Manipulation Of Optical Fields In Topological Waveguide Arrays

Artificial photonic structures enable flexible control of the frequency,wave vector,polarization,and phase of light.In recent years,photonic topological order-a property of photonic materials that quantifies the overall behavior of the wave function over the entire energy band-has become another new degree of freedom in manipulating the photonic systems,which provides a fundamental basis for exploring new photonic states and opens the door for many application possibilities.Among various photonic topological systems,the waveguide array has become an important platform due to its flexibility,simple in design,and loose fabrication requirement,based on which a variety of boundary states with topological characteristics have been demonstrated,such as topological zero mode,Floquet ? mode,etc.More interestingly,the development of non-Hermitian and parity-time(PT)photonics in recent years has further extended the degree of freedom of the photonic system to new complex parameter space.By designing and manipulating the imaginary part of the waveguide refractive index(i.e.,optical gain and loss),a series of novel optical phenomena and effects can be realized.In addition to providing a good platform for exploring new topological phases and states,topological waveguide arrays also endow the photonic system with unique effects and have application potential in developing brand-new optical devices.Focusing on the high-density photonic topological waveguide array,this thesis launches a series of theoretical and experimental researches on topological photonics and non-Hermitian photonics.By changing the spatial arrangement,bending configuration,and loss modulation of the waveguides,we reveal the delicate interplay of the topological states,Floquet quasi-energy spectrum,and PT symmetry.On the basis of investigating novel optical effects,the principles of topological photonics are applied to the design of new integrated photonic devices and components with highdensity photonic integration functionalities,which would open up new paths for a wide range of applications in optical communications,computing,and sensing.The particular contents include:1.The intrinsic properties and mutual coupling characteristics of the zero modes and the bound states in one-dimensional(1D)topological waveguide arrays with multiple "kink" structures were studied,as well as the multi-channel optical field transmission function.We constructed a 1D topological waveguide array with multiple "kink" structures and systematically investigated the mode distributions of the topological zero mode,bound states,and the coupling effect between these modes.The robustness of the zero-mode coupling between the "anti-kink" structures was found to realize functionalities of robust and broadband topological coupler and beam splitter.Besides,using the antisymmetric characteristic of the zero modes of the "kinked" structure,stable phase inverter,mode conversion,and asymmetric light propagation functionalities were constructed.In addition,we realized high-density topological information transmission channels with low crosstalk.2.The manipulation of evanescent wave coupling,Floquet topological state,artificial gauge fields,and high-density photonic integration in the curved waveguide array were studied.We investigated the coupling control in a strongly coupled curved silicon waveguide system and realized the superlens function and high-density low-crosstalk waveguide array transmission scheme at the subwavelength scale.Besides,we found dispersionless coupling conditions of curved waveguides and developed broadband photonic integrated devices(such as couplers,beam splitters,etc.).Furthermore,the waveguide array of complex curved/straight waveguide combination was investigated in Floquet frameworks,and the characteristics of its quasi-band structure,topological? mode,as well as the influence of the artificial Floquet gauge modulation were studied.The asymmetric topological light propagation controlled by the artificial gauge fields in the Floquet waveguide array was found.3.The influence of PT-symmetry on the topological waveguides systems and optical field evolutions were studied.We investigated the interplay between the PT phase transition and the topological phase transition in open systems and revealed the influence of PT phases on topological modes.Besides,the breakup of the zero modes in a finite topological system was found able to be recovered by non-Hermitian modulation using chromium-deposited silicon waveguides.The enhancement of the topological protection by the non-Hermiticity was verified.Furthermore,we revealed the analogy between the non-Hermitian curved silicon waveguide Hamiltonian and the relativistic Dirac particles.By introducing the non-Hermitian modulation to the Dirac energy band and dispersions,the dynamics of the imaginary mass particles(e.g.,tachyon)were successfully demonstrated experimentally in chromium-deposited curved silicon waveguides platform for the first time.