WO2019141646A1

WO2019141646A1 - Optical sensor system, in particular for a lidar system in a vehicle, and method for operating same

Info

Publication number: WO2019141646A1
Application number: PCT/EP2019/050861
Authority: WO
Inventors: Fabian Utermoehlen; Stefan Leidich
Original assignee: Robert Bosch Gmbh
Priority date: 2018-01-16
Filing date: 2019-01-15
Publication date: 2019-07-25
Also published as: DE102018200640A1

Abstract

The invention relates to an optical sensor system (100), in particular for a LIDAR system in a vehicle, comprising a light source (112), a deflecting device (114), a receiving optical system (108), and a detecting device (110). The sensor system (100) is characterized in that the light source (112) is designed to provide light (102) with an adjustable wavelength, and the deflecting device (114) is designed to deflect the light (102) depending on the wavelength.

Description

description

Optical sensor system, in particular for a LIDAR system in one

Vehicle, and method of operating the same

Field of the invention

The invention relates to an optical sensor system, in particular for a LIDAR system in a vehicle, and a method for operating the

Sensor system.

State of the art

An optical sensor system may scan a detection area using a light beam. For example, a LIDAR system (Light Detection And Ranging) in a vehicle can be used to optically measure distances to objects or a speed of the vehicle by means of a suitably designed optical sensor system. For this purpose, the light beam can be pivoted, for example, line by line through the detection area. When the light beam strikes objects, a distance to the objects can be determined over a running time of the light. To move the light beam, a source of the light beam or a mirror can be rotated about an axis of rotation aligned transversely to the light beam. About the

Distance and an angular position of the light source or the mirror, a position of the object in the detection area can be determined.

Disclosure of the invention

KU: GR Against this background, an optical sensor system and a method for operating an optical sensor system according to the independent claims are presented with the approach presented here. Advantageous developments and improvements of the approach presented here emerge from the description and are described in the dependent claims.

Advantages of the invention

Embodiments of the present invention may advantageously enable to provide an optical sensor system without moving parts. The sensor system can be made small and swivel its scanning light beam quickly. A scanning direction can be changed quickly because no inertia of moving parts has to be overcome.

It is an optical sensor system, in particular for a LIDAR system in a vehicle, proposed which a light source, a

Deflection device, a receiving optical system and a detection means and characterized in that the light source is adapted to provide light with an adjustable wavelength and the deflection device is adapted to deflect the light as a function of the wavelength.

Furthermore, a method for operating an optical sensor system, in particular in a LIDAR system of a vehicle, presented according to the approach presented here, which is characterized in that the light source is driven to provide light with a certain wavelength, the deflection device, the light in Dependence on the

Distracting wavelength, a reflection of the light using the

Detecting means is detected and imaged in an electrical signal, and a distance to a light-reflecting object over a period between the provision of the light and the reception of the reflection is determined, wherein a direction to the object using the wavelength of the light and a deflection characteristic the

Deflection is determined. Ideas for embodiments of the present invention may be considered, inter alia, as being based on the thoughts and findings described below.

In a scanning optical sensor system, light in the form of an angularly movable light beam, for example as a laser beam or as collimated light, is emitted into a detection area of the sensor system. The light beam projects a spot of light onto at least the first surface it encounters. The light is scattered in the spot of light. The point of light is thereby itself a passive light source. The light spot also reflects undirected light against a direction of the light beam, ie back to the sensor system. At the sensor system, the reflected light is collected and detected a duration of the light. From the runtime, a distance to the light spot can be determined. If the light beam does not hit any surface, it will not

Point of light projected. The light beam can be emitted pulsed.

By pivoting the light beam, the one impact point of the light beam changes in the detection area. If the light beam hits an object to be detected, the distance to the light spot on the object is determined. The object can be hit in succession at several locations and the distance can be determined. This results in a

Point cloud of distance values and directional values.

In the concept presented herein, the beam is at least in one

Spaced spatial direction without a movement of a component. The direction of the light beam is set by adjusting the wavelength of the light emitted by the light source or a frequency of the light.

The deflection device may be a diffractive element for

Have wavelength-dependent bending of the light. For example, the diffractive element may be an optical grating configured to diffract the light in a diffraction direction by a wavelength-dependent diffraction angle. In a diffractive element, the light is due to its

Wave property bent. In mixed light with multiple wavelengths, the individual wavelength components are diffracted into different diffraction angles or directions and thus a spectrum of light visible. The diffractive element can deflect the light one-dimensionally. So points can be scanned on a line.

The deflection device may further comprise an angularly movable element for adjusting a deflection angle transverse to a diffraction direction of the diffractive element. An angularly movable element may be a movable mirror and / or a movable diffractive element. The angularly movable element can be angularly movable transversely to the diffraction direction. The diffractive element can be arranged, for example, on the movable mirror. The diffractive element may also be spatially separate from the mirror. By two-dimensional deflection of the light, several adjacent lines in the detection area can be scanned.

The detector may be an array of different ones

Wavelengths have tuned receiving structures. The reflection can be detected by using the reception structure of the detection means tuned to the wavelength of the emitted light. A receiving structure can only light in its intended

Wavelength range received. The receiving structure has a matched to the respective wavelength filter element and a detector. The receiving structure can receive light from a wide angle range. Extraneous light with other wavelengths is reliably prevented. This allows a very sensitive detector to be used. Because only one

Wavelength is emitted, always only the signal of a

Receiving structure are evaluated. This reduces the required

Computing power and from one receiving structure to another

Tuning wavelength received extraneous light can be ignored.

The array can be essentially one-dimensional. The receiving optics may be configured to concentrate reflected light onto a focus area aligned with the array. The focus area may substantially correspond to a shape of the array. In particular, the focus area may be line-shaped and concentrate the reflected light along the array. This will expose the whole array. The receiving optics can, for example, a

Cylindrical lens have. A receiving structure can be at least one on the respective

Wavelength tuned resonator for filtering the

Wavelength range of the reflected light. A resonator only passes a certain wavelength range around its resonance wavelength. The wavelength range can pass through the resonator approximately lossless. The resonator may be, for example, a ring resonator. The resonator may have a coupling-in structure for coupling in the light and a coupling-out structure for coupling out the light. The

Resonant wavelength can be adjusted over a length of the resonator. In particular, a circumference of the ring resonator can determine its resonance wavelength. The resonator can also be formed between two reflective surfaces.

The resonator may be doped, in particular, the resonator may be formed with a doped solid. Due to the doping light of certain wavelengths can be amplified. Thereby, the resonator can amplify light with the tuned wavelength range. The amplification can be done without the external energy input, in particular without external pumping, apart from the light coupled into the resonator. The gain can improve a signal-to-noise ratio of the detector. So even weak reflections can be detected.

A receiving structure may include a funnel for concentrating the reflected light. In a funnel, the light of a large incident surface is collected on a small exit surface, thus increasing illuminance at the exit surface. The funnel can consist of light-reflecting material or surfaces of the funnel can with light-reflecting

Be coated material.

It should be noted that some of the possible features and advantages of the invention are described herein with reference to different embodiments as a sensor system and as a method of operating the sensor system. One skilled in the art will recognize that the features may be suitably combined, adapted, or interchanged to others

To arrive embodiments of the invention.

Brief description of the drawings Embodiments of the invention will now be described with reference to the accompanying drawings, in which neither the drawings nor the description are to be construed as limiting the invention.

FIG. 1 shows an illustration of an optical sensor system according to an embodiment; FIG. and

FIG. 2 shows an illustration of a sensor system with a two-dimensional deflection device according to an exemplary embodiment.

The figures are only schematic and not to scale. Like reference numerals in the figures designate the same or equivalent

Characteristics.

Well known LiDAR macroscanners, where all the required optical

Elements as well as the laser and the detector sit on a rotor, but also scanners, in which only one mirror rotates for beam deflection. In either case, a beam is emitted by a pulsed light source (e.g., laser) and its reflection is detected to provide a distance measurement and capture a "picture" of the scene. Conventional systems can use a so-called coaxial arrangement. At the same time, the reflected light is guided via the light path of the emitting optics. In order to collect enough light in the receiver, the components of the light path are correspondingly large.

Micromirrors have not been used for the receive path so far. The

Use of biaxial arrays requires a large detector due to lens size and magnification. Since this one would not be fast enough for a pulse measurement and on the other hand would collect the optical noise power, for example, from the sun or other extraneous light sources of the overall scene, is in such arrangements

Detector array used. In both embodiments, the pulsed beam is deflected both horizontally and vertically to scan an object. Micromirrors can be used to deflect the beam. Micromirrors require little space, but provide at least in one axis a limited deflection of the beam. Embodiments of the invention

1 shows a representation of an optical sensor system 100 according to one exemplary embodiment. The sensor system 100 is designed to a

Detection range of the sensor system 100 with light 102 to scan. When the light 102 strikes an object 104, the light 102 is scattered as a reflection 106 on the object 104. A portion of the reflection 106 is reflected back to the sensor system 100. The light arriving at the sensor system 100 of the reflection 106 is concentrated by a receiving optical system 108 of the sensor system 100 to a detection device 110 of the sensor system 100. In the

Detector 110, an electrical received signal is generated when a light intensity of the reflection 106 is greater than a threshold value. A

Distance between the sensor system 100 and the object 104 may be calculated using the transit time of the light 102 to the object 104 and the transit time of the reflection 106 from the object 104 to the detector 110.

The light 102 may be, for example, laser light. In particular, the light 102 may be emitted from a light source 112, for example in the form of a laser or a laser diode, which is variable with respect to the wavelength of the emitted light, i. trimmable, is. Preferably, the wavelength of the emitted light can be varied over several nanometers, several tens of nanometers or even up to several hundred nanometers. For example, the light may be emitted in the visible range, UV, NI R and / or I R.

After the light 102 has been emitted from the light source 112 of the sensor system 100, the light 102 is laterally deflected in a deflector 114 of the sensor system 100 to scan the detection area. Here, the light source 112 generates light 102 having a selectable wavelength. The light 102 strikes the deflection device 114, from which it is deflected laterally depending on the wavelength in a diffraction direction. Light 102 having a first wavelength is deflected by a first angle. Light 102 having a second wavelength is deflected by a second angle. Through a change in the

Wavelength is achieved by changing the angle. The light 102 is deflected one-dimensionally. A deflection characteristic of

Deflector 114 and one of the light source 112 bereitstellbarer

Wavelength range define lateral limits of the detection range. A light output provided by the light source 112 and a sensitivity of the Detector 110 determines a detection range of the

Sensor system 100.

In one embodiment, the light 102 is diffracted at a diffractive element 116 of the deflector 114 wavelength-dependent in the diffraction direction. The diffractive element 116 is, for example, an optical grating. The deflector 114 has no moving parts. Cross to the

Diffraction direction, the light 102 is not deflected wavelength independent.

The receiving optics 108 collects the light reflected from the object 104. In a focus of the receiving optics 108, the reflected light is concentrated. The detection device 110 is in the range of the focus

arranged.

In one embodiment, the detection device 110 has a plurality of reception structures 118. The receiving structures 118 are on

tuned different design wavelengths. Thus, each leaves

Receive structure 118 only light within a narrowband

Wavelength range by the tuned design wavelength to a detector 120 through.

In one embodiment, the light source 112 for driving the sensor system 100 is driven to provide, in a temporal sequence, light 102 having wavelengths to which the receive structures 118

are coordinated. Alternatively, the receiving structures 118 are on

Tuned design wavelengths, which can provide the light source 112. Thus, the received signal at that receiving structure 118 can be tapped, which is tuned to the currently provided wavelength, since on the one hand by the other receiving structures 118 no useful signal is provided and on the other hand so disturbing influences are reduced by extraneous light.

Since it is known in which direction the light 102 has been emitted due to the deflection characteristic of the deflector 114 and the wavelength of the light 102 provided, the direction to a point of incidence of the light 102 on the object 102 calculated at runtime can also be known Object 104 can be assigned. A sequence of several light pulses provided with different wavelengths becomes several Measurements carried out in different directions. The light is fanned out depending on the wavelength. In this case, the light 102 may hit the object 104 or miss the object 104. If the object 104 is missed and no light 102 is reflected, no distance value is determined.

In one embodiment, a single receive structure 118 has at least one tuned to the respective design wavelength

Resonator 122 on. The light incident on the receiving structure 118 is coupled into the resonator 122. When the light contains the design wavelength, the resonator 122 is excited and resonates. Also

Wavelengths of the wavelength range around the design wavelength excite the resonator, but it does not resonate. In particular, when the resonator 122 is excited, light is also decoupled from the resonator 122 and imaged by the detector 120 in the received signal.

The resonator 122 may be, for example, a toroidal resonator. The

Design wavelength is determined by an effective scope of

Toroidal resonator determined. The scope is a multiple

Design wavelength.

The light may be concentrated by a funnel 124 in the direction of the resonator 122. In this case, the light is reflected on inner walls of the funnel 124 in the direction of a center of the funnel 124. The light may be coupled into a light guide 126 which directs the light to the resonator 122.

The light guide 126 extends at least in sections tangentially to the

Resonator 122. As a result, the light is coupled into the resonator 122. For decoupling, another optical fiber 128 can be used. The further optical waveguide 128 also runs at least in sections tangentially to the resonator 122 and leads to the detector 120. As a result, the light is coupled out of the resonator 122.

FIG. 2 shows a representation of a sensor system 100 having a

two-dimensional deflector 114 according to one embodiment.

The sensor system 100 essentially corresponds to the sensor system in FIG. 1. In addition, the deflector 114 has an angularly movable element 200 which deflects the light 102 transversely to the diffraction direction. Thus, the sensor system 100 can scan the detection area two-dimensionally. In the diffraction direction, the angle is set over the wavelength of the light. Transverse to the diffraction direction, the angle is set via an angular position of the element 200.

In one embodiment, the diffractive element 116 is on the

arranged angular movable member 200 and is moved by this.

Alternatively, the elements 116, 200 may be arranged one behind the other.

In one embodiment, the receiving optics 108 include a cylindrical lens 202 that produces a linear focus area. The focus area is aligned with the array of receive structures 118. As a result, reflected light is incident on each receiving structure 118. The focus area may be larger than the array. Thus, even with two-dimensional deflection, the reflection 106 falls on the receiving structures 118.

In one embodiment, the resonator 122 is doped with a dopant material. The doping material is excited by coupled light to illuminate and amplifies the coupled light. The light emitted by the doping material may have a different wavelength than the design wavelength.

In other words, a LiDAR system is presented which includes a tunable wavelength laser that is deflected via a diffractive optical element 116 (e.g., a grating) and interacts with an object 104. Via a separate reception path, the beam is then at least one

one-dimensional detector array 110 and fed to a detector 120 via a funnel 124 and a narrowband resonant structure with optional gain. The adjustable wavelength of the laser in conjunction with the diffractive element 116 results in a direct

Correlation of wavelength and location of the beam on the object 104. If a two-dimensional image of the scene is to be taken, the diffractive element 116 is applied to a micromirror.

An adjustable wavelength laser, a diffractive optic and an at least one-dimensional, narrow-band detector array 110 are used for the LiDAR system. Since a correlation of wavelength and location results directly from this arrangement, with an ID LiDAR an additional beam deflection can be dispensed with. For a 2D LiDAR, one is

(micro) mechanical beam deflection only required in one direction. The wavelength selectivity of the filter element in the receiving path results in a very high sensitivity, since the detector shown here is Fremdlichtrobust. The filter element may be made using MEMS and / or Si

Technology to be made. Due to the wavelength-selective deflection, the sensor system 100 has few to no moving parts and builds very small.

The system consists of a laser of continuously varying frequency or wavelength, which generates a pulsed laser beam. This is deflected via a diffractive element 116 at an angle corresponding to the wavelength. The diffractive element 116 is preferably a grid. A deflected beam then strikes the object 104 and then interacts as a reflected or scattered beam with an optical system.

In conventional Li DAR systems, a narrow-band bandpass filter is arranged here to separate extraneous light, in particular sunlight, from the useful beam of the frequency. Such a filter requires that it be able to filter light from a wide range of angles. Since the bandwidth of optical filters depends strongly on the angle of incidence, the filter limits the signal-to-noise ratio (SN R) of the overall system. Compared to a conventional filter whose filter effect depends little on the angle of incidence, the approach presented here is inexpensive.

In the approach presented here, after interaction with the optical system, the beam interacts with an array 110 of 100 to 1000 receiving structures 118 arranged side by side. The receiving structures 118 are for example 10 μm wide and 0.1 mm to 1.0 mm high. The array 110 thus has a width of 5 mm to 10 mm and a height of 0.1 mm to 1 mm.

Each of the receiving structures 118 each includes at least one hopper 124, e.g. micromechanically can be realized as Taper or Einkoppler.

At the end of the funnel 124 is an optical waveguide 126, which acts as a coupling element in a ring resonator 122. This ring resonator 122 is preferably made of Si or Si0 ₂ and has a diameter adapted to a specific wavelength, which of

Receiving structure 118 to receiving structure 118 varies. The variation is adapted to the deflection characteristics of the diffractive element 116. The diameter of the gyro or ring resonator 122 is in each case selected such that the circumference of the resonator corresponds to an integer multiple of a wavelength of the laser. This results in constructive interference and all other frequency components, which arise for example by extraneous light, are suppressed.

Optionally, the ring resonator 122 may be doped and thus amplify the signal. The gain prior to conversion to an electrical signal has fundamental advantages in terms of noise characteristics

Receive channel, because the noise of the detector 120 is not amplified. Another waveguide 128 acts as an output coupler of the ring resonator 122 and directs a portion of the signal to the detector 120. This may be a photodiode, an avalanche diode or a spad diode.

The combination of adjustable wavelength of the laser with the diffractive element 116 results in a clear correlation of the set wavelength and location of the laser beam on the object 104. It follows that for a distance measurement only the signal of that detector 120

can be evaluated for which currently a laser pulse has been sent.

If a two-dimensional image of the scene is to be taken, the beam is additionally deflected. Here, a deflection element 200 can be used, which contains a micromirror in addition to the diffractive element 116.

The object 104 is compressed with the lens of the optical system and imaged onto the receiving structures 118, so that the second scanning direction does not lead to a significant expansion of the image. This can be achieved by using a cylindrical lens 202 in the optical system. The height of the detector structures 118 of 0.1 mm to 1.0 mm is thus still sufficient. As with the one-dimensional deflection, only the evaluation of a detector 120 is required simultaneously. The knowledge about the place

or the angle in the two scan axes is known by the wavelength of the laser and by the angular position of the mirror.

Finally, it should be noted that terms such as "comprising," "comprising," etc., do not exclude other elements or steps, and terms such as "a" or "an" do not exclude a multitude. Reference signs in the claims are not to be considered as limiting.

Claims

claims

1. Optical sensor system (100), in particular for a LIDAR system in

a vehicle having a light source (112), a deflection device (114), a receiving optical system (108) and a detection device (110), characterized in that the light source (112) is adapted to provide light (102) with an adjustable wavelength and the deflecting means (114) is adapted to control the light (102) in dependence on

Distracting the wavelength.

2. Sensor system (100) according to claim 1, wherein the deflection device

(114) has a diffractive element (116) for the wavelength-dependent bending of the light (102).

The sensor system (100) of claim 2, wherein the diffractive element (116) is an optical grating configured to diffract the light (102) in a diffraction direction by a wavelength-dependent diffraction angle.

4. Sensor system (100) according to one of claims 2 to 3, wherein the

Deflector (114) comprises an angularly movable member (200) for adjusting a deflection angle transverse to a diffraction direction of the diffractive element (116).

5. Sensor system (100) according to one of the preceding claims, wherein the detection device (110) an array of different

Wavelength ranges matched receiving structures (118).

The sensor system (100) of claim 5, wherein the array is substantially one-dimensional, and the receiving optic (108) is configured to focus reflected light onto a focus area aligned with the array.

7. Sensor system (100) according to one of claims 5 to 6, wherein one of the receiving structures (118) at least one of the respective

Wavelength range tuned resonator (122) for filtering the wavelength range from the reflected light.

8. A sensor system (100) according to claim 7, wherein the resonator (122) is doped.

A sensor system (100) according to any one of claims 5 to 8, wherein one of the receiving structures (118) comprises a funnel (124) for concentrating the reflected light.

10. A method of operating an optical sensor system (102) according to

one of the preceding claims, characterized in that the light source (112) is driven to provide light (102) of a certain wavelength, the deflector (114) deflects the light (102) in dependence on the wavelength, a reflection (106) of the light (102) is detected using the detector (110) and imaged in an electrical signal, and a distance to an object (104) reflecting the light (102) over a period of time between providing the light (102) and receiving the reflection (106) is determined, wherein a direction to the object (104) is determined using the wavelength of the light (102) and a deflection characteristic of the deflector (114).

11. The method according to claim 10, wherein the reflection (106) under

Using the matched to the wavelength of the light (104) receiving structure (118) of the detection device (110) is detected.