Shifting colors for on-chip photonics

In the top device, two coupled resonators form a figure eight-like structure. Input light travels from the waveguide through the resonators, entering as one color and emerging as another. The bottom device uses three coupled resonators: a small ring resonator, a long oval resonator called a racetrack resonator, and a rectangular-shaped resonator. As light speeds around the racetrack resonator, it cascades into higher and higher frequencies, resulting in a shift as high as 120 gigahertz. Credit: Second Bay Studios/Harvard SEAS