Attenuation of mirror image and enhancement of the signal-to-noise ratio in a Talbot bands optical coherence tomography system

Abstract

Abstract.A Fourier domain optical coherence tomography setup is presented built around an optical configuration that exhibits Talbot bands. A low astigmatism spectrometer is used, employing a spherical mirror and a cylindrical lens between a diffraction grating and a linear CCD camera. To produce Talbot bands, the two interferometer beams-object and reference-are laterally shifted in respect to each other in their way toward the diffraction grating. This allows attenuation of mirror terms and optimization of the sensitivity profile. We evaluate the optimization of the sensitivity profile with depth, in respect to its overall strength and its position peak, which can be shifted toward a larger optical path difference in the interferometer. We demonstrate the efficiency of such a configuration at large depths by imaging a thick phantom and human skin in vivo for different values of the lateral distance between the two beams. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

Two-grating Talbot bands spectral-domain interferometer

“…Previous reports on Talbot bands [2,12] developed the explanation of the visibility curve versus OPD as determined by the product of C (shown in Fig. 1 for three values of gap g) with a sinc factor.…”

“…Several mirror term removal methods have been described in the literature, such as sequential phase-shifting interferometry [6], phase shifting using a 3x3 splitter [7], resorting to phase modulation [8]or dispersion [9] to restore the full range and address the ambiguity of the OPD sign. These methods, however, require several images or steps in order to attenuate the mirror terms [12]. A TB configuration only requires a single spectral acquisition and no post-processing.…”

“…In order to employ the theory developed in previous reports [12,17], an equivalent gap g is inferred from the present configuration and extrapolated to the case of a conventional Talbot Bands configuration using parallel beams incident on a single DG. It can be shown that at the grating level, the gap g between the two beams is approximately given by…”

“…In addition, in a TB-based system such as those reported in [11,12,15,16] a Mach-Zehnder configuration must be used in order to ensure a spatial separation between the footprints of the two beams on the diffraction grating or prism. In both cases, a splitter or a combination of splitters are employed to direct the output of the two arms of the interferometer towards the spectrometer.…”

“…Therefore, according to the Talbot Bands theory [2], the profile of modulation contrast versus OPD, C, is shifted by Nλ 0 . The OPD value where C exhibits a maximum, OPD max , is shifted from OPD = 0 by the same amount [12]:…”