Graphene Phase Modulators Operating in the Transparency Regime

Area of Science:

• Photonics and Optical Communications
• Materials Science
• Electrical Engineering

Background:

• Next-generation data networks require Terabit per second (Tb/s) data rates, necessitating advancements in optical modulation technologies.
• In-phase and quadrature (IQ) modulation enhances data density and noise tolerance but requires pure phase modulation to minimize intersymbol interference.
• Current silicon (Si) and lithium niobate (LiNbO3) modulators struggle to meet the low drive voltage (<1 V) and compact dimensions (<1 cm) required for efficient IQ modulation, with VπL products typically exceeding 1 Vcm.

Purpose of the Study:

• To develop a novel Mach-Zehnder modulator (MZM) capable of pure phase modulation with reduced drive voltage and footprint.
• To investigate the performance of a double single-layer graphene (SLG) MZM in the transparency regime for low-loss optical modulation.
• To demonstrate a modulator that meets the stringent requirements for next-generation IQ modulators, specifically VπL < 1 Vcm.

Main Methods:

• Fabrication of a double single-layer graphene (SLG) Mach-Zehnder modulator (MZM).
• Characterization of the MZM's phase modulation performance in the optical transparency regime.
• Measurement of key performance metrics including VπL, optical insertion loss, and drive voltage.

Main Results:

• The developed SLG MZM achieved pure phase modulation with a VπL product of approximately 0.3 Vcm.
• The device exhibited low insertion loss (∼5 dB) and maintained constant optical losses with increasing voltage.
• The VπL product is approximately 5 times lower than the best thin-film LiNbO3 MZMs and 3 times lower than the best Si MZMs.

Conclusions:

• The double SLG MZM offers a promising solution for achieving pure phase modulation with significantly reduced VπL, meeting the <1 Vcm requirement.
• This technology enables compact, low-power IQ modulators compatible with complementary metal-oxide semiconductor (CMOS) fabrication.
• The device's performance improvements in drive voltage and footprint pave the way for enhanced circuit density and an order of magnitude reduction in power consumption for optical networks.