Page 160 - Optofluidics Fundamentals, Devices, and Applications

Optofluidic Photonic Crystal Fibers: Pr operties and Applications 135

125 μm

125 μm

20 μm 100 μm

FIGURE 7-1 A selection of MOFs imaged in cross section. (from top left, clockwise)
A grapefruit fi ber whose inclusions shape the guided mode can be fi lled with a fl uid;
a simple hollow core fi ber, with a ring of dopant surrounding the air core. The mode
is ring shaped; a high air fi ll fraction, bandgap guidance hollow-core PCF; an
effective index-guiding PCF. The microstructure lowers the refractive index of the
medium, guiding a mode in the solid core.

fiber’s optical properties. One of the earliest examples of an all-fiber
optofluidic device that utilized the “grapefruit” fiber is mentioned in
the preceding text [23].

7-1-2 Optical Fiber Postprocessing
A number of postprocessing techniques are used to improve opto-
fluidic operation of existing fibers and MOFs. These include taper-
ing to control the overlap between light and fluids, writing Bragg
gratings and long-period gratings, for example, to couple two
modes with higher overlap with the fluids, and surface treatments
to improve microfluidic properties. Fiber tapering and grating
writing play key roles in the development of fiber-based optofluidic
structures, and are discussed here. Surface treatments will be dis-
cussed in Sec. 7-4.