Caltech Chip Steers Light in 74 Femtoseconds

California Institute of Technology (Caltech) researchers have developed a device that can redirect a beam of light in 74 femtoseconds. A femtosecond is one quadrillionth of a second. This speed is roughly the time light travels across the width of a human hair.

The device uses one light beam to alter the optical properties of a nanoscale silicon metasurface. A second, weaker beam then passes through this modified material. The second beam's direction changes according to the pattern created by the first beam.

Traditional light steering technologies rely on changing a material's electronic properties. These methods have speed limitations due to the time electrons need to return to lower energy states. The Caltech team's approach bypasses this bottleneck.

The new system utilizes the optical Kerr effect. This phenomenon causes an intense light beam to briefly change a material's refractive index. The change occurs from electron movement within their orbitals, not by pushing electrons into excited states. This allows for rapid changes.

To amplify the weak optical Kerr effect, researchers created a metasurface with nanoscale pillars on a thin film of amorphous silicon. These pillars, smaller than the light's wavelength, increase the interaction time between light and the metasurface. This enhanced interaction strengthens the refractive index change, allowing the probe beam to be redirected by up to 13 degrees.

The modulation speed is currently limited by the duration of the laser pulses used, which was also 74 femtoseconds. Researchers believe even faster light control is possible. This advancement could lead to faster photonic communications, computing, and sensing technologies.