Ru-Lian Fu

Hybrid diffractive-refractive ultra-wide-angle eyepieces

Summary Two kinds of hybrid diffractive-refractive ultra-wide-angle (70°) eyepieces are designed which are with considerably reduced apparent size and weight and with comparable or improved aberrations as compared with the conventional refractive countertype. The designing strategy including the consideration and the steps of the optimization, the most important specification of the diffractive efficiency, and the manufacture issues is presented. The structures and the performance merits of the designed systems are given in a comparison of the traditional Scidmore eyepiece. The designed eyepieces have potential applications in various kinds of modern head-mounted displays.

Computer-generated amplitude-compensated matched filter

A computer-generated binary amplitude-compensated matched filter is proposed. The filter has only a few discrete gray levels. As compared with the filters made by the optical method, the perfor- mance of filters made by computer-generated holography appears no worse, and fewer discrete gray levels are obtained; it is compatible with an e-beam lithography or an amplitude-modulated spatial light modula- tor. The excellent performance in discrimination and in Horner efficiency of the amplitude-compensated matched filter is preserved. The circular harmonic version of the amplitude-compensated matched filter is also investigated.

Design of refractive/diffractive objective for head-mounted night vision goggle

Summary A refractive/diffractive objective for head-mounted night vision goggle was designed. This objective consists of six elements, including one binary surface and two hyperboloids. It has a 40° field of view, a 1.25 f-number, and a 18 mm image diameter, with a compact structure and a light weight. All optical specifications reach proposed designing targets. Besides, we considered fabrication issues about special surfaces of the system.

Rotation-invariant phase-shifting joint transform correlator by use of circular harmonic expansion

The performance merits of the phase-shifting joint transform correlator (PSJTC) are evaluated based on the criteria of light efficiency and discrimination capability. The PSJTC is shown to possess much higher light efficiency (three orders of magnitude) and much better discrimination capability (three times with the selected images) than does the conventional joint transform correlator (JTC). The PSJTC is combined with the circular harmonic expansion to achieve a full rotationinvariant correlation with high light efficiency and high discrimination capability. Computer simulation results and 3-D computer plots are presented.

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.

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.

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.

Quantized amplitude-compensated matched filter

A new spatial filter, the quantized amplitude compensated matched filter is proposed. It is characterized as amplitude modulation only with several discrete grey levels. As compared with the amplitude-compensated matched filter, the Horner efficiency is quite poor. However, the high discrimination is preserved, and an amplitude-modulated spatial light modulator might be accommodated. The circular harmonic version of this filter is also investigated.

Moving gratings and optical bias in holography with the photorefractive crystal Bi12SiO20

Moving gratings at large fringe modulation and optical bias in photorefractive crystal Bi12SiO20 are investigated. With two-wave mixing architecture, the optimum fringe velocity and the enhancement of the diffraction efficiency exhibit strong nonlinear dependence on the fringe modulations. With four-wave mixing architecture, not only these nonlinear effects still exist but also the optimum pump beam ratio is totally different from a stationary grating. It is also found applying optical bias into moving gratings that the diffraction efficiency exhibits unexpected behavior. Experimental results of these nonlinear effects are presented.