  Interferometric interrogation technique realized for conventional fiber Bragg
grating (FBG) sensors is historically known to offer the highest sensitivity
measurements, however, it has not been yet explored for {\pi}-phase-shifted FBG
({\pi}FBG) sensors. This, we believe, is due to the complex nature of the
reflection/transmission spectrum of a {\pi}FBG, which cannot be directly used
for interferometric interrogation purpose. Therefore, we propose here an
innovative as well as simple concept towards this direction, wherein, the
transmission spectrum of a {\pi}FBG sensor is optically filtered using a
specially designed fiber grating. The resulting filtered spectrum retains the
entire characteristics of a {\pi}FBG sensor and hence the filtered spectrum can
be interrogated with interferometric principles. Furthermore, due to the
extremely narrow transmission notch of a {\pi}FBG sensor, a fiber
interferometer can be realized with significantly longer path difference. This
leads to substantially enhanced detection limit as compared to sensors based on
a regular FBG of similar length. Theoretical analysis demonstrate that high
resolution weak dynamic strain measurement down to 4 p{\epsilon}/sqrt(Hz) is
easily achievable.
