A U.S.-based team has demonstrated the slowest light ever propagated on a single silicon chip.
Silicon wafer with 32 atomic spectroscopy devices that can be used to create and control slow light on a chip. The wafer's diameter is roughly 4 inches or 10 cm.
A U.S.-based team has demonstrated the slowest light ever propagated on a single silicon chip. Most "slow-light" experiments have been performed under cryogenic or other extreme conditions, hardly an operating environment for practical photonic devices.
Researchers at the University of California, Santa Cruz (UCSC) and Brigham Young University, U.S.A., created tiny optical waveguides filled with warm rubidium vapor on a silicon chip. These cavities slowed the group velocities of light pulses by up to a factor of 1,200. The team reported their work online in Nature Photonics.
According to Holger Schmidt, an electrical engineering professor at UCSC, the researchers wanted to combine the effects previously demonstrated in alkali vapors with the convenience of a photonic integrated system based on micron-scale waveguides. The team created a chip containing waveguides with hollow cores measuring 4.75 × 12 mm. Since the rubidium vapor has a refractive index lower than the outer guiding medium—the opposite of an optical fiber—the team lined the waveguides with a thin dielectric coating to confine light within the channels.
Unlike ultracold slow-light experimental setups, the rubidium-filled waveguides operate at 80 °C, a temperature that can be achieved with an inexpensive heater. The team could speed up or slow down the pulses by simply changing the power of the control laser.
The self-contained chip slowed the group velocity of light by a factor of 1,200, or some 250,000 m/s—still not as "slow" as more complex experiments involving Bose-Einstein condensates. Still, a future instrument designer could use the tiny waveguides to increase the spectral resolution of a spectrometer by a factor of 1,200. Alternatively, someone could make the instrument 1,200 times smaller but get the same spectral resolution, and that would point the way toward on-chip integrated spectrometers. Other potential applications include quantum communication, quantum memory and integrated all-optical switches.
Patricia Daukantas is a freelance science writer who specializes in optics and photonics.