2. Fujian Provincial Key Laboratory of Photonics Technology, Fuzhou, Fujian 350117, China;
3. Fujian Provincial Engineering Technology Research Center of Photoelectric Sensing Application, Fuzhou, Fujian 350117, China
Overview: The development of optical holographic data storage technology in the past 50 years is reviewed briefly according to time line in this paper. With the continuous development of key devices and materials, optical holographic data storage technology is becoming more and more mature. At present, in the era of Big Data, the demands for data storage density and data transfer rate are greater than ever before. Optical holographic data storage has become a potential candidate for the next generation of data storage technology because of its advantages of high storage capacity, fast data transfer rate, and long storage life. The theoretical researches of holographic data storage were done mainly in 1970s~1980s including some multiplexing technologies. The developments of key devices such as spatial light modulator and detector and recording material such as lithium niobate crystal and photopolymer pushed holographic data storage technology into practicability quickly in 1990s~2000s. In the aspect of system, there are two kinds of holographic data storage systems on-axis and off-axis. For instance, collinear holographic data storage system (CHDSS) by Optware corporation and 2-axis HDSS by InPhase corporation. 2-axis HDSS can provide sensitive Bragg selectivity to achieve high storage density by using angular multiplexing. CHDSS owns more compact structure, simpler operation and stronger compatibility by combining with servo system and by faster recording shifting multiplexing. In this paper, a comparison between two systems was given. We believe CHDSS may be the cornerstone of further practicality of holographic storage technology. In the aspect of code, conventional HDSS owns low code rate because it uses amplitude modulation which meanwhile gets low signal noise ratio (SNR) due to the overconsumption of dynamic range of recording material. To solve this problem, phase modulation is used in the HDSS to increase code rate and SNR. One challenge of phase modulation is that phase cannot be detected by the camera which can be solved by using interferometric and non-interferometric methods. Several phase retrieval methods are also mentioned in this paper.