Hydroxyl ion absorption in on-chip high-Q resonators.

Area of Science:

• Materials Science
• Photonics
• Optical Engineering

Background:

• Thermal silica is a prevalent dielectric in silicon photonics.
• Optical loss in thermal silica is often attributed to bound hydroxyl ions (Si-OH).
• Quantifying hydroxyl ion absorption is crucial for optimizing optical circuit performance.

Purpose of the Study:

• To precisely measure hydroxyl ion absorption loss in thermal silica.
• To distinguish OH absorption from scattering loss in microresonators.
• To determine hydroxyl ion concentration using optical measurements.

Main Methods:

• Fabrication of ultra-high-quality factor (Q-factor) thermal-silica wedge microresonators.
• Measurement of optical loss spectra from 680 nm to 1550 nm.
• Secondary Ion Mass Spectrometry (SIMS) depth profiling for material analysis.

Main Results:

• Record-high on-chip resonator Q-factors were achieved in near-visible and visible wavelengths.
• The absorption-limited Q-factor reached 8 billion in the telecom band.
• Hydroxyl ion content was inferred to be approximately 2.4 ppm (weight).

Conclusions:

• Hydroxyl ion absorption is a quantifiable loss mechanism in thermal silica.
• High-Q resonators enable precise measurement of optical loss in photonic materials.
• The low inferred hydroxyl content suggests potential for ultra-low loss silicon photonic devices.