Abstract
Tunable notch filters with multiple transmission lines have been proposed
and demonstrated by temporarily inducing phase-shifts in chirped fiber Bragg
gratings through the application of stress or thermal perturbations. These
filters find application in many fields including microwave photonics or
optical communications. So far, study of this type of filter has been mostly
experimental with occasional numerical modeling based on coupled-mode
theory. This paper presents a theoretical analysis using the WKB
approximation that highlightens the presence of resonators and
quantitatively describes both the phase-shift accumulated in the propagation
region and the reflection strength of the surrounding grating regions. The
model provides an approximated function of the transmission peak amplitude
that gives good insight into its dependence on the grating parameters and
perturbation profile. This analysis predicts the filter bandwidth, tuning
capability and minimum spectral separation between two transmission lines
leading to straightforward design and optimization of the filter
parameters.
© 2012 IEEE
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