Fabry-Perot etalon devices

Fabry-Perot etalon devices based on materials sensitive to electric fields have been studied as tuneable optical filters. Gan et al. [165] presented in their work a hybrid organic/inorganic sol-gel material based on 3-methacryloxypropyl trimethoxysilane as precursor and TCBD (15% mol) as NLO chromophore that was covalently incorporated into the silica network. They demonstrated an optical filter having large tunability and high finesse. The EO sol-gel film was corona poled with 5 kV/cm at 170°C for 30 min. 

Tunable filters in the form of AOTF devices, liquid crystal tunable filter (LCTF) and also tunable cavity Fabry-Perot etalon (FPE) devices have been considered in non-moving part instrument designs for many years. Today, the AOTF and the LCTF devices are used in the NIR spectral region.9,10 Originally, designs were also proposed for mid-IR AOTF devices, but these have not become available, mainly because of fabrication issues (cost and material purity). Tunable FPE devices, which are really just variable cavity interference filters, have been developed for the telecommunications industry. While these have been primarily used in the NIR, in most cases they can be fabricated to work also in the mid-IR, the latter being only an issue of material/substrate selection. 

Another important device based on interference is the Fabry-Perot etalon. The device consists of a plate made of a transparent material with highly parallel faces coated with a nonabsorbing, highly reflective material. Alternatively, a spacer of the chosen thickness made of invar or quartz with highly parallel faces is sandwiched between two mirrors to form the etalon. The bandwidth... 

The simplest implementation of an interferometric device is that of the so-called Fabry-Perot (FP) etalon. It consists of two plane-parallel, highly reflecting optical surfaces separated by some distance d, to form a wavelength-selective resonator, akin to that in lasers (see Chapter 3). The reflecting surfaces are formed by multilayer dielectric films on the surface of glass plates. 

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