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.
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.
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.
By using entangled photon pairs instead of a laser light, Quantum Optical Coherence Tomography (Q-OCT) outperforms conventional OCT, providing twice better axial resolution and immunity to image-degrading even-order chromatic dispersion. Despite these very sought-after features, its applicability is hindered by long acquisition times, image-scrambling artefacts and chromatic dispersion which reappears in configurations enabling the artefact suppression. Here, we experimentally demonstrate Q-OCT with a Fourier-domain acquisition scheme which allows both fast imaging and immunity to the re-appearance of chromatic dispersion. By delivering two-dimensional joint spectra, our Fourier-domain Q-OCT enables comfortable manipulation of spectral relationships between the photon pairs, and consequently the removal of the dispersion effects. We report attractive acquisition times, accompanied by a demonstration of two joint spectrum pre-processing algorithms, aimed at controlling dispersion effects within the setup. While the first algorithm reverses the effects specific to the joint spectral acquisition, the other one removes the effects leading to the weakening of even-order dispersion cancellation, impossible to be mitigated in other Q-OCT implementations. Contrasted with both the original, time-domain implementation and the conventional OCT, Fourier-domain Q-OCT is shown to be an important step forward towards becoming a practical and competitive solution.
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.
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 square root 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: Q-OCT with joint spectrum detection (JS-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.
Optical coherence tomography (OCT) has been widely used in many applications owing to its non-invasive nature. However, its axial resolution can be degraded due to dispersion in samples and optical systems. Quantum optical coherence tomography (QOCT) can overcome this problem and has thus attracted attention. However, QOCT exhibits two challenges: insufficient volume resolution and artifacts in images. Here, we realize high-volume-resolution QOCT imaging with efficient artifact removal. We evaluate our QOCT system to have an axial resolution of 1.5 μm and a lateral resolution of 1.6 μm, giving a volume resolution of 4.0 μm 3 (4.0 fL). We show that high-volume-resolution QOCT imaging is achievable even under group velocity dispersion. We also show that artifacts appearing inherently in the QOCT images can be removed by fast post-processing using the maximum clique search in graph theory. We believe that this study paves the way for QOCT imaging of three-dimensional fine structures.