Short optofluidic directional couplers for low power switches

We demonstrate optical directional couplers made of polydimethylsiloxane channels filled with nematic liquid crystals in view of low power flexible optical switches. Transmission of light through such optical channels is polarization insensitive. Coupling of light can be performed with an extinction ratio of over 20 dB at the wavelength of 1550 nm for any input polarization. Directional couplers as short as 45 μm can also be obtained with a gap between the waveguides of just 0.3 μm. Preliminary fabrication of ITO electrodes deposited on PDMS is described to change the coupler state. By applying a voltage a reorientation of the liquid crystal molecules parallel to the applied electric field raises the refractive index of liquid crystal therefore light injected in one waveguide remains in the same waveguide without coupling determining a bar-state of the directional coupler. Images at a scanning electrode microscope show that ITO electrodes with good uniformity can be obtained with a thickness of about 27 nm. Photolithographic masks have been also fabricated for final switch fabrication.