Study Of The High Density Optical Data Storage Using Solid Immersion Lens

The technique of optical data storage is an important data storage that arises from 1970s following magnetic storage. This technique has been paid popular attention by its virtues such as high density, large capacity, long life and multi-functions etc. It is crying out for exploitation and introduction higher density storage techniques to satisfy the high-speed development of information storage. The favorable developmental trend of optical data storage to high density, high data rates, multi-function and small size make it occupy the dominant position and become the pillar in the domain of data storage.In this article, the fundamental principle and current research of optical data storage including CD and DVD, three-dimensional optical data storage and near-field high-density optical data storage are summarized. A two-dimensional finite difference time domain program for analysis of solid immersion lens system is compiled. The optical near-field distribution and propagation properties of solid immersion lens system are analyzed in detail when illuminated by linearly polarized focusing gauss beam. The change of the optical intensity and beam dimension at the bottom of solid immersion lens with different refractive index and different distance are discussed. The simulated results reveal that the higher the refractive index is, the stronger the optical intensity and the smaller the beam dimension at the bottom of the solid immersion lenswill be. The optical field attenuates as exponential function and the transmitted beam expands quickly with the increase of the distance away from solid immersion lens. And it is also found that the polarized incident gauss beam become depolarized after emitting from the bottom of solid immersion lens. The beam dimension of the emitting optical field at the near-field bottom of solid immersion lens is "broadened". When only allows the total internal reflection beams focus on the small aperture, which is formed at the center of metal film coated on the bottom of solid immersion lens, the optical fields propagated from the aperture of different dimension is first simulated. It turns out that the beam diameter increases more slowly within half of the wavelength in specified aperture size, and indicates that it is possible to increase the distance between the recording layer and solid immersion lens without decreasing the recording density. Meanwhile, solid immersion lens is also applied to focus femtosecond laser pulse in three-dimensional optical data storage. High-density optical data has been recorded at the surface of polyethylene methacrylate (PMMA) and a 5-layers reading and writing of data is achieved in fused silica using 800nm, 150 femtosecond laser pulses. The data arrays in fused silica shows 2.5um separation between two layers and 0.6um separation between two bits, theoretically, 1.1Tbits/cm3 volumetric density has been demonstrated in this way. To our best knowledge, it is the highest writing density in transparent materials with femtosecond laser pulse. The feasibility and some advantages of employment of SIL have been discussed. The numerical aperture arecalculated when laser pulse is defocusing. In contrast with traditional microscopy objective, the employment of solid immersion lens can effectively increase the numerical aperture of the recording system; thereby it can increase the volumetric density and decrease the demand of the incident laser power. In conclusion, solid immersion lens, which is feasible to focus femtosecond laser pulse in three-dimensional optical data storage, shows the rather potential to increase the volumetric density.