The Fourier-domain version of the a/LCI system uses a superluminescent diode (SLD) with a fiber-coupled output as the light source. A fiber splitter separates the signal path at 90% intensity and the reference path at 10%.
The light from the SLD passes through an optical isolator and subsequently a polarization controller. It has been shown that control of light polarization is important for maximizing optical signal and comparing angular scattering with the Mie scattering model. A polarization-maintaining fiber is used to carry the illumination light to the sample. A second polarization controller is similarly used to control the polarization of the light passing through the reference path.
The output of the fiber on the right is collimated using lens L1 and illuminates the tissue. But because the delivery fiber is offset from the optical axis of the lens, the beam is delivered to the sample at an oblique angle. Backscattered light is then collimated by the same lens and collected by the fiber bundle. The fibers are one focal length from the lens, and the sample is one focal length on the other side. This configuration captures light from the maximum range of angles and minimizes light noise due to specular reflections.
At the distal end of the fiber bundle, light from each fiber is imaged onto the spectrometer. Light from the sample and reference arms are mixed by a beamsplitting cube (BS), and are incident on the entrance slit of an imaging spectrometer. Data from the imaging spectrometer are transferred to a computer via USB interface for signal processing and display of results. The computer also provides control of the imaging spectrometer.