75 research outputs found
Graphene Based Waveguides
Graphene, which is well known as a one-atom thick carbon allotrope, has drawn lots of attention since its first announcement due to remarkable performance in mechanical, electrical, magnetic, thermal, and optical areas. In particular, unique properties of graphene such as low net absorption in broadband optical band, notably high nonlinear optical effects, and gate-variable optical conductivity make it an excellent candidate for high speed, high performance, and broadband electronic and photonics devices. Embedding graphene into optical devices longitudinally would enhance the light-graphene interaction, which shows great potential in photonic components. Since the carrier density of graphene could be tuned by external gate voltage, chemical doping, light excitation, graphene-based waveguide modulator could be designed to have high flexibility in controlling the absorption and modulation depth. Furthermore, graphene-based waveguides could take advantages in detection, sensing, polarizer, and so on
Three dimensional photonic Dirac points in metamaterials
Topological semimetals, representing a new topological phase that lacks a
full bandgap in bulk states and exhibiting nontrivial topological orders,
recently have been extended to photonic systems, predominantly in photonic
crystals and to a lesser extent, metamaterials. Photonic crystal realizations
of Dirac degeneracies are protected by various space symmetries, where Bloch
modes span the spin and orbital subspaces. Here, we theoretically show that
Dirac points can also be realized in effective media through the intrinsic
degrees of freedom in electromagnetism under electromagnetic duality. A pair of
spin polarized Fermi arc like surface states is observed at the interface
between air and the Dirac metamaterials. These surface states show linear
k-space dispersion relation, resulting in nearly diffraction-less propagation.
Furthermore, eigen reflection fields show the decomposition from a Dirac point
to two Weyl points. We also find the topological correlation between a Dirac
point and vortex/vector beams in classic photonics. The theoretical proposal of
photonic Dirac point lays foundation for unveiling the connection between
intrinsic physics and global topology in electromagnetism.Comment: 15 pages, 5 figure
Phenomenological modeling of Geometric Metasurfaces
Metasurfaces, with their superior capability in manipulating the optical
wavefront at the subwavelength scale and low manufacturing complexity, have
shown great potential for planar photonics and novel optical devices. However,
vector field simulation of metasurfaces is so far limited to
periodic-structured metasurfaces containing a small number of meta-atoms in the
unit cell by using full-wave numerical methods. Here, we propose a general
phenomenological method to analytically model metasurfaces made up of
arbitrarily distributed meta-atoms based on the assumption that the meta-atoms
possess localized resonances with Lorentz-Drude forms, whose exact form can be
retrieved from the full wave simulation of a single element. Applied to phase
modulated geometric metasurfaces, our analytical results show good agreement
with full-wave numerical simulations. The proposed theory provides an efficient
method to model and design optical devices based on metasurfaces.Comment: 16 pages, 8 figure
Recovering lossless propagation of polaritons with synthesized complex frequency excitation
Surface plasmon polaritons and phonon polaritons offer a means of surpassing
the diffraction limit of conventional optics and facilitate efficient energy
storage, local field enhancement, high sensitivities, benefitting from their
subwavelength confinement of light. Unfortunately, losses severely limit the
propagation decay length, thus restricting the practical use of polaritons.
While optimizing the fabrication technique can help circumvent the scattering
loss of imperfect structures, the intrinsic absorption channel leading to heat
production cannot be eliminated. Here, we utilize synthetic optical excitation
of complex frequency with virtual gain, synthesized by combining the
measurements taken at multiple real frequencies, to restore the lossless
propagations of phonon polaritons with significantly reduced intrinsic losses.
The concept of synthetic complex frequency excitation represents a viable
solution to compensate for loss and would benefit applications including
photonic circuits, waveguiding and plasmonic/phononic structured illumination
microscopy.Comment: 20 pages, 4 figure
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