Isothiocyanato-Tolanes Based High Birefringence and Fast Response Time Mixtures for Photonic Applications

Abstract

We have developed some high birefringence (Dn $ 0.3 at k ¼ 633 nm) and relatively low viscosity nematic mixtures using isothiocyanato tolanes. These mixtures exhibit a high figure-of-merit (FoM) which is desirable for reducing the device response time. Using such a high FoM liquid crystal mixture in a 2-lm homogeneous cell, we demonstrate a 1p phase modulator at k ¼ 633 nm with submillisecond response time.

Determination of ordinary and extraordinary refractive indices of nematic liquid crystals by using wedge cells

“…The errors dV, dN, dE, and dO were found as empirical mean deviations and from them the errors dn o , dn e , and dDn were estimated. These results are in good agreement with those taken from the literature [14][15][16][17][18][19][20][21] …”

“…The second one was filled with the 4−trans−4'−n−hexylcyclohexyl isothiocyanatobenzene (6CHBT), the well−known NLC [13]. The third and fourth ones were filled with two NLC mixtures, LCJ 1650 and LCJ 1791A, of large optical aniso− tropy, recently produced in our university [16][17][18][19][20][21].…”

High Birefringence Liquid Crystals

“…Many such mixtures with Δn values in the range 0.3-0.7 have been demonstrated so far [49,50,91,93,94,101,111,122,124,128]. Mixtures with a broad range of nematic phases and birefringence values of Δn = 0.3-0.45 are now available with an acceptable level of viscosity (γ < 300 mPa· s), see example Mixtures 1791 and 1825 composed of fluoro-substituted alkyltolane and alkylphenyl tolane isothiocyanates have the highest birefringence among those presented in Table 17.…”

“…To estimate which liquid crystal mixtures or compounds are better for preparations, instead of making a comparison of their individual parameters: Δn, k 11 , γ, V th , the more effective way is to compare their combined features defined by a more complex parameter called Figure of Merits (FoMs) [49,50,64].…”

“…Different devices such as tunable spatial modulators for light and laser beam steering and for holography [26][27][28][29][30][31][32][33], switchable phase shifters [34][35][36], various types of tunable filters which select or remove bands [37][38][39][40], tunable capacitors [41], antennas [42], lenses [43,44] were manufactured, and others such as photonic fiber [45] (see also, for more information, reviewed papers [46,47]). For these purposes, different high birefringence materials from 0.2 to more than 0.5 are now available [48][49][50][51][52], but further development and improvement of their properties is still necessary. To reanalyze the experimental results that have been obtained so far may be helpful for this task.…”