Koichi Sayano

Compact read-only memory with lensless phase-conjugate holograms

A new approach to holographic storage that uses lensless phase-conjugate holograms is proposed and demonstrated. Near-field holography is used for data recording, and a phase-conjugate reference beam is used for data retrieval. The data array can be directly transferred from the storage medium to the sensor without the need for imaging optics. It is shown that large space -bandwidth product holographic images (N x N x 10(6)) with pixel sizes of a few micrometers are feasible with a reasonable-sized recording material.

Photorefractive properties of Ce‐ and Ca‐doped Sr0.6Ba0.4Nb2O6

We present the results of experimental study of the absorption coefficient, two‐beam photorefractive coupling constant, and photorefractive response time of a doubly Ce‐ and Ca‐doped Sr0.6Ba0.4Nb2O6. This crystal displays enhanced photorefractive response at near infrared wavelengths when compared to Ce‐doped SBN:60. The temperature dependence of the coupling constant over the range from −30 to 40 °C has also been studied.

Photorefractive gain and response time of Cr‐doped strontium barium niobate

We present experimental results on the photorefractive two-beam coupling constant and response time of two Cr-doped strontium barium niobate crystals with different dopant concentrations. Both showed significantly faster response times over Ce-doped SBN:60, but with corresponding decreases in their coupling constants.

Photorefractive dark conductivity in Cr-doped strontium barium niobate.

We present the theoretical and experimental results of photorefractive two-beam coupling in Cr-doped strontium barium niobate:60, using thermal excitation (i.e., dark conductivity) to model the experimentally observed temperature-dependent behavior of the two-beam coupling constant and response time.

Self‐starting passive phase conjugate mirror with Ce‐doped strontium barium niobate

We report the use of Ce-doped SrxBa1−xNb2O6, x=0.60 and 0.75, as the holographic four-wave mixing medium in the construction of a self-starting passive phase conjugate mirror using internal reflection. Without correcting for Fresnel reflections, a steady-state phase conjugate reflectivity of 25% was measured with Sr0.75Ba0.25Nb2O6:Ce. The distortion correcting property of such a mirror was demonstrated using an imaging experiment.

Order-of-magnitude reduction of the photorefractive response time in rhodium-doped Sr0.6Ba0.4Nb2O6 with a dc electric field

We present what is to our knowledge the first report on the photorefractive properties of Rh-doped Sr(0.6)Ba(0.4)Nb(2)O(6) and experimental results showing a reduction of the photorefractive two-beam coupling response time by more than an order of magnitude with an external dc field of 10 kV/cm.

Enhanced photorefractive gain in Cr‐doped strontium barium niobate with an external dc electric field

We present experimental results of field‐enhanced photorefractive two‐beam coupling and gain in Cr‐doped strontium barium niobate crystals and its dependence on dopant concentrations. Increases in the exponential gain factor by more than a factor of 2 were observed by applying a field of up to 10 kV/cm. This property has potential applications such as switchable optical phase conjugators, limiters, and thresholding devices.

Thresholding semilinear phase-conjugate mirror.

We have demonstrated thresholding in a semilinear self-pumped phase-conjugate mirror by introducing grating motion within the photorefractive crystal and using the dependence of photorefractive response time on the intensity of the incident beam. The threshold level Ith was found to be a function of the grating velocity. This property has potential applications in optical computing and optical signal processing.

Modular WDM add/drop multiplexers

Ann add/drop multiplexer/demultiplexer using volumetric holographic crystal Bragg gratings and without use of circulators has been demonstrated. Multiplexed gratings with angle multiplexed reflection filters provide wavelength- selective reflection of one or more channels into or out of the fiber without disturbing the through channels. Overall channel add/drop losses of less than 3 dB and through channel losses of less than 0.5 dB have been demonstrated. Fabrication of holographic filters with the desired passband characteristics has also been demonstrated.

Photorefractive Properties Of KTa1-xNbxO3 In The Paraelectric Phase

We report the growth of doped Potassium Tantalate Niobate (KTN) crystals, and the characterization of their photorefractive properties L. the paraelectric region. First the Top Seeded Solution Growth Method is reviewed and the growth process of a KTN:Cu,V crystal is described. Results of diffraction efficiency measurements of photorefractive gratings in these crystals at the paraelectric phase, are then presented. These experiments show high diffractio- efficiencies, and indicate the possibility of amplitude modulation of the gratings by an external field. Results showing fixation of the gratings when the sample is close to the phase transition temperature are also described.