Liquid-crystal photonic applications

Abstract

Abstract. Liquid crystals are nowadays widely used in all types of display applications. However their unique electro-optic properties also make them a suitable material for nondisplay applications. We will focus on the use of liquid crystals in different photonic components: optical filters and switches, beam-steering devices, spatial light modulators, integrated devices based on optical waveguiding, lasers, and optical nonlinear components. Both the basic operating principles as well as the recent state-of-the art are discussed. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).[ DOI: 10.1117/1.3565046] Subject terms: liquid crystals; photonic applications; review; liquid-crystal lasers; spatial light modulators; tunable lenses; nematicons; optical nonlinearity.Paper 100913SSR received Nov. 5, 2010; revised manuscript received Jan. 11, 2011; accepted for publication Jan. 13, 2011; published online Jun. 14, 2011. IntroductionLiquid crystals (LCs) are organic materials that are liquid but that show a certain degree of ordering (positional and/or orientational). With this definition, many materials can be classified as liquid crystals, but the majority of liquid crystals that are used in photonic applications are of the thermotropic type. Thermotropic means that the liquid-crystal phase exists within a certain temperature interval (in contrast to lyotropic materials for which the material is liquid-crystal within a certain concentration range). Various types of thermotropic liquid-crystal materials exist, and many different mesophases have been discovered in the last decades: nematic, smectic A, smectic C, columnar, blue phases, and many many more. The diversity of liquid-crystal materials is huge, but this diversity is even overshadowed by the number of applications in which liquid crystals are used nowadays. The majority of applications are related to informationdisplay applications. Liquid crystals have conquered the major market share in different display application areas: television screens, laptop screens, screens in mobile phones, etc. Only in projection displays does a tough competitor exist, namely microelectromechanical systems or licenced by Texas Instruments: Digital light processing. Organic light emitting diodes (OLEDs) are the obvious next generation technology that could overtake the LC domination, but today OLED displays have not penetrated the market and only the future will tell if they will. In this review article, we will focus on nondisplay applications, but because we cannot go too broad, we restrict ourselves to photonic applications in which the light is actively manipulated by the LC. In this review article, a certain external influence (surface anchoring, electric fields, optical fields) is used to (re)orient the LC in a certain way. In turn, the LC then changes the light that is propagating through it. Of course, as in every review article, it is impossible to list all the fascinating new scientific results or breakthroughs. Therefore, the authors apologize for not i...

High Birefringence Liquid Crystals

“…They are connected with telecommunication devices needs or nondestructive microwaves apparatus to control goods and people [19], cholesteric lasers [20,21], manufacturing tunable metamaterial [22][23][24][25]. 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.…”

Wave propagation and acoustic band gaps of two-dimensional liquid crystal/solid phononic crystals

“…Beyond the nematic phase transition range, some other mesophases may exist. There are many different types of LC mesophases discovered in the last decades such as nematic, smectic A (SmA), smectic C (SmC), columnar, and blue phases, respectively [20]. Based upon material selection, like LC polymers, different phases can exist in one material at different temperatures.…”

On liquid crystal diffractive optical elements utilizing inhomogeneous alignment

“…The needed spatial distribution of the LC director is achieved in the majority cases by means of an inhomogeneous electric field [1][2][3][4][5][6][7][8][9][10][11][12] or with a thickness variations [1,2,13,14]. Adaptation of such approaches for micron-scaled systems poses technological difficulties due to that electrodes are required or due to geometrical non-uniformities.…”

“…Several types of LC optical elements have been proposed [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. The needed spatial distribution of the LC director is achieved in the majority cases by means of an inhomogeneous electric field [1][2][3][4][5][6][7][8][9][10][11][12] or with a thickness variations [1,2,13,14].…”