Research On Optical Absorption Enhancement Mechanism Of Ultra-thin Two-Dimensional Material Microstructures

Since graphene is discovered in 2004,exploring novel two-dimensional materials has been a hot topic of research.In addition to graphene,two-dimensional materials such as phosphoenene,transition metal sulfide,oxide,and hexagonal boron nitride are successively prepared,which effectively broadens the field of the use of two-dimensional materials.Because of their unique structure,outstanding physical and optical properties,these two-dimensional materials have significantly potential applications in electronics,transparent electrodes,chemistry,biology,and medicine.This paper focuses on the realization of the absorption enhancement of micro-nano structures based on two-dimensional materials graphene and molybdenum disulfide.Some simple and flexible waveguide structures are designed and the optical absorptivity of these structures was theoretically calculated.The physical mechanism responsible for absorption enhancement was analyzed.The geometrical parameters of the optical structures,the incident angle and the polarization state on the modulation of optical responses are systematically studied.The main research contents of this paper are as follows:1.Monolayer graphene-based sensor with photonic crystal slabs:This part mainly uses graphene to cut off periodic photonic crystals to excite Bloch surface waves,which can achieve light absorption?or reflection attenuation?in the visible-near-infrared waveband.The mechanism corresponding to this optical phenomenon can be applied to the sensor.First,graphene is a two-dimensional material with excellent properties in various aspects.More importantly,graphene exhibits a wavelength-independent fixed absorptivity of 2.3%in the visible-near-infrared band.By introducing graphene into the photonic crystal to excite the Bloch surface wave resonance,the total absorption of light can be achieved while the attenuation of the reflected light is attained.Here,we apply the attenuated total internal reflection to the sensor and theoretically achieve high sensitivity sensing performance.2.Wide-angle and polarization-insensitive graphene absorber:This part mainly designs a graphene/germanium-based one-dimensional stacked grating structure with high absorptivity under the condition of wide angle,two polarizations in the atmospheric transmission window wavelength range.The absorption of monolayer graphene is very low and germanium is a lossless material with a high refractive index in the wavelength range of interest.Although grating structures generally exhibit polarization dependence,the grating structure exhibits polarization insensitivity when we use such a stacked structure grating.The grating structure excites cavity mode resonance?CMR?under the transverse electric field?TE?polarization and surface magnetic resonance?MR?modes under transverse magnetic?TM?polarization.In addition,the corresponding resonant modes for both polarizations are angularly independent.Therefore,whether it is TE polarized wave or TM polarized wave,through structural design,we can achieve wide-band high absorption at 2.9?m at any angle.3.Enhanced absorption of a low-contrast dielectric grating structure based on molybdenum disulfide?MoS₂?:The main content of this part is to design a simple all-dielectric waveguide grating structure with excited Fano resonance mode.Then,by adding the two-dimensional material MoS₂ on the top of the structure,an enhanced absorptivity at the wavelength corresponding to the Fano resonance is attained.The optical structures in the conventional structural design are complicated,making the fabrication process of the micro/nano structure relatively difficult.Here,the absorber structure of our design is absolutely simple and easy to manufacture.Finally,improvements have been made on the basis of this simple grating structure in order to achieve higher absorptivity.Through analysis,it is found that the relationship between the period and width of the modulated MoS₂ strips can modulated to further promote the interaction of light with MoS₂ and realize higher absorptivity.