Sensing with optical vortices in photonic-crystal fibers.

We demonstrate optical polarization vortex generation in a photonic-crystal fiber (PCF) by means of a CO(2) laser-induced long period grating. Vortices are a special subclass of fiber modes that result in polarization-insensitive resonances even when grating perturbations are asymmetric, as is the case with structural perturbations in single-material PCFs. The physics of vortex generation, combined with the use of structural perturbations alone, in single-material fibers, opens up a new schematic for realizing harsh-environment sensors. We show that the temperature and polarization stability of our vortex devices is maintained for prolonged periods of time (tested up to 34 h) at temperatures exceeding 1000 °C. We envisage that this demonstration opens up a new way of realizing high-temperature sensors in a cost-effective manner.