Mode beating in spot-size converter lasers

An anomalous modulation in the wavelength spectrum has been observed in lasers with spot-size converters. This intensity modulation is shown to be caused by beating between the fundamental lasing mode and radiation modes in the taper. This results in a periodic modulation in the net gain spectrum, which causes wavelength jumps between adjacent net gain maxima, and a drive current dependent spectral width that is expected to affect system performance. The amplitude of this spectral modulation is reduced significantly by either using an angled rear-facet which reflects the beating radiation modes away from the laser axis, or by using a nonlinear, adiabatic taper.     

THERMODYNAMIC AND PARTICLE-DYNAMIC STUDIES ON SYNTHESIS OF SILICA NANOPARTICLES USING MICROWAVE-INDUCED PLASMA CVD

1. Introduction1.1 Silica nanoparticles and synthesis methods Silica (SiO2) nanoparticles are widely used in industry asan active filler for polymer reinforcement, a rheologicaladditive in fluids, a free flow agent in powders, and anagent for chemical mechanical polishing during IC (inte-grated circuit) fabrication (Sniegowski & de Boer, 2000).Silica powder is also used for producing silicon carbide(Koc & Cattamanchi, 1998) or opaque silica aerosols (Leeet al., 1995). Many methods can …     

Green's functions for Maxwell's equations: application to spontaneous emission

We present a new formalism for calculating the Green's function for Maxwell's equations. As our aim is to apply our formalism to light scattering at surfaces of arbitrary materials, we derive the Green's function in a surface representation. The only requirement on the material is that it should have periodicity parallel to the surface. We calculate this Green's function for light of a specific frequency and a specific incident direction and distance with respect to the surface. The material properties entering the Green's function are the reflection coefficients for plane waves at the surface. Using the close relationship between the Green's function and the density of states (DOS), we apply our method to calculate the spontaneous emission rate as a function of the distance to a material surface. The spontaneous emission rate can be calculated using Fermi's Golden Rule, which can be expressed in terms of the DOS of the optical modes available to the emitted photon. We present calculations for a finite slab of cylindrical rods, embedded in air on a square lattice. It is shown that the enhancement or suppression of spontaneous emission strongly depends on the frequency of the light. This revised version was published online in November 2006 with corrections to the Cover Date.     

Nonlinear compression of optical solitons

In this paper, we consider nonlinear Schrödinger (NLS) equations, both in the anomalous and normal dispersive regimes, which govern the propagation of a single field in a fiber medium with phase modulation and fibre gain (or loss). The integrability conditions are arrived from linear eigen value problem. The variable transformations which connect the integrable form of modified NLS equations are presented. We succeed in Hirota bilinearzing the equations and on solving, exact bright and dark soliton solutions are obtained. From the results, we show that the soliton is alive, i.e. pulse area can be conserved by the inclusion of gain (or loss) and phase modulation effects.     

Symplectic supercuspidal representations and related problems

In this paper, we summarize the basic structures and properties of irreducible symplectic supercuspidal representations of GLn(F) over a p-adic local field F with characteristic zero, and explore possible topics for further investigation.     

Ultra-low-frequency dust-electromagnetic modes in self-gravitating magnetized dusty plasmas

Obliquely propagating altra-low-frequency dust-electromagnetic waves in a self-gravitating, warm, magnetized, two fluid dusty plasma system have been investigated. Two special cases, namely, dust-Alfvén mode propagating parallel to the external magnetic field and dustmagnetosonic mode propagating perpendicular to the external magnetic field have also been considered. It has been shown that effects of self-gravitational field, dust fluid temperature, and obliqueness significantly modify the dispersion properties of these ultra-low-frequency dust-electromagnetic modes. It is also found that in parallel propagating dust-Alfvén mode these effects play no role, but in obliquely propagating dust-Alfvén mode or perpendicular propagating dust-magnetosonic mode the effect of self-gravitational field plays destabilizing role whereas the effect of dust/ion fluid temperature plays stabilizing role.     

Two different copper sites in hexakis(1-methyltetrazole)copper(II) bis(tetrafluoroborate)

An electron spin resonance study at temperatures between 300 and 4 K demonstrates that the two crystallographically inequivalent Cu(II) sites in the title compound are subject to different Jahn-Teller behaviour. It is shown that this is not induced by cooperative interactions between the Jahn-Teller sites but arises from the different lattice symmetries of the two sites.     

From Multi-Site to On-Site Transfer Matrix Models for Self-Similar Chains

We show how transfer matrix models on chains that are self-similar (renormalizable) with respect to a substitution rule can be transformed from multi-site models in which transfer matrices depend on the nature of a finite number of neighboring sites, to on-site models in which transfer matrices depend on the nature of one site only. We present sufficient conditions and show that these conditions are satisfied in the case of quasiperiodic chains of two symbols that are renormalizable with respect to an invertible substitution rule. We illustrate the application of our results to tight-binding Schrödinger equations modeling the electronic behavior of self-similar chains of atoms and to models describing the transmission of light through self-similarly stacked multilayers.