Bo Thidé

Bio: Bo Thidé is an academic researcher from Swedish Institute of Space Physics. The author has contributed to research in topics: Ionosphere & Angular momentum. The author has an hindex of 37, co-authored 129 publications receiving 5875 citations. Previous affiliations of Bo Thidé include Uppsala University & University of Padua.

Utilization of photon orbital angular momentum in the low-frequency radio domain

Abstract: We show numerically that vector antenna arrays can generate radio beams that exhibit spin and orbital angular momentum characteristics similar to those of helical Laguerre-Gauss laser beams in paraxial optics. For low frequencies (1 GHz), digital techniques can be used to coherently measure the instantaneous, local field vectors and to manipulate them in software. This enables new types of experiments that go beyond what is possible in optics. It allows information-rich radio astronomy and paves the way for novel wireless communication concepts.

Orbital Angular Momentum in Radio—A System Study

Abstract: Recent discoveries concerning rotating (helical) phase fronts and orbital angular momentum (OAM) of laser beams are applied to radio frequencies and comprehensive simulations of a radio OAM system are performed. We find that with the use of vector field-sensing electric and magnetic triaxial antennas, it is possible to unambiguously estimate the OAM in radio beams by local measurements at a single point, assuming ideal (noiseless) conditions and that the beam axis is known. Furthermore, we show that conventional antenna pattern optimization methods can be applied to OAM-generating circular arrays to enhance their directivity.

Encoding many channels in the same frequency through radio vorticity: first experimental test

Abstract: We have shown experimentally that it is possible to propagate and use the properties of twisted non-monochromatic incoherent radio waves to simultaneously transmit to infinity more radio channels on the same frequency band by encoding them in different orbital angular momentum states. This novel radio technique allows the implementation of, at least in principle, an infinite number of channels on one and the same frequency, even without using polarization or dense coding techniques. An optimal combination of all these physical properties and techniques represents a solution for the problem of radio band congestion. Our experimental findings show that the vorticity of each twisted electromagnetic wave is preserved after the propagation, paving the way for entirely new paradigms in radio communication protocols.

Twisting of light around rotating black holes

Abstract: Kerr black holes are among the most intriguing predictions of Einstein's general relativity theory(1,2). These rotating massive astrophysical objects drag and intermix their surrounding space and time, deflecting and phase-modifying light emitted near them. We have found that this leads to a new relativistic effect that imprints orbital angular momentum on such light. Numerical experiments, based on the integration of the null geodesic equations of light from orbiting point-like sources in the Kerr black hole equatorial plane to an asymptotic observer(3), indeed identify the phase change and wavefront warping and predict the associated light-beam orbital angular momentum spectra(4). Setting up the best existing telescopes properly, it should be possible to detect and measure this twisted light, thus allowing a direct observational demonstration of the existence of rotating black holes. As non-rotating objects are more an exception than a rule in the Universe, our findings are of fundamental importance.

Experimental verification of photon angular momentum and vorticity with radio techniques

Abstract: The experimental evidence that radio techniques can be used for synthesizing and analyzing non-integer electromagnetic (EM) orbital angular momentum (OAM) of radiation is presented. The technique used amounts to sample, in space and time, the EM field vectors and digitally processing the data to calculate the vortex structure, the spatial phase distribution, and the OAM spectrum of the radiation. The experimental verification that OAM-carrying beams can be readily generated and exploited by using radio techniques paves the way to an entirely new paradigm of radar and radio communication protocols.

The Observation of Gravitational Waves from a Binary Black Hole Merger

Abstract: On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160) Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

Terabit free-space data transmission employing orbital angular momentum multiplexing

Abstract: Researchers demonstrate the ability to multiplex and transfer data between twisted beams of light with different amounts of orbital angular momentum — a development that provides new opportunities for increasing the data capacity of free-space optical communications links.

Linear and nonlinear waves, by G. B. Whitham. Pp.636. £50. 1999. ISBN 0 471 35942 4 (Wiley).

Abstract: to be done in this area. Face recognition is a problem that scarcely clamoured for attention before the computer age but, having surfaced, has involved a wide range of techniques and has attracted the attention of some fine minds (David Mumford was a Fields Medallist in 1974). This singular application of mathematical modelling to a messy applied problem of obvious utility and importance but with no unique solution is a pretty one to share with students: perhaps, returning to the source of our opening quotation, we may invert Duncan's earlier observation, 'There is an art to find the mind's construction in the face!'.

Orbital angular momentum: origins, behavior and applications

Abstract: As they travel through space, some light beams rotate. Such light beams have angular momentum. There are two particularly important ways in which a light beam can rotate: if every polarization vector rotates, the light has spin; if the phase structure rotates, the light has orbital angular momentum (OAM), which can be many times greater than the spin. Only in the past 20 years has it been realized that beams carrying OAM, which have an optical vortex along the axis, can be easily made in the laboratory. These light beams are able to spin microscopic objects, give rise to rotational frequency shifts, create new forms of imaging systems, and behave within nonlinear material to give new insights into quantum optics.