Thermo-optical polymer devices

Some of the latest work on high refractive index polyphosphazenes makes use of polymers that contain both fluoroalkoxy and di- or tri-chlorophenoxy side groups.261 These amorphous glasses are thermally stable up to 400 °C, show a large variation of refractive index with temperature, and refractive index values that vary from 1.39-1.56 depending on composition. Thus, they are candidates for uses in thermo-optical switching devices. 

In this chapter we shall only be concerned with electro-optic and thermo-optic switching effects in thermotropic side-chain polymer liquid crystals. We will consider briefly the synthesis and structure of such compounds and show how the nematic, cholesteric and smectic phases arise. Since the optical properties of each of these phases are different, and may be altered depending on alignment within the phase, each gives rise to different electro-optic effects. If these are coupled to the use of dye additives or substituents, then it will be realized that a wide range of electro-optic devices based on dichroism or fluorescence as well as birefringence or scattering power may be fabricated. These will be considered and discussed in terms of their performance and potential applications. Finally, possible uses of polymer-low molar mass liquid crystal solutions will be considered in terms of electro-optic device applications. 

Waveguide components are also applied in photonic devices. Based on polymers, these can be easily manufactured at low cost, with typical applications ranging from computer backplanes that combine electrical and optical cables, thermo-optical switches, optical splitters of multichannel high-density planar lightwave circuits to polyimide-based electro-optical (EO) modulators. 

Moreover, polymer dispersed liquid crystals (PDLC) have been extensively studied as promising candidates new materials for application in the field of thermo- and electro-optical devices, such as optic shutters, smart windows, optical sensors, memories and flexible display devices. 

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