Ching Cherng Sun

Point spread function of a collinear holographic storage system

A paraxial solution to the coaxial holographic storage algorithm is proposed based on the scalar diffraction theory and a VOHIL model (volume hologram being an integrator of the lights emitted from elementary light sources), which can give insight into the optical characteristics of the collinear holographic storage system in an effective way, including the point spread function and shift selectivity. The paraxial solution shows that the reference pattern is the key issue in the point spread function. Thus, the bit error rate of the system can be improved by changing the reference pattern. The proposed solution will be useful in the design of a new reference pattern to perform a high-quality readout pattern in the coaxial holographic storage system.

One-beam recording in a LiNbO 3 crystal

We propose a new way to record images in a photorefractive LiNbO3 crystal. This method involves only a single object light without any reference light. We believe that the recording is attained by fanning holograms that result from interference between the object light and its scattered light. Although volume gratings are involved, the recorded pattern can be viewed not only with a laser light beam that is incident over a certain angular range but also with white light.

Photorefractive effect in hydrogen-reduced BaTiO3

Abstract Optical and photorefractive properties of hydrogen-reduced BaTiO3 are investigated. Hydrogen-reduction induced a broad optical absorption around 620 nm. From two beam coupling, the electrooptic gain is highly dependent on intensity, with electrons being the major carriers. When the annealing temperature increases, the electrooptic gain decreases, though the trap density increases. From light-induced erasure decay measurement, the response time has a little change with intensity at low intensity, though it is much faster than that of the as-grown sample. These properties can be attributed to high dark conductivity of the reduced sample. The dark conductivity increases about three orders after hydrogen-reduction. It is about 6.6 × 10 −11 1/( cm Ω) for the reduced sample, compared with 2.3 × 10 −14 1/( cm Ω) for the as-grown.

The optical and photorefractive properties of reduced Rh-doped BaTiO3 at wavelength of 514 nm

Abstract Optical and photorefractive properties of reduced Rh-doped barium titanate are reported. Reduction eliminates energy levels of Rh +4 and Rh +5 , and induces an absorption around 480 nm, which has a large light-induced transparency of ∼4 cm −1 . After reduction, the speed increases by a factor of 30 though the electrooptic gain decreases by a factor of 1.6. In addition, it induces an increase of dark conductivity by three orders.

Wavelength dependence of carrier-type in reduced BaTiO3:Rh

We report that in BaTiO3:Rh the carrier-type depends not only on the postprocessing condition but also on the incident wavelength in two beam coupling. Carriers are the holes for the as-grown sample, and change to electrons for the sample reduced in the atmosphere of 10−14 atm oxygen partial pressure. However, for the sample reduced in the atmosphere of 10−10 atm oxygen partial pressure, the carrier is an electron for the incident wavelength of 514 nm, and a hole for 633 nm. Its absorption, photoinduced absorption, and two beam coupling are investigated and discussed.

One-dimensional optical imaging with a volume holographic optical element

We propose a novel imaging structure based on a volume holographic optical element that allows one-dimensional optical imaging through a specific Bragg window. The lateral magnification is shown to be linear and negative. Lateral magnifications of 2.5, 5, and 10 of the imaging element are demonstrated theoretically and experimentally.

Volume holographic optical elements for point-to-point imaging with local cross talk

A novel volume holographic optical element serving as an atypical mirror with a lateral magnification of 1 in both the horizontal and the vertical directions is proposed. Optical imaging is performed by point-to-point imaging with local cross talk, which prevents ghost diffraction spots from the holographic element of multiple gratings.

Enhanced rotational Bragg selectivity by use of random phase encoding in volume holographic filter.

An out-of-plane angular detection scheme with random phase encoding is proposed. A ground glass is attached on a rod, which is rotated around a center point, so that the rotation of the rod induces the displacement of the ground glass in a circular path. To enhance the rotational sensitivity we adjust the Bragg selectivity of the volume holographic optical element encoded by random phase. Therefore, the rotational sensitivity can be tuned over a large range from several degrees to ten thousandth degrees by changing the radius of rotation. The theoretical calculation, as well as experiment, is demonstrated.

Enlarging multiplexing capacity with reduced radial cross talk in volume holographic discs

A novel design for a volume holographic optical disc to reduce radial cross talk is proposed. By adopting a proper spatial filter, the radial cross talk can be reduced and the radial selectivity increases so that the multiplexing capacity can increase effectively. The theory and the corresponding experiment are 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.