Many optofluidic devices rely on interfacing optical waveguides with microfluidic channels. Often it can be difficult to
realize micron scale waveguides and fluidic channels that are 100 times larger on the same platform. Further, it is often
desirable for an optical waveguide intersection to occur at the vertical centre of a fluidic channel rather than at its top or
at its bottom where the fluid is effectively stationary.
We present a platform for optofluidics which can achieve straightforward integration of large scale fluidic channels and
micron scale waveguides in the epoxy material SU8. A soft imprinting technique is used to define the optical waveguides
as a thin inverted rib core layer between two thick cladding layers. The core is doped with Rhodamine dye to increase the
refractive index and render it optically active for potential use as a lasing material. The fluidic channels are then formed
by a single exposure through the core and both claddings.
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 3×3 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.