DE102019112857A1 - Coaxial optical system for LIDAR measurements (Light Detection and Ranging) - Google Patents

Abstract

A LIDAR system (100) for measuring the range of an object (110) using primary light and secondary light that is reflected off the object (110) is provided. The LIDAR system (100) comprises: - a laser (200) arranged to emit the primary light along a transmission beam (210) to a scanning element (800), - a plurality of detectors arranged to detect the secondary light along a receive beam from the scanning element, a lens (600) positioned between (i) the laser and the plurality of detectors and (ii) the scanning element. The lens (600) comprises: a transmission lens (610), which is assigned to the transmission beam, and a plurality of reception lenses (621, 621a, 621b, 621c, 622, 622a, 622b, 622c), which have a plurality of reception partial beams (330, 331, 332, 333), each of the plurality of receiving lenslets (621, 622) being arranged to focus the respective receiving partial beam (330, 331521, 522) onto a corresponding detector (400, 410) from the plurality of detectors.

Description

TECHNICAL AREA

Various examples of the invention generally relate to LIDAR (light detection and ranging). Various examples of the invention relate specifically to a coaxial optical system with a plurality of detectors for LIDAR.

BACKGROUND

Light detection and ranging (LIDAR; sometimes also referred to as laser ranging or LADAR) makes it possible to provide a 3D point cloud of a scene. Objects can be precisely detected. A distance measurement is possible. Pulsed or continuous wave laser light is sent along a transmission beam and, after reflection on an object, is detected along a reception beam. This enables the distance to the object (z-position) to be determined.

A key process in LIDAR systems is to collimate the light provided for distance measurement, sometimes called primary light, and receive the light emitted by an object, sometimes called secondary light. This can be achieved by focusing the secondary light on a detector.

In coaxial LIDAR structures, off-axis systems can be used in which a detector is arranged off-axis (off-axis) in relation to an axis defined by the laser. In order to achieve the compactness of the laser device, short focal lengths of a lens element in the off-axis LIDAR system may be desirable. However, the achievable focal length for a given lens thickness may be limited, e.g. in off-axis structures where a minimum thickness of the off-axis lens may be required.

In similar or different LIDAR setups, the working area of a system can be affected by the presence of ambient light conditions, e.g. Daylight or night ambient lighting conditions. In the case of LIDAR structures, the achievable range can be determined by the presence of background photons, e.g. Sunlight during daytime operation. This effect can be partially counteracted by using bandpass filters in front of a LIDAR detector. Laser systems used in LIDAR applications, however, can have a drift in the spectral range, which places a limit on the minimum spectral width of bandpass filters.

SUMMARY

Therefore, there is a need for improved lidar systems. There is a need for techniques that overcome or mitigate at least some of the above limitations and disadvantages.

This need is met by the features of the independent claims. The features of the dependent claims define embodiments.

• einen Laser, der angeordnet ist, um das primäre Licht entlang eines Sendestrahls zu einem Scanelement zu emittieren, eine Vielzahl von Detektoren, die angeordnet sind, um das sekundäre Licht entlang eines Empfangsstrahls von dem Scanelement zu detektieren, und eine Linse, die zwischen dem Laser und der Vielzahl von Detektoren und dem Scanelement positioniert ist. Die Linse umfasst:
  • ein dem Sendestrahl zugeordnetes Sendelenslet und eine Vielzahl von Empfangslenslets. Die Vielzahl von Empfangslenslets definiert eine Vielzahl von Empfangsteilstrahlen, wobei jedes der Vielzahl von Empfangslenslets angeordnet ist, um den jeweiligen Empfangsteilstrahl auf einen entsprechenden Detektor aus der Vielzahl von Detektoren zu fokussieren.

In one example, a LIDAR system is provided for measuring the range of an object using primary light and secondary light reflected from the object. The LIDAR system includes:

• a laser arranged to emit the primary light along a transmit beam to a scanning element, a plurality of detectors arranged to detect the secondary light along a receive beam from the scanning element, and a lens interposed between the laser and the plurality of detectors and the scanning element is positioned. The lens includes:
  • a transmitting lenslet assigned to the transmitting beam and a plurality of receiving lenslets. The plurality of receiving lenslets defines a plurality of receiving sub-beams, each of the plurality of receiving lenslets being arranged to focus the respective receiving sub-beam onto a corresponding one of the plurality of detectors.

The plurality of receiving lenslets is thus assigned to the receiving beam.

In other words, the lens is arranged next to the laser and the plurality of detectors in a direction offset towards the scanning element.

• einen Laser, der angeordnet ist, um das primäre Licht entlang eines Sendestrahls zu einem Scanelement des LIDAR-Systems zu emittieren, und eine Vielzahl von Detektoren, die angeordnet sind, um das sekundäre Licht entlang eines Empfangsstrahls von dem Scanelement zu detektieren. Das LIDAR-System umfasst ferner:
  • eine Vielzahl von Bandpassfiltern, die den Detektoren der Vielzahl von Detektoren zugeordnet sind, wobei sich Bandpassbereiche von mindestens zwei der Bandpassfilter voneinander unterscheiden.

In one example, a LIDAR system is provided for measuring the range of an object using primary light and secondary light reflected from the object, the LIDAR system comprising:

• a laser arranged to emit the primary light along a transmit beam to a scanning element of the lidar system, and a plurality of detectors arranged to detect the secondary light along a receive beam from the scanning element. The LIDAR system also includes:
  • a plurality of bandpass filters which are assigned to the detectors of the plurality of detectors, wherein bandpass ranges of at least two of the bandpass filters differ from one another.

Various examples described above can also be combined to form further examples. For example, it is possible for the plurality of bandpass filters to be used in connection with the lens or for the bandpass filters to be integrated into one or more receiving lenslets.

Figure list

• 1 shows schematically a LIDAR system with a coaxial optical system.
• 2 shows schematically an exemplary implementation of the LIDAR system 100 .
• 3 shows another side view of the LIDAR system 100 from 2 .
• 4a and 4b Fig. 13 shows a front view of examples of lenses 600 that are in the LIDAR systems 100 can be used according to the invention, for example those in 1 to 3 shown lidar systems.
• 4c Figure 3 shows a side view cross section of the lens 600 out 4a .
• 5 illustrates a possible effect in a LIDAR system, for example the LIDAR system 100 of the figures 1 to 3 .
• 6th to 8th show different configurations for different bandpass filter characteristics.

DETAILED DESCRIPTION OF EMBODIMENTS

Some examples of the present disclosure generally provide for a variety of circuits or other electrical devices. All references to the circuits and other electrical devices and the functionality they provide from each other are not intended to be limited to encompassing only what is illustrated and described herein. While specific labels may be assigned to the various circuits or other electrical devices disclosed, such labels are not intended to limit the functionality of the circuits and other electrical devices. Such circuits and other electrical devices can be combined and / or separated from each other in any manner based on the particular type of electrical implementation that is desired. It is recognized that any circuit or other electrical device disclosed herein, any number of microcontrollers, a graphics processing unit (GPU), integrated circuits, memory devices (e.g., FLASH, random access memory (RAM), read only memory (ROM), electrically programmable Read only memory (EPROM), electrically erasable programmable read only memory (EEPROM) or other suitable variants thereof) and software that interact with one another in order to carry out the function (s) disclosed herein. In addition, any one or more of the electrical devices may be configured to execute program code embodied in a non-transitory computer readable medium that is programmed to perform any number of the functions disclosed herein.

In the following, embodiments of the invention are described in detail with reference to the accompanying drawings. It is to be understood that the following description of embodiments is not to be understood in a restrictive sense. The scope of the invention is not intended to be limited either by the embodiments described below or by the drawings, which are intended for purposes of illustration only.

The drawings are to be regarded as schematic representations and the elements shown in the drawings are not necessarily shown to scale. Rather, the different elements are shown in such a way that their function and general purpose can be recognized by a person skilled in the art. Any connection or coupling between functional blocks, devices, components or other physical or functional units shown in the drawings or described here can also be implemented by an indirect connection or coupling. A coupling between components can also be established via a wireless connection. Function blocks can be implemented in hardware, firmware, software, or a combination thereof.

1 shows schematically a LIDAR system 100 comprising a coaxial optical system. The LIDAR system 100 can be used to measure the distance of an object 110 using primary light and secondary light shining on the object 110 can be used. The LIDAR system 100 includes a laser 200 (e.g. a laser diode such as an edge emitter diode) that is arranged to shed the primary light along the transmit beam 210 to a scan element 800 of the LIDAR system 100 to emit.

The LIDAR system 100 further comprises a plurality of detectors, in the example of 1 a first detector 400 and a second detector 410 . The variety of detectors 400 , 410 are arranged to divert the secondary light along a receiving beam (dashed lines in 1 ) from the scan element 800 to detect.

In the example of 1 the receiving beam is shown as two receiving partial beams 330 , 331 includes.

The LIDAR system 100 includes a central axis 300 passing through the optical axis of the transmission beam between the laser and the scanning element 800 can be defined.

The plurality of detectors can be associated with a variety of band pass filters F1 , F2 be equipped. In the example of 1 is the first detector 400 with a first band pass filter F1 and the second detector 410 with a second band pass filter F2 fitted. In the example of 1 is the multitude of band pass filters F1 , F2 between the plurality of detectors described below 400 , 410 and a lens 600 arranged. Examples of lidar systems with filters are given below with reference to FIG 5 to 8th described.

In other examples, different positions can be chosen for one or more filters. For example, a filter in the detector or in optical elements, for example in elements of the lens 600 , be included. In other examples, a plurality of filters may have substantially identical properties for a single filter to replace, or the filters may not be present at all.

The scan element 800 can effect both the primary light and the secondary light of the LIDAR system 100 to be scanned. This can have the effect that the primary light is in relation to the aforementioned central axis 300 can be scanned to scan the area if the lidar system 100 is not moved or is only moved slowly (compared to the scanning frequency). The scan element 800 can at the same time also cause the direction from which the secondary light is received to be scanned in a similar way to the scanning of the primary light. Thus, the scan element 800 act to direct the secondary light onto the above mentioned central axis 300 directing, resulting in a coaxial beam consisting of both the primary and secondary light in the LIDAR system 100 is constructed. Usually the scanning element is used 800 to deflect the light passing through. As a result, the primary light can be emitted in the direction of different areas in the environment and the secondary light can be detected from the respective areas. For example, one or more MEMS mirrors could be used. It would also be possible to use a multi-faceted mirror such as a polygon mirror.

The LIDAR system 100 further includes the lens 600 that is between a first end that is determined by the position of the laser 200 and the multitude of detectors 400 , 410 and a second end that passes through the scanning element 800 is defined, is positioned.

As a rule, the receive beam and the transmit beam 210 be arranged coaxially, at least in a portion between the lens 600 and the object 110 . That is, they can have a common central axis of the light field. The receiving partial beams can through the lens 600 To be defined.

The lens can be a segmented lens, e.g. a free-form shape that can be a combination of different lens functionalities. It can also be an arrangement of several lenses, for example shaft lenses such as biconvex lenses or meniscus lenses. This can have the advantage that compact and inexpensive structures are possible, for example through the use of optical shaft elements with a short focal length and a thin diameter for on-axis focusing applications.

Details regarding the lens 600 are discussed below with reference to FIG 2 and the figures 4a to 4c described.

The Lens 600 comprises several lens elements, which are referred to as lenslets. Each lenslet can have a unique optical surface and define its own optical effect. The term lenslet generally denotes a comparatively small lens element.

A Sendelenslet 610 can be between at least two of a plurality of receiving lenslets 621 , 622 be arranged in a direction perpendicular to the transmit beam.

2 shows schematically an exemplary implementation of the LIDAR system 100 .

2 Figure 3 is a schematic side view showing optical beams of primary light emitted by a laser 200 and secondary light that is emitted from the reflection of the laser light by the object 110 in 1 behind the sensing element 800 originates, shows.

In the following, the functionality in relation to the primary light is shown first. Then second is the functionality in terms of the secondary light described. It should be understood that, for example, features relating to the beam path of the primary light can be viewed in isolation and combined with other examples relating to the beam path of the secondary light. In other words: combinations of different techniques related to 2 or can be described across the entire application.

Regarding the primary light is in the example of 2 a laser 200 on the central axis 300 arranged to emit primary light for measuring the range of an object. The laser 200 can have a fast axis and a slow axis: the divergence along the slow axis is smaller than the divergence along the fast axis; this may be due to a corresponding shape of the active area of the laser 200 be conditional. In the example of 2 is the laser 200 a laser diode that emits a laser beam with the fast axis and one slow axis. The fast axis is at least partially covered by a lens 688 collimated. In some examples, the collimation is achieved by two lenses, namely a first lens 688 and another lens 690 that work together, comparable to a telescope structure, e.g. a Newton telescope or a Galilean beam expander. The first lens 699 and / or the further lens 690 can act on either or both of the fast and slow axes of the laser beam.

However, other options and additional lenses may exist. This is explained below with reference to FIG 3 discussed.

The primary light propagates along the central axis 300 towards the lens 600 out.

In the example of 2 includes the lens 600 a Sendelenslet 610 and two receiving lenslets 621 , 622 .

The Sendelenslet 610 may be a single lens element, for example a focusing lens, which acts to collimate the slow axis of the primary light. In other examples, it can be a more complex lenslet element, for example a microlens array.

The Sendelenslet 610 can be arranged to at least partially collimate the primary light. For example, the Sendelenslet 610 collimate the beam along the slow axis of the transmit beam. In other examples, the Sendelenslet 610 additionally or exclusively collimate the fast axis of the laser beam or do not differentiate between fast axis and slow axis.

The transmit beam 210 is so collimated and the sensing element 800 fed. The LIDAR system 100 can also be an optical shielding material 1100 include.

The optical shielding material 1100 can be in a range between the plurality of detectors 410 , 400 , the laser 200 and the lens 600 to be ordered. The optical shielding material 1100 can be set up to prevent the propagation of light between the transmission beam and the receiving partial beams.

Some of the primary light that is on the object 110 in 2 is reflected, comes to the scanning element as secondary light 800 back. The scan element 800 the secondary light can be essentially parallel to the central axis 300 to steer. Thus is the central axis 300 aligned with the optical axis of the coaxial optical system.

The following describes the light path of the secondary light.

The multitude of receiving lenslets 620 , in the example of 2 a first receiving lenslet 621 and a second receiving lenslet 622 , may define a plurality of receiving sub-beams, for example a first receiving sub-beam 330 and a second receiving sub-beam 331 .

The multitude of receiving lenslets 621 , 622 can be arranged around the respective partial beams 330 , 331 on appropriate detectors 400 , 410 focus from the multitude of detectors.

In some examples, some or all of the respective sub-beams are traveling 330 , 331 through an appropriate filter F1 , F2 before they use the respective detector 400 , 410 to reach. The use of filters is explained with reference to the following figures 5-8 explained.

In some examples, the plurality of receive lenslets is 621 , 622 arranged to the respective partial beams 330 , 331 to focus without the transmission beam 210 to cut.

In those examples where the plurality of receiving sub-beams 330 , 331 and the transmit beam 210 not cut the light, shielding material can 1100 between areas used only for primary light and other areas used only for secondary light. This can enable improved light shielding, for example against stray light from the laser 200 , the one or more of the detectors of the plurality of detectors 400 , 410 reached. This may not be possible in some off-axis setups that have a certain volume in the Device may be required to propagate light for both the primary and secondary light, making efficient shielding difficult.

Typically the shielding material could be metal, e.g. a metal foil. The shielding material can comprise a reflective layer or a light-absorbing layer. The shielding material can consist of plastic.

This can be useful to suppress internal reflections from primary light arriving at one of the plurality of detectors. Each receiving lenslet of the plurality of receiving lenslets can have a reduced aperture area / field width compared to a LIDAR system with a receiving lens design, for example a segmented lens with an off-axis focus.

Thus, for example, in 2 The construction shown allow a reduced focal length of the optical component, for example one or more of the plurality of receiving lenslets for a given material. In other words, the example in 2 can enable a compact optical structure.

Different detectors from the multitude of detectors can have different sensitivities. For example, the first detector can 400 and the second detector 410 have different sensitivities. This can have the advantage that the dynamic range of the LIDAR system 100 can be expanded. The sensitivity can describe an amplification factor between incoming photons and the output electrical signal. The sensitivity can describe a minimum number of photons per sample interval in order to trigger any electrical signal output.

In other words, for example, the first detector 400 a first sensitivity and the second detector 410 have a second sensitivity. The first sensitivity can differ from the second sensitivity. For example, the first sensitivity can be optimized for a signal that is received during daylight operation, the second sensitivity can be optimized for a signal that is received during night-time operation.

Alternatively or additionally, the first sensitivity can be optimized in order to overcome a detector dead time. In some LIDAR applications, a detector may not operate shortly after laser emission due to strong signals received by the detector from scattered laser light or laser light emitted from objects near the LIDAR system, e.g. less than 10 m from the lidar system, it can be difficult.

By using a first detector with a first sensitivity and a second detector with a second sensitivity, the dynamic range of the entire LIDAR system can be improved. For example, the first sensitivity can be selected, for example by adapting a gain setting of the first detector, so that it differs from the second sensitivity by a factor of 5-20, for example 10, for example by a factor of 50-200, for example Example 100, differs.

Various types of detectors can be used. For example, at least one of the plurality of detectors can comprise a silicon photomultiplier.

• • hohe maximale Verstärkung, zum Beispiel bis zu 10⁶. Dies kann die Detektion von wenigen oder sogar einzelnen Photonen ermöglichen,
• • die hohe interne Verstärkung kann das Auslesen erleichtern,
• • eine schnelle Anstiegszeit, zum Beispiel eine Anstiegszeit unter 300ps,
• • SiPMs können niedrige Kosten pro Einheit haben,
• • SiPMs können keine oder fast keine Temperaturkompensation benötigen,
• • SiPMs können eine große aktive Fläche bereitstellen.

Silicon photomultipliers, SiPMs, can have some or all of the following characteristics:

• • high maximum gain, for example up to 10 ⁶ . This can enable the detection of a few or even single photons,
• • the high internal amplification can make reading easier,
• • a fast rise time, for example a rise time below 300ps,
• • SiPMs can have a low cost per unit,
• • SiPMs may require little or no temperature compensation,
• • SiPMs can provide a large active area.

However, some SiPMs can suffer from poor photon detection efficiency.

• • geringe Verstärkung, daher können manche APDs nicht in der Lage sein, wenige oder einzelne Photonen zu detektieren,
• • APDs können aufgrund der geringen Verstärkung vergleichsweise komplizierte Ausleseanforderungen haben,
• • APDs können eine Temperaturkompensation erfordern,
• • APDs können eine hohe Betriebsspannung erfordern, zum Beispiel im Bereich von 100 V-200 V,
• • APDs können vergleichsweise teuer sein,
• • APDs können eine hohe Detektionseffizienz und/oder einen hohen Dynamikbereich haben.

In some examples, one or more detectors of the plurality of detectors are avalanche photo diodes, APDs. APDs can have some or all of the properties listed below:

• • low gain, therefore some APDs may not be able to detect a few or single photons,
• • APDs can have comparatively complicated readout requirements due to their low gain,
• • APDs may require temperature compensation
• • APDs can require a high operating voltage, for example in the range of 100 V-200 V,
• • APDs can be comparatively expensive,
• • APDs can have a high detection efficiency and / or a high dynamic range.

In some examples, the use of one or more APDs may be impractical because of the readout requirements and the costs involved. Thus, in some examples, fewer APDs or even no APDs are used.

In some examples, such as in 2 shown, the LIDAR system 100 a variety of entrance apertures 401 , 411 include. These entrance aperture diaphragms can each be assigned to one of the detectors of the plurality of detectors. Any entrance aperture 401 , 411 can implement a field stop. For example, there is a first input pinhole 401 the first detector 400 and a second input pinhole 411 the second detector 410 assigned. In some examples, filters can be inside or adjacent to the entrance panels 401 , 411 to be placed.

The laser 200 and the variety of entrance apertures 401 , 411 can be located on a focal surface FS. The focal area FS can be through the focal points of the plurality of receiving lenslets 621 , 622 To be defined. In the example of 2 the focal surface FS is a plane perpendicular to the central axis 300 of the transmission beam is arranged.

3 shows another side view of the LIDAR system 100 from 2 .

In this view, which is perpendicular to that in 2 is a different view of the Sendelenslet 610 shown that causes the slow axis of the primary light from the laser 200 at least partially collimate. The fast axis collimator lens 688 and / or the optional additional lens 690 can be designed so as not to act on the slow axis, for example by using a tube lens as a fast axis collimator 688 . This is due to the square shape of the fast axis collimator 688 in the example of 3 symbolizes.

In the example of 3 the other lens works 690 on both the fast and the slow axis.

In other examples, the additional lens 690 however designed to predominantly or exclusively influence only one of the axes, for example the fast axis. The other lens 690 can be a concave lens, for example a cylindrical concave lens. In alternative examples, the further lens 690 be a convex lens, for example a cylindrical convex lens that creates an additional focal point or plane in front of the lens so that the lens effectively expands the laser beam.

In this way, the quality of the collimation of the primary light can be further improved. As in 3 shown, the optical shielding material 1100 be arranged in accordance with the different space requirements of fast and slow axis, ie in the in 3 direction shown have a larger dimension than in 2 .

The following are examples of the lens 600 discussed in the in to LIDAR systems shown 100 can be used.

and show a front view of examples of lenses 600 that according to the invention in the LIDAR systems 100 , for example the in to LIDAR systems shown can be used. Figure 3 shows a side view cross section of the lens 600 from .

In the , and shown lens 600 has a disk-like cross-sectional shape. This is for illustrative purposes only. Other shapes can be used, for example rectangular or square shapes, but any shapes are also possible.

In , and the functional areas A, B and C are indicated. Different functional areas can be implemented using different lenslets.

Areas A and C are used predominantly or exclusively for guiding the secondary light that propagates along the receiving beam, while area B is used predominantly or exclusively for guiding the primary light. In the example of 4a and 4b Area B is completely covered by a Sendelenslet 610 covered. In this example, the transmitting elenslets have a larger extension along the slow axis, as a result of which a rectangular beam profile of the primary light is collimated onto the object. This is not to be taken as a limitation. For example, different lenses could be used in area B instead of a single large lens, and the relationships between the different areas A, B, C can also be varied with respect to one another in different examples.

Areas A and C are set up around that of the scanning element 800 to guide received secondary light to the plurality of detectors, for example the first detector 400 and to the second detector 410 in the example of .

shows a possible lens 600 to guide the secondary light to two different detectors. The Lens 600 from 4a can for example as a lens 600 in 2 be used. A first reception lenslet 621A defines a first receive sub-beam 330 in area A and thus in 2 and a second receiving lenslet 622A defines the second receiving sub-beam 331 in 2 .

shows an alternative implementation for a lens 600 . In this example, the receiving lenslet structure of the plurality of receiving lenslets is compared to modified. Instead of the receiving lenslets 621A , 622A as in shows four receiving lenslets 621B , 621C , 622B , 622C . These four receiving lenslets in turn define a large number of receiving partial beams, namely for the receiving partial beams 330 , 331 , 332 , 333 . These four receiving sub-beams 330 to 333 can then be guided to a large number of four detectors.

Figure 3 shows a side view of the lens 600 , for example from .

In LIDAR systems, for example in the LIDAR systems described above 100 (but also in other LIDAR systems with a different optical configuration) that have a large number of detectors 400 410 different bandpass filters can be used. The use of multiple and different bandpass filters is discussed below along with 5 to 8th described.

In the examples of the to This aspect of the invention will be discussed in terms of a plurality of detectors including three different detectors, but it is in no way limited to this case. The methods and considerations discussed below can also be applied to only two detectors or to a larger number of detectors.

To illustrate the advantage of using different bandpass filters in a LIDAR system, reference is first made to FIG a possible effect in a LIDAR system is discussed. Thereafter, referring to FIG Examples of improvements to lidar systems are discussed.

illustrates a possible effect in a LIDAR system, for example in the LIDAR system 100 from to .

shows the laser emission intensity I as a function of the wavelength A. As in FIG indicated by the solid line, a laser, for example the laser 200 from , have a laser center wavelength AL and a laser peak spectral width W. There are different methods for describing the laser parameters, in the following, for the sake of simplicity, it is assumed that W is a measure of the full half-width, FWHM of the laser spectral emission profile. In some laser systems, the laser center wavelength AL and / or the laser peak spectral width W can depend on different parameters, for example on the temperature of the laser, the aging conditions of the laser, the supply voltage of the laser, etc.

In this parameter dependency of the laser emission profile is indicated by different dashed laser intensity profiles AL1-AL6, which can be the result of different operating conditions of the laser. In one non-limiting example, for a given laser system, this change in emission center wavelength and spectral laser intensity profile can be most affected by temperature. This can be described as a temperature shift of the laser. In a given example system, the laser center wavelength can be influenced to a greater extent, while the laser bandwidth can remain essentially constant over a given temperature range, for example a temperature range between −20 ° C. and + 80 ° C. If the operating conditions of the LIDAR system are known, for example from the requirements of automotive applications, a given laser system can be characterized by a laser emission bandwidth BWL, which is determined by the minimum wavelength Amin and the maximum wavelength Amax, as in specified, can be described. The emission bandwidth of the laser can depend on the operating parameters.

In the following, the discussion will be limited to such an example, but the same reasoning can be applied in other circumstances, for example when a particular laser is more susceptible to changes in supply voltage than to changes in temperature. In such cases, the emission bandwidth BWL can mainly be determined by a range of possible supply voltages analogous to the temperature shift window described here.

The BWL emission range can be specified by $$\mathrm{B.}\mathrm{W.}\mathrm{L.}=\lambda max-\lambda min.$$

If only a single detector or a plurality of detectors, but without a bandpass filter or without different bandpass filters, are used, the temperature-variable laser emission intensity between Amin and Amax can be the disadvantage have that the signal-to-noise ratio is negatively affected compared to an ideal stable laser, which has a fixed spectral emission profile and thus would allow a bandpass filter with a narrow spectral width.

Instead, in such cases of a significant temperature dependence of the laser emission, a large spectral width in which light must be accepted by the detector, or a large number of detectors between Amin and Amax. This can lead to a large background signal, for example due to ambient light, and thus to a comparatively poor signal-to-noise ratio.

Now to the figures to ., possible improvements to this situation by using a plurality of detectors together with a plurality of different bandpass filters are discussed.

In to the spectral range between Amin and Amax possibly covered by the laser is divided into different bandpass ranges of different bandpass filters. The figures 6th to 8th show the transmission T as a function of the wavelength A, where λ is the wavelength of 5 corresponds. The one in the figures 6th to 8th The bandpass filters shown are applied to different detectors. The different detectors can be the plurality of detectors described above.

According to the example shown, each of the bandpass filters covers a bandwidth BW1, BW2 and BW3. In the example, the relationship BW1 + BW2 + BW3 = BWL applies.

The number of three transmission filters is chosen for illustrative purposes only. It is also possible to use only two or more bandpass filters together with a corresponding number of detectors of the plurality of detectors.

In the example shown, the spectral width of the bandpass filters is identical, but this is not necessarily the case.

A spectral shift of the laser due to changes in the operating conditions, for example a temperature shift of an emission bandwidth of the laser, which is associated with an operating temperature range of -20 ° C. and + 80 °, can include both bandpass ranges of the at least two bandpass filters.

erfüllt sein. In einigen Beispielen ist diese Beziehung nur näherungsweise erfüllt, zum Beispiel weil die unterschiedlichen Bandpassfilter eine Überlappung im Spektralbereich haben können, wie weiter unten besprochen wird.In some examples, if N detectors are provided with N different filters, each covering a spectral range BWi, the relationship $$\mathrm{B.}\mathrm{W.}\mathrm{L.}={\displaystyle \sum _{i=1}^N\mathrm{B.}\mathrm{W.}i}$$

be fulfilled. In some examples, this relationship is only approximately fulfilled, for example because the different bandpass filters can have an overlap in the spectral range, as will be discussed further below.

In some examples, the bandpass ranges of the plurality of bandpass filters may be evenly distributed across the emission bandwidth of the laser that is associated with the operating temperature range. Thus, the filter width of the bandpass ranges for the bandpass filters can be approximately the same.

The different bandpass ranges BWi can have the advantage that for given operating conditions, for example a measurement during a point in time, the laser emission light is restricted to one of the bandwidths BW1 to BW3. For example, when the laser is in an operating state in which the laser emission profile AL6 of substantially all of the secondary light can be received by the detector connected to the bandwidth filter covering area BW1. In another example, when the laser is operating under laser center wavelength λL3 conditions, the detector associated with the filter that covers bandwidth BW3 can receive substantially all of the secondary light.

In applications with large light signals, for example, this can lead to an improvement in the signal-to-noise ratio for the LIDAR signal compared to a single detector structure that covers the entire bandwidth, for example BW1 to BW3.

For an idealized example, the reason for the improvement can be given as follows. If only a single detector is used, the amount of secondary light that can reach the detector is proportional to the area through which the secondary light passes. For example, if the area in a LIDAR system is through the lens 600 is limited, for example a lens 600 that the in shown lens 600 the amount of light that can be received by the individual detector is limited by $$area\mathrm{A.}0=area\mathrm{A.}+area\mathrm{C.}$$

However, since only a single detector is used, a band pass filter must be used in front of the individual detector can be selected in order to span the full laser emission bandwidth BWL. If we assume that the background light has a uniform spectral distribution over the full laser emission bandwidth BWL and an intensity BG, the full intensity of the background light BG arrives at the individual detector. The detector signal is then limited by a received laser intensity IL that covers the area A0 passes through. The signal-to-noise power ratio PSN0 can then be approximated by $$P\mathrm{S.}N0=\frac{\mathrm{I.}\mathrm{L.}}{\mathrm{B.}G}.$$

At high intensities of BG this can lead to a poor signal-to-noise ratio SNR0.

Instead, a plurality of N detectors can be used, and each detector i can be equipped with a filter transmitting a different band path area BWi as described above. The different tape path areas can be chosen to satisfy the relationship given by Eq. (2) is given.

In such a case, each detector of the plurality of detectors receives only a background light intensity BGi given by $$\mathrm{B.}Gi\sim \frac{\mathrm{B.}G}{N^2}.$$

Note that a reduction compared to BG by a factor of 1 / N is due to the fact that each detector only has background light from a 1 / N part of the area A0 receives. The reduction by a further factor of 1 / N is due to the fact that the bandpass filter in front of the given detector only lets through the 1 / Nth part of the background light. It is assumed here that BWi have a uniform spectral width when covering the laser emission bandwidth BWL. In other examples, non-uniform spectral widths of BWi can be used, then this second factor changes accordingly.

However, as in connection with discussed, while the laser can drift during operation, the laser is limited to a certain spectral distribution at a certain point in time, for example AL6 in .

Typically the temperature drifts rather slowly, e.g. on the order of minutes.

In such a case, the laser light will only be received by the corresponding detector, for example detector i = 1, in the event that the laser is in an operating regime of λL5 or AL6, and i = 3, in the event that the laser is in an operating regime of AL3 or AL2.

In such a case, the detector signal from the detectors which do not receive the laser can be neglected.

For example, if the laser light is in an operating regime in which the secondary light only reaches the first detector, only the BGi background signal reaches the detector due to the bandpass filter width BW1.

an.However, the full laser intensity IL does not reach the first detector for the following reason either: The available area must be used to accommodate the large number of detectors A0 the lens can be divided into the different partial beams for the respective detectors. This means that a fraction of the light comes from each detector $$\mathrm{I.}\mathrm{L.}i=\frac{\mathrm{I.}\mathrm{L.}}{N}$$

at.

Thus, the PSN (Power of Signal over Noise) ratio for the i-th detector receiving the secondary light, selected from the plurality of N detectors, is given by: $$P\mathrm{S.}N=\frac{\mathrm{I.}\mathrm{L.}/N}{\mathrm{B.}G/N^2}=N\times \frac{\mathrm{I.}\mathrm{L.}}{\mathrm{B.}G}$$

This increases the PSN by N.

wobei SNRO das Signal-Rausch-Verhältnis für das Signal-Rausch-Verhältnis für den oben beschriebenen Einzeldetektor-Fall ist und SNRi das Signal-Rausch-Verhältnis für den i-ten Detektor ist, wobei i entsprechend dem aktuellen Laserintensitätsprofil gewählt ist, so dass der i-te Detektor das sekundäre Licht empfängt.If a signal-to-noise ratio SNR is defined as the ratio of the average signal to the standard deviation of noise, the relationship holds $$\frac{\mathrm{S.}N\mathrm{R.}O}{\mathrm{S.}N\mathrm{R.}i}=\sqrt{N}$$

where SNRO is the signal-to-noise ratio for the signal-to-noise ratio for the single detector case described above and SNRi is the signal-to-noise ratio for the i-th detector, where i is chosen according to the current laser intensity profile, so that the i-th detector receives the secondary light.

In other words, the use of a variety of detectors as described here can be used have the advantage that the signal-to-noise ratio is improved compared to applications with a single detector or with a large number of detectors that do not have different bandpass ranges for different laser emission profiles. While the above calculation is based on the above assumptions, this argument essentially also applies to different cases, for example uneven bandpass filter areas BWi and / or overlapping between bandpass filter areas BWi, although the numerical values can vary.

It should be noted that in some applications the optimal number of N may be limited, for example by factors such as the spectral width W of the laser compared to the laser emission bandwidth BWL, the number of signal photons received at the i-th detector and / or practical considerations the number of detectors.

Thus, in most applications, an application-dependent optimal number of N can be determined.

In the example of the plurality of detectors is carried out by N = 3 detectors. Therefore, the signal-to-noise ratio for this setup is c, as shown by Eq. (8) to be improved by 73% compared to a single detector design.

In some examples, the noise signal from the other detectors that are not receiving the laser light of the plurality of detectors can be used to obtain further information regarding the noise. In some embodiments, the spectral bandwidth can be taken into account, for example by correcting the signal using spectral sensitivity characteristics and assumptions regarding the background signal, for example Planck's law, in order to map the noise received at a first detector onto a corresponding noise at a second detector.

Various alternatives with regard to the shape of the transmission curves for realizing the bandpass ranges BW1, BW2 and BW3 are shown in the figures to shown. The transmission curves are in With F1 , F2 and F3 , in With F1A , F2A and F3A and in With F1B , F2B and F2C marked.

The shape of the transmission curves are shown for illustrative purposes only.

The transmission curves F1 , F2 and F3 are designed so that there is no overlap between adjacent bandwidth areas. This can have the advantage that a very clear separation and good suppression of background light is possible. This can be particularly advantageous if the laser central wavelength can be restricted to different ranges, for example if the wavelength of the laser can be stabilized to different operating windows, for example by adjusting the supply voltage of the laser as a function of the temperature in order to ensure that the laser emission always falls within the range in which the respective transmission of the filter F1 to F3 is great.

7th shows a different example. In the example of have the transmission curves F1A , F2A and F3A an overlap in the transmission with adjacent filter areas. In the example of have the transmission curves F1B , F2B and F3B, which cover the bandpass areas BW1, BW2 and BW3, have a larger overlap. This can have the advantage that there is no area in which the light from the laser is reduced due to the edge shape of the bandpass filters. Combinations are also possible. For example, a first filter could have an overlap with a second filter, but not an overlap with a third filter.

The LIDAR system can include control electronics which are set up to carry out a selection of a single detector or a plurality of detectors from the plurality of detectors and to carry out the distance measurement of the object on the basis of measurement data from the one or more detectors from the plurality of detectors.

In examples in which the installed control electronics carry out a selection of a single detector from the plurality of detectors, the LIDAR system can only have a single detection electronics that are matched to the selected single detector. In other examples, the number of detection electronics can be correspondingly smaller than the number of detectors, for example if the control electronics are set up to carry out a selection of multiple detectors with a maximum number of the multiple detectors of 3, only 3 detection electronics may be required to for example to operate 6 detectors. This can reduce cost and equipment volume, as fewer detection circuits are required in these examples. In other examples, the number can also be identical to the number of detectors or even greater. This allows optimized detection electronics to be provided for each detector and / or operating conditions. If the number for at least one detector is larger, even optimized detection electronics can be provided for different conditions, eg weak light detection electronics and strong light detection electronics.

• - eine Temperatur des Lasers, vorzugsweise durch einen Temperatursensor detektiert,
• - Intensität eines detektierten Signals auf der Vielzahl von Detektoren,
• - Spektralinformationen bezüglich der Laserwellenlänge,
• - Spannungs-/Strom-Kennlinien des Lasers.

The selection can be based on any one or a combination of the following:

• - a temperature of the laser, preferably detected by a temperature sensor,
• - intensity of a detected signal on the plurality of detectors,
• - spectral information related to the laser wavelength,
• - Voltage / current characteristics of the laser.

In some examples, the selection is made using a look-up table. For example, in the look-up table, the selection can be specified according to a laser temperature.

In further examples or in addition, the one or the plurality of detectors can comprise at least two detectors, wherein the control electronics can be set up to carry out the selection in such a way that the bandpass ranges of the associated bandpass filter are adjacent or overlapping.

This can have the advantage that in cases in which the bandpass ranges overlap, for example BW1 and BW2 in , the laser signal can be fully recovered even though it is split between two detection bandwidths.

The methods and techniques described here can be combined. Examples are provided below.

As a first example it may be desirable to use the existing, i. to measure existing background light independently of the laser. This can be achieved through the use of at least one bandpass filter which is assigned to at least one detector of the plurality of detectors with a bandpass range outside the laser spectral range. The signal from this at least one detector can be used to obtain a background value, for example a background photon rate per nanosecond. This background value can then be used to improve the pulse detection of another detector of the plurality of detectors which detects the laser light.

As a second example, which can be combined with the first example, in LIDAR applications it may be desirable to overcome a dead time due to the strong light present immediately after the laser emission. This strong light can be caused by internal reflections during triggering of the LIDAR system's laser. The laser light can saturate the detector and / or amplifier, causing or adding to the dead time. As a result, the LIDAR system may not be able to detect the secondary light from nearby objects due to the dead time.

This limitation can be overcome by using a plurality of detectors which include a second detector with a different sensitivity and / or a bandpass filter in front of the second detector, the bandpass filter associated with the second detector being misaligned with respect to the laser wavelength. This can have the effect that the misaligned band pass filter attenuates the laser light.

These two possibilities described above can be combined. For example, a detector with a reduced sensitivity can be selected in a first option. In a second option, a misaligned bandpass filter can be used with a detector with identical sensitivity. In a third option, a detector with reduced sensitivity can be used in conjunction with a misaligned band pass filter connected to the detector, thereby further attenuating the signal.

By using the techniques described above, alone or in combination, the saturation of the detector can be reduced or avoided. This can improve the LIDAR results for close objects, for example in an area under 10 m.

In a third example, which can be combined with the first and / or the second example, at least one detector of the plurality of detectors can be used to detect electrical crosstalk in the LIDAR system, for example crosstalk caused by the laser. Optical detection may not be desirable for this sensor. Therefore, an overvoltage of this sensor can be switched off so that this particular detector is not sensitive to optical light. Additionally or alternatively, the light path to this special detector can be blocked.

• Ein LIDAR-System zur Entfernungsmessung eines Objekts unter Verwendung von primärem Licht und sekundärem Licht, das an dem Objekt reflektiert wird, wobei das LIDAR-System umfasst:
  • - einen Laser, der angeordnet ist, um das primäre Licht entlang eines Sendestrahls zu einem Scanelement zu emittieren,
  • - eine Vielzahl von Detektoren, wobei mindestens ein Detektor der Vielzahl von Detektoren angeordnet ist, um das sekundäre Licht entlang eines Empfangsstrahls von dem Scanelement zu detektieren,
• - eine Linse, die zwischen dem Laser und der Vielzahl von Detektoren und dem Scanelement positioniert ist, wobei die Linse umfasst:
  • ein Sendelenslet, das dem Sendestrahl zugeordnet ist, und
  • eine Vielzahl von Empfangslenslets, die eine Vielzahl von Empfangsteilstrahlen definieren, wobei jede der Vielzahl von Empfangslenslets angeordnet ist, um den jeweiligen Empfangsteilstrahl auf einen entsprechenden Detektor aus der Vielzahl von Detektoren zu fokussieren.

In some variations of this third example, the detector used to detect the electrical crosstalk may be mechanically blocked, ie it may not be arranged to detect the secondary light along a received beam from the scanning element. In one example, a lidar system can be deployed as follows:

• A LIDAR system for measuring the range of an object using primary light and secondary light reflected from the object, the LIDAR system comprising:
  • - a laser which is arranged to emit the primary light along a transmission beam to a scanning element,
  • - a plurality of detectors, wherein at least one detector of the plurality of detectors is arranged to detect the secondary light along a received beam from the scanning element,
• a lens positioned between the laser and the plurality of detectors and the scanning element, the lens comprising:
  • a transmission lens that is assigned to the transmission beam, and
  • a plurality of receive lenslets defining a plurality of receive sub-beams, each of the plurality of receive lenslets being arranged to focus the respective receive sub-beam onto a corresponding one of the plurality of detectors.

In some examples, the plurality of detectors can include a second detector. The second detector can be arranged so as not to receive any light along the receive beam. The second detector can be arranged to detect an electrodynamic signal from the environment and / or the LIDAR system. The electromagnetic signal can be a signal caused by the laser and / or readout noise and / or crosstal noise. The LIDAR system can be set up to correct the signal of the at least one detector based on the electrical signal detected by the second detector.

In other words, electrical noise can be at least partially removed from the signal from at least one detector by subtracting the signal from a different detector that is not used for light detection.

While the invention has been shown and described with respect to certain preferred embodiments, equivalents and modifications to others skilled in the art will occur upon reading and understanding the specification. The present invention includes all such equivalents and modifications and is limited only by the scope of the appended claims.

For example, different examples have been described in which (i) several detectors, which are assigned to different bandpass filters, were combined with (ii) a lens comprising two receiving lenslets and a transmitting lenslet lying in between. However, it would generally be possible that (i) multiple detectors associated with different bandpass filters could be used in other optical configurations, e.g. using multiple separate detector lenses or non-coaxial optical assemblies.

Claims (18)

LIDAR system (100) for measuring the range of an object (110) using primary light and secondary light that is reflected from the object (110), the LIDAR system (100) comprising: - a laser (200) which is arranged to emit the primary light along a transmission beam (210) to a scanning element (800), a plurality of detectors which are arranged to detect the secondary light along a received beam from the scanning element, - a lens (600) positioned between (i) the laser and the plurality of detectors and (ii) the scanning element, the lens (600) comprising: a transmit maillet (610) associated with the transmit beam, and a plurality of receive lenslets (621, 621a, 621b, 621c, 622, 622a, 622b, 622c) defining a plurality of receive sub-beams (330, 331, 332, 333), each of the plurality of receive lenslets (621, 622) being arranged is to focus the respective receiving partial beam (330, 331) on a corresponding detector (400, 410) from the plurality of detectors. LIDAR system Claim 1 wherein the transmitting lenslet (610) is arranged between at least two of the plurality of receiving lenslets (621, 622) in a direction perpendicular to the transmitting beam. LIDAR system Claim 1 or 2 wherein the LIDAR system further comprises: - an optical shielding material (1100) arranged in an area between the plurality of detectors, the laser (200) and the lens (600), wherein the optical shielding material (110) is arranged to prevent light propagation between the transmit beam and the receive sub-beams. The lidar system of any one of the preceding claims, wherein the transmitter lens (610) is arranged to at least partially collimate the primary light along a slow axis of the transmitter beam. LIDAR system Claim 4 , the LIDAR system also having another lens (690) which is positioned between the laser and the lens and which is arranged to expand at least the slow axis of the transmit beam. The lidar system of any of the above claims, wherein the plurality of detectors (400, 410) comprises a first detector (400) and a second detector (410), the first detector having a first sensitivity and the second detector having a second sensitivity has, wherein the first sensitivity is different from the second sensitivity. The lidar system of any of the preceding claims, wherein at least one of the plurality of detectors (400, 410) comprises a silicon photomultiplier. The lidar system of any of the above claims, further comprising a plurality of input pinholes (401, 411), each input pinhole being associated with one of the detectors of the plurality of detectors, and wherein the laser and the plurality of input pinholes are positioned on a focal surface ( FS), which is defined by focal points of the plurality of receiving lenslets (621, 622). LIDAR system Claim 8 , the focal surface (FS) being a plane, the plane preferably being arranged perpendicular to a central axis (300) of the transmission beam. LIDAR system according to any of the above claims, further comprising a plurality of bandpass filters (F1, F1) associated with the detectors of the plurality of detectors, the bandpass ranges (BWi, BW1, BW2, BW3) of at least two bandpass filters of the plurality of band pass filters. LIDAR system Claim 10 , whereby a temperature shift of an emission bandwidth (BWL) of the laser, which is assigned to an operating temperature range of - 20 ° C and + 80 °, which comprises at least two bandpass ranges (BWi, BW1, BW2, BW3) of the at least two bandpass filters (F1, F2) . LIDAR system Claim 10 or 11 , wherein the bandpass areas (BWi, BW1, BW2, BW3) of the plurality of bandpass filters (F1, F2) are evenly distributed over the emission bandwidth of the laser (BWL), which is assigned to the operating temperature range. LIDAR system according to any of the Claims 10 - 12 wherein the band pass filters of the plurality of band pass filters have an overlap in the band pass areas (BWi, BW1, BW2, BW3). LIDAR system according to any of the Claims 10 - 13 wherein the LIDAR system comprises control electronics that are configured to perform a selection from the plurality of detectors and to perform the determination of the distance of the object on the basis of measurement data in accordance with the selection from the plurality of detectors. LIDAR system Claim 14 , the selection being based on any one or a combination of the following: a temperature of the laser, optionally detected by a temperature sensor, an intensity of a detected signal on the plurality of detectors, spectral information relating to a wavelength of the laser, or a voltage - / current characteristic of the laser. LIDAR system Claim 14 or 15th wherein the selection comprises at least two detectors, the control electronics being set up to perform the selection of the plurality of detectors so that the bandpass ranges of the associated bandpass filters of the plurality of bandpass filters of the at least two detectors of the selection are adjacent or overlapping. A method of operating a LIDAR system (100) for measuring the distance of an object (110) using primary light and secondary light that is reflected off the object (110), the method comprising: Performing a selection from a plurality of detectors of the LIDAR system which are arranged to detect the secondary light, each detector of the plurality of detectors being associated with a respective one of a plurality of band pass filters of the LIDAR system, with band pass ranges of at least two differ from one another in the multitude of bandpass filters, and - Distance measurement of the object based on measurement data from the plurality of detectors in accordance with the selection. Procedure according to Claim 17 wherein the selection is based on any one or a combination of these: a temperature of the laser, optionally detected by a temperature sensor, an intensity of a detected signal on the plurality of detectors, spectral information relating to a wavelength of the laser, or a voltage - / current characteristic of the laser.

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