Magnetic tape and hard disk drives hold much of the world’s archival data. Compared with other memory and storage technologies, optical data storage in tape and disk drives cost less and are more reliable. Archivists may soon have another option—using an extremely fast laser to write data into a 2-millimeter-thick piece of glass, roughly the size of a Post-it note, where that information can remain essentially forever. With this optical data storage method, researchers could theoretically store up to 360 terabytes of data on a disc the size of a DVD.
Writing data to glass involves focusing a femtosecond laser, which pulses very quickly, on a point within the glass. The glass itself is a sort known as fused silica. It’s the same type of extremely pure glass used for the Hubble Space Telescope’s mirror as well as the windows on the International Space Station.
The laser’s pulse deforms the glass at its focal point, forming a tiny 3D structure called a voxel. Two properties that measure how the voxel interacts with polarized light—retardance and change in the light’s polarization angle—can together represent several bits of data per voxel. The research is part of an initiative to improve cloud storage through optics.