Approach for Temperature-Sensitivity Enhancement in a Tapered Dual-Core As2Se3-PMMA Fiber With an Antisymmetric Long-Period Grating

We propose and demonstrate an approach for temperature-sensitivity enhancement based on effective group-velocity matching between the even and odd modes of a dual-core As
₂
Se
₃
-PMMA fiber taper on which an antisymmetric long-period grating is inscribed. The transmission of optical pulses in the dual-core As
₂
Se
₃
-PMMA taper inscribes the antisymmetric long-period grating that causes the electric fields to couple back and forth between the even and odd modes leading to effective group-velocity matching between the two modes. The variation of the difference between phases of the two modes φ
_d
(λ) with respect to wavelength tends to 0 (∂φ
_d
(λ)/∂λ → 0) near the resonance wavelength of the grating due to effective group-velocity matching between the two modes, and consequently, thermally induced change of the difference between phases of the two modes φ
_d
(λ) leads to a large wavelength shift indicating enhancement of the temperature measurement sensitivity. Experimental results show that temperature measurement sensitivity in the wavelength range with effective group velocity matching is enhanced by a factor of 4.0 in comparison with the sensitivity in the wavelength range that does not have effective group velocity matching in the dual-core taper with As
₂
Se
₃
core diameter of 1.5 μm. Exploiting sensitivity enhancement within the group-velocity matching wavelength range opens the path toward the realization of novel high-sensitivity fiber sensors for temperature and strain measurement.