179,095 research outputs found
Finite element method analysis of band gap and transmission of two-dimensional metallic photonic crystals at terahertz frequencies
Photonic band gap and transmission characteristics of 2D metallic photonic crystals at THz frequencies
have been investigated using finite element method (FEM). Photonic crystals composed of metallic rods
in air, in square and triangular lattice arrangements, are considered for transverse electric and transverse magnetic polarizations. The modes and band gap characteristics of metallic photonic crystal structure are investigated by solving the eigenvalue problem over a unit cell of the lattice using periodic
boundary conditions. A photonic band gap diagram of dielectric photonic crystal in square lattice array
is also considered and compared with well-known plane wave expansion results verifying our FEM
approach. The photonic band gap designs for both dielectric and metallic photonic crystals are consistent
with previous studies obtained by different methods. Perfect match is obtained between photonic band
gap diagrams and transmission spectra of corresponding lattice structure
Realization of a three-dimensional photonic topological insulator
Confining photons in a finite volume is in high demand in modern photonic
devices. This motivated decades ago the invention of photonic crystals,
featured with a photonic bandgap forbidding light propagation in all
directions. Recently, inspired by the discoveries of topological insulators
(TIs), the confinement of photons with topological protection has been
demonstrated in two-dimensional (2D) photonic structures known as photonic TIs,
with promising applications in topological lasers and robust optical delay
lines. However, a fully three-dimensional (3D) topological photonic bandgap has
never before been achieved. Here, we experimentally demonstrate a 3D photonic
TI with an extremely wide (> 25% bandwidth) 3D topological bandgap. The sample
consists of split-ring resonators (SRRs) with strong magneto-electric coupling
and behaves as a 'weak TI', or a stack of 2D quantum spin Hall insulators.
Using direct field measurements, we map out both the gapped bulk bandstructure
and the Dirac-like dispersion of the photonic surface states, and demonstrate
robust photonic propagation along a non-planar surface. Our work extends the
family of 3D TIs from fermions to bosons and paves the way for applications in
topological photonic cavities, circuits, and lasers in 3D geometries
Degeneracy analysis for a super cell of a photonic crystal and its application to the creation of band gaps
A method is introduced to analyze the degeneracy properties of the band
structure of a photonic crystal making use of the super cells. The band
structure associated with a super cell of a photonic crystal has degeneracies
at the edge of the Brillouin zone if the photonic crystal has some kind of
point group symmetry. Both E-polarization and H-polarization cases have the
same degeneracies for a 2-dimensional (2D) photonic crystal. Two theorems are
given and proved. These degeneracies can be lifted to create photonic band gaps
by changing the transform matrix between the super cell and the smallest unit
cell. The existence of the photonic band gaps for many known 2D photonic
crystals is explained through the degeneracy analysis.Comment: 19 pages, revtex4, 14 figures, p
Efficient excitation of self-collimated beams and single Bloch modes in planar photonic crystals
Using finite-difference time-domain calculations, we investigate out-of-plane coupling between a square-lattice
planar photonic crystal and a conventional waveguide located above the photonic crystal. We couple a waveguide
oriented in the GX direction to a photonic crystal mode in the second band and show that anticrossing takes place. In this way, a self-collimated beam is launched in the planar photonic crystal, with full power transfer. Furthermore, we investigate the coupling between a waveguide oriented in the GM direction and a photonic crystal and show that single photonic crystal modes can be selectively excited
Graphene-based photonic crystal
A novel type of photonic crystal formed by embedding a periodic array of
constituent stacks of alternating graphene and dielectric discs into a
background dielectric medium is proposed. The photonic band structure and
transmittance of such photonic crystal are calculated. The graphene-based
photonic crystals can be used effectively as the frequency filters and
waveguides for the far infrared region of electromagnetic spectrum. Due to
substantial suppression of absorption of low-frequency radiation in doped
graphene the damping and skin effect in the photonic crystal are also
suppressed. The advantages of the graphene-based photonic crystal are
discussed.Comment: 4 pages, 3 figure
Photonic Crystal Laser Accelerator Structures
Photonic crystals have great potential for use as laser-driven accelerator
structures. A photonic crystal is a dielectric structure arranged in a periodic
geometry. Like a crystalline solid with its electronic band structure, the
modes of a photonic crystal lie in a set of allowed photonic bands. Similarly,
it is possible for a photonic crystal to exhibit one or more photonic band
gaps, with frequencies in the gap unable to propagate in the crystal. Thus
photonic crystals can confine an optical mode in an all-dielectric structure,
eliminating the need for metals and their characteristic losses at optical
frequencies.
We discuss several geometries of photonic crystal accelerator structures.
Photonic crystal fibers (PCFs) are optical fibers which can confine a
speed-of-light optical mode in vacuum. Planar structures, both two- and
three-dimensional, can also confine such a mode, and have the additional
advantage that they can be manufactured using common microfabrication
techniques such as those used for integrated circuits. This allows for a
variety of possible materials, so that dielectrics with desirable optical and
radiation-hardness properties can be chosen. We discuss examples of simulated
photonic crystal structures to demonstrate the scaling laws and trade-offs
involved, and touch on potential fabrication processes.Comment: 3 pages, 3 figures; Submitted to Particale Accelerator Conference
(PAC 2003), May 12-16, 2003, Portland, Oregon (IEEE
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