We propose multi-layer near-field recording with using inner focus mode. The restricted conditions for multi-layer near-field recording are discussed from the viewpoint of both media structure and optical setup. One solution is presented for dual layer recording with a numerical aperture (NA) of 1.5 and a wavelength of 405 nm as a light source of GaN laser diode.
In the proposed layer structure, a Nb2O5 material has been adopted as the intermediate layer because of its high refractive index, n = 2.4, in order to prevent the decrease of beam propagation that corresponds to NA>1. Almost the same signal characteristics can be obtained from both recording layers at the air gap of 40 nm. The adjustment of focusing position and the compensation of spherical aberrations have been implemented by the combination of an expander lens unit and a liquid crystal (LC) panel in the optical setup.