Investigations Of Light-induced Photorefractive Spatial Channel Waveguides

Photorefractive waveguide is one of the basic units of integrated optical and optoelectronic integrated circuit (OEIC). It allows a wide variety of applications in optical communication, optical interconnections and optical information processing. There are many methods to fabricate photo refractive waveguides. Among them, light irradiation method is flexible and simple. In this paper, various model of photorefractive waveguides are fabricated in LiNbO3:.Fe crystals and different dopant SBN crystals by using light irradiation method. And some relevant property parameters of waveguides are measured.Based on the band transport model, the buildup of space charge field and the light-induced refractive index changes in photorefractive crystals are discussed. Then, according to waveguide theory, planar waveguide is analyzed. The main parameters, such as spread constant, decay coefficient, cut-off wavelength and so on, are deduced from dispersion formula of planar waveguide. The distributions of electromagnetic wave in the planar waveguide are obtained also. On the basis of these theories, detailed experiment investigations are carried out as follows: (1) The interference pattern of two-prism is adopted to illuminate LiNbO3:Fe crystals. Then array of planar waveguides are fabricated in the crystals due to photorefractive effect. The transversal distribution of refractive index and the period of the array waveguides are measured. And the guiding tests of the waveguides are performed. (2) Two methods are used to write array channel waveguides in LiNbO3:Fe crystal. One require to illuminate the crystal twice using a two-prism interference pattern at different directions, another only require to illuminate the crystal once using the interference pattern which produced by a couple of perpendicular two-prism. The experiment results show that the two methods are feasible to write array channel waveguides in LiNbO3:Fe crystal. (3) Illuminating SBN crystal using a sleet light, and applying an electric field along c axis of the crystal simultaneously. The relationship between the index changes and applied field is studied. The results indicate that the sign and the strength of the index changes are controllable by changing the polarity and the amplitude of the applied filed. Only appropriate field is applied, can planar waveguide be fabricated in SBN crystal. (4) Illuminating doped SBN crystals using a two-prisrn interference pattern, and applying an appropriate electric field along c axis of the crystals at the same time, array planar waveguides can be made in the crystals. The transversal distributions of refractive index are measured in real time and the guiding tests are carried out. The experiment results demonstrate that SBN crystal has high photorefractive sensitivity and rapid response. So the array waveguides written into the doped SBN crystals have important applications in spatial optical dynamic interconnections and light-light modulations.