A single fiber may be employed to emit and collect light from a optically diffusing medium such as biological tissues. However, the light collected by the fiber consists of two components: diffusely scattered light from within the tissue and specularly reflected light from the surfaces. Only the diffuse reflection contains the desired information regarding the optical absorption and scattering properties of the tissue, but the specular component is comparable in magnitude to the diffuse reflection with visible light. The refractive index mismatch between the fiber and tissue account for a portion of the specular reflection. However, imperfect contact of the fiber with the surface of tissue creates additional boundaries and thus additional specular reflections. Experiments are performed with a 200 micron diameter fiber and a 632.8 nm He-Ne source to characterize the specular reflection collected through the same fiber using water as a coupling medium. The angular collection efficiency is measured for a fiber in contact with the surface on a glass substrate (specular reflection only) and an epoxy resin tissue phantom (specular and diffuse reflection components). Next, the collection efficiency is measured for a separation between the fiber and the samples for perpendicular illumination to the surface, 14 degrees, and 25 degrees from the normal. Imperfect contact is demonstrated to vary the amount of specular reflection collected using a single fiber where changes in angle greater than 4 degrees or a separation between the fiber and the surface in excess of 400 micron caused a minimum of 7 percent reduction of the collected specular reflection.
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