Enhanced subwavelength coupling and nano-focusing with optical fiber-plasmonic hybrid probe

Heat and Temperature Localization via Fabry–Pérot Resonances at the Tip of a Nanofocusing Cone

“…This aspect points to the fact that, along with the broadband nanofocusing effect, [9,29,43] FP-like resonances due to the interference of SPPs propagating forward (moving toward the apex) and backward (SPPs reflected at the finite size apex moving away from the apex) leads to well-defined resonance peaks. [22,24,44] To demonstrate this aspect, we calculated the expected frequencies for the FP-like resonances using the semi-analytical method of Tuccio et al [45] and compared them with the spectral position of the peaks in Figure 3a, obtaining satisfactory agreement, see Table S1, Supporting Information. From this table we can identify the resonance at 1065 nm as the seventh order resonance, in agreement with the number of lobes present in Figure 2b.…”

“…This aspect points to the fact that, along with the broadband nanofocusing effect, [ 9,29,43 ] FP‐like resonances due to the interference of SPPs propagating forward (moving toward the apex) and backward (SPPs reflected at the finite size apex moving away from the apex) leads to well‐defined resonance peaks. [ 22,24,44 ]…”

“…[4] The apex size is another important parameter, where two scenarios can be identified: i) if the apex is infinitely small (e.g., an atomically sharp cone), the propagating SPPs would infinitely slowdown when approaching the infinitely small apex, resulting in negligible reflection and scattering of the SPPs and an extreme (infinite) increase of the EM local field; [4] ii) if the apex is finite, as in actual fabricated cones, together with the slowdown of the SPPs propagating toward the apex, the finite-size apex will cause the SPPs to be reflected back and, for particular excitation frequencies, constructively interfere with SPPs propagating toward the apex, giving rise to resonances akin a Fabry-Pérot (FP) cavity. [22,24] In particular, if the apex size is sufficiently small, the adiabatic compression component would dominate over the FP component. However, the most realistic scenario, considering current nanofabrication techniques, is an apex of ≈5 nm radius, [5,[18][19][20] still far from atomic dimensions.…”

Numerical Calculation of the Light Propagation in Tapered Optical Fibers for Optical Neural Interfaces

“…One of the most recent approaches to expand the functionalities of optical fibers consists in modifying the endface or the tip of tapered optical fibers to include different types of structures that interact with the incident light in intriguing ways [17,18]. For example, several studies demonstrate that the use of plasmonic structures surrounding the fiber could help confine and concentrate light at the nanoscale [19,20,21,22]. Also, structures made of high-index dielectrics [23] or metals [24] have been shown to enable sub-diffraction light confinement.…”