A quantitative analysis of the performance of an all-fiber electronically tunable wavelength filter using a four-layer model

In this work, an investigation of the tuning characteristics of electrically tunable long-period gratings (LPGs) is presented. A precise four-layer model is used to quantitatively analyze the tuning potential of the gratings and experimental data is provided to support the analysis. The four-layer model includes a silica core layer with an inscribed LPG, a thin silica cladding layer (~40 μm), an ultra-thin (~ 50 nm) high refractive index indium-tin dioxide (ITO) inner electrode layer, and a tunable electro-optic polymer layer. It has been found that the inner electrode layer, made of high refractive index ITO, can be modeled as a high index overlay and causes the forward propagating modes in the thin silica cladding to reorganize as the ambient refractive index changes. This reorganization effect can lead to a significant increase (10 plus fold) in the tuning range of LPG tunable filters. Moreover, the required specifications of the tunable polymer layer are quantitatively analyzed. Finally, the required characteristics of the electro-optic polymer are realized by using a nano-composite of zinc sulfide and ferroelectric relaxor poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer.

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