Bound states in the continuum in a two-dimensional PT-symmetric system

Area of Science:

• Nonlinear Optics
• Waveguide Optics
• Quantum Mechanics

Background:

• Parity-time (PT)-symmetric systems offer unique optical properties.
• Waveguide arrays are fundamental structures in integrated photonics.
• Bound states in the continuum (BICs) are exotic states with potential applications.

Purpose of the Study:

• Investigate the emergence and properties of BICs in a 2D PT-symmetric waveguide chain.
• Analyze the influence of gain/loss domain orientation on BIC characteristics.
• Understand the role of energy flow direction in symmetry breaking and BIC formation.

Main Methods:

• Theoretical modeling of a 2D PT-symmetric waveguide array with a split central waveguide.
• Analysis of bound states in the continuum (BICs) under varying gain/loss configurations.
• Examination of symmetry breaking scenarios and their impact on mode propagation.

Main Results:

• PT-symmetric waveguide arrays support BICs whose properties are sensitive to the orientation of gain/loss domains.
• Perpendicular energy flow leads to narrow BICs formed via defect mode collision.
• Parallel energy flow results in weakly localized BICs emerging from the continuous spectrum.

Conclusions:

• The orientation of gain/loss domains critically dictates BIC behavior and energy flow direction in PT-symmetric waveguide arrays.
• All identified BICs are the most rapidly growing modes, suggesting experimental excitability from noisy inputs.
• These findings have implications for controlling beam dynamics in photonic experiments.