The Study Of Mid-Wave Infrared Modulation Based On Graphene

The Mid-Wave infrared(MWIR)range refers to the infrared wave with the wavelength of3?5 ?m in the electromagnetic spectrum,which always has been an important optical window due to its outstanding functions in the fields of communication,high temperature remote detection and gas detection.However,the development of MWIR had been still slower compared with shorter wavelength range such as poor optical infrastructure,low efficiency,high price and even non-existence of optical components.In this thesis,two kinds of MWIR optical modulator are designed by graphene for amplitude modulator and tunable wavelength filter.With varying Fermi levels of graphene,these optical devices can continuously modulate the amplitude and resonance wavelength respectively.The main research contents are explained in the following paragraphs.Firstly,an amplitude modulator was invented and consisted of graphene and subwavelength metallic structure in MWIR range.The designed metallic structure,the periodic metallic rectangular hole array,can be used for extraordinary optical transmission(EOT).And,this EOT comes from the interaction of surface plasmons of metal and local resonance.Graphene flake under the metal can influence the transmission of EOT with different conductivity.The EOT design can enhance the effect of graphene without affecting transmission.By optimizing the metallic structure,a resonant transmission peak was located at3.5 ?m.The simulation results show that the modulator can achieve continuous amplitude modulation,and the modulation efficiency reaches 69.1 %.This reaches the higher level of graphene amplitude modulation.Secondly,a tunable bandpass filter was designed and consisted of graphene and metal grating with slanted wall in MWIR range.Here,the surface plasmons of the whole graphene layer is excited by the metal grating.It can effectively absorb the incident wave and then reradiate,and shows obvious transmission enhancement at the resonant wavelength.In this thesis,a slanted wall grating is designed for the resonance wavelength at MWIR.When the Fermi level of graphene is 0.8 e V,a resonant transmission peak can be designed nearby 3.5 ?m.The good bandpass filtering performances were obtained,such as the 352 nm full width at half maximum.The simulation results also show that the design can realize the continuous modulation of the resonant wavelength in the whole MWIR range.At the end of this paper,the integrated structure of amplitude modulation and modulated bandpass filter is designed.For different polarized light,the system can be realized in the same structure and has two functions.It improves the utilization rate of space and materials.