ABSTRACT
The tomograms shown in this paper have been obtained with a prototype SOCT instrument based on an optical fibre Michelson interferometer setup (Fig. 1), constructed in the Nicolaus Copernicus University. A broadband (λ= 50 nm, central wavelength 845 nm) superluminescent diode (LS) was employed as the light source. The light of high spatial but low temporal coherence is launched into a single mode 50 : 50 fibre coupler (FC) through an optical isolator (OI).The optical isolator protects the light source from the light back reflected from the elements of the interferometer. Light beam is then divided by the fibre coupler into two arms of the interferometer. The light propagating in a reference arm passes through a polarization controller (PC) to provide the optimal conditions for interference, the neutral density filter (NDF) for adjustment of the power of light to achieve the shot noise limited detection and a block of glass acting as a dispersion compensator (DC). The light is then back reflected from the stationary reference mirror (RM) to the reference arm fibre and coupler (FC). The sample arm
comprises transversal scanners (X-Y) and lens which form the measuring head. The light beam is scanned across the object and backscatters and/or reflects from the elements of its structure and returns to the coupler FC. The light beams returning from the reference mirror and from the sample are brought to interference at the output of the interferometer and analyzed by a customized spectrometer. It consists of a volume phase holographic grating (DG) with 1200 lines/mm and achromatic lens (SL) which focuses the spectrum on a 12 bit line scan CCD camera (2048 pixels, 12 bit A/D conversion, Atmel). The spectral fringe pattern registered by this detector is then transferred to a personal computer (COMP). This signal, after Fourier transformation, yields one line of the crosssectional image (A-scan). The A-scan carries information about the location of structural interfaces in the object along the path of the penetrating beam. Scanning across the sample enables collecting 2D slice cross-sections (B-scan). Additional scanning in the perpendicular direction gives 3D information about a structure.
