Transmitter unit and LIDAR device for scanning a scanning area

Abstract

A transmission unit (2) of a LIDAR device (1) having at least two radiation sources (4, 5) for generating and emitting point-shaped or line-shaped electromagnetic beams (6, 7) into a scanning area (A), wherein at least one radiation source (4, 5) has an adjustable operating temperature (T0, T1, T2) and / or adjustable emission wavelength depending on an emission angle of the electromagnetic beams (6, 7) generated by the at least one radiation source (4, 5); and wherein the operating temperature (T0, T1, T2) of at least one radiation source (4, 5) is adjustable by dissipating operating heat to a passive heat sink (26).

Description

[0001] The invention relates to a transmitting unit of a LIDAR device with at least two radiation sources for generating and emitting point-shaped or line-shaped electromagnetic beams into a scanning area, as well as to a LIDAR device for scanning a scanning area defined by a vertical and a horizontal scanning angle with electromagnetic beams. State of the art

[0002] LIDAR (light detection and ranging) devices typically have a transmitting and receiving unit. The transmitting unit generates and emits electromagnetic beams. The emitted beams can be used to irradiate and scan a scanning area. If these beams strike a moving or stationary object, the object reflects them toward the receiving unit. The receiving unit can detect the reflected electromagnetic radiation and assign a reception time to the reflected beams. This can be used, for example, in a "time of flight" analysis to determine the distance of the object from the LIDAR device.

[0003] To optimize the signal-to-noise ratio, optical bandpass filters, such as interference filters, can be placed in the receive path of the LIDAR device to block interference reflections. The narrower the transmitted wavelength range of the filter, the less interference or ambient light falls on the detector and the better the signal quality. However, when detecting beams with an angle of incidence greater than 0° relative to an optical axis of the LIDAR device, a shift in the transmitted wavelength range of the bandpass filter to smaller wavelengths occurs. Therefore, bandpass filters with a wider transmitted wavelength range must be used so that beams with angles of incidence deviating from an optical axis can also pass through the bandpass filter. However, a filter with a wider transmitted wavelength range can impair the signal-to-noise ratio.

[0004] Document DE 10 2016 108437 A1 discloses a multi-wavelength lidar array system, wherein multiple lasers are arranged in an array to emit multiple respective beams, a lens is arranged to scatter the multiple beams at multiple respective angles, and a bandpass filter is arranged to filter multiple reflections received at multiple respective angles of incidence.

[0005] Document DE 10 2013 002683 A1 describes a method for a vehicle for determining distance information and transmitting transmission data. In the method, a modulated signal is generated depending on transmission data to be transmitted by the vehicle. The modulated signal is used to control a light source of the vehicle. Light emitted by the light source and reflected by an object in the vehicle's surroundings is received, and a received signal is generated depending on the received light. By combining the modulated signal with the received signal, a combination signal is generated, and a distance to the object is determined depending on the combination signal.

[0006] Document DE 10 2016 213446 A1 discloses an optical system for detecting a scanning field, a system for controlling the optical system, and a method for controlling the optical system. The optical system comprises at least one source for emitting electromagnetic radiation and at least one deflection unit for deflecting the beam path of the electromagnetic radiation emitted by the source into the scanning field. The optical system further comprises at least one optical receiver comprising at least one optical filter element for filtering the electromagnetic radiation backscattered and / or reflected in the scanning field and at least one detector element for detecting the filtered electromagnetic radiation.

[0007] Document DE10 2014 211073 A1 describes a vehicle lidar system comprising a solid-state laser with a brilliance of at least 100 kW / (mm 2 sr), which is designed to emit laser pulses with a wavelength of at least 900 nm and a maximum power per laser pulse of at least 50 W, at least one deflectably arranged mirror for deflecting the laser pulses in the direction of objects to be detected and a receiver for detecting the laser pulses reflected by the objects.

[0008] The document DE 10 2006 052 770 A1 discloses an environment detection system in which the transmitting device selectively transmits at least two different wavelengths and the receiving device can be tuned to the respective wavelength.

[0009] Document DE 11 2011 100 812 T5 describes a system and method for increasing the output power and the spatial and / or spectral brightness when using or combining a plurality of laser elements. Disclosure of the invention

[0010] The object underlying the invention can be seen in the provision of a method and a LIDAR device which enable the use of a filter with a smaller transmitted wavelength range and which has an improved signal-to-noise ratio.

[0011] This object is achieved by means of the respective subject matter of the independent claims. Advantageous embodiments of the invention are the subject matter of the respective dependent subclaims.

[0012] According to one aspect of the invention, a transmitting unit of a LIDAR device is provided with at least two radiation sources for generating and emitting point-shaped or line-shaped electromagnetic beams into a scanning area. According to the invention, at least one radiation source has an adjustable operating temperature and / or an adjustable emission wavelength depending on an emission angle of the electromagnetic beams generated by the at least one radiation source. The different operating temperatures generate, for example, angle-dependent emission wavelengths of the beam sources, which can lead to an improvement in the signal-to-noise ratio of a LIDAR system.

[0013] Semiconductor lasers, for example, can be used as a radiation source. The wavelength of the generated laser radiation or electromagnetic radiation depends on the temperature of the semiconductor laser.

[0014] Unstabilized semiconductor lasers, such as Fabry-Perot lasers, exhibit a relatively large temperature dependence. The temperature dependence of the wavelength of the generated beams can be as low as 0.3 nm / K at a fundamental wavelength of 905 nm and using gallium arsenide technology.

[0015] Semiconductor lasers with monolithically integrated frequency stabilization, such as DFB lasers, DBR lasers, VCSELs, VeCSELs and the like, can exhibit a temperature-dependent wavelength dependence of 0.07 nm / K.

[0016] By operating multiple radiation sources at different and defined operating temperatures, the individual emitters or radiation sources can generate and emit electromagnetic radiation with defined wavelengths. In particular, the respective radiation sources can be thermally adjusted so that the generated radiation has wavelengths adapted to a bandpass filter used. This allows the generated radiation to be adapted to an angle-dependent shift in the transmission range of the bandpass filter of the LIDAR device depending on their emission angle. The transmission range or filter bandwidth can, for example, be less than 25 nm. The transmitting unit can preferably have a vertical scanning range of more than + / - 1°.

[0017] In particular, the transmitting unit according to the invention can significantly reduce the filter bandwidth of the LIDAR device, thereby improving the signal-to-noise ratio. Furthermore, such a LIDAR device can be manufactured cost-effectively.

[0018] The radiation sources of the transmitting unit can generate point-shaped, planar, or linear beams. The generated beams can be spaced apart from one another or at least overlap in certain areas. In particular, overlaps between differently generated beams can create a homogeneous line for scanning a scanning area.

[0019] According to one embodiment, the operating temperature of at least one radiation source can be passively adjusted by dissipating operating heat to an environment or to a passive heat sink. With passive adjustment of the temperature of the radiation sources, the self-heating caused by the laser operation itself can be used to achieve different operating temperatures. This can be achieved, for example, by stacking laser chips or emitters, by varying the pumping current, or by implementing different thermal resistances of the emitters on a common heat sink. The radiation sources can, for example, be arranged in an exposed position or equipped with passive heat sinks, which enables defined heat dissipation and temperature control of the respective radiation sources. This allows the transmitter unit to be designed in a particularly simple technical manner.

[0020] According to a further embodiment, the operating temperature of at least one radiation source can be actively adjusted by dissipating operating heat to an active cooling element and / or an active heating element. The operating temperature of the different radiation sources or emitters can be controlled, for example, by at least one heating element or at least one Peltier element in combination with a temperature controller.

[0021] According to a further embodiment, the operating temperature can be regulated depending on the radiation angle of the at least one radiation source. By emitting the generated rays at different radiation angles, the respective wavelength of the generated rays can be specifically controlled within defined solid angles. The wavelengths are selected according to the optical bandpass filter used in the LIDAR device or in the receiving unit, specifically such that the wavelengths of the emitted rays match the shift experienced by the bandpass filter due to the large angle of incidence of the reflected rays corresponding to the generated rays.

[0022] According to a further embodiment of the transmitting unit, the operating temperature of the at least one radiation source decreases with increasing radiation angle. Preferably, the radiation sources generate beams with different wavelengths, so that a filter installed in the detector path of the receiving unit or the LIDAR device can be passed by the reflected beams with as little loss as possible. Beams with larger emission angles should have a shorter wavelength than beams emitted by the transmitting unit at smaller emission angles.

[0023] According to a further embodiment, the transmitting unit has at least one optical element arranged in the beam path of the emitted electromagnetic beams. The at least one optical element can, for example, be a generating optics of the transmitting unit. For example, the generating optics can be a coated or uncoated cylindrical lens, convex lens, concave lens, or a combination of several identical or different lenses. The generating optics can bundle or fan out the generated beams, or change their divergence. For example, the beams are collimated if at least one lens is positioned at a distance of the focal length from the emitter surface.

[0024] In particular, the generation optics can convert a distance between the beam sources or a beam offset into an angular deflection of the emitted beams. Beam shaping by the generation optics or the at least one optical element can change the emission angle of the generated beams depending on the position of the emitters.

[0025] The emission angle caused by the generation optics depends in particular on the optical properties of the generation optics and the distance from the optical axis. Beams shaped in this way can then be emitted from the LIDAR device into the scanning area directly or via a deflection unit. Preferably, the beams can be deflected in a meandering pattern along a horizontal angle and a vertical angle. This allows the scanning area spanned by the horizontal angle and the vertical angle to be scanned with the generated and shaped beams.

[0026] According to a further embodiment of the transmitting unit, the electromagnetic beams can be generated by the at least two beam sources simultaneously or sequentially. Thus, individual points can be emitted simultaneously or sequentially. Alternatively, illuminated areas or a continuous line can be emitted with generated beams. The individual emitters or the at least two beam sources can be activated simultaneously, as a so-called "line flash," sequentially, or in another defined sequence.

[0027] According to a further embodiment, the at least two radiation sources are stacked or adjacently arranged surface emitters or edge emitters. This allows the at least two radiation sources to be arranged in the transmitting unit in a space-saving and cost-efficient manner.

[0028] According to a further aspect of the invention, a LIDAR device is provided for scanning a scanning area defined by a vertical and a horizontal scanning angle with electromagnetic beams. The LIDAR device has at least one transmitting unit according to the invention for generating electromagnetic beams and for distributing or deflecting the electromagnetic beams at least along the vertical scanning angle. Furthermore, the device has at least one receiving unit for receiving beams reflected from at least one object arranged in the scanning area, a bandpass filter for absorbing or reflecting interference reflections, and at least one evaluation unit for evaluating the received reflected beams.

[0029] The beams generated by the transmitting unit, which are generated at a distance from an optical axis of the generating optics, have an emission angle after passing through a generating optics. The emission angle or the radiation angle depends in particular on the optical properties of the generating optics and the distance from the optical axis. Beams shaped in this way can then be emitted from the LIDAR device into the scanning area directly or via a deflection unit. Preferably, the beams can be deflected in a meandering manner along a horizontal angle and a vertical angle. This allows the scanning area spanned by the horizontal angle and the vertical angle to be scanned with the generated and shaped beams.

[0030] If an object is located in the scanning area, the shaped and emitted beams are reflected by the object. At least one beam reflected by the object also has a larger reflection angle. The at least one reflected beam can be received and detected by the receiving unit. For this purpose, the receiving unit preferably has receiving optics that direct the at least one reflected beam onto a detector. An optical bandpass filter is also arranged in the receiving path. The filter can be arranged, for example, upstream of the receiving optics, within the receiving optics, or downstream of the receiving optics, starting from the incoming reflected beam. The filter is usually an interference filter that has a transmission for rays of a specific wavelength range.Depending on the angle of incidence of the reflected rays on the filter, the transmitted wavelength range of the filter shifts. In particular, the transmitted wavelengths of the filter become smaller as the angle of incidence of a reflected incoming beam increases. Incoming rays with a wavelength outside the transmitted wavelength range can be reflected by the filter from the LIDAR device or absorbed by the filter.

[0031] In the LIDAR device according to the invention, the wavelength of at least one generated or shaped beam can be adjusted depending on its emission angle by passing through the generation optics. The wavelengths are selected according to the optical bandpass filter used in the reception path of the LIDAR device. Preferably, the wavelength of at least one generated or shaped beam is adjustable such that the wavelength corresponds to the wavelength shift of the transmitting wavelength range of the optical bandpass filter after reflection of the beam from an object.At least one generated beam spaced from the optical axis of the generating optics can, for example, have a shorter wavelength and thus, despite a resulting larger angle of incidence on the optical bandpass filter, lie within the transmitted wavelength range and preferably transmit through the filter without loss. This allows, in particular, the transmitted wavelength range to be made smaller, so that fewer interfering reflections pass through the filter and can be registered by the detector. Multiple reflections from the environment, which strike the receiving unit and the filter from different angles, can also be more effectively blocked by an optical bandpass filter with a shorter transmitted wavelength range. This also results in a reduced probability of the LIDAR device detecting "ghost objects."Furthermore, a narrower transmitted wavelength range of the filter can improve the signal-to-noise ratio of the LIDAR device. Alternatively, or in addition, generated beams with larger emission angles can be used to enable a larger scanning range.

[0032] According to one embodiment, the LIDAR device has at least one temperature sensor for determining an operating temperature of at least one radiation source of the transmitting unit and is connected to a control unit for actively adjusting an operating temperature of the at least one radiation source by means of at least one active cooling element and / or an active heating element. The control unit can directly or indirectly measure and actively control the operating temperature of the various radiation sources. The operating temperature can be controlled by applying thermal energy to the radiation sources or by actively extracting thermal energy. Alternatively, the operating temperature can be adjusted by adjusting an operating power of the at least one radiation source. This allows the at least one radiation source to generate electromagnetic rays with a wavelength adapted to a bandpass filter.

[0033] In the following, preferred embodiments of the invention are explained in more detail using highly simplified schematic representations. Fig. 1 a schematic representation of a LIDAR device according to a first embodiment, Fig. 2 a schematic representation of a radiation source arrangement of a transmitting unit according to a first embodiment, Fig. 3 a schematic representation of a radiation source arrangement of a transmitting unit according to a second embodiment and Fig. 4 a schematic representation of a dependence of the transmitted wavelength of a bandpass filter on an emission angle of the incoming rays.

[0034] In the figures, the same structural elements have the same reference numerals.

[0035] In the Fig. Figure 1 shows a schematic representation of a LIDAR device 1 according to a first embodiment. The device 1 has a transmitting unit 2, which consists of several emitters or radiation sources 4, 5.

[0036] The divergence of the beams 6, 7 generated and emitted by the beam sources 4, 5 can be varied by a downstream optical element 8. According to the exemplary embodiment, the beams 6, 7 are bundled. By spacing a beam source 4 from the optical axis of the optical element 8, the correspondingly shaped beams 6 have an emission angle that deviates from 0°. Beam shaping thus changes the emission angle of the generated beams 6 depending on the position of the emitters or beam sources 4, 5.

[0037] The generated beams 6, 7 are radiated into a scanning area A and can impinge on an object 10. The generated beams 6, 7 can be at least partially reflected by the object 10 and thus become reflected beams 12, 13.

[0038] The reflected beams 12, 13 are then filtered by an optical bandpass filter 14 and can then be detected by the receiving unit 16 and evaluated by the evaluation unit 18.

[0039] The reflected rays 13 of the first radiation source 5 hit the bandpass filter 14 at an emission angle of 0° and can transmit through it unhindered.

[0040] The rays 6 emitted at an emission angle greater or smaller than 0°, or the corresponding reflected rays 12, no longer impinge perpendicularly on the bandpass filter 14. The bandpass filter has a transmission range shifted towards smaller wavelengths. This relationship is shown in the Fig. 4 is illustrated by way of example. By thermally adapting the radiation source 4, the wavelength of the generated rays 6 can be reduced according to the emission angle, whereby the reflected rays 12 can pass through the bandpass filter 14 unhindered despite the shifted transmission range.

[0041] The Fig. Figure 2 illustrates a schematic representation of a radiation source arrangement of a transmitting unit 2 according to a first exemplary embodiment. According to the exemplary embodiment, the radiation sources 4, 5 are semiconductor lasers. The operating temperature of the radiation sources 4, 5 is actively controlled. For this purpose, the transmitting unit 2 has a temperature sensor 20 on each radiation source 4, 5. All temperature sensors 20 are read by a common or separate control unit 22.

[0042] Based on the determined temperature of the temperature sensors 20, the control unit 22 can activate Peltier elements 24 arranged on the radiation sources 4, 5 as heating or cooling elements for acting on the radiation sources 4, 5. Beams 7 generated along the optical axis of the optical element 8 or by a centrally arranged radiation source 5 have a reference temperature T0, which is adapted to the bandpass filter 14. The further the additional radiation sources 4 are spaced from the centrally arranged radiation source 5, the lower their operating temperature T1, T2 is set compared to the reference temperature T0. As a result, the generated beams 6 are generated with a shortened wavelength corresponding to the emission angle or a shift in the transmission range of the bandpass filter 14.

[0043] The Fig. 3 shows a schematic representation of a radiation source arrangement of a transmitter unit 2 according to a second exemplary embodiment. In contrast to the first exemplary embodiment, the radiation sources 4, 5 are connected to one another to form a stack. The radiation sources 4, 5 are thermally conductively coupled. The two radiation sources 4 arranged at an outer edge of the stack are each thermally conductively connected to a passive or active heat sink 26. This results in heat dissipation, as shown by the arrows, which generates two temperature gradients. The emitter or radiation source 5 arranged in the middle of the stack has the highest operating temperature. Towards the outer edges, the temperature of the radiation sources 4 drops due to the heat sinks 26. As a result, the Fig. 4, the wavelength shifts of the beams 6, 7 adapted to the exemplary wavelength shift shown in FIG. 4 can be realized by the thermally adjusted radiation sources 4, 5. The temperature gradient can be varied or influenced by additional thermal resistors arranged between the radiation sources 4, 5.

[0044] In the Fig. 4 shows a schematic representation of a dependence of the transmitted wavelength of a bandpass filter 14 on an emission angle of the incoming beams 12, 13.

Claims

[1] Transmitter unit (2) of a LIDAR device (1) with at least two radiation sources (4, 5) for generating and emitting point-shaped or line-shaped electromagnetic beams (6, 7) into a scanning area (A), wherein at least one radiation source (4, 5) has an adjustable operating temperature (T0, T1, T2) and / or adjustable emission wavelength depending on a radiation angle of the electromagnetic beams (6, 7) generated by the at least one radiation source (4, 5); and wherein the operating temperature (T0, T1, T2) of at least one radiation source (4, 5) is adjustable by dissipating operating heat to a passive heat sink (26). [2] Transmitting unit according to claim 1, wherein the operating temperature (T0, T1, T2) is adjustable depending on a radiation angle of the at least one radiation source (4, 5). [3] Transmitting unit according to claim 2, wherein the operating temperature (T0, T1, T2) of the at least one radiation source (4, 5) decreases with increasing radiation angle. [4] Transmitting unit according to one of claims 1 to 3, wherein the transmitting unit (2) has at least one optical element (8) arranged in the beam path of the emitted electromagnetic beams (6, 7). [5] Transmitting unit according to one of claims 1 to 4, wherein the electromagnetic beams (6, 7) can be generated by the at least two beam sources (4, 5) simultaneously or successively. [6] Transmitting unit according to one of claims 1 to 5, wherein the at least two radiation sources (4, 5) are stacked or adjacent surface emitters or edge emitters. [7] LIDAR device (1) for scanning a scanning area (A) defined by a vertical and a horizontal scanning angle with electromagnetic beams (6, 7), comprising: - at least one transmitting unit (2) according to one of the preceding claims for generating electromagnetic beams (6, 7) and for distributing or deflecting the electromagnetic beams (6, 7) at least along the vertical scanning angle, - at least one receiving unit (16) for receiving beams (12, 13) reflected from at least one object (10) arranged in the scanning area (A), - a bandpass filter (14) for absorbing or reflecting interference reflections and - at least one evaluation unit (18) for evaluating the received reflected beams (12, 13).

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