QUANTUM-CASCADE LASERS: Optical illumination modulates quantum-cascade laser

摘要

Rapid modulation of the emission wavelength (optical frequency) of a mid-infrared (mid-IR) quantum-cascade laser (QCL) is difficult due to the nature of its parallel laser subbands and unipolarity; and although self-heating can cause a wavelength redshift, it cannot be used for high-speed modulation due to its thermal time constant, which is on the order of microseconds. But fortunately, researchers at the Stevens Institute of Technology (Hoboken, NJ), Chongqing University (Chongqing, China), and the National Research Council (Ottawa, ON, Canada) have developed a way to optically induce rapid wavelength modulation in a mid-IR QCL by illuminating its front facet with a near-IR femtosecond laser. Enabling wavelength modulation at frequencies up to 1.67 GHz, QCLs look even more attractive for environmental sensing and free-space optical (FSO) communications applications (see "Sophisticated optical systems extend reach of free-space communications," page 51, this issue).