Digital Holographic Storage Research Articles

Green upconversion emission in tellurite optical fibre codoped with Yb3+/Er3+

In the paper the spectroscopic properties of Yb 3+ /Er 3+ codoped tellurite glass has been investigated. Upconversion luminescence at 525 nm, 546 nm, 651 nm corresponding to the Er 3+ : 2 H 11/2 -> 4 I 15/2 , 4 S 3/2 -> 4 I 15/2 , 4 F 9/2 -> 4 I 15/2 transitions, respectively was obtained as a result of energy transfer between Yb 3+ and Er 3+ ions. Developed tellurite glass characterized by highest intensity of upconversion luminescence (0.5mol% Yb( 2 O 3 /0.1mol% Er 2 O 3 ) was used as core of optical fiber. The amplified spontaneous emission in the fabricated optical fiber resulting from the optical transition in the structure of erbium was observed. Full Text: PDF References J. Zhang, S. Dai, G. Wang, L. Zhang, H. Sun, L. Hu., "Investigation on upconversion luminescence in Er3+/Yb3+ codoped tellurite glasses and fibers", Physics Letters A 345, 409?414 (2005). CrossRef D. Lande, S.S. Orlov, A. Akella, L. Hesselink, R. R. Neurgaonkar, "Digital holographic storage system incorporating optical fixing", Optics Letters, Vol. 22, Issue 22, 1722-1724 (1997). CrossRef T. Yamashita, Y. Ohishi, "Spectroscopic properties of Tb3+-Yb3+-codoped borosilicate glasses for green lasers and amplifiers", Proc. SPIE 6389, 638912 (2006). CrossRef Y.H. Li, G.Y. Hong, Y.M. Zhang, Y.M. Yu, "Red and green upconversion luminescence of Gd2O3:Er3+, Yb3+ nanoparticles", J. Alloys Compd. 456, 247-450 (2008). CrossRef J. S. Wang, E. M. Vogel, E. Snitzer, "Tellurite glass: a new candidate for fiber devices", Opt. Mater. 3, 187-203 (1994). CrossRef J. Dorosz, "Optical Fibers Technology", Ceramics vol. 86 (2005)

Azopolymer/Liquid Crystal Complex for Polarization Holograms

We have proposed and demonstrated a new holographic medium that can act as a write once read many (WORM) polarization-recordable medium. The new medium, composed of azobenzene-containing polymer and photocurable liquid crystal, exhibited birefringence when irradiated by polarized light. Additionally, the diffraction efficiency and the birefringence of this recorded complex increased to several times those of the simple rewritable azopolymer. This occurred because the orientation of photocurable liquid crystals was as good as that of the azopolymer because of the interaction with the mesogens. By measuring the birefringence, we confirmed that unlike the azopolymer, the orientation of the liquid crystal polymer was maintained even after circularly polarized beam irradiation. In this medium, only the photocurable liquid crystals were cured and became polymers with fixed orientation. Therefore, we propose that the new medium, which is polarization-recordable, WORM and highly sensitive, is very promising and practical for digital holographic storage.

High-transfer-rate high-capacity holographic disk data-storage system.

We describe the design and implementation of a high-data-rate high-capacity digital holographic storage disk system. Various system design trade-offs that affect density and data-rate performance are described and analyzed. In the demonstration system that we describe, high-density holographic recording is achieved by use of high-resolution short-focal-length optics and correlation shift multiplexing in photopolymer disk media. Holographic channel decoding at a 1-Gbit/s data rate is performed by custom-built electronic hardware. A benchmark sustained optical data-transfer rate of 10 Gbits/s has been successfully demonstrated.

Polarization Encoding for Digital Holographic Storage

We have proposed polarization encoding for digital holographic storage, in which each pixel or bit encodes two orthogonal polarization states, 0 and 90 degrees, corresponding to binary 1 and 0, respectively. We recorded the polarization-encoded page within an azobenzene-containing polyester film that is capable of recording arbitrary polarization states. After retrieval from the hologram, the polarization-encoded page was divided into mutually orthogonal polarization components. The two polarization components had an intrapage variation, and their bit error rates (BERs) were estimated to be 10-3 and 10-5. Subsequently, to remove the intrapage variation, we calculated the difference between the two polarization components. The intrapage variation successfully decreased on the subtraction image, and its BER was improved to 10-7. Therefore, this method is of great use for eliminating intrapage variations on a reconstructed data page.

Distortions in pixel-matched holographic data storage due to lateral dimensional change of photopolymer storage media

Dimensional changes in polymerizable storage materials during exposure are a source of pixel misregistration in digital holographic storage. Lateral shrinkage or expansion of photopolymer recording materials can be deduced from quantitative measurement of the shift and the magnification errors of reconstructed holograms.

Architecture for trellis-coded modulation in page memories

Distortion and noise promote detection errors in digital holographic storage systems. Trellis-coded modulation (TCM) combines modulation and error-correction coding to reduce the bit error rate. The author describes a novel implementation of TCM for these systems that exploits two-dimensional pixel dependence. Relative computational efficiency is provided, facilitating high data throughput.

Experimental study of the effects of a six-level phase mask on a digital holographic storage system

We measure the M/# and the bit-error rate of a digital holographic storage system with a 4f optical arrangement for three configurations: recording at the Fourier plane with and without a phase mask and recording outside the Fourier plane without a phase mask. Unexpectedly, no significant change in the dynamic range was observed when a phase mask was used to record in thick crystals. However, we show that a phase mask is a key component in a 4f digital holographic storage system if high-fidelity holograms with optimum volumetric density are to be stored.

Digital holographic storage system incorporating optical fixing

Digital holograms have been written in stoichiometric Pr:LiNbO(3) in a two-color recording scheme, demonstrating what is to our knowledge the first all-optical nondestructive readout of digital data. Using writing light at 800nm and gating light at 476 nm, we stored and retrieved 256-kbit digital data pages with a raw bit-error rate BER of <10(-4) .

Effects of multilevel phase masks on interpixel cross talk in digital holographic storage

We study the interpixel cross talk introduced to digital holographic data storage by use of a multilevel phase mask at the data-input plane. We evaluate numerically the intensity distribution at the output detector for Fourier plane hologram storage in a limited-aperture storage medium. Only the effect at an output pixel of interpixel cross talk from the four horizontal and vertical neighboring pixels is considered, permitting systematic evaluation of all possibilities. For random two-level and pseudorandom six-level phase masks, the influence of the pixel fill factor, as well as the aperture size of the storage medium, is studied. Our simulations show that, for a given aperture size, a random two-level mask is more susceptible to interpixel cross talk than is a pseudorandom six-level mask. Decreasing the pixel fill factor below 94% with a pseudorandom six-level phase mask makes it theoretically possible to have a system with no errors from interpixel cross talk if one particular 5-pixel pattern is forbidden through modulation coding. Reducing the input fill factor below 85% means that no patterns need to be excluded.

Modulation coding for pixel-matched holographic data storage

We describe a digital holographic storage system for the study of noise sources and the evaluation of modulation and error-correction codes. A precision zoom lens and Fourier transform optics provide pixel-to-pixel matching between any input spatial light modulator and output CCD array over magnifications from 0.8 to 3. Holograms are angle multiplexed in LiNbO(3):Fe by use of the 90 degrees geometry, and reconstructions are detected with a 60-frame/s CCD camera. Modulation codes developed on this platform permit image transmission down to signal levels of ~2000 photons per ON camera pixel, at raw bit-error rates (BER's) of better than 10(-5). Using an 8-12-pixel modulation code, we have stored and retrieved 1200 holograms (each with 45,600 user bits) without error, for a raw BER of <2x10(-8).