Nanofocusing probe limitations for a ultra-high density optical memory

Abstract

The limitation aspects of nanofocusing recording probes are discussed in this paper. Thedefinitions of nanophotonics and nanofocusing are underlined. In this nano-age opticalnanophenomena are described for nanometric architectures and nanostructural photonicdevices. The nanofocusing probe limitations are connected with the wave-optics diffractionlimit, geometrical beam tiny focusing, electromagnetic wave design, fabricationerrors, nanoprobe energetic efficiency, near-field air gap and optical disk surfaceconditions. 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. Thecomputed finite differential time domain (FDTD) power density spot is under 200 nmwithout any optical optimization. The far-field functions have a diffraction limit of150 nm. The energy intensity can be elevated by more than 70 times in the FDTDcalculated focal point using a convex microlens (ML) surface for focusing of a8 µm vertical-cavity surface-emitting laser (VCSEL) beam. The optical power density iscompressed up to 1024 times to the exact nanofocused spot in comparison with theentrance VCSEL micro-beam. The experimentally fabricated ML arrays and single lensesare presented. The optical quality and ML radius control with an AFM method isfulfilled. The optical integration technology for the proposed nanofocusing probefabrication is announced. The nanofocusing probe spots are 10–13 nm for thecentral zone of the ML surface. The merit spot sizes are 10–18 nm for the entireML nanofocusing diameter. For a single ML nanofocusing near-field head theenergy spots have sizes from 9 to 15 nm, limited by technological aberrations.