We propose a concept of near-field imaging for the complete experimental description of the structure of light in three dimensions around nanodevices. It is based on a near-field microscope able to simultaneously map the distributions of two orthogonal electric-field components at the sample surface. From a single 2D acquisition of these two components, the complementary electric and magnetic field lines and Poynting vector distributions are reconstructed in a volume beneath the sample using rigorous numerical methods. The experimental analysis of localized electric and magnetic optical effects as well as energy flows at the subwavelength scale becomes possible. This work paves the way toward the development of a complete electromagnetic diagnostic of nano-optical devices and metamaterials.
Using the N-order finite-difference time-domain (FDTD) method, we show that optical resonances of the bowtie nanoaperture (BNA) are due to the combination of a guided mode inside the aperture and Fabry-Perot modes along the metal thickness. The resonance of lower energy, which leads to the well-known light confinement in the gap zone, occurs at the cutoff wavelength of the fundamental guided mode. No plasmon resonance is directly involved in the generation of the light hot spot. We also define a straightforward relationship between the resonance wavelengths of the BNA and its geometrical parameters. This brings a simple tool for the optimization of the BNA design.
We report a simple method for generating microaxicons at the extremity of commercial optical fibers. The proposed solution, based on a polishing technique, can readily produce any desired microaxicon cone angle and is independent of the nature of the fiber. An optical study of microaxicon performance, in terms of confinement ability and length of the generated Bessel-like beams, is presented as a function of the microaxicon angle. This study, made possible by the experimental acquisition of the 3D light distribution of the Bessel-like beams, reveals the relationship between the Bessel-like beam confinement zone and the beam length. Finally, the effect of diffraction of the Bessel-like beams, induced by the limited lateral extent of the incident fiber mode, is studied and discussed.
We propose and validate a concept of multichannel near-field fiber probe for the collection and discrimination of optical fields of orthogonal polarizations (linear, elliptic, and circular). The system is achieved by connecting to scanning near-field optical microscope fiber tips an optical stage made up of commercial polarizers, fiber couplers, and polarization controllers. Using radially polarized Bessel beams as test objects, we demonstrate the ability of a three-channel fiber tip to simultaneously and independently probe the transverse vector components of the electric field (parallel to the sample surface) and the overall transverse intensity. The polarization ratio of the near-field collection system exceeds 1:1500. The system can be implemented in collection-mode or reflection-mode near-field microscope configurations, with various kinds of probe and light source (of high or low coherence lengths) for a deeper insight of light polarization effects and vector fields at a subwavelength scale.
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