Magnetic-Free Optical Mode Degeneracy Lifting in Lithium Niobate Microring Resonators

Area of Science:

• Integrated photonics
• Acousto-optics
• Nonreciprocity

Background:

• Breaking time-reversal symmetry is crucial for integrated photonics but challenging without magnetic fields.
• Existing methods often require complex structures or intermodal conversion.

Purpose of the Study:

• To demonstrate a novel method for achieving optical nonreciprocity without magnetic fields.
• To utilize phonon-induced effects for mode degeneracy lifting in microring resonators.

Main Methods:

• Coherent acousto-optic coupling was employed to induce differential AC Stark shifts.
• Microwave excitation of integrated piezoelectric transducers controlled the nonreciprocal response.
• Fundamental optical modes in microring resonators were used, avoiding intermodal conversion.

Main Results:

• Phonon-induced nonreciprocity was successfully demonstrated by lifting mode degeneracy.
• Experimentally achieved mode splitting exceeded twice the optical linewidth.
• A linear relationship between splitting and acoustic power allowed real-time reconfigurability.

Conclusions:

• This approach offers a universal, electrically controlled functionality for optical nonreciprocity.
• It simplifies nonreciprocity from a specialized technique to a readily implementable feature.
• The findings establish a new paradigm for magnetic-free optical isolation and dynamic topological photonics.