Narrow bandwidth liquid crystal tunable filter based on Lyot-Solc composite structure

We propose here a design of Lyot-Solc composite structure for liquid crystal tunable filter (LCTF) using nematic liquid crystal, which is with high efficiency, narrow bandwidth and electrical tunability. LCTF with high efficiency has many important applications in the fields of optical communication, spectral imaging, and displays. However, most LCTFs adopt cascaded Lyot-type or Solc-type structure, in which multiple pieces of polarizing optical elements exist, causing intensive loss of light intensity. The Lyot-type filter has narrower full width at half maximum (FWHM), but the transmittance is lower. The Solc-type filter has high transmittance and larger free spectral range (FSR) but broader FWHM. We propose a new structure of LCTF composed of Solc-type and Lyot-type structure. The composite 3-levelSolc and 2-level-Lyot LCTF transmission spectrum is a combination of the advantages of the two structures. Through the reasonable structural design, the spectral transmittance is improved, and the secondary transmission peak in the visible spectrum is effectively minimized. At the same time, the output central wavelength can be electrically tunable in the range from 400nm to 650nm by loading different amplitude of driving signals. When the driving signals with amplitude of 1.61V, 1.45V and 1.25V are respectively loaded on the liquid crystal cells of the LCTF, the central wavelengths of the output spectrum are respectively 433nm, 510nm and 595nm, corresponding to the FWHM of 13nm, 16nm and 22nm.