Ultrahigh-Q integrated flame-hydrolysis-deposited germano-silicate resonators on silicon.

Area of Science:

• Photonics
• Materials Science
• Optical Engineering

Background:

• Global telecommunications rely on optical fibres with ultra-low transmission loss.
• Integrated photonic devices are crucial for data-intensive communications, especially in the AI era.
• Extending low-loss performance to integrated photonics remains a significant challenge.

Purpose of the Study:

• To translate the flame hydrolysis deposition (FHD) mass-production process from optical fibre manufacturing to wafer-scale integrated photonics.
• To demonstrate ultrahigh-Q integrated microresonators using this adapted process.
• To establish a scalable route for achieving fiber-level loss in photonic integrated circuits.

Main Methods:

• Leveraging high GeO2 doping in germano-silicate (Ge:silica) films for full densification at moderate thermal budgets.
• Employing a post-processing furnace-reflow technique to repair etch-induced defects and enhance optical Q.
• Utilizing deep-UV lithography in conjunction with the Ge:silica films to fabricate microresonators.

Main Results:

• Demonstrated ultrahigh Q factors of up to 566 million at 1064 nm.
• Achieved waveguide propagation loss as low as 0.07 dB m⁻¹.
• Devices exhibit broad transmission windows with Q factors > 100 million across telecommunications to violet spectrum, with Q recovery up to two orders of magnitude via furnace reflow.

Conclusions:

• The adapted FHD process successfully extends high-quality, high-rate deposition to integrated photonics.
• The developed Ge:silica films and furnace-reflow technique offer high process tolerance and enable ultrahigh Q factors.
• This work presents a scalable pathway towards achieving fiber-level loss in photonic integrated circuits, crucial for future AI applications.