High-speed polarization-independent plasmonic modulator on a silicon waveguide

Area of Science:

• Photonics
• Materials Science
• Electrical Engineering

Background:

• Optical communication systems rely on high-throughput electro-optic modulators.
• Achieving high electrical bandwidth in modulators is crucial for increasing data rates.
• Plasmonic devices offer potential for miniaturization and high-speed operation.

Purpose of the Study:

• To propose and demonstrate a broadband plasmonic electro-optic modulator.
• To utilize free carrier dispersion in indium tin oxide (ITO) near its epsilon-near-zero (ENZ) point for modulation.
• To integrate the modulator with silicon photonics for telecommunications wavelengths.

Main Methods:

• Fabrication of metal-insulator-metal (MIM) waveguide structures on a silicon waveguide.
• Utilizing indium tin oxide (ITO) within metal-oxide-semiconductor (MOS) structures driven through its ENZ point.
• Employing adiabatic mode transformation tapers to excite plasmonic supermodes.
• Characterizing modulator performance including bandwidth, extinction ratio, and insertion loss.

Main Results:

• Demonstrated a broadband plasmonic electro-optic modulator operating at 1550 nm.
• Achieved electrical bandwidths exceeding 200 GHz (3 dB, RC-limited) with a short active section (1.5-2 µm).
• Obtained an extinction ratio of 3.5–6 dB and insertion loss of 4–7.5 dB.
• Operated with an AC drive voltage of ±1.75 V.

Conclusions:

• The proposed ITO-based plasmonic modulator offers a viable solution for high-speed optical communications.
• The device leverages free carrier dispersion in ITO near its ENZ point for efficient modulation.
• The modulator is compatible with standard fabrication techniques and comprises only inorganic materials.