Applications of Nonlinear Super-Resolution Thin Films in Nano-optical Data Storage

Abstract

Optical storage is very useful for high-definition digital television, data distribution, and memory. With the development of information technology, the capacity of optical storage devices is required to become larger and larger. Correspondingly, the density is also required to become higher and higher. In order to improve the density, one has to reduce the information bit size. The size is determined by the optical diffraction limit. That is, D ∼ 1.22 /NA, where D is the size of the focused spot, laser wavelength in vacuum, and NA the numerical aperture of optical pickup. In order to improve the capacity and density of optical storage devices, one has to shorten the laser wavelength and increase the numerical aperture of optical pickup. However, a larger NA will reduce the focal depth of pickup and increase comatic aberration when the disk tilts against the optical axis. So far, for farfield optical storage, the NA of pickup has been very close to the theoretical limit (NA = 1). To reduce the mark size, a short wavelength laser source must be used. The laser wavelength has been decreased from 780 nm for compact discs to 405 nm for blue ray disks. Further shortening the laser wavelength is difficult due to the high product cost and low transmission of general optical elements at wavelength below 360 nm.In this regard, the near-field optical probe is a very good method to generate small spot due to avoidance of the diffraction limit, and it can also record nanometric information marks. However, the low optical transmission and some problems in controlling the near-field distance between the probe tip and the sample surface meet difficulties in application to the high-speed rotation optical disk system. The solid immersion lens near-field method can obtain a subwavelength spot and produce nanometric information marks. It can also maintain a higher optical