Groundbreaking Alumina-Based UV Optical Resonators Herald Compact Quantum Computing and Communication Devices

Scientists have engineered photonic resonators that function on a chip and exhibit significantly reduced ultraviolet (UV) light loss, setting the stage for cutting-edge UV photonic integrated circuits (PICs). Fabricated from thin alumina films, these resonators hold promise for multiple applications such as spectroscopic detection and subaqueous communication.

This breakthrough establishes a foundation for compact instruments designed for spectroscopy, telecommunications, and quantum computation.

The engineered photonic resonators operate within the UV and visible spectrum and set a new standard for minimal UV light loss. This development contributes to the expansion in terms of size, intricacy, and reliability of UV photonic integrated circuit designs. Such advances could facilitate the creation of scaled-down chip-based devices for spectroscopic analysis, underwater data transmission, and quantum information handling.

Chengxing He, a member of the research team from Yale University, noted, “The field of UV photonics has been less investigated compared to its counterparts like telecom and visible photonics. However, UV wavelengths are critical for accessing specific atomic transitions in quantum computing based on atoms or ions and for exciting specific fluorescent molecules in biochemical sensing. Our study serves as a foundational step for creating photonic circuits operating in UV wavelengths.”

Technological Innovations in UV PICs

Published in the journal Optics Express by the Optica Publishing Group, the researchers elaborated on the construction of alumina optical microresonators. They achieved unparalleled low UV light loss by utilizing an optimal combination of materials, design, and manufacturing methods.

A chip-based ring resonator was developed that operates in both UV and visible spectral ranges, displaying an unprecedentedly low UV light loss. Hong Tang, the head of the research group, stated, “UV PICs have now reached a pivotal juncture where the loss of light in waveguides is not notably inferior to their visible-spectrum equivalents. This opens the possibility of applying all interesting PIC structures, like frequency combs and injection locking, to UV wavelengths.”

Mitigating Light Loss

High-quality alumina thin films were used to construct the microresonators. These films were prepared by co-authors Carlo Waldfried and Jun-Fei Zheng from Entegris Inc., using an easily scalable atomic layer deposition (ALD) process. Due to its large bandgap of approximately 8eV, alumina is transparent to UV photons, which have a substantially lower energy (~4eV) than the bandgap, thereby avoiding absorption of UV wavelengths.

“Alumina has fewer defects compared to single-crystal aluminum nitride and presents less of a fabrication challenge, which aided us in achieving a lower loss,” He remarked.

To construct the microresonators, etching processes were used on the alumina, forming a structure known as a rib waveguide. The researchers used simulations to determine the optimal etch depth, balancing light confinement and scattering loss.

Fabrication of Ring Resonators

The team then used this knowledge to manufacture ring resonators with a 400-micron radius. They discovered that radiation loss could be minimized to less than 0.06 dB/cm at 488.5 nm and less than 0.001 dB/cm at 390 nm when the etch depth exceeded 80 nm in a 400-nm thick alumina film.

Upon measuring the quality (Q) factors of these fabricated resonators, record-high Q factors were found, signifying minimal light loss.

He concluded by stating that UV PICs may offer advantages in communication due to greater bandwidth or in environments where other wavelengths are absorbed, like underwater. Moreover, the ALD process used for alumina fabrication is compatible with CMOS technology, allowing for future CMOS integration.

Future Directions

Ongoing research aims to develop alumina-based ring resonators that can be fine-tuned for various wavelengths. This could enable precise wavelength control or the creation of modulators via the use of dual resonators that interact with each other. There are also plans to develop a PIC-integrated UV light source to constitute a comprehensive PIC-based UV system.

Reference: “Ultra-high Q alumina optical microresonators in the UV and blue bands” by Chengxing He, Yubo Wang, Carlo Waldfried, Guangcanlan Yang, Jun-Fei Zheng, Shu Hu and Hong X. Tang, published on September 26, 2023, in Optics Express.
DOI: 10.1364/OE.492510

Frequently Asked Questions (FAQs) about Alumina-Based UV Optical Resonators

More about Alumina-Based UV Optical Resonators

• Optics Express Journal
• Yale University Research
• Entegris Inc. Official Website
• Photonic Integrated Circuits (PICs)
• Introduction to Alumina
• Quantum Computing Basics
• Spectroscopic Sensing
• Underwater Communication Technologies
• Atomic Layer Deposition (ALD) Process
• CMOS Technology