Multimode-enabled silicon photonic delay lines: break the delay-density limit.

Area of Science:

• Photonics
• Integrated Optics
• Waveguide Technology

Background:

• Integrated optical delay lines are crucial for microwave beamforming, optical communication, and quantum photonics.
• Existing single-mode waveguide designs face limitations in achieving large delay ranges, small footprints, and broad bandwidths simultaneously due to propagation loss and group refractive index trade-offs.
• There is a growing demand for compact, high-performance delay lines to support advanced applications.

Purpose of the Study:

• To propose and experimentally demonstrate a novel multimode-enabled silicon photonic delay line.
• To overcome the delay-density limitations of traditional single-mode waveguide spirals.
• To achieve broadband operation, mm²-scale footprint, and ultra-large time delay capabilities.

Main Methods:

• Introduction of a novel multimode delay unit integrating mode (de)multiplexers.
• Utilizing an ultralow-loss multimode waveguide spiral supporting parallel propagation of TE₀, TE₁, and TE₂ modes.
• Experimental demonstration of low-loss propagation for different polarizations and modes.

Main Results:

• Measured propagation losses of 0.2 dB/cm (TE₀), 0.31 dB/cm (TE₁), and 0.49 dB/cm (TE₂).
• Achieved a line delay-density of 376.9 ps/cm and a low delay loss of 0.004 dB/ps.
• Demonstrated a 7-bit tunable multimode photonic delay line with a 12.7 ns delay range, 100 ps resolution, and 3.85 mm² footprint, yielding a delay density over 3299 ps/mm².

Conclusions:

• The proposed multimode silicon photonic delay line offers the largest delay range and highest delay density reported to date for on-chip devices.
• This technology breaks the delay-density limit of single-mode waveguide spirals.
• The demonstrated performance enables significant advancements in broadband, compact, and ultra-large time delay applications.