This paper presents a transmissive rapid scanning optical delay line (RSOD) for balance detection based optical
coherence tomography (OCT). This transmissive RSOD, consisting of a reflective blazed grating, a Fourier lens, a
fast-scanning galvo-mirror, a right-angle prism and a mirror, functions for phase modulation, axial scanning and
dispersion compensation in OCT just as a reflective RSOD. The developed transmissive RSOD is implemented in OCT
for balance detection. Comparison study indicates that improved quality of imaging is archived by the transmissive
RSOD based OCT, in contrast to that by a conventional reflective RSOD based OCT.