Photorefraction data storage

A major application of photorefractive polymers as holographic data storage media is a real possibility. In this application two interfering laser beams write a hologram... 

Hessehnk, L., Orlov, S.S., Liu, A., Akella, A., Lande, D., and Neurgaonkar, R.R., Photorefractive materials for nonvolatile volume holographic data storage, Science, 282, 1089, 1998. 

The photorefractive effect used in rewritable 3D optical data storage is based on nonuniform space-charge distribution produced by interfering beams... 

A photorefractive material for a three dimensional bit optical data storage device in the near infrared range consists of either PVK or PMMA as matrix with DMNPAA and TNF and V-ethylcarbazole (ECZ) in various amounts. " ... 

The two-photon excitation technique was used to achieve rewritable bit data storage in the photorefractive polymer. This results in a quadratic dependence of the excitation on the incident intensity producing an excitation volume that is confined to the focal region in both the transverse and axial directions. 

A photorefractive polymer consisting of DMNPAA, TNF, ECZ, and PVK has been used for erasable/rewritable three dimensional bit optical data storage under two-photon excitation. A three dimensional bit density of 5 Gbits/cm(3) is achieved by pulsed beam illumination at an infrared wavelength of 800 nm in the recording process. 

D. Day and M. Gu. Use of two-photon excitation for erasable-rewritable three-dimensional bit optical data storage in a photorefractive polymer. Opt. Lett., 24(14) 948-950, July 1999. 

B. Kippelen, Overview of Photorefractive Polymers for Holographic Data Storage, in J. Coufal, D. Psaltis, G.T. Sincerbox (eds.), Holographic Data Storage,... 

We have prepared multi-component photorefractive polymers for optical data storage applications (8). This photorefractivity is a combination of two functionalities electro-optic effect and photoconductivity. We have achieved holographic diffraction efficiencies up to >30% in our composites. 

To overcome volatility problems, two-photon absorption (TPA) is the most promising long-term data storage technique to date. TPA can be observed in all materials and lacks the noncentrosymmetric symmetry requirements of even-order nonlinear optical effects. Nevertheless, in centrosymmetric polymers two-photon absorption is allowed between states that have the same parity according to parity selection rules (112). Such a system has been demonstrated with nondestructive readout (113). Additionally, use of two-photon absorption on photorefractive polymer dispersed liquid crystals has been used to record a high 3D data density of 204.8 Gbits/cm (158). 

Optical Devices. Of most interest in this application are those studies related to the nonlinear optical effects in polyphosphazene derivatives bearing aromatic azo imits (217-219) and the photorefractive effect with pol5q)hosp-hazenes bearing carbazolyl substituents (220). Possible applications include optical switches, frequency doublers for lasers, holographic data storage, and real-time image processing. 

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