Study On Design,Fabrication And Performance Of THz Metal Mesh Band Pass Filters

Metal mesh structures which have wavelength dependent resonance transmission properties are used as filter devices.However,a common problem that the mesh filters have side lobes in high frequency region exists in taditional stuctres,which affects the filtering effect.In this paper,a new type of fold cross metal mesh band pass filter which shows much better side lobes suppression is designed and fabricated.Firstly,mechanisms of side lobes are explored and a new type of fold cross metal mesh structure is designed.We find side lobes are composed of diffraction,high-order resonance and F-P effect by using finite element method simulation.The introduction of folding arm in our structure with smaller period makes the diffraction side lobe more away from the main transmission peak.Meanwhile the high-order resonance and F-P effect are suppressed by controlling graphic parameters and thickness of the film.Secondly,based on the above design structure,the fabrication process of substrate-free metal film is studied by using the photo-lithography,magnetron sputtering coating and electroplating techniques.The designed metal mesh film filters without substrate are successfully fabricated.Measurement results show that for 0.75THz and 1.25THz filters the main peak transmittances are 88.4%,89.2%and the side lobes are 0.230THz,0.537THz away from their main peaks respectively.By comparing the structures with the cross shape structures under the same condition of transmission and bandwidth,fold cross structures show better side lobes suppression than the traditional cross structures.Furthermore,filters centered at frequencies of 1.0THz,1.5THz,2.0THz and 2.5THz are also fabricated.Measurement results show that transmittances are 86.17%,84.08%,83.30%,90.86%and the side lobes are 1.006THz,1.123THz,0.779THz,0.431THz away from their main peaks respectively.