Optical frequency combs (OFCs) have applications ranging from metrology to molecular spectroscopy and optical telecommunications. Progress in miniaturization of the technology has brought chip-scale electrically pumped OFC sources closer to reality. A chip-scale OFC sensitive to the 2 μm wavelength region is crucial to realizing real-world applications but has yet to be explored in depth due to lack of commercial availability.

Sterczewski et al. developed and demonstrated a quantum well diode laser (QWDL) OFC operating in the 2 μm wavelength region and used the device to perform dual-comb spectroscopy measurements.

“Our main motivation for researching this spectral region stems from growing demand for LIDAR systems used in global-scale measurements of CO2 and other trace gases,” said author Lukasz Sterczewski. “A chip-scale high power frequency comb can greatly expand spectroscopic capabilities by enabling measurement of multiple gas species at multiple wavelengths simultaneously, while providing the reliability and simplicity of semiconductor lasers.”

The QWDL OFC had an optical power of 50 mW with the wavelength centered around 2060 nm and consumed less than 1 W of electrical power at room temperature. Due to a lack of intracavity saturable absorption losses the device was 10 times more powerful than previous mode-locked QWDL devices. Its great stability and high line-to-line coherence allowed for completely free-running mode-resolved dual-comb spectroscopy.

“The dual-comb technique enables high-resolution moving-parts-free measurements of gaseous or condensed samples in microseconds over large spectral ranges,” said Sterczewski. “Given the high optical power and low noise operation of our comb sources, we envision rapid remote detection of multiple trace gases in the near future.”

Source: “Frequency-modulated diode laser frequency combs at 2 μm wavelength,” by Lukasz Antoni Sterczewski, Clifford Frez, Siamak Forouhar, David Burghoff, and Mahmood Bagheri, APL Photonics (2020). The article can be accessed at https://doi.org/10.1063/5.0009761.