Optical isolation in topological-edge-state photonic arrays

Area of Science:

• Photonics
• Topological Physics
• Materials Science

Background:

• Topological insulators offer unique edge states for robust wave propagation.
• Optical isolators are crucial for preventing back reflections in photonic systems.
• Su-Schrieffer-Heeger (SSH) models provide a framework for topological phenomena in condensed matter and photonics.

Purpose of the Study:

• To introduce a new type of optical isolator.
• To break time-reversal symmetry in dissipative finite Su-Schrieffer-Heeger (SSH) waveguide arrays.
• To leverage topological edge states for nonreciprocal light propagation.

Main Methods:

• Utilizing dissipative finite Su-Schrieffer-Heeger (SSH) waveguide arrays.
• Exciting localized topological midgap states with forward propagating light.
• Inducing a propagation constant mismatch for backward reflected light.
• Engineering spatial distribution of optical dissipation.
• Depositing a magnetic garnet film on the edge waveguide to break time-reversal symmetry.

Main Results:

• Achieved high optical isolation ratio of -50 dB.
• Demonstrated transmission of most input optical power in the forward direction.
• Showcased delocalization of backward reflected light into the bulk bands due to propagation mismatch.
• Successfully broke time-reversal symmetry using an integrated micromagnet and magnetic garnet film.

Conclusions:

• The proposed device offers a novel approach to optical isolation using topological principles.
• Dissipative topological waveguide arrays provide a robust platform for nonreciprocal photonic devices.
• The concept is extendable to optical resonator-based SSH arrays.