Impact of phase aberrations caused by multilayer optical data storage in weakly inhomogeneous media

Various multilayer optical data storage methods have been proposed in which bits are written in an initially homogeneous material. To varying degrees, all of these methods will be constrained by phase aberrations that decrease the Strehl ratio as the number of layers and index perturbation of each bit are increased. Although the exact problem is theoretically and numerically intractable, statistical derivations of the impact are possible. These analytic expressions are derived and validated with simulations of low-capacity disks, and then are used to establish limits in the interesting high-capacity case. The resulting approximate expressions are shown to be remarkably simple and also potentially serious in limiting multilayer data storage capacities.