Thermo-optic switching

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. 

Zhujun Wan, Yarning Wu, Sihua Li (2007) "Experimental research on an integrated thermo optic switch based on multimode interference couplers" Frontiers of Electrical and Electronic Engineering in China, Volume 2, Nxunber 1, March, 2007. 

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. 

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. 

That the critical switch power is inversely proportional to the magnitude of thermo-optic coefficient dn/dT) was confirmed by experiment, and led to the choice of nematic phase liquid crystals as suitable, low absorption, spacer materials. Their high thermo-optic coefficient dn /dT — —2xl0 K at room temperature) produced all optical bistability at critical power levels of 140//W, allowing the demonstration of submilliwatt laser diode operation of these devices. 

Keil, N., Yao, H. H., Zawadzki, C., and Strebel, B., Rearrangeable nonblocking polymer waveguide thermo-optic 4x4 switching matrix with low power consumption at 1.55 pm. Electron. Lett., 31, 403, 1995. 

T.M. Brophy, Design of an Optical Switch in a Polymer Rectangular Waveguide using the Thermo-Optic Effect , Masters Thesis, Drexel University, March 1991. 

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