where is the free-space center wavelength of the input light
that will be back-reflected from the Bragg grating and
is Bragg wavelength shift after applied the force . The cantilever
beam is made up of poly methyl methacrylate (PMMA)
with strain sensitivity (unit: Strain/Newton) according
to the FEM simulation. is the Strain-optic coefficient
( , where and are
Pockel’s coefficients of the strain-optic tensor, is the Poisson’s
ratio) and it has a numerical value of [9]. Fig. 1 shows
the dimension of the sensing structure, and the structure is rightand-
left symmetry along the center line.