Hybrid multi-channel electrically tunable bandstop filter based on DAST electro-optical material

Abstract

A voltage tunable hybrid multi-channel bandstop filter based on a metal–insulator–metal (MIM) waveguide is presented in this work, which can realize three narrowband and one broadband filtering functions simultaneously. The filter comprises two asymmetric composite cavities, which are filled with organic electro-optical material of 4-dimethylamino-N-methyl-4-toluenesulfonate (DAST). The composite cavity is composed of a rectangular cavity and an annular cavity, and the annular cavity is formed by two rectangular cavities connected with two semi-elliptical annular cavities. The transmission spectrum and magnetic field distribution of the filter are studied and analyzed by the finite element method (FEM), and the effects of the structure parameters on the transmission spectrum are discussed. Our analysis indicates that the bandstop filter has minimum transmittances of 0.02%, 0.29%, and 0.1%, minimum bandwidths of 5 nm, 9 nm, and 25 nm, and maximum quality factors (Q) of 123.7, 87.1, and 44.2, respectively, in three narrowband modes. The stopband bandwidth at the broadband mode is 70 nm, and the adjustable range is 1695–2065 nm. Additionally, the filter characteristics can be adjusted by imposing a control voltage, providing a high degree of tunability and maintaining stable filter performance. Finally, the basic structure is optimized yielding an increased bandwidth of 238 nm for the broadband mode, which does retain great electrical tuning characteristics. Consequently, the proposed structure can be applied with huge potential in high-density integrated circuits and nano-optics.