Sony Corp. announced that it has succeeded in enhancing the data transfer rate of its coaxial type holographic data storage system from 3 Mbps to 107 and 92 Mbps when writing and playing back, respectively (lecture number: WDPDP2).
In the coaxial type holographic data storage system, recording and reference lights are provided on the same optical axis. In Sony's system, a recording light with embedded data is arranged in the center of a laser beam while a reference light is located on the periphery of the beam so that the two lights interfere with each other, thereby recording two-dimensional barcodes (page) including information onto a recording medium.
Sony utilizes the image-stabilizing technique to enhance the data transfer rate at the time of recording and playback. The laser beam is controlled to follow the rotation of the disc medium so that the disc can be irradiated with the beam on one spot for as long as possible, thus increasing the data transfer rate. An optical component called scanning device that reflects the laser beam is employed to control the beam to follow the disc.
This time, two major improvements have been added in order to enhance the data transfer rate at the time of recording. First, Sony has revised the page format. Second, the company has employed an optical deflector with a high driving frequency as the scanning device. The amount of information contained per page is 63.5 kb and the number of pixels in the signal light is set to 252 x 252. The maximum driving frequency is 20 MHz.
In addition to these improvements, a CMOS sensor featuring a frame frequency of 1.5 kfps has been adopted to increase the data transfer rate at the time of playback. The pixel count is 512 x 512. The data transfer rate at the time of playback increases as the frame frequency of CMOS sensor that receives the reproduced signal light and converts it into an electric signal is enhanced.
The system employs a blue laser unit composed of a semiconductor laser diode and an external oscillator. The laser output when recording is 2.9 mW, while that at the time of playback is 2.1 mW. The system performs multiplex recording of 100 pages of data and plays them back. In the future, the company aims to increase the transfer rate to 1 Gbps by enhancing the laser output and sensitivity of the recording medium as well as increasing the data amount per page.