Integrated Optics Based on Liquid Crystals Embedded in PDMS Microfluidic Channels

The combination of photonics with microfluidic techniques has been discovered to be a viable new technology to make inexpensive, flexible and reconfigurable devices for many applications ranging from datacom to sensing and biomedical lab on a chip applications [1]. Recently polydimethylsiloxane (PDMS) gained a lot of interest to fabricate microfluidic flexible channels. Optical waveguides made of PDMS channels filled with nematic liquid crystals (LC), referred as LC:PDMS waveguides, were demonstrated showing polarization independent transmission of light at both visible and near infrared wavelengths [2]. LC molecules are homeotropically aligned to the PDMS surface, without using any alignment layer as usually required in LC standard electro-optic devices. This is due to the interface hydrophobic interaction between the PDMS inner surface and the nematic LC molecules. Such optical waveguides can be made through a standard casting and molding technique, combined with filling procedure by capillarity to infiltrate the LC in its isotropic phase at 80 °C under vacuum in the PDMS channels. Such solution allows the design and fabrication of switchable and tunable devices by exploiting the efficient electro-optic and nonlinear optical effects in LC. One advantage of such approach with respect of classical integrated devices is a strong reduction of the power budget in terms of both energy dissipation and driving power. In this paper we show fabrication techniques and characterization of LC:PDMS waveguides and the potentialities to obtain low consuming power integrated electro-optic devices. As an example we report short directional couplers in view of low power flexible optical switches, which are polarization insensitive with an extinction ratio of over 20 dB at the wavelength of 1550 nm.