Victor Leyva

Optical data storage by using orthogonal wavelength-multiplexed volume holograms

We propose a volume holographic data storage scheme that employs counterpropagating reference and image beams and wavelength multiplexing for page differentation. This method is compared with that based on angular multiplexing. A reduction in holographic cross talk is predicted. Further cross-talk reduction that is due to sidelobe suppression is observed in experiments by using photorefractive crystals and the proposed orthogonal data storage.

Volume holographic narrow-band optical filter

An 0.0125-nm (FWHM) bandwidth optical filter with >10% throughput, clean sidebands, f/12 speed, and a response roll-off of -40 dB/decade has been developed by using volume holography in photorefractive materials. The performance of the Accuwave holographic filter is characterized and compared with that of a Lyot filter, which is the standard for solar astronomy today. Moreover, this device represents the first commercial application of volume holography in photorefractive crystals.

Precise control of broadband frequency chirps using optoelectronic feedback

We demonstrate the generation of wideband frequency sweeps using a semiconductor laser in an optoelectronic feedback loop. The rate and shape of the optical frequency sweep is locked to and determined by the frequency of a reference electronic signal, leading to an agile, high coherence swept-frequency source for laser ranging and 3-D imaging applications. Using a reference signal of constant frequency, a transform-limited linear sweep of 100 GHz in 1 ms is achieved, and real-time ranging with a spatial resolution of 1.5 mm is demonstrated. Further, arbitrary frequency sweeps can be achieved by tuning the frequency of the input electronic signal. Broadband quadratic and exponential optical frequency sweeps are demonstrated using this technique.

Narrow bandwidth volume holographic optical filter operating at the Kr transition at 1547.82 nm

We describe and characterize a narrow bandwidth volume holographic optical filter operating at the Krypton transition line (1s2‐2p8) at 1547.82 nm, which corresponds to the center wavelength of the proposed International Telecommunications Union wavelength standard. A reflectivity of 98% and a bandwidth full width at half‐maximum of 0.18 nm are measured. The filter exhibits clean sideholes with a −20 dB optical response 0.5 nm away from the peak. The filter can be fabricated and operated with an absolute wavelength precision better than 0.005 nm.

Voltage-controlled photorefractive effect in paraelectric KTa1−xNbxO3:Cu,V

Experimental results that demonstrate the formation of photorefractive gratings in KTN:Cu,V in theparaelectric phase are presented. These gratings are formed using the quadratic electro-optic effect, which allows amplitude modulation of the diffracted beam by an external electric field. High diffraction efficiencies of over 50% in a 3-mmthick sample and amplitude modulation of the diffracted beam by an external field at frequencies of up to 20 kHz were observed.

Holographic fixing, readout, and storage dynamics in photorefractive materials

Holographic gratings in photorefractive crystals that are based on charge redistribution inevitably decay as a result of ionic and electronic conduction. Under certain and restricted conditions these decay times can be acceptably long. Relevant decay rates and transient hologram field expressions are derived with special reference to LiNbO(3). Some experimental data are presented.

Fixing of a photorefractive grating in KTa1-xNbxO3 by cooling through the ferroelectric phase transition

We report the fixing of a photorefractive grating in KTa(1-x)Nb(x)O(3). The procedure involves the writing of a photorefractive grating in the cubic phase and the cooling of the sample under an applied field into the rhombohedral phase. We discuss possible mechanisms responsible for the effect.

Fixing of photorefractive volume holograms in K1-yLiyTa1-xO3

We report the f ixing of photorefractive holographic gratings with high eff iciency in a sample of K1-yLiyTa1-xNbxO3 doped with Cu, V, and Ti. Holograms are thermally fixed through the screening of a photorefractive space-charge field by a nonphotoactive species at elevated temperatures. Fixed holograms are revealed by illumination at lower temperatures. Diffraction efficiencies of 25% in a 0.54-cm-thick sample are measured. Holograms undergo thermal decay with a 0.67-eV activation energy.

Determination of the physical parameters controlling the photorefractive effect in KTa1-xNbx O3:Cu,V

We report photorefractive, absorption, and photoconductivity measurements made on a KTa1-xNbxO3:CuY sample after a series of reduction and oxidation treatments. All relevant physical parameters that enter into the Kukhtarev model of the photorefractive effect are determined. Photorefractive measurements are compared with those expected from theory. The oxidation-reduction process is modeled, which permits us to determine the heat treatment that is necessary to produce a given index change and response time. We discuss approaches to optimization of the photorefractive sensitivity.

Dependence of the photorefractive properties of KTa1−xNbxO3:Cu,V on Cu valence state concentration

Absorption measurements and electron microprobe analysis are used to determine the density of Cu1+ and Cu2+ ions in a photorefractive KTa1−x Nbx O3 :Cu,V sample. Photorefractive measurements are made over a wide range of Cu1+ and Cu2+ concentrations, altered by a series of oxidation and reduction treatments. Diffraction efficiencies were varied by over an order of magnitude while erasure rates were varied by over two orders of magnitude.