Volume81, number 6 OPTICSCOMMUNICATIONS 15 March 1991 Color holographic storage in LiNbO3 Francis T.S. Yu, Shudong Wu, Andy Mayers and Sumati Rajan The PennsylvaniaState University, Department of ElectricalEngineering, UniversityPark, PA 16802, USA and Don A. Gregory The U.S. Army Missile Command, Research Directorate, RedstoneArsenal, AL 35898-5248, USA Received 3 August 1990 Experimentaldemonstrationsof real-time color holographicstorage in LiNbOs using a "white light" laser are presented. The geometry of the recording setup and wavelengthcrosstalkare discussed. Two of the most widely used white-light holo- grams must be the reflection hologram of Denisyuk [1 ] and the rainbow hologram of Benton [2,3]. In reflection hologram, a thickness emulsion of about 20 ~m would have a wavelength selectivity about A2/ = 1/40, which is high enough to produce color hol- ogram images without significant color blur. How- ever, the physical requirements for constructing a re- flection hologram is rather stringent, which prevents its wide spread use of applications. On the other hand, construction of a rainbow hologram requires a narrow slit, for which the parallax information of the hologram image would be partly lost. In this communication, we shall demonstrate that color holograms can be constructed in a photore- fractive crystal using a "white-light" laser. Since photorefractive crystal is much thicker than conven- tional photographic emulsion, it provides a higher wavelength selectivity such that the color blur can be minimized. Furthermore, the construction of pho- torefractive holograms is in real-time mode and the shrinkage of the emulsion can be prevented. As in contrast with the photographic film, multiplexing color holograms in a photorefractive crystal is possible. By applying the coupled wave theory [4 ] in thick emulsion hologram, as illustrated in fig. 1, wave- (a) (b) Fig. I. Wdting angle. (a) Transmission hologram. (b) Reflec- tion hologram. length selectivities for transmission and reflection hologram can be shown as [ 5 ] (~) (~ - sin2a)'/2 A -A- t = sin2a d' ( 1 ) and T ,= (n2-cos2ap/ ' (2) where a is the incident angle and q is the refractive index of the hologram. The normalized wavelength selectivities as a function of incident angle are plot- ted in fig. 2, where we notice that the wavelength se- 348 0030-4018/91/$03.50 © 1991 - ElsevierSciencePublishers B.V. (North-Holland)