Brillouin zone

About: Brillouin zone is a research topic. Over the lifetime, 13849 publications have been published within this topic receiving 383077 citations.

Electronic structure of Ge/Si monolayer strained-layer superlattices.

Abstract: We report the results of a study of Ge/Si strained-layer superlattices grown on (001) Si substrates. These results allow us to study the transition between superlattice and bulk states. We have examined samples whose superlattice period lies between 3 and 15 A\r{}, similar to the lattice parameter of the crystalline unit cell. All of the samples in this study are ordered superlattices with an average composition of ${\mathrm{Ge}}_{0.5}$${\mathrm{Si}}_{0.5}$. Intentional ordering on a monolayer scale was achieved by molecular-beam epitaxy. The optical energy-level spectra of these structures at critical points in the Brillouin zone were measured by Schottky-barrier electroreflectance in the energy range 0.6 to 4 eV. Some features of these spectra can be attributed to the creation of new band-to-band optical transitions that are induced by the artificial periodicity imposed on the sample during growth. These new energy levels are derived from bulk Si and Ge energy levels modified by heterojunction offset, strain, and the lower symmetry of the new unit cell. Several of the new optical transitions observed between 0.6 and 1.5 eV are normally forbidden or weakly allowed. The observation of relatively strong transition amplitudes in electroreflectance suggests that electric field effects and deviations from an ideal diamond-lattice structure may play an important role in the enchancement of transition probabilities in superlattice structures.

Brillouin optomechanics in nanophotonic structures

Abstract: The interaction between light and mesoscopic mechanical degrees of freedom has been investigated under various perspectives, from spectroscopy in condensed matter, optical tweezer particle trapping, and long-haul optical fiber communication system penalties to gravitational-wave detector noise. In the context of integrated photonics, two topics with dissimilar origins—cavity optomechanics and guided wave Brillouin scattering—are rooted in the manipulation and control of the energy exchange between trapped light and mechanical modes. In this tutorial, we explore the impact of optical and mechanical subwavelength confinement on the interaction among these waves, coined as Brillouin optomechanics. At this spatial scale, optical and mechanical fields are fully vectorial and the common intuition that more intense fields lead to stronger interaction may fail. Here, we provide a thorough discussion on how the two major physical effects responsible for the Brillouin interaction—photoelastic and moving-boundary effects—interplay to foster exciting possibilities in this field. In order to stimulate beginners into this growing research field, this tutorial is accompanied by all the discussed simulation material based on a widespread commercial finite-element solver.The interaction between light and mesoscopic mechanical degrees of freedom has been investigated under various perspectives, from spectroscopy in condensed matter, optical tweezer particle trapping, and long-haul optical fiber communication system penalties to gravitational-wave detector noise. In the context of integrated photonics, two topics with dissimilar origins—cavity optomechanics and guided wave Brillouin scattering—are rooted in the manipulation and control of the energy exchange between trapped light and mechanical modes. In this tutorial, we explore the impact of optical and mechanical subwavelength confinement on the interaction among these waves, coined as Brillouin optomechanics. At this spatial scale, optical and mechanical fields are fully vectorial and the common intuition that more intense fields lead to stronger interaction may fail. Here, we provide a thorough discussion on how the two major physical effects responsible for the Brillouin interaction—photoelastic and moving-boundary ef...

Double Dirac cones in triangular-lattice metamaterials

Abstract: It is shown by tight-binding approximation and group theory that a double Dirac cone, or a pair of two identical Dirac cones, of the electromagnetic dispersion relation can be created in the Brillouin zone center by accidental degeneracy of E1 and E2 modes in triangular-lattice metamaterials of C6v symmetry. The Dirac point thus obtained is equivalent to a zero-index system, so we can expect unique optical propagation phenomena such as constant-phase waveguides and lenses of arbitrary shapes. Zitterbewegung is also expected without disturbance due to an auxiliary quadratic dispersion surface, which is present for other combinations of mode symmetries to materialize the Dirac cones. To the best of the author’s knowledge, this is the first prediction of the presence of a double Dirac cone in metamaterials.

Comparison of the methods for discriminating temperature and strain in spontaneous Brillouin-based distributed sensors.

Abstract: A recently proposed method of measuring the two Brillouin frequencies in a multicompositional fiber core for unambiguously resolving temperature and strain in a distributed sensor is compared with the previously established technique of measuring the intensity and frequency of the single Brillouin peak in a standard single-mode fiber

Band representations and symmetry types of bands in solids

Abstract: Symmetry types of bands in solids are specified by means of band representations of space groups. This is a new kind of representation that corresponds to bands of energies rather than to single energies as in the case of usual representations. It is shown that each band representation defines a symmetry type of a band by specifying the symmetry of localized orbitals with respect to a whole lattice of point group centers. In this symmetry specification the quasicoordinate $\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}$ in the Wigner-Seitz cell plays a similar role to what is played by the quasimomentum $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ in the symmetry specification of Bloch states in the Brillouin zone.