Polarization-dependent extraction properties of bare fiber probes

Abstract

Despite their modest spatial resolution, uncoated tapered fiber probes are now widely used by the nano-optics community for mapping, with scanning near-field optical microscopy (SNOM), the nonradiative fields at the surface of optical and plasmonic microstructures and nanostructures. Given the significant complexity of the vectorial optical phenomena associated with subwavelength structures, the correct interpretation of SNOM acquisitions requires a complete and accurate understanding of the intrinsic image-formation procedure. In this theoretical study, we show that the SNOM imaging process with uncoated tapered fiber probes is highly polarization dependent and that the dominant effect is, surprisingly, the choice of optical fiber from which the tapered probe was fabricated. We demonstrate that although a tapered monomode fiber is unable to collect the component of the vector electric field parallel to the tip axis, a tapered multimode fiber can successfully collect all the three field components. However, we show that the signal from the longitudinal field component is collected only 10% as efficiently as the signal from the two transverse field components.

Polarization-Resolved Near-Field Mapping of Plasmonic Aperture Emission by a Dual-SNOM System

“…By precharacterizing the tips in far-field experiments and using different experimental configurations, we succeeded to selectively map different components of the plasmonic near-fields. Numerous experimental and theoretical studies have been aimed at elucidating the orientation of the electromagnetic field components in the near-field of an aperture SNOM tip and their role in image formation. − In contrast to radiative fields in homogeneous media that can be described in terms of transverse waves, the electromagnetic near-fields around subwavelength structures (including the aperture of a SNOM tip) are fully vectorial in nature, so that the notion of polarization is generally not applicable in the near-field regime. − However, typical aperture SNOM tips with circular, subwavelength apertures have been shown to probe only the vector components of the electromagnetic field that are transverse to the tip axis, that is, parallel to the aperture plane. In contrast, bare fiber tips, scattering tips, ,, split-ring type aperture tips, , and tips with apertures approximately a full wavelength in diameter can probe longitudinal field components as well.…”

“…14−18 However, typical aperture SNOM tips with circular, subwavelength apertures have been shown to probe only the vector components of the electromagnetic field that are transverse to the tip axis, that is, parallel to the aperture plane. In contrast, bare fiber tips, 18 scattering tips, 16,17,19 splitring type aperture tips, 20,21 and tips with apertures approximately a full wavelength in diameter 13 can probe longitudinal field components as well.…”

Optical polarization response at gold nanosheet edges probed by scanning near-field optical microscopy

“…Since polarization characteristics of the fiber probe play an important role in the SNOM measurement, a number of experimental and theoretical researches have been performed to study the orientations of electromagnetic field components in the near-field of the probe. [19][20][21][22][23][24] Unlike the radiating fields in homogeneous media that can be described in terms of transverse wave, the near-fields around sub-wavelength structures are completely vectorial, and the concept of polarization was reported to be unsuitable in the near-field region. [20][21][22][23][24] However, due to the fact that the predominate orientation of transverse field is preserved over the transmission through the straight fiber probe, the polarization contrast has been widely used for SNOM in the collection, [25][26][27] illumination, [28][29][30] and reflection modes, [31][32][33] as well as in a dual-probe SNOM system.…”

Optical characterization of active photon cages

“…The photon cage modes, though, are yet to be pinpointed, probably due to their weak quality factors in the observed samples. Alternative techniques to characterize them include studying the losses from photon cage modes, producing active NSOM probes or using metal-coated multimode NSOM [4] probes on active photon cages. These ways are currently being explored in our team.…”