Systems and methods are disclosed for optical coherence tomography (OCT). For example, imaging can use optical phase modulators based on optical delay lines that, in conjunction with a swept-source laser, can be used to achieve heterodyne swept source optical coherence tomography (SSOCT). These techniques resolve the complex conjugate ambiguity in SSOCT, thereby doubling the usable imaging range. This increased imaging range has numerous important clinical applications in ophthalmology, cardiology and radiology, as well as applications in small animal and non-biological imaging. These methods are superior to prior disclosed methods requiring acousto-optic or electro-optic modulators with respect to complexity, efficiency, imaging speed and image quality.