Using the polarisation response of planar optical waveguides to determine the anisotropic complex refractive index of graphene oxide thick films

The polarisation response of graphene oxide (GO) coated planar silica optical waveguides has been studied. GO films with different thicknesses have been coated onto a planar optical waveguide with its top cladding removed via plasma etching. The solution drop-casting technique was used for GO coating. GO film thicknesses between 0.1 m and 1.0 m were used. GO-coated waveguides exhibit large polarisation dependent losses and the polarisation response depends strongly on the GO coating thickness. The response was used, together with finite element analysis, to determine the complex refractive index of the GO film. The complex refractive indices of the GO film, with TEand TM-polarised light at a wavelength of 1550 nm, were found to be 1.65+0.07i and 1.63+0.001i, respectively. The uncertainty values for the real parts of the refractive index were 0.02 and 0.01 for TMand TE-polarised light, respectively whereas the uncertainty values for the imaginary part of the refractive index were found to be 0.0001 and 0.01 for TMand TE-polarised light, respectively. The estimated uncertainty values are smaller by an order of magnitude when compared with values measured using the conventional method of spectroscopic ellipsometry.