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Single chip houses spectroscopy setup

15 Jun 2007

Miniaturizing spectroscopy onto a single chip is allowing researchers to study atoms in a portable device.

An atomic spectroscopy set-up that uses integrated optics has been miniaturized to fit on a single silicon chip. The team hopes that its compact and portable platform will find applications in frequency stabilization, single–photon nonlinear optics and eventually quantum information processing. (Nature Photonics 1 331).

The researchers have been studying rubidium vapor in their initial experiments. "We can now detect atoms on a small chip," Holger Schmidt, associate professor at the University of California Santa Cruz, told optics.org. "This could be extended to other atoms and molecules, and could even lead to other integrated devices such as detecting particles in the atmosphere."

The team hopes that its portable and easy–to–use device will replace current frequency stabilization methods that use bulk rubidium cells. One key breakthrough was finding a way to fill the hollow waveguides on the chip with rubidium vapor.

"Rubidium reservoirs (metallic cylinders) are mounted on the chip," explained Schmidt. "We drop solid rubidium into these cylinders and the rubidium's vapor pressure sets atoms free that fill the space between the reservoirs – in particular the hollow-core waveguide channels." The team then probes the waveguides with an external cavity diode laser.

The specially–designed waveguides use antiresonant reflecting optical waveguide principles. "Guiding light through a hollow core cannot be done with the conventional waveguiding method which requires the refractive index of the core to be higher than the cladding," explained Schmidt.

Schmidt and colleagues designed the cladding materials using dielectric layers with a precisely calculated thickness. "These layers act as highly reflective Fabry–Perot layers which keep the light in the low-index core," he explained. "In essence, the core is made of a highly reflective dielectric mirror."

According to Schmidt, a loss in sensitivity would be incurred by scaling down the device. "For stabilization, we will probably be a little worse than the best tabletop setups, but we are still at the beginning," he said. "For nonlinear experiments you win because you can increase the intensity of the light confining it to a small mode area. The waveguide allows me to maintain high intensity over longer distances."

The long–term goal is to use the device to generate single photons for quantum communication systems.

This research was a collaboration between Holger Schmidt's group at UCSC, US (Wenge Yang and Bin Wu) and Aaron Hawkin's group at Brigham Young University, US (Don Conkey and John Hulbert).

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