Page 456 - Fiber Bragg Gratings
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9.3 Phase and temporal response of Bragg gratings 433
Figure 9.25: Four commonly encountered grating refractive index modula-
tion profiles.
implemented by Fonjallaz et al. [46]. It therefore is a polarimetric mea-
surement, which requires the polarization of the incident beam to be at
45° to the orthogonal birefringent axes of the fiber. The fiber is immersed
in index-matching fluid to minimize beam deviations. The transmitted
light is analyzed as a function of the translation distance of the incident
beam. The retardation S at the output provides the information on the
stress distribution o- z(z) from an Abel integral equation [44],
where the prime indicates differentiation with respect to the transverse
coordinate^, R is the radius of the fiber, and C is the stress-optic coefficient
of silica. A change in the axial stress changes the refractive index by
the stress-optic coefficient. The three components of the refractive index
change, n n n e, and n z, are related to the axial, circumferential, cr£r}, and
radial, cr p(r) components of the stress-optic coefficients as [47]
In Eq. (9.3.9) the refractive index components are for light waves that
have their electric field components in each of the three directions. The
