5. Conclusion

Throughout this chapter, the author has discussed novel plasmonic structures implemented on various optical fiber platforms. These fiber-optic-based plasmonic devices demonstrated novel features of SPP-based functionality in a compact, flexible, and cost-effective form leveraged by optical fiber technology.

First, fiberized TA-CMNSs that can produce a low-noise C-SPP hotspot were introduced and discussed. The trench structures were designed based on the MPCM in order to suppress the co-existing NCDL at the hotspot location. Two types of novel TA-CMNSs were designed and investigated: an RT-CMNS was proposed for its simple fabrication procedure, and an APT-CMNS was proposed for maximally exploiting the multipole cancelation effect. Numerical analysis of them verified that the auxiliary trench structure can substantially improve the SNR performance of the CMNS, being capable of producing a low-noise plasmonic hotspot at the center of the whole structure. These schemes will be useful for designing various plasmonic devices that particularly require high SNR characteristics, such as bio-sensing, imaging, surface-enhanced Raman spectroscopy, etc.

Second, fiberized and fiberizable metal-optical lenses based on the FZP were introduced and discussed, which included an MFZP-OFF and an SPP-MFZP. The former exhibited supervariable focusing with respect to incident wavelength, and the latter had substantially high radial-polarization selectivity owing to the EOT effect from the auxiliary subwavelength annular slits inserted in the openings of the FZP structure. Numerical and experimental analyses verified their novel functionality. These schemes will be useful for various applications that require accurate, flexible, and centrosymmetric optical focusing with a broad focal-length tuning range, such as in micro/nanomachining and optical trapping. In addition, these schemes can also be exploited for mono-chromatic-multi-focal or multi-chromatic-mono-focal lenses [43, 44].

Third, a fiberized SPP coupling scheme and its application to a CA-MCAFF were introduced and discussed. The former realized the Kretschmann SPP coupling scheme in the optical fiber platform, and the latter exhibited novel WODB functionality. Numerical and experimental analyses verified that the MCAFF-based SPP coupling scheme worked efficiently and has great potential for being used as an excellent, alternative SPP generation method, which provides high efficiency, unidirectionality, and full compatibility with fiber-based optical sources. The CA-MCAFF scheme will also be very useful for various plasmonic and optical applications where WODB functionality is required, such as a nanophotonic wavelength-division-multiplexer, a compact spectrometer, etc.

Optical fibers are an excellent platform for plasmonics studies and applications. The novel plasmonic nanostructures realized on various optical fiber platforms successfully demonstrated fascinating characteristics of plasmonics in a compact, flexible, and cost-effective format. The author believes that the investigations and discussions given in this chapter will broaden the fiber-optic and plasmonics research fields, as well as expecting further advances and convergence of them to come.
