Page 196 - Fiber Bragg Gratings
P. 196
4.7 Radiation mode couplers 173
Figure 4.25: The coupling constants for the fundamental guided mode to
168 even- (/ = 2) and odd-order cladding modes with azimuthal order 1 (type
LP Qn) (from: Erdogan T, "Cladding mode resonances in short and long period fiber
grating filters," Opt. Soc. Am. A 14(8), 1765, 1997.).
in a shift in the propagation constants, and thereby strongly affect the
resonance wavelength. This aspect does not affect the counterpropagating
resonance strongly, since the percentage change in the sum of the propaga-
tion constants is small. The change in the resonance condition for the
STG in which only the core mode is affected can be calculated as [55]
whereas the resonance condition for the LPG changes as
/3 0 is the average propagation constant of the core and cladding modes,
and TjSfiuv is the effect of the additional UV-induced detuning over and
