Thermal tuning of a thin-film optical filter based on porous silicon and liquid crystal

Abstract

Spectral characteristics of an 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 a resonance near 1600 nm. Optical transmission spectra of the filter are measured in the temperature range from 27°C to 80°C. For the temperatures less than 62 o C (a clearing point of the liquid crystal), we have observed continuous red shift of resonant wavelength of the microcavity in the range of 11 nm. The thermal dependence of the shift measured by us has sharply increasing slope near the clearing point. The resonant wavelength of the microcavity exhibits a slow linear decrease for the temperatures exceeding 62 o C. We have also studied the spectra of the filter under local heating of the sample by a laser. Our results demonstrate that the laser beam with the power of 100 mW provides total tuning of the microcavity.

Propagation of Electromagnetic Waves in Anisotropic Photonic Structures

“…These include microcavities [11,32], photonic crystals [33], waveguide structures [34], photodetectors [35], sensors [36], etc. Besides, PSi has the potential to be an optically active material in the case when an acceptable electro-or thermooptic media is infiltrated into the pores [32]. Therefore, porous silicon is an excellent candidate for tunable optical interconnects and optical switches.…”

“…The advantage of using PSi microcavities is that the position of the transmittance peak is completely tunable by changing the properties of the central layer (i.e. porosity and thickness) during the electrochemical etching condition and by the infiltration of organic molecules (for example liquid crystals [32]).…”