Tunable optical filter based on nanocomposite (liquid crystal)/(porous silicon)

Spectral characteristics of the interference optical filter based on a free-standing mesoporous silicon film containing nematic liquid crystal E7 are studied experimentally. The porous structure represents two distributed Bragg reflectors divided by a quarter-wave microcavity having resonance near 1600 nm. Transmission spectra of the filter are measured in the temperature range from 27°C to 80°C. For the temperatures less than 62°C (clearing point of the liquid crystal), we have observed continuous red shift of the microcavity resonant wavelength in the range of 11 nm. Measured thermal dependence of the shift has sharply increasing slope near the clearing point. For temperatures exceeding 62°C the microcavity resonant wavelength exhibits slow linear decrease. We have also investigated spectra of the filter using local heating of the sample with laser. Our studies have shown, that laser beam with power of 100 mW provides total tuning of the microcavity. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).