Laser frequency sweep linearization by iterative learning pre-distortion for FMCW LiDAR

Abstract

We report on a laser frequency sweep linearization method by iterative learning pre-distortion for frequency-modulated continuous-wave (FMCW) light detection and ranging (LiDAR) systems. A pre-distorted laser drive voltage waveform that results in a linear frequency sweep is obtained by an iterative learning controller, and then applied to the FMCW LiDAR system. We have also derived a fundamental figure of merit for the maximum residual nonlinearity needed to achieve the transform-limited range resolution. This method is experimentally tested using a commercial vertical cavity surface-emitting laser (VCSEL) and a distributed feedback (DFB) laser, achieving less than 0.005% relative residual nonlinearity of frequency sweep. With the proposed method, high-performance FMCW LiDAR systems can be realized without expensive linear lasers, complex linearization setups, or heavy postprocessing.

Frequency Sweep Linearization for Semiconductor Laser Using a Feedback Loop Based on Amplitude-Frequency Response

“…A schematic diagram of a triangular FMCW LiDAR is shown in Figure 1. Probe light from the target interferes with the reference and the beat signal is recorded by a detector [7]. Since the laser frequency sweep is linear, the beat signal frequency b f is proportional to the target distance D, is given by…”

FPGA-Based EO-PLL With Repetitive Control for Highly Linear Laser Frequency Tuning in FMCW LIDAR Applications

“…Nevertheless, it is hard to completely model the laser tuning behavior. Therefore, in [8] an iterative learning control (ILC) is implemented, where the laser tuning waveform is iteratively improved over many chirps. This allows a very linear laser frequency tuning.…”

Frequency-Modulated Chirp Signals for Single-Photodiode Based Coherent LiDAR System

“…The simplest approach to generate such linear FM chirp signals is to directly modulate a laser [14], [15]. Nevertheless, due to the inherent nonlinear relation between the output frequency and the driving waveform of the tunable laser, a linearization technique is often required to optimize the signal waveform [16]- [18]. Frequency modulation of the laser by varying the injection current into the gain section also comes with an unwanted intensity modulation.…”

“…Additionally, an electrical mixer is no longer required and the receiver configuration can be greatly simplified. For this type of coherent detection scheme, it is possible to use a 3-dB coupler to combine signal and LO, with either a single-ended photodiode (PD) [16], or balanced detectors [20]. Alternatively, a balanced phase-diversity coherent receiver based on an optical 90 • hybrid can be employed [24].…”