This paper introduces the concept of TwoDimensional Optical Storage (TwoDOS). In this concept, bits are written in a broad spiral consisting of a number of bitrows stacked together in a hexagonal packing. Bits with a value '1' are represented physically as circular pit-holes on the disc, while bits with a value '0' are characterized by the absence of such a pit-hole. A scalar diffraction model is used to calculate the signal levels for various diameters of the pits. A stripe-wise Viterbi detector is proposed to perform 2D bit-detection with a limited state complexity of the trellis. Simulation results are shown for various diameters of the pits. A 2D modulation code is applied to eliminate patterns that yield a high probability of erroneous detection.

With storage capacities increasing much faster than data rates, fast read-out of content is becoming a bottleneck for the convenient use of optical storage devices. Two-Dimensional Optical Storage (TwoDOS) is a new concept that solves this data-rate problem by using a multi-spot parallel readout system. In addition, the storage capacity is increased with a factor of at least 2. Using the same read-out physics as in the Blu-ray Disc standard, single layered 12 cm discs with capacities up to 50 GB have been read out successfully at bit-rates as high as 560 Mbit/sec. Basic pillars of TwoDOS are advanced signal processing and disc mastering techniques, and a proper design of the optical path.