Study On Micro/Nano Fiber-Based Plasmonic Waveguides And Grating Devices

Plasmonic waveguide possesses the advantages of high electric field confinement,strengthening the system integration,and will potentially be one of the important components of the nanophotonics devices,especially for compact nano-photonic integration.Plasmonic waveguide is the waveguide based on the interaction between the electromagnetic wave and free carriers on the surface of the conductor.It supports guided mode beyond the light diffraction limit,enabling ultra-high integration of photonic devices.Therefore,plasmonic waveguide has become one of the hot research topics currently.This dissertation focuses on the theoretical and experimental study of plasmonic waveguide.For the plasmonic waveguide constituted by the micro/nano fiber and the metal thin film,the simulation results obtained using Lumerical software and the experimental investigation of the transmission performances are provided.The filtering performances of the plasmonic waveguide composed of the micro/nano fiber and the metal grating are next studied by simulations and experiments.Finally,the filtering performances of a plasmonic waveguide made of Ge-Sb-Te(GST)grating sandwiched in a micro/nano fiber and an Au thin film are explored theoretically and experimentally.The main contents of this dissertation are as follows:Firstly,the transmission characteristics of two plasmonic waveguide structures using both a straight micro/nano fiber and a curved micro/nano fiber attached to the metal thin film are analyzed by simulation.We experimentally obtain the transmission spectra of different modes in a plasmonic waveguide.The dependence of the transmission spectrum on various device structure parameters are analyzed in detail.The propagation loss of the plasmonic waveguide is extracted by linear fitting.It is shown that higher-order modes of plasmonic waveguide can be excited in the straight micro/nano fiber-based structure while only the fundamental mode can be excited in the curved micro/nano fiber-based plasmonic waveguide.The propagation loss is reduced with the increased micro/nano fiber radius.Secondly,a Bragg grating based on the plasmonic waveguide is presented.We study the filtering performances of the Bragg grating and effects of various parameters,including the coupling length,the rotational angle between the micro/nano fiber and the metal grating,and the radius of the micro/nano fiber.Using the optimal dimensions of the metal grating obtained by simulations,we fabricate the metal grating using the standard CMOS technology.The process flow is presented in details.The dependence of the metal grating reflection spectrum on various structural parameters is experimental explored.The results show that the plasmonic mode can enhance the filtering performance of the Bragg metal grating.There are two reflection peaks in the reflection spectrum,due to reflection by the fundamental and the first-order modes of theplasmonic waveguide.The reflection peaks experience red-shift with the increase of the micro/nano fiber radius and the rotational angle between the micro/nano fiber and the metal grating.The peaks in the reflection spectrum are absent when the angle becomes too large.The coupling length between the micro/nano fiber and the metal grating has almost no effect on the reflection peak profile.Thirdly,to explore more features of the plasmonic waveguide,we sandwiched a GST grating between the micro/nano fiber and the Au film.We analyze its filtering performances and the effect of various structural parameters,including the coupling length between the micro/nano fiber and the GST grating,the radius of the micro/nano fiber,the period and the filling factor of the GST grating.The impact of GST phase change on the filtering performances is studied.The fabrication process of the GST grating is briefly introduced.GST exhibits two phase states: amorphous and crystalline.In its amorphous state,GST shows semiconductor characteristics,and the optical field is mainly confined in the GST grating.In contrast,when the GST is in its crystalline state,it exhibits metal characteristics with its optical field propagating along the interface between the micro/nano fiber and the GST grating.The extinction ratio of the reflection peaks decreases substantially when the GST phase is changed from the amorphous state to the crystalline state.Such phenomenon indicates that the GST grating can also function as an optical switch.The center wavelength of the reflection passband experiences a red-shift with the increase of the micro/nano fiber radius.The micro/nano fiber and GST grating coupling length has no significant effect on the filtering performances.Finally,we summarize the main work and innovations of the dissertation.The outlook of micro/nano fiber-based plasmonic waveguide is pointed out.