Abstract

We have demonstrated high density (>10¹¹ bits/cc) optical recording of information in a 3-D multilayer format. Information is written in a homogeneous negative photoresist as volume elements of increased index of refraction. The index increase results from crosslinking and shrinkage of the polymer induced by two-photon excitation of the photosensitizer at the waist of a highly focused beam of subpicosecond colliding pulse mode-locked laser. Quadratic dependence of two-photon excitation on incident instantaneous intensity confines crosslinking to the focal volume; therefore bit array layers may be written with thicknesses of the order of the confocal parameter. We have succeeded in writing eight well resolved bit planes in a ~30-µm thick polymer film. Information may be read by differential interference contrast or confocal microscopy. The potential for employing this technique in multilayered write-once-read-many optical storage disks is compared with other schemes for implementing 3-D optical data storage including two-photon fluorescence methods.

© 1991 Optical Society of America