Ultralow-loss spiral resonators for precise LiDAR

TL;DR

This paper presents an ultralow-loss silicon nitride spiral resonator acting as a highly precise on-chip frequency ruler to correct laser nonlinearities, significantly enhancing the accuracy of LiDAR and other optical measurement technologies.

Contribution

Introduction of a millimeter-scale, ultralow-loss silicon nitride spiral resonator serving as a compact, high-precision frequency ruler for nonlinear correction in tunable laser systems.

Findings

Resonator achieves 2 MHz linewidth and 25.57 MHz frequency ticks.

Demonstrated precise nonlinearity correction in laser sweeping.

Applied in FMCW LiDAR for improved measurement accuracy.

Abstract

Swept laser interferometry is an extremely powerful solution embedded in several recent technologies such as absolute distance measurement, light detection and ranging, optical frequency domain reflectometry, optical coherence tomography, microresonator characterization, and gas spectroscopy. Nonlinearity in the optical frequency sweeping of tunable lasers is a fatal drawback in gaining the expected outcome from these technologies. Here, we introduce an onchip, millimeter scale, 7 m spiral resonator that is made of ultralow loss silicon nitride to act as a frequency ruler for correction of the tunable lasers sweeping nonlinearities. The sharp 2 MHz frequency lines of the 85 M high-quality resonator and the narrow spaced 25.57 MHz frequency ticks of the 7 m spiral allow unprecedented precise nonlinearity correction on an integrated photonics platform. Accurate measurements of the rulers frequency spacing, linewidth, and temperature and wavelength sensitivities of the frequency ticks are performed here to demonstrate the quality of the frequency ruler. In addition, the spiral resonator is implemented in an FMCW LiDAR experiment to demonstrate a potential application of the proposed onchip frequency ruler.