Abstract
Nanophotonics–photonic structures with subwavelength features–allow accessing high intensity and localized electromagnetic field and hence is an ideal platform for investigating and exploiting strong lightmatter interaction. In particular, such a strong light-matter interaction requires investigating the interaction of a magnetic dipole with the electromagnetic field– a less-explored topic, which has usually been ignored within the framework of electric dipole approximation. Motivated by recent advances in the emerging field of multipolar nanophotonics, here we develop an analytical model that provides a new insight into analyzing a magnetic dipole and a nanofiber. This method enables us to examine the effect of second term in the multipolar expansion of light-matter interaction, magnetic dipole approximation, with individual guided and radiation modes of the nanofiber. This is a critical key in developing nanophotonic integrated devices based on magnetic nature of light for super-imaging, biosensing, and optical computing.
Highlights
Nanophotonics–photonic structures with subwavelength features–create unique opportunity for subwavelength control of light
A common missing element in nanophotonics examples discussed above is the investigation of light-matter interaction beyond the electric dipole (ED) approximation, i.e. examining the effect of second term in the multipolar expansion of light-matter interaction, magnetic dipole approximation[30,31,32,33]
There is a great interest to understand the effect of magnetic dipole approximation for the following main reasons: (1)- atomic or molecular energy-level transitions with dominant magnetic dipole nature[34,35,36], (2)- possibility to selectively excite the MD transitions[31,37] (3)- possibility to selectively access dominant magnetic or electric responses in high index optical nanostructures[9,25] and (4)- the existence of confined and enhanced EM fields with strong spin-orbit angular momentum in nanophotonic devices
Summary
The radiation is localized within a transverse plane normal to the fiber axis and at the position of the dipole and we observe the formation of WGM in the core cross section, as shown in the inset of Fig. 5(b), while this is not the case away from the resonance This is similar to ED-fiber system where a self-formed cavity appears for higher. The field decomposition method has enabled us to identify diameters/wavelengths, where the emission power–either collected by guided modes or radiated by the fiber–can be larger than the total power emitted by a MD source This is a key information in designing fiber based nanophotonic devices, e.g. nanoantenna, nanolasers, and read-in/read-out access. As a future work, using our approach, one is able to investigate the potential asymmetry in the power distribution of a MD-fiber system into forward and backward guided and radiated modes due to chiral properties of modes of a nanofiber
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