Polarization independent electro-optical waveguides with liquid crystals in isotropic phase

Electro-optically induced waveguides can be used in fiber optic networks for optical power control and the distribution of optical signals transmitted over optical fibers. Reliable operation is ensured with this type of waveguides due to their non-mechanical principle of operation. Their polarization dependent behavior caused by field-induced birefringence effects may limit however their practical applications. We report on a method to reduce the polarization dependent loss in electro-optically induced waveguides with a core made of liquid crystals in isotropic phase. The concept design enables a controlled adjustment of the electric field distribution, which is responsible for inducing and shaping the optical mode, by employing an optimized electrode arrangement. In this new waveguide structure, the TM and TE modes coexist spatially and are guided in a similar way. In order to demonstrate this concept, straight and bending waveguides in 1x1 and 1x2 light input to output configurations have been designed and fabricated. The electrode arrangement and single mode waveguide geometry were optimized using FEM simulations. Bulk silicon micromachining was used to fabricate these waveguides. In particular, the manufactured device consisted of two processed silicon substrates with a liquid crystal layer enclosed in between. Devices tested with varying driving voltage have revealed comparable transmitted power for both TE and TM modes. Very low polarization dependent losses over a more than 20 dB wide dynamic attenuation range have been obtained.