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

Abstract

We developed a digital electro-optical phase-locked-loop (EO-PLL) utilizing a repetitive control, allowing the use of very nonlinear tunable lasers for frequency-modulated continuous-wave (FMCW) light detection and ranging (LIDAR) applications. This approach allows reducing the phase error of continuously repeated frequency chirps to virtually zero by using information of previous chirps and additionally guaranties sub-second settling times. With this method, much higher nonlinearities in the laser frequency modulation slope γ are tolerable than with common real-time analog PLLs. Furthermore, we applied a Goertzel algorithm generalized to non-integer multiples of the fundamental frequency to achieve a mean measurement precision of 5.41 μm and 16.35 μm at a distance from the interferometer baseline of 3 m and 10.3 m, respectively.