Light Propagation In Novel Nanostructured Waveguides

Nowadays great efforts have been devoted in manipulating light signals in order to make photons as an alternative carrier for information transfer.New principles and technology for trapping,storing and releasing light signals become extremely important.Various schemes have been proposed to trap the light.For example,by introducing defects in photonic crystals,photons can be localized in the structures.Very recently,the spatial separation of optical spectrum and the formation of a trapped "rainbow" in metamaterials have been theoretically demonstrated at both terahertz frequencies and telecommunication wavelengths.In some senses,these artificial structures play the role of "waveguides".It is well known that waveguides confine and guide the light waves,and play an important role in the modern optoelectronics and telecommunications.The development of communication science and technology calls for more miniature and compact optical waveguides.In the following,we present our results on optical waveguide.First,we present the frequency selection and the spatial separation of light waves in a self-similar dielectric waveguide,where a hollow core is surrounded by a coaxial Thue-Morse multilayer.Due to self-similar furcation feature in its photonic band structure,the transmission multi-bands are achieved.More interestingly,the electromagnetic fields for different modes are spatially separated in different cladding layers,therefore,a "rainbow" can be trapped in the Thue-Morse waveguide.The finding can be applied in designing miniaturized multifunctional optical waveguides.Second,we develop a method to tune the propagating modes and "rainbow" by changing the thicknesses and refractive indexes ratio of the cladding dielectrics.The method makes it realistic and convenient to design optical waveguide for different needs.For example,by changing refractive indexes in the cladding multilayer,we achieve a waveguide with ultra-narrow band and enhanced quality factor.Such a waveguide can act as a narrowband filter or laser resonator.It is of benefit to designing miniaturized multifunctional optical devices,such as spectroscopy on chip.Third,in technical applications,it is worthwhile to tune the devices by external fields.We demonstrate a self-similar waveguide infiltrated by liquid crystal to achieve tunable "rainbow.trapping".Due to the self-similar furcation feature,we show that the multiple transmission bands appear in the photonic band structure,a"rainbow" is trapped as cladding modes in the waveguide.Furthermore,by changing temperature,the refractive index of the liquid crystal varies,thereafter,both the photonic bands and the transmission modes are tuned.As the result,the "rainbow" in the waveguide significantly changes its color when the temperature is increased.Fourth,it has been demonstrated that metallic nanowires can act as sub-wavelength waveguide,and propose a realistic method to achieve surface plasmon polaritons(SPP)transmission.Here we investigate the dispersion relationships of SPP propagating for different size of silver nanowires and different surrounding media both theoretically and experimentally.Further,we introduce nanostructures to the silver nanowire to control the propagation of SPP.It has been demonstrated experimentally.