Hon Fai Yau

Wave-front reconstruction without twin-image blurring by two arbitrary step digital holograms.

We discuss a novel approach for numerical wave-front reconstruction which utilizes arbitrary phase step digital holography. Our experimental results demonstrate that only two digital holograms and a simple estimation procedure are required for twin-image suppression, and for numerical reconstruction. One advantage of this approach is its simplicity. Only one estimate equation needs be applied. In addition the optical system can be constructed from inexpensive, generally available elements. Another advantage is the effectiveness of the method. The tolerance of the estimated value is less than 1% different than the actual value. This means that the quality of the reconstructed image is superior. This novel approach should make the application of digital holography easier and more widely available.

Phase-only circular harmonic matched filtering.

The idea of a phase-only matched filter [J. L. Horner and P. D. Gianino, Appl. Opt. 23, 812-816 (1984)] is incorporated in the scheme of circular harmonic component matched filtering [Y. N. Hsu and H. H. Arsenault, Appl. Opt. 21, 4016-4019 (1982)]. Computer simulation showed that the phase-only circular harmonic matched filter possesses the rotational invariant property for 2-D recognition. Furthermore, it does a better job in recognizing closely placed targets compared with traditional circular harmonic filters. The simulation also demonstrated that a pure phase circular harmonic filter is less liable to give rise to false alarms in recognition because the sidelobe produced by it is much less pronounced and much less extensive than that produced by a traditional circular harmonic filter.

Experimental demonstration of phase-only circular harmonic filtering using computer generated filters

Experimental results of phase-only circular harmonic filtering implemented in a standard Fourier transform correlator are presented. The filter is a computer generated hologram which contains only the phase information of a single circular harmonic component of the target. The result with simple binary objects bears out the simulation result published earlier [H. F. Yau and C. C. Chang, Appl. Opt. 28, 2070-2074 (1989)] in that the filter is indeed shift- and rotational-invariant and that the correlation peak is more prominent than that produced by ordinary circular harmonic filtering.

Hybrid Holographic Multiplexing for Data Storage and Application to Optical Encryption

We have implemented a rotationally shifted random-phase encoded multiplexing suitable for the holographic data storage in a photorefractive LiNbO3:Fe crystal. A rotating and shifting circular holographic diffuser is placed as a random-phase modulator in the reference beam of the holographic storage system to provide a simple yet effective approach of increasing data storage capabilities. Experimental results show that the proposed multiplexing scheme can also be combined with angular multiplexing to produce rotationally shifted random-phase encoded and angular multiplexing, offering not only further data storage capabilities but data encryption possibilities as well.

Self-pumped and mutually pumped phase conjugation using pentagon-shaped BaTiO3 crystal

Tokamak experimental research in China has made important progress. The main efforts were related to quasi-steady-state operation, LHCD, plasma heating with ICRF, IBW, NBI and ECRH, fuelling with pellets and supersonic molecular beams, and first wall conditioning techniques. Plasma parameters in the experiments were much improved, for example n(e) = 8 x 10(19) m(-3) and a plasma pulse length of > 10 s were achieved. ICRF boronization and conditioning resulted in Z(eff) close to unity. Steady state full LH wave current drive has been achieved for more than 3 s. LHCD ramp-up and recharge have also been demonstrated. The best eta (exp)(CD) approximate to 0.5(1 + 0.085 exp(4.8(B-T - CD, 1.45)))n(e)I(CD)R(p)/P-LH = 10(19) m(-2) A W-1. Quasi-steady-state H-mode-like plasmas with a density close to the Greenwald limit were obtained by LHCD, where the energy confinement time was nearly five times longer than in the ohmic case. The synergy between IBW, pellet and LHCD was tested. Research on the mechanism of macroturbulence has been extensively carried out experimentally. AC tokamak operation has been successfully demonstrated.

Double phase conjugation with orthogonally polarized beams in a BaTiO(3) crystal.

We have demonstrated experimentally the simultaneous self-conjugation of extraordinarily and ordinarily polarized light waves (lambda=514 nm), with the polarization state preserved, in a Ce:BaTiO(3) crystal. Conjugate o waves originate from coupling between o and e waves by means of a circular photogalvanic effect. The conjugator also takes advantage of the Ce:BaTiO(3) crystal, for which it is easy to generate an extraordinary conjugate beam by photorefractive backscattering. This beam of light is necessary for double phase conjugation.

Coherent optical signal transferring on request by use of a BaTiO 3 crystal

We demonstrate experimentally a setup with which a two-dimensional picture can be transmitted from one plane to another at a signal request of the latter plane and the original picture continues to propagate unhindered along its original direction to the next stage. The setup makes use of photorefractive four-wave mixing and the self-pumped phase conjugation for its operation. Some means for increasing the contrast of the final transmitted image have been discussed.

Elimination of Dynamic Instabilities in the +c-face Incident Photorefractive BaTiO3 Mutually Pumped Phase Conjugator.

Experimental observations of the dynamic instabilities in the +c-face incident mutually pumped phase conjugator (MPPC) of a BaTiO3 crystal are reported for the first time. Experiments show that it is possible to stabilize the phase-conjugate output by choosing a proper geometry formed from the crystal and two incident beams. By choosing the proper geometry the essential configuration of the MPPC attained is a kite rather than a fish head. Data also indicate that the phase-conjugate output can reach a very steady state with a high value (~32%) and is insensitive to angular and positional variations.

Two-dimensional optical interconnection using two photorefrative crystals

We demonstrate an optical setup being capable of transferring a two-dimensional picture in either way from one plane to another. The transferring takes place only when the receiving port sends a requesting signal. This setup consists of a LiNbO3 crystal for the purpose of four-wave mixing, and a BaTiO3 crystal for the purpose of producing self pumped phase conjugate wave. The characteristic of this setup is that it does not require any change in the experimental arrangement when the transferring direction of the picture is reversed. Finally, this setup can perform not only static but also dynamic image transferring.

Ordinary polarized phase conjugator using the photovoltaic effect

Abstract Self-pumped phase conjugators so far always work with extraordinary (e) polarized light waves. Theoretical analysis however has pointed out that the e-polarized waves and ordinary (o) polarized waves could be coupled together via the circular photovoltaic effect. We report here an experimental realization of this theoretical prediction and present an o-polarized conjugator. The core element of this setup is a 0°-cut undoped BaTiO 3 crystal, which is aligned in a Cat-conjugator architecture with respect to an incident beam of e-polarized waves. Simultaneously we shine a beam of o-polarized waves on the crystal. Upon the appearance of the e-conjugate waves, we also observed the o-conjugate waves. The resolution of this ordinary polarized phase conjugator is comparable to that of the prevailing e-waves conjugators.