Edwin P. Walker

Two-Photon Three-Dimensional Optical Storage Memory

We describe the design and construction of ultrahigh capacity three-dimensional, 3D, optical storage devices that operate by two-photon absorption. The molecular systems and their properties that are used as two photon media for writing and one photon for accessing the stored information within the volume of the device are presented in some detail and the nonlinear two-photon absorption mechanism is briefly visited. The optical system and its components, which facilitated writing and reading, are also described and the bit density, bit error rate, store and access speeds, cycle times, and stability of the materials under various experimental conditions are also topics addressed in this review. The first ever storage of terabyte data in a removable storage disk is described in detail.

Two-photon technology: A new dimension

Conventional optical technologies store data on the surface of a recording medium. Two-photon technology, which relies on overlapping light beams, can be used for three-dimensional multilayer storage and promises capacities of up to 10 Tbyte on a DVD-size disk.

Multi-layer Optical Data Storage Based on Two-photon Recordable Fluorescent Disk Media

In this paper, we present a technology that can be used for random accessed mass optical data storage. The technology uses a two-photon recordable plastic disk medium that can fluoresce when recorded and that can support multiple stored data layers inside one disk. This technology is capable of achieving 200GB data capacity with a 120mm diameter, 10mm thick disk, and a data transfer rate of Gigabits/Sec by using parallel readout.

3-D parallel readout in a 3-D multilayer optical data storage system

The conventional approach to achieve high readout data rates in single-layer disk media data storage systems is to decrease the physical bit size and increase the velocity at the head/media interface. Further increase in data throughput may be achieved by parallel readout architectures that read information across a number of data tracks simultaneously within a given data layer. Call/Recall, Inc. has developed and demonstrated a parallel readout architecture where data tracks are read in parallel across multiple layers in depth, as well as across a number of radial tracks. Theory, simulations, and experimental results of this 3D multiple-layer multiple-track parallel readout system are presented. The experimental result presented is from a 64 parallel data channel readout system that reads 16 radial data tracks on 4 data layers in parallel from a two-photon recorded monolithic multilayer disk.

Two-photon volumetric optical disk storage systems experimental results and potentials

Recent performance in two-photon volumetric data storage is presented. Experimental results are presented and theoretical potentials are analyzed.

Parallel access 3D multilayer optical storage using 2-photon recording

Three-dimensional parallel readout of 2-photon multilayer optical disks can simultaneously offer high capacities (greater than 100 GB/disk) and high data transfer rates (greater than 1 Gb/s). The robust system tolerances should enable cost effective storage systems with capacities and transfer rates that are scaleable to match various application requirements.

Present performance and future directions in two-photon addressed write once read many (WORM) volumetric optical disk storage systems

Current performance in two-photon WORM volumetric write once read many data storage systems is presented and future directions discussed. Influence of numerical aperture in a 3-D multi-layer optical data storage system is analyzed.

Two-photon 3D high-density optical storage media: optical properties, temperature, radiation, and fatigue studies

We have employed new molecular media for volumetric data storage by means of two photon absorption. The optical and spectroscopic characteristics of the materials that are relevant to volumetric optical storage are described. In addition, fatigue characteristics of the photochromic media and substrates used in the fabrication of the storage devices are presented. These include temperature, read/write/erase cycles and space environments such as heavy ion and proton radiation, and heat under vacuum.

Two-photon 3D optical data storage disk recording and readout

Two-photon 3D optical data storage techniques can achieve hundreds of GB data capacity per disk by storing data in multi-layer volumetric media. This approach can also provide fast data transfer rates by using parallel access techniques. It is a promising solution for the high data capacity demands in imaging and video applications, and the high-speed data access requirements in large-scale high- speed data processing. Development of this technology integrates and leverages developments in parallel sensors, spatial light modulators, novel optics, parallel signal processing, and micro-optic packaging.

Capacity of a 3-D multi-layer optical data storage system

A high capacity 3D multi-layer optical data storage system is being developed at Call/Recall, Inc. A single beam two-photon recording technique is used to record data tracks and layers within a monolithic thick plastic disk (D.A. Parthenopoulos and P.M. Rentzepis, Science vol. 245, pp. 843-845, 1989; H. Zhang et al., Proc. SPIE vol. 4090, pp. 174-178, 2000). The recorded bits emit broadband fluorescence when excited by a laser beam within the absorption band of the written molecule. The recorded volume has no noticeable index change in the visible spectrum. The recorded bits are non-reflective for the readout beam and recording beam. These properties allow the recording and readout beams to access multiple layers in parallel (H. Zhang, 18th IEEE Symp. Mass Storage Systems, pp. 225-236, 2000; E.P. Walker et al., ODS 2002; E.P. Walker et al., ODS 2001, Proc. SPIE, 2001). The capacity of the two-photon 3D multi-layer optical data storage system is influenced by the recorded bit volume, track pitch and layer separation.