Phase-stability optimization of swept-source optical coherence tomography

Abstract

Phase-resolved imaging of swept-source optical coherence tomography (SS-OCT) is subject to phase measurement instabilities involved with the sweep variation of a frequency-swept source. In general, optically generated timing references are utilized to track the variations imposed on OCT signals. But they might not be accurately synchronized due to relative time delays. In this research, we investigated the impact of the signal delays on the timing instabilities and the consequent deviations of the measured phases. We considered two types of timing signals utilized in a popular digitizer operation mode: a sweep trigger from a fiber Bragg grating (FBG) that initiates a series of signal sampling actions clocked by an auxiliary Mach-Zehnder interferometer (MZI) signal. We found that significant instabilities were brought by the relative delays through incoherent timing corrections and timing collisions between the timing references. The best-to-worst ratio of the measured phase errors was higher than 200 while only the signal delays varied. Noise-limited phase stability was achieved with a wide dynamic range of OCT signals above 50 dB in optimized delays. This demonstrated that delay optimization is very effective in phase stabilization of SS-OCT.

Ultrahigh-sensitive optical coherence elastography

“…The phase stability of SS-OCT can be improved through optical and electrical optimization, but reducing the phase fluctuation in a conventional SS-OCT setup is fundamentally challenging, as the reference and sample signals travel through different optical paths. We have previously demonstrated a method to optimize the electrical components in an SS-OCT system to achieve high-phase stability 38 , and in this study, we employed a common-path configuration to further attain the peak performance of SS-OCE. This was accomplished by enhancing the SNR through averaging, minimizing the timing jitter by adjusting the electrical delay, and reducing the fluctuation of the OPD via the common-path configuration.…”

“…To achieve the best stability, the signal delays are adjusted to the optimal values for the k-clock, λtrigger and OCE signals. A previous study on the phase stability with the same type of swept lasers suggested that a very high stability could be obtained using this method 38 .…”

“…In conventional SS-OCT or SS-OCE imaging systems, a series of OCT signal points is digitized starting at the edge of the λ-trigger, while the signal digitization is clocked by the k-clock signal for k-linear signal sampling. However, in this mode of operation, random timing errors of the signal edges can be magnified to significant timing fluctuations between the k-clock and λ-trigger through a process termed edge collision 38 . To achieve the best stability, the signal delays are adjusted to the optimal values for the k-clock, λtrigger and OCE signals.…”

Full-range space-division multiplexing optical coherence tomography angiography

“…One common issue for SS-OCT is trigger jitter, in which data acquisitions of OCT/MZI spectral fringes exhibits sweep to sweep variations, i.e. starting from different wavelengths, yielding the irregular movements of spectral ranges for different OCT/MZI fringes and corrupted phase relationships between adjacent sweeps or A-scans [25,26]. Illustrations of the trigger jitter phenomenon for SDM-OCT are shown in Fig.…”

“…3(B)). In previous studies, the trigger jitter can be resolved by using the split, FBG-filtered source signals as the acquisition trigger (λ -trigger) [26,27], using an FBG to generate a sharp peak in each OCT fringe as a timing reference [25] and a fixed range of accumulated MZI phase to crop each pair of OCT and MZI spectra and perform data resampling [24]. The data resampling technique employed in this study is adapted from previous work [24,25].…”