Transmitter unit and LIDAR device for scanning a scanning area

Abstract

Transmitter unit (1) of a LIDAR device (14) with at least two radiation sources (2) designed as semiconductor lasers for generating and emitting electromagnetic beams (6) into a scanning area (A), characterized in that the at least two radiation sources (2) are individual emitters (2) directly connected to each other mechanically and electrically in series, which are designed in the form of a semiconductor bar-like arrangement, wherein the transmitter unit (1) has a beam shaping optic arranged in the beam path of the generated beams (6), which comprises an aspherical lens (8) for beam homogenization and an aspherical cylindrical lens (10) downstream of the aspherical lens (8) for collimation.

Description

The invention relates to a transmitting unit of a LIDAR device having at least two radiation sources designed as semiconductor lasers for generating and emitting electromagnetic beams into a scanning region, and to a LIDAR device.Prior ArtScanning LIDAR devices usually have permanently arranged or horizontally rotating transmitting and receiving units. In the case of a horizontally rotating arrangement, a vertical line can be emitted, so that the entire environment is detected during a complete rotation. Due to the high requirements for the output power of the emitted source and the robustness, size and cost of the LIDAR device, semiconductor lasers are preferably used as radiation sources. US 2015 / 0131 080 A1 likewise discloses a LIDAR device which has an emitter array as a radiation source and a detector array.The output power of semiconductor lasers that can be achieved depends, inter alia, on the optical power density on an emission surface or a facet of the radiation source. If the power density is too high, this can result in destruction of the radiation source. In semiconductor lasers designed as edge emitters, therefore, the emission area is increased by widening the emitting edge. Edge emitters cannot be realized in any width, however, since otherwise lossy undesired modes can form. Instead, individual emitters with widths of up to 400 μm are used. A plurality of emitters or radiation sources are used at a distance of, for example, more than 10 μm from one another as an integral semiconductor structure or as a so-called laser bar. EP 3 605 757 A1 discloses a production method for such a laser bar, which consists of a plurality of integrally configured single emitter layers. The laser ingot is formed by the wafer-based manufacturing method. The respective individual emitter layers are provided with a solder layer which functions as a connecting layer and enables an integral connection of a plurality of individual emitter layers.US 2017 / 0098923 A1 discloses laser systems for wavelength beam combining (WBC) using different beam forming and collimating optics. Configurations including cylindrical lenses, spherical lenses, and dispersive elements such as diffraction gratings to combine and shape the beams of multiple emitters are described, among others.US 2018 / 0062348 A1 describes the housing and assembly technique for high-power lasers, in which the use of aspherical lenses for collimating the beams emitted by diode bars or stacks while maintaining the beam quality is mentioned in particular. The aim is to improve thermal management and beam forming.For achieving high optical output powers with simultaneously short laser pulse durations in the nanosecond range, in addition to the design of the laser geometry, the laser driver used for electronically driving the laser sources plays an essential role. In the case of the bar structure described, the required electric current scales proportionally with the number of emission areas. This makes it increasingly difficult to provide a laser driver which makes it possible to switch the required current in the range of a few nanoseconds.To reduce the requirement for the driver, individual semiconductor structures can be operated in parallel. Instead of arranging the individual emission surfaces in a semiconductor structure, the structure consists of individual semiconductor laser chips which are arranged at a defined distance from one another. Increasing the distance between the semiconductor structures has the advantage that each semiconductor structure can be energized separately by one driver and the required total current or total power can thus be distributed over many drivers. With a corresponding arrangement of optical components, a laser line can be formed from a plurality of independent semiconductor structures and emitted into the environment. In such a parallel arrangement of a plurality of semiconductor structures, however, the dimensions and in particular the overall height of the transmitting unit increase. The beam distribution resulting from this can thus have a greater diffraction index and therefore makes the design of the beam-shaping optical unit more difficult. In order to achieve the specification of homogeneous line illumination, the generated beams of the individual radiation sources are typically formed separately with the aid of a multiplicity of individual lenses or a lens array.Disclosure of the InventionThe object on which the invention is based can be seen in the fact that it proposes a simplified transmitter unit for a scanning LIDAR device, which unit connects the advantages of laser bars to those of laser diodes controlled in parallel and thereby offers the possibility of achieving homogeneous line illumination with simple optical elements.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 dependent claims.According to one aspect of the invention, a transmitting unit of a LIDAR device is provided, having at least two radiation sources configured as semiconductor lasers for generating and emitting electromagnetic beams into a scanning region, wherein the at least two radiation sources are individual emitters directly mechanically and electrically connected to one another.By means of a direct mechanical and electrical connection of the individual emitters, an optimized combination of laser geometry and optics for simplified generation of a homogeneous laser line with a high output power can be implemented. The transmission unit is preferably configured to be scalable and can thus be extended as desired by additional radiation sources.The radiation sources can be arranged mechanically in series. For example, one or more parallel rows of radiation sources may be used to generate electromagnetic beams. The radiation sources can be electrically and mechanically connected to one another, for example, directly by soldered connections. As a result, the distances between the individual semiconductor structures or radiation sources can be set to be particularly small, so that the use of complex channel-specific lenses or lens arrays can be dispensed with. Instead, the beam characteristic of the laser stack or of the transmission unit can already be influenced with individual lenses in such a way that a homogeneous line illumination can be generated.The transmission unit according to the invention allows the advantages of a laser bar with a compact shape and a simplified beam shaping to be combined with advantages of separate laser diodes driven in parallel with lower requirements imposed on a driver.The radiation sources can be connected electrically in parallel or in series, for example, at the electrical connection pins or electrical contacts. The electrical connecting pins or electrical contacts of the radiation sources can be used as mechanical connections.The transmission unit has a beam shaping optics or generating optics, respectively, arranged in the beam path of the generated beams, with at least one optical element. Due to the compact size of the transmitting unit, the line characteristic for illuminating an environment or a scanning region can already be produced with individual lenses. The omission of microlenses makes it possible to use beam shaping optics with lower requirements for tolerances.The at least one optical element is an aspherical lens or a diffractive optical element, a so-called Powell lens or a diffractive optical element which generates the homogeneous line distribution in the vertical direction. A second aspherical lens performs the necessary horizontal collimation. In this case, the distance between collimating lens and beam source can be selected such that the arrangement at the exit is eye-safe.The beam shaping optics has two specifically shaped aspherical lenses. In this case, the intensity distribution emitted by the laser arrangement is initially shaped using a first aspherical lens in such a way that, in addition to the homogeneous line distribution in the vertical, widening in the horizontal is achieved. A second aspherical lens then provides the required horizontal collimation. This embodiment can be designed to be particularly compact.According to a further embodiment of the transmitting unit, the at least two radiation sources are directly mechanically and electrically connected to one another by soldered connections. The radiation sources of the transmitting unit, which are embodied as semiconductor structures, can be arranged mechanically in series. For example, the semiconductor chips can be soldered directly to one another. A particularly compact transmitting unit can thereby be achieved.According to a further embodiment of the transmission unit, the at least two radiation sources are surface emitters or edge emitters stacked or arranged adjacent to one another. As a result, for example, available semiconductor chips can be used to produce a transmission unit. Depending on a desired illumination characteristic of the LIDAR device, surface emitters or edge emitters can be directly connected to one another mechanically and electrically.According to a further embodiment, the transmitting unit has at least one driver for electrically driving the at least two radiation sources. As a result, the radiation sources can be electrically regulated by the at least one driver. In particular, a radiation intensity of the generated electromagnetic beams can be adjusted and stabilized by the at least one driver.According to a further embodiment of the transmitting unit, the at least two radiation sources are electrically connected to the at least one driver by a serial circuit. By means of the serial interconnection of the radiation sources, the transmitting unit can already be operated with a laser driver. In the case of a series connection of the radiation sources, the driver only has to apply that peak current which is required by an individual emitter and thus is more cost-effective.According to another aspect of the invention, there is provided a lidar device for scanning electromagnetic beams over a scanning range defined by a vertical and a horizontal scanning angle. 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. At least one receiving unit of the LIDAR device serves to receive beams reflected at at least one object arranged in the scanning area. Furthermore, the LIDAR device has at least one evaluation unit for evaluating the received reflected beams.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 emission angle is dependent in particular on the optical properties of the generating optics and the distance from the optical axis. Beams shaped in this way can subsequently be emitted directly or via a deflection unit from the LIDAR device into the scanning region.If an object is arranged in the scanning region, the shaped and emitted beams are reflected on the object. At least one reflected laser pulse or beam can be received and detected by the receiving unit. For this purpose, the receiving unit can have a receiving optics, which directs the at least one laser pulse onto a detector.In the LIDAR device according to the invention, the transmitting unit is particularly compact and of inexpensive construction. This is achieved by direct stacking of the semiconductor emitters or the radiation sources. The radiation sources can have a direct body contact with each other. Preferably, the radiation sources can be coupled to one another by chemical or mechanical compounds. In addition to the body contact between the radiation sources, the chemical or mechanical connection can also establish an electrical contact for electrically driving the radiation sources by at least one driver.Due to the particularly compact and semiconductor bar-like arrangement of the individual emitters, the generating optics can be configured in a particularly simple manner.In particular, complex lens arrays for shaping the generated beams can be omitted.The individual radiation sources are preferably electrically connected to the driver in a series circuit. As a result, the maximum current to be provided by the driver is lower compared to a parallel circuit, as a result of which the driver can be designed to be technically simpler.Preferred exemplary embodiments of the invention are explained in more detail below with the aid of greatly simplified schematic representations. Shown here are: FIG. 1 shows a schematic illustration of a transmission unit according to an exemplary embodiment, FIG. 2 shows a schematic illustration of a transmission unit according to an exemplary embodiment, FIG. 3 shows a schematic illustration of a transmission unit according to an exemplary embodiment, and FIG. 4 shows a schematic illustration of a LIDAR device according to an exemplary embodiment.In the figures, the same structural elements have the same reference numerals.FIG. 1 shows a schematic illustration of the principle of a transmitting unit 1 for generating a laser line with series-connected individual lasers. For the sake of simplicity, the driver and the detailed electronic control of the radiation sources 2 are not shown.The transmitting unit 1 has six radiation sources 2, which are designed as edge emitters. According to the exemplary embodiment, the radiation sources 2 are arranged one above the other in a vertical direction and are electrically connected in series to one another. The arrow here illustrates a current flow through the radiation sources 2 connected in series. The total overall height with 6 individual emitters is thus approximately 0.5 mm.Due to the direct or stacked arrangement of the radiation sources 2, the emission surfaces are positioned particularly close to one another. Consequently, it is possible here to dispense with lens arrays and to utilize the advantages of macroscopic lenses in comparison with a macroscopically extended arrangement of individual emittersFIG. 2 ashows a schematic representation of a transmitting unit 1 according to an embodiment.The Powell lens 8 is the first lens 8 here and performs the task of beam shaping in the vertical direction and homogenization of the generated beams 6.FIG. 2 bshows the intensity distribution of the shaped beams 12 emitted into the scanning region A, as it results at a distance of 200 m from the laser source. In this case, analogously to the second exemplary embodiment, a vertical divergence angle of approximately 20° and a horizontal divergence angle of approximately 0.2° result.FIG. 3 ashows a schematic representation of a transmitting unit 1 according to a further exemplary embodiment.At a distance of, for example, 15 mm from the emission surfaces of the radiation sources 2, a lens 8 having a bi-convex contour in the vertical direction is arranged. As a result, the inhomogeneous vertical intensity distribution of the beams 6 generated by the radiation sources 2 is homogenized (rectangular profile).In addition, the lens 8 also has a bi-concave contour in the horizontal direction, as a result of which an additional horizontal expansion is forced. The aim of this expansion is to achieve a more compact design in comparison with the exemplary embodiment described in FIG. 2, which design still satisfies eye safety requirements.The lens or the optical element 10 subsequently ensures the required horizontal collimation at the total distance of approximately 40 mm from the emission surfaces of the radiation sources 2.FIG. 3 bshows the intensity distribution of the shaped beams 12 emitted into the scanning region A, as it results at a distance of 200 m from the laser source. This results in a vertical divergence angle of approximately 20° and a horizontal divergence angle of approximately 0.2°.FIG. 4 shows a schematic illustration of a LIDAR device 14 according to a first exemplary embodiment. The device 14 has a transmitting unit 1 with three serially operated radiation sources 2.The radiation sources 2 are electrically controlled by a driver 16. The beams 12 formed by the generating optics 4 are radiated into the scanning region A.Beams 20 reflected at an object 18 can then be received by a receiving unit 22 and evaluated by an evaluation unit 24. The receiving unit 22 can be a detector, for example. For example, a time-of-flight analysis for ascertaining a distance of the object 18 can be carried out by the evaluation unit 24.

Claims

Transmitting unit (1) of a LIDAR device (14) having at least two radiation sources (2) designed as semiconductor lasers for generating and emitting electromagnetic beams (6) into a scanning region (A), characterized in that the at least two radiation sources (2) are individual emitters (2) which are connected directly mechanically and electrically in series to one another and are designed in the form of a semiconductor bar-like arrangement, wherein the transmitting unit (1) has a beam shaping optical unit which is arranged in the beam path of the generated beams (6) and comprises an aspherical lens (8) for beam homogenization and an aspherical cylindrical lens (10), connected downstream of the aspherical lens (8), for collimation.Transmitting unit according to Claim 1, wherein the at least two radiation sources (2) are directly mechanically and electrically connected to one another by soldered connections.Transmitting unit according to Claim 1 or 2, wherein the at least two radiation sources (2) are surface emitters or edge emitters stacked or arranged adjacent to one another.Transmitting unit according to one of Claims 1 to 3, wherein the transmitting unit (1) has at least one driver (16) for electrically driving the at least two radiation sources (2).Transmitting unit according to Claim 4, wherein the at least two radiation sources (2) are electrically connected to the at least one driver (16) by a serial circuit.LIDAR device (14) for scanning a scanning region (A) defined by a vertical and a horizontal scanning angle with electromagnetic beams (6, 12), comprising: - at least one transmitting unit (1) according to one of the preceding claims for generating electromagnetic beams (6) and for distributing or deflecting the electromagnetic beams (6, 12) at least along the vertical scanning angle, - at least one receiving unit (22) for receiving beams (20) reflected at at least one object (18) arranged in the scanning region (A), and - at least one evaluation unit (24) for evaluating the received reflected beams (20).

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