Electrically tunable optical filter for infrared wavelength using liquid crystals in a Fabry–Perot étalon

Abstract

Using the refractive index modulation in liquid crystals by an externally applied electric field, we show that common nematic liquid crystals can be used in a Fabry–Perot étalon to produce an electrically tunable optical filter for use in the infrared region. Using commercial liquid crystals we demonstrate that the wavelength can be tuned over 175 nm using less than 10 V. In our first device the free-spectral range of the étalon is about 75 nm with a passband of about 1–2 nm which is determined by the quality of the mirrors that we have used.