OPTICAL PULSE GENERATOR AND METHOD FOR OPERATING AN OPTICAL PULSE GENERATOR

Description

[0001] The present invention relates to a LiDAR system and a method for operating a LiDAR system. In particular, the present invention relates to a LiDAR system comprising an optical pulse generator for high-frequency (HF) pulse-width modulation. State of the art

[0002] LiDAR (light detection and ranging) is a method for optical distance and speed measurement using laser beams. LiDAR systems are increasingly being used in motor vehicles, particularly for obstacle detection. Corresponding LiDAR systems for use in motor vehicles are known, for example, from US 7,969,588 B2.

[0003] In general, however, such systems operate with a fixed pulse width, meaning that reliable measurements can only be performed with a limited number of independently operating systems. If the signals from a large number of systems are superimposed, for example in dense urban traffic with numerous reflective obstacles, reliable detections are no longer possible. Therefore, the increasing use of LiDAR raises the risk of correspondingly serious misinterpretations. Autocorrelation of transmitted and received signals, a common feature of related radar systems for improving signal detection, is only achievable in the optical range with considerable technological effort.

[0004] One way to uniquely identify individual LiDAR signals is to imprint a unique signature using pulse-width modulation. However, such modulation is only feasible with a very fast logic circuit and a very low-inductance design to achieve the necessary switching times.

[0005] Laser diodes and other semiconductor-based radiation-emitting optical components (e.g., luminescent diodes, optical amplifier elements) generally lack the necessary electronics for rapid pulsed control. Individual chips are separated from a manufacturing wafer and typically controlled via an external electronic circuit.

[0006] The connection of laser diodes is often achieved via a multitude of individual bond wires, which form a conductive connection between contact pads on the surface of the laser diode and corresponding contact pads on the electronic circuit. To achieve a uniform current density within the active layer, especially in high-power laser diodes, a large number of small-diameter bond wires are typically distributed as evenly as possible along the entire laser length. Due to the small cross-section of the bond wires and the large area spanned by the current, such connections exhibit inductances that are too high for the intended application. While the use of ribbons for contacting can reduce the resulting inductances, these are still far too high, particularly for fast RF pulse-width modulation of the emitted radiation. Typical inductances for wire bonding are 0.8–1.0 nH / mm of bond wire length.

[0007] US patent 2015 / 0229912 A1 discloses a VCSEL array for a 3D camera with time-of-flight detection, in which the optical component and a corresponding driver are arranged on a common mounting bracket. CN 102 610 998 B discloses a pulsed semiconductor laser in which the driver module and the laser module are connected via a simple coaxial cable. JP H06 334169 A teaches the adaptation of the electronic coupling of an optical component to a control line in the form of a microstrip conductor. JP 2016-14665 A addresses the problem of shortening the length of a wiring connection between a light-emitting element and an associated control circuit. Further prior art is represented by JP S63 67792 A, EP 2 963 445 A2, and JP 2015 065255 A. Disclosure of the invention

[0008] It is therefore an object of the present invention to provide a LiDAR system and a method for operating a LiDAR system which overcome the described disadvantages of the prior art. In particular, an optical pulse generator of a LiDAR system according to the invention should enable RF pulse-width modulation in LiDAR systems.

[0009] These problems are solved according to the invention by the features of independent claims 1 and 7. Advantageous embodiments of the invention are contained in the dependent claims.

[0010] A LiDAR system according to the invention comprises an optical pulse generator, wherein the pulse generator includes: an active optical component configured to emit optical radiation, the optical component having contact surfaces for electrical contact; a means for electronically controlling the optical component, configured to excite the optical component to pulsed emission of optical radiation, the means for electronic control having contact surfaces for electrical contact and electronic components;a first subrack, wherein the means for electronic control is arranged on the first subrack, wherein the electronic components are arranged on a first side of the first subrack, the contact surfaces are arranged on an opposite second side of the first subrack, and the electronic components are connected to the contact surfaces via electrically conductive feedthroughs in the first subrack; a second subrack, wherein the optical component is arranged on the second subrack, wherein the optical component is arranged between the first subrack and the second subrack;and wherein at least one contact surface of the means for electronic control is directly or by means of a solder point connected to at least one contact surface of the optical component. The LiDAR system according to the invention is characterized in that the optical component is completely recessed in a recess in the surface of the second component carrier;or that the first component carrier is a flexible printed circuit board and the means for electronic control is a high-frequency circuit for electronically exciting the optical component to pulsed emission of optical radiation. Preferably, the active optical component is a laser diode, a luminescent diode, or an optical amplifier element. The optical component can have several contact surfaces for electrical contact. Electrically conductive surface elements provided for contact on the surface of an optical component are preferably used as contact surfaces. The contact surfaces can be formed on a single surface or on different surfaces of the optical component.

[0011] Preferably, the means for electronically controlling the optical component is a driver circuit adapted to the electronic parameters of the active optical component for generating high-frequency pulses. The electronic control means is preferably configured to drive the optical component via high-frequency, high-current pulses. In particular, the electronic control means can generate the high-current pulses on one or both sides relative to the center position of the optical component. The driver circuit can be composed of one or more pairs of drive transistors and storage capacitors. The contact surfaces for connecting the electronic control means preferably consist of an electrically conductive material (e.g., metal).The means for electronic control can include, in addition to the aforementioned electronic components and contact surfaces, further electronic components, conductor tracks and connecting elements.

[0012] According to the invention, the first subrack is a special, flexible printed circuit board material, preferably LTCC (ceramic). The electronic control means can be permanently connected to the first subrack. An example of such an electronic control means ("circuit") permanently connected to a subrack is a fully assembled and wired circuit board.

[0013] The second subrack is preferably a heat sink. The optical component can be permanently or detachably attached (e.g., with a removable adhesive) to the heat sink. Preferably, the heat sink is metallic and has a large surface area. It is also preferred that the second subrack is made of an electrically conductive material. This allows the optical component to be powered via the second subrack as well. However, power can also be supplied exclusively from the first subrack.

[0014] According to the invention, the second sub-carrier has a recess in one of its surfaces in which the optical component can be completely recessed. Preferably, the surface of the second sub-carrier containing the recess and the outwardly facing surface of the optical component completely recessed in the recess form a common plane.

[0015] The idea of ​​the present invention is that, for the use of an optical pulse generator in a LiDAR system, hybrid integration without parasitic inductive effects through the leads can be achieved by coupling the optical component (e.g., laser) and the electronic control means as directly as possible. This is made possible in particular by directly integrating the optical component into the circuit of the electronic control means, thereby achieving extremely low inductances. This can be achieved in particular by a small spatial distance between the individual circuit elements, the largest possible width of the leads within the electronic control means, with the width adapted to the active length of the optical component, and a small distance between the leads. The latter is achieved in particular by using wiring carriers (i.e.,first component carrier) which consists of a particularly thin dielectric (e.g., a special, flexible printed circuit board material or LTCC (ceramic)). The total inductance typically achieved with an optical pulse generator according to the invention is approximately 100–200 pH.

[0016] By avoiding conventional bond wires or contact ribbons, the resulting inductances can be significantly reduced. These low inductances allow for both rapid switching on and off of the generated radiation pulses. This enables, in particular, very high-frequency pulse width modulation in the optical range for imprinting a unique pulse width signature. Preferably, the switching times of the pulses are in the single-digit nanosecond range, more preferably in the picosecond range.

[0017] Preferably, the system is assembled for measurement purposes using a clamping technique or, for practical application, via a direct connection between at least one contact surface of the electronic control device and at least one contact surface of the optical component. The optical component can preferably be clamped between the first and second subracks. Clamping can be achieved using a suitable fixing or holding device. Adhesive bonding or soldering can also be used as possible alternatives to direct clamping.

[0018] Preferably, the electronic control means is configured to imprint an individual signature on the radiation pulses emitted by the optical component via variable pulse width modulation. This individual signature can be, for example, a predefined pulse width modulation scheme, a pulse sequence variation randomly assigned to individual pulses or pulse sequences, or any other modulation scheme suitable for unambiguous pulse assignment.

[0019] According to the invention, the electronic components of the means for electronic control are arranged on a first side of the first sub-carrier, while the contact surfaces of the means for electronic control are arranged on a second side of the first sub-carrier opposite the first side.

[0020] The electronic components and contact surfaces are connected to each other by conductive traces to form a circuit. According to the invention, electrically conductive feedthroughs (vias) are used in the first subrack to connect the electronic components arranged on the first side of the first subrack to the contact surfaces located on the opposite second side of the first subrack.

[0021] In a first embodiment of the present invention, the optical component is supplied with a two-pole current from one side only, from the surface of the optical component facing the first sub-carrier. Current is thus supplied exclusively via the first sub-carrier.

[0022] In a second embodiment of the present invention, the optical component can be supplied with a bipolar current from both the surface of the optical component facing the first sub-support (with a first polarity) and the surface of the optical component facing the second sub-support (with a second polarity). In this case, the current is supplied via both the first and the second sub-support.

[0023] In particular, the high-frequency pulse width modulation made possible by the low inductance of the optical pulse generator allows for the imprinting of an individual pulse signature for unambiguous pulse identification in LiDAR systems. A sufficient bandwidth for pulse width modulation enables reliable measurements even with a large number of independent LiDAR signals. The present invention further comprises a method for operating an optical pulse generator in a LiDAR system according to the invention, comprising providing an active optical component, wherein the optical component has contact surfaces for electrical contact; and providing the means for electronically controlling the optical component, wherein the means for electronic control has contact surfaces for electrical contact and electronic components.the provision of a first subrack, wherein the means for electronic control is arranged on the first subrack, wherein the electronic components are arranged on the first side of the first subrack, the contact surfaces are arranged on the opposite second side of the first subrack, and the electronic components are connected to the contact surfaces via electrically conductive feedthroughs in the first subrack;Providing the second subrack, wherein the optical component is arranged on the second subrack, wherein the optical component is completely recessed in the recess in the surface of the second subrack, or wherein the first subrack is the flexible printed circuit board and the electronic control means is the high-frequency circuit for electronically exciting the optical component to pulsed emission of optical radiation; arranging the optical component between the first subrack and the second subrack, wherein at least one contact surface of the electronic control means is directly connected to the contact surfaces of the optical component; clamping the optical component between the first subrack and the second subrack;and the excitation of the optical component to pulsed emission of optical radiation via the means of electronic control.

[0024] The method according to the invention is particularly suitable for testing individual optical components. An optical component excited according to the aforementioned method for operating an optical pulse generator for pulsed emission of optical radiation can be tested non-destructively in short-pulse operation by means of a clamping according to the invention (i.e. pressing the RF circuit directly onto the optical component), thereby enabling rapid replacement of the optical component without extensive bonding processes. Brief description of the drawings

[0025] The invention is explained below using exemplary embodiments with reference to the accompanying drawing. The drawing shows: Fig. 1 is a schematic representation of a first embodiment of an optical pulse generator in a LiDAR system according to the invention, and Fig. 2 is a schematic representation of a second embodiment of an optical pulse generator in a LiDAR system according to the invention. Detailed description of the drawings

[0026] Fig. 1Figure 1 shows a schematic representation of a first embodiment of an optical pulse generator in a LiDAR system according to the invention. The optical component 10 is completely recessed in a recess in the surface of the second sub-carrier 40, wherein, in particular, the surface of the second sub-carrier 40 facing towards the first sub-carrier 30 forms a common plane with the surface of the optical component 10, which also faces towards the first sub-carrier 30. In such an arrangement, however, the surface of the optical component 10 facing towards the first sub-carrier 30 can also be aligned above or below the surface of the second sub-carrier 40 facing towards the first sub-carrier 30.

[0027] The first sub-carrier 30 serves as a carrier for the electronic control means 20, which in the illustrated embodiment is composed of various electronic components, conductor tracks, and at least two contact surfaces 22, 24 designed for contacting. Preferably, as also shown in Fig. 1 The electronic components are shown arranged on a side of the first subrack 30 opposite the contact surfaces 22, 24 (i.e., on the top of the first subrack 30), with electrically conductive connections between the conductor tracks connecting the electronic components to a circuit on the top of the first subrack 30 and the contact surfaces 12, 14 located on the bottom of the subrack 30 being passed through the first subrack 30 (vias).

[0028] The means for electronic control 20 is designed to couple high-current pulses for electronic excitation of the optical component 10 into the optical component on both sides with respect to the center position of the optical component 10, i.e. the high-current pulses are generated both by the arranged electronic components to the left of the optical component 10 and by the arranged electronic components to the right of the optical component 10.

[0029] The optical component 10 is preferably clamped between the first subrack 30 and the second subrack 40, wherein at least one contact surface 14 of the optical component 10 contacts at least one contact surface 24 of the electronic control means 20. The contact can be made simply by touching the contact surfaces 14, 24 or by means of a solder joint between the contact surfaces 14, 24. Furthermore, any contact medium acting as an electrically conductive contact mediator can be used to improve the contact (e.g., graphite-containing electrically conductive paste with corrosion protection).

[0030] In the illustrated embodiment, the electronic control means 20 has at least one further contact surface 22 which does not have direct contact with at least one contact surface 12 of the optical component 10. Preferably, the second sub-carrier 40 comprises an electrically conductive material (e.g., a metal) configured to allow current flow between the contact surface 12 of the optical component 10 and the contact surface 22 of the electronic control means 20 via the second sub-carrier 40. Preferably, the entire second sub-carrier 40 consists of a thermally and electrically conductive material (e.g., silver, copper, gold, aluminum). In the illustrated embodiment, the optical component 10 is thus energized from opposite sides of the optical component 10.

[0031] Fig. 2Figure 1 shows a schematic representation of a second embodiment of an optical pulse generator in a LiDAR system according to the invention. The basic structure largely corresponds to that shown in Figure 2. Fig. 1 The illustrated embodiment. The respective reference numerals and their assignments apply accordingly. In contrast to Fig. 1The optical component 10 is energized exclusively from one side of the optical component 10. The surface of the optical component 10 facing the first subrack 30 is aligned below the surface of the second subrack 40 facing the first subrack 30, so that the independent contact surfaces 22, 24 of the electronic control means 20, located on the underside of the first subrack, lie flat on the surface of the underlying optical component 10, i.e., on the contact surfaces 12, 14 of the optical component 10 located there. Reference symbol list

[0032] 10 Optical component 12 Contact surface (optical component 10) 14 Contact surface (optical component 10) 20 Electronic control means 22 Contact surface (electronic control means 20) 24 Contact surface (electronic control means 20) 30 First subrack 40 Second subrack

Claims

1. A LiDAR system with an optical pulse generator, comprising: a) an active optical component (10) configured to emit optical radiation, wherein the optical component (10) has contact surfaces (12, 14) for electrical contacting; b) a means for electronically driving (20) the optical component (10), configured to excite the optical component (10) to a pulsed emission of optical radiation, wherein the means for electronically driving (20) comprises contact surfaces (22, 24) for electrical contacting and electronic components; c) a first submount (30), wherein the means for electronically driving (20) is arranged on the first submount (30), wherein the electronic components are arranged on a first side of the first submount (30), the contact surfaces (22, 24) are arranged on an opposite second side of the first submount (30), and the electronic components are connected to the contact surfaces (22, 24) via electrically conductive vias in the first submount (30); d) a second submount (40), wherein the optical component (10) is arranged on the second submount (40); e) wherein the optical component (10) is arranged between the first submount (30) and the second submount (40); and f) wherein at least one contact surface (22, 24) of the means for electronically driving (20) is connected directly or by means of a solder point to at least one contact surface (12, 14) of the optical component (10); g) wherein the optical component (10) is completely recessed in a recess in the surface of the second submount (40); or h) wherein the first submount (30) is a flexible circuit board and the means for electronically driving (20) is a high-frequency circuit for electronically exciting the optical component (10) to a pulsed emission of optical radiation.

2. The LiDAR system according to claim 1, wherein the contact surfaces (22, 24) of the means for electronically driving (20) are made of a metal.

3. The LiDAR system according to one of the preceding claims, wherein the means for electronically driving (20) is a driver circuit for high-frequency pulse generation adapted to electronic parameters of the optical component (10).

4. The LiDAR system according to one of the preceding claims, wherein the optical component (20) is powered via the first submount (30) and the second submount (40) or exclusively via the first submount (30).

5. The LiDAR system according to one of the preceding claims, wherein the optical component (10) is clamped between the first submount (30) and the second submount (40).

6. The LiDAR system according to one of the preceding claims, wherein the means for electronically driving (20) is configured to apply an individual signature to radiation pulses emitted by the optical component (10) via variable pulse width modulation.

7. A method for operating an optical pulse generator in a LiDAR system according to one of the preceding claims, comprising: a) providing the active optical component (10), wherein the optical component (10) comprises contact surfaces (12, 14) for electrical contacting; b) providing the means for electronically driving (20) the optical component (10), wherein the means for electronically driving (20) comprises contact surfaces (22, 24) for electrical contacting and electronic components; c) providing the first submount (30), wherein the means for electronically driving (20) is arranged on the first submount (30), wherein the electronic components are arranged on the first side of the first submount (30), the contact surfaces (22, 24) are arranged on the opposite second side of the first submount (30), and the electronic components are connected to the contact surfaces (22, 24) via electrically conductive vias in the first submount (30); d) providing the second submount (40), wherein the optical component (10) is arranged on the second submount (40); wherein the optical component (10) is completely recessed in the recess in the surface of the second submount (40), or the first submount (30) is the flexible circuit board and the means for electronically driving (20) is the high-frequency circuit for electronically exciting the optical component (10) to a pulsed emission of optical radiation; e) arranging the optical component (10) between the first submount (30) and the second submount (40), wherein at least one contact surface (22, 24) of the means for electronically driving (20) is directly connected to the contact surfaces (12, 14) of the optical component (10); f) clamping the optical component (10) between the first submount (30) and the second submount (40); g) exciting the optical component (10) to a pulsed emission of optical radiation via the means for electronically driving (20).