(INVITED)A review on dielectric resonant gratings: Mitigation of finite size and Gaussian beam size effects

Abstract

Resonant gratings made of dielectrics and semiconductors sustain guided mode resonances with very high lifetime due to the intrinsic lossless properties of the materials involved. Upon out of plane multi-wavelength illumination, resonant grating present very sharp peaks and/or dips in the reflection and/or transmission spectrum at specific resonant wavelength. Theoretical quality factors of the spectral features (which reach values in the order of 105) can be obtained only considering an infinite grating area and an incident plane wave. In practice, the finite dimension of the patterning area and the non-ideal characteristics of the input optical beam (typically with a Gaussian-like profile) cause a broadening and a visibility reduction of the resonant peaks/dips. This prevents from the effective exploitation of micro-sized dielectric structures in many applications, including their integration onto the optical fibers for the realization of High-Q Lab-on-fiber resonant optrodes. In this framework, this review shades light on the non–idealities of the guided mode resonances in dielectric gratings, browsing the solutions proposed by the scientific community during the last decades aimed at overcoming the finite size and finite beam effects, such as the use of distributed Bragg reflectors, and the exploitation of bi-periodic gratings.

Keywords

• Optical fibers
• Dielectric resonators
• Guided mode resonances
• High quality factor