Two-color unidirectional reflections by modulating the spatial susceptibility in a homogeneous atomic medium

Area of Science:

• Photonics and optical physics.
• Quantum optics and atomic physics.

Background:

• Non-reciprocal reflections are crucial for photonic devices but challenging to achieve.
• Previous methods required specific conditions, like the spatial Kramers-Kronig (KK) relation in homogeneous media.
• Achieving complete non-reciprocal reflection (unidirectional reflection) is a key goal.

Purpose of the Study:

• To propose and investigate a novel method for realizing dynamically tunable two-color non-reciprocal reflections.
• To explore a coherent four-level tripod model for optical signal manipulation.
• To overcome the limitations of existing methods for achieving unidirectional reflection.

Main Methods:

• Utilizing a coherent four-level tripod atomic system.
• Applying two control fields with linearly modulated intensities.
• Analyzing the probe susceptibility and its spatial modulation.

Main Results:

• Demonstrated dynamically tunable two-color non-reciprocal reflections.
• Unidirectional reflection achieved when non-reciprocal frequency regions are within electromagnetically induced transparency (EIT) windows.
• The spatial symmetry breaking via susceptibility modulation eliminates the need for the spatial KK relation.

Conclusions:

• The proposed tripod model offers a new pathway for creating advanced non-reciprocal photonic devices.
• This method provides dynamic tunability and overcomes the stringent KK relation requirement.
• The findings pave the way for practical applications in optical circuits and signal processing.