An apparatus and method for performing optical coherence domain reflectometry. The apparatus preferably includes a single output light source to illuminate a sample with a probe beam and to provide a reference beam. The reference beam is routed into a long arm of an interferometer by a polarizing beamsplitter. A reflected beam is collected from the sample. A 90° double pass polarization rotation element located between the light source and the sample renders the polarizations of the probe beam and reflected beam orthogonal. The polarizing beamsplitter routes the reflected beam into a short arm of the interferometer. The interferometer combines the reference beam and the reflected beam such that coherent interference occurs between the beams. The apparatus ensures that all of the reflected beam contributes to the interference, resulting in a high signal to noise ratio.