An interferometer configured for use in optical coherence domain (OCT) reflectometry systems is disclosed. In the preferred embodiments, efficient routing of light and a balanced detection arrangement provide a high signal to noise ratio. In one set of embodiments, a pair of cascaded 2×2 couplers is used to split light along separate sample and reference paths and also for combining light returning from those paths and supplying the interfered collected light to the detection system. The interferometer can be used with various OCT modalities including time-domain and frequency domain approaches.