Design and optimization of a passive PT-symmetric grating with asymmetric reflection and diffraction

Area of Science:

• Photonics and Optical Engineering
• Non-Hermitian Physics
• Materials Science (Silicon-on-Insulator)

Background:

• Non-Hermitian physics and parity-time (PT) symmetry are emerging concepts in photonics.
• These principles enable the design of novel optical structures with unique functionalities.
• Existing PT-symmetric devices often require gain or loss materials, limiting their practicality.

Purpose of the Study:

• To propose, design, and optimize a compact, passive PT-symmetric grating.
• To achieve asymmetric reflection and diffraction using a silicon-on-insulator (SOI) platform.
• To explore the use of scattering loss as a mechanism for PT symmetry.

Main Methods:

• Design of a passive PT-symmetric grating composed of interleaved tailored gratings on a silicon waveguide.
• Modulation of effective index and scattering loss through structural design, without active gain/loss elements.
• Optimization using the particle swarm optimization (PSO) algorithm for complex multi-parameter tuning.

Main Results:

• Realization of asymmetric reflection with a high contrast ratio.
• Significant suppression of waveguide-to-free-space diffraction from one side, achieving asymmetric diffraction.
• Investigation of fabrication tolerance for the proposed PT-symmetric grating design.

Conclusions:

• Demonstrated the first use of grating-induced scattering loss to create an efficient PT-symmetric structure.
• Successfully achieved asymmetric reflection and diffraction in a compact, passive SOI device.
• Opened new avenues for designing complex on-chip PT-symmetric photonic devices.