In this paper, a method for interrogation of Fibre Bragg Grating (FBG) and single mode-multimode-single mode (SMS) fiber for simultaneous measurement of temperature and strain using is proposed and demonstrated. A half etched FBG is deployed in the optical circuitry for sensitivity enhancement. The sensor exhibits the temperature and strain sensitivity of 20.2 pm/°C and 1.91 pm/με over the range of 20-200 °C and 100-2020 με respectively. The resolution for temperature and strain measurement is ±0.5 °C and ±12 με. The experimental results show that the sensor is able to measure strain and temperature simultaneously by sensitivity matrix with additional advantages such as simple structure, compact size, ease of fabrication, and low cost.
Poincare sphere (PS) representation for all possible modes of a few-mode optical fiber is presented. The fiber that can support up to two scalar modes is considered for the study. The polarization aspects of first-order linearly polarized degenerate modes and their possible combinations that generate inhomogeneously polarized vector vortex modes (VVMs) are discussed using Stokes analysis. A class of VVMs such as spiral and hybridly polarized modes, apart from well-known radial and azimuthal vector modes, are generated by the linear combination of first-order orthogonal linearly polarized modes with tilted polarization vector. All homogeneously polarized fiber modes are accommodated on standard PS, and inhomogeneously polarized vortex modes are accommodated on a pair of higher order PS. The location of VVM on higher order PS is justified by the positions of orthogonal linearly polarized modes on standard PS.
We have generated a vortex beam with spiral polarization using a few-mode optical fiber. The excitation of the beam is controlled by coupling conditions of incident light beam with the fiber and the state of polarization of input Gaussian beam. The constituent orthogonal linearly polarized modes that contribute to the generation of such spiral vortex beam by inherent mode-mixing are also selectively excited by launching orthogonally polarized light into the fiber input end. Our experimental results suggests a strong dependency of polarization and phase of the fiber output beam on the state of polarization of input beam and are expected to be useful in mode conversion and controlled OAM beam generation. The obtained experimental results are best matched with simulation results.
An intensity modulated Fiber optic prism based liquid concentration sensor is proposed. The sensing principle is based on total internal reflection (TIR) inside the prism which gets modulated in the vicinity of liquid as a function of refractive index. The precise movement of sensor head in liquids, gives rise to a hysteresis curve which is considered as a measure of liquid concentration. Different liquid concentrations of Sucrose, Saline solution (NaCl) and Glycerin are taken for the study. The sensor exhibits sensitivity of 371.16, 2133.25 and 1501.89 Sucrose, Saline water and Glycerin solutions respectively.
Photonic bandgap of two dimensional semiconductor photonic crystal structures of square and triangular lattices are
studied using plane wave expansion method. The bandgap and dispersions also studied by introducing point and line
defect in that structure. Hence a comparative study has been presented among the various structures.