A Laser Cavity Close to the Size of the Diffraction Limit

Researchers in Japan have developed a laser that operates at room temperature and measures only about 9 × 15 μm.

Toshihiko Baba and his colleagues Kengo Nozaki and Shota Kita at Yokohama National University constructed the device by drilling an array of holes in a slab of gallium indium arsenide phosphate using electron beam lithography. The wafer had a photoluminescence peak of 1.55 μm. Unlike with typical quantum-well wafers fabricated in this manner, the investigators offset two of the holes near the center of the slab (see figure). With this intentional “defect,” the array enabled the device to exclude most wavelengths that might pass through the device.

Courtesy of Yokohama National University, Japan.

They pumped the wafer with a 0.98-μm CW laser with a spot diameter of 2.5 μm. They observed that the device could generate CW beams in either of two different designs. At an effective pump power of 1.2 μW, the device reached a 40-dB peak over background and a resolution-limit spectral width of 0.06 nm, providing a Q of 20,000 in the first design; and, at 2.4 μW, a 25-dB peak, a spectral width of 1.0 nm and a Q of 1500 in the second design with a near-thresholdless operation. The entire device’s ability to use a pump operating at 1.2 μW ensures that it can operate at room temperature with no external cooling.

Time-domain measurements made using a photomultiplier tube from Hamamatsu showed that the laser’s spontaneous emissions were enhanced by the Purcell effect.

The device ultimately may find use in subminiaturized optical communications systems or as single-photon emitters. The researchers report their findings in the June 11 issue of Optics Express.