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 Physics , 2009, DOI: 10.1088/1464-4266/6/11/006 Abstract: In this paper, we investigate the single mode quantum properties of the codirectional Kerr nonlinear coupler when the frequency mismatch is involved and a condition for an exact solution of equations of motion is fulfilled. Particularly, we investigate quadrature and principal squeezing, Wigner function, quadrature distribution, phase distribution and phase variance. We show that the quadrature squeezing and the phase variance can exhibit collapse-revival and collapse-revival-subrevival phenomena, respectively, based on the values of the detuning parameter. Furthermore, we analytically demonstrate that the system can generate cat states, in particular, Yurke-Stoler states.
 Physics , 2009, DOI: 10.1016/j.physleta.2004.10.051 Abstract: In this Letter we study the evolution of the higher-order squeezing, namely, $n$th-order single-mode squeezing, sum- and difference-squeezing for the codirectional Kerr nonlinear coupler. We show that the amount of squeezing decreases when $n$, i.e. the squeezing order, increases. For specific values of the interaction parameters squeezing factors exhibit a series of revival-collapse phenomena, which become more pronounced when the value of $n$ increases. Sum-squeezing can provide amounts of squeezing greater than those produced by the $n$th higher-order ($n\geq 2$) squeezing for the same values of interaction parameters and can map onto amplitude-squared squeezing. Further, we prove that the difference-squeezing is not relevant measure for obtaining information about squeezing from this device.
 Physics , 2014, DOI: 10.1103/PhysRevA.90.013808 Abstract: Higher order nonclassical properties of fields propagating through a codirectional asymmetric nonlinear optical coupler which is prepared by combining a linear wave guide and a nonlinear (quadratic) wave guide operated by second harmonic generation are studied. A completely quantum mechanical description is used here to describe the system. Closed form analytic solutions of Heisenberg's equations of motion for various modes are used to show the existence of higher order antibunching, higher order squeezing, higher order two-mode and multi-mode entanglement in the asymmetric nonlinear optical coupler. It is also shown that nonclassical properties of light can transfer from a nonlinear wave guide to a linear wave guide.
 Physics , 2004, DOI: 10.1088/1464-4266/6/3/007 Abstract: We discuss a model comprising two coupled nonlinear oscillators (Kerr-like nonlinear coupler) with one of them pumped by an external coherent excitation. Applying the method of nonlinear quantum scissors we show that the quantum evolution of the coupler can be closed within a finite set of n-photon Fock states. Moreover, we show that the system is able to generate Bell-like states and, as a consequence, the coupler discussed behaves as a two-qubit system. We also analyze the effects of dissipation on entanglement of formation parametrized by concurrence.
 Physics , 2009, DOI: 10.1364/JOSAB.26.001289 Abstract: We analyse the entanglement dynamics in a nonlinear Kerr-like coupler interacting with external environment. Whenever the reservoir is in a thermal vacuum state the entanglement (measured by concurrence for a two-qubit system) exhibits regular oscillations of decreasing amplitude. In contrast, for thermal reservoirs we can observe dark periods in concurrence oscillations (which can be called a "sudden death" of the entanglement) and the entanglement rebuild (which can be named the "sudden birth" of entanglement). We show that these features can be observed when we deal with 2-qubit system as well as $2\otimes 3$ system.
 Dharmadas Kumbhakar International Journal of Optics , 2012, DOI: 10.1155/2012/173250 Abstract: Finite difference beam propagation method is an accurate numerical procedure, used here to explore the switching dynamics of a nonlinear coherent directional coupler. The coupling lengths derived from this simulation are compared with coupled mode theories. BPM results for the critical power follow the trend of the coupled mode theories, but it lies in between two coupled mode theories. Coupled mode theory is sensitive to numerical approximations whereas BPM results practically do not depend on grid size and longitudinal step size. Effect of coupling-region-width and core-width variations on critical power and coupling length is studied using BPM to look at the aspects of optical power-switch design. 1. Introduction Beam propagation method [1] is a versatile tool to investigate or model various optical phenomena in photonic devices. Earlier, the method was popular to find the guided modes in dielectric waveguide structures [2]; even in microstructure fibers like holey fibers it can be used to find the modes [3]. With suitable boundary conditions, it gave proper estimates of the propagation constant in leaky structures like arrow waveguides [4]. The method was used in linear directional couplers to simulate switching of a CW signal and filtering TE/TM mode signals [5]. With growing interest in nonlinear fibers, it was the only tool to model the pulse propagation [6] in conjugation with split-step Fourier transform. It has been also used to model various other nonlinear phenomena like second harmonic generation [7], leakage loss in buried silicon substrate [8], and so forth. Beam propagation method can be incorporated either in the finite element or finite difference framework. In cases where the interfaces are parallel to the axes, the two methods are almost the same in terms of accuracy, but the latter is sometimes preferred due to its simplicity in implementation. Nonlinear directional coupler (NLDC) is a very useful device in photonic circuits; it can be used as all optical modulator, switches, logic gates, and so forth. Jenson [9] first showed that total power exchange in a linear coherent coupler is lost in a nonlinear coherent coupler above a critical input power in one guide. This fact was used to design power-controlled all optical switches [10, 11]. The device can also be used as phase-controlled switches [12] and optical modulator [13]. So, the knowledge of the dependence of the critical power and phase variations on the NLDC parameters is important. There are numerous studies on this device; analytic methods include coupled mode theory [9,
 H. Harsoyono Songklanakarin Journal of Science and Technology , 2005, Abstract: A study of coupling characteristics between two optically nonlinear planar waveguides has been performed in terms of their individual analytical solutions. It is shown that with an appropriate choice of guide widths and proper redefinition of effective propagation constants, the commonly adopted dual waveguide coupled equations can be formally retained even when the optical nonlinearity in each guide is fully taken into account. A specific numerical illustration of the power flow patern was given on the basis of its analytical expression derived from the coupled equations. The result describes the detailed coupling characteristics and its variation with respect to input optical power, demonstrating its viability for active optical device applications.
 Physics , 2013, DOI: 10.1364/JOSAB.30.000549 Abstract: We demonstrate a Kerr-lens mode locked folded cavity using a planar (non-Brewster) Ti:sapphire crystal as a gain and Kerr medium, thus cancelling the nonlinear astigmatism caused by a Brewster cut Kerr medium. Our method uses a novel cavity folding in which the intra-cavity laser beam propagates in two perpendicular planes such that the astigmatism of one mirror is compensated by the other mirror, enabling the introduction of an astigmatic free, planar-cut gain medium. We demonstrate that this configuration is inherently free of nonlinear astigmatism, which in standard cavity folding needs a special power specific compensation.
 EPJ Web of Conferences , 2013, DOI: 10.1051/epjconf/20134112010 Abstract: We present an ultrafast nonlinear coupler fabricated by selectively filling of two strands of a PCF with the liquid CCl4 which exhibits a large Kerr nonlinearity. We demonstrate power dependent switching in this optofluidic device.
 M. K. Olsen Physics , 2006, DOI: 10.1103/PhysRevA.73.053806 Abstract: We show that the intracavity Kerr nonlinear coupler is a potential source of bright continuous variable entangled light beams which are tunable and spatially separated. This system may be realised with integrated optics and thus provides a potentially rugged and stable source of bright entangled beams.
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