Photonic molecules: tailoring the coupling strength and sign.

Area of Science:

• Optics and Photonics
• Materials Science

Background:

• Photonic crystal cavities enable light confinement and manipulation.
• Coupling strength in photonic crystal molecules dictates their optical properties.
• Tuning coupling strength typically requires altering cavity geometry or separation.

Purpose of the Study:

• To demonstrate a novel method for tuning coupling strength in photonic crystal molecules.
• To achieve large wavelength splitting control and sign inversion without changing inter-cavity distance.
• To introduce and validate "photonic barrier engineering" for optical device design.

Main Methods:

• Fabrication and characterization of photonic crystal L3 cavities.
• Numerical simulations (e.g., finite-difference time-domain) to model optical coupling.
• Experimental measurements of wavelength splitting and mode properties.
• Modification of air-hole radii in the central barrier region.

Main Results:

• Achieved a 5x increase in wavelength splitting through photonic barrier engineering.
• Demonstrated continuous control over coupling strength by adjusting barrier hole sizes.
• Successfully inverted the sign of wavelength splitting, altering the fundamental mode symmetry.
• Validated numerical predictions with experimental results.

Conclusions:

• Photonic barrier engineering offers a powerful and versatile method for tuning photonic molecule coupling.
• This technique allows for unprecedented control over optical mode properties in coupled cavities.
• The findings have implications for designing advanced photonic devices and integrated optics.