The Band Structure Study Of Photorefractive Photonic Crystal Lattices

Photonic crystal has very wide application foreground in optical comm -unications and integration optics. But its making techniques are very complicated, and bring many difficulty in application. All aptical method is a kind of the simplest, most convenient and most feasible method to induce photonic crystal lattices making use of photorefractive effect in photorefractive material. The photorefractive photonic crystal lattice have more longer dark storage time and reversible holographic data storage. Therefore it has lofty investigation worth and wide application foreground, at the same time also offer a kind of new-style material. Concerning photonic crystal band structure researching of theoretics aspect had went ripeness. Using different methods had calculated band structure of all kinds of photonic crystal. But most of techniques are very complex. At present, photorefractive photonic crystal lattices has already become an investigation hotspot in the field. LiNbO₃ is a self-focusing photorefractive material, fabricating wave-guide arrays and photonic crystal are the same structurally, just the difference of the refractive index are less. Therefore, studying refractive index change law of LiNbO₃ crystal play an important role to researching photorefractive photonic crystal lattices.In the work of this thesis, Have studied making using of pair of light beams to intervene in crystal induce in the photonic crystal lattice,in different iron-doped concentrations of LiNbO₃ crystal,when using red and green light respectively , the relation of the crystal lattices period , iron-doped concentrations, wavelength of the recording light and the refractive index modulation degree.The experiment result indicates:While using the red light (λ= 632.8 nm) induce in photonic crystal lattices, iron-doped concentrations no greater than 0.05 wt %, green light (λ= 532 nm) no greater than 0.03wt %,the refractive index modulation of LiNbO₃ increase up and exists a extremely large value along with changing of the crystal lattices, corresponding the extremely large value alse enhancing with increasing iron-doped concentrations,and moving to the direction of small crystal lattices period,the result is one another consistent with one-centre model theory;If iron-doped concentrations is greater than the worth all above, the theory is not agree with experiment completely, This showes that the space charge field theory of one-centre model only applies to the LiNbO₃ crystal of little iron-doped concentration;The experiment also discovers that refractive index modulation of LiNbO₃: Fe crystal is connected with wavelength of the recording ligh,using the same crystal,inducing in green,refractive index modulation is more than red light, and corresponding extremely large value move bigger than red light to smaller crystal lattices period.At the same time, wo detail introduce Plane-Wave Expansion Method, and calculated band structure of 1D Photorefractive photonic crystal which making use of the double coherent light beam interference induce-in utilizing Plane-Wave Expansion Method, and comparing band structure in different refractive index modulation degree.In experiment,we illuminate the area of inducing photorefractive photonic crystal,which the frequency of the latter is the same as the frequency of light of forming the photonic crystal.when the angle,which is betten incidence and the direction of the period of photorefractive photonic lattice,is bigger than 78 ,we observed the localized phenomenon of photorefractive photonic lattice.Utilizing the property of transmission , which is about optically-propagation in straticulate medium,we calculate the relationship beteen the reflectivity R and the angle of incidence which is big incidence and the direction of the period of photorefractive photonic crystal lattices theoretically when the light is propagating this medium and found the consistent of theorical results and experimental results.