KEYWORDS: Nanophotonics, Holograms, Near field optics, Polarization, Nano opto mechanical systems, Near field, Nanolithography, Data processing, Holography, Prototyping
A nanophotonic hierarchical hologram works in both optical far-fields and near-fields, the former being associated
with conventional holographic images, and the latter being associated with the optical intensity distribution based on a
nanometric structure that is accessible only via optical near-fields. In principle, a structural change occurring at the
subwavelength scale does not affect the optical response functions, which are dominated by propagating light. Therefore,
the visual aspect of the hologram is not affected by such a small structural change on the surface, and retrieval in both
fields can be processed independently. We propose embedding a nanophotonic code, which is retrievable via optical
near-field interactions involving nanometric structures, within an embossed hologram. Due to the one-dimensional grid
structure of the hologram, evident polarization dependence appears in retrieving the code. Here we describe the basic
concepts, numerical simulations, and experimental demonstrations of a prototype nanophotonic hierarchical hologram
with a nanophotonic code and describe its optical characterization.
"Nanophotonics" uses the local interaction between nanometric particles via optical near-fields to bring "qualitative
innovation" to the field of optical technology. Optical near-field interactions respond hierarchically at the nanometer
scale, allowing unique nanophotonic functions. We defined two kinds of hierarchical optical near-field interactions:
those between optical far- and near-fields, and those in the optical near-field only. We demonstrated these hierarchical
effects numerically and experimentally using several prototype "nanophotonic architectures." The first, a "hierarchical
hologram," operated in both the far- and near-fields with few adverse effects. We also demonstrated hierarchical effects
in the optical near-field by core-shell metal nanostructures. Hierarchical nanoscale architectures could allow single
optical devices to perform multiple functions. The practical realization of such devices could have a major impact, for
example, in the field of optical security.
To decrease the sizes of photonic devices beyond the diffraction limit of light, we propose nanophotonic devices based
on optical near-field interactions between semiconductor quantum dots (QDs). To drive such devices, an optical signal
guide whose width is less than several tens of nanometers is required. Furthermore, unidirectional signal transfer is
essential to prevent nanophotonic devices operating incorrectly due to signals reflected from the destination. For
unidirectional signal transfer at the nanometer scale, we propose a nanophotonic signal transmitter based on optical nearfield
interactions between small QDs of the same size and energy dissipation in larger QDs that have a resonant exciton
energy level with the small QDs. To confirm such unidirectional energy transfer, we used time-resolved
photoluminescence spectroscopy to observe exciton energy transfer between the small QDs via the optical near-field, and
subsequent energy dissipation in the larger QDs. We estimated that the energy transfer time between resonant CdSe/ZnS
QDs was 135 ps, which is shorter than the exciton lifetime of 2.10 ns. Furthermore, we confirmed that exciton energy did
not transfer between nonresonant QD pairs. These results indicated that the proposed nanophotonic signal transmitters
based on optical near-field interactions and energy dissipation could be used to make multiple transmitters and selfdirectional
interconnections.
To overcome the restriction of the density of optical memory systems due to diffraction limit, we have been studying photonic DNA memory, which utilizes photonic technologies and the DNA computing methodology. Our scheme is on the basis of local DNA reaction using laser irradiation and transportation of DNA using parallel optical tweezers with fabricating DNA clusters by attaching DNA onto beads. This paper reports on a new dynamic optical tweezers system, which combines a spatial light modulator (SLM) and a diffractive optical element (DOE) for manipulating DNA clusters. With this combination, real-time programmable manipulation of DNA clusters is achievable in a large spatial range. We also can choose simple patterns for the SLM, and decrease computation cost. In this experiment, a laser beam (633nm wavelength) illuminates a SLM (Hamamatsu Photonics K. K.; PPM8267), which is imaged on an 80-lp/mm transmission-type grating, then the beam is focused with a water immersible objective lens (x 100, NA 1). Simple blazed-phase patterns have different grating constants that are perpendicular to that of the grating are displayed on the SLM. We succeeded in lifting up three 6-micron-diameter polystyrene beads on a glass slide with light spots duplicated by the grating, then transporting the beads in three dimensions simultaneously with changing the grating constants on the SLM. We demonstrated that a same manipulation was implemented at different positions by duplicating a pattern that was generated when only using the SLM. This is usable in implementing a same operation for different data at multiple positions with a single instruction. The promising applications of the method include a nano-scale image memory with encryption.
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