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Register a new userZitterbewegung-like effect near the Dirac point in metamaterials and photonic crystals
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We present a physical explanation of Zitterbewegung-like effect near the zero-refractive-index point in a metamaterial slab in this paper. Between the negative and positive refractive index regions centered at the zero-refractive-index point, the transmittance spectrum distribution of the metamaterial slab is asymmetrical. When a symmetrical pulse propagates through the metamaterial slab, its transmitted spectrum becomes asymmetrical due to the asymmetry of the transmittance spectrum of the slab, leading to a transmitted pulse with an asymmetrical temporal shape. The asymmetry manifests a kind of temporally tailed oscillations, i.e., the Zitterbewegung-like effect. Further, the effect of the temporal and spatial widths of pulse, and the thickness of metamaterial slab on the tailed oscillations of the transmitted pulse has also been discussed. Our results agree well with what the other researchers obtained on the strength of relativistic quantum concepts; however, the viewpoint of our analysis is classical and irrelevant to relativistic quantum mechanics.
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At the exit surface of a photonic crystal, the intensity of the diffracted wave can be periodically modulated, showing a maximum in the positive (forward diffracted) or in the negative (diffracted) direction, depending on the slab thickness. This thickness dependence is a direct result of the so-called Pendellosung phenomenon, consisting of the periodic exchange inside the crystal of the energy between direct and diffracted beams. We report the experimental observation of this effect in the microwave region at about 14 GHz by irradiating 2D photonic crystal slabs of different thickness and detecting the intensity distribution of the electromagnetic field at the exit surface and inside the crystal itself.
Simulation of fermionic relativistic physics (such as Dirac and Weyl points) has led the dicovery of versatile and exotic phenomena in photonics, of which the optical-frequency realization is, however, still a challenging aim. Here we discover that the commonly-used woodpile photonic crystals for optical-frequency applications host novel fermionic relativistic degeneracies: a Dirac linenode and a topological quadratic degeneracy point, as {em guaranteed} by the nonsymmorphic crystalline symmetry. By reducing the space symmetry, type-II Dirac/Weyl points emerge as the descendants of the quadratic degeneracy point. These exotic optical waves mimicking the physics of unconventional fermionic relativistic waves and hosting anomalous optical properties in subwavelength, all-dielectric photonic crystals could open a new avenue for future optical science.
We develop a dynamic description of an effective Dirac theory in metamaterials, in which the wavefunction is modeled by the corresponding electric and magnetic field in the metamaterial. This electro-magnetic field can be probed in the experimental setup, which means that the wavefunction of the effective theory is directly accessible by measurement. Our model is based on a plane wave expansion, which ravels the identification of Dirac spinors with single-frequency excitations of the electro-magnetic field in the metamaterial. The characteristic Zitterbewegung is shown to emerge in simulations of the effective theory and we verify this signature with an analytic solution.
Weyl points are point degeneracies that occur in momentum space of periodic materials, and are associated with a quantized topological charge. We experimentally observe in a 3D micro-printed photonic crystal that a charge-2 Weyl point can be split into two charge-1 Weyl points as the protecting symmetry of the original charge-2 Weyl point is broken. Moreover, we use a theoretical analysis to confirm where the charge-1 Weyl points move within the Brillouin zone as the strength of the symmetry breaking increases, and confirm it in experiments using Fourier-transform infrared spectrometry. This micro-scale observation and control of Weyl points is important for realizing robust topological devices in the near-infrared.
We show that point defects in two-dimensional photonic crystals can support bound states in the continuum (BICs). The mechanism of confinement is a symmetry mismatch between the defect mode and the Bloch modes of the photonic crystal. These BICs occur in the absence of bandgaps and therefore provide an alternative mechanism to confine light. Furthermore, we show that such BICs can propagate in a fiber geometry and exhibit arbitrarily small group velocity which could serve as a platform for enhancing non-linear effects and light-matter interactions in structured fibers.
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