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.
Optofluidics offers new functionalities that can be useful for a large range of applications. What microfluidics can bring
to microphotonics is the ability to tune and reconfigure ultra-compact optical devices. This flexibility is essentially
provided by three characteristics of fluids that are scalable at the micron-scale: fluid mobility, large ranges of index
modulation, and adaptable interfaces. Several examples of optofluidic devices are presented to illustrate the achievement
of new functionalities onto (semi)planar and compact platforms. First, we report an ultra-compact and tunable
interferometer that exploits a sharp and mobile air/water interface. We describe then a novel class of optically controlled
switches and routers that rely on the actuation of optically trapped lens microspheres within fluid environment. A tunable
optical switch device can alternatively be built from a transversely probed photonic crystal fiber infused with mobile
fluids. The last reported optofluidic device relies on strong fluid/ light interaction to produce either a sensitive index
sensor or a tunable optical filter. The common feature of these various devices is their significant flexibility. Higher
degrees of functionality could be achieved in the future with fully integrated optofluidic platforms that associate complex
microfluidic delivery and mixing schemes with microphotonic devices.
Electrowetting, the phenomena of changing interfacial energy of an interface, has been demonstrated to be an excellent actuation and pumping mechanism for microfluidics and lab-on-a-chip applications. Individual droplets can be moved and deformed on microchips using voltages as low as 15V. In electrowetting, application of a voltage across the electrodes of a micro-droplet causes it to change the interfacial energy of solid-liquid interface which in turn changes the contact angle of the liquid on the solid. The contact angle is a measure of the extent of wetting of the liquid on the surface. In conventional electrowetting, it has been found that the polarity of the applied potential does not affect the contact angle change. However, our experimental results show that the change of polarity across the electrodes of a micro-droplet can reverse the contact angle change. We call this phenomenon 'dewetting'. The actual physics behind this still remains unexplored. In our experiments we used 100 nm of aluminium on a silicon substrate to form the bottom electrode. A 60 nm silicon dioxide or a 1.4 μm thickness strontium doped lead zirconium titanate (PSZT) layer was used as the dielectric and 380 nm of Teflon was used to make a hydrophobic surface. A platinum wire, which was inserted into the micro-droplet, formed the top electrode. The highest dewetting contact angle change was found to be 9<sup>o</sup> for a 5μl droplet at 60 V. This compared to a maximum of 41<sup>o</sup> which we obtained for conventional electrowetting.