Towards Optical Coherence Tomography Using Temporally Entangled Photons

Abstract

The primary objective of this work is the experimental characterization of a non-classical light source designed for Quantum-Optical Coherence Tomography (QOCT) applications. Utilizing Spontaneous Parametric Down-Conversion (SPDC) in a Type-II Beta Barium Borate (BBO) crystal, a stream of temporally entangled photon pairs was generated and spatio-temporally correlated. Experimental results demonstrate successful biphoton characterization using a high-resolution coincidence counting architecture. Measurement of the second-order correlation function, $g^{(2)}(\tau)$, yielded a value of $g^{(2)}(0) = 0.0027$, providing definitive proof of anti-bunching and the non-classical nature of the heralded photon source.

The hallmark result of this study is the observation of a Hong-Ou-Mandel (HOM) dip with a visibility measure of $61.4\%$, achieved through the precise balancing of optical path lengths within a symmetric interferometer. This quantum interference effect confirms the HOM effect of photon wave-packet overlap. These findings establish a stable experimental prerequisite for advancing towards a functional QOCT system capable of overcoming the resolution and dispersion barriers inherent in classical incoherent OCT imaging.