We report an optimized implementation of spectral-domain quantum optical coherence tomography (SD-QOCT) capable of acquiring axial scans (A-scans) of multilayer samples in the absence of mechanical scanning, at an unprecedented speed. Implementing a novel strategy, we demonstrate a proof-of-concept system that integrates a diffraction grating, a high-resolution intensified CCD camera and a high-flux photon-pair source operating in the VIS-NIR region (≈800 nm). This configuration enables the acquisition of an entire marginal SD-QOCT interferogram in a single camera exposure, yielding a transverse A-scan with a record acquisition time of 100 ms for a mirror sample, which extends to 10 s for a glass coverslip, and a penetration depth of ≈4 mm. The measured interferometric response shows excellent agreement with the theoretical model. These results represent a decisive step toward the practical deployment of SD-QOCT as a competitive imaging modality for biomedical applications.
We report an optimized implementation of spectral-domain quantum optical coherence tomography (SD-QOCT) capable of acquiring axial scans (A-scans) of multilayer samples in the absence of mechanical scanning, at an unprecedented speed. Implementing a novel strategy, we demonstrate a proof-of-concept system that integrates a diffraction grating, a high-resolution intensified CCD camera and a high-flux photon-pair source operating in the VIS-NIR region (≈800 nm). This configuration enables the acquisition of an entire marginal SD-QOCT interferogram in a single camera exposure, yielding a transverse A-scan with a record acquisition time of 100 ms for a mirror sample, which extends to 10 s for a glass coverslip, and a penetration depth of ≈4 mm. The measured interferometric response shows excellent agreement with the theoretical model. These results represent a decisive step toward the practical deployment of SD-QOCT as a competitive imaging modality for biomedical applications.
We present, to the best of our knowledge, the first implementation of full-field quantum optical coherence tomography (FF-QOCT). In our system, we are able to obtain full three-dimensional (3D) information about the internal structure of a sample under study by relying on transversely resolved Hong–Ou–Mandel (HOM) interferometry with the help of an intensified CCD (ICCD) camera. Our system requires a single axial scan, obtaining full-field transverse single-photon intensity in coincidence with the detection of the sibling photon for each value of the signal-idler temporal delay. We believe that this capability constitutes a significant step forward toward the implementation of QOCT as a practical biomedical imaging technique.
Using spectrally correlated photon pairs instead of classical laser light and coincidence detection instead of light intensity detection, Quantum Optical Coherence Tomography (Q-OCT) outperforms classical OCT in several experimental terms. It provides twice better axial resolution with the same spectral bandwidth and it is immune to even-order chromatic dispersion, including Group Velocity Dispersion responsible for the bulk of axial resolution degradation in the OCT images. Q-OCT has been performed in the time domain configuration, where one line of the two-dimensional image is acquired by axially translating the mirror in the interferometer's reference arm and measuring the coincidence rate of photons arriving at two single-photon-sensitive detectors. Although successful at producing resolution-doubled and dispersion-cancelled images, it is still relatively slow and cannot compete with its classical counterpart. Here, we experimentally demonstrate Q-OCT in a much faster Fourier-domain configuration, theoretically proposed in 2020, where the reference mirror is fixed and the joint spectrum is acquired by inserting long fibre spools in front of the detectors. We propose two joint spectrum pre-processing algorithms, aimed at compensating resolution-degrading effects within the setup. While the first one targets fibre spool dispersion, an effect specific to this configuration, the other one removes the effects leading to the weakening of even-order dispersion cancellation, the latter impossible to be mitigated in the time-domain alternative. Being additionally contrasted with both the time-domain approach and the conventional OCT in terms of axial resolution, imaging range and multilayer-object imaging, Fourier-domain Q-OCT is shown to be a significant step forward towards a practical and competitive solution in the OCT arena.
Quantum-optical coherence tomography (QOCT) is an optical sectioning modality based on the quantum interference of entangled photon pairs in the well-known Hong-Ou-Mandel interferometer. Despite its promise, the technique is far from being competitive with current classical OCT devices due to the long required acquisition times, derived from the low photon-pair emission rates. In this work, we, on the one hand, demonstrate a quantum optical coherence microscopy technique, based on full-field QOCT, which employs entangled collinear photon pairs in a Linnik interferometer designed to overcome some of the limitations of previous QOCT implementations, and, on the other hand, test it on representative samples, including glass layers with manufactured transverse patterns and metal-coated biological specimens. In our setup, while the idler photon is collected with a multimode fiber, the signal photon is detected by an intensified charge-coupled device camera, leading to full-field transverse reconstruction through a single-axial acquisition sequence. Interestingly, our setup permits concurrent OCT and QOCT trace acquisition, the former with greater counts and the latter with the benefit of quantum-conferred advantages. We hope that our current results will represent a significant step forward towards the actual applicability of QOCT, e.g., in clinical settings.
We report Fourier-domain Quantum Optical Coherence Tomography employing a photon pair source covering a very broad wavelength range spanning from around 1350 to 1750 nm. With nearly 180 nm full width at half maximum, it enables high axial resolution of 2.7 μm, most commonly achieved only in classical OCT working at a much shorter wavelength of 800 nm. The light of such considerable bandwidth is especially vulnerable to axial-resolution-degrading effects of chromatic dispersion, and although the even-order dispersion - responsible for the bulk of resolution degradation - is inherently cancelled, the odd-order dispersion becomes non-negligible, with the third-order-dispersion effects already observed in various Quantum OCT setups. We introduce a dimensionless parameter χ₃, dependent on the photon pair source and medium parameters, facilitating prediction of the appearance of these image-distorting dispersion effects. Also, we show that this issue - impossible to be removed in time-domain Quantum OCT - is easily mitigated in its Fourier-domain configuration by mere post-processing of a joint spectrum, resulting in the high axial resolution being maintained throughout most of the imaging depth, here approx. 0.35 mm. Finally, we show that the imaging depth can be extended to 0.7 mm if the fibre spools - central to the joint spectral detection - are extended from 5 km to 10 km, however at the expense of a longer acquisition time.
We report Fourier-domain Quantum Optical Coherence Tomography employing a photon pair source covering a very broad wavelength range spanning from around 1350 to 1750 nm. With nearly 180 nm full width at half maximum, it enables high axial resolution of 2.7 μm, most commonly achieved only in classical OCT working at a much shorter wavelength of 800 nm. The light of such considerable bandwidth is especially vulnerable to axial-resolution-degrading effects of chromatic dispersion, and although the even-order dispersion - responsible for the bulk of resolution degradation - is inherently cancelled, the odd-order dispersion becomes non-negligible, with the third-order-dispersion effects already observed in various Quantum OCT setups. We introduce a dimensionless parameter χ₃, dependent on the photon pair source and medium parameters, facilitating prediction of the appearance of these image-distorting dispersion effects. Also, we show that this issue - impossible to be removed in time-domain Quantum OCT - is easily mitigated in its Fourier-domain configuration by mere post-processing of a joint spectrum, resulting in the high axial resolution being maintained throughout most of the imaging depth, here approx. 0.35 mm. Finally, we show that the imaging depth can be extended to 0.7 mm if the fibre spools - central to the joint spectral detection - are extended from 5 km to 10 km, however at the expense of a longer acquisition time.
Quantum optical coherence tomography (Q-OCT) is the non-classical counterpart of optical coherence tomography (OCT), a high-resolution 3D imaging technique based on white-light interferometry. Because Q-OCT uses a source of frequency-entangled photon pairs, not only is the axial resolution not affected by dispersion mismatch in the interferometer but is also inherently improved by a factor of two. Unfortunately, practical applications of Q-OCT are hindered by image-scrambling artefacts and slow acquisition times. Here, we present a theoretical analysis of a novel approach that is free of these problems: Fourier domain Q-OCT (Fd-Q-OCT). Based on a photon pair coincidence detection as in the standard Q-OCT configuration, it also discerns each photon pair by their wavelength. We show that all the information about the internal structures of the object is encoded in the joint spectrum and can be easily retrieved through Fourier transformation. No depth scanning is required, making our technique potentially faster than standard Q-OCT. Finally, we show that the data available in the joint spectrum enables artefact removal and discuss prospective algorithms for doing so.