Ren-Han Tsou

Random phase-coded multiplexing of hologram volumes using ground glass

We apply an encoding method, random phase-coded multiplexing, to volume hologram multiplexing and demonstrate the recording of 100 holograms in LiNbO3: 0.01% Fe. A theory is developed to interpret the noise generated by this method, and a computer simulation is provided for direct comparison.

Temperature dependence of two-beam coupling and dark decay in photorefractive BaTiO3

The temperature dependence of two-beam coupling and dark decay in photorefractive BaTiO3 is reported. We show that the competition between deep and shallow traps depends on temperature and writing intensity, and influences two-beam coupling and dark decay. The dynamics of dark decay, characterized by a fast decay of partial erasure and a subsequent slow decay, is influenced by the presence of deep and shallow traps. Partial erasure, due to thermal excitation of charges from the shallow traps, decreases with temperature and increases with writing intensity. The time constant of the slow decay, due to thermal excitation of charges from the deep traps, depends strongly on temperature, but not on the writing intensity. At room temperature, the existence of deep and shallow trap leads to intensity-dependent photorefractive gains. As temperature increases, the influence from the shallow trap decreases, and the photorefractive gain becomes independent of the intensity. However, at much higher temperatures (∼100°C), the photorefractive gain resumes its dependence on intensity due to an increase in dark conductivity at elevated temperature.

Random phase-coded multiplexing in LiNbO3 for volume hologram storage by using a ground glass

An encoding method, random phase-coded multiplexing, was applied to the volume hologram multiplexing and demonstrated the recording of 100 holograms in a LiNbO3:0.01% Fe. The multiplexing method is simple because the encoding material is just a ground glass. A theory was also developed to interpret the properties of the method.

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.

Shearing interferometer with a Kitty self-pumped phase-conjugate mirror

A shearing interferometer with a Kitty-type self-pumped phase-conjugate mirror is developed. The measurement of the focal length of a lens is demonstrated with a standard deviation of 1.5%. In addition, we measured the microdisplacement in the range of tens of micrometers with an error less than 2% by using the interferometer.

Real-time photorefractive interferometer for dynamic phase perturbation by self-interference in LiNbO 3

We propose a simple real-time system and demonstrate its use for measuring dynamic optical phase perturbation. In this system we used a 0.1-wt. % Fe:LiNbO(3) to record the self-interference grating with incident light. The system is a new kind of real-time holographic interferometer. After rise time in the interferometer, the speed for showing the fringes is as fast as that of dynamic phase perturbations. Characteristics of the interferometer are proposed and examined.

Self-diffraction conical ring by multiple scatterings in LiNbO3

We report our observation of the generation of a conical ring when two extraordinarily polarized beams are incident upon a heavy-doped LiNbO3. We demonstrate that large refractive index change, multiple scatterings and diffractions through Bragg- mismatching condition exist in the crystal. It leads to the generation of the conical ring.

Optical storage capacity of volume holograms with random phase-coded multiplexing

The storage capacity of the random phase-coded volume hologram multiplexing which uses a ground glass as the random phase diffuser is reported. We found that the role of the ground glass imply the storage capacity of the random phase-coded multiplexing. From the experimental results, the tolerance of the position mismatch of the decoding ground glass is with a typical value of decades of micrometers, as reading an image. On the other hand, from the computer simulation, the signal-to-noise ratio of the readout images can be obtained by the pixel size of the ground glass. After mainly considering the tolerance of the position mismatch of the ground glass and the signal-to-noise ratio of the reconstructed image, the storage capacity of the random phase-coded multiplexing can be estimated.

Sensing dynamic phase perturbation by self-interference of a photorefractive interferometer

As for our knowledge, a simplest real-time system for measuring dynamic optical phase perturbation is proposed and demonstrated. In this system a 1% weight Fe:LiNbO3 is used to record the self-interference grating by the incident light. The interferometer is a new kind of double-exposure one. The speed of the interferometer is as fast as that of the dynamic phase perturbations.