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Two-color all-optical switching is demonstrated in azo dye doped nematic liquid crystals by means of the spatial cross-phase modulation (SXPM) method. A 633 nm light with the power below the diffraction excitation threshold diffracts into concentric rings under the irradiation of a 532 nm light. The ring number and size of the diffraction pattern of the 633 nm light increases with the power of the 532 nm light rising. Taking advantages of the unique physical and optical properties of the liquid crystals, the circular symmetry of the diffraction pattern of the 633 nm is well preserved. It indicates that the irregular and unpredictable distortion of the diffraction pattern caused by the light induced thermal convection could be eliminated, providing potential applications prospect in designing advanced optical devices for all-optical information conversion. In addition, it is found that the SXPM phenomenon between the two lights only happens when the two beams are merged together. Even a small intersection angle between the two lights could change the obtained pattern of the 633 nm light completely.

A new optical system for an augmented reality (AR) display is proposed in this paper. The optical system mainly includes a ray deflector, coupling input grating, optical waveguide, and coupling output grating. Both the ray deflector and the coupling input grating are designed based on the diffraction characteristics of the polarization grating, and the coupling output grating is the Bragg reflection grating. Compared with other AR schemes, this AR optical system not only reduces the number of projections from two to one, but also improves the efficiency of light coupling into the optical waveguides. The energy loss is reduced by utilizing the single-order diffraction characteristics of the polarization grating in its coupling input structure. The light deflector uses the polarization selectivity of the polarization grating and the characteristics of the rotating light of the twisted nematic liquid crystal layer to realize beam deflection. The working principle of the optical system is experimentally and theoretically demonstrated.

Methods Material preparation. The sample is a kind of supermolecular materials synthesized through the ionic self-assembly of poly ionic liquid and azobenzene dyes. The preparation process has been reported in ref. 47. For the preparation of ionic self-assembly complex, 2 mg/ml poly ionic liquid aqueous solution is added to methyl orange aqueous solution at the molar charge ratio of 1:1. The precipitated complex is filtrated and washed several times with doubly distilled water, then dried in vacuum at 60 °C for 12 h. The complex powder melts at 180 °C and the Schlieren textures appear during cooling.

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