Recent recording areal density and integrated drive performance demonstrations using Heat Assisted Magnetic
Recording (HAMR) suggest that it is a viable technology to succeed conventional magnetic recording. However
challenges still remain for the near field transducer, in particular reliability and sufficient thermal confinement. We
explore a new NFT design, Near field Transducer Gap (NTG), which offers the potential to mitigate some of the issues
in track confinement and thermal profile compared to earlier published studies . The design offers efficiency
improvements, and the potential to reduce unwanted background light and heating that can lead to erasure in the writing
track, and neighbors.
In this invited paper, we review some of our latest works on plasmonic antennas and their interactions with photonic
angular momentum. As receiving antennas, both theoretical and experimental results reveal that spiral plasmonic
antenna responds differently to photons with left-hand circular polarization and right-hand circular polarization. This
spin degeneracy removal finds many potential applications including extremely small circular polarization analyzer for
polarimetric imaging, parallel near field probes for optical imaging and sensing, nano-lithography and high density heat assisted magnetic recording. On the transmitter side, through coupling quantum dot nano-emitters to spiral plasmonic antenna, nano-scale spin photon sources with high directivity and circular polarization extinction ratio is demonstrated. Numerical modeling and experimental evidences also indicate that the emitted photons can be imprinted with the photonic spin angular momentum and orbital angular momentum information simultaneously via the interactions between photonic angular momentum and plasmonic antennas. These findings not only are useful for the fundamental understanding of the interaction between plasmonic antennas and photonic angular momentum but also illustrate the versatility of plasmonic antennas as building blocks for practical spin optics and quantum optics devices and systems.
We proposed a discrete complex amplitude filter to create a focused hollow field with ultra long depth of focus. As for a
high numerical aperture lens (NA=0.95), the focused field in the focal region can be engineered into a field like a long
"tube" with flat wall through manipulating the distribution of the transmitted amplitude and phase at the pupil plane.
This complex amplitude filter at the pupil plane can be discretized into multiple annular zones with different radius,
transmittances and phase delays. A focused tube field with long depth of focus(~9λ) has been created as an example
through separating and averaging of the projected pupil radiation pattern of magnetic dipole array in the focal region.
Imperfections of the designed filter will influence the quality of the generated optical tube field and tolerance deviation
of the radius, transmittance and phase delay in each zone is discussed. For the optical trapping, this created tube field can
expand the manipulated distance and increase the trapped particles' numbers.
Subwavelength metallic structures capable of creating strongly localized electromagnetic field with enormous
enhancement under illumination/excitation are designed for direct radio frequency (RF) imaging. Three dimensional
finite element method models are applied to investigate the electromagnetic field concentrations of two types of split
ring resonators. Under appropriate linearly polarized illumination, a highly confined field located at the gap of the ring
resonator is found due to strong scattering resonance. The numerical studies show that field enhancement as high as
6,800 is achieved for a planar D-shaped split ring resonator. The enhancement can be further increased through shrinking
the gaps size or the ring width. Crescent shaped split ring resonator is designed for broadband application. It provides an
enhanced bandwidth which is 1.15 times of the resonant frequency. The concentrated electromagnetic field facilitates
nonlinear processes that find lots of applications. Optimized RF concentrators integrated with electro-optic modulators
are demonstrated to directly modulate optical carrier. The combination of RF concentrator and EO modulator could
enable a focal plane RF imager array that allows direct RF imaging, and significantly decrease RF aperture size and
weight. Additional benefits include enhanced functionality such as inherent polarimetric imaging capability.
When a radially polarized beam is focused onto a metal-dielectric interface, the entire beam is TM polarized with respect
to the interface. Consequently surface plasmons can be excited at all directions. These surface plasmons will propagate
to the geometric center, constructively interfere with each other and generate a strongly focused evanescent nondiffracting
Bessel beam. In this paper, we report the experimental results on the direct imaging of such plasmonic
focusing. Radially polarized beam is tightly focused onto a silver-glass interface with a high numerical aperture oil
immersion objective lens. The intensity distribution at the back focal plane of the objective lens after reflection is
captured with a CCD camera. A dark ring corresponding to surface plasmon resonance excitation by a focused radially
polarized beam is observed. A collection mode near field scanning optical microscope is applied to map the two-dimensional
intensity distributions at different distances from the sample to verify the non-spreading and decaying
natures of the evanescent Bessel beam.
Surface plasmon is collective oscillation of free electrons at metal/dielectric interface. As a wave phenomenon, surface
plasmon can be focused using appropriate excitation geometry and metallic structures. The strong spatial confinement
and high field enhancement make plasmonic lenses very attractive for near-field optical imaging and sensing in
biological applications. In this paper, we show that optimal plasmonic focusing can be achieved through a combination
of radially polarized illumination and axially symmetric dielectric/metal plasmonic lens structures. As examples,
plasmonic lens with planar interface, conical shape and annular rings under radial polarization illumination are studied.
The focusing properties and field enhancement effect of these plasmonic lenses are numerically studied with a finite-element-
method model. The numerical simulation results show that the field distribution with a full-width-half-maximum
of as small as 10 nm and intensity enhancement factor of five orders of magnitude can be achieved with 632.8
nm optical excitation.
In reflective liquid crystal light valve (LCLV) or LCOS light valve large screen projection display system, Philips color separation and color recombination prism system is widely used to make the projection system compact. There are two factors which influence the contrast of projection optical systems. One is the extinction ratio of Polarizing beam splitter (PBS) and the other is the dark-state output of Philips prism system because of geometrical polarization rotations. Optical thin films exhibit inevitable polarization effects at oblique incidence. Here, Geometrical polarization rotation is analyzed in detail. The factors affecting the contrast performance of Philips prism system are quantitatively analyzed. Polarization aberration in this display system is analyzed based on the theory of Jones polarization ray tracing. It can be conclude that the contrast of projection display system is intimately correlated with phase shift difference of the two polarization component. It is concluded that optical design should combine lens design and coating design to improve the contrast and image quality of the projection display system.