Slow-light, band-edge waveguides for tunable time delays

Area of Science:

• Photonics
• Integrated Optics
• Waveguide Technology

Background:

• Optical time delays are crucial for various photonic applications.
• Existing methods for optical time delays often require large device footprints.
• Miniaturization and tunability are key challenges in integrated photonics.

Purpose of the Study:

• To propose and analyze slow-light, band-edge waveguides for compact, integrated, tunable optical time delays.
• To introduce figures of merit for quantifying device sensitivity and signal degradation.
• To demonstrate a design strategy for efficient and tunable optical delay lines.

Main Methods:

• Utilizing slow-light phenomena at the photonic band edge of waveguides.
• Developing figures of merit to assess device performance (sensitivity and dispersion).
• Employing adiabatic taper designs for low-reflection grating structures.
• Cascading gratings to achieve constant tunable time delay and compensate for dispersion.

Main Results:

• Slow group velocities at the band edge enable large time delays with small refractive index changes, reducing device size.
• A simple quadratic-band model accurately predicts performance for realistic 3D grating structures.
• Adiabatic tapers achieve <0.1% reflection in short grating lengths (10-20 periods).
• Cascading two gratings provides a constant tunable time delay over bandwidths >100 GHz.

Conclusions:

• Slow-light, band-edge waveguides offer a promising route to compact, integrated, tunable optical time delay devices.
• The proposed design methodology simplifies device engineering and performance prediction.
• Picosecond-range tunable delays are achievable with current silicon-on-insulator fabrication technology.