Study of in fiber Mach-Zehnder interferometer based on two spaced 3-dB long period gratings surrounded by a refractive index higher than that of silica
O. Duhem et al., Study of in fiber Mach-Zehnder interferometer based on two spaced 3-dB long period gratings surrounded by a refractive index higher than that of silica, OPT COMMUN, 180(4-6), 2000, pp. 255-262
The paper deals with the response of a Mach-Zehnder interferometer composed
by two 3-dB long period gratings (LPG) with different external refractive
indices higher than that of silica (leaky configuration). A rough analysis
of the cladding propagation arising in leaky configuration has allowed us t
o establish a model that is sufficient to describe the interferometer coupl
ings evolution at the resonance. In particular, we have shown that the inte
rferometer sensitivity depends strongly on its phase-shift a cp and is opti
mized for a Delta phi equal to pi [2 pi] or 3 pi/4 [2 pi]. An experimental
study was undertaken and allowed us to validate our model. Finally, a compa
rison with a single LPG demonstrated an increased sensitivity to the extern
al index, suggesting the conception of a new fiber sensor operating with ex
ternal refractive indices higher than that of silica. (C) 2000 Published by
Elsevier Science B.V. All rights reserved.