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Journal of Physical Studies 20(1/2), Article 1401 [9 pages] (2016)
DOI: https://doi.org/10.30970/jps.20.1401 DUAL AND TRIPLE BANDPASS OPTICAL FILTERS BASED ON SYMMETRICAL STRUCTURESO. P. Kushnir
Lviv National Agrarian University, Physics Department, |
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The simplified method of dual and triple bandpass optical filters design has been proposed. Usage of simple mathematical relations for determining the phase thicknesses of two symmetrical layers that provide two or three bandpasses within a rejection band is the main advantage of this method. The proposed method allows to select an arbitrary spectral position of both bandpasees for a dual bandpass filter considering the dispersion of the refractive index. Such a possibility is realised by means of the found dependence of the relative spectral position of both bandpasses on the phase thickness of the central layer. The dependence of the phase thickness of the central layer $\delta _c$ both on the relative position of bandpasses $\lambda _2 /\lambda _1 $ and on the number of layers $k$ and their refractive indices $n_i$ allows to calculate the corresponding magnitude $\delta _c$ for the necessary magnitudes $\lambda _2 /\lambda _1$, $n_i$ and $k$. In most cases such magnitude $\delta _c$ is not multiple of $\pi /2$ (non-standard layer) and consequently the usage of the non-standard central layer in the proposed method allows to select an arbitrary position of both bands $\lambda_1$ and $\lambda_2$ for the dual bandpass interference filter. It also provides a possibility of an arbitrary selection of the filter's materials and bandwidth while maintaining the necessary wavelengths $\lambda_1$ and $\lambda_2$. The use of the proposed approach allows to design triple bandpass filters with an asymmetrical position of all bands.
PACS number(s): 42.79.Wc, 78.20.-e