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From master-slave to down-conversion optical coherence tomography
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Paper Abstract

We present here advances on the Master Slave (MS) concept, applicable to spectral/Fourier/frequency-domain optical coherence tomography (OCT) technology. Instead of obtaining an A-scan from the sample investigated via a Fourier Transform (FT) or equivalent, the amplitude of the A-scan for each resolvable point along the depth is obtained along a separate output. A multiplier produces the product of the photo-detected signal from the OCT system with that generated by an Electrical or an Optical Master. This allows acquisition at a frequency comparable to that of the sweeping, much inferior to the frequency bandwidth of the channeled spectrum. 3 advantages of the down-conversion method are demonstrated here: (a) real time delivery of an en-face image; (b) axial optical path difference (OPD) range at the level of the source’s dynamic coherence length and (c): tolerance to fluctuations in the sweep of the swept source. The most important advantage of the down-conversion method is that it reduces the signal bandwidth considerably, to the level of the sweeping rate. This facilitates real-time operation. Conventional A-scan production can only be performed real-time if the FT processing is carried out in a time comparable to or less than the sweep time, which depending on the number of sampled points and dynamic range determines a limit of ∼ MHz sweep rate. Before even calculating a FT, acquisition may also be limited by the sampling rate of the digitiser. In conventional SS-OCT, the number of depth points can exceed 1,000, which for a sweeping time of 1 μs would determine signals in the GHz range. Using long coherence length swept sources, this number of depths could be even larger, hence the conventional FT-based method faces a bottleneck due to the time needed to calculate the FT, combined with the need to acquire data at many GS/s.

Paper Details

Date Published: 21 February 2020
PDF: 4 pages
Proc. SPIE 11228, Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXIV, 1122819 (21 February 2020); doi: 10.1117/12.2548617
Show Author Affiliations
Adrian Podoleanu, Univ. of Kent (United Kingdom)
Adrian Bradu, Univ. of Kent (United Kingdom)
Ramona Cernat, Univ. of Kent (United Kingdom)
Manuel Jorge M. Marques, Univ. of Kent (United Kingdom)

Published in SPIE Proceedings Vol. 11228:
Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXIV
Joseph A. Izatt; James G. Fujimoto, Editor(s)

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