Optical nano-apertures for near and far field applications

Nan Zhou, Purdue University


By providing a connection between the freely propagating radiation and the localized energy, optical antennas are important for subwavelength manipulation of light. This report focused on aperture-based optical antennas and the associated physical properties. The efficiency of different energy transfer processes can be enhanced taking advantage of surface waves. It is found that to enhance optical transmission through subwavelength apertures, propagating waves have to be resonantly coupled to surface plasmons and localized surface plasmons. For an aperture in real metals, the waveguide and circuit analysis indicates that the cutoff wavelength, mode index and effective impedance can be controlled over a wide range of frequencies. Inspired by the Babinet’s principle, strong magnetic resonances have been demonstrated in complementary bowtie apertures (CBA), and the magnetic enhancement can be further improved by adding periodic grooves. When the apertures are placed in an array and combined with a metal ground, a near-perfect absorption/emission is demonstrated in the near- and mid-infrared. Extracted effective optical constants indicate a significant light manipulation through engineered nanostructures, which is promising for enhancing near-field radiative heat transfer. Optical nano-apertures play an important role in heat-assisted magnetic recording (HAMR), where they function as near field transducers (NFTs) to temporally and locally heat a sub-diffraction-limited region in the recording medium to reduce its magnetic coercivity. We investigate the possibility of applying half-bowtie and full bowtie apertures as NFTs. Using the bowtie aperture NFT, the parametric study of permittivity indicates that it is promising to simultaneously deliver higher power and reduce heating by engineering materials with as small as possible loss and a moderate real part of the permittivity. for generating elongated thermal spots to match the bit aspect ratio on the recording track Finally, we also carry out full simulations and experiments out to demonstrate that the scattering-type near field scanning optical microscope (s-NSOM) can resolve both the amplitude and phase of near fields of a bowtie aperture, provided that signals are demodulated at higher order harmonics of the tip oscillation.




Xu, Purdue University.

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