A relative humidity (RH) sensor based on a seven-core fiber (SCF) coated with graphene oxide (GO) is proposed. The sensing structure consists of a part of the SCF sandwiched between two parts of no-core fibers (NCFs). The SCF was corroded by hydrofluoric acid until the six outer cores were exposed to air and then coated with a layer of GO. The two NCFs play splitting and coupling roles because of the core diameter mismatch. The center core of the SCF acts as the reference arm, and the outer six cores of the SCF act as the sensing arm to construct a Mach–Zehnder interferometer. When GO absorbs water molecules, its refractive index changes. Consequently, the phase difference between the center core and outer core modes varies, and the resonant dip moves. The experimental results indicate that the RH sensitivity can reach 0.165 nm/%RH in the range of 30% to 100%, and the corresponding linear fitting coefficient is 99.9%.
Photonic crystals(PCs)have many potential applications because of their ability to control light-wave propagation. In
this paper, we theoretically investigate the tunability of light propagation in photonic crystal waveguides in
two-dimensional photonic crystals with square lattices composed of heat-resistant silicon resin. Waveguides can be
obtained by the infiltration of silicon resin into air regions in two-dimensional photonic crystals composed of air holes
with square lattices of dielectric cylinders. The refractive index of silicon resin can be changed by manipulating the
temperature of the sample. Numerical simulation by solving Maxwell's equations using the plane wave expansion(PWE)
method shows that the band gaps can be continuously tuned by silicon resin, accordingly the light propagation in
photonic crystal waveguides can be controlled. The band gap is analyzed in the temperature range of 20°C-120°C. In our
work, the gap map for a square lattice of dielectric cylinders is also simulated. The method can separate TM- and
TE-polarized modes in the waveguide. Such a mechanism of band gap adjustment should open up a new application for
designing field-sensitive polarizer in photonic integrated circuits.
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