Complete photonic bandgaps in supercell photonic crystals

We develop a class of supercell photonic crystals supporting complete photonic bandgaps based on breaking spatial symmetries of the underlying primitive photonic crystal. One member of this class based on a two-dimensional honeycomb structure supports a complete bandgap for an index-contrast ratio as low as $n_{high}/n_{low} = 2.1$, making this the first such 2D photonic crystal to support a complete bandgap in lossless materials at visible frequencies. The complete bandgaps found in such supercell photonic crystals do not necessarily monotonically increase as the index-contrast in the system is increased, disproving a long-held conjecture of complete bandgaps in photonic crystals.Comment: 5 pages, 4 figure

Ab-initio theory of quantum fluctuations and relaxation oscillations in multimode lasers

We present an \emph{ab-initio} semi-analytical solution for the noise spectrum of complex-cavity micro-structured lasers, including central Lorentzian peaks at the multimode lasing frequencies and additional sidepeaks due to relaxation-oscillation (RO) dynamics. In~Ref.~1, we computed the central-peak linewidths by solving generalized laser rate equations, which we derived from the Maxwell--Bloch equations by invoking the fluctuation--dissipation theorem to relate the noise correlations to the steady-state lasing properties; Here, we generalize this approach and obtain the entire laser spectrum, focusing on the RO sidepeaks. Our formulation treats inhomogeneity, cavity openness, nonlinearity, and multimode effects accurately. We find a number of new effects, including new multimode RO sidepeaks and three generalized $\alpha$ factors. Last, we apply our formulas to compute the noise spectrum of single- and multimode photonic-crystal lasers.Comment: 27 pages, 3 figure

Effects of non-Hermitian perturbations on Weyl Hamiltonians with arbitrary topological charges

We provide a systematic study of non-Hermitian topologically charged systems. Starting from a Hermitian Hamiltonian supporting Weyl points with arbitrary topological charge, adding a non-Hermitian perturbation transforms the Weyl points to one-dimensional exceptional contours. We analytical prove that the topological charge is preserved on the exceptional contours. In contrast to Hermitian systems, the addition of gain and loss allows for a new class of topological phase transition: when two oppositely charged exceptional contours touch, the topological charge can dissipate without opening a gap. These effects can be demonstrated in realistic photonics and acoustics systems.Comment: 11 pages, 9 figure

Italian Roots, American Ways: Cultural Issues in Twentieth-Century Italian American Communities

In this essay the cultural issues of Italian American communities in the 20th century USA have been examined on the examples from three novels: Christ in Concrete by Pietro Di Donato, The Godfather by Mario Puzo and Household Saints by Francine Prose. The cultural issues elaborated here were dealing with problems of assimilation, acculturation and other social and economic questions. The mentioned issues were studied on Italian – American literary works, but sometimes there were also comparisons to Croatian-American and Lithuanian-American literature, based on the novels Anna Marinkovich by Edward Ifkovic and The Jungle by Upton Sinclair. First, the essay offers a definition of an immigrant novel based on the examples from William Boelhower’s The Brave New World of Immigrant Autobiography and The Immigrant Novel as a Genre. Special emphasis was put on the opposition between the Old World and the New World, i.e. the opposition between tradition and modern world. In regards to the Old World, the essay discusses how Italian immigrants made peace with the new and modern, combining the elements of both worlds into a unique Italian American community. Given that the essay deals with the period of the twentieth century, it was important to mention the position of women and their progressive role from the Thirties to the Eighties. The feminine role developed from being solely housewives to becoming confident, independent and working women. Some historic events like world wars have changed the viewpoint and have made women become emancipated by getting jobs and expanding their role from a completely maternal one to a role of woman being capable of not only working but also taking care of the household

Quantitative test of general theories of the intrinsic laser linewidth

We perform a first-principles calculation of the quantum-limited laser linewidth, testing the predictions of recently developed theories of the laser linewidth based on fluctuations about the known steady-state laser solutions against traditional forms of the Schawlow-Townes linewidth. The numerical study is based on finite-difference time-domain simulations of the semiclassical Maxwell-Bloch lasing equations, augmented with Langevin force terms, and thus includes the effects of dispersion, losses due to the open boundary of the laser cavity, and non-linear coupling between the amplitude and phase fluctuations ($\alpha$ factor). We find quantitative agreement between the numerical results and the predictions of the noisy steady-state ab initio laser theory (N-SALT), both in the variation of the linewidth with output power, as well as the emergence of side-peaks due to relaxation oscillations.Comment: 24 pages, 10 figure