Master-slave principle applied to an electrically tunable swept source-OCT system

In this communication, we evaluate the suitability of Master-Slave (MS) optical coherence tomography (OCT) for processing of interferograms generated by an interferometer driven by an akinetic, electrically-tunable swept source from Insight with an ultra-large instantaneous coherence length. The akinetic source is programmed to sweep linearly, but within the sweep, at predictable times, the laser tuning introduces invalid regions in the interferogram, which are normally removed post-acquisition using a pre-calibration file. This makes sure that any optical frequency component is used once only and enables correct operation of a Fourier transform (FT). A FT applied to an unprocessed emitted spectrum leads to wide and numerous peaks in the A-scan. MS processing was introduced to avoid the necessary corrections demanded by conventional FT signal processing or its derivatives. The MS procedure consists of comparing photo-detected signals at the output of two interferometers, a Slave and a Master interferometer. The MS method was advanced along two avenues, either by using (i) electricallygenerated master signals (making use of the same interferometer twice) or (ii) optically-generated master signal via a recently introduced MS down-conversion procedure. We apply both avenues to the Insight source. Approach (i) tests the MS principle as an alternative to the Insight file correction while (ii) demonstrates near coherencelimited operation at a large axial range (>80 mm) for which a too-high sampling rate digitizer would have been needed. In this communication, we evaluate for the first time the suitability of the MS procedure to OCT measurements performed with the akinetic swept source commercialized by Insight. Two modalities are evaluated to implement the MS processing, based on: (i) digital generation of the master signals using the OCT interferometer and (ii) down conversion using a second interferometer driven by the swept source.