2. Information Photonics Research Center, College of Photonic and Electronic Engineering, Fujian Normal University, Fuzhou, Fujian 350117, China
Overview: Optical data storage is suitable and economical for a data center and an archive storage system with the advantages of long lifetime for storing digital data. However, traditional optical data storage methods including CDs, DVDs, and Blu-ray Discs face technical obstacles in obtaining further large-capacity optical data storage. Holographic optical data storage is a potential technology in the next generation of optical storage due to its high capacity for data storage and its high speed of data transmission.
In this paper, the concept of polarization holography is firstly introduced. In contrast to conventional holography which record the intensity gratings formed by two waves with same polarization, polarization holography records polarization gratings fabricated by waves with mutually orthogonal polarization. The polarization holographic gratings can diffract laser wave and shift the polarization state of diffraction wave at the same time. With the unique capacity of recording and retrieving intensity, phase and polarization state simultaneously, the polarization holographic gratings are expected to be applied in high density optical storage. Then, theory of polarization holography is briefly investigated and some unique properties based on newly developed vector theory are discussed. Compared with conventional holography, the reconstruction of polarization holography is more complicated. The Jones matrix has been applied to polarization holography for a long time. However, the calculation of the Jones matrix is commonly limited in paraxial approximation, as the solution of it would become quite complex without the limitation. In 2011, Kuroda et al. proposed a new tensor theory that provides a simple solution of polarization holography under non-paraxial approximation. In this theory, the hologram was divided into intensity and polarization parts and expressed as a tensor product of the interference electric field. Therefore, the crossing angle can be arbitrary with any polarized waves. Henceforth, several theoretical and experimental research studies have been proposed based on this new tensor theory.
At last, the further applications of polarization holography in high density data storage are briefly overviewed. Sever methods of polarization multiplexed holographic recording have been proposed with polarization holography. In dual-channel holographic recording with orthogonal linear polarization holography, two polarization encoded holograms were recorded in a dual-channel recording system with negligible inter-channel crosstalk. And the two polarization multiplexed holograms could then be sequentially or simultaneously realized by shifting the polarization state of reference wave. Further, vector hologram in which the vector beams are recorded and reconstructed has been realized by polarization holography.
In conclusion, polarization holography is an attractive technique for its unique capacity of recording intensity, phase, and polarization of a wave simultaneously. With the help of polarization holography, holographic data storage can further improve its storage density by fully using of multi-parameter of light wave including intensity, phase and polarization states.