Research And Design Of Surface Plasmon Polaritons Devices Based On Metal-insolator-metal Waveguides

Integrated optical devices based on traditional dielectric waveguides have encountered bottlenecks in the miniaturization and high-integration because of the limitation of the diffraction limit.Surface plasmon polartions(SPPs)is a kind of electromagnetic wave with strong localized field on the surface of metal and propagates along the interface between metal and insulator.The field intensity of SPPs is maximum at the interface and decays exponentially to the two sides.SPPs provides a possibility to control and manipulate light in nanoscale thanks to the properties of breaking the limitation of diffraction limit and possessing great local electromagnetic field enhancement effect.Metal-insulator-metal(MIM)waveguide is one of the typical plasmonic waveguides,MIM waveguides can control and guide light in subwavelength scale and have been regarded as one of the most promising nano-waveguides to realize compact photonic devices and integrated photonic circuits.A variety of SPPs devices based on MIM waveguides,such as splitters,modulators,M-Z interferometers,optical switches,lasers,and so on,have been theoretically and experimentally investigated.Moreover,some special optical effects,such as Fano resonances,electromagnetically induced transparency and slow light,have been achieved based on MIM waveguide structures and attracted a lot of attentions in recent years.In this paper,the transmission characteristics of the MIM waveguide coupled with resonant cavities and some special optical phenomena are theoretically and numerically studied.Some functional SPPs devices have been designed and investigated,the details are as follows:1.High-sensitivity refractive index sensor based on MIM waveguide structure.A compact structure is designed based on a defective MIM waveguide coupled to a square cavity.The transmission characteristics of the structure are analyzed using the temporal coupled mode theory(CMT),then numerically simulated by the finite element method.The results show that two sharp Fano resonances were originated from the interference between the wide resonant mode supported by the defective waveguide and narrow resonant modes in square cavity.The influences of geometrical parameters and refractive index of dielectric on the Fano resonances are numerically investigated.The simulation results show the Fano can be easily tuned by the structural parameters and refractive index,this structure can be utilized as a refractive index sensor with a sensitivity of 1120 nm/RIU,and the FOM can reach to 1.7×105.In addition,four Fano resonances are achieved in this structure by introducing a new square cavity on the other side of MIM waveuide.2.SPPs demultiplexer based on Fano resonances.On the basis of previous work,here a single Fano resonance structure unit is studied.The tuning property of the structure is analyzed by the finite element method.Then a 1×2 demultiplexer based on a T-shaped MIM waveguide is proposed.Two output ports of the structure contain a single Fano resonance structural unit,respectively.When the lengths of two side-coupled cavities are different,two optical signals with different resonant wavelengths can be selected using the Fano resonance peak in each output port.Similarly,a 1×3 demultiplexer based on the crossed MIM waveguide is designed.By controlling the cavities length or the refractive index of medium in three side-coupled cavities,three optical signals with different wavelengths can be selected in each output port.Since the sharp and asymmetric line shape of Fano resonance,the wavelength shift from peak to dip is very small and the contrast ratio between peak and dip is very high,so the wavelength resolution of SPPs demultiplexer based on Fano resonance can be evidently improved.3.Active control of slow light in a MIM waveguide structure.A novel MIM waveguide structure,which consists of an aperture-coupled square cavity and a slot cavity,is proposed and investigated theoretically and numerically.The results show plasmon-induced transparency(PIT)effect is achieved in the structure.By changing the quality factor of the aperture-coupled cavity,the delay of slow light in the structure can be tuned at the communication wavelength of 1.55 ?m.Simulation results show that,as the quality factor becomes smaller,the greater group index is obtained.In order to dynamically tune the slow light effect and obtain larger group index,the gain medium was introduced in slot cavity.By optically pumping the gain medium,active control of slow light is achieved.Further studies show that,with increasing of gain coefficient,the transmittance and group index increases exponentially in transparent window.Finally,three PIT effects is achieved in an extended structure.This structure plays an important role in highly integrated all-optical circuits,especially for ultrafast switches,optical buffers,lasers and nanosensors.