Research On Spatiotemporal Instabilities In Nonlinear Asymmetric Oppositely Directed Coupler With A Negative-index Metamaterial Channel

Recently, metamaterials with unique characteristics such as negativepermittivity and permeability which can not occur in ordinary materialwill lead to an electromagnetic revolution. Artificially designing theconstitution of a unit of geometry, size, embedded objects can determinethe the electromagnetic parameters of metamaterials such as dielectricconstant, magnetic permeability. The spatiotemporal instability in theasymmetric coupler has been investigated focusing on the new featuresand we compare it with coupler designed with ordinary material. The mainresults are as follows:Firstly, by combining the generalized nonlinear Schr dinger equationderivation methods and the properties of metamaterials, theoretical modelof nonlinear asymmetric oppositely directed coupler with a negative-indexmetamaterial channel has been investigated based on Maxwell equations.The ultrashort pulse new magnetic response and copropagatingtransmission mechanism in metamaterials coupler has been revealed. It provides theoretical support while we are investigating how theseelements impact instability.Secondly, the spatiotemporal instability in the asymmetric couplernegative-index metamaterial is investigated. The influences of input power,power ratio of the forward-and backward-propagating waves, andcoupling coefficients on the spatiotemporal instability are discussed. It isfound that the MI can occur only if the transverse wave numbers satisfythe threshold condition. The results also show that increasing the inputpower or decreasing power ratio of the forward-andbackward-propagating waves promotes the spatiotemporal instability andmerges the different instability regions together. Moreover, decreasing thecoupling coefficient suppresses the peak gain, spreads the gain spectrum.The controllable electromagnetic parameters of negative-indexmetamaterials will provide more methods to engineer the MI and solitonformation in this coupler.Thirdly, the electromagnetical simulation model of asymmetricdirectional coupler waveguide is estabilished. We found that the different incident light ports lead to different light waves loss. The importantelectromagnetic parameters like the electrical field strength, the ratio ofthe transmission and reflection is totally different with ordinary materialcoupler. In addition, by investigating the ratio of the transmission andreflection, we found that under the circumstance that the incident light isfrom metamaterials, the loss is more pronounced than the incident light isfrom ordinary material. The coupler which is a typical type of mixingusing the conventional materials and metamaterials will provide a valuablereference on designing optical devices.