Multiple source generation using air-structured optical waveguides for optical field shaping and transformation within and beyond the waveguide

In this paper we review recent results describing the generation of optical modes within waveguides based on coherent scattering from artificially structured interfaces. The generation of optical waveguide propagation similar to free space propagation enables possible solutions to controlling and shaping optical field generation in free space using coherent scattering of multiple sources. It is shown that the controlled fabrication of such sources can be done simply with air-material structured waveguides such as air-silica structured fibres. Further, the technique of coherent superposition is well known in Fresnel optics, exploiting zone plates to correct the necessary phase adjustments for a desired lens performance. Similarly, in waveguide form this allows fine control of the interference process resulting in the desired mode field and its properties within the waveguide, at the end of the waveguide in the near field regime and well beyond the waveguide into the far field. A factor that can contribute significantly to the coherent scattering within the Fresnel waveguide is resonant-like scattering inside the low index regions since the critical angle of propagation can be very small, increasing Fresnel reflections between interfaces. The results presented here open up a range of hitherto unexplored possibilities in controlling and shaping at first glance disparate phenomena, including free space diffraction.