Specialty Optical Fibers Handbook

microbends) from the ideal condition leads to a change in propagating fields and

radiation loss. On the other hand, the high sensitivity of such a guiding fiber to

small perturbations may be useful in sensing applications that require high

sensitivity.

11.3.3 Group Velocity and Waveguide Dispersion

The diameter-dependent group velocity of the HE

11

mode for the air-clad

silica nanofiber is given by [14]

v

g

¼

c

n

2

1

b

k

1

1  2D(1  h)

(11:20)

and shown in Fig. 11.8 for two wavelengths. When the fiber diameter D is very

small, v

g

approaches the speed of light in vacuum c because most of the light

energy propagates in air. As D increases, an increasing fraction of ...