In this study, we investigate the optical bistability of graphene-coated nanoparticles with cylindrical core– shell structure at terahertz frequency, because graphene displays optical bistability and multistability in a broad range of incident optical intensity. The choice of core– shell system is due to its larger local electric field enhancement, where this characteristic is important for the optical bistable systems. This optical bistability strongly depends on the geometry of the nanoparticle, the fractional volume of the metallic core as well as Fermi energy of graphene. The surrounding medium could also finely affect the optical bistability and induce switching from optical bistability to optical tristability. Since the prosperity of optoelectronics properties of graphene and the importance of core– shell nanoparticles have attracted enormous interest, this model may find potential applications in optical bistable devices such as all-optical switches and biosensors at terahertz communication in near future.

Due to the growing demand for higher bandwidth, employing optical devices instead of electronic devices in data transmission systems has attracted much attention in recent years. Optical switches, modulators and wavelength converters are a few examples of the required optical devices. CMOS compatible fabrication of these devices, leads to much more growing of this technology. Optical pulse compression, is required for generating ultra-short pulses for high bandwidth optical transmission systems. In this work, we present a CMOS fabrication process compatible, integrated optical pulse compressor. A Silicon waveguide coated by MoS2 for nonlinearity enhancement is used for self-phase modulation and a chirped Bragg grating utilizing corrugated silicon waveguides is employed to achieve the required anomalous dispersion. Low power and high compression ratio were considered in this work. We achieved a compression ratio of 3. 5 by using a relatively low power optical pulse of 8W and a short waveguide length of 1mm.

A theory is presented for the dispersion relations of the nonlinear phononpolaritons arising when phonons are coupled to the electromagnetic waves in multilayered structures of nonlinear materials. The calculations are applied to a multilayered structure consisting of a thin film surrounded by semi-infinite bounding media where each layer may have a frequency dependent dielectric function and Kerr-type nonlinearity. At least one of the media is an ionic crystal supporting optical phonon modes. The resulting analytic and numerical solutions for the dispersion relations of phonon-polaritons with s-polarization are considered for several cases. We find that the presence of nonlinearities leads to multiple branches in the dispersion relation. The results are plotted as frequency versus wave vector and frequency versus nonlinearity for different phononpolariton modes. The parameters that modify the modes correspond to the inplane wave vector, the thickness of the film, the phonon frequencies and the nonlinearity of each layer.

One of the most important issues in controller design and analysis of a nonlinear system is its degree of nonlinearity. Helbig et al. proposed a method in which the system, along with a linear reference model (which is the sum of a couple of first order transfer functions), is stimulated with a set of input patterns. The outputs of these systems are then compared and the nonlinearity measure of the system is obtained as the normalized difference between the outputs of these two systems. In this paper, the linear reference model is replaced with two simpler linear ones. The proposed method has been used for assessment of the nonlinearity measure of various nonlinear systems that are used as standard benchmarks by the nonlinear process control research community. The results show that, despite the use of this simpler model with less parameters, the calculated nonlinearity measure is almost similar to the one obtained by Helbig's method. Furthermore, the nonlinearity measure obtained by the proposed method can be calculated very much faster.

A compatible theory of relativistic geodesy is quite necessary for future development of any formulation of the subject. In this paper, following recent studies which invoke an idea of relativistic geoid, i. e. the chronometric definition implied by the gravitational redshift, we revisit known calculations on some standard spacetimes. Among all, the notion of frame dragging in the Kerr spacetime and its relationship to the rotative observers needed for the consistent definition of the geoid is analyzed.