Advancing Optical Coherence Tomography through Opto-Electronic Frequency Shifting

Optical Coherence Tomography (OCT) stands out for its ability to combine the high resolution of microscopy with the penetration-depth of clinical imaging. However, in practice this is still limited to a few millimetres. Interestingly, the imaging-depth of the latest swept-source systems is not limited by their spectral width but by the analog-to-digital sampling rate. In lieu of slow reference arm length adjustments, we leverage opto-electronic frequency shifting. This allows for depth adjustments on the microsecond timescale and a modest detector bandwidth of 200 MHz. The opto-electronic scheme immediately gives us access to an 8 mm range, a fourfold increase over the nominal 2 mm range of the source. Moreover, by circumventing the need for a mechanical reference arm, changes in the axial displacement of the sample can be compensated in real-time. This makes it attractive for imaging arbitrarily-curved surfaces. We showcase this with wide-field OCT imaging of the curved retina.