Study On The Wavelength-selective Graphene Photodetector Based On The Novel Micro-nano Grating

Photodetector is regarded as a stone of the optical receiver,which plays an important role in optical communication field.With the continuous development of communication rate and communication quality,photodetectors with wide response wavelength range and high responsivity have attracted more attentions.Graphene is a novel typical two-dimensional material,which demonstrates strong application potential in the field of photodetection due to its excellent photoelectric properties.In order to overcome the shortcomings of large size and low integration of the traditional optical receiver discrete device structure in the wavelength division multiplexing system.In this thesis,we take graphene-based photodetectors as the main research object,starting from the key problem of low responsivity in graphene photodetectors which is due to poor graphene absorption efficiency.Then,we proposed the model of graphene photodetectors based on the different micro-nano grating structures.Thanks to the ability of the resonant waveguide grating and the resonant cavity structure to regulate the light field,the proposed structural model can realize wavelength-selective detection and also have the function of regulating the bandwidth.The main research work and corresponding results of this thesis are as follows:(1)Different models of graphene photodetectors with wavelength selectivity are proposed based on the zero-contrast grating and high-contrast grating structures.For the graphene photodetector with zero-contrast grating,the physical model of the device is established based on the coupled mode theory,and its physical mechanism is revealed to be the combination of the grating guided mode resonance effect and the Fabry-Perot cavity effect in the structure.Corresponding results show two remarkable near-perfect narrowband absorption peaks appeared at 1535.8 nm and 1555.0 nm,with absorption of99.8% and 99.9%,respectively.For the high-contrast grating graphene photodetector model,we mainly studied the influence of the high-contrast grating on the output spectrum.According to the results,we can find that the change of the thickness of the grating layer can make the wavelength shift in the wavelength range of 1.5 μm–1.6 μm while maintaining high absorption efficiency,and the change of the resonant cavity length will make the spectrum appear periodically.(2)A graphene photodetector model with a double-layer asymmetric metamaterial grating structure is constructed based on the ability of the resonant grating structure to control the light field mode.The physical model of the device is established according to the coupled mode theory,and analyzed with the finite element method.Studies have shown that changing the cavity length of the proposed structure can realize the function of bandwidth regulation while wavelength-selective absorption is achieved,which is because changes in the eigenvalue information of the structure.The line width of the absorption spectra can vary in the range of 0.2 nm–1.2 nm.In addition,the dynamic adjustment of absorption efficiency is realized based on the adjustable chemical potential of graphene materials.