High‐Performance, Nondiffusive Crosslinked Polymers for Holographic Data Storage

Research into the development of new data-storage strategies is fueled by the continuing demand for ultrahigh information capacity, increased data density, smaller form factor, and faster readout rates. Conventional data-storage devices such as magnetic hard-disk drives, optical disks, and semiconductor memories all rely on storing information bit by bit on the surface of a recording medium. However, these two-dimensional storage strategies are rapidly reaching fundamental physical limits, beyond which individual bits become too small to easily write or read and/or are inherently unstable. A promising alternative approach is based on holographic data storage, in which information is stored three-dimensionally, throughout the volume of a storage medium. This emerging field of volume holography, however, is faced with the challenge of developing suitable storage materials that meet all the stringent requirements, such as high photosensitivity, good storage capacity, dimensional stability, high optical quality, low cost, and efficient manufacturing capabilities, all necessary for commercial viability. For commercially viable holographic data-storage systems, a complete page of information is recorded as an optical interference pattern created by two intersecting laser beams within a thick (>200mm) photosensitive material. The interference pattern of these two coherent writing beams induces a periodic change in the refractive index of the recording material. A variety of photochemical reactions can be utilized to achieve such refractive index modulation. However, very few reactions exhibit quantum yields greater than unity, where one photon of light triggers numerous chemical reactions. This nonlinearity is essential for the high sensitivity and ultrafast recording speeds required for commercial holographic data storage. To achieve this, diffusion-based systems involving photoinduced polymerization reactions are currently the primary area of focus for both