SERODS: A NEW MEDIUM FOR HIGH-DENSITY OPTICAL DATA STORAGE
Recently, extensive efforts have been devoted to investigating new generations of data storage devices based on nonmagnetic principles, such as optical data storage systems. Optical data storage systems can provide a unique combination of superior performance features that make them most appropriate for large-memory applications. Optical data storage disks also promise to offer low cost-per-byte, improved accessing characteristics and higher storage efficiency. We describe here recent developments of a unique approach for optical data storage based on the surface-enhanced Raman scattering (SERS) effect (1). The application of this SERODS technology for high-density optical data writing and reading in conjunction with three-dimensional data storage is also demonstrated. The SERODS technology is based on the principle that the enhanced light-emitting properties of certain molecules embedded in an optical medium can be altered at the molecular level to store information (1, 2). With the SERODS technology, the molecular interactions between the optical layer molecules and the substrate are modified by the writing laser, changing their SERS-emission properties, so that they are encoded to store information as bits. The Raman effect occurs when light, such as from a laser, is directed at a substance and induces a back-scattering emission of the light. When molecules are close to a rough metal surface, they emit a strongly enhanced Raman emission, called "surface-enhanced Raman scattering" (SERS). Normal Raman signals are very weak and cannot be easily detected. The SERS effect, however, can enhance the Raman signal up to 108 times, and make Raman detection possible for optical data reading with the SERODS technology. Conventional optical disks store data in the form of microscopic pits that have been physically burned by a writing laser onto a reflective surface of a disk. With the SERODS technology, the molecular interactions between the optical layer molecules and the substrate are modified by the writing laser, changing their SERS-emission properties, so that they are encoded to store information as bits. In the SERODS system, information is recovered from the recorded medium by detecting the changes in the SERS signal from the altered molecules by using a photometric detector to track the changes in the amplitude and spatial distribution of the SERS signal from different sub-microregions on the disk. Since the SERS-emitting properties are extremely sensitive to molecular microenvironments, lower laser energies (shorter pulses and/or faster rate) producing much smaller "molecular holes" are required for the writing process. A reading laser with much lower energy and a photometric detector, tuned to the frequency of the Raman emissions, are used to retrieve the stored information.