Long period grating in a liquid crystal waveguide

Abstract

This paper introduces, for the first time to the best of our knowledge we theoretically report the long period grating (LPG) in the liquid crystal (LC) layer of planar optical waveguide. LPG has the ability to couple the light between core and cladding modes of waveguide. LPG can be used for the development of band rejection filter, gain flattening in erbium-doped fiber amplifiers (EDFA) and for sensing applications. We have shown the realization of proposed LPG in temperature sensing. First, we theoretically analyzed the propagation of light through a 6-layer planar optical waveguide by analyzing its modal field profiles and effective index profile of fundamental mode TE0 and two higher order modes TE1 and TE2. Then we investigated in details the phase-matching curves of the long period grating, which supervise the association between the grating period and the resonance wavelength. Using phase matching curve to choose grating period, we have studied the transmission spectrum of the PLG which display evident elimination of bands at individual wavelengths, noted as the resonance wavelengths. High sensitivity of LC to the environmental temperature makes it a good choice for temperature sensing. The performance of LPG has been studied for the temperature ranging from 306 K to 329 K. The novelty of this structure is the realization of LPG in the LC, which is a key component of display devices. Hence, our structure can provide freedom to use this in variety of pragmatic applications.