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

Abstract A voltage-tunable hybrid multichannel bandstop filter utilizing a metal-insulator-metal (MIM) waveguide is presented in this work. The unique aspect of this filter is its ability to achieve three narrowband and one broadband filtering functions simultaneously. The filter design comprises two asymmetric composite cavities filled with an organic electro-optical material called 4-dimethylamino-N-methyl-4-toluenesulfonate (DAST). These composite cavities consist of a rectangular cavity combined with an annular cavity. The annular cavity is formed by connecting two rectangular cavities with two semi-elliptical annular cavities. Using the finite element method (FEM), we thoroughly study and analyze the transmission spectrum and magnetic field distribution of the filter. We also delve into the impact of various structural parameters on the transmission spectrum. Our analysis demonstrates that the bandstop filter achieves a remarkable minimum transmittance of 0.02%, 0.29%, and 0.1%, alongside minimum bandwidths of 5 nm, 9 nm, and 25 nm in three narrowband modes, respectively. These modes attain maximum quality factors (Q) of 123.7, 87.1, and 44.2. In the broadband mode, the stopband bandwidth covers 70 nm, and the adjustable range spans from 1695 nm to 2065 nm. The filter's characteristics can be dynamically adjusted by applying a control voltage, introducing a remarkable level of tunability while maintaining stable filter performance. To enhance its performance, we optimize the basic structure, yielding a broadened bandwidth of 238 nm for the broadband mode. This extended bandwidth comes with exceptional electrical tuning characteristics intact. Our proposed voltage-tunable hybrid multichannel bandstop filter presents a versatile solution with significant potential applications in high-density integrated circuits and nano-optics.