Despite the relatively high implementation costs and the complexity of the system, Frequency-modulated Continuouswave Light Detection and Ranging (FMCW LIDAR) has attracted special attention as the next generation LIDAR because generally existing LIDARs using pulse or amplitude modulation have limitation for high-resolution and interference phenomenon. Bandwidth and its linearity of the optical wavelength modulation in FMCW LIDAR have remarkable effects on spatial and range resolution including detection range. Hence, most FMCW LIDAR systems need to linearize the optical frequency sweep for best performance. However, since the linearization techniques normally require high-cost and complex systems, its adoption can be restricted in some application fields where low-cost and simple architecture are important. In this paper, measurement and analysis results for high-resolution of low-cost FMCW LIDAR using non-linear sweep characteristics of different lasers were presented. DFB laser and VCSEL of wavelengths near 1550 nm were utilized in these experiments, and the optical frequency sweep and beat frequency characteristics of each laser were analyzed in detail. The problem of low spectral resolution that occurs due to sweep nonlinearity was improved by the partial-waveform technique. Furthermore, by means of the beat frequency distribution which was obtained from repeat measurement and spline interpolation, the detailed analysis of beat frequency stability and distance resolution for various modulation frequencies were presented. Finally, using the multi-peak-averaging (MPA) method which efficiently utilizes high modulation frequency to improve the distance resolution, it is possible to achieve um-level range detection accuracy in the implemented FMCW system based on the uncompensated FMCW sources.
Scanners are widely used in modern industry and daily life, and they have a wide range of applications. They are used not only for medical measuring and imaging equipment but also for cutting and processing equipment in the industrial field, as well as for information processing, display and data collection in various technologies, such as projectors and 3D image sensors. With the development of technology, the use of scanners has been increasing as automation has progressed. In particular, with the development of unmanned mobile technology, sensors using scanners are being developed. It is a common problem that it is difficult to precisely control a mechanically moving scanner, although the manner of controlling the scanner varies according to the application technology. When a scanner is operated at a high speed, a scan error occurs because of the difference of scan speed between the acceleration region and the constant region. Scan error also leads to serious problems in a LIDAR sensor. In a LIDAR sensor, scan error prevents the user from achieving the objective of detecting the exact position of the object by collecting or transmitting information that is different from what the user desires. In this paper, we present a technique to compensate for the scanning error that occurs in a LIDAR sensor. In most cases where a commercial scanner is used, the user has restricted methods to control the scanner. It is difficult to control the scanner precisely because the scanner needs to be controlled using only one or two pieces of information. Also, conditions that can be changed depending on application technology may be limited. We propose a method to reduce the scan error and to improve the 3D image of the LIDAR sensor through the limited scanner control.
LIDAR (light distance and ranging) systems use sensors to detect reflected signals. The performance of the sensors significantly affects the specification of the LIDAR system. Especially, the number and size of the sensors determine the FOV (field of view) and resolution of the system, regardless of which sensors are used. The resolution of an array-type sensor normally depends on the number of pixels in the array. In this type of sensor, there are several limitations to increase the number of pixels in an array for higher resolution, specifically complexity, cost, and size limitations. Another type of sensors uses multiple pairs of transmitter and receiver channels. Each channel detects different points with the corresponding directions indicated by the laser points of each channel. In this case, in order to increase the resolution, it is required to increase the number of channels, resulting in bigger sensor head size and deteriorated reliability due to heavy rotating head module containing all the pairs. In this paper, we present a method to overcome these limitations and improve the performance of the LIDAR system. ETRI developed a type of scanning LIDAR system called a STUD (static unitary detector) LIDAR system. It was developed to solve the problems associated with the aforementioned sensors. The STUD LIDAR system can use a variety of sensors without any limitations on the size or number of sensors, unlike other LIDAR systems. Since it provides optimal performance in terms of range and resolution, the detailed analysis was conducted in the STUD LIDAR system by applying different sensor type to have improved sensing performance.
The accuracy of timing jitter is of prime importance in the prevalent utilization of Light Detection and Ranging (LiDAR) technology for the real-time high-resolution three-dimensional (3D) image sensor, especially for relatively small object detection in various applications, such as in the fully automated car navigation and military surveillance. To assess the accuracy of timing, that is, the accuracy of the distance or three-dimensional shape, the standard deviation method can be used in the Time-of-Flight (ToF) LiDAR technology. While most timing jitter analyses are mainly based on a fiber-network or open space at a relatively short range distance, more accurate analyses are required to extract more information about the timing jitter at in a 3D image sensor long-range free space conditions for extended LiDAR-related applications.
In this paper, utilizing a Single-Shot LiDAR System (SSLs) model with a 400 MHz wideband InGaAs Avalanche Photodiode and a 1550 nm 2 nsec full width at half maximum MOPA fiber laser, we analyzed the precise timing jitter for the implemented SSLs to characterize the measurement results. Additionally, we report the enhanced results for the resolution and precision in the given SSLs using the spline interpolation method from the measured results, and multiple-shot averaging (MSA). Finally, by adapting the proposed method to an implemented high resolution 3D LiDAR prototype, called the STUD LiDAR prototype, which can be understood as one kind of SSLs because it has a single source and a single detector as in a SSLs, we observed and analyzed the 3D resolution enhancement.
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