The Recording Method And Applications Of Photorefractive Multiple Volume Gratings

Photorefractive gratings are promising to be applied to wavelength division multiplexing (WDM) systems and electro-optic integration due to the advantages of small size, simple structure, easy erasing, high diffraction efficiency, low temperature sensitivity, narrow band filtering and so on. Iron-doped photorefractive lithium-niobate crystals (LiNbO3:Fe) have good electro-optic, acoustic-optic, nonlinear characterizations, and hardly light absorption and photorefractive sensitivity in the wavelength around 1550nm, which makes them attractive for using as passive optical components in telecommunication networks. In this paper we present the theory of the formation of photorefractive gratings and its filtering mechanism, and discuss the recording method in LiNbO3:Fe crystal and its application in demultiplexing system. The main contents are following:(1) The formation mechanism, diffraction efficiencies and wavelength sensitivity of the photorefractive volume grating in photorefractive crystals are theoretically analyzed. The angular multiplexing technology for photorefractive grating and exposure technology in the formation of photorefractive multiple volume gratings are further discussed, by which eight photorefractive volume gratings in a LiNbO3:Fe crystal sample with size of 10x10x 10mm3 have been successfully recorded. In the end, the properties of volume holograms and the filtering principles of multiple photorefractive volume gratings are discussed by using volume holograms theory and Bragg condition.(2) The optimal condition for recording single hologram in LiNbO3:Fe crystal is experimentally discussed. At the different recording angles, the Raman-Nath diffraction and Bragg diffraction phenomenon are observed, respectively. Then, the wavelength selectivity and the relationship of diffraction efficiency and polarization state are discussed when the recording angle of 60?formed by two writing beam.(3) The Bragg-shift phenomenon of transmission holographic grating is investigated in theory and experiment. As a result, the Bragg-shift phenomenon will be restrained when the intensity ratio of initial writing beams is one.(4) By using the excellent angle and wavelength selectivity of the photorefractive volume gratings, the wavelength of LD are measured exactly in experiment. The feasibility of the multiple photorefractive volume applying to WDM system is demonstrated by analyzing the diffractive properties of the eight holographic gratings superimposed in the LiNbO3:Fe crystal. In the end we have superimposed two photorefractive volume gratings in a LiNbO3:Fe sample with size of 10x 10x 10mm3 to make double wavelength filter, by which the beam with two wavelengths of 632.8nm and 635nm or 635nm and 650nm at the same angle of incidence are successfully separated in space.