Propagation of light beams in microstructured nematic liquid crystals

Electrically controlled waveguides implemented in spatially structured liquid crystals (LC) are promising for use as switching elements of fiber-optic communication lines, in the devises for optical signal processing and... [ view full abstract ]

Electrically controlled waveguides implemented in spatially structured liquid crystals (LC) are promising for use as switching elements of fiber-optic communication lines, in the devises for optical signal processing and transmission, are becoming more popular in today's market. Manifestation in the nematic LC media optical Fredericks transition effect and the nonlinear light-induced orientation effect make these materials promising functional environments for creating managed waveguide channels.

A method of creating an integrated optical devices based on LC waveguides for spatial-polarization control of the light beams is presented. Waveguide channels in planar nematic LC layer implemented by using a patterned electrode layer deposited on the one substrate of the LC cell. The periodic refractive index modulation in the LC layer appears due to the action of an external electric field and causes the formation of controlled LC waveguides in the cell. An external AC voltage applied to the LC element controls the depth of modulation of optical anisotropy. The waveguide properties of the LC cell disappear when external AC voltage is not applied.

The experimental picture of propagation of linearly polarized light beams along the waveguide channels with an optical power below the threshold of nonlinear light-induced orientation effect is shown in Fig.1. As seen from Fig.1 a, at low power light beam (P = 0.5 mW) waveguide mode propagation of light is realized under external voltage (U=4 V) significantly exceeding the threshold of the Fredericks transition (U = 1.1 V). Waveguide mode propagation of light beams in this case is realized by electrically controlled total internal reflection (TIR) effect in a microstructured nematic LC layer.  Fig.1 b shows that in this case the effect of self-focusing and formation of spatial soliton can be observed even when the light beam power is P = 3 mW.

Thus, the combination of two mechanisms of the nematic LC director reorientation (electrical and optical) extends the functional characteristics of photonic devices based on the waveguide mode propagation of light and nonlinear light-induced orientation effects. Developed portable LC devices with low working voltages are promising for spatial-polarization control of light beams with different optical power.