Computational framework for combining multiple swept-sources for high-resolution in-vivo optical coherence tomography

Axial resolution in swept-source-based Fourier-domain optical coherence tomography (FD-OCT) is limited by the sweep range of the source. However, broad swept-sources are not readily available, and passively combining two laser sources is not straightforward. In this paper, we develop a framework to overcome this limit by computationally combining independently sweeping sources to increase the bandwidth and subsequently the axial resolution of full-field Fourier-domain optical coherence tomography (FF-FD-OCT) systems. To this end, we demonstrate a dual-laser full-field FD-OCT system that uses two lasers, which sweep sequentially and are stitched phase-correctly in post-processing to obtain high-bandwidth spectra. After combining, we achieve an effective bandwidth of 145 nm at a central wavelength of 878 nm. The system has a high axial resolution of 3.1 µm and can operate at an A-scan rate of 50 MHz. Our method requires a one-time calibration measurement to determine the non-linear sweeps from the lasers and the wavelength overlap, as well as a volume-by-volume phase matching procedure to compensate for sample motion. We demonstrate this for ex-vivo phantoms as well as in-vivo retinal data. Overall, the framework allows for extension to multiple lasers to further improve the axial resolution.