Directional coupling with parity-time symmetric Bragg gratings

Area of Science:

• Photonics
• Plasmonics
• Nonlinear Optics

Background:

• Parity-time (PT) symmetry in optical systems enables unique phenomena like unidirectional reflection.
• Exceptional points (EPs) in PT-symmetric systems are critical for directional effects.
• Long-range surface plasmon polaritons (LRSPPs) offer potential for miniaturized optical devices.

Purpose of the Study:

• To propose and investigate directional coupling in PT-symmetric waveguide Bragg gratings.
• To explore the use of gain and loss modulation for unidirectional light propagation.
• To analyze coupling configurations and their impact on optical response.

Main Methods:

• Fabrication of silver (Ag) stripe waveguides with step-in-width modulation.
• Integration of IR140 dye molecules for optical gain in the upper cladding.
• Periodic modulation of the grating cladding to balance real and imaginary index perturbations.
• Numerical investigation of coupled PT-symmetric waveguide Bragg gratings in various configurations.

Main Results:

• Demonstration of PT-symmetric waveguide Bragg gratings operating near an exceptional point.
• Prediction of unidirectional multi-wavelength reflection.
• Observation of coupled supermode conversion in different grating arrangements.
• Successful balancing of real and imaginary index perturbations through structural design.

Conclusions:

• PT-symmetric Bragg gratings can achieve highly directional light manipulation.
• Gain and loss modulation combined with LRSPPs provide a viable route for unidirectional devices.
• The proposed configurations offer promising functionalities for integrated optics and signal processing.