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Register a new userControlling the Emission of Electromagnetic Sources by Coordinate transformation
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The coordinate transformation on the space that contains electromagnetic sources is studied. We find that, not only the permittivity and permeability tensors of the media, but also the sources inside the media will take another form in order to behave equivalently as the original case. It is demonstrated that, a source of arbitrary shape and position in the free space can be replaced by an appropriately designed metamaterial coating with current distributed on the inner surface and would not be detected by outer observers, because the emission of the source can be controlled at will in this way. As examples, we show how to design conformal antennas by covering the sources with transformation media. The method proposed in this letter provides a completely new approach to develop novel active EM devices.
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We use coordinate transformation theory to realize substrates that can modify the emission of an embedded source. Simulation results show that with proper transformation functions the energy radiated by a source embedded in these space variant media will be concentrated in a narrow beam. The thickness of the slab achieved with our transformations will no longer be restricted by the evanescent modes and the source can be placed at any position along the boundary of the substrate without affecting the radiation pattern. We also discuss the case where reduced parameters are used, which still performs well and is physically realizable.
The coordinate transformation technique is applied to the design of perfect lenses and superlenses. In particular, anisotropic metamaterials that magnify two-dimensional planar images beyond the diffraction limit are designed by the use of oblate spheroidal coordinates. The oblate spheroidal perfect lens or superlens can naturally be used in reverse for lithography of planar subwavelength patterns.
The transformation media concept based on the form-invariant Maxwells equations under coordinate transformations has opened up new possibilities to manipulate the electromagnetic fields. In this paper we report on applying the finite-embedded coordinate transformation method to design electromagnetic beam modulating devices both in the Cartesian coordinates and in the cylindrical coordinates. By designing the material constitutive tensors of the transformation optical structures through different kinds of coordinate transformations, either the beam width of an incident Gaussian plane wave could be modulated by a slab, or the wave propagating direction of an omni-directional source could be modulated through a cylindrical shell. We present the design procedures and the full wave electromagnetic simulations that clearly confirm the performance of the proposed beam modulating devices.
We review the theory for photon-photon scattering in vacuum, and some of the proposals for its experimental search, including the results of our recent works on the subject. We then describe a very simple and sensitive proposal of an experiment and discuss how it can be used at the present (HERCULES) and the future (ELI) ultrahigh power laser facilities either to find the first evidence of photon-photon scattering in vacuum, or to significantly improve the current experimental limits.
Orbital angular momentum (OAM) carried by helical light beams is an unbounded degree of freedom of photons that offers a promising playground in modern photonics. So far, integrated sources of coherent light carrying OAM are based on resonators whose design imposes a single, non-tailorable chirality of the wavefront (i.e. clockwise or counter clockwise vortices). Here, we propose and demonstrate the realization of an integrated microlaser where the chirality of the wavefront can be optically controlled. Importantly, the scheme that we use, based on an effective spin-orbit coupling of photons in a semiconductor microcavity, can be extended to different laser architectures, thus paving the way to the realization of a new generation of OAM microlasers with tunable chirality.
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