Wavelength-encoded multi-channel spectral-domain optical coherence tomography (SD-OCT) for spatiotemporally resolved imaging

In conventional spectral domain optical coherence tomography (SD-OCT), a beam is focused to one spot on the surface of the sample to acquire depth information beneath that spot. Adjacent spots are serially scanned to obtain a tomographic image of the sample; thus, available OCT techniques can take significant time to scan large objects. This paper illustrates an SD-OCT system involving spectral-slicing of a broadband spectrum to enable the simultaneous acquisition from multiple lateral positions of the sample. Using a wavelength encoding of spatial information, where each lateral location is associated with a specific portion of a source spectrum, multiple lateral spots are interrogated concurrently to improve the imaging speed of SD-OCT. A triple-channel SD-OCT system was devised using a broadband source of centre wavelength 840 nm and full width half maximum (FWHM) bandwidth of 50 nm. Both sample and reference arm beams were split into three channels using two dichroic splitters of 50% cut-on wavelength at 825 nm and 848 nm, resulting in a FWHM spectral distribution of 13.5 nm, 19 nm and 17.5 nm in the three channels, respectively. The imaging performance of the technique was demonstrated by concurrently acquiring tomographic images of a 3D-printed phantom. Despite the relative drop in the per-channel axial resolution and depth sensitivity, this new approach presents a straightforward way of interrogating a sample simultaneously in multiple locations, provides the additional advantage of allowing different delay lines for each spectral section and offers the potential of such a system to be used in a wide range of applications that demand a small product foot print.