Optical properties effects upon the collection efficiency of optical fibers in different probe configurations

When optical fibers are used for delivery and collection of light, two major factors affect the measurement of collected light: 1) light transport in the medium from the source to the detection fiber and 2) light coupling to the optical fiber (which depends on the angular distribution of photons entering the fiber). This paper studies the latter factor, describing how the efficiency of the coupling depends on the optical properties of the sample. The coupling dependence on optical properties is verified by comparing experimental data to a simple diffusion model and to a Monte Carlo (MC)-corrected diffusion model. Mean square errors were 7.9% and 1.4% between experiments and the diffusion, and experiments and the MC-corrected models, respectively. The efficiency of coupling was shown to be highly dependent on the numerical aperture (NA) of the optical fiber. However, for lower scattering, such as in soft tissues, the efficiency of coupling could vary two- and three-fold from that predicted by fiber NA. The collection efficiency can be used as a practical guide for choosing optical fiber-based systems for biomedical applications.