(Received November 30, 2007; accepted March 6, 2008; published online July 18, 2008)
Page-oriented holographic data storage systems (HDSSs) generally use spatial light modulators (SLMs) to generate two-dimensional (2D) digital patterns, so-called data pages. These data pages are stored via interference patterns of the object and reference beam in the holographic medium and are retrieved from the medium by exposing it to the reference beam. The reconstructed data pages are then detected by a matrix detector. One important challenge in designing an HDSS is to develop a suitable modulation, which takes into account the specific characteristics of the transfer channel and enables high data capacity, high data transfer rate and low symbol error rate (SER). In this paper, we present a new method for modulating data in an HDSS. The main idea is to adapt the general concept of 2D run-length limited modulation (RLL) to a numerically more efficient implementation usable for HDSS. We demonstrate that this 2D block coding method with a constant weight and a sparse code increases the amount of user data per data page, while the SER remains low compared with standard sparse modulation coding. This results in a higher data rate and higher data density.
KEYWORDS:holography, storage, modulation, run-length limited