Design of cover-layer-incident dual layer near-field recording optics using elliptical solid immersion lens

We propose the design of novel optics for media within a dual-layer near-field recording (NFR) device using an elliptical solid immersion lens (E-SIL). E-SIL-based near-field optics is designed for cover-layer-incident dual focus positions with a high numerical aperture of 1.4 in the region around lambda = 405 nm. In this design, to improve the small optical tolerance for each imaging position and to insure the ability to fabricate the device, an additional aspheric lens surface is added on top of the hemispheric lens, and it is combined with zoom optics which are composed of two single lenses. To compensate for serious chromatic aberrations which happen seriously in optics using blue laser diodes, a diffractive optical element (DOE) is used. Using zoom optics, an additional aspheric lens surface, and DOEs together, wavefront aberration is effectively reduced over a broad range of variation in cover layer thickness and wavelength. In addition, in this study, an air-gap-induced aberration in the designed NFR optics is briefly observed.