| 摘要 |
The liquid crystal cell (1) comprises a diffraction grating (10) formed on one face (7) of a liquid crystal layer (2) in the form of parallel strips (11,12) separated by intervals (13,14) containing the liquid crystal in a chamber whose opposite faces (7,8) are defined by two substrates (3,4) equipped with transparent electrodes (5,6). The liquid crystal is birefringent, that is presents the ordinary and the extraordinary indices of refraction according to the direction of axis. <??>The strips (11,12) are made of a transparent isotropic material having a refraction index substantially equal to one of the refraction indices of the liquid crystal. The material of the strips (11,12) is a polymer, in particular a photopolymer, and the strips are formed by etching a layer of photopolymer. The cell is switchable between two states, excited and non-excited. The excited state is obtained by applying an electric voltage to the electrodes (5,6) sufficient to orientate the liquid crystal axis parallel to the beam of light (21) when the liquid crystal presents the extraordinary index of refraction. In the non-excited state the liquid crystal axis is aligned with the strips (11,12) and the liquid crystal presents the ordinary index of refraction which is substantially equal to the refraction index of the material of the strips. The cell can be used for optical beam splitting by selectively applying a voltage to the electrodes of the cell. In the second embodiment, the liquid crystal cell comprises a second diffraction grating different from the first and formed on the other face (8) of the liquid crystal layer in the form of parallel strips separated by liquid crystal intervals. The strips are made of a transparent optically isotropic material having an index of refraction substantially equal to the other of two indices of refraction, that is the extraordinary index. The geometry of the second grating is different from that of the first grating. The liquid crystal is of nematic type, and the electrodes (5,6) are extended over the total surface of the useful region of the cell. |
