Content area
Full Text
Introduction
With the development of information technology, the amount of data is increasing in the exploding way. International Data Corporation (IDC) forecasted that the global datasphere will grow to 163 ZB (1 ZB=109 TB) by 20251. That is ten times the 16.1 ZB of data generated in 2016. The pressure of data storage is increasing sharply. Traditional huge data storage ways are mainly hard disc, tapes and optical disc which will be difficult to cover the demand of data growth in several years. Since cold data (data long time without use) occupies majority, the demand of data long time storage becomes more important. Traditional hard disc storage consumes huge electricity to cooling data base. The cost of electricity has been over 50% of total cost of data storage. Optical storage has the advantage of saving data for a long time due to its preserving data almost without electricity. Collinear holographic data storage technology presented mainly in the following content is one of the optical storage technologies, which also has this advantage.
Since holography was proposed by Dennis Gabor in 19482 and laser was invented in 1960s, holographic applications were paid attention to widely. One of its applications is the holographic data storage, an optical storage technology. The concept of holographic data storage was proposed by Van Heerden in 19633. In the writing process, the data to be recorded are encoded into 2-dimensional data pattern, called 2-D signal page data. A laser beam is modulated by the signal page data, called signal beam. The signal beam interferes with another laser beam called reference beam. The interference pattern is recorded in the holographic media, as shown in Fig. 1(a). In the reading process, only the reference beam is employed to illuminate the holographic media to reconstruct 2-D page data image as shown in Fig. 1(b). After decoding the reconstructed 2-D page data image, the user data will be obtained.
[Image omitted: See PDF]
There are three main characteristics in the holographic data storage including volume holographic recording, multiplexing recording and 2-D signal page data transfer. Compared with traditional optical data storage technologies, shown in Fig. 2, the volume holographic recording can increase the storage density, multiplexing recording can increase the storage...