Ultracompact Graphene-Assisted Tunable Waveguide Couplers with High Directivity and Mode Selectivity

Area of Science:

• Photonics
• Materials Science
• Nanotechnology

Background:

• Graphene offers high flexibility for tunable integrated photonic devices.
• Silicon photonics and plasmonic antennas are key components in on-chip optical systems.

Purpose of the Study:

• To propose ultracompact, tunable on-chip waveguide couplers with mode-selectivity and polarization sensitivity.
• To leverage graphene's tunable carrier density and plasmonic antennas for versatile light coupling.

Main Methods:

• Fabrication of graphene-laminated silicon waveguides patterned with gold nanoantennas.
• Utilizing deep-subwavelength areas (210 × 210 nm²) for device integration.
• Tuning coupling via the chemical potential of graphene (0–1.8 eV).

Main Results:

• Achieved versatile, tunable couplings in a compact area.
• Demonstrated selective coupling into different fundamental modes with high directionality (>25 dB).
• Showcased wavelength tunability over a 107-nm range around 1.55 µm.
• Proposed devices function as mode-sensitive detectors with high extinction ratios (>10 dB).

Conclusions:

• Graphene-assisted tunable integrated photonic devices offer a new paradigm.
• The proposed waveguide couplers provide high performance and tunability for on-chip applications.
• This work advances the development of flexible and efficient integrated photonic systems.