Ultra-compact, low-loss silicon photonic phase shifter enabled by a ferroionic two-dimensional material

Area of Science:

• Materials Science
• Optoelectronics
• Nanotechnology

Background:

• Tunable optical materials are critical for electro-optic functions in photonic integrated circuits (PICs).
• Two-dimensional (2D) materials provide strong light-matter interactions, ideal for compact tunable devices.
• Achieving efficient, low-loss broadband phase modulation in the short-wave infrared (SWIR) is a persistent challenge.

Purpose of the Study:

• To demonstrate electro-refractive tuning in silicon photonic imbalanced Mach-Zehnder interferometers (UMZIs).
• To investigate the use of multilayer CuCrP2S6 (CCPS), a ferroionic 2D material, for phase modulation.
• To assess the performance of CCPS-based phase shifters in terms of efficiency, loss, and voltage-length product.

Main Methods:

• Hybrid integration of multilayer CCPS with silicon photonic UMZIs.
• Modulation driven by reversible copper ion migration at the metal-semiconductor interface.
• Characterization of refractive index change and phase shift across devices.

Main Results:

• Achieved a significant refractive index change of 1.5 × 10^-2 refractive index units (RIU).
• Observed a consistent redshift of 7.0-7.4 nm at 8 V, corresponding to a 0.8π phase shift.
• Demonstrated a low half-wave voltage-length product (Vπ·L) of 0.033 V·cm with negligible optical loss at 1.55 µm.

Conclusions:

• CuCrP2S6 (CCPS) exhibits excellent electro-refractive tuning capabilities for silicon photonics.
• CCPS outperforms existing transition metal dichalcogenides (TMDs) in phase shifter performance.
• These findings highlight CCPS as a promising material for high-efficiency, ultra-compact phase shifters in SWIR applications.