Robust fluorescence enhancement with different orientations based on a hybrid silicon-silver bilayer grating

Abstract

The intensity of fluorescence signals is a key factor determining the sensitivity of low-concentration biosensors; however, achieving fluorescence enhancement that is both directional and robust to dipole orientation remains challenging. In this work, a silicon-silver bilayer hybrid grating with independently tunable structural parameters is proposed to simultaneously enhance fluorescence emission and control radiation directionality. Finite-difference time-domain simulations are employed to investigate the fluorescence response of dipoles with three orthogonal orientations over multiple emission wavelengths, demonstrating that the bilayer grating provides strong near-field enhancement, together with narrow-angle directional far-field radiation, yielding an average fluorescence emission enhancement factor of 397 for the three dipole orientations. The enhancement originates from hybrid electromagnetic modes formed through the coupling between the dielectric silicon grating and silver grating, which jointly modify the local electromagnetic environment and radiative channels of the emitter. These results provide a promising strategy for designing efficient directional fluorescence emitters for high-sensitivity biosensing applications.