Axial resolution is a key factor in optical coherence tomography (OCT). Biomedical applications will benefit from
improved resolution and quality that ultrahigh resolution OCT can provide. Existing approaches to improve axial
resolution of OCT mostly depend on new broadband light sources, which are always costly and inconvenient in
instrumentation. In this paper we adopt an alternative method to enhance the axial resolution of OCT by combining
coherence gate with optical superresolution. A three-zone phase pupil filter is designed and inserted into the sample
arm of OCT. The depth responses measured demonstrate that an improvement of more than 15% in axial resolution is
achieved in the proposed OCT system.