Laser-based detection device, motor vehicle and method for operating a laser-based detection device

Abstract

The invention relates to a detection device (10) for the detection of an environment, wherein the detection device (10) has a transmitting unit (14) with a laser light source (36), which is designed to transmit a pulse train (46) with a plurality of first light pulses (18a), which have a predetermined time spacing (T, T1, T2) from one another, and a receiving unit (16), which is designed to detect second light pulses (18b). The invention provides that the transmitting unit (14) is designed to change the predetermined time spacing (T, T1, T2) in the course of the transmission of the pulse train (46) in accordance with a preset modulation pattern (56), wherein the detection device (10) has an evaluation unit (24), which is designed to evaluate the second light pulses (18b) detected by the receiving unit (16) in accordance with the preset modulation pattern (56).

Description

Technical Field

[0001] This invention relates to a detection device for detecting surrounding environments, comprising: a transmitting unit with a laser light source designed to transmit a pulse train (Pulszug) containing a plurality of first optical pulses, the first optical pulses having a predetermined time interval between them; and a detection device designed to detect second optical pulses. The invention also includes a motor vehicle equipped with such a detection device and a method for operating the detection device. Background Technology

[0002] Laser-based detection devices, such as LiDAR (Light Detection and Range) systems, are known from existing technologies. These systems are increasingly used in the automotive sector because reliable environmental perception is essential for autonomous driving. In particular, LiDAR plays a crucial role in redundant and robust environmental detection, as this sensor type can accurately measure distances and can also be used for classification. Conventional LiDAR systems rely heavily on time-of-flight (TOF) measurements, where the time of light travel is measured to determine the distance traveled. This involves emitting light pulses that are reflected and detected by the surrounding environment. The maximum effective range of the system is related to the number of reflected photons. The more photons reflected from the surface of an object or obstacle, the sooner the object or obstacle is detected by a photodiode (which serves as an example of a receiving unit) mounted in the sensor. The number of detectable photons scales linearly with the emitted power. Therefore, TOF LiDAR systems typically operate close to their maximum emitting power for use in autonomous driving functions. The correspondingly high number of emitted photons makes these systems particularly vulnerable to interactions with other lidar systems or sources of the same wavelength. Thus, for example, ghost targets can appear as interactions with spatially adjacent systems (e.g., systems used on other vehicles). Therefore, it is desirable to be able to reliably distinguish the light pulses emitted and detected by one lidar from those of another lidar, in order to avoid ghost targets and thus improve detection quality. Summary of the Invention

[0003] Therefore, the object of the present invention is to provide a laser-based detection device for detecting the surrounding environment, a motor vehicle, and a method for operating the laser-based detection device, thereby achieving the highest possible detection quality in detecting the surrounding environment.

[0004] This objective is achieved by the detection device, vehicle, and method according to the present invention. The advantageous embodiments of the invention are described in the specification and accompanying drawings.

[0005] The detection device for detecting the surrounding environment according to the present invention comprises: a transmitting unit with a laser light source, which is designed to transmit a pulse train with a plurality of first optical pulses, the first optical pulses having a predetermined time interval between each other; and a receiving unit, which is designed to change the predetermined time interval according to a preset modulation scheme during the transmission of the pulse train, wherein the detection device further comprises an evaluation unit, which is designed to evaluate the second optical pulse detected by the receiving unit according to the preset modulation scheme.

[0006] By altering the time interval of the transmitted light pulses according to a preset modulation mode, it is advantageously possible to distinguish these light pulses from those of other detection devices upon reception by the transmitting unit, based on the preset modulation mode. Changing the time interval of the light pulses effectively avoids ghost targets and thus significantly improves detection quality when detecting the surrounding environment through the detection device. Compared to other modulation variants (e.g., amplitude modulation), the maximum possible operating range of the detection device remains essentially unaffected because the amplitude of the light pulse is directly related to its intensity, not the pulse interval.

[0007] Here, a pulse train is a sequence of multiple individual optical pulses. A pulse train may include at least two optical pulses. The pulse train may also have multiple sub-pulse trains, which in turn include multiple (that is, at least two) optical pulses, wherein, for example, optical pulses within a sub-pulse train may be emitted at a constant time interval, and the time interval between optical pulses in different sub-pulse trains may be modulated according to a modulation mode, and / or may be configured to change the time interval between optical pulses within the same sub-pulse train.

[0008] The detection device can be, in particular, the laser-based detection device described at the beginning, which is based on the time-of-flight measurement method. To detect the second light pulse, the receiving unit may, for example, have a photodiode. Furthermore, the laser source is preferably a monochromatic laser source. However, this is not necessarily the case. The laser source may, for example, have a laser with a high bandwidth. In addition, the duration of the light pulse should preferably be less than, and especially significantly less than, the time interval between the two light pulses, thereby simplifying the distinction between the two light pulses.

[0009] Furthermore, the second light pulse can be the first light pulse reflected from an object or obstacle in the environment. However, the second light pulse can also be other light pulses, such as those transmitted by other transmitting units of other such detection devices. To distinguish this, the evaluation unit can now advantageously consider a preset modulation pattern, which must also be reflected in the detected second light pulses if these second light pulses are at least a portion of the transmitted first light pulses. Therefore, another advantageous design of the invention is that the evaluation unit is designed to check, according to a preset modulation pattern, whether and / or which of the detected second light pulses are at least a portion of at least some of the first light pulses transmitted by the transmitting unit and emitted from an object in the environment. Here, the light pulses received by the transmitting unit can include not only light pulses transmitted by the transmitting unit but also light pulses transmitted by external transmitting units. This can now advantageously be distinguished by the evaluation unit according to the modulation pattern. Accordingly, only such received light pulses (which, according to the modulation pattern, are identified as light pulses transmitted by their own transmitting unit) can also aid in the evaluation in view of objects present in the environment. Furthermore, typically, not all of the power initially contained in the transmitted and reflected light pulses is received by the transmitting unit. Light loss is unavoidable due to scattering at objects in the environment and also depends on the path of the light pulse. Accordingly, only a portion of the transmitted light pulse can always be received again by the transmitting unit after the light pulse is reflected. Thus, even though the reception of the first reflected light pulse is referred to simply within the scope of this invention, it should be understood as the corresponding reception of at least a portion of the first transmitted and reflected light pulses.

[0010] According to another advantageous design of the invention, the evaluation unit is designed to, in order to evaluate the second optical pulse, transform the temporal intensity curve of the detected pulse sequence to the frequency space by means of a Fourier transform and determine the corresponding time interval of the second optical pulse based on the result of the Fourier transform. Here, the receiving unit detects the optical pulses in the form of an intensity signal, which is a temporal intensity curve. By Fourier transforming this temporal intensity curve to the frequency space, the time interval between two optical pulses can be determined very accurately. This is particularly advantageous if the optical pulses are transmitted at a very high pulse frequency and therefore with a very short time interval. Such a pulse frequency or pulse repetition rate is preferably in the kilohertz range. Accordingly, it is particularly advantageous to determine the time interval between the optical pulses detected by the receiving unit based on a Fourier transform. This Fourier transform can, for example, be implemented in the evaluation unit as an FFT (fast Fourier transform).

[0011] A particularly advantageous aspect is that the evaluation unit is designed to determine the frequency spacing based on the result of the Fourier transform (which is a frequency comb with multiple frequencies spaced apart from each other), and to determine the corresponding time spacing of the second pulse based on the frequency spacing. The time spacing of consecutively emitted light pulses is represented in frequency space by corresponding frequency spacings, with each frequency of the frequency comb having such a frequency spacing. The inverse Fourier transform of this frequency spacing correspondingly provides the time spacing between two light pulses. Thus, the time spacing can be measured with both particular simplicity and particular accuracy.

[0012] Therefore, the frequency spacing is the pulse repetition frequency (by which optical pulses are transmitted or received) and is defined as the number of optical pulses per unit of time. Furthermore, within the scope of this invention, the terms pulse repetition frequency, pulse repetition rate, repetition rate, and repetition frequency are used synonymously.

[0013] Furthermore, it is preferable that the interval between the transformed pulse trains is as small as possible and comprises only a few optical pulses. This has the advantage that, although the time interval of the first transmitted optical pulses is changed, the optical pulses observed in the smaller interval have an almost constant time interval between each other in the shorter observed interval, which manifests as a frequency comb with frequencies having a constant frequency interval between each other. Thus, the time interval between two pulses can be measured with particular accuracy. Here, the Fourier transform of the received pulse train segments is repeatedly performed, especially continuously, so that the change in the time interval between the received optical pulses (if these optical pulses originate from their own transmitting unit) manifests as different frequency intervals, which are determined by the corresponding spectrum obtained by the Fourier transform. By comparing with a predetermined modulation pattern, it can thus be determined whether the received optical pulse is still the first optical pulse transmitted by its own transmitting unit. In order to now provide such a temporal change in the interval of the optical pulses transmitted by the transmitting unit, several possibilities now exist:

[0014] In an advantageous embodiment of the invention, the laser source has a resonant cavity for generating a pulse train, which provides an optical path with an optical path length. The transmitting unit is designed to change the optical path length temporally in order to change a predetermined time interval during the transmission of the pulse train. Here, the optical path length in the resonant cavity determines the pulse repetition rate and therefore also determines the time interval between two transmitted optical pulses. By changing the optical path length, the time interval between the transmitted optical pulses can advantageously be changed. The optical path length of the resonant cavity can be changed according to a preset modulation mode. The type of temporal change in the optical path length determines the modulation mode, according to which the time interval of the first optical pulse is changed, or the optical path length can be changed according to the modulation mode, causing a corresponding temporal change in the time interval of the transmitted optical pulses. In other words, the desired modulation mode (which should change the time interval of the transmitted optical pulses) can be achieved in a particularly simple way, i.e., by modulating the optical path length of the resonant cavity according to the modulation mode. Several possibilities exist for achieving this.

[0015] For example, the transmitting unit can be configured such that, in order to change the optical path length over time, the resonant cavity length of the resonant cavity is mechanically changed over time. Here, the resonant cavity length should be understood in particular as the length of the cavity provided by the resonant cavity. Typically, such a resonant cavity has two specular reflective elements with an active medium arranged between them. The spacing between these specular reflective elements (especially with an optical standing wave constructed between them) is here the length of the cavity of the resonant cavity. That is, if the resonant cavity length is mentioned here, it should be understood here as the length of the cavity of the resonant cavity. By changing the resonant cavity length, the optical path length can be modified in a particularly simple way, and the time interval of the change in the transmitted light pulse can be provided accordingly. This can be achieved, for example, in a simple way by an actuator designed to, for example, move one of the two reflective or specular reflective elements (with the cavity of the resonant cavity constructed between them) so as to thereby change the spacing between these specular reflective elements, which is the resonant cavity length. Here, the length change is preferably a multiple of at least a half-integer of the wavelength of the transmitted light pulse.

[0016] Another advantageous possibility for temporally changing the optical path length lies in having an active medium with an optical density within the resonant cavity, wherein the transmitting unit is designed to temporally change the optical density of the active medium in order to change the optical path length. As described, this active medium is typically located in a cavity (in which an optical standing wave is constructed) of the resonant cavity between two mirror-reflecting elements. The optical density of this medium is described by its refractive index. A change in the refractive index of the active medium correspondingly results in a change in the optical path length within the resonant cavity. Such a change in refractive index can be induced, for example, by an optical component for electronically changing the refractive index, which can be used within the resonant cavity. Such an optical component can modulate the refractive index of the active medium according to a preset modulation mode, which automatically results in modulation of the time interval of the light pulses transmitted by the transmitting unit corresponding to that modulation mode. For example, an electro-optic modulator, an acousto-optic modulator, or an LCD beamshaper can be applied to modulate the refractive index. Other possibilities are also considered.

[0017] Furthermore, the optical path length can be combined with modulation by changing the resonant cavity length and by modulating the refractive index. This advantageously provides even more and faster modulation possibilities. Modulating the optical path length by means of optical components to modulate the refractive index or by changing the resonant cavity length has the advantage that the power and therefore intensity of the emitted light pulse can be kept constant, thus providing maximum range of action at all times.

[0018] In another advantageous embodiment of the invention, the transmitting unit is designed to change the transmitting power of the detection device in order to alter the predetermined time interval during the transmission of the pulse train. This advantageous design is based on the knowledge that a nonlinear component of the refractive index begins to be noticeable at higher intensities, which can be attributed to nonlinear effects (e.g., the Kerr effect). Accordingly, the refractive index is derived as: n(I) = n + n²·I, where n(I) is the total refractive index of the active medium in the resonant cavity. This total refractive index consists of an intensity-independent component n and an intensity-dependent component n², where, in particular, I represents the intensity. Typically, extremely high intensities occur within the laser resonant cavity, making the contribution of this nonlinearity n²·I non-negligible. The parameter n² thus provides, in this case, the possibility of modulating the optical path length by changing the optical density. This modulation is correspondingly achieved via the transmitting power of the detection device, which in turn depends on the pump power of the laser system, which in turn affects the intensity within the resonant cavity. Thus, the optical density of the active medium in the resonant cavity can also be modulated by the modulation of the pump power, thereby actively changing the pulse repetition rate and thus also actively changing the time interval between the transmitted pulses.

[0019] Therefore, it generally provides many advantageous possibilities for how to simply modulate the time interval between transmitted optical pulses according to a preset modulation mode.

[0020] In another advantageous embodiment of the invention, the modulation mode is designed such that the time interval changes randomly according to a generated random number. The transmitting unit is designed to change the time interval randomly according to the generated random number. This significantly reduces the probability of detecting light pulses from other laser systems, where the change in the time interval between transmitted light pulses is the same as detecting light pulses transmitted by its own detection device or its own transmitting unit. Therefore, the probability of detecting ghost targets can be further reduced.

[0021] Another advantage is that the modulation pattern is designed so that the time interval is changed based on the Barker code. In other words, the transmitting unit is designed to change the time interval based on the Barker code as the modulation pattern. This has the advantage that orthogonal signals can be provided. The similarity to itself is very small over time, so even if these pulses are received according to the same modulation pattern (although they are time-shifted), it is still possible to distinguish the incoming pulse from the original pulse.

[0022] What is particularly advantageous here is that the modulation scheme is designed such that the time interval is varied based on a Barker code of length 13. Correspondingly, the transmitting unit is also designed to vary the time interval based on a Barker code of length 13. This is the longest Barker code and therefore provides the greatest possible reliability in terms of single-valuedness. Furthermore, it is advantageous that the examples mentioned above can be combined with each other; that is, the sequence of Barker codes can be superimposed using random numbers, thereby providing a correspondingly more reliable modulation scheme. However, in principle, any other modulation scheme can also be applied, for example, simple linear modulation.

[0023] The transmitting unit is designed to randomly change the time interval based on the generated random number. Accordingly, the transmitting unit is also designed to change the time interval based on a Barker code of length 13.

[0024] Furthermore, it is preferable that the detection equipment is constructed as a lidar system. Lidar systems are frequently used in the automotive field to detect the surrounding environment.

[0025] Therefore, the combination of the detection device's design as a lidar system and the modulation-based distinguishability between its own pulse and incoming pulses is a significant advantage, as such distinguishability is extremely beneficial for ambient environment detection in the motor vehicle field. This results in two problems: firstly, an increasing number of vehicles equipped with lidar systems are increasingly interfering with each other due to the lack of distinguishability between their own and incoming pulses; secondly, multiple lidar systems can be used on the same vehicle, which may also have overlapping detection areas due to redundancy in data detection, leading to significant mutual interference even without the possibility of distinguishing between their own and incoming pulses.

[0026] Furthermore, the present invention also relates to a motor vehicle equipped with a testing device according to the invention or a design thereof. The advantages mentioned for the testing device and its design according to the invention also apply to the motor vehicle according to the invention.

[0027] Furthermore, the present invention relates to a method for operating a detection device for detecting the surrounding environment, wherein the detection device comprises: a transmitting unit with a laser light source that transmits a pulse train containing a plurality of first optical pulses, the first optical pulses having a predetermined time interval between them; and a receiving unit designed to detect second optical pulses. Furthermore, the transmitting unit changes the predetermined time interval according to a preset modulation mode during the transmission of the pulse train, wherein the detection device includes an evaluation unit that evaluates the second optical pulse detected by the receiving unit according to the preset modulation mode.

[0028] The advantages mentioned for the detection equipment and its design according to the invention also apply to the method according to the invention.

[0029] The present invention also includes improvements to the method according to the invention, which have the features described herein as in conjunction with improvements to the detection apparatus according to the invention. For this reason, corresponding improvements to the method according to the invention will not be described again here.

[0030] The present invention also includes combinations of features of the described embodiments. Attached Figure Description

[0031] The embodiments of the present invention will now be described. Wherein:

[0032] Figure 1 A schematic diagram of lidar point cloud acquisition of a test vehicle with five conventional lidar systems according to the prior art is shown.

[0033] Figure 2A schematic diagram of a motor vehicle with a laser-based detection device according to an embodiment of the present invention is shown in top view;

[0034] Figure 3 A schematic diagram of the transmitting unit of a detection device according to an embodiment of the present invention is shown;

[0035] Figure 4 A graphical illustration of a pulse train with multiple optical pulses (having a first time interval between them) according to an embodiment of the present invention is shown in the time domain and in the frequency domain;

[0036] Figure 5 A graph is shown illustrating a pulse train with multiple optical pulses (which have a second time interval between them) in the time domain and in the frequency domain;

[0037] Figure 6 A graphical illustration of an exemplary modulation pattern for modulating the time interval of an optical pulse according to an embodiment of the present invention is shown; and

[0038] Figure 7 A flowchart illustrating a method for operating a laser-based detection device according to an embodiment of the present invention is shown. Detailed Implementation

[0039] The embodiments described below are preferred embodiments of the invention. In these embodiments, the described components are correspondingly features of the invention that should be considered independently of each other, and they also independently improve the invention and can therefore be considered as part of the invention individually or in combinations different from those shown. Furthermore, the described embodiments can be supplemented by additional features among the features already described in the invention.

[0040] In the accompanying drawings, elements with the same function are respectively given the same reference numerals.

[0041] For autonomous driving, reliable environmental perception is essential. This is typically achieved using sensors such as radar, lidar, and cameras. Of particular importance is comprehensive 360° 3D environmental detection, enabling the detection of all static and dynamic objects. LiDAR plays a crucial role in redundant and robust environmental detection, as this sensor type can accurately measure distances and can also be used for classification. However, these sensors are costly and structurally complex. 360° 3D environmental detection is particularly challenging because it either requires numerous small individual sensors (which typically operate using many individual light sources and guiding elements) to ensure this, or it necessitates the installation of larger sensors, such as mechanically rotating lidar systems.

[0042] Conventional lidar systems, in particular, rely on time-of-flight measurement methods, in which the travel time of light is measured to determine the distance traveled, and this is also the case for a laser-based detection device according to an embodiment of the present invention. Here, Figure 2 A laser-based detection device 10 according to an embodiment of the present invention is schematically shown as part of a motor vehicle 12. The laser-based detection device 10 can be configured, for example, as a lidar system. Here, the detection device 10 includes, on one hand, a transmitting unit 14 (which includes a laser source) and a receiving unit 16 having a photodetector (e.g., a photodiode). The transmitting unit 14 is designed to transmit light pulses 18a, for example, in the form of one or more pulse trains spaced apart by time intervals. If these light pulses 18a are reflected in the direction of the detection device 10 by an object 20 in the environment 22, these reflected light pulses 18b can be detected by the receiving unit 16 of the detection device 10. Furthermore, the detection device 10 also includes an evaluation unit 24, which is designed to evaluate the signal detected by the receiving unit 16. Based on the direction in which the light pulses 18a are transmitted and based on the travel time elapsed between the transmission and reception of the reflected light pulses 18b, the evaluation unit 24 can determine the direction and distance at which the object 20 or object point is located. This involves emitting light pulses (Lichtimpuls) or light pulses 18a that are reflected from and detected by the surrounding environment 22. The maximum range of the system (e.g., the detection device 10) is related to the number of photons reflected. The more photons reflected back from the surface of the obstacle 20, the sooner they are detected by the photodiode installed in the transmitting unit (i.e., in the detection device 10). The number γ of photons per pulse is determined by:

[0043] γ=E P / E γ =P / (E γ ·f rep )

[0044] Among them, E P Describes pulse energy, E γ Describing the energy of a single photon, f rep Let P describe the repetition rate of the laser system and P describe the average power emitted. According to this formula, the number of detectable photons scales linearly with the emitted power. Time-of-flight lidar systems used in autonomous driving functions operate close to their maximum emittable power. Consequently, the number of emitted photons is so high that these systems are particularly vulnerable to interactions with other lidar systems or emission sources of the same wavelength. Thus, for example, ghost targets may appear as interactions with spatially adjacent systems, such as those used in a second vehicle. This is in… Figure 1This is illustrated exemplarily. Here, Figure 1 A schematic diagram of a lidar point cloud 26 is shown on a test vehicle equipped with five mounted conventional lidar systems. The test vehicle is located at... Figure 1 The measurement points detected by such a lidar sensor are recorded in a point cloud 26. By evaluating this point cloud 26, other vehicles 28, as well as lane boundaries 30, can be detected accordingly. However, false detections also occur due to interference effects between multiple lidar sensors. Such false detections are also called "ghost targets". In this example, three ghost targets 32 are detected exemplary, which are located in... Figure 1 The corresponding points are shown as circled dots. These virtual objects 32 move at high speed toward the test vehicle at position X (this should be illustrated by arrow 34), causing the driving function, based on the detection of the surrounding environment, to anticipate a collision and initiate braking action. This can advantageously be avoided by the present invention or its embodiments, as it provides the possibility of distinguishing between light pulses from its own detection device and light pulses sent by other detection devices. This is now based on Figure 2 The following diagrams will illustrate this in more detail.

[0045] This is achieved by designing the transmitting unit 14 to modulate the emitted radiation for single-value encoding, so that the radiation can be clearly distinguished from radiation from other sources. Here, in particular, the repetition rate f of the modulated laser system (i.e., the detection device 10) is... rep And therefore the time interval between the transmitted optical pulses 18a. These modulation possibilities are based on this. Figure 3 Let me elaborate in more detail.

[0046] A lidar system (such as the laser-based detection device 10 described herein) uses a laser as a source of coherent radiation to detect the surrounding environment 22. Such an exemplary laser source 36 (which is part of the transmitting unit 14 of the laser-based detection device 10) is exemplary in... Figure 3 As shown in the diagram. In time-of-flight and other pulse train-based systems, as well as in the laser-based detection device 10 which is still within the scope of this invention, optical pulses (referred to as optical pulses 18a) are emitted and the reflected light rays 18b are detected. Here, Figure 3The structure of a laser 36, designed to emit optical pulses 18a, is schematically shown. Here, the laser 36 includes an active medium 38 surrounded by two reflective elements 40. These two reflective elements 40, together with the active medium 38, provide a resonant cavity 42. Light is generated by optical pumping / electric pumping, which, under given resonant cavity conditions, constructs a standing wave 44 (cavity) between the reflective elements 40 and results in stimulated emission. A portion of the light 44 within the resonant cavity is decoupled in the form of pulses 18a. A plurality of consecutive pulses 18a form a pulse train 46. In particular, the pulse train 46 includes at least two optical pulses 18a. The resonant cavity 42 further has a resonant cavity length L. This resonant cavity length L defines the spacing between the two reflective elements 40. Furthermore, the active medium 38 has a refractive index n. Here, the resonant cavity length L and the refractive index n of the active medium 38 determine the pulse repetition rate f. rep according to

[0047] f rep =c / (2nL)

[0048] c here represents the speed of light in a vacuum. According to this equation, the pulse repetition rate f... rep This can be changed by altering the resonant cavity length L and also by changing the refractive index n. For example, the pulse train 46 emitted in the first time interval can therefore be configured with a specific pulse repetition rate f. rep It is emitted. By measuring the pulse train 46, especially by means of the receiving unit 16, and Fourier transforming the temporal pulse sequence 46 into the frequency space, the pulse repetition rate f can be measured with extremely high precision. rep This is in Figure 4 The explanation is as follows.

[0049] Figure 4 The diagram on the left shows a schematic representation of the intensity curve of the pulse train as a function of time t. Here, I represents intensity. The pulse repetition rate f rep According to T=1 / f rep The time interval T1 between each optical pulse 18a is defined. The intensity curve of the pulse train 46 with multiple optical pulses 18a, 18b (especially six optical pulses 18a, 18b in this example) over time is shown in... Figure 4 In addition, it is denoted as 48a. The intensity maxima corresponding to each optical pulse 18a, 18b are in Figure 4 In addition, these are also denoted as 18a and 18b. If we now perform a Fourier transform on this intensity spectrum, we obtain a frequency comb in the frequency space, which is... Figure 4The image is shown on the right. Furthermore, the Fourier transform is illustrated by arrow 50. Each optical pulse 18a, 18b consists of many different optical frequencies that propagate below envelope 52a in frequency space. The pulse duration τ in time describes the half-value width in time and defines the half-value width of envelope 52a. The Fourier transform of pulse train 46 to frequency space is a frequency comb, as already mentioned. The single-mode (Einzelmode) 54a is represented by the pulse repetition rate f1. rep They are separated from each other. The linewidth of the spectrum of single-mode 54a is further limited by the length of pulse train 46. Therefore, it can be seen that the pulse repetition rate f1 can be determined in a particularly simple and accurate manner by the Fourier transform 50 of the temporal intensity curve 48a of pulse train 46. rep And therefore the time interval T of each optical pulse 18a, 18b.

[0050] This advantageously allows for the use of the pulse repetition rate f1 rep The modulation of the pulse interval T1 in time clearly identifies the optical pulse 18a emitted by the transmitting unit 14, because the pulse repetition rate f1 rep The temporal pulse interval T1 is also reflected in the detected optical pulses 18b, assuming these optical pulses are transmitted and reflected by the transmitting unit 14. That is, if the resonant cavity length L is changed, for example, during a second time interval (which is longer than the first time interval mentioned above), the pulse train 46 emitted in this second time interval will have a different second repetition rate f2. rep This is symbolic in Figure 5 This is explained in the text. Figure 5 A schematic diagram of the intensity curve 48b over time for the second pulse train 46 is shown on the left, where the maximum intensity values ​​corresponding to each optical pulse 18a, 18b are also represented by 18a, 18b. Due to the other second repetition rate f2 rep Each optical pulse 18a, 18b has a different time interval T2, which is particularly greater than the time interval T2 between them. Figure 4 The first time interval T1 is described. The Fourier transform of the intensity curve 48b at this time is... Figure 5 The frequency comb with corresponding single-mode 54b (which propagates below envelope 52b) is then derived in the frequency space shown on the right. These single-mode 54b now operate at a second repetition rate f2 in this case. rep They are spaced apart from each other. The Fourier transform is... Figure 5 This is further illustrated by arrow 50. Therefore, the two pulse trains 46 emitted in the corresponding first and second time intervals can be determined according to their different repetition rates f1 that can be extracted from the spectrum. rep f2 rep They are distinguished from each other. Pulse train 46 is distinguished by its respective repetition rate f1.rep f2 rep To encode. The evaluation device 24 can be designed to first subject the intensity signals 48a, 48b received by the receiving unit 16 to a Fourier transform 50, so as to determine the repetition rate f1 from the resulting spectrum. rep f2 rep Alternatively, the corresponding time intervals T1 and T2 of each optical pulse 18a and 18b can be determined through inversion. The repetition rate f1, determined from the corresponding spectrum, is then used. rep f2 rep Or, corresponding time intervals T1 and T2, can be correlated with the corresponding repetition rate f1. rep f2 rep Alternatively, the time intervals T1 and T2 of the light pulses 18a emitted by the transmitting unit 14 can be compared. If a consistency is found, the light pulse 18b detected by the receiving unit 16 can be identified as the light pulse 18b emitted and reflected by the transmitting unit 14.

[0051] By pulse repetition rate f1 rep f2 rep The random sequences can be encoded relative to each other by lidar systems (such as laser-based detection devices 10), thereby filtering out interference effects between systems.

[0052] In addition to simply modulating the continuous pulse train 46, the repetition rate f within the pulse train 46 can be changed. rep . Figure 6 The repetition rate f is schematically shown. rep Linear modulation as a function of time t 56. Pulse repetition rate f rep The applied linear frequency modulation can be achieved through continuous tuning of the resonant cavity length L and is the only identifying feature, because, for example, the slope can be changed.

[0053] Alternatives for pulse repetition rate f rep Special coding can be performed using linear tuning. Here, the following coding is particularly suitable, exhibiting good correlation characteristics even in cases where Doppler shift (Doppler-Verschiebung) may occur. This is, for example, a Barker code, preferably a Barker code of length 13. As mentioned above, modulation of the refractive index n also results in a pulse repetition rate f. rep The change. Thus, for example, an optical component for changing the refractive index n by electrons can be used in the resonant cavity 42, which modulates f. rep Another possibility lies in utilizing nonlinear effects, such as the Kerr effect. At higher intensities I, the nonlinear fraction of the refractive index n² must be considered because...

[0054] n(I) = n + n²·I

[0055] This applies, and the second addend is negligible only when the intensity I is small. However, the extremely high intensity I within the laser resonator 42 makes this contribution non-negligible. Therefore, parameter n2 advantageously also provides the modulation repetition rate f. rep The possibility of this is that the intensity inside the resonant cavity depends on the power of the pump P of the laser system 36, and the product n2·I can be modulated by modulating the pump power P, and thus the pulse repetition rate f can be actively changed. rep .

[0056] Figure 7 A flowchart illustrating a method for operating a laser-based detection device 10 according to an embodiment of the present invention is shown. Here, the method begins in step S10, in which a modulation mode 56 is provided. Based on this provided mode 56, the resonant cavity length L can now be modulated in step S12 and / or the refractive index n can be modulated in step S14 accordingly. As a result, in step S16, a pulse train 46 with optical pulses 18a, the optical pulses having a repetition rate f given their time intervals T1, T2, is provided. rep The pulse train 46 is then modulated accordingly. The modulated pulse train 46 is subsequently emitted by the transmitting unit 14 in step S18 and reflected by an object 20 in the environment 22, such as that of the vehicle 12, in step S20. Furthermore, the light pulse is subsequently detected by the receiving unit 16 in step S22 and evaluated by the evaluation unit 24 in step S24. During this evaluation, the evaluation unit 24 performs a Fourier transform 50 of the temporal intensity curves 48a, 48b detected by the receiving unit 16 in step S24, and determines the repetition rate f of the received pulse train based on the spectrum in step S26. rep In the next step S28, a reliability check is performed by evaluation unit 24, in which the modulated pulse train 46 provided in step S16 is applied. Specifically, the modulated repetition rate f provided in step S16 is applied here. rep (This is in) Figure 7 (Illustrated by dashed arrows) and compared with the repeatability f determined in step S26. rep The repetition rates are compared in step S28. If these repetition rates are consistent, the received optical pulse 18b is identified as optical pulse 18a transmitted by the transmitting unit 14 and further processed in step S30. Otherwise, that is, the repetition rate f rep If there is an inconsistency, the data is discarded because the detected light pulses were emitted by other systems. These light pulses are therefore of no help in detecting the surrounding environment. Thus, it is advantageous to avoid detecting ghost targets 32.

[0057] The example generally illustrates how the present invention can provide a method for channel coding of a lidar system to suppress interference, thereby enabling interference-resistant and interference-free measurement of distances through the lidar system, in which interference signals can be suppressed by emitters of the same wavelength.

[0058] List of reference numerals

[0059] 10 Laser-based detection equipment

[0060] 12 Motor vehicles

[0061] 14 Transmitting Unit

[0062] 16 Receiving Units

[0063] 18a transmitted light pulse

[0064] 18b reflected light pulse

[0065] 20 objects

[0066] 22 Environment

[0067] 24 Evaluation Units

[0068] 26 point clouds

[0069] 28 Motor vehicles

[0070] 30 lane boundary

[0071] 32 Ghost Targets

[0072] 34 arrows

[0073] 36 Laser source

[0074] 38 Active media

[0075] 40 Reflective element

[0076] 42 Resonant Cavity

[0077] 44 Standing Waves

[0078] 46 pulse train

[0079] 48a Intensity Curve

[0080] 48b intensity curve

[0081] 50 Fourier Transform

[0082] 52a envelope

[0083] 52b envelope

[0084] 54a single-mode

[0085] 54b single-mode

[0086] 56 Modulation Modes

[0087] f frequency

[0088] f rep Pulse repetition rate

[0089] f1 rep Pulse repetition rate

[0090] f2 rep Pulse repetition rate

[0091] I Intensity

[0092] L Resonant cavity length

[0093] T time

[0094] τ Pulse width

[0095] T time interval

[0096] T1 time interval

[0097] T2 time interval

[0098] X The location of the test vehicle

[0099] S10 Step

[0100] Step S12

[0101] Step S14

[0102] Step S16

[0103] S18 Step

[0104] S20 Step

[0105] S22 Step

[0106] Step S24

[0107] Step S26

[0108] S28 Step

[0109] Step S30.

Claims

1. A detection device (10) for detecting the surrounding environment, wherein, The detection device (10) comprises: a transmitting unit (14) with a laser light source (36) designed to transmit a pulse train (46) with a plurality of first optical pulses (18a), the first optical pulses having a predetermined time interval (T, T1, T2) between each other; and a receiving unit (16) designed to detect second optical pulses (18b), characterized in that the transmitting unit (14) is designed to change the predetermined time interval (T, T1, T2) according to a preset modulation mode (56) during the transmission of the pulse train (46), wherein the detection device (10) comprises an evaluation unit (24) designed to evaluate the second optical pulse (18b) detected by the receiving unit (16) according to the preset modulation mode (56) to determine the predetermined time interval changed according to the preset modulation mode (56). Whether the time interval (T, T1, T2) is reflected in the second optical pulse (18b), wherein the modulation mode (56) is designed such that the time interval (T, T1, T2) is randomly changed according to a generated random number, wherein the laser source (36) has a resonant cavity (42) for generating the pulse train (46), the resonant cavity providing an optical path with an optical path length, wherein the transmitting unit (14) is designed to change the optical path length in time in order to change the predetermined time interval (T, T1, T2) during the transmission of the pulse train (46), wherein the resonant cavity (42) has an active medium (38) with an optical density, wherein the transmitting unit (14) is designed to change the optical density of the active medium (38) in time in order to change the optical path length in time.

2. The detection device (10) according to claim 1, characterized in that, The evaluation unit (24) is designed to check, according to the preset modulation mode (56), whether and / or which of the detected second light pulses (18b) are at least a portion of at least some of the first light pulses (18a) that were transmitted by the transmitting unit (14) and reflected at an object (20) in the environment.

3. The detection device (10) according to any one of claims 1 to 2, characterized in that, The evaluation unit (24) is designed to transform the intensity curve (48a, 48b) of the detected second light pulse (18b) into the frequency space by means of Fourier transform (50) in order to evaluate the second light pulse (18b), and determine the corresponding time interval (T, T1, T2) of the second light pulse (18a) according to the result (54a, 54b) of the Fourier transform (50).

4. The detection device (10) according to claim 3, characterized in that, The evaluation unit (24) is designed to determine the frequency spacing (f) based on the results (54a, 54b) of the Fourier transform (50). rep f1 rep f2 rep The result is a frequency comb with multiple frequencies (54a, 54b) having the frequency spacing between them, and according to the frequency spacing (f) rep f1 rep f2 rep The corresponding time interval (T, T1, T2) of the second optical pulse (18b) is determined.

5. The detection device (10) according to any one of claims 1 to 2, characterized in that, The transmitting unit (14) is designed to mechanically change the resonant cavity length (L) of the resonant cavity (42) in time in order to change the optical path length in time.

6. The detection device (10) according to any one of claims 1 to 2, characterized in that, The transmitting unit (14) is designed to change the transmitting power of the detection device (10) in order to change the predetermined time interval (T, T1, T2) during the transmission of the pulse train (46).

7. The detection device (10) according to any one of claims 1 to 2, characterized in that, The modulation mode (56) is designed such that the time interval (T,T1,T2) is changed based on the Barker code.

8. The detection device (10) according to any one of claims 1 to 2, characterized in that, The modulation pattern (56) is designed such that the time interval (T, T1, T2) is changed based on a Barker code of length 13.

9. The detection device (10) according to any one of claims 1 to 2, characterized in that, The detection device (10) is constructed as a lidar system (10).

10. A motor vehicle (12) equipped with a detection device (10) according to any one of the preceding claims.

11. A method for operating a detection device (10) for detecting the surrounding environment, wherein, The detection device (10) comprises: a transmitting unit (14) with a laser light source (36) that transmits a pulse train (46) with a plurality of first optical pulses (18a), the first optical pulses having a predetermined time interval (T, T1, T2) between each other; and a receiving unit (16) designed to detect second optical pulses (18b), characterized in that the transmitting unit (14) changes the predetermined time interval (T, T1, T2) according to a preset modulation mode (56) during the transmission of the pulse train (46), wherein the detection device (10) comprises an evaluation unit (24) that evaluates the second optical pulse (18b) detected by the receiving unit (16) according to the preset modulation mode (56) to determine the predetermined time interval changed according to the preset modulation mode (56). Whether T, T1, T2) is reflected in the second optical pulse (18b), wherein the modulation mode (56) is designed such that the time interval (T, T1, T2) is randomly changed according to a generated random number, wherein the laser source (36) has a resonant cavity (42) for generating the pulse train (46), the resonant cavity providing an optical path with an optical path length, wherein the transmitting unit (14) is designed to change the optical path length in time in order to change the predetermined time interval (T, T1, T2) during the transmission of the pulse train (46), wherein the resonant cavity (42) has an active medium (38) with an optical density, wherein the transmitting unit (14) is designed to change the optical density of the active medium (38) in time in order to change the optical path length in time.

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