  Spatial resolution in optical microscopy has traditionally been treated as a
fixed parameter of the optical system. Here, we present an approach to enhance
transverse resolution in beam-scanned optical coherence tomography (OCT) beyond
its aberration-free resolution limit, without any modification to the optical
system. Based on the theorem of invariance of information capacity,
resolution-enhanced (RE)-OCT navigates the exchange of information between
resolution and signal-to-noise ratio (SNR) by exploiting efficient noise
suppression via coherent averaging and a simple computational bandwidth
expansion procedure. We demonstrate a resolution enhancement of 1.5 times
relative to the aberration-free limit while maintaining comparable SNR in
silicone phantom. We show that RE-OCT can significantly enhance the
visualization of fine microstructural features in collagen gel and ex vivo
mouse brain. Beyond RE-OCT, our analysis in the spatial-frequency domain leads
to an expanded framework of information capacity and resolution in coherent
imaging that contributes new implications to the theory of coherent imaging.
RE-OCT can be readily implemented on most OCT systems worldwide, immediately
unlocking information that is beyond their current imaging capabilities, and so
has the potential for widespread impact in the numerous areas in which OCT is
utilized, including the basic sciences and translational medicine.
