Study On Refractive Index Modulation Of Light Induced Photonic Lattice

The photorefractive photonic lattice, a component that writes refractive index changes into photo- refractive crystal periodically following optics field distribution through the photorefractive effect, has a lot of application in optics . The refractive index modulation is an important technology parameter to photorefractive photonic lattice,and affects its photorefractive function directly. Generally, its applications have been limited for the lower refractive index modulation. Therefore, it is important to make clear what factors are related to the improvement of the performance of the photorefractive photonic lattice.This dissertation is divided into five chapters such as: Introduction. Theoretical calculation and numerical simulation of space-charge field in two-beam coupling.The studying on influence factor of refractive index moudulation .The change of diffraction efficiency with time .conclusions.In chapter 1, the conception of photorefractive effect and its analysis model is introduced,and the photorefractive effect in LiNbO₃: Fe crystal is discussed detailly, and introduce the photorefractive photonic lattice.In chapter 2 ,theoretically, space-charge field was obtained by band transport model in two-beam coupling photovoltaic LiNbO₃ :Fe crystal. The relation between space-charge field and photonic lattice period in LiNbO₃ was simulated with different dose of doped Fe. Considering the simple linear relationship between the refractive index modulation and the space charge field, so the relationship between the refractive index modulation and the photonic lattice period was obtained. we found that there is a maximum value of refractive index modulation related to certain lattice period. The value of refractive index modulation is increased with the dose of donation Fe and the maximum value will drift toward the direction of the low period.In chapter 3,from the measurement of diffraction efficiency with diverse angle, through the relationship between the diffraction efficiency and refractive index modulation ,we indirectly obtained the relationship between refractive index modulation and photonic lattice periods. It indicates that the refractive index modulation has a maximum value with the changing of photonic lattice periods. It demonstrates that different refractive index modulation is corresponding to different photonic lattice periods truly. The maximum of the refractive index modulation will increase with the dose and its value drift toward the direction of the low photonic lattice periods. These results are good agreement with the theoretical calculation. Therefore the refractive index modulation is relevant to the photonic lattice period as well as the dose in experiment and theory.In chapter 4, the two-beam coupling experiment was first carried out. The diffraction efficiency of the LiNbO₃ doped with Fe was recorded and the relationship between the diffraction efficiency and the time was investigated in diverse writing- angle(photonic lattice periods) as the e-light write and o-light write with time. The relationship indicates that the diffraction efficiency is oscillational following time . Moreover , The oscillating phenomenon was analyzed qualitatively .And through analysis we found that this oscillating phenomenon was caused by the spacial second harmonic and the transient stripe mismatch and dynamic energy shifting. The fixing time of photon crystal lattice recorded is obtained from the experiment and theory. It is the time corresponding to the first peak value of diffraction efficiency .In chapter 5,conclusions.