RECONFIGURABLE LARGE MODE AREA LIQUID CRYSTAL CORE RIB WAVEGUIDE

Abstract

Large-mode-area (LMA) waveguides with single mode operation have always been a matter of interest for application in compact integrated optical devices with high-power handing capacity without the nonlinear effects. Significant efforts have been made recently to construct LMA single mode waveguides, such as small index contrast large core polymer waveguides, graded index waveguide, multilayered alternatively low and high index cladding structure leaky planar waveguide, large-core multi-trench rectangular channel waveguide, and deep etching in semiconductor waveguides. In this thesis we propose a novel approach to design a large mode area waveguide with single mode operation in Liquid crystal (LC) rib waveguide structure by exploiting the properties of liquid crystals. Effective area of a waveguide can be increased by changing the refractive index profile and the relative index contrast between the cladding and the core region. This is achieved by creating low refractive index region in rib region compared to the slab region of the waveguide by applying the electric field. We have shown that, effective mode area of waveguide can be tuned from 380 𝜇𝑚2 – 430 𝜇𝑚2. We have verified the single-mode condition which is shown by the plot between 𝑊/𝐻 and ℎ/𝐻 and further we have shown that the difference between the effective mode index of fundamental mode and the higher-order mode decreases with rib width and the index difference between the slab and the rib regions. In this work, the finite difference mode (FDM) approach has been used to simulate the mode area of the rib structure. Within the optical communication band, the proposed waveguide structure can single-moded in the optical communication band of 1550 nm. Further, we have studied the filter characteristics of the LMA LC rib waveguide, and it has been observed that the designed structure can couple light from fundamental mode to higher-order slab mode with the help of a long period grating, which results in transmission dip at resonance wavelength. This works as a wavelength rejection filter, whose rejection wavelength can be tuned by externally applied electric field across the LC core region.