Biophotonics_Concepts_to_Applications

fibers. Figure7.7shows a classic example of hexagonal packing for a probe con-
sisting of sevenfibers [ 3 ]. The arrangement shown in Fig.7.7a uses the centralfiber
as the light delivery channel for purposes such as illumination, scattering-based
diagnosis,fluorescence excitation, or imaging. The surrounding sixfibers are
assigned as the collection channels. In Fig.7.7b threefibers are assigned as the light
delivery channels and the remainingfibers are used for light collection. Optionally,
opticalfilters with different spectral pass bands can be deposited on the end faces of
individual collectionfibers for evaluating specific wavelength data.
Adding more rings offibers around the central opticalfiber can create larger
bundles, as is shown in Fig.7.8. The number of opticalfibers Nhexthat can be
packaged hexagonally in a circular cross section is given by

Nhex¼ 1 þ

Xm

n¼ 0

6n ð 7 : 1 Þ

Illumination

fibers

Collection

fibers

Cable

jacket

(a) (b)

Fig. 7.7 End-face views of two different arrangements for hexagonal packing of multiple-fiber
probes (J. Biomed. Opt. 19(8), 080902 (Aug 28, 2014). doi:10.1117/1.JBO.19.8.080902)

Ring 1

Ring 2

Fig. 7.8 Multiple
hexagonally packaged rings
of opticalfibers

204 7 Optical Probes and Biosensors