OH absorption in on-chip high-Q resonators

Kavli Affiliate: Kerry J. Vahala

| First 5 Authors: Lue Wu, Maodong Gao, Jin-Yu Liu, Hao-Jing Chen, Kellan Colburn

| Summary:

Thermal silica is a common dielectric used in all silicon-photonic circuits.
And bound hydroxyl ions (Si-OH) can provide a significant component of optical
loss in this material on account of the wet nature of the thermal oxidation
process. A convenient way to quantify this loss relative to other mechanisms is
through OH-absorption at 1380 nm. Here, using ultra-high-Q thermal-silica wedge
microresonators, the OH absorption loss peak is measured and distinguished from
the scattering loss base line over a wavelength range from 680 nm to 1550 nm.
Record-high on-chip resonator Q factors are observed for near-visible and
visible wavelengths, and the absorption limited Q factor is as high as 8
billion in the telecom band. OH ion content level around 2.4 ppm (weight) is
inferred from both Q measurements and by Secondary Ion Mass Spectroscopy (SIMS)
depth profiling.

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