Characterization of thin layered structures using deconvolution techniques in time-domain and Fourier-domain optical coherence tomography

Much of the current activity in optical coherence tomography aims at increasing the image resolution. Nowadays, two kinds of OCT techniques are available. The first approach is the Time-Domain OCT (TD-OCT) which usually relies on a moving part into the reference arm to probe the sample in depth. The second approach is the Fourier-Domain OCT (FD-OCT) in which the signal is acquired as a function of the wavelength and the depth profile of the sample is obtained by Fourier transform. Theoretically, in both techniques, the resolution is limited by the central wavelength of the source and by its full width at half maximum. Nevertheless, it is shown in this paper that this resolution may be improved by using deconvolution technique based on Wiener filtering and Autoregressive Spectrum Extrapolation (ASE). In our experiment, thanks to deconvolution an improvement of a factor up to 4 is obtained in TD-OCT and about 2 in FD-OCT. As an illustration, the approach is applied to TD and FD-OCT measurements of the profile of a carbon-epoxy composite to evaluate the performance in determining the thickness of the upper layer within a resolution better than that provided by the conventional processing of the OCT envelope.