Exceptional lines and higher-order exceptional points enabled by uniform loss.

Area of Science:

• Non-Hermitian physics
• Electromagnetism
• Optical phenomena

Background:

• Conventional approaches to exceptional points (EPs) often rely on differential losses.
• Lorentz dispersive media are crucial for understanding wave propagation with frequency-dependent permittivity and permeability.

Purpose of the Study:

• To theoretically investigate the realization of EPs in space-time invariant Lorentz dispersive media with uniform loss.
• To explore the mechanisms of non-Hermitian couplings and their role in EP formation.
• To identify potential applications of EPs in such media.

Main Methods:

• Theoretical analysis using derived full and reduced Hamiltonians.
• Investigation of uniform loss effects on eigenmodes in Lorentz dispersive media.
• Characterization of reciprocal and non-reciprocal non-Hermitian couplings.

Main Results:

• Uniform loss in Lorentz dispersive media leads to reciprocal and non-reciprocal non-Hermitian couplings, enabling EPs.
• EPs manifest as exceptional lines (ELs) in parameter space.
• A fourth-order EP (EP4) is formed by the intersection of three ELs.
• At EP4, eigenmodes exhibit maximum optical chirality density.

Conclusions:

• Uniform loss provides a novel pathway to EPs in Lorentz dispersive media, distinct from differential loss methods.
• The identified non-Hermitian couplings are key to EP formation.
• The high optical chirality density at EP4 suggests applications in chiral sorting and sensing.