The excitation wavelength for all-optical modulation of a 10.6 μm mid-infrared (MIR) quantum cascade laser (QCL) was varied in order to obtain maximum modulation depth. Both amplitude and wavelength modulation experiments were conducted at 820 nm and 1550 nm excitation respectively, whereby the latter matches the interband transition in the QCL active region. Experimental results show that for continuous-wave mode-operated QCL, the efficiency of free carrier generation is doubled under 1550 nm excitation compared with 820 nm excitation, resulting in an increase of the amplitude modulation index from 19% to 36%. At the same time, the maximum wavelength shift is more than doubled from 1.05 nm to 2.80 nm. Furthermore, for the first time to our knowledge, we demonstrated the optical switching of a QCL operated in pulse mode by simple variation of the excitation wavelength.
© 2013 Optical Society of America
Lasers and Laser Optics
Original Manuscript: January 16, 2013
Revised Manuscript: March 1, 2013
Manuscript Accepted: March 4, 2013
Published: April 1, 2013
Tao Yang, Gang Chen, Chao Tian, and Rainer Martini, "Optical modulation of quantum cascade laser with optimized excitation wavelength," Opt. Lett. 38, 1200-1202 (2013)