For the first time ever, scientists have created the first quantum cascade laser on silicon, an achievement that will help researchers in fields that span from chemical bond spectroscopy to astronomy.
Although integrating lasers onto silicon chips is difficult, it is much more efficient than coupling external laser light to the chips. Using diode lasers crafted with III-V materials such as indium phosphide (InP) and gallium arsenide (GaAs), the team integrated quantum lasers onto silicone. However, given the limitations of diode lasers, which prevent going to longer wavelengths, the team then turned their focus to quantum cascade lasers.
Despite the promise of this process, silicon dioxide becomes very absorptive at longer wavelengths in the mid-infrared, which gave the team a difficult task when it came to building a quantum cascade layer on silicone.
"This meant that not only did we have to build a different type of laser on silicon, we had to build a different silicon waveguide too," said Alexander Spott, a researcher from the University of California, Santa Barbara, who led the study. "We built a type of waveguide called a SONOI waveguide [silicon-on-nitride-on-insulator], which uses a layer of silicon nitride [SiN] underneath the silicon waveguide, rather than just SiO2."
The new breakthrough has the potential to create numerous novel applications for the device.
"Traditionally, silicon photonic devices operate at near-infrared wavelengths, with applications in data transmission and telecommunications," Spott said. "However, there is emerging research interest in building these silicon photonic devices for longer mid-infrared wavelengths, for a range of sensing and detection applications, such as chemical bond spectroscopy, gas sensing, astronomy, oceanographic sensing, thermal imaging, explosive detection, and free-space communications."
The team now hopes to improve the heat dissipation of their quantum cascade laser in order to improve their performance and achieve the highest level of efficiency possible. If they can accomplish this, the team believes that the technology could easily be scaled for use in the real world.
"Silicon is inexpensive, the fabrication can be scaled up to significantly reduce the cost of individual chips, and many small devices can be built on the same silicon chip - for example multiple different types of sensors operating at different mid-infrared wavelengths," Spott concluded.
