Research On Optical Propagation Properties Of Subwavelength Structure Based On Metal/graphene Waveguide

Surface plasmon polaritons?SPPs?structures based on the metal-insulator-metal?MIM?or graphene waveguide have attracted great interest of domestic and interna-tional researchers due to their remarkable optical properties.Meanwhile,many SPPs optical devices are also widely studied.However,some optical devices are still in the initial stage,and the corresponding mechanisms need to be further studied.Moreover,SPPs optical devices with better performance need to be further investigated.To in-vestigate these problems,in this paper,the optical propagation properties of sub-wavelength structure based on metal/graphene waveguide has been investigated theo-retically and numerically.I believe theses results can be conducive to lay a solid the-oretical foundation for developing advanced optical devices and integrated circuits.The main results of this thesis are listed blow.?1?A plasmon-induced transparency?PIT?spectral response in an ultra-compact plasmonic structure composed of a metal–insulator–metal?MIM?waveguide Bragg grating coupled with an air rectangle cavity is proposed,and the corresponding transmission characteristics are investigated theoretically and numerically.By using the transmission line theory?TLT?,a remarkable PIT transmission can be proposed in this structure.Moreover,we study the transmission as a function of the coupling dis-tance between the air cavity and insulator layer,and we also discuss the transmission as a function of the thickness of air cavity.To validate the correctness of the TLT re-sults,we have compared them with the finite-difference time-domain method.Both of them agree well with each other.Thus,these results can offer a new possibility and important theory analysis for the designs of the optical switching devices,sensors,and slow light devices in highly integrated optical circuits.?2?In the visible and near-infrared range,monolayer molybdenum disulfide?MoS₂?has only about 10%absorption rate,which limits its optoelectronic applica-tions.In order to remarkably enhance its absorption capability,a tunable dual-band MoS₂-based perfect absorber inspired by metal-insulator-metal?MIM?metamaterial is proposed.By using the finite-difference time-domain simulations,dual-band perfect absorption peaks are realized in the visible light regime,and the absorptions of mon-olayer MoS₂ are enhanced up to 57%and 80.5%at the peak wavelengths.By manip-ulating related structural parameters,the peak wavelengths of MoS₂ absorption can be separately tuned in a wide wavelength range.Furthermore,the proposed absorber can tolerate a relatively wide range of incident angles and demonstrate polariza-tion-dependence.Thus,our results have a promising potential for developing ad-vanced nanoscale photonics devices working in the visible region.?3?A narrow-band plasmonic filter based on graphene waveguide with asymmet-rical structure is proposed and the corresponding transmission characteristics are in-vestigated.The asymmetrical structure consists of two sets of five air trenches with different trench sizes.Since the Bragg wavelength could be changed with the length and depth of each air trench,the bandgap?or the passband?of the single set with five short thick air trenches and the passband?or the bandgap?of the single set with five long thin air trenches are overlapped and the cascaded transmission of the two struc-tures is very low in a certain wavelength range.Due to the overlapping between the left edge of the passband of the short thick set and the right edge of the passband of the long thin set is non-zero,a narrow-band transmission peak with 3 dB bandwidth of0.12?m appears in the mid-infrared region around 6.9?m could be obtained in this way by using the finite-difference time-domain method.The proposed plasmonic fil-ters and the novel transmission characteristics obtained would be greatly beneficial to the fabrication of versatile,ultra-compact devices in the mid-infrared region for opti-cal communication and processing.?4?A novel nonreciprocal graphene waveguide with Kerr nonlinear material in mid-infrared region is proposed and the corresponding transmission characteristics are investigated by using the finite-difference time-domain method.In the proposed gra-phene waveguide,a transmission contrast ratio up to 19.2 dB can be achieved between forward and backward transmission,revealing an excellent nonreciprocal effect.Moreover,the proposed nonreciprocal graphene waveguide can also be flexibly con-trolled as forward transmission or backward transmission at different wavelengths by adjusting the structural parameters and input intensity.Thus,our tunable optical diode based on the graphene waveguide can be greatly beneficial in highly integrated optical circuits.