Properties of nematic LC planar and smoothly-irregular waveguide structures: research in the experiment and using computer modeling

Abstract

Nematic liquid crystal planar and smoothly-irregular waveguide structures were studied experimentally and by the computer modeling. Two types of optical smoothly-irregular waveguide structures promising for application in telecommunications and control systems are studied by numerical simulation: liquid crystal waveguides and thin film solid generalized waveguide Luneburg lens. Study of the behavior of these waveguide structures where liquid crystal layer can be used to control the properties of the entire device, of course, promising, especially since such devices are also able to perform various sensory functions when changing some external parameters, accompanied by a change in a number of their properties. It can be of interest to researchers not only in the field of the integrated optics but also in some others areas: nano-photonics, optofluidics, telecommunications, and control systems. The dependences of the attenuation coefficient (optical losses) of waveguide modes and the effective sizes (correlation radii) of quasi-stationary irregularities of the liquid-crystal layers on the linear laser radiation polarization and on the presence of pulse-periodic electric field were experimentally observed. An estimate was made of the correlation radii of liquid-crystal waveguide quasi-stationary irregularities. The obtained results are undoubtedly important for further research of waveguide liquid crystal layers, both from the theoretical point of view, and practical – in the organization and carrying out new experimental researches, for example, when developing promising integrated-optical LC sensors.

Computer simulation of the pulse-periodic electric field effect on the 2D director orientation of nematic liquid crystal. Experimental research of multimode nematic liquid crystal waveguides.

“…The results of the numerical modeling showed that the considered twodimensional model with a constant electric field varying within wide limits did not allow us to give a complete explanation of the effect observed in the experiment with 2D LC cell [12,13,15,16], which apparently is conditioned by the pulse-periodic character of the applied electric field [15] and 2D character of the Frederiks's effect [16][17][18]21]. Note that we didn't take into account other possible effects, e.g.…”

“…If the directions of the field and director in the initial state do not satisfy the condition of the minimum of the free energy at quite a high field which is capable of overcoming the NLC's elastic forces, the director will be reoriented and its new stationary distribution will be established. In our previous paper when carrying out the standard minimization procedure for the free energy of the ensemble of NLC molecules [15] in the external electric field E and not going beyond the qualitative estimation of the final results to simplify the problem's solution, we obtained the second-order partial differential equation [12,15,16,18,21]. Then the numerical solutions of this equation with known boundary conditions were obtained and studied.…”

“…To accelerate the iterative processes, control of the accuracy of the obtained solutions and precision of the results, the calculations were carried out on a sequence of grids. The programs for solving the boundary-value problem were realized in FORTRAN and C/C++ [12,15,16,18,21,22].…”

“…Corresponding partial differential equation of the second order can be written in the next form [12,15,16,18,21]: 0.1 s; in the beginning of each period (during the time interval ≈ 10 -5 s),   6 10  t E V/m, whereas during the rest of the period the field was zero.…”

“…The importance of these studies is determined by the practical application and prospects of these materials in high-speed low-energy LC data imaging devices; lowcost organic light-emitting displays and solar cells; and integrated optical devices, for example, coupling elements, modulators, distributed Bragg reflectors, sensors, processors; and is also perspective for optofluidics applications (see e.g. [17][18][19][20][21]).…”