the coating may comprise gold, silver, aluminum, and / or any combination thereof. Alternatively or additionally, the coating may comprise one or more dielectric layers. Such dielectric layers preferably comprise a high refractive and a low refractive index material. As a result, an even higher reflectivity can be effected in an advantageous manner. A

Layer thickness of the coating can be, for example, a maximum of 1 μηι. For dielectric layers, for example, the following layer materials magnesium fluoride, silica, alumina,

Zirconia, praseodymium titanium oxide, titanium oxide or zinc sulfide, or a combination thereof. In particular, the coating may comprise a plurality of layers, which are in particular the same or preferably formed differently. In particular, the coating may be formed as a dichroic mirror. Such a mirror is a wavelength-selective mirror and allows only a certain wavelength range. Such a

Wavelength range may be 900 nm to 1200 nm in one embodiment. In particular, a layer thickness of the coating can be less than 50 nm. In particular, layer thicknesses of the coating of 100 nm, in particular of a few 100 nm, for example of up to 200 nm, can be provided.

In another embodiment, it is provided that the mirror is designed as a microelectromechanical mirror. That is, the microelectromechanical mirror is formed as a microelectromechanical element.

According to another embodiment it is provided that a

Evaluation device is formed, which is designed to determine a distance to a detected object based on the detected laser pulses. This in particular by means of a transit time measurement of the laser pulses.

In one embodiment, the vehicle lidar system is used to detect or detect objects around the vehicle. In particular, a transit time measurement of the laser pulses is performed. That is, the solid-state laser emits laser pulses. If these laser pulses hit objects, they are reflected by them. This at least partially in the direction of the receiver, which may also be referred to as a detector. Based on transit time measurements of the laser pulses, a distance between the object and the vehicle lidar system can then be determined in a manner known per se.

In a further embodiment it is provided that the receiver has a CMOS-compatible image sensor for detecting the reflected laser pulses and for capturing an image of a region that can be illuminated by means of the deflected laser pulses. In particular, this embodiment thus encompasses the idea of providing a receiver (which can also be referred to as a detector) for detecting the laser pulses reflected by the objects, the receiver having a CMOS-compatible laser beam.

Image sensor includes, which can detect both the reflected laser pulses and record an image of an area illuminated by the deflected laser pulses area. The CMOS-compatible image sensor according to the invention thus has a dual function: detecting the reflected laser pulses and taking an image. Thus, only a single sensor is needed to provide both a lidar function (especially for range finding) and an image capture function. In contrast, two sensors are necessary in the prior art for the aforementioned functions to be effected or provided. The vehicle lidar system according to the invention is thus smaller and more compact in comparison to the known systems and can therefore be installed in a smaller installation space.

In one embodiment, the CMOS compatible image sensor is a CMOS image sensor.

For a CMOS image sensor, the CMOS process can be used without modification and / or modification. For a CMOS compatible image sensor, the basic CMOS process is applicable, but changes in the process (modification, new process step ...) are possible. This means that the CMOS

Image sensor is manufactured in the CMOS process. The CMOS compatible image sensor was at least partially fabricated in the CMOS process, ie based on the CMOS manufacturing process, with respect to the CMOS manufacturing process changes and / or innovations in the production of the CMOS compatible image sensor were performed.

According to one embodiment, it is provided that the CMOS-compatible image sensor comprises a plurality of pixels, and wherein evaluation electronics are provided, which are designed to read out signals of the pixels of the CMOS-compatible image sensor and, based on the read-out signals To determine distance to a detected object. This will

In particular, the technical advantage causes one for each pixel

corresponding transit time measurement of the laser pulses can be performed. That is, each pixel signal per se can be used to determine the distance to a detected object. In particular, it is provided that a group of pixels is read, wherein the

read signals of the group of these pixels is used to make a

To determine distance to a detected object. It is thus in

Advantageously, a so-called "time of flight (TOF)" - measurement

carried out, in German a transit time measurement.

In another embodiment, it is provided that an optical element for imaging the illuminable region is provided on the CMOS-compatible image sensor. As a result, the technical advantage in particular that the area that can be illuminated is optimally adjusted to the CMOS-compatible

Image sensor can be imaged so that the CMOS-compatible image sensor can detect the entire area that can be illuminated and in this way also detect objects that are located in this illuminable area. The optical element is for example a lens or a mirror, for example a parabolic mirror. Preferably, a plurality of optical elements are provided, which are formed in particular the same or different.

According to another embodiment, it is provided that the optical element has a transmission of at least 95%, preferably> 99%, for a

Having a wavelength range corresponding to the laser wavelength plus minus <20 nm, preferably plus minus <10 nm, the transmission for wavelengths outside the wavelength range being less than 50%,

preferably less than 20%. As a result, in particular the technical advantage is achieved that a signal-to-noise ratio can be increased.

In another embodiment, it is provided that the CMOS-compatible image sensor is designed to detect electromagnetic radiation having a wavelength of at least 900 nm, preferably of at least 1000 nm. This has the technical advantage in particular that the CMOS-compatible image sensor can also detect laser pulses that have a wavelength of at least 900 nm. In this wavelength range greater than 900 nm, the sensitivity to damage to the eye for this electromagnetic radiation is usually reduced, so that when using the vehicle lidar system generally no danger to road users in the vicinity of the vehicle emanates.

In another embodiment, it is provided that the CMOS-compatible image sensor has doped and / or surface-modified silicon as the sensor material. This has the particular technical advantage that such silicon is more sensitive to wavelengths greater than 1000 nm in comparison to undoped or not surface-modified silicon.

Such silicon is known, for example, as black silicon (black silicon) or as pink silicon (pink silicon). For example, sulfur can be provided as dopant.

In a surface modification, a reflectivity through a

Refractive index jump from air to silicon greatly reduced, so that more incoming photons penetrate into the image sensor and then detected accordingly. The surface modification is for example by means of a

Structuring carried out by means of short laser pulses. These laser pulses have, for example, a pulse duration of <10 ns, for example of <1 ns. For example, a surface modification by means of a

Coating be performed. This means that the silicon is coated. By doping the silicon, in particular, the technical effect is caused that thereby an absorption probability for photons is increased, so that a sensitivity of the detector is increased even at longer wavelengths. The invention will be described below with reference to preferred

Embodiments explained in more detail. This shows

Fig. 1 is a vehicle lidar system.

1 shows a vehicle lidar system 101. The system 101 includes a solid-state laser 103, which is referred to as a

Vertical resonator surface emitting laser (VCSEL) is formed. The reference numeral 103 shows once by means of an arrow on a switching symbol which is to symbolically represent the solid-state laser. Furthermore, this shows

Reference numeral 103 to a curly bracket showing a more detailed structure of the vertical resonator surface emission laser. The VCSEL 103 may emit laser pulses upon appropriate excitation.

Furthermore, the system 101 includes a mirror 105, which is referred to as

microelectromechanical element is formed. Such a mirror may also be referred to as a MEMS mirror. The mirror 105 is deflectably arranged. The mirror 105 deflects the laser pulses of the solid-state laser 103 in the direction of objects to be detected. Such an object is identified here by way of example by the reference numeral 11 1. Due to the deflectability of the mirror 105, an illuminable region can be formed by means of the deflected laser pulses. In English, such an illuminable area is also referred to as a "field of view". If objects, here for example the object 11 1, are located within the illuminable area, then these can be detected by means of the vehicle lidar system.

The solid-state laser 103 comprises a vertical emitter 109 with a cavity 107, from which laser pulses are coupled out. The decoupled laser pulses are only symbolically marked by an arrow with the reference numeral 108.

When the mirror 105 is in its center position, the laser radiation reflected by the mirror 105 is indicated by a solid arrow 110. When the mirror 105 is in its maximum possible deflection positions, the reflected

Laser radiation by means of two dashed arrows with the reference numerals 110a and 110b marked. Laser radiation (ie the laser pulses), which is deflected by means of the mirror 105 on the object 11 1, is indicated by a solid arrow with the reference numeral 112. From there, that is from the object 11 1, the laser radiation, so the laser pulses, in the direction a receiver or detector 113 of the system 101. This reflected laser radiation is symbolically identified by the reference numeral 114 by means of a dashed arrow. Based on the running direction of the laser radiation 1 14 in front of the detector or receiver 1 13, a filter 1 15 is provided so that only electromagnetic radiation with a wavelength corresponding to the filter to the receiver 1 13 is transmitted. Here, the filter 1 15 for a wavelength range of plus minus <20nm, preferably plus minus <10 nm, permeable to the laser wavelength and for the other wavelengths (ie not the laser wavelength including the above-mentioned plus-minus ranges) permeable with <50% , preferably <20%.

The receiver 113 is also shown symbolically by means of a switching symbol analogous to the solid-state laser 103. The receiver 13 may comprise, for example, an indium gallium arsenide sensor or a PIN diode or an avalanche photodiode. "PIN" stands for "positive intrinsic negative diode".

It is thus advantageously allows a transit time measurement of the laser pulses, so that a distance 117 between the object 11 and the system 101 can be determined or determined.

The vertical cavity surface emitting laser 103 has a brilliance of at least 100 kW / (mm ² sr) and emits laser pulses of one

Wavelength of at least 900 nm, preferably between 1000 nm to 1100 nm. Furthermore, a maximum power per laser pulse is at least 50 W, preferably between 50 W and 100 W, in particular 100 W. Such high beam qualities or brilliance can be realized or effected, for example, as follows ,

For example, it is provided that the resonator length (cavity) is increased. As a result, less transversal modes can oscillate, which has a positive influence on the beam quality or brilliance. In addition to or instead of the extension of the cavity, a double cavity is preferably provided. In such a double cavity, not only one outcoupling mirror is used for the resonator, but two. Preferably, the inner mirror of the Double cavity has a lower reflectivity for the laser wavelength compared to the outer output mirror of the double cavity. Even with such a double cavity, the oscillation of higher transverse modes is made more difficult by a corresponding design of this double cavity, which advantageously increases a beam quality or brilliance. The double cavity is usually referred to in English as "coupled cavity".

Claims

A vehicle lidar system (101) comprising:

- A solid-state laser (103) with a brilliance of at least 100 kW / (mm ² sr), which is formed, laser pulses having a wavelength of at least 900 nm and a maximum power per

Emitting a laser pulse of at least 50 W,

- At least one deflectable mirror (105) for

Deflecting the laser pulses in the direction of objects to be detected (1 1 1),

- A receiver (1 13) for detecting the of the objects (11 1) reflected laser pulses.

A vehicle lidar system (101) according to claim 1, wherein said solid state laser (103) is formed as a vertical resonator surface emitting laser (103).

A vehicle lidar system (101) according to claim 1 or 2, wherein the mirror (105) is deflectable in two different directions.

Vehicle lidar system (101) according to one of the preceding claims, wherein two mirrors are provided which are each deflectable in a different direction.

Vehicle lidar system (101) according to one of the preceding claims, wherein the mirror (105) is magnetically and / or piezoelectrically deflectable.

Vehicle lidar system (101) according to one of the preceding claims, wherein a diameter of the mirror (105) is greater than or equal to 1 mm, in particular greater than or equal to 3 mm.

7. vehicle lidar system (101) according to any one of the preceding claims, wherein the mirror (105) over at least an angle of 20 °, in particular 30 °, is deflectable

8. vehicle lidar system (101) according to any one of the preceding claims, wherein the mirror (105) has a reflectivity of at least 80%, in particular of at least 90%.

The vehicle lidar system (101) of any of the preceding claims, wherein the mirror (105) is formed as a microelectromechanical mirror (105).

10. Use of the vehicle lidar system (101) according to one of the preceding claims for detecting objects (11 1) in the environment of a vehicle.