Surface field enhancement of guided-mode resonance by using metallic nanoslits

Guided-mode resonance (GMR) in metal–insulator–metal (MIM) waveguides presents an attractive scheme for developing wavelength-selective and resonance-enhanced devices due to its advantageous properties of narrow bandwidth, high diffraction efficiency, and frequency tunability. However, due to its guided mode nature, GMR exhibits an exponentially decayed electric field on the waveguide surface, which limits its interaction with matter as unfavorable, especially in sensing applications. In this work, we develop an approach for enhancing the surface field of GMR by using plasmonic nanoslits. An MIM waveguide grating with nanoslits is designed and proposed. Our numerical simulations show that by using metallic slits perpendicular to the electric field, surface fields of both TE and TM GMRs can be enhanced by a factor between 12.34 and 13.99. Under oblique incident conditions, the split GMRs are blueshifted and redshifted, exhibiting wavelength tunability while maintaining the intensified surface field. In addition to the field enhancement, which leads to an improved sensitivity of the GMRs to environmental refractive index, the nanoslits also affect the linewidth and quality factor of the GMRs via both enhanced ohmic loss and impedance change of the mode. Our results establish an effective method for enhancing the surface field of GMR, which paves a pathway for improving the GMR-based optoelectronic applications.