Electro-optical switching

Sharpness. This describes the steepness of the electro-optical switching as a function of voltage. This is defined in tenns of the ratio of voltages required to achieve 90% compared to 10% transmission of light. This ratio should be as close to unity as possible. 

Clark N A and Lagerwall S T 1980 Submicrosecond bistable electro-optic switching in liquid crystals App/. Phys. Lett. 36 899-901... 

An alternative approach is to add gelling agents to LCs. The gelling materials that have been nsed range from low MW materials to dendrimers. Potential applications inclnde large area displays and electro-optical switches. ... 

Many current NLO devices are based upon crystalline materials (such as lithium niobate for the electro-optic switch) and nonlinear optical glasses, but there is intense... 

Figure 6.107 Schematic illustration of an electro-optic switch, (a) An open circuit causes light to switch channels, and (b) a closed switch keeps light in the same channel. Reprinted, by permission, from P. Ball, Made to Measure, p. 53. Copyright 1997 by Princeton University Press.

Two of the most important nonlinear optical (NLO) processess, electro-optic switching and second harmonic generation, are second order effects. As such, they occur in materials consisting of noncentrosymmetrically arranged molecular subunits whose polarizability contains a second order dependence on electric fields. Excluding the special cases of noncentrosymmetric but nonpolar crystals, which would be nearly impossible to design from first principles, the rational fabrication of an optimal material would result from the simultaneous maximization of the molecular second order coefficients (first hyperpolarizabilities, p) and the polar order parameters of the assembly of subunits. (1)... 

A conglomerate in real liquid crystalline phases was first observed in the smectic phase of a rod-shaped mesogen with two stereogenic centers in its tail [42], We used a racemic mixture which was supposed not to electrically switch. Evidence for conglomerate formation was provided by clear electro-optic switching and texture observation under a polarizing microscope domains with stripes, which themselves display fine stripes. These stripes are tilted in two different directions with respect to the primary stripes. This is a still very rare example now that fluid soft matter is known to resolve spontaneously into a three-dimensional conglomerate. 

Phosphates showing a bulk polarization (i.e. ferroelectric phases) may be used for nonlinear optical processes see Nonlinear Optical Materials) such as second harmonic generation and electro-optic switching. KTP (Section 5.2.2) and related phases (NH4T10P04 and KTi0As04) are very efficient nonlinear materials. The ferroic phosphates described above also show nonlinear properties. KDP materials are inferior to KTP types but they find use in electro-optics as they are very transparent over a wide frequency range. 

Okazaki, S., Uto, S., Ozaki, M., and Yoshino, K. Guest-host electro-optic switching m spin-coated polymer ferroelectric liquid crystal film. Appl. Phys. Lett. 71, 3373 (1997). 

Another important category of optical application uses the electro-optic switching character of perovskites. The system (Pb, La)(Zr, Ti)03 has been hot pressed and sintered to transparency by Haertling [26] and Snow [65], respectively. Phase relations are critical to successful fabrication where Pb volatility makes it difficult to retain compositional limits, and compositional variations make possible memory, linear, or quadratic applications. 

Catenanes and rotaxanes (for a review see [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]), belong to a new class of supramolecules composed from, mechanically bond, constituent smaller molecules, able to move independently. Due to this unique property these new class of organic molecules represent a great interest for potential applications in photonics, particularly in all optical and electro-optic switching [14, 15, 16, 17, 18],... 

Certain thieno[2,3-Z)]- and -[3,2-Z)]thiophene derivatives can be used in Kquid-crystalline mixtures for electro-optical switches and evaluation devices (85GEP3342631, 96GEP4422488, 98NJC771). 

Tong X, Zhao Y. 2003. Self assembled cholesteric liquid crystal gels for electro optical switching. J Mater Chem 13 1491 1495. 

The alignment of the LC molecules is crucial for successful operation of an LCD. Not only does it control the electro-optical switching mode of the display, appropriate alignment also prevents the formation of random mul-tidomains, disclination lines or small mismatches in LC director orientation that deteriorate the displayed image. An alignment layer imposes the orientation onto the LC molecules. Conventionally this alignment layer is rubbed by synthetic or natural fabric, e.g. polyester or velvet [1-4]. 

Electrically polarizable polymer films which are macroscopically noncentrosymmetric (i.e., those containing bulk polar order) are of interest for electro-optic switches and... 

Detailed investigation on the optical characteristics, including the electro-optic phase modulation, electric hysteresis property, and thermo-optic coefficient, of transparent PMN-PT electro-optic ceramics have been conducted [229]. A polarization independent PMNT electro-optic switch by using s -shifted fiber Sagnac interferometer stmcture was constracted and analyzed experimentally. Some switch performances, including thermal characteristic and different switching frequency response, were also realized. 

Qiao L, Ye Q, Gan JL, Cai HW, Qu RH (2011) Optical characteristics of transparent PMNT ceramic and its application at high speed electro-optic switch. Opt Commun 284 3886-3890... 

Fig. 10.15 Schematic diagram of the proposed electro-optic switch. Reproduced with permission from [133]. Copyright 2011, Elsevier...

Fig. 10.18 Birefrengences of the ZlOY-5 wt% Ti02 ceramics before (a) and after (b) postannealing at 1600 °C for 3 h. Schematic diagram of the proposed electro-optic switch. Reproduced with permission from [139]. Copyright 2009, Elsevier...

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