The transverse electromagnetic waves are major information and energy carriers. In 1996, Hellwarth and Nouchi theoretically identified a radically different, non-transverse type of electromagnetic pulses of toroidal topology. These pulses, which are propagating counterparts of localized toroidal dipole excitations in matter and exhibit unique electromagnetic wave properties, have never been observed before. Here, we report the generation and characterization of such optical and terahertz Toroidal Light Pulses (TLPs), launched from tailored nanostructured metasurfaces comprising toroidal emitters. This achievement paves the way for experimental studies of energy and information transfer with TLPs, their space-time "entanglement", and their light-matter interactions involving anapoles, localized space-time entangled excitations, skyrmions, and toroidal qubits that are of growing interest for the fundamental science of light and applications.

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Flying doughnuts (FDs) are exact propagating solutions of Maxwell equations in the form of single-cycle, space-time non-separable toroidal pulses. Here we review their properties and reveal the existence of a complex and robust fine topological structure. In particular, the electric and magnetic fields of the FD pulse vanish across a number of planes, spherical shells and rings, and display a number of point singularities including saddle points and vortices. Moreover, the instantaneous Poynting vector of the field exhibits a large number of singularities, which are often accompanied by extended areas energy backflow.

Maxwell's equations can be satisfied not only by plane electromagnetic waves, but also by more exotic space-time non-separable electromagnetic pulses which cannot be represented as a product of time and space dependent functions. A family of such pulses with finite energy was identified by R. Ziolkowski in 1985. Later R. W. Hellwarth and P. Nouchi highlighted a subset of Ziolkowski's pulses, now known as Flying Donuts, a formation of polarization singularities of toroidal topology traveling at the speed of light. Spurred by recent advances in ultrafast and topological optics, space-time non-separable electromagnetic excitations are now becoming the focus of growing experimental efforts as they hold promise for topological information transfer, probing and inducing transient excitations in matter such as anapole and toroidal modes. Many practical questions are yet to be answered regarding their generation, detection and light-matter interactions. Here we demonstrate that the Flying Donut is bandwidth limited and can be constructed from an ensemble of monochromatic plane waves with continuous spatial and frequency spectrum and hence can be generated by converting broadband conventional transverse electromagnetic pulses.

A distributed curvature sensor based on Brillouin optical time-domain reflectometry interrogation technique in a D-shaped 7-core fibre is presented. By comparing the relative Brillouin frequency shift between the central core and three of the outer cores of the 7-core fibre, the curvature of various spools with different diameters is measured with a deviation from the actual value ranging between 9% and 15%. The analysis and results presented in this study show the first demonstration of distributed bend sensing using a specially designed multicore D-shaped fibre, paving the way for fully distributed 3D shape sensing.

Ultrafast vectorially polarized pulses have found many applications in information and energy transfer owing mainly to the presence of strong longitudinal components and their space-polarization non-separability. Due to their broad spectra, such pulses often exhibit space–time couplings, which significantly affect the pulse propagation dynamics. Although such couplings usually result in reduced energy density at the focal spot, they have been utilized to demonstrate pulse shaping as in the case of a rotating or sliding wavefront as the pulse travels through its focal point. Here, we present a new method for the spatiotemporal characterization of ultrashort cylindrical vector pulses based on a combination of spatially resolved Fourier transform spectroscopy and Mach–Zehnder interferometry. The method provides access to spatially resolved spectral amplitudes and phases of all polarization components of the pulse. We demonstrate the capabilities of the method by completely characterizing a 10 fs radially polarized pulse from a Ti:sapphire laser centered at 800 nm.

Ultrafast vectorially polarized pulses have found many applications in information and energy transfer owing mainly to the presence of strong longitudinal components and their spacepolarization non-separability. Due to their broad spectrum, such pulses often exhibit space-time couplings, which significantly affect the pulse propagation dynamics leading to reduced energy density or utilized to create new effects like a rotating or sliding wavefront at focus. Here, we present a new method for the spatio-temporal characterization of ultrashort cylindrical vector pulses based on a combination of spatially resolved Fourier transform spectroscopy and Mach-Zehnder interferometry. The method provides access to spatially resolved spectral amplitudes and phases of all polarization components of the pulse. We demonstrate the capabilities of the method by completely characterizing a 10 fs radially polarized pulse from a Ti:sapphire laser at 800 nm.

The transverse electromagnetic waves are major information and energy carriers. In 1996, Hellwarth and Nouchi theoretically identified a radically different, non-transverse type of electromagnetic pulses of toroidal topology. These pulses, which are propagating counterparts of localized toroidal dipole excitations in matter and exhibit unique electromagnetic wave properties, have never been observed before. Here, we report the generation and characterization of such optical and terahertz Toroidal Light Pulses (TLPs), launched from tailored nanostructured metasurfaces comprising toroidal emitters. This achievement paves the way for experimental studies of energy and information transfer with TLPs, their space-time "entanglement", and their light-matter interactions involving anapoles, localized space-time entangled excitations, skyrmions, and toroidal qubits that are of growing interest for the fundamental science of light and applications.