| In the past decades, azobenzene containing polymers have attracted considerable interest in optical storage owing to their outstanding photoactive characteristics. It is well known that azo molecules undergo trans-cis-trans isomerization cycles under the irradiation at a wavelength lying in the absorption region. If the pump light is linearly polarized, the molecules are oriented perpendicular to the pump polarization direction. This photoinduced orientation results in macroscopic anisotropy, thus the dichroism and birefringence in polymer films. Since azo molecules can be photo-oriented, irradiating with a light field whose polarization is periodically modulated in space can induce the periodical orientation of molecules correspondingly, i.e. polarization holographic recording. The obtained polarization gratings are very useful for highly functionalized optical devices because they can control both the beam propagation direction and polarization state. This thesis gives a detailed description of the photoinduced anisotropy and polarization holography in azo polymer films.First of all, the chemical and optical properties of azo polymers are introduced. Especially the characteristics of nonlinear optics, photo-isomerization and photoinduced anisotropy are emphasized, because they are crucial for optical storage. Furthermore, the optical properties of an azo ionic liquid-crystalline (LQ) polymer are investigated experimentally. The third-order nonlinear refractive index is determined by Z-scan measurements, and the photoinduced anisotropy is studied through dichroism. The large value of nonlinear refractive index and pronounced photoinduced anisotropy indicates that the polymer is an ideal material for optical storage.Secondly, the photoinduced birefringence of three azo polymers is investigated. The influence of pump intensity on birefringence value is studied, and the experimental results are analyzed by theoretical fitting. The results also indicate that the two azo LQ polymers possess larger birefringence value (～10-2) than that of the ordinary azo side-chain polymer (～10-3) in room temperature, and the stored birefringence in LQ polymers is very stable (even exhibits self-enhancement in relaxation). This phenomenon is attributed to the self-organization effect of the LQ molecules. Moreover, it is proved that the photoinduced birefringence has a strong dependence on the temperature, therefore the birefringence value can be controlled effectively by varying the temperature, and the mechanism is discussed.Thirdly, based on the characterization of photoinduced anisotropy, polarization holographic recordings are accomplished in two azo LQ polymers. Pure polarization gratings are recorded by two 532 nm laser beams with both orthogonal linear and circular polarizations. The polarization properties of the gratings are investigated experimentally and theoretically. Especially, the unusual diffraction properties of gratings in azo side-chain LQ polymer reveal that circular birefringence is induced in linear-polarization holographic recording. Furthermore, a method of image storage based on circular-polarization holography is presented, which provides high diffraction efficiency of the reconstructed image and an effective approach to control the image brightness by changing reconstructing polarization.At last, the polarization holography in LQ polymers is extended to two-dimensional (2D) recordings, i.e. polarization gratings overlap at the same place through multiple recordings. The 2D polarization grating in present makes up of two orthogonal 1D polarization gratings, which are written by two orthogonally polarized 532 nm beams (linearly or circularly). The diffraction properties of the 2D gratings are investigated. It is found that the diffraction efficiency of 2D grating is lower than that of 1D grating, and the 2D grating acts as the integration of its componential 1D gratings. Furthermore, the 2D grating is applied in a stokes-meter, which simplifies the system. Test results show that the improved stokes-meter can provide a high accuracy, which also indicates the stable performance of the 2D polarization grating.
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