Fig. 1. Molecular director at the SSFLC can adopt two synclinic structures where the tilt angle θ is defined by an angle between the n⃗ and k⃗ versors. These states are metastable and can exist without any external electric fields as a result of the minimum energy condition for the SSFLC structure at particular boundary conditions. These states [(a) and (b)] are characterized by the different orientation of the optical axes; polarized light passing through the SSFLC can be modulated by switching between these states. When the external field reaches +Esat, the SSFLC layer will be fully switched to the state shown in (b), and the application of the negative field of value −Esat drives the liquid crystal (LC) layer to the state shown in (a).

Fig. 2. (a) Creation of the interference gratings onto the SSFLC slab. Initial state of the LC layer in the cell with one of the orienting layer doped by dye (POR). (b) I1 and I2 are the interfering laser beams, The interference pattern consists of neighboring areas with a minimum and maximum intensity of the illumination (Imax and Imin, respectively), the green line is for show purposes only and roughly denotes a border between these areas. The illumination locally affects the effective electric field (Eeff) that is superposed with the applied electric field (Eu) which exceeds the threshold level (Eth) and drives the director n⃗ locally to an opposite state. (c) The reading laser beam illuminates the SSFLC slab uniformly and when the reading beam intensity (Iread), hence Eillum, is superposed with Eu does not reach the Eth level, the grating should be ready for optical reconstruction.

Fig. 3. LC cell with the POR prepared as a mixture of the basic solution (nylon 6/6) and dye-dopant (explanation in text).

Fig. 4. Photomicrograph of the SSFLC cell with the POR filled with W212-2E ferroelectric LC observed under the polarizing microscope BIOLAR PI (by PZO Poland) within the birefractive setup. The cross denotes the polarizer and analyzer orientation. (a) Left area is the view of the SSFLC between the ITO electrodes while the E+ electric field is applied. (b) The same cell while the E− electric field is applied.

Fig. 5. Electro-optical response of the cell with SSFLC structure (W212-2E mixture) with the orienting layer (nylon 6/6) and the POR (Nylon 6/6 + dye—blue 2590). Measurements were performed for Upp=8  V, f=1  Hz, and t=25°C. The cell shows a W-shaped behavior.

Fig. 6. Equivalent electrical circuit of the photosensitive cell. For clarity, the influence of the electrical properties of the electrical wires and assembled cell (including aligning layers) were omitted and treated as a constant in reference to the assumed conditions.

Fig. 7. Charge analysis in the complex capacitor with voltage applied; cases without and with the illuminating photon beam are shown as (a) and (b), respectively.

Fig. 8. Measuring setup. A collimated laser beam is applied as an option. All wires and an LC cell under investigation were very precisely shielded by the ground.

Fig. 9. Current flow through the SSFLC structure without the polarizing voltage applied (U=0  V) in darkness. The smoothened curve represents measurements points collected every 0.36 s (1  a.u.=0.36  s).

Fig. 10. Electro-optical response of the SSFLC structure in a function of the polarizing voltage; the current measurements and results represent the absolute difference between the current flow when the illumination of the cell was switched on or off (“dark–>illum” and “illum–>dark,” respectively). At the level of U≥2−2.4  V, a kind of saturation of the observed effect is present (showed by trend lines).

Fig. 11. Measurement of the current flow as an LC cell response for illumination. Measurements were done when U=2  V was applied to the cell.