Search

DE-102024133101-A1 - Lidar device and method for operating a lidar device

DE102024133101A1DE 102024133101 A1DE102024133101 A1DE 102024133101A1DE-102024133101-A1

Abstract

The present invention relates to a lidar device (1) for detecting the environment of a vehicle, wherein the lidar device comprises the following: a laser light source (10) designed to emit laser light, an optical head (18) with an optical transmitting and receiving unit for emitting laser light into the environment and for receiving laser light reflected from the environment, and at least one detector (40, 58) designed to convert received laser light (22) into electrical signals. According to the invention, the lidar device (1) further comprises the following: a first splitter (14) for splitting the emitted laser light into a portion to be emitted (20) and a portion to be stored, an optical storage element (28), for storing the portion to be stored, a second optical splitter (32) which is designed to direct the portion to be stored, after storage, proportionally via a first optical (34) connection directly and via a second optical connection (64) via a polarization rotator (62) in the direction of the at least one detector (40, 58).

Inventors

  • Jonathan Fischer

Assignees

  • BAYERISCHE MOTOREN WERKE AKTIENGESELLSCHAFT

Dates

Publication Date
20260513
Application Date
20241112

Claims (10)

  1. Lidar device (1) for detecting the surroundings of a vehicle, the lidar device comprising: a laser light source (10) for emitting laser light, an optical head (18) with an optical transmitter and receiver unit for emitting the laser light into the surroundings and for receiving laser light reflected from the surroundings, and at least one detector (40, 58) for converting received laser light (22) into electrical signals, characterized in that: the lidar device (1) further comprises: a first splitter (14) for splitting the emitted laser light into a component to be emitted (20) and a component to be stored, an optical storage element (28) for storing of the portion to be stored, a second optical splitter (32) which is designed to direct the portion to be stored, after storage, proportionally via a first optical (34) connection directly and via a second optical connection (64) via a polarization rotator (62) in the direction of the at least one detector (40, 58).
  2. Lidar device according to Claim 1 , characterized in that the polarization rotator (62) is designed to rotate the polarization direction of linearly polarized light by 90°.
  3. Lidar device according to one of the preceding claims, characterized in that the detector (40) is provided to mix received laser light (22) with two mutually perpendicular linear polarization states with stored laser light after storage with also two mutually perpendicular linear polarization states for the execution of a heterodyne process, wherein laser light components with the same linear polarization state are mixed in each case.
  4. Lidar device according to Claim 3 , characterized in that a combiner (36) is provided upstream of the detector (40) to combine the light after passing through the polarization rotator (62) with the light from the first optical connection (34) and with the received laser light and to forward it to the detector (40).
  5. Lidar device according to one of the preceding Claims 1 and 2 , characterized in that two detectors (40, 58) are provided for mixing received laser light (22) with two mutually perpendicular linear polarization states with stored laser light after storage for the execution of a heterodyne process, wherein in a first of the two detectors (40) light components with a first linear polarization state are mixed and in a second (58) of the two detectors light components with a second linear polarization state are mixed and the first and the second linear polarization states are perpendicular to each other.
  6. Lidar device according to Claim 5 , characterized in that a polarization separator (50) is provided between the optical head (18) and the two detectors (40, 58) for dividing received laser light (22) into two parts with mutually perpendicular linear polarization states, and two optical connections (54, 56) are provided for directing the two parts separately to the two detectors (40, 58).
  7. Lidar device according to one of the preceding claims, characterized in that at least one or all optical connections (12, 16, 26, 30, 34, 38, 46, 48, 52, 54, 56, 64) installed between the laser light source (10) and the at least one detector (40, 58) are polarization-preserving and preferably designed as polarization-preserving fiber optic connections or as a polarization-preserving waveguide structure on a photonic chip.
  8. A method for operating a lidar device (1) of a vehicle in an FMCW mode, wherein, in the course of the method: a portion (20) of laser light emitted by a laser light source (10) is emitted into the vehicle's surroundings and laser light reflected from the surroundings is received, a portion of the emitted laser light is stored in an optical storage element (28), and the received (22) and stored laser light is converted into electrical signals by means of a heterodyne process by at least one detector (40, 58), characterized in that: the emission and storage take place in a linear polarization state of a first polarization direction, the stored light, after storage, is partly guided through a polarization rotor (62) which rotates the first polarization direction by 90° into a second polarization direction before the execution of the heterodyne process, and partly guided past the polarization rotor (62), and both parts are then connected to the at least one detector (40, 58) to be mixed with received laser light (22) of the same polarization direction in the heterodyne process to generate the electrical signal.
  9. Lidar device according to Claim 8 , characterized in that two detectors (40, 58) are provided, and in the first detector (40) laser light of the first polarization direction and in the second detector (48) laser light of the second polarization direction is mixed and converted into an electrical signal, and wherein for this purpose the received laser light (22) is first split into the two polarization directions by means of a polarization separator (50) and directed to the two detectors (40, 58).
  10. Lidar device according to Claim 8 characterized in that a detector (40) is provided hen is in which laser light of the first and second polarization directions is mixed with received laser light of both polarization directions and converted into an electrical signal, wherein a combiner is provided which mixes the two parts of the light from the optical storage element (28) with the received laser light (22).

Description

The present invention relates to a lidar device according to the preamble of claim 1, and to a method for operating a lidar device according to claim 8. A lidar device of this type is used to detect the surroundings of a vehicle. Such a lidar device includes a laser light source designed to emit laser light. An optical head with an optical transmitter and receiver unit is designed to transmit the laser light into the surroundings and to receive laser light reflected from the surroundings. A lidar device of this type also includes at least one detector designed to convert received laser light into electrical signals. Known lidar devices of this type continuously emit laser beams in an FMCW (Frequency Modulated Continuous Wave) method. Distance determination when using quasi-continuous frequency-modulated light is achieved by determining frequency differences using a heterodyne method. In a heterodyne method, waves of an unknown frequency are detected by mixing them with waves of a reference frequency. Here, the electric field of a received signal is mixed with the electric field of a local oscillator. This mixing is based on a non-linear product of the input signals, such that at least part of the output signal is proportional to the square of the input signals. Essentially, mixing products with sum and difference frequencies are determined. The amplitude of the downmixed signal is larger than the amplitude of the original signal itself, so a large amplitude of the local oscillator also results in a large "difference frequency amplitude." Laser light reflected and received from the environment is mixed with a stored portion of the laser light. Optical mixing of emitted and reflected laser light takes place on a detector. Since both components are temporally coherent (the coherence length of the laser must be sufficiently large to meet this condition), the electric fields of the light from the local oscillator and the light from the reflection interfere, so that the corresponding signal of the difference frequency of the two optical interference partners is detected at the detector. The heterodyne mixing frequencies (signal frequency plus oscillator frequency and signal frequency minus oscillator frequency) allow for improved detection because, on the one hand, downmixing to lower frequencies occurs, and on the other hand, the comparatively high intensity of the emitting laser simplifies the detection of the lower intensity of reflected laser light through heterodyne detection. The other frequency components, such as the oscillation frequency of the two electric fields of the light rays, as well as the sum frequency, are also present, but are in a frequency range that the electronics cannot follow. Known lidar devices use laser light sources that emit polarized laser light. The polarization state of the light can be, for example, linear or circular. To distinguish between emitted and received laser light, polarization-dependent filters are used. However, this has the disadvantage that only a portion of the received laser light is actually used and analyzed. Reflection of the laser light in the environment, for example, from an object near a vehicle, changes the polarization state. For instance, the polarization direction of emitted laser light with linear polarization can be rotated upon reflection. FMCW lidar technology faces the additional problem that only laser light components with the same polarization direction can interfere. Components of the received laser light that do not have the same polarization as the stored laser light cannot be detected using heterodyne detection and do not contribute to the so-called beat signal of the heterodyne method. Depending on the object from which the emitted laser light is reflected in the environment, the received laser light has the same polarization as the emitted laser light (polarization-preserving object), or polarization rotated by any angle, or a mixture of circular/elliptical polarization states. In known FMCW methods, only received laser light of a specific polarization state is detected, for example with a specific polarization direction in the case of linearly polarized emitted laser light. The object of the present invention is to provide a lidar device and a method for operating a lidar device of a vehicle in which these problems do not occur. This problem is solved by a lidar device according to the characterizing portion of claim 1 and by a method for operating a lidar device according to the characterizing portion of claim 8. In a lidar device according to the invention as defined in claim 1, the lidar device comprises a first splitter for splitting the emitted laser light into a portion to be emitted and a portion to be stored. An optical storage element is provided for storing the portion to be stored. A second optical splitter is provided for directing the portion to be stored, after storage, proportionally via a first optical connection directly