improvement in the performance of biosensors, because it results in a stronger
optical coupling between a light signal and the surrounding biosensor analyte. More
details on biosensors are given in Chap. 7.
3.11 Side-Emitting or Glowing Fibers
In applications such as telecom links, it is necessary that opticalfibers transport
light to the intended destination with low optical power loss and small signal
distortion. However, a different type of opticalfiber that emits light along its entire
length has been used in applications such as decorative lamps, submersible lighting,
event lighting, and lighted signs and also thesefibers are being incorporated into
biomedical applications [ 41 – 46 ]. Such aside-emittingfiberorglowingfiberacts as
an extended emitting optical source [ 5 ].
Another embodiment for lateral emission of light is theside-firingfiber[ 5 ]. As
described further in Sect.7.1, this structure consists of an angled end face at the
distal end of thefiber. This enables the light to be emitted almost perpendicular to
thefiber axis. Uses of side-emitting and side-firingfibers for biomedical procedures
include photodynamic therapy, therapy for atrialfibrillation, treatment of prostate
enlargements, and dental treatments.
A variety offiber materials and construction designs have been used to fabricate
side-emittingfibers [ 5 ]. Both plastic and silicafibers are available. One popular
method of achieving thefiber glowing process is to add scattering materials into
either the core or cladding of thefiber. Thereby a side-emitting effect is created
through the scattering of light from thefiber core into the cladding and then into the
medium outside of the fiber. As Fig.3.14 shows, one implementation of a
side-emittingfiber is to attach a length of this type offiber (e.g., 10–70 mm for
short diffusers or 10–20 cm for long diffusers) to a longer deliveryfiber (nominally
2 – 2.5 m), which runs from the laser to the side-emitting unit.
As a result of scattering effects, the light intensity in a side-emittingfiber
decreases exponentially with distance along thefiber [ 5 ]. Therefore, the intensity of
the side-emitted light will decrease as a function of distance along thefiber. If it is
Red light sourceDiffuser segment emits red light
along its length (10 to 70 mm)Transmission fiber
(typically 2 to 2.5 m)Fig. 3.14 Theredinput light
is scattered radially along the
length of the side-emitting
fiber (J. Biomed. Opt. 19(8),
080902 (Aug 28,
2014). doi:10.1117/1.JBO.19.
8.080902)
80 3 Optical Fibers for Biophotonics Applications