Smallest semiconductor laser breaks diffraction limit

A plasmon-based laser too small to be seen by the naked eye emits continuous green wavelengths at low energy levels and cold temperatures while operating below the 3-D optical diffraction limit.

Physicists at The University of Texas at Austin, in collaboration with colleagues in Taiwan, created the spaser that improves the performance of nanolasers through the growth of a smooth layer of silver on a silicon substrate. Miniaturizing semiconductor lasers is crucial for developing faster, smaller and lower-energy photon-based technologies such as ultrafast computer chips, highly sensitive biosensors and next-generation communications technologies.

Making semiconductor lasers smaller could lead to faster, smaller photon-based technologies such as ultrafast computer chips, biosensors and communications technologies. Here, an artistic view of the plasmonic nanolaser created at the University of Texas at Austin.

These photonic devices could use nanolasers to generate optical signals and transmit information, and potentially replace electronic circuits. But the size and performance of the devices have been restricted by the 3-D optical diffraction limit. That barrier limits the ability of optical instruments to distinguish between objects separated by a distance of less than about half the wavelength of the light used to image the specimens.

The spaser is constructed of a gallium nitride nanorod that is partially filled with indium gallium nitride. Both alloys are semiconductors commonly used in LEDs. The nanorod is placed on top of a thin layer of silicon that covers a layer of silver film that is atomically smooth.

“Atomically smooth plasmonic structures are highly desirable building blocks for applications with low loss of data,” said Chih-Kang “Ken” Shih, a physics professor at UT-Austin who spent more than 15 years perfecting the material.

Research by graduate student Charlotte Sanders, shown, and professor Ken Shih helped develop the world’s smallest nanolaser. Sanders stands here with a molecular beam epitaxy machine that she designed and built in collaboration with the department of physics’ machine shop and with assistance from co-author Dr. Jisun Kim. The machine is used to create a smooth silver thin film critical to the function of the laser.

The new nanolaser device could provide for the development of on-chip communications systems, which would prevent heat gains and information loss typically associated with electronic devices transmitting between multiple chips.

“Size mismatches between electronics and photonics have been a huge barrier to realize on-chip optical communications and computing systems,” said Shanjr Gwo, a professor at National Tsing Hua University and formerly Shih’s doctoral student.

The findings appeared in Science (doi: 10.1126/science.1223504).