Study On The Construction Of Photorefractive Device And Its Internal Refractive Index

Photorefractive effect is a special phenomenon of photoinduced refractive index change.The incident light excites electrons or holes in shallow traps formed by impurities or defects in certain crystals or organic matter,enters the conduction band,and migrates along the photovoltaic field to a trap outside the illumination region to form a space charge field.The space charge field changes the refractive index of materials by electro-optic effect,which is the photorefractive effect.By changing the form of the incident light field and utilizing the photorefractive effect,a variety of photonic elements can be fabricated in photorefractive materials.Lithium niobate?LiNbO₃?crystal A kind of crystal in photorefractive effect device,it is a kind of multifunctional material which integrates piezoelectric,electro-optic,nonlinear and so on.Good physical and chemical stability and reusable advantages.In this paper,the photonic devices are fabricated by using the photorefractive lithium niobate crystal as the main medium and the laser as the light source,using different experimental methods to irradiate the lithium niobate crystal.Different characteristics were observed and studied.The following tasks were specifically completed:1.The refractive index change of high-density photorefractive photonic lattices was almost impossible to be observed directly.In this paper,the Fourier transform system with Mach Zende optical path plus amplification is used.The refractive index variation of LiNb O₃ crystal in high density photorefractive photonic lattice written in different wavelengths is studied in real time.The direct observation of refractive index change of high density photonic lattice is realized.This method not only can observe the quality of high density photonic lattice but also can be observed and controlled in real time,which provides a new control way for making high quality photonic lattice.2.Band plate is an important optical device and has many applications.We have fabricated a band plate with a photorefractive lithium niobate crystal and studied its properties.Using laser holography to adjust the convergent spherical wave and the divergent spherical wave,the waveband plates were prepared on the iron-doped lithium niobate crystal and on the holographic dry plate,respectively.The similarities and differences between the waveband plates made of different materials are studied and compared.It is found that the waveband plates made from holographic dry plates have multiple focal points when irradiated by parallel light,while those made of lithium niobate crystals have only one focal point when irradiated with parallel light,and the focal length can be controlled by the write light path.This article gives an account of these phenomena.Some related analysis and explanation are given.Using laser holography to fabricate zone plates in photorefractive materials is a simple and convenient method,which opens up a new experimental method for studying the characteristics of waveband plates.3.A study of the effect of second harmonic generation on photonic lattice.The YAG laser is used as the light source to generate two-beam interference to write the lithium niobate crystal into the one-dimensional photonic lattice.The variation of its diffraction efficiency with the writing time is measured.After continuous writing for a period of time,it is found that the writing stripes will split into two,that is,the spatial second harmonic wave will be produced.The condition of second harmonic generation is studied and it is found that it is related to the angle between the two beams written.The angle between two beams can be measured when lithium niobate crystal can produce spatial second harmonic.Then the space 2 of lithium niobate crystal was observed by Mach Zende device.The change of refractive index after subharmonic.It is shown that the written lattice is a double lattice in two.