Vertical-cavity surface-emitting lasers (VCSELs) are small, semiconductor-based lasers that emit optical beams from their top surface and one of their main applications is in gas sensing.
Several gases can be detected with mid-IR light – having wavelengths between 3 and 4µm – including methane, carbon dioxide and nitrogen dioxide. Application-grade VCSELs, however, aren’t yet available for this wavelength range, but the increasing need for compact, portable and affordable gas sensors is spurring demand.
Typical VCSELs suffer in performance due to heating. These effects are minimised by the ‘buried tunnel junction’ configuration of VCSELs, where a material barrier is embedded between the standard p- and n-type materials of the semiconductor.
“The buried tunnel junction VCSEL concept has already yielded high performance VCSELs within the entire 1.3 to 3µm range,” said doctoral student Ganpath Veerabathran.
“And type-II ‘W’ quantum well active regions have been used successfully to make conventional edge-emitting semiconductor lasers with excellent performance within the 3 to 6µm range.”
By combining the tunnel junction VCSEL concept with conventional edge-emitting laser designs, the researchers created a buried tunnel junction VCSEL with a single-stage, type-II material active region to extend the VCSELs’ wavelength coverage.
According to the team, it’s the first known demonstration of electrically pumped, single-mode, tuneable VCSELs emitting continuous wave up to 4µm.
“The VCSEL demonstrates that low power, battery-operated, portable and inexpensive sensing systems are within reach,” Veerabathran concluded. “Once sensing systems become more affordable, there’s great potential for deployment in the auto industry for emission monitoring and control, and they may even find uses within our homes.”
