Navigation in Curved Space-Time

A covariant and invariant theory of navigation in curved space-time with respect to electromagnetic beacons is written in terms of J. L. Synge's two-point invariant world function. Explicit equations are given for navigation in space-time in the vicinity of the Earth in Schwarzschild coordinates and in rotating coordinates. The restricted problem of determining an observer's coordinate time when their spatial position is known is also considered

The origin of the spacetime metric: Bell's `Lorentzian pedagogy' and its significance in general relativity

The purpose of this paper is to evaluate the `Lorentzian pedagogy' defended by J.S. Bell in his essay ``How to teach special relativity'', and to explore its consistency with Einstein's thinking from 1905 to 1952. Some remarks are also made in this context on Weyl's philosophy of relativity and his 1918 gauge theory. Finally, it is argued that the Lorentzian pedagogy - which stresses the important connection between kinematics and dynamics - clarifies the role of rods and clocks in general relativity.Comment: To be published in ``Physics Meets Philosophy at the Planck Length'', C. Callender and N. Huggett (eds.), Cambridge University Press (1999). 22 pages, no figures, LaTeX, uses harvard.sty; 3 references added, typos corrected and minor changes to conten

Optical anapoles in nanophotonics and meta-optics

Interference of electromagnetic modes supported by subwavelength photonic structures is one of the key concepts that underpins the subwavelength control of light in meta-optics. It drives the whole realm of all-dielectric Mie-resonant nanophotonics with many applications for low-loss nanoscale optical antennas, metasurfaces, and metadevices. Specifically, interference of the electric and toroidal dipole moments results in a very peculiar, low-radiating optical state associated with the concept of optical anapole. Here, we uncover the physics of multimode interferences and multipolar interplay in nanostructures with an intriguing example of the optical anapole. We review the recently emerged field of anapole electrodynamics explicating its relevance to multipolar nanophotonics, including direct experimental observations, manifestations in nonlinear optics, and rapidly expanding applications in nanoantennas, active photonics, and metamaterials.Comment: 14 pages, 6 figure

A photonic-crystal selective filter

A highly selective filter is designed, working at 1.55 μm and having a 3-dB bandwidth narrower than 0.4 nm, as is required in Dense Wavelength Division Multiplexed systems. Different solutions are proposed, involving photonic crystals made rectangular- or circular-section dielectric rods, or else of holes drilled in a dielectric bulk. The polarization and frequency selective properties are achieved by introducing a defect in the periodic structure. The device is studied by us- ing in-house codes implementing the full-wave Fourier Modal Method. Practical guidelines about advantages and limits of the investigated solutions are given