A far-field method for characterizing thin planar optical waveguides

A modified far-field method for characterizing optical waveguides is proposed and demonstrated. The method is based on the formation of an intermediate near-field image which is spatially filtered to obtain a final far-field image with a much higher signal to noise ratio. This represents an important improvement when the out-coming guided light is blurred by a high level of spurious light as is frequent in many thin planar guides. The method is demonstrated with a h-thick proton exchanged waveguide, whose thickness and refractive index are determined within a 10% error using the simple slab approximation.