Baolai Liang

Four-wave mixing and edge-enhanced optical correlation in a Ce:KNSBN crystal

In the case of degenerate four-wave mixing in a cerium-doped potassium sodium strontium barium niobate (Ce:KNSBN) crystal, it is found that the transmission grating is dominant when the incident beams are extraordinarily polarized, the crystal response is more rapid, and the conjugate beam is more intense. Furthermore, the variation of the conjugate beam intensity forms a loop as the fringe modulation of the transmission grating varies. Based on this observation, we have implemented edge enhancement of an image and edge-enhanced optical correlation via four-wave mixing in a Ce:KNSBN crystal without the requirement of reversal of the signal-pump-beam intensity ratio.

Real-time edge-enhanced optical correlation via four-wave mixing in a cerium-doped potassium sodium strontium barium niobate crystal

Degenerate four-wave mixing in a cerium doped potassium sodium strontium barium niobate photorefractive crystal is studied. The transmission grating is dominated in our experimental geometry that the bisector of the pump beam and the signal beam is normal to the c-axis of the crystal. As the fringe modulation depth of this transmission grating varies, the variation of the conjugated beam intensity forms a loop. Based on this nonlinear property, real-time optical image edge-enhancement processing as well as real-time edge- enhanced optical correlation is obtained without the reverse of the signal-to-pump beam intensity ratio. The full-width- at-half-maximum intensity of the auto-correlation peak is one fifth of that without the edge-enhancement operation. The computer simulation results are given, which are coincident with the experimental data very well.

Property of the photorefractive volume grating written by orthogonally polarized beams in Ce:KNSBN crystal

Two-wave coupling between orthogonally polarized beams in a Cerium doped potassium sodium strontium barium niobate crystal is studied. The coupling gain coefficient, the response time and the saturation diffraction efficiency of the volume grating are measured with respect to the angle (phi) between the polarized direction of the pump beam and the c-axis of the crystal. It is found that they have the similar variation behavior. In our experimental condition, the maximum coupling gain coefficient is 3.2 cm-1, the maximum response time is about 55 seconds and the maximum saturation diffraction efficiency is about 18.5%. The maximum values are obtained at (phi) =20 degree(s) and (phi) =160 degree(s). Numerical calculated results from the couple-wave equations are given, which are coincident with the experimental data.

Reflection properties of four-wave mixing with Bi12SiO20 crystal at small incident beam ratio

The nonlinearity of phase-conjugate beam reflection with four-wave mixing in BSO crystal by the moving grating at large fringe modulation formed by the incident-beams ratio is investigated. The experimental results have shown that the optimum fringe velocity is the incident-beam ratio and the total-light-intensity dependent, the reflectivity at the optimum fringe velocity is the incident-beam ratio and the fringe-spacing dependent. Based on these nonlinear properties, the edge-enhancement of an object is achieved.

Diffraction property of photorefractive volume grating in Ce: KNSBN for ordinarily polarized reading beam

The diffraction efficiency of volume grating written by two wave mixing in Ce:KNSBN photorefractive crystal versus the writing beam ratio for ordinarily polarized reading beam is experimentally studied. The result is different from that for the extraordinarily polarized reading beam. Then the modified coupled-wave theory is used to fit the experimental data. The theoretical results are coincident with the experimental data quite well. This research gives a significant support to the applications of Ce:KNSBN crystal in holographic recording and optical information processing.

Edge-enhanced correlation with four-wave mixing in bismuth silicon oxide crystal by use of moving gratings

The nonlinearity of phase-conjugate beam reflection with four-wave mixing in bismuth silicon oxide crystal by use of moving gratings at large fringe modulation formed by the incident-beam ratio is investigated. On the basis of this investigation, the edge enhancement of an object and the edge-enhanced optical correlation with improved discrimination capability are achieved by use of moving gratings at an appropriate fringe velocity. Experimental results are presented.

Loop behavior of diffraction efficiency in Ce:KNSBN crystal

The diffraction behavior is the most important matter characterizing the performance ofa photorefractive crystal in applications and has attracted much attention recently. In this research, we study the relation between the diffraction efficiency of the volume gratings written in Ce:KNSBN and the fringe modulation.

Effect of the reading beam on the diffraction efficiency of volume grating in Ce:KNSBN

The polarization and the incident direction of the readout beam strongly affect the diffraction efficiency of a volume grating in a Ce:KNSBN photorefractive crystal. The modified coupled-wave theory fitting results are coincident with the experimental data.

Rotation-invariant phase-shifting joint transform correlator

The performance merits of the phase-shifting joint transform correlator (PSJTC) is evaluated. The PSJTC is combined with the circular harmonic expansion to achieve a dramatic rotation-invariant correlation with high light efficiency and high discrimination capability.

Diffraction property of volume grating in Ce:KNSBN with differently polarized reading beam

The diffraction efficiency of volume grating written by two- wave mixing in Ce:KNSBN photorefractive crystal as a function of the writing beam ratio for different polarized reading beam is experimentally studied. It is found that, the polarization and the incident direction of the reading beam strongly affect the diffraction efficiency. In the selected direction, the extraordinarily polarized reading beam obtains enhanced diffraction and achieves nearly fifteen times larger diffraction efficiency than the ordinarily polarized reading beam. The modified coupled-wave theory is used to fit the experimental data and the fitting result are coincident with the experimental result. We also theoretically examined the realization between the diffraction efficiency and the amplitude coupling constant k of the reading beam and its diffracted beam. As k < 6cm-1, the diffraction efficiency has single maximum and the maximum diffraction efficiency increases as k increases. As k > 6cm-1, the diffraction efficiency curves exhibit two peaks. But the central position of the curves does not change with the variation of k.