The Research On Volume Holographic Storage Of Ce Fe Doped Lithium Niobate Crystal

With the increasing demands of big data storage in the information society,holographic optical storage technology has become an important direction for the future development of storage technology due to its large storage capacity and fast writing speed.It have the advantages of simple growth process,easy adjustment,high diffraction efficiency,and excellent holographic storage performance.Doped lithium niobate crystals are doped with appropriate amount of photorefractive ions or anti-refractive ions in pure lithium niobate crystals,and the properties of doped lithium niobate crystals will be greatly improved in some aspects.Based on the study of photorefractive theory and volume holographic theory,the storage characteristics of a Ce:Fe:Li NbO₃ crystal doped with Ce Fe 0.55%:0.55%are studied in this paper.1)Through the light induced scattering experiment of Ce:Fe:Li NbO₃ crystal,it is found that the scattering light fan with symmetrical distribution is observed in the back of the crystal by using 532 nm green light to illuminate the crystal vertically with e light,and the area of the light fan will increase with the increase of irradiation time.The scattering rate also increases.When the irradiation time is 1040s,the scattering rate reaches 49%.The results show that the photoinduced light scattering of Ce:Fe:Li NbO₃ crystal is more serious than that of pure LiNbO₃crystal because of its doping two photorefractive factors,which has a negative effect on holographic storage.2)Through the experimental study of the crystal response time and diffraction efficiency,it is found that the response time of the doped crystal is in the range of 22s to 29s.Under the same experimental conditions,the response time of pure LiNbO₃ crystal is about 1060s.Compared with other research results,it can be concluded that the response time of Ce:Fe:Li NbO₃ crystal is shorter,which will facilitate the fast storage and reading of information.At the same time,the diffraction efficiency of ce:Fe:LiNbO₃ crystal varies with the change of the angle between the two incident light.The maximum diffraction efficiency is obtained when the incident angle of ce:Fe:LiNbO₃ crystal is about 20°,andη_max=7.06%。Compared with the maximum diffraction efficiency of pure lithium niobate crystal 11.6%,the diffraction efficiency of ce:Fe:LiNbO₃crystal is slightly weaker.3)The holographic storage experiments were carried out with the wavelength sources of473nm、532nm and 671nm,respectively.The results show that both doped lithium niobate crystals and pure lithium niobate crystals are more sensitive to the green light with wavelength of 532 nm.The two crystals are more suitable for volume holographic storage using 532nm laser as the light source.4)The experimental study of image information storage based on Ce:Fe:Li NbO₃ crystal shows that when the distance between the focal point of the incident spot and the front plane of the crystal is changed,the image quality of the reconstructed image changes from the difference to the better and worse as the spot converges from the front of the crystal to the inner of the crystal.And the position of the spot convergent point is 1.0mm behind the front surface of the crystal（1.0mm inside the crystal）,and the image quality is the best.Keeping the position of the spot convergent point at 1.0mm behind the front surface of the crystal,changing the size of the incident spot,the diameter of the reference spot is less than,equal to,Larger than the diameter of the signal spot,it is found that when the diameter of the two incident light spots is equal,the image quality is the best and the diffraction efficiency is the highest.It is found that the diffraction efficiency of the crystal is the highest when the signal intensity is close to the reference light intensity and the modulation system approaches 1.The above study shows that the change of the incident light parameters will have a great influence on the holographic storage reconstruction.5)By using the optimal condition of holographic storage of Ce:Fe:Li NbO₃ crystal obtained from 1)⁴),the fast storage and reading experiments of the crystal are carried out.The results show that the writing time of 0.2s can read out the clearer reconstructed image,and the quality of the reconstructed image is the best when the writing time is 6s⁸s.When the writing time exceeds 10s,the distortion of the reconstructed image becomes more and more serious.Therefore,the doped crystal can read the reconstructed image with high fidelity after hundreds of millisecond time storage,and the fast storage and reading performance is better.