Sculpting the vacuum in a photonic band gap micro-chip

We describe the engineering of the electromagnetic vacuum in a 2D–3D photonic bandgap (PBG) hetero-structure. This facilitates the development of novel active devices and the observation of novel quantum electrodynamic phenomena. We consider a specific architecture suitable as an all-optical micro-transistor capable of novel ultra-fast response with low switching power requirements. This relies on a unique collective atomic switching and population inversion achieved by coherent resonant pumping in a suitably engineered vacuum. Specific waveguide architectures within the 3D PBG micro-chip provide local density-of-states (LDOS) peaks near their cutoff frequency. These provide “building blocks” for electromagnetic vacuum engineering without recourse to conventional high Q-factor micro-cavities. For the all-optical micro-transistor, a fork shape LDOS within the micro-chip is desirable, using trimodal waveguide architecture. We delineate the functional robustness of these architectures to disorder caused by manufacturing errors within the PBG micro-chip.     

Electromagnetically induced exciton mobility in a photonic band gap

It is suggested that an exciton in the engineered vacuum of a photonic-band-gap-quantum-well heterostructure exhibits electromagnetically induced anomalous quantum dynamics. The exciton is dressed by coherent emission and reabsorption of virtual photons near the photonic band edge and captured in momentum space, lowering its energy by 1-10 meV and lowering its effective mass by 4-5 orders of magnitude. The photonic band gap simultaneously enables strong coupling to confined optical modes and long exciton lifetime.     

Second indirect band gap in silicon

We report the first observation of the г₂₅→L₁ (second indirect) transition in Si based on optical absorption studies. The energy, (1650 ± 10) meV, measured for this critical point shows that there remains a large discrepancy between theoretical band structure calculations and experimental results for this material.     

Three-dimensional photonic quasicrystal with a complete band gap

The band structure of three-dimensional cubic approximants of a photonic quasicrystal has been determined by numerical calculation. The approximants of different orders appear to have large, almost isotropic, band gaps in a wide range of relative permittivity values. The existence of the complete band gap in the photonic quasicrystal with the six-dimensional bcc lattice is shown.     

Microstrip microwave band gap structures

Microwave band gap structures exhibit certain stop band characteristics based on the periodicity, impedance contrast and effective refractive index contrast. These structures though formed in one-, two- and three-dimensional periodicity, are huge in size. In this paper, microstrip-based microwave band gap structures are formed by removing the substrate material in a periodic manner. This paper also demonstrates that these structures can serve as a non-destructive characterization tool for materials, a duplexor and frequency selective coupler. The paper presents both experimental results and theoretical simulation based on a commercially available finite element methodology for comparison.      

Energy transmission in the forbidden band gap of a nonlinear chain

A nonlinear chain driven by one end may propagate energy in the forbidden band gap by means of nonlinear modes. For harmonic driving at a given frequency, the process occurs at a threshold amplitude by sudden large energy flow that we call nonlinear supratransmission. The bifurcation of energy transmission is demonstrated numerically and experimentally on the chain of coupled pendula (sine-Gordon and nonlinear Klein-Gordon equations) and sustained by an extremely simple theory.     

Properties of the angular gap in a one-dimensional photonic band gap structure containing single negative materials

Properties of the angular gap in a one-dimensional photonic band gap structure containing single negative materials are investigated. This gap forms at oblique incidence due to the total internal reflection into air when the Snell's law breaks down. Its lower edge occurs at the frequency where the refractive index of one or both layers of the structure approaches zero. This gap is found to be highly sensitive to the incident angle and the polarization of the incident light, but is not affected by the thickness ratio of the layers. It is also shown that the electric field gets extremely enhanced at the lower edge of this gap for transverse magnetic polarization. This highly enhanced electric field can be utilized for certain applications.     

Optical band gap of Si nanoclusters

We discuss the nature of the optical transitions in porous silicon and in Si nanoclusters in the light of recent theoretical calculations. The accuracy of the different techniques used to calculate the band gap of Si nanoclusters is analyzed. We calculate the electronic structure of crystallites in the Si-III (BC8) crystalline phase which is known to have a direct gap and we examine the effect of quantum confinement on clusters of SiGe alloy and amorphous silicon. The comparison with the experiments for all the systems suggests the possibility of different channels for the radiative recombination.     

Excitons in direct band gap cubic semiconductors

Perturbation is applied to study of the Wannier-Mott excitons in direct band gap cubic semiconductors with a fourfold degenerate highest valence band. The fine structure of exciton energy levels is investigated. General formulae are derived for the matrix elements of the perturbation. From these expressions it is straightforward to obtain values of the fine structure splittings of the energy levels and the wave functions of corresponding staes in any order of perturbation theory. A comparison with results of previous works is made.     

Sizable band gap in organometallic topological insulator

Based on first principle calculation when Ceperley–Alder and Perdew–Burke–Ernzerh type exchange-correlation energy functional were adopted to LSDA and GGA calculation, electronic properties of organometallic honeycomb lattice as a two-dimensional topological insulator was calculated. In the presence of spin–orbit interaction bulk band gap of organometallic lattice with heavy metals such as Au, Hg, Pt and Tl atoms were investigated. Our results show that the organometallic topological insulator which is made of Mercury atom shows the wide bulk band gap of about ∼120 meV. Moreover, by fitting the conduction and valence bands to the band-structure which are produced by Density Functional Theory, spin–orbit interaction parameters were extracted. Based on calculated parameters, gapless edge states within bulk insulating gap are indeed found for finite width strip of two-dimensional organometallic topological insulators.     

Acoustic beam splitting in a sonic crystal around a directional band gap

Beam splitting upon refraction in a triangular sonic crystal composed of aluminum cylinders in air is experimentally and numerically demonstrated to occur due to finite source size,which facilitates circumvention of a directional band gap.Experiments reveal that two distinct beams emerge at crystal output,in agreement with the numerical results obtained through the finite-element method.Beam splitting occurs at sufficiently-small source sizes comparable to lattice periodicity determined by the spatial gap width in reciprocal space.Split beams propagate in equal amplitude,whereas beam splitting is destructed for oblique incidence above a critical incidence angle.     

Avalanche multiplication in graded band gap structures

Properties and peculiarities of avalanche multiplication in the p-i-n structures with the graded i-region are discussed. It is shown that the grading of the band gap of semiconductors in the high field region of infrared avalanche photoheterostructure governs the process of multiplication gain and improves noise characteristics of such photodiodes.     

Variation of band gap in Se-based chalcogenide glasses

The random network model for amorphous alloys proposed by White has been developed for the system irradiated with light. The model suggests that the photobleaching in GeSe₂ film and the photodarkening in AsSe film may be due to change in the number of the bonds.     

Dual-beam-reflection phenomenon due to leaky modes in a photonic band gap

We show a dual-beam-reflection phenomenon for a Gaussian beam illuminating a hybrid structure of a dielectric waveguide and photonic crystal (WG-PC) inside the photonic band gap by numerical simulations. One reflection beam has a giant negative lateral shift, but the other has a positive lateral shift. The finite-difference time-domain (FDTD) simulations show that this phenomenon has a time delay effect and comes from the leaky surface mode of the hybrid structure. Field profile of the leaky mode demonstrates a strong localized stationary field in the higher dielectric medium. Furthermore, the maximum lateral shift is almost two times of the waist of the incident beam.