Multiple source frequency-modulated continuous-wave optical reflectometry: theory and experiment

Abstract

We propose and demonstrate a novel approach to increase the effective bandwidth of a frequencymodulated continuous-wave (FMCW) ranging system. This is achieved by algorithmically stitching together the swept spectra of separate laser sources. The result is an improvement in the range resolution proportional to the increase in the swept-frequency range. An analysis of this system as well as the outline of the stitching algorithm are presented. Using three distinct swept-frequency optical waveforms, we experimentally demonstrate a threefold improvement in the range resolution of a three-sweep approach over the conventional FMCW method.

Dispersion compensation method based on focus definition evaluation functions for high-resolution laser frequency scanning interference measurement

“…Laser frequency scanning interference measurements involve completing heterodyne calculations of transmitted and local light to measure distances [1][2][3][4][5]. This method is advantageous in that it does not produce range ambiguities, it exhibits strong anti-interference capacities and non-cooperative targets, and it is highly precise.…”

Terahertz Chirp Generation Using Frequency Stitched VCSELs for Increased LIDAR Resolution

“…The key component of an FMCW experiment is the swept-frequency (chirped) laser, since its performance directly affects important system metrics. Specifically, the axial resolution is given by δ d = c/2B, where B is the total frequency excursion, and c is the speed of light [4]. The ranging depth is limited by the coherence of the optical wave and varies inversely with its instantaneous linewidth [5].…”

“…The key to extending the system's optical bandwidth, and therefore improving the axial resolution, is to concatenate multiple chirps over distinct but adjacent regions of the optical spectrum. This technique, stitching, has been used to improve the axial resolution three-fold in a distributed feedback laser (DFB) based system [4].In the present work we demonstrate the stitching of two off-the-shelf vertical-cavity surface-emitting lasers (VCSELs) at 1550 nm. When compared to DFB lasers, VCSELs offer increased tunability, a faster chirp rate, as well as a significant cost reduction.…”

“…The key to extending the system's optical bandwidth, and therefore improving the axial resolution, is to concatenate multiple chirps over distinct but adjacent regions of the optical spectrum. This technique, stitching, has been used to improve the axial resolution three-fold in a distributed feedback laser (DFB) based system [4].…”

“…To fully satisfy the requirement for stitching, we add an external reference target to the imaging experiment, shown in the right part of Fig. 1, and follow the algorithm developed in [4] to extract the value of this integer. Therefore, the frequency as a function of time is known exactly, and a measurement with enhanced axial resolution can be synthesized.…”