Near-field probing of slow Bloch modes on photonic crystals with a nanoantenna

We study the near-field probing of the slow Bloch laser mode of a photonic crystal by a bowtie nano-aperture (BNA) positioned at the end of a metal-coated fiber probe. We show that the BNA acts as a polarizing nanoprobe allowing us to extract information about the polarization of the near-field of the slow-light mode, without causing any significant perturbation of the lasing process. Near-field experiments reveal a spatial resolution better than λ/20 and a polarization ratio as strong as 110. We also demonstrate that the collection efficiency is two orders of magnitude larger for the BNA than for a 200 nm large circular aperture opened at the apex of the same metal-coated fiber tip. The BNA allows for overcoming one of the main limitations of SNOM linked to the well-known trade off between resolution and signal-to-noise ratio.

Bowtie nano-aperture as interface between near-fields and a single-mode fiber

We present the development and study of a single bowtie nano-aperture (BNA) at the end of a monomode optical fiber as an interface between near-fields/nano-optical objects and the fiber mode. To optimize energy conversion between BNA and the single fiber mode, the BNA is opened at the apex of a specially designed polymer fiber tip which acts as an efficient mediator (like a horn optical antenna) between the two systems. As a first application, we propose to use our device as polarizing electric-field nanocollector for scanning near-field optical microscopy (SNOM). However, this BNA-on-fiber probe may also find applications in nanolithography, addressing and telecommunications as well as in situ biological and chemical probing and trapping.

Linear to radial polarization conversion in the THz domain using a passive system

This paper addresses a passive system capable of converting a linearly polarized THz beam into a radially polarized one. This is obtained by extending to THz frequencies and waveguides an already proven concept based on mode selection in optical fibers. The approach is validated at 0.1 THz owing to the realization of a prototype involving a circular waveguide and two tapers that exhibits a radially polarized beam at its output. By a simple homothetic size reduction, the system can be easily adapted to higher THz frequencies.

Conical optics: the solution to confine light

We compare the performances in terms of confinement and depth of field of spherical and conical optics. It turns out that, if the spherical optics is adapted to the usual parallel imaging, conical optics seems to be the optimized solution for systems based on scanning (sequential imaging). It is shown that the optimized confinement capability of conical optics is due to the ability of conical components to generate a single Bessel beam with high efficiency. The calculations are based on Weyl formulas.

Light transmission by subwavelength square coaxial aperture arrays in metallic films

Using the Fourier modal method, we study the enhanced transmission exhibited by arrays of square coaxial apertures in a metallic film. The calculated transmission spectrum is in good agreement with FDTD calculations. We show that the enhanced transmission can be explained when we consider a few guided modes of a coaxial waveguide.