Optical resonators trap light and amplify it to build power. They then emit it in a more controlled powerful form. They are used as laser sources, signal amplifiers, and sensors. They make telecommunications more efficient by enabling information to be transmitted simultaneously on different frequencies of light. 

Resonators in commercial use can operate in a single symmetric mode. The team in Federico Capasso’s lab have invented a resonator that can transmit light in multiple orthogonal modes, can change the beam mode when reflected, and can be asymmetric. They were able to change the free spectral range, resonance linewidth, and quality factor, and produce mode-independent resonances, which allow a single resonator to generate different spatial profiles. The cascade resonators are fabricated using silicon-on-insulator techniques, which are expected to facilitate customization, highly scalable production, and ready integration into existing optical systems.