Theory and experimental studies of all-optical transmission switching in a twist-alignment dye-doped nematic liquid crystal

MULTIPLE TIME SCALES OPTICAL NONLINEARITIES OF LIQUID CRYSTALS FOR OPTICAL-TERAHERTZ-MICROWAVE APPLICATIONS (Invited Review)

“…The dynamics of the transmitted pulse, the input pulse energy threshold to generate noticeable transmission switching are close to theoretical expectations. The switch-off occurs earlier for higher input lasers energies and response times as short as 50 nanoseconds have been observed [4,5,[73][74][75].…”

“…(d) Nematic liquid crystals in nanostructured metamaterial [12]. their electro-optical counterparts that operate at milliseconds speed, several of these optically activated mechanisms can enable ultrafast all-optical switching operations in conjunction with sub-microseconds to nanoseconds and femtoseconds lasers [65][66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83][84]. All-optical interactions and activation processes also do not require electrodes or complex circuitry, and can be mediated with a large degree of freedom in the direction and polarization states of the incident electromagnetic waves.…”

“…In photo-excitable NLC, another effective mechanism for order parameter change is Trans-Cis isomerism of azo-NLC or azo-molecule doped-NLC [71,73,76]. In the ground or unexcited state, the azo-molecule is in the Trans-state and conforms to the oblong shape of surrounding LC molecules.…”

“…Perhaps the most illustrative NLC cell for all-optical switching is the 90 • twist-aligned nematic cell [73] sandwiched between two crossed polarizers as shown in Figure 9. An incoming vertically polarized light would have its polarization vector rotated by the director axis's twist alignment to emerge from the cell with a horizontal polarization which is fully transmitted by the exit polarizer.…”

“…• -twist alignment cell using a Modified Jones Matrix method similar to those described in [73] for the set up as depicted in Figure 9. The mechanism employed in this simulation is the thermal effect, with the following parameters chosen to be close to experimental values.…”