Directional Smith-Purcell radiation via coupled high-index gratings

Area of Science:

• Optics and Photonics
• Condensed Matter Physics
• Materials Science

Background:

• Smith-Purcell radiation (SPR) is generated when electrons interact with periodic structures, enabling tunable light sources.
• Existing methods for directional SPR often require complex mirror-based designs.
• Controlling the directionality of SPR is crucial for developing advanced light sources.

Purpose of the Study:

• To investigate directional or asymmetric SPR from a high-index dielectric double-grating structure.
• To achieve directional SPR emission by breaking the symmetry of the structure.
• To provide a compact and efficient method for controlling SPR directionality.

Main Methods:

• Utilizing full-wave simulations and eigenmode analysis to identify radiation modes and coupling properties.
• Introducing a lateral shift between double gratings to break symmetry.
• Developing a coupled mode theory (CMT) model to analyze symmetric and asymmetric emission regimes.

Main Results:

• Demonstrated directional SPR emission from a dielectric double-grating structure by introducing a lateral shift.
• Identified coupled Bloch modes responsible for the directional radiation.
• Developed a CMT model that accurately captures the transition between symmetric and asymmetric emission.

Conclusions:

• A novel, compact, and efficient method for controlling SPR directionality in dielectric photonic structures has been presented.
• The proposed double-grating design offers an alternative to traditional mirror-based approaches for directional SPR.
• This work paves the way for new tunable and directional light sources based on dielectric photonic structures.