Synthesis of Rugate Optical Filter
Synthesis of Rugate Optical Filter
A rugate filter exploits dielectric interference produced by a continuous variation of the refractive index. This Demonstration simulates a one-line rugate optical filter. You can select the central wavelength, maximum and minimum refraction indices, and the desired filter reflectance. The program calculates the corresponding reflectance profile and filter geometrical length. A material with these properties could be fabricated from crystalline silicon by anodic etching.
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The propagation properties of an optical medium with a sinusoidally varying refraction index are the principle behind so-called rugate filters. A narrow, one-line rugate filter can be specified with a reflection , usually in the range 0.5–0.99. Light propagation in such a linear medium with position-dependent refraction index is approximated in this Demonstration by subdividing the propagation path into small constant refraction index segments and solved by means of the matrix method [1]. An infinite-length filter is designed with Sossi's Fourier transform method [2,3] and then truncated to a finite length with a Dirichlet window [4]. Bartlett and Bartlett–Hann windows are also included in the program; their purpose is to reduce sidelobe amplitudes. Porous silicon-based rugate filters have been applied, for instance, to the detection of biological substances and chemical vapors [5].
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