Photorefractive Barium Titanate Crystal Research Articles

2 × 8 photorefractive reconfigurable interconnect with laser diodes

We report the demonstration and characterization of a 2 x 8 optical reconfigurable interconnect with laser diodes at 780 nm and a ferroelectric liquid crystal spatial light modulator in conjunction with a photorefractive barium titanate crystal. The photorefractive holograms improve the energy efficiency by 6 to 10 dB over the conventional approach.

Pulsed amplification of continuous-wave signal fields in photorefractive BaTiO3

High-gain pulsed amplification of low intensity continuous-wave optical signals via two-wave mixing in a photorefractive barium titanate (BaTiO3) crystal is demonstrated. The technique relies on the nonlinear mixing between a signal field and a pump field produced via pulsed amplification of a continuous-wave field in excimer-pumped dye amplifiers.

Experimental study of achromatic volume holography with dispersive compensation in barium titanate

We carried out an experimental study to verify a proposed theory for achromatic volume holography using dispersive compensation in photorefractive barium titanate crystals. Compensation of the phase mismatch was observed and was consistent with the theory.

Effects of feed material and annealing atmosphere on the properties of photorefractive barium titanate crystals

Growth and fabrication of commercial BaTiO3 photorefractive crystals are described. Crystals grown from two different titanium dioxide sources and annealed in oxygen partial pressures between 1 and 10−17 atm were characterized by chemical analysis, optical absorption spectra, and two-beam coupling gain. Equal mixtures of the two starting materials yielded crystals with the highest photorefractive gain, whereas the extremes either were inactive or exhibited photochromic damage. Reduction of the inactive crystals below 10−11 atm of oxygen yielded a tenfold increase in photorefractive carrier density related to a sharp absorption peak at 450 nm tentatively assigned to a nickel–oxygen-vacancy complex.

The transient detection microscope

We describe a microscope that preferentially displays moving objects. This all-optical device operates in real-time using the nonlinear coupling of optical beams in a photorefractive crystal of barium titanate. A holographic image is continuously written and compared with the real image, and any discrepancy between the two images is immediately visible. The device can be used to highlight moving objects, such as protozoans, while suppressing the image of any stationary objects in the background. The device needs only milliwatts of laser power, and can detect objects moving at velocities of a few micrometres per second.

Optical switch using the photorefractive effect and ferroelectric polarization reversal

A new form of optical switching in photorefractive ferroelectric materials is described. Ferroelectric polarization reversal is used to reverse the c axis and, consequently, the direction of nonlinear gain in a photorefractive barium titanate crystal. We report optical switching in 100 microsec with a 60-to-1 on-off ratio when this technique is used. Onoff ratios of 500 to 1 are predicted for typical crystals with gain-length products of 4.

Double phase-conjugate mirror: analysis, demonstration, and applications

We report on the operation of the double phase-conjugate mirror (DPCM). Two inputs to opposite sides of a photorefractive barium titanate crystal, which may carry different spatial images, are shown to pump the same four-wave mixing process mutually and are self-refracted without any external or internal crystal surface. This results in the phase-conjugate reproduction of the two images simultaneously. This device is analyzed theoretically, and applications in image processing, interferometry, and rotation sensing are discussed. We also demonstrate the operation of a ring laser, using the DPCM, as well as a photorefractive resonator with two facing DPCM's that can support spatial information in its oscillations.

Partial cancellation of specular reflection in the presence of a phase-conjugate mirror

We present experimental results showing the partial cancellation of the specular reflection off a partially transmitting ordinary plane mirror in the presence of a phase-conjugate mirror. The extent of cancellation for the measured phase- conjugate reflectivities agrees well with the proposed theory. A single domain photorefractive crystal of barium titanate operating via four wave mixing acted as the phase-conjugate mirror.

Tunable frequency shift of photorefractive oscillators

We report on an experimental study of the self-frequency detuning in wave mixing oscillators with the photorefractive barium titanate crystal. We show its dependence on a dc electric field on the crystal, optical phases in the oscillator cavity, and light intensity in the crystal. This resolves many aspects of previously observed and unexplained self-frequency detuning effects with similar oscillators and indicates the existence of an internal electric field in the mixing crystal.

Experimental studies of phase conjugation with depleted pumps in photorefractive media

We describe the experimental measurement of phase-conjugate reflectivity versus various ratios of input-beam intensities in photorefractive barium titanate and strontium barium niobate crystals. The experimental results are compared with the theoretical prediction from the coupled-wave theory. Three different methods to measure the nonlinear coupling constant of the crystal are also presented and compared.

Asymmetric transmission through a photorefractive crystal of barium titanate

We have investigated the feasibility of using a barium titanate crystal as a unidirectional device. The nonlinear interaction between a beam and its own reflection from the back face of the crystal causes an effective increase or decrease in the transmission through the crystal, depending on whether the incident beam propagates along or against the crystal c-axis, respectively. This effect was investigated for several wavelengths and compared with theory. It is possible to make a device that has an average transmission of ≈94% and a transmission asymmetry of 1% by using a crystal whose front and back faces are cut so that their normals are at angle of ≈30° to the crystal c-axis.

Theory of a self-pumped phase conjugator with two coupled interaction regions

We present a plane-wave analysis of a recently demonstrated self-pumped phase conjugator. This device uses four-wave mixing to produce the phase-conjugate replica of an incident optical wave. All the waves are derived from the single incident wave: there are no externally supplied pumping beams. We consider the case of four-wave mixing in two interaction regions coupled by simple reflection. We calculate the phase-conjugate reflectivity as a function of coupling strength, taking into account imperfect coupling between the two interaction regions, and show that there is a threshold coupling strength below which the reflectivity is zero and above which the reflectivity is multiple valued. We also compute the coupling strength per unit length for a photorefractive crystal of barium titanate.