Ultra-low-loss optical delay line on a silicon chip

Area of Science:

• Photonics
• Materials Science
• Integrated Optics

Background:

• Optical fibers provide true time delay crucial for various applications but require coiling for compactness, limiting integration.
• Integrated waveguides offer potential for improved shock resistance and system-on-a-chip (SoC) functionality but suffer from high attenuation rates compared to optical fibers.

Purpose of the Study:

• To develop and demonstrate a long, monolithic waveguide with optical loss rates comparable to early-stage optical fibers.
• To explore the potential for on-chip integration of true time delay functionalities.

Main Methods:

• Fabrication of a monolithic waveguide with a 27-meter length (39-meter optical path length).
• Measurement of broadband loss rate using optical backscatter over a 7-meter section.
• Characterization of optical loss using resonator measurements.

Main Results:

• Achieved broadband loss rate values of (0.08±0.01) dB m⁻¹ measured over 7 meters.
• Resonator measurements indicated a further reduction in loss to 0.037 dB m⁻¹, approaching the performance of early optical fibers.
• Demonstrated the feasibility of fabricating long waveguides on a chip.

Conclusions:

• The developed monolithic waveguide significantly reduces optical loss, making it competitive with optical fibers for true time delay applications.
• This advancement supports the integration of delay lines into chip-based platforms, enabling compact and robust systems.
• The study discusses the scalability of this technology for integrated spans exceeding 250 meters with attenuation rates below 0.01 dB m⁻¹.