Sealed air-core planar waveguide arrays in SU8 epoxy

Nonlinear optics in fluid infiltrated air structured 'holey' fibres has attracted much research interest due to the flexibility of infiltration materials and geometries that are possible. Equivalently to these 2D examples, planar structures with 1D arrays of air holes can offer a complimentary platform for nonlinear optics investigations. Importantly, if these structures can be photolithographically defined with longitudinal variations, then a rich array of periodic nonlinear phenomena can be studied. We present a novel planar integrated optic platform for fluid infiltration experiments. The platform consists of layers of SU8 epoxy fabricated with 3x3 µm photolithographically defined microfluidic channels. The channel layer can be doped with rhodamine in order to increase its refractive index to enable vertical confinement and also provides a fluorescent trace to clearly indicate the path of the light. The air channels can be filled with fluids, such as high refractive index oil, to act as optical waveguides in the visible range. Our fabrication consists of spin coating and curing the SU8 lower cladding. We then spin-coat and cure the doped SU8 channel layer and pattern using conventional photolithography. In order to seal the channels with the upper cladding, an SU8 dry film is applied using lamination techniques. The fabrication process is highly flexible and can be easily extended to more complex waveguides like splits, mach zehnder structures. Multiple layers of fluid-infiltrated channels are also possible.