Harvard Researchers Develop Scalable Method for Ultra-Smooth NIR Microcavities

Researchers at Harvard University have developed a new method for fabricating near-infrared (NIR) microcavities with ultra-smooth surfaces, a development published in Optica (doi: 10.1364/OPTICA.582994). This approach is designed to be scalable and compatible with standard cleanroom environments, addressing a growing demand for compact, high-performance optical cavities in quantum optical applications. These applications include quantum computing, quantum networks, integrated lasers, and environmental sensing.

Research Background

The development of quantum optical applications has increased the demand for smaller optical cavities that exhibit high performance in both the near-infrared and visible ranges. Achieving optimal performance at shorter wavelengths also necessitates superior surface quality compared to that required for telecom wavelengths.

Traditional fabrication methods, which often rely on polished mirrors, typically result in large, non-scalable cavities.

The research originated from the objective to construct quantum networks from ultracold single atoms. This endeavor required optical cavities with exceptionally smooth mirrors to facilitate strong coupling between atoms and photons. Existing microfabrication techniques were often found to have performance and size limitations that were not suitable for these advanced quantum applications.

Novel Fabrication Method

The new approach developed by the Harvard researchers utilizes buckled dielectric membrane mirrors. This method integrates high finesse, standard silicon fabrication, a small mode volume, and a small radius of curvature.

The process involves an engineered stack of transparent oxide layers. When these layers are released from a silicon wafer, built-in compressive strain within the dielectric coating causes them to naturally buckle into a precisely curved shape. Researchers noted that leveraging the intrinsic properties of materials can contribute to robust results.

Leveraging the intrinsic properties of materials can contribute to robust results.

Performance and Applications

The microcavities produced using this method achieved a finesse of 0.9 million at 780 nm. This performance metric indicates that light can reflect approximately one million times within the cavity before scattering.

The fabrication process is characterized by its flexibility, scalability, compatibility with standard cleanroom environments, and high tolerance to errors.

The developed devices are intended for use in areas such as quantum computing, quantum networks, integrated lasers, and environmental sensing equipment.