Holography: Advances and Modern Trends II

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1 PROCEEDINGS OF SPIE Holography: Advances and Modern Trends II Miroslav Hrabovský Miroslav Miler John T. Sheridan Editors April 2011 Prague, Czech Republic Sponsored and Published by SPIE Cooperating Organisations ELI Beamlines HiPER Volume 8074 Proceedings of SPIE, X, v SPIE is an international society advancing an interdisciplinary approach to the science and application of light. Downloaded from SPIE Digital Library on 30 May 2011 to Terms of Use:

2 The papers included in this volume were part of the technical conference cited on the cover and title page. Papers were selected and subject to review by the editors and conference program committee. Some conference presentations may not be available for publication. The papers published in these proceedings reflect the work and thoughts of the authors and are published herein as submitted. The publisher is not responsible for the validity of the information or for any outcomes resulting from reliance thereon. Please use the following format to cite material from this book: Author(s), "Title of Paper," in Holography: Advances and Modern Trends II, edited by Miroslav Hrabovský, Miroslav Miler, John T. Sheridan, Proceedings of SPIE Vol (SPIE, Bellingham, WA, 2011) Article CID Number. ISSN X ISBN Published by SPIE P.O. Box 10, Bellingham, Washington USA Telephone (Pacific Time) Fax SPIE.org Copyright 2011, Society of Photo-Optical Instrumentation Engineers Copying of material in this book for internal or personal use, or for the internal or personal use of specific clients, beyond the fair use provisions granted by the U.S. Copyright Law is authorized by SPIE subject to payment of copying fees. The Transactional Reporting Service base fee for this volume is $18.00 per article (or portion thereof), which should be paid directly to the Copyright Clearance Center (CCC), 222 Rosewood Drive, Danvers, MA Payment may also be made electronically through CCC Online at copyright.com. Other copying for republication, resale, advertising or promotion, or any form of systematic or multiple reproduction of any material in this book is prohibited except with permission in writing from the publisher. The CCC fee code is X/11/$ Printed in the United States of America. Publication of record for individual papers is online in the SPIE Digital Library. SPIEDigitalLibrary.org Paper Numbering: Proceedings of SPIE follow an e-first publication model, with papers published first online and then in print and on CD-ROM. Papers are published as they are submitted and meet publication criteria. A unique, consistent, permanent citation identifier (CID) number is assigned to each article at the time of the first publication. Utilization of CIDs allows articles to be fully citable as soon as they are published online, and connects the same identifier to all online, print, and electronic versions of the publication. SPIE uses a six-digit CID article numbering system in which: The first four digits correspond to the SPIE volume number. The last two digits indicate publication order within the volume using a Base 36 numbering system employing both numerals and letters. These two-number sets start with 00, 01, 02, 03, 04, 05, 06, 07, 08, 09, 0A, 0B 0Z, followed by 10-1Z, 20-2Z, etc. The CID number appears on each page of the manuscript. The complete citation is used on the first page, and an abbreviated version on subsequent pages. Numbers in the index correspond to the last two digits of the six-digit CID number. Downloaded from SPIE Digital Library on 30 May 2011 to Terms of Use:

3 8074 0X Multiplexed holographic reflection gratings in sol-gel [ ] A. Murciano, S. Blaya, L. Carretero, P. Acebal, R. F. Madrigal, A. Fimia, Univ. Miguel Hernández de Elche (Spain) Y Technology of integrating diffractive elements into an image-matrix hologram [ ] A. Bulanovs, E. Kirilova, V. Gerbreder, Daugavpils Univ. (Latvia) Z Design and research of parameters of an objective of the ultra-high resolution for producing HOE-DOE by a method a dot-matrix [ ] I. K. Tsiganov, S. B. Odinokov, A. Gerdev, Bauman Moscow State Technical Univ. (Russian Federation); V. V. Pozdnyakov, Joint-Stock Co. (Russian Federation) Optoelectronic system "HOLOINID" for automatic individualization and identification of security holograms [ ] D. S. Lushnikov, S. B. Odinokov, A. Y. Pavlov, Bauman Moscow State Technical Univ. (Russian Federation) Axial intensity distribution of converging spherical wave behind an elliptic aperture [ ] M. Miler, T. Martan, Institute of Photonics and Electronics of the ASCR, v.v.i. (Czech Republic) Simulation analysis of co-axis dual-reference-beam holographic data recording [ ] T. Yamada, K. Katakura, A. Nakajima, S. Yoshida, M. Yamamoto, Tokyo Univ. of Science (Japan) Reduction of zero-order spatial frequencies by using binary intensity and phase modulations in holographic data storage [ ] E. Fernández, A. Marquez, D. Piñol, J. Padilla, I. Pascual, Univ. de Alicante (Spain) Compact slot-in-type optical correlator for retrieving shape, colour, and texture [ ] H. Kuboyama, K. Moriyama, K. Yamaguchi, S. Arai, M. Fukuda, Toyohashi Univ. of Technology (Japan); M. Kato, T. Kawaguchi, PaPaLaB Co., Ltd. (Japan); M. Inoue, Toyohashi Univ. of Technology (Japan) Research of properties of the holographic screen [ ] D. S. Lushnikov, S. B. Odinokov, V. V. Markin, Bauman Moscow State Technical Univ. (Russian Federation) Coupled-wave theory analysis of holographic structures for slow-light applications [ ] L. Carretero, S. Blaya, A. Murciano, P. Acebal, A. Fimia, R. Madrigal, Univ. Miguel Hernández de Elche (Spain) Author Index vi Downloaded from SPIE Digital Library on 30 May 2011 to Terms of Use:

4 Conference Committee Symposium Chairs Miroslav Hrabovský, Palacký University Olomouc (Czech Republic) Wolfgang Sandner, Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie (Germany) and Laserlab Europe Bahaa Saleh, CREOL, The College of Optics and Photonics, University of Central Florida (United States) Jan Řídký, Institute of Physics of the ASCR, v.v.i. (Czech Republic) Symposium Honorary Chair Jan Peřina, Sr., Palacký University Olomouc (Czech Republic) Conference Chairs Miroslav Hrabovský, Palacký University Olomouc (Czech Republic) Miroslav Miler, Institute of Photonics and Electronics of the ASCR, v.v.i. (Czech Republic) John T. Sheridan, University College Dublin (Ireland) Programme Committee Radim Chmelik, Brno University of Technology (Czech Republic) Antonio Fimia, Universidad Miguel Hernández de Elche (Spain) Milos Kopecky, Institute of Physics of the ASCR, v.v.i. (Czech Republic) Libor Kotacka, Optaglio s.r.o. (Czech Republic) Dagmar Senderáková, Univerzita Komenského v Bratislave (Slovakia) Mitsuo Takeda, The University of Electro-Communications (Japan) Vladimir Yu. Venediktov, S.I. Vavilov State Optical Institute (Russian Federation) Przemyslaw W. Wachulak, Military University of Technology (Poland) Günther K. G. Wernicke, Humboldt-Universität zu Berlin (Germany) Session Chairs 1 Digital Holography and Computer Generated Holograms I John T. Sheridan, University College Dublin (Ireland) 2 Digital Holography and Computer Generated Holograms II Radim Chmelik, Brno University of Technology (Czech Republic) vii Downloaded from SPIE Digital Library on 30 May 2011 to Terms of Use:

5 3 Security Holography and Holographic Diffractive Optics Richard M. Kowarschik, Friedrich-Schiller-Universität Jena (Germany) 4 Recording Materials and Information Storage I Kalaichelvi Saravanamuttu, McMaster University (Canada) 5 Recording Materials and Information Storage II Miroslav Miler, Institute of Photonics and Electronics of the ASCR, v.v.i. (Czech Republic) 6 Holographic Methods and Other Applications Antonio Fimia, Universidad Miguel Hernández de Elche (Spain) viii Downloaded from SPIE Digital Library on 30 May 2011 to Terms of Use:

6 Reduction of zero-order spatial frequencies by using binary intensity and phase modulations in holographic data storage Elena Fernández 1*, Andres Marquez 2, Diego Piñol 2, Javier Padilla 2 and Inmaculada Pascual 1 1 Departamento de Óptica, Farmacología y Anatomía, Universidad de Alicante, Apartado 99, E Alicante, Spain 2 Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Apartado 99, E Alicante, Spain * Elena.fernandez@ua.es ABSTRACT Holographic data storage is a new optical technology which allows storing an important number of bits in a recording material. In this work, two different types of modulations, defocused binary intensity modulation and phase modulation, are compared to obtain which modulation could be the most suitable for holographic data storage. The best modulation would be the modulation with a homogeneous distribution of energy in the FT plane with no zero frequency peak. Keywords: Holographic data storage, LCD, modulations. 1. INTRODUCTION In the present society new storage technologies are very important because they provide more capacity, higher density and faster data transfer, and enable more efficient data search. Conventional optical memory technologies, twodimensional surface-storage-based (like CD-ROMs and DVDs) have almost arrived at the limit of their capacity and they are becoming obsolete. In recent years there has been a focusing on the development of holographic storage techniques, in which information is not stored on the surface of the material, but in the volume 1-4. Holographic memories promise to increase storage density with higher reading speeds partly due to the inherent parallelism in the pursuit of information, and a very attractive and unique property, such as associativity allowing searches by content in parallel in all the memory. For holographic data storage, liquid crystal displays (LCD) are used as spatial light modulators which introduce the information to be stored in the material 5-8. This information is stored by holographic techniques with the interference between the Fourier Transform (FT) of the object beam and a reference beam. In general, Binary intensity (BI) modulation is commonly used for the information sent to the LCD. However, this type of modulation produces a high zero spatial frequency in the Fourier plane with an intensity several orders of magnitude higher than the other frequencies 9. As a result, the dynamic range of the material is saturated, limiting the storage capacity. The problems caused by the lack of homogeneity in the spectrum can be solved by using some other modulation schemes, such as binary phase modulation (BP) 9-12, or storing a slightly blurred version of the FT through defocusing when the BI modulation scheme is used. This paper analyzes the behaviour of these two modulations and compares the results obtained to see what modulation could be the most suitable for holographic data storage. To this end, two important parameters are compared to optimize holographic data storage: the Bit Error Rate (BER) 13, which gives us an idea of the fidelity of information stored, and a Holography: Advances and Modern Trends II, edited by Miroslav Hrabovský, Miroslav Miler, John T. Sheridan, Proc. of SPIE Vol. 8074, SPIE CCC code: X/11/$18 doi: / Proc. of SPIE Vol

7 parameter of homogeneity of the FT, which takes into account the finite dynamic range of the material. Different aspects of a realistic experimental setup are considered in the simulation, such as the finite aperture in the recording plane and the complex amplitude modulation capabilities of actual LCDs. 2. RESULTS A good storage system must allow both to store the maximum number of bits possible and that the information stored presents a high fidelity, that is, the BER of stored images is minimized. In a holographic storage device two beams interfere in the plane where the recording material is placed: the object beam which carries the information to be stored, and the reference beam, a plane wave. The information to be stored is introduced into the object beam through the LCD so that, generally, the Fourier Transform (FT) of the object is stored in the material. Since it is the FT which is stored in the material, its properties will markedly influence the fidelity of the information when reconstructed. Fig. 1 shows a basic scheme of this storage device. The polarized beam emitted by the laser was split into two beams with a beam-splitter. Each beam was expanded and filtered using a microscope objective and a pinhole. Then the beams passed through a series of lenses and diaphragms in order to obtain collimated beams with the desired diameter. The two laser beams were spatially overlapped at the recording medium intersection. An LCD was placed in the object beam between two polarizers and two quarter wave plates used as an SLM. A lens (L1) was placed in front of the SLM and the Fourier transform (FT) of the data page was obtained at a finite distance. Once the object was stored, the hologram was illuminated in the reconstruction step with the same reference beam used in the recording. Another lens (L2) was placed behind the material and the Fourier transform (FT) of the diffracted beam is obtained in the plane of the camera. z Fig. 1: Experimental setup: Li lens, SLM spatial light modulator, Δz defocus distance, z distance from data SLM to Fourier plane. Therefore, the FTis stored in the recording material. It is therefore very important to analyze the FT of the objects stored. If the FT of the object has very intense frequencies, as with binary modulation of intensity (Fig. 2a), the dynamic range of the material will be quickly consumed, thus limiting the storage capacity. To avoid this, there are other modulations for the object beam (defocused binary intensity modulation, Fig 2b, and binary phase modulation, Fig 2c), which produce a more homogeneous distribution of the energy in the Fourier plane. Proc. of SPIE Vol

8 a) b) c) Fig. 2: FT of a) Binary intensity modulation, b) defocused binary intensity modulation, and c) binary phase modulation. This paper will analyze the FT for different types of modulations to get a FT plane suitable for holographic data storage. The modulations to be compared will be: binary intensity modulation, defocused binary intensity modulation and binary phase modulation. To compare the three modulations, an object of 256x256 bits with a bit size of 4x4 pixels, i.e. 64x64 bits data page, will be chosen to do the simulations. Up and low bits are randomly distributed with a 50/50 balance, and with the following restrictions: : half of the bits have a transmittance value of 0 and half a transmittance value of 1. * : All bits have a transmittance of 1, half with a phase difference of π rad in comparison with the other half. Furthermore, in order to simulate as best as possible the laboratory system, the data page will be framed with a filling of zeros (zero padding) to simulate the finite aperture of the LCD plane. Thus the spectrum of the signal is magnified in the same proportion as the ratio of the zero padding length with respect to the data page length. This ratio is a factor of 2 in our simulation. The bandwidth is not altered, but an interpolation occurs at the frequency plane. Fig. 3a shows a random data page of the same type to be analyzed, and Fig 3b is the same figure with the zero padding. a) b) Fig. 3: a) Data page and b) data page with the zero padding. To compare the three modulations, the influences of three important parameters in the optimization of a holographic storage system are going to be discussed: the maximum peak intensity, the homogeneity and the Bit Error Rate (BER). The maximum intensity peak is defined as the highest intensity of all frequencies of the FT of the object. The homogeneity is defined as the relation between the maximum intensity peak and the mean intensity of the FT. The BER is defined as the probability of having erroneous bits in the image. To calculate the BER 13, first, we represent Proc. of SPIE Vol

9 the number of pixels obtained with a certain gray level in the black or in the white regions (Fig. 4) Zero One 40 Number Pixels Gray Level Fig. 4: Number of pixels versus grey level for black and white regions. In this figure, the number of pixels in the black region is represented by full circles and the number of pixels in the white region is represented by empty squares. As can be seen, the two distributions are clearly distinguishable, although there is an interval at which they overlap. In this interval, a certain grey level must be established as the threshold point. This threshold point is called x. From this figure, the BER is calculated from x 1 BER = W W + WB (1) N 0 x where W W and W B are the white and black pixels distributions respectively, x is the threshold point and N is the total number of pixels of the object. The BER calculation process is repeated for all grey levels in the overlap interval, obtaining the BER for each threshold point inside this interval. Fig. 5 shows the BER versus the grey level for all these threshold points. The final threshold point x and BER value of the object correspond to the minimum BER obtained. In the case of Fig. 5, the threshold point is the gray level 90, and its BER value BER Gray Level Fig. 5: BER versus grey level in the overlap interval. As mentioned, the FT of the data page will be stored in the material. So, it is desirable that this FT has a small size in order to occupy less space in the holographic memory, and then store a greater number of holograms in a certain surface area of material. To achieve this, we will limit the extent of the frequency spectrum that is recorded on the material (low pass filter), reaching a compromise between the cut-off frequency and the fidelity of the image after the reconstruction. Proc. of SPIE Vol

10 During the simulation, the spectrum will be low pass filtered applying a pupil function with a given aperture size. Having described the parameters with which the modulations are to be compared, the next step will be to generate the data page and analyze these parameters. In order to obtain realistic results, simulations with the parameters obtained from the calibration and optimization of a real SLM are used. The parameters are obtained for a LCD model Sony LCD LCX016AL-6 sold by the company Holoeye (LC2002) (Table 1). This LCD has a resolution of 800x600 and a pixel size of 32μm. The calibration and optimization processes are described in Ref. 8,14,15. The value used in the simulation for the parameter z (distance from the LCD to the Fourier plane, see figure 1) is 150 mm. We consider an aperture of the LCD of 256 pixels, i.e mm. Maximum Amplitude Minimum Amplitude Minimum Phase 0º 0º Maximum Phase 148º º As explained above, the maximum intensity peak, the homogeneity and the BER have been calculated and these parameters have been represented versus the cut-off frequency in Fig. 6 for the binary phase modulation (full squares) and for the binary intensity modulation (empty circles). The frequency has been normalized to the Nyquist frequency. We have done some calculations using the values already presented for the parameters in the simulation. For the binary intensity modulation we obtain that the intensity peak is several orders of magnitude higher than the peak obtained with the binary phase modulation: for our simulation parameters the intensity peak is about 10 9 for the binary intensity modulation whereas it is about 10 6 for the binary phase modulation. Accordingly we obtain that the homogeneity defined above is higher for the binary intensity modulation, which means that the FT of the modulation is less homogeneous than the binary phase modulation. Fig. 6 represents the BER versus the cut-off frequency of the low pass filter in the plane of the material. In this case, for cut-off frequencies higher than the fundamental frequency of the data page information (1/2 of the Nyquist frequency required to properly sample the data page), the BER is equal to zero; for the fundamental frequency, the BER for the binary intensity modulation is near to zero and the BER value for the binary phase modulation is near to 0.1. But for frequencies smaller than the fundamental frequency, the BER values are higher than 0.3, so the quality of the reconstructed image is not acceptable BER Frequency Fig. 6: BER versus the cut-off frequency. So if we compare the binary intensity and the binary phase modulation, the second one is more appropriate for holographic data storage because it has a maximum intensity peak and a homogeneity lower than the first one. And the cut-off frequency more appropriate could be 0.75 F Nyquist because it is the minimum frequency with a BER value nearest to zero. From Fig. 6 we obtain that with a cut-off frequency of 0.75 F Nyquist the BER value is closed to zero for the two modulations, but the maximum intensity peak and the homogeneity are higher with the binary intensity modulation than Proc. of SPIE Vol

11 with the binary phase modulation. Now we will analyze the usefulness of defocus binary intensity modulation applied for holographic data storage. Fig. 7 represents the maximum intensity peak, the homogeneity and the BER for the binary phase modulation (full squares), for the binary intensity modulation (empty circles with Δz = 0) and for the defocused binary intensity modulation (empty circles with Δz > 0) for a cut-off frequency of 0.75 F Nyquist. Fig. 7a represents the maximum intensity peak for the three modulations. As can be seen, the binary intensity modulation with Δz = 0 has an intensity peak 10 5 times higher than the binary phase modulation. However, the intensity peak diminishes when Δz increases (when defocus increases) and for a defocus Δz=16 mm the two modulations have approximately the same intensity peak value. Moreover, if we observe Fig. 7b, we can see that homogeneity diminishes too when defocus increases. Homogeneity is even lower than binary phase modulation for a Δz>8mm. In Fig. 7c the BER increases with Δz. However, for a Δz=16 mm, the BER value is about 0.02, so it is not very high and can be considered acceptable. In summary, binary intensity modulation may be used for holographic data storage when a defocus FT plane is registered in the material; even it could be better than the binary phase modulation for a Δz=16 mm because the intensity peak is the same, the homogeneity is lower and the BER is small. 1.E+10 1.E+05 1.E+08 1.E+04 Intensity Peak 1.E+06 1.E+04 Homogeneity 1.E+03 1.E+02 1.E+02 1.E E+01 1.E Δz (mm) Δz (mm) BER Δz (mm) Fig. 7: a) Intensity peak, b) homogeneity and c) BER versus the blur parameter for the cut-off frequency of 0.75 F Nyquist. Fig. 8 represents the maximum intensity peak, the homogeneity and the BER for a cut-off frequency of 0.5 F Nyquist versus the defocus Δz. As in Fig. 7, the maximum intensity peak and the homogeneity decrease when Δz increases, and the BER increases with Δz. For a Δz=6 mm, more and less the same values as the binary phase modulation are obtained for the intensity peak and the homogeneity. And the BER is even lower (BER phase =0.085, BER defocus =0.025). However, these values are higher than the ones obtained for the cut-off frequency of 0.75 F Nyquist. Proc. of SPIE Vol

12 1.E+10 1.E+05 1.E+08 1.E+04 Intensity Peak 1.E+06 1.E+04 Homogeneity 1.E+03 1.E+02 1.E+02 1.E Δz (mm) E+01 1.E Δz (mm) BER Δz (mm) Fig. 8: a) Intensity peak, b) homogeneity and c) BER versus the blur parameter for the cut-off frequency of 0.5 F Nyquist. 3. CONCLUSIONS In this work we have simulated the behavior of three different modulations, the binary phase modulation, the binary intensity modulation and the defocus binary intensity modulation to see which one would be most suitable to be used in the manufacture of a holographic memory. Appropriate modulation would be one providing an intensity peak, a homogeneity and a BER values as low as possible. In this sense binary phase modulation and defocus binary intensity modulation are good choices. REFERENCES [1] Dhar, L., Curtis, K., Facke, T., "Holo graphic data storage: Coming of age," Nat. Photonics 2, , (2008). [2] Graham-Rowe, D., "The drive for holography," Nat. Photonics 1, , (2007). [3] Fernández, E., Ortuño, M., Gallego, S., García, C., Beléndez, A., Pascual, I., "Comparison of peristrophic multiplexing and a combination of angular and peristrophic holographic multiplexing in a thick PVA/acrylamide photopolymer for data storage," Appl. Opt. 46, , (2007). [4] Fernández, E., Ortuño, M., Gallego, S., Márquez, A., García, C., Beléndez, A., Pascual, I., "Multiplexed holographic data page storage on a PVA/acrylamide photopolymer memory," Appl. Opt. 47, , (2008). [5] Lu, K. and Saleh, B. E. A., "Theory and design of the liquid-crystal TV as an optical spatial phase modulator," Opt. Eng. 29, , (1990). [6] Yamauchi, M. and Eiju, T., "Optimization of twisted-nematic liquid-crystal panels for spatial light phase modulation," Opt. Comm 115, 19-25, (1995). [7] Kim, H. and Lee, Y. H., "Unique measurement of the parameters of a twisted-nematic liquid-crystal display," Appl. Opt. 44, , (2005). [8] Márquez, A., Iemmi, C., Moreno, I., Davis, J. A., Campos, J., Yzuel, M. J., "Quantitative prediction of the Proc. of SPIE Vol

13 modulation behavior of twisted nematic liquid crystal displays based on a simple physical model," Opt. Eng. 40, , (2001). [9] Márquez, A., Gallego, S., Mendez, D., Alvarez, M. L., Fernández, E., Ortuño, M., Neipp, C., Beléndez, A., Pascual, I., "Accurate control of a liquid-crystal display to produce a homogenized Fourier transform for holographic memories," Opt. Lett. 32, , (2007). [10] Joseph, J. and Waldman, D. A., "Homogenized Fourier transform holographic data storage using phase spatial light modulators and methods for recovery of data from the phase image," Appl. Opt. 45, , (2006). [11] Remenyi, J., Varhegyi, P., Domjan, L., Koppa, P., Lorincz, E., "Amplitude, phase, and hybrid ternary modulation modes of a twisted-nematic liquid-crystal display at similar to 400 nm," Appl. Opt. 42, , (2003). [12] Renu, J., Joby, J., Kehar, S., "Holographc digital data storage using phase-modulated pixels," Opt. Laser Eng. 43, , (2005). [13] Coufal, H., Psaltis, D., Sincerbox, G. T., Holographic Data Storage, Springer-Verlag, New Cork, (2000). [14] Márquez, A., Campos, J., Yzuel, M. J., Moreno, I., Davis, J. A., Iemmi, C., "Characterization of edge effects in twisted nematic liquid crystal displays," Opt. Eng. 39, , (2000). [15] Fernández, E., Márquez, A., Ortuño, M., Fuentes, R., García, C., Pascual, I., "Optimization of twisted-nematic liquid crystal displays for holographic data storage," OPA 42, , (2009). ACKNOWLEDGMENTS This work was supported by Ministerio de Ciencia e Innovación (Spain) under projects FIS C02-01 and FIS C02-02 and by the University of Alicante under project GRE Proc. of SPIE Vol