Unidirectional amplification in the frozen mode regime enabled by a nonlinear defect

Area of Science:

• Physics
• Photonics
• Materials Science

Background:

• Stationary inflection points (SIPs) are spectral singularities in periodic structures, characterized by vanishing first and second derivatives of the Bloch dispersion relation.
• SIPs lead to third-order exceptional point degeneracy, causing a collapse of Bloch modes and enabling efficient conversion of incident waves into a 'frozen mode' (FMR).
• The frozen mode regime offers advantages over traditional cavity resonances for applications like light amplification due to its non-resonant nature.

Purpose of the Study:

• To propose a novel scheme for unidirectional amplifiers based on the frozen mode regime (FMR).
• To leverage a tailored amplification/attenuation mechanism and a single nonlinear defect to achieve directional control.
• To demonstrate the robustness of the proposed amplification mechanism.

Main Methods:

• Utilized a periodic structure with a stationary inflection point (SIP) to access the frozen mode regime (FMR).
• Introduced a single nonlinear defect to break directional symmetry and induce nonlinearity-related unidirectional amplification/attenuation.
• Investigated the amplification mechanism's performance and robustness against local impurities and parasitic nonlinearities.

Main Results:

• Successfully demonstrated a scheme for FMR-based unidirectional amplifiers.
• The nonlinear defect enabled efficient, direction-dependent amplification near the SIP frequency.
• The amplification mechanism showed robustness against local impurities and parasitic nonlinearities.

Conclusions:

• The proposed scheme offers a novel approach for creating unidirectional amplifiers leveraging the frozen mode regime.
• The use of a single nonlinear defect provides an effective method for directional control and amplification.
• The demonstrated robustness suggests practical applicability in various photonic devices.