Surface plasmon resonance (SPR) has been actively researched for sensor applications. Based on the subwavelength scale enhancement of light field and its sensitivity to refractive index, SPR can be used for surface enhanced Raman spectroscopy and various bio and chemical sensors. This talk will provide comparative overview of the potentials of SPR for optical sensors and its practical limitations in implementation.
We propose an approach that improves the characteristics of a subwavelength light spot from a tapered aperture without
increment of the subwavelength spot size, via simply introducing a taper along the aperture shape. Two advantageous
features of the proposed tapered structure are investigated: At first, by enlarging the entrance area of the aperture, it
could collect more light with respect to the regular one. Thus the funneled light contributes to the field enhancement.
Furthermore, the tapered edges of the exit surface of the aperture provide confined field, a wedge mode, which is
bounded strongly and enhances the local electric field around the edge of the aperture. The enhanced characteristics of
subwavelength spot in vertically-tapered aperture, including peak intensity, power throughput, and full width half
maximum were obtained numerically using finite difference time domain method. The proposed device is fabricated
using conventional planar fabrication techniques and focused ion beam milling to realize the tapered structure. The
relative tapered angle-dependent enhancements are presented with experimental and quantitative demonstrations of the
proposed structure.
New Airy beam manipulation method based on the metallic slit array is presented. By controlling the phases and
intensities of the transmitted lights from each subwavelength metallic slit via the variations of the parameters such as
widths, heights, positions, and numbers of the slits, the overall phase and intensity distributions of the transmitted light
are designed to mimic that of Airy beam. The proposed method can effectively produce the Airy wave packet in microscale
without any spatial light modulator (SLM) and lens. The numerical result and considerations on the design method
to make compact structure to generate the Airy wave packet will be presented.
We propose a resonant optical Yagi-Uda nano-antenna fabricated at the end of the optical fiber probe for the sake of
extracting the information of the angular directivity by absorption of directional emission as a subwavelength optical
microscopy. A Yagi-Uda nano-antenna consists of a feed element surrounded by a reflector and three directors. The
reflector and directors are optimized in pitches with regards to resonance of the antenna elements using the finiteelement
method. We used a focused ion beam (FIB) to cut the end of the fiber probe tip away and make the flattened
surface to mount the metal nano-antenna structure, followed by FIB platinum deposition patterning for the nano-antenna.
To verify the characteristics of the probe based nano-antenna, directional emission from the metal slit with asymmetric
metallic surface gratings is probed and detected using the photomultiplier tube. Our approach of the nano-antenna based
fiber probe is suitable for scanning applications such as detection of directional emission.
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