Simulation and optimization of liquid crystal gratings with alternate twisted nematic and planar aligned regions.

Electro-optical properties of liquid crystal (LC) gratings with alternate twisted nematic (TN) and planar aligned (PA) regions are simulated. Three typical steps are introduced: first, the LC director distributions of the two different regions are simulated. Then, the phase and amplitude of the emergent light in each region are calculated through Jones matrix. Based on this information, the voltage-dependent diffraction efficiency is achieved by Fourier transformation, finally. It gives an exact explanation for the mechanism of this kind of gratings. Experiments with optimized parameters are carried out through photopatterning. The trend of the measured voltage-dependent efficiency fits the simulation result very well. This method can be used to optimize the performance of LC gratings with alternate TN and PA regions, and exhibits great potential in the simulation of corresponding photonics and display applications.

Complex liquid crystal alignments accomplished by Talbot self-imaging.

We introduce Talbot self-imaging into photoalignment technique to record Talbot carpet into an LC cell. Through the design of the setup, different images are presented on a single sample. By taking a simple 1D grating mask as an example, an LC cell with complex alignment structures applicable as Mach-Zehnder interferometer arrays is demonstrated. Further mask design permits feasibility of various structures which are practicable for many applications. This method may facilitate the fabrication of photonic applications such as optical communication, computing and sensing, etc.

Fast response dual-frequency liquid crystal switch with photo-patterned alignments.

A dual-frequency liquid crystal based optical switch with orthogonally photo-patterned alignments is designed and fabricated. The cell gap is theoretically optimized for high switching performance. The measured extinction ratio of first diffraction order is over 20 dB with a low electric field of 3 V/µm. The switch On-Off time are measured to be 350 µs and 600 µs, respectively, both of which have reached submillisecond scale. Moreover, the switch is polarization independent, which has been predicted theoretically and further proved experimentally. This design is suitable in wide applications requiring fast response and polarizer free properties.

A bidirectional tunable optical diode based on periodically poled LiNbO3.

We propose a bidirectional tunable optical diode based on a periodically poled lithium niobate (PPLN) with defect. An acoustic wave propagates together with the light beam so that a collinear photon-phonon interaction happens, which affects the nonlinear optical processes in PPLN. The fundamental wave exhibits an optical diode effect, i.e., the light only may travel toward a single direction while the opposite way is isolated. However, the acoustic wave could be used to adjust the contrast of optical isolation from -1 to 1. A direction-optional operation is thus realized. Moreover, the advantages of our tunable PPLN optical diode are also discussed.