Analysis of temperature-dependent mode transition in nanosized liquid crystal layer-coated long period gratings

The cladding mode reorganization in high refractive-index (HRI)-coated long period gratings (LPGs) is theoretically analyzed and experimentally observed with the aim of exploring the sensitivity of the resonance wavelength to the change of the refractive index in a nanoscale overlay. Experimental results show that the transition between cladding modes and overlay modes occurs when the refractive index of the liquid crystal (LC) overlay is changed from 1.477 to 1.515 by increasing its temperature from 20 degrees C to 65 degrees C. The spectral tuning ability of LPGs coated with a HRI LC layer by electro-optic modulation on a LC layer is also demonstrated, and the maximum tuning range can reach approximately 10 nm by choosing a highly sensitive operating point in the transition region.