Silicon QCL Forgoes External Light Source
SANTA BARBARA, Calif. — A novel laser technology, consisting of a quantum cascade laser built on silicon, eliminates the need for an external light source for mid-infrared (MIR) silicon photonic devices or photonic circuits. This advance may have multiple applications that range from chemical bond spectroscopy and gas sensing to astronomy and free-space communications.
By directly bonding an III-V layer on top of a silicon wafer and then using the III-V layers to generate gain for the laser, researchers at the University of California, Santa Barbara, were able to integrate a multiple quantum well laser on silicon that operates at 2 μm. Because diode lasers are not able to go to longer wavelengths (where there are many more applications), the researchers focused instead on the development and use of quantum cascade lasers.
Building a quantum cascade laser on silicon was a challenging task made more difficult by the fact that silicon dioxide becomes heavily absorptive at longer wavelengths in the MIR.
“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, University of California, Santa Barbara. “We built a type of waveguide called a silicon-on-nitride-on-insulator [SONOI] waveguide, which uses a layer of silicon nitride (SiN) underneath the silicon waveguide, rather than just silicon dioxide (SiO2).”
The team plans to improve the design of their laser to achieve higher power and efficiency. Their next step will be to improve the heat dissipation of the quantum cascade laser, which will boost the performance of the laser and enable the team to make continuous-wave quantum cascade lasers on silicon.
“This work brings us closer to building fully integrated mid-infrared devices, such as spectrometers or gas sensors, on a silicon chip,” said Spott. “This offers numerous benefits: 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, many different types of sensors operating at different mid-infrared wavelengths.”
Traditionally, silicon photonic devices operate at near-infrared wavelengths, with applications in data transmission and telecommunications. However, there is emerging research interest in building silicon photonic devices for longer MIR 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.
This work was done in collaboration with the U.S. Naval Research Laboratory and the University of Wisconsin, Madison. The researchers will present their work at CLEO:2016 in June.
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