Optical gain-tunable wideband metasurface device with high electric field enhancement

The metasurface devices with high electric field enhancement factor values have been widely discussed in recent years. However, these types of metasurface devices usually have very strict minimum spacing limitations, which seriously affect the difficulty of device fabrication and the reproducibility of experiments. In this work, we proposed a metasurface based on a metal-insulator-metal configuration that significantly enhances the electric field enhancement factor of the surface plasmon resonance structure on the upper surface by utilizing a bottom metal-SiO2 spiral lens. The results indicated that the gain bandwidth of this proposed device is more than 100 nm with a maximum electric field gain of 377 within the orange-red wavelength range. Furthermore, the electric field enhancement factor can be adjusted based on the number of rings in the spiral lens. Moreover, the minimum fabrication scale of this device is 130 nm, which facilitates easier fabrication and experimental replication. The focal pattern of the electric field generated inside the spiral lens with different polarization states of light was also examined. •Spiral lens excites surface plasmon polaritons for inward focusing is introduced.•The tunable electric field enhancement factor is controlled by SPP waves.•The device can achieve high electric field enhancement factors over a wideband of wavelengths.•The incident light polarization state is decoupled from the electric field enhancement factor.