Nanofocusing probe limitations for a ultra-high density optical memory

The limitation aspects of nanofocusing recording probes are discussed in this paper. The definitions of nanophotonics and nanofocusing are underlined. In this nano-age optical nanophenomena are described for nanometric architectures and nanostructural photonic devices. The nanofocusing probe limitations are connected with the wave-optics diffraction limit, geometrical beam tiny focusing, electromagnetic wave design, fabrication errors, nanoprobe energetic efficiency, near-field air gap and optical disk surface conditions. The micro-structure of the designed near-field optical head is discussed. The obtained nanofocused spot size is about 20 nm for the near-field space. The computed finite differential time domain (FDTD) power density spot is under 200 nm without any optical optimization. The far-field functions have a diffraction limit of 150 nm. The energy intensity can be elevated by more than 70 times in the FDTD calculated focal point using a convex microlens (ML) surface for focusing of a 8 mum vertical-cavity surface-emitting laser (VCSEL) beam. The optical power density is compressed up to 1024 times to the exact nanofocused spot in comparison with the entrance VCSEL micro-beam. The experimentally fabricated ML arrays and single lenses are presented. The optical quality and ML radius control with an AFM method is fulfilled. The optical integration technology for the proposed nanofocusing probe fabrication is announced. The nanofocusing probe spots are 10-13 nm for the central zone of the ML surface. The merit spot sizes are 10-18 nm for the entire ML nanofocusing diameter. For a single ML nanofocusing near-field head the energy spots have sizes from 9 to 15 nm, limited by technological aberrations.