Electro-optic switching

Keywords catenanes. rotaxanes. molecular switching, electro-optic effect, Kerr effect, photoiso-... 

The molecule is a liquid crystalline polymer with chiral smectic C phase forming parts attached as side chains. The field required to switch the direction of polarization of the polymer is very low (0.3 MVm ). There is a lot of interest in liquid crystalline ferroelectric polymers, because of their possible use for fast-switching electro-optical devices. More information about ferroelectric liquid crystals can be found in references [36,37]. 

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... 

In addition to the sensitivity to ring structure, slight alterations of the hydrocarbon chain may lead to dramatic differences in electro-optic performance in chiral compounds [43]. For example, in some electroclinic Sm-A materials it has been reported that if the chain is shortened or if a double bond is localised at the end of the hydrocarbon chain, the tilt angle, electroclinic coefficient, and switching time are significantly suppressed [43]. 

In recent years advances in the chemistry of leuco dyes have taken place particularly in the areas of structural identification by means of H- and 13C-NMR and selective syntheses of aminoquinones, etc. New applications of leuco quinones such as in electro-optical devices and information recording media have enhanced their importance. In these applications, the chemistry of leuco quinones is interesting mainly due to switching from a colored to a colorless system by a redox process. 

Intense nanosecond pulses (Ins = 10 9s) can be produced by Q-switching. A shutter is placed between the laser rod and one of the mirrors, thus inhibiting lasing. If the shutter is suddenly opened, the excitation is dumped in one huge burst. One type of shutter is the electro-optic Pockels cell (KH2P04 crystal with a high applied potential). 

An electro-optic shutter within the cavity ) in addition to the normal 0-switching produces even shorter light pulses by truncating both edges of the pulse. 

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.

Until recently a general drawback of this passive Q-switching scheme was the difficulty of obtaining an exact synchronization of the giant pulse with other events in more complex experiments. This difficulty does not exist with active Q-switching in which an electro-optic device, e.g. a Kerr-cell or Pockels-cell, is used instead of a dye cell, and one is able to determine exactly the time at which... 

There is another way to obtain giant laser pulses of a few ns duration, known as active Q-switching. The shutter is an electro-optical cell which is triggered at some preset time after the pump flash. These electro-optical shutters are Kerr cells or Pockels cells. 

Fig. 26a and b. Influence of the electric field frequency on the electro-optical behaviour of the nematic polymer XII and scheme of mesogenic groups orientation before (A) and after (B) the application of electric field (a) optical transmission as a function of time at different frequencies (U = 30 V T = 75 °C) (b) optical transmission as a function of time upon application of an electric field at U = 85 V (f = 50 Hz) (1) relaxation upon switching the electric field off (2), upon application of an electric field (U = 80 V) of different frequency f = I (3) 5 (4) 7 (5) and 20 kHz (6) during the relaxation process... 

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