Holographic Recording In LiNbO3 Research Articles

Oscillation of nonvolatile holographic recording in LiNbO3:Fe:Cu crystals

The oscillation of diffraction efficiency is observed in the nonvolatile holographic recording of lithium niobate crystals doped with iron and copper. The physics of oscillation in doubly doped lithium niobate crystals is studied by using Runge–Kutta methods, and the oscillation can be attributed to the redistribution of electrons in the deeper and shallower traps of the crystals in the initial phase of holographic recording. The effects of Fe concentration and intensity ratio of red beams to UV beam (IR/IUV) on the oscillation are investigated theoretically. The results show that with lower Fe concentration, the amplitude of oscillation is larger and with lower intensity ratio IR/IUV, the duration of the oscillation is longer.

Holographic recording in LiNbO3 using various polarized lights

Holographic recordings in a LiNbO3 crystal using ordinary and extraordinary light in transmission-type geometry were performed. The system parameters of storage capacity (M/#), sensitivity, and signal-to-noise ratio were measured. Although extraordinary light will induce stronger fanning light (nonlinear enhanced scattered light) in LiNbO3, our experimental results indicate that the system using extraordinary light is superior to that using ordinary light. Our demonstrations and results can help to optimize the holographic recording in some applications of volume holographic optical element (VHOE), such as wavelength division multiplexing (WDM) filters in optical communication.

LiNbO3:Ce:Cu晶体中绿光非挥发全息记录优化

LiNbO₃:Ce:Cu晶体中绿光非挥发全息记录优化

Magnetophotorefractive effect of holographic recording in LiNbO3:Fe crystals

An experimental investigation of the magnetophotorefractive effect for different holographic recording configurations is presented. Our results show that the diffraction efficiency of holographic grating strongly depends on the applied magnetic field for each configuration, since the magnetophotorefractive effect induces a change of the electric current. The diffraction efficiencies of the refractive-index gratings decrease markedly for all configurations we investigated. The reason for our results is discussed.

Improvement in refractive-index change in LiNbO 3 :Ce:Cu by applying an external electric field

By jointly solving two-centre material equations with a nonzero external electric field and coupled-wave equations, we have numerically studied the dependence of the non-volatile holographic recording in LiNbO3:Ce:Cu crystals on the external electric field. The dominative photovoltaic effect of the non-volatile holographic recording in doubly doped LiNbO3 crystals is directly verified. And an external electric field that is applied in the positive direction along the c-axis (or a large one in the negative direction of the c-axis) in the recording phase and another one that is applied in the negative direction of the c-axis in the fixing phase are both proved to benefit strong photorefractive performances. Experimental verifications are given with a small electric field applied externally.

Effect of dopant composition ratio on nonvolatile holographic recording in LiNbO3:Cu:Ce crystals.

The effect of dopant composition ratio on nonvolatile holographic recording in LiNbO3:Cu:Ce crystals is investigated experimentally. The results show that the dopant composition ratio affects the recording sensitivity and fixed diffraction efficiency by altering the UV light absorption characteristics of the crystals during nonvolatile, holographic recording. Increasing the dopant composition ratio of Cu and Ce leads to an increase in the absorption of UV light and further to an increase in the recording sensitivity and fixed diffraction efficiency. The UV light absorption characteristics of LiNbO3:Cu:Ce crystals and their roles in nonvolatile holographic recording are theoretically analyzed. The theoretical results are consistent with those of the experiments.

Recording and fixing dynamics of nonvolatile photorefractive holograms in LiNbO_3 :Fe:Mn crystals

A theoretical explanation of nonvolatile holographic recording in LiNbO3:Fe:Mn crystals is given based on jointly solving the two-center material equations and the coupled-wave equations. The nonuniformity of the dynamics of the photorefractive grating can be effectively described and analyzed by using this method. The time–space evolution, including the space-charge field, the diffraction efficiency, the light modulation depth, the phases of the space-charge field and the interference field, as well as the relative spatial phase shift between them, is studied for both oxidized and reduced crystals. The optimal conditions for material prescriptions and oxidation–reduction processing are discussed in detail. The bending isophase of the fringe pattern and the redistributed intensities of the two-coupled beams inside the crystal are presented. The theoretical results can confirm and predict experimental results. Some new effects are also discovered, such as: The fixed diffraction efficiency can exceed the saturation diffraction efficiency for strongly recorded gratings; the energy transfer direction between two-coupled beams can be reversed with crystal thickness; and the holographic readout in reduced crystal is always accompanied by fast phase changes, which results in the slow deterioration of the recorded holograms as a result of the production of homogeneous distributions of electrons.

The role of carrier mobility in holographic recording in LiNbO3

We investigate the role of carrier mobility in holographic recording in LiNbO3 crystals. Both normal holographic recording (single wavelength, single trap) and two-center recording are considered, and the differences between the performances of the two methods are explained. We show that increasing mobility by using stoichiometric crystals or by doping with Mg does not improve sensitivity considerably, but does reduce M/# by at least one order of magnitude.

Pixel size limit in holographic memories

The bandwidth of holographic recording in LiNbO(3) (Fe doped) in the 90 degrees geometry is studied theoretically and experimentally. The wide holographic bandwidth of LiNbO(3) makes it possible to record submicrometer pixels and reconstruct them by phase conjugation in a holographic memory system. This approach reduces the system cost and increases the system storage density. We demonstrate the recording and the phase-conjugate reconstruction of various pixel sizes down to 1 mumx1 mum . The signal-noise ratio and the bit-error rate are examined.

Hologram recording in Zn-doped LiNbO_3 crystals

Holographic recording in LiNbO3 doped with 2–5% ZnO is reported. High photoconductivities of these crystals result in high-speed recording. Holograms are formed by a combined mechanism including photovoltaic and diffusion fields simultaneously. The contribution from the photovoltaic mechanism increases with light intensity because of strong intensity dependence of the photovoltaic field. The observed values of the photovoltaic fields are higher than those calculated from the available data on photoconductivity and absorption coefficient. The enhanced values of the photovoltaic field are obviously related to the intensity dependence of the optical absorption coefficient that results from a multilevel charge-transport scheme in LiNbO3:Zn crystals.

Infrared holographic recording in LiNbO3:Cu

Holograms may be recorded in photorefractive LiNbO3:Cu with pulsed infrared light (wavelength λ=1064 nm, Q-switched Nd:YAG laser), if the crystals are previously or simultaneously illuminated with a green (λ=532 nm) light pulse. We study refractive index changes and time constants of as-grown and thermally treated crystals with different copper concentrations. A model explaining this effect is discussed.

Dynamic holographic interconnects using static holograms

In this paper, a dynamic information routing architecture, which uses fixed volume holograms accessed by a ferroelectric liquid crystal spatial light modulator (SLM), is presented. The interconnects are therefore reconfigurable at the SLM frame rate. The design of two routing networks is presented, and experimental results are given for each network. Since multiple-exposure holographic recording is necessary to implement these networks, results demonstrating maximum diffraction efficiency holographic recording in LiNbO3 are presented.