Time-domain holographic optical-storage technique yields digital memory

Time-domain holographic optical-storage technique yields digital memory

A grou¥from SRI International (Menlo Park, CA) has demonstrated an optical-storage method for page-formatted digital data based on time-domain holography--a technique that could allow high-performance input and output of data to an optical-storage system. Digital data pages were generated by illuminating a spatial light modulator with 11.2-µs pulses from a ring dye laser operating at about 580 nm. Each page was stored by wavelength-division multiplexing in a distinct channel of about 500 kH¥within the inhomogeneously broadened absorption line of a 7-mm-thick crystal of europium-doped yttrium oxy-orthosilicate (Eu3+:Y2SiO5) held at a temperature of about 4 K. The Eu3+ ions responsible for data recording are resonantly excited by the laser pulses to form population gratings that resemble the Fourier spectra of the pulse pair--reference and data beams. After recording, data were retrieved at a peak rate of 300 Mbit/s without the use of error-correcting codes. Using a detection scheme for the extraction of binary data, the system raw bit-error rate was 10-7, meaning that 10 Mbit of data could be stored without generating an error.