A Highly-Efficient Room -Temperature Nanolaser

A highly-efficient room-temperature nanolaser has been demonstrated by scientists at the Yokohama National University in Japan. Made of a semiconductor material known as gallium indium arsenide phosphate (GaInAsP), the overall device has a width of several microns (millionths of a meter), while the part of the device where laser light actually gets produced has dimensions at the nanometer scale in all directions.

The nanolaser produces steady continuous streams of near-infrared light and uses only a microwatt of power, one of the smallest operating powers ever achieved. The design should be useful in future miniaturized circuits containing optical devices.

The laser's small size and efficiency were made possible by employing a design, first demonstrated at the California Institute of Technology in 1999, known as a photonic-crystal laser. In this design, researchers drill a repeating pattern of holes through the laser material. This pattern is called a "photonic crystal." The researchers deliberately introduced an irregularity, or "defect," into the crystal pattern, for example by slightly shifting the positions of two holes.

Together, the photonic crystal pattern and the defect prevent light waves of most colors (frequencies) from existing in the structure, with the exception of a small band of frequencies that can exist in the region near the defect. By operating at room temperature and in a mode where well-defined laser light is emitted stably and continuously, the new nanolaser from Yokohama National University distinguishes itself from previous designs.

According to Yokohama researcher Toshihiko Baba (baba@ynu.ac.jp), the new nanolaser can be operated in two modes depending what kind of "Q" value is chosen. Q refers to quality factor, the ability for an oscillating system to continue before running out of energy. Nanolasers operated in a high-Q mode (20,000) will be useful for optical devices in tiny chips (optical integrated circuits).

In a moderate-Q (1500) configuration the nanolaser requires an extremely small amount of external power to bring the device to the threshold of producing laser light. In this near-thresholdless operation, the same technology will permit the emission of very low light levels, even single photons. (Nozaki et al., Optics Express, 11 June 2007 issue, full text available at http://www.opticsexpress.org/abstract.cfm?id=138211; picture and extended writeup at http://osa.org/news/pressroom/release/06.2007/Nanolaser.aspx)