Huitian Wang

Incoherent-to-coherent conversion by use of the photorefractive fanning effect

A dynamic incoherent-to-coherent converter using the photorefractive fanning effect is demonstrated in a BaTiO(3):Ce crystal, and high-quality positive replicas of the incoherent image are obtained with a resolution of 32line pairs/mm. In this method the incoherent image-bearing beam modulates the transmission intensity of the coherent beam directly, and no readout beam is required. When the intensity ratio of the incoherent beam to the coherent beam is smaller than 5, the transmission intensity of the coherent beam increases almost linearly with increased intensity of the incoherent beam.

Mutually pumped phase conjugator with a rainbow configuration in BaTiO 3 :Ce crystal using nanosecond pulses

A new type of mutually pumped phase conjugator with a rainbow configuration has been demonstrated experimentally in cerium-doped barium titanate crystal that uses pulsed beams with a pulse width of 3.0 ns and a repetition rate of 40 Hz at a wavelength of 532 nm. The highest phase-conjugate reflectivity was ~24%. The dependence of the phase-conjugate reflectivity on the incident angle and distance, as well as the grating formation time for achieving 1 - e(-1) of equilibrium reflectivity, has been measured.

ONE-WAY IMAGE TRANSMISSION THROUGH A THICK DYNAMIC DISTORTER WITHOUT A REFERENCE BEAM

We demonstrated a method to perform one-way image transmission through a dynamic distorter without a reference beam. In this method, a photorefractive four-wave mixing configuration was used to pick up the reconstructed image from the image-bearing signal beam, which acted as an erase beam. The fluctuation period of the dynamic distorter must be much shorter than the response time of the nonlinear material. Reconstructed images with high-fidelity have been obtained. Because use of a reference beam is unnecessary this method is simpler and more effective.

Image transmission through a thick dynamic distorter by the photorefractive fanning effect.

A new method of one-way image transmission through a thick dynamic distorter without the need for a reference beam or four-wave mixing is demonstrated. In this method there are only one object beam and one sampling beam. The response time of the photorefractive crystal must be much longer than the fluctuation period of the dynamic distorter. Thus the crystal responds only to the time-averaged intensity pattern of a rapidly varying object beam. The images, reconstructed with high fidelity, are picked up through the photorefractive fanning effect.

Theory and properties of quasiwaveguide modes

A theory is developed to explain the origin of physical phenomena in quasiwaveguide, based on the forward scattering and multiple‐wave interference effects. The properties of quasiwaveguide modes, such as positions, linewidths, the reflectivity of the reflected light spot, and the reflectivity distribution of scattered light are described. The shape of the m‐lines is derived theoretically. Applications of the theory are also discussed.

High-resolution photorefractive incoherent-to-coherent optical converter

Abstract We demonstrate a novel photorefractive incoherent-to-coherent optical converter in which there is a ∼45° angle between the propagation direction of the incoherent image and the grating vector. Thus the number of the grating periods in one pixel is large even for a very high resolution. When the output image has the same direction with the incoherent incident beam, the resolution does not depend on the interaction length between the incoherent beam and the grating. A resolution as high as 283 line pairs/mm, which is the resolution of out projection system, is obtained for a one-dimensional resolution target. Two-dimensional incoherent-to-coherent conversion is also demonstrated.

Incoherent-to-Coherent Conversion and Image Reconstruction for a White-Light Image.

We present a technique of photorefractiveffects for white-light incoherent-to-coherent conversion and oneway image transmission through a thick turbulent medium. A high resolution photorefractive incoherent-tocoherent optical converter was realized even for white light transmission by applying the same technique as we used in incoherent laser beam transmission. Analogical reconstructed laser images with high-fidelity were obtained, correcting the image blurring due to the thick turbulent medium.

High-resolution incoherent-to-coherent conversion by use of the photorefractive fanning effect

We demonstrate that high-resolution incoherent-to-coherent conversion can be carried out in an incoherent-to-coherent converter based on the photorefractive fanning effect. The output coherent image has the same direction as the incident coherent beam, and thus the resolution is not limited by the grating diffraction. We obtained a resolution as high as 90.5 line pairs/mm in this experiment. The transmittance of the coherent beam relative to the intensity of the incoherent beam was measured. We also theoretically estimated the resolving power with respect to the interaction length. The numerical results agree well with the experiments.

Image transmission through a thick dynamic distorter without a reference beam

We demonstrate one-way optical field imaging through a thick dynamic distorter using the photorefractive fanning effect without a reference beam and a four-wave mixing process. In this method, there are only one object beam and one sampling beam. The response time of the photorefractive crystal must be much longer than the fluctuation period of the dynamic distorter. Thus the crystal only responds the time-averaged intensity pattern of the rapidly varying object beam. The reconstructed images with high-fidelity are picked up.

Numerical analysis of diffraction of image-bearing beam from a fixed index grating in photorefractive media

We analyzed numerically the diffraction of the image-bearing beam from a fixed index grating in a photorefractive medium on the steady state, using a 2D model that takes into account the newly photoinduced index grating by the incident and the diffracted Fourier plane waves. In this analysis, we ignore all the absorption and assume the transverse dimensions of the medium and all the gratings to be infinite. The results point out that the intensity patterns of the diffracted image-bearing depend strongly on the following factors: (i) the feature spatial size of the incident image; (ii) the coupling coefficient and the wave number of the fixed index grating; and (iii) the thickness of the crystal and the gratings. On the other hand, they do not nearly depend on the photorefractive coupling coefficient for all the exiting photorefractive media. The effects of the spatial displacement of the diffracted images is also predicted.