Chirped-pulse interferometry for dispersion-cancelled OCT

Abstract

Optical coherence tomography (OCT) is a non-invasive imaging technology based on low-coherence interferometry that is rapidly finding novel applications in biological sciences and medicine, particularly in disease detection, since it allows high-resolution depth profiles of the samples under consideration [1]. However, material dispersion is a major problem in OCT since it both reduces contrast and resolution with increasing sample depths, hence drastically limiting its potential range of applications.Exciting developments in quantum interferometry have led to the proposal and demonstration of quantum optical coherence tomography (Q-OCT) [2]. This technique relies on Hong-Ou-Mandel (HOM) interferometry which utilizes frequency-entangled photon pairs. The most important advantage of this technique is that it automatically cancels the most pronounced type of dispersion. In addition, it is insensitive to phase fluctuations and unbalanced photon loss in the interferometer, and has a better resolution than OCT. However, entangled photon pairs are difficult to create, manipulate and detect and this has restricted Q-OCT to basic proof-of principle demonstrations in specialized laboratories.Here we report on a completely classical technique based on the time-reversal symmetry of quantum mechanics that achieves all the advantages of HOM interferometry by using oppositely-chirped laser pulses [3]. Since our technique relies on classical lasers instead of entangled photons, it achieves these features with millions of times larger signal -making it an attractive candidate for dispersion-free OCT [4]. In particular, the visibility and width of the CPI interferogram is insensitive to dispersion and photon loss, and inherently robust against phase-fluctuations. Further, we achieve higher resolution than classical interferometers using the same bandwidth. On a fundamental level, our work emphasizes the importance of delineating truly quantum effects from those with classical analogues, and shows how insights gained from quantum mechanics can inspire novel classical technologies.In this talk I will introduce the technique of Chirped-pulse interferometry (CPI), demonstrate its advantageous properties and show how this technique might be suitable for practical bio-medical imaging.