Here a new scheme for mode filtering is proposed. Based on the ponderomotive force effect, propagation of the microwave dual-mode through a plasma-filled metallic rectangular waveguide is investigated. To excite the TE 20 mode in a rectangular waveguide, the existence of fundamental modes is unavoidable. To filter the destructive mode (TE 10), the waveguide is filled with a collisional plasma. Based on the coupling effect, the energy of this destructive TE 10 mode is transferred to the TE 20 mode. The proposed structure acts like a mode convertor. The TE 10 mode become more attenuated and instead the TE 20 mode is amplified. The plasma filled rectangular waveguide acts as a mode filtering tool.

Purpose This study aims to propose a new scheme for designing a high-sensitivity optical biosensor. For this, two agents have been considered: reflection-type micro-resonators, which filter the noise of the pump, and coupled-ring reflectors (CRRs), which are coupled to partial reflecting elements in the bus waveguide to create Fano-resonance. These two agents improve the sensor sensitivity and have low-power optical switching/modulation. Design/methodology/approach The proposed model is based on the coupling of the CRRs with the Fabry–Pérot cavity. The slope of the Fano-resonance line shape and consequently the sensitivity of the proposed CRRs are higher than those of conventional microring resonators. Findings The proposed scheme has many characteristics: CRRs have been used to create a higher slope of the Fano-resonance line shape; the sensitivity of the sensor shows improvement on the basis of reflection-type micro-resonators and by the removal of the pump noise; the designed sensor has low-power optical switching/modulation; and the modeling and designing of a novel high-sensitivity resonator is based on coupling the CRRs with the Fabry–Pérot cavity. Originality/value This study has proposed a new scheme for designing a high-sensitivity optical biosensor. This method is based on the improvement of the sensitivity by two agents: reflection-type micro-resonators, which filter the noise of the pump, and coupled-ring reflectors, which are coupled to partial reflecting elements in the bus waveguide to create Fano-resonance.