An Overview of Lidar Imaging Systems for Autonomous Vehicles

Abstract

Lidar imaging systems are one of the hottest topics in the optronics industry. The need to sense the surroundings of every autonomous vehicle has pushed forward a race dedicated to deciding the final solution to be implemented. However, the diversity of state-of-the-art approaches to the solution brings a large uncertainty on the decision of the dominant final solution. Furthermore, the performance data of each approach often arise from different manufacturers and developers, which usually have some interest in the dispute. Within this paper, we intend to overcome the situation by providing an introductory, neutral overview of the technology linked to lidar imaging systems for autonomous vehicles, and its current state of development. We start with the main single-point measurement principles utilized, which then are combined with different imaging strategies, also described in the paper. An overview of the features of the light sources and photodetectors specific to lidar imaging systems most frequently used in practice is also presented. Finally, a brief section on pending issues for lidar development in autonomous vehicles has been included, in order to present some of the problems which still need to be solved before implementation may be considered as final. The reader is provided with a detailed bibliography containing both relevant books and state-of-the-art papers for further progress in the subject.

A Review and Perspective on Optical Phased Array for Automotive LiDAR

“…5. The obvious advantage of these devices is that a single sensor is able to cover front, back and side views around the ego-vehicle [73]. However, 360 o LiDAR usually has a large sensor unit that needs to be mounted on the vehicle roof, resulting in it being an extremely unaesthetic and impractical solution for production vehicles.…”

“…This technology has evolved in the last few years, and there are some solutions for short medium range almost ready for commercialization. Unlike scanning LiDARs, FLASH LiDAR generates an electromagnetic pulse (usually in the near infrared, NIR) that floods completely the sensor field of view and detection range [73]. Each object in the covered detection volume will reflect the emitted beam, and the LiDAR unit will detect reflected light on an array of pixels, designed to detect light in the wavelength range of the emitted pulse [85].…”

Data Processing Approaches on SPAD-Based d-TOF LiDAR Systems: A Review

“…Due to the dead time, SPADs suffer from a saturation effect in the outdoor scenario [9]. Laser sources in LiDAR systems generate laser pulses in a specific wavelength, typically from 800 nm to 1550 nm [10], while the solar irradiance covers the full wavelength range. Therefore, optical bandpass filters can be used to remove irradiance at unwanted wavelengths [35].…”

“…Depending on the sensor type, LiDAR technology can implement digital or analog readout. According to the scanning mechanism, LiDAR can be divided into flash, mechanical, MEMs, and optical phased arrays (OPA) [10]. According to the measuring mode, it can be categorized into direct time-of-flight (d-TOF) or indirect time-of-flight (i-TOF) mode.…”

“…Basic principles of both modes are introduced and their advantages and limitations are discussed in [3] and [11]. Modern outdoor LiDAR systems employ mostly d-TOF mode [10]. Although LiDAR technology have not been deployed in production automobiles to date [5], many LiDARbased product prototypes are build both in the commercial sector [12][13][14][15] and for research uses [16][17][18][19][20][21][22][23].…”