How to Create Continuous Visible Light from Low-Power Infrared

Do you think it's possible to shine a red laser through a glass window and to get a blue one on the other side? Normally not, but at high intensities light energy tends to combine and redistribute, meaning that red light can really turn into blue light.

To do this, two scientists at the California Institute of Technology used a much brighter beam of laser and really did much out of less, producing a continuous beam of visible light from an infrared source with less than a milliwatt of power.

"Usually this is accomplished using very brief, concentrated bursts of light," says Kerry Vahala, the Ted and Ginger Jenkins Professor of Information Science and Technology and professor of applied physics at Caltech. "To be able to do this continuously and at power levels below a milliwatt is remarkable."

Infrared light is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves, essential to modern telecommunications, flowing through millions of miles of optical fiber.

The new technology brings the infrared light into the center of the visible spectrum, by converting it into visible blue light. "When we developed this, we knew there were a number of potential applications," Vahala says.

"Our device has several important features," Vahala says. "First it triples the light frequency, and second, it works in a wide range of frequencies. This means full access to the entire visible spectrum, and likely ultraviolet. Right now there isn't a way of doing UV generation on a chip. Tunable ultraviolet-that's exciting."

Practical applications of coherent UV sources are found in sensors and data storage devices, where, for example, wavelength determines the physical size of the information bit on a compact disk. The microresonator developed by the two researchers could be used in on-chip optical devices using the silica-on-silicon platform, which is compatible with the electronics of ordinary computer chips.