ABSTRACT
We investigate the effect of defects in the metal-coating layer of a scanning near-field optical microscopy (SNOM) probe on the coupling of polarization modes using rigorous electromagnetic modeling tools. Because of practical limitations, we study an ensemble of simple defects to identify important trends and then extrapolate these results to more realistic structures. We find that a probe with many random defects will produce a small but significant coupling of energy between a linearly polarized input mode and a radial/longitudinal polarization mode, which is known to produce a strongly localized emitted optical field and is desirable for SNOM applications.
ABSTRACT
We analyze the propagating optical modes in a Silicon membrane photonic crystal waveguide, based on subwavelength-resolution amplitude and phase measurements of the optical fields using a heterodyne near-field scanning optical microscope (H-NSOM). Fourier analysis of the experimentally obtained optical amplitude and phase data permits identification of the propagating waveguide modes, including the direction of propagation (in contrast to intensity-only measurement techniques). This analysis reveals the presence of two superposed propagating modes in the waveguide. The characteristics of each mode are determined and found to be consistent with theoretical predictions within the limits of fabrication tolerances. An analysis of the relative amplitudes of these two modes as a function of wavelength show periodic oscillation with a period of approximately 3.3 nm. The coupling efficiency between the ridge waveguide and the photonic crystal waveguide is also estimated and found to be consistent with the internal propagating mode characteristics. The combination of high-sensitivity amplitude and phase measurements, subwavelength spatial resolution, and appropriate interpretive techniques permits the in-situ observation of the optical properties of the device with an unprecedented level of detail, and facilitates the characterization and optimization of nanostructure-based photonic devices and systems.
ABSTRACT
A study of the optical properties of microfabricated, fully-metal-coated quartz probes collecting longitudinal and transverse optical fields is presented. The measurements are performed by raster scanning the focal plane of an objective, focusing azimuthally and radially polarized beams by use of two metal-coated quartz probes with different metal coatings. A quantitative estimation of the collection efficiencies and spatial resolutions in imaging both longitudinal and transverse fields is made. Longitudinally polarized fields are collected with a resolution approximately 1.5 times higher as compared with transversely polarized fields, and this behavior is almost independent of the roughness of the probe's metal coating. Moreover, the coating roughness is a critical parameter in the relative collection efficiency of the two field orientations.
ABSTRACT
A confined, evanescent nano-source based on the excitation of Surface Plasmon Polaritons (SPP) on structured thin metal films is proposed. With the help of a suitable cavity, we numerically demonstrate that it is possible to trap SPP over a spatial region smaller than the diffraction limit. In particular, the enhanced plasmonic field associated with the zero-order cavity mode can be used as a virtual probe in scanning near-field microscopy systems. The proposed device shows both the advantages of a localized, non-radiating source and the high sensitivity of SPP-based sensors. The lateral resolution is limited by the lateral extension of the virtual probe. Results from simulated scans of small objects reveal that details with feature sizes down to 50 nm can be detected.
