17 Jun 2002
A novel production technique solves holographic data storage problems.
Researchers from the National Research Council of Canada and the Complutense University of Madrid, Spain, have developed a new photopolymerizable glass, which they claim is ideal for holographic data storage.
Pavel Cheben and Maria Calvo's material is based on a titanocene photo-initiator and a high-refractive-index acrylic monomer dispersed in a porous silica matrix. They claim that the glass has all of the properties that are crucial for permanent data storage, including easy fabrication into thick films or monoliths to optimize storage density.
In the past, holographic photopolymers have contained photo-initiators and monomers dispersed in a polymer binder, but Cheben claims that these binders have two major drawbacks. "The binders limit the thickness [of the holographic photopolymers] to less than 200 µm," he said in Applied Physics Letter 78 1490-1492. "Also, temperature and light-induced shrinkage can distort the holograms and degrade data retrieval."
To overcome these problems, Cheben experimented with a processing method called the "sol-gel technique" which allowed him to replace the binder with an inorganic glassy host. With help from colleagues at Madrid's National Institute for Aerospace Technology and the Consejo Superior de Investigaciones Cientificas, Cheben managed to record the first thick holograms in an organically modified glass. He now believes that the latest material meets most of the critical requirements for volume holographic data storage.
"Our glass allows us to fabricate samples that are several milimeters thick, and experiments show that the holograms stored in the glass are permanent and stable," he said. "The failure to make photopolymers like these has been the main obstacle in developing holographic write-once memories."
Cheben and Calvo will now optimize the photopolymerizable compositions of the glass and also look at chemical and environmental stability issues. The potential for rewritable storage materials has already been tackled in previous research (see Nature 408 64-67).