Diffractive optical elements (DOEs), with attractive features such as excellent performance and compact configuration, are now becoming increasingly important to a wide range of optical system applications. In this paper, we have used the patterned photoalignment method to produce switchable gratings. It is found that these gratings combine good optical quality with very fast dynamical response at very low driving voltage. A sub-millisecond steering with active FLC as a polarization selector and passive polarization grating (PG) as a diffractive element. A systematic analysis is conducted from the device fabrication to the element working mechanism with their potential problems and corresponding solutions included. The polymerizable liquid crystal PG shows compact size, light weight, robustness, and low cost. Switching time of 82μs is realized by binary switching between two circular polarizations before incident on PG utilizing FLC driven by two electrical polarities. Overall efficiency of 95.7% is achieved with steering angle of 17.66° by 1064nm laser.
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.