Optimized second-harmonic generation in quantum cascade lasers

• Published in: IEEE journal of quantum electronics Vol. 39; no. 11; pp. 1345 - 1355
• Main Authors: Gmachl, C., Belyanin, A., Sivco, D.L., Peabody, M.L., Owschimikow, N., Sergent, A.M., Capasso, F., Cho, A.Y.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.11.2003; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Cascades; Conversion; Design optimization; Integrated optics; Laser transitions; Lasers; Nonlinear optics; Nonlinearity; Optical coupling; Optical design; Optical harmonic generation; Power lasers; Quality control; Quantum cascade lasers; Quantum wells; Resonance; Semiconductors; Wavelengths
• ISSN: 0018-9197; 1558-1713
• DOI: 10.1109/JQE.2003.818315

Optimized second-harmonic generation (SHG) in quantum cascade (QC) lasers with specially designed active regions is reported. Nonlinear optical cascades of resonantly coupled intersubband transitions with giant second-order nonlinearities were integrated with each QC-laser active region. QC lasers with three-coupled quantum-well (QW) active regions showed up to 2 /spl mu/W of SHG light at 3.75 /spl mu/m wavelength at a fundamental peak power and wavelength of 1 W and 7.5 /spl mu/m, respectively. These lasers resulted in an external linear-to-nonlinear conversion efficiency of up to 1 /spl mu/W/W/sup 2/. An improved 2-QW active region design at fundamental and SHG wavelengths of 9.1 and 4.55 /spl mu/m, respectively, resulted in a 100-fold improved external linear-to-nonlinear power conversion efficiency, i.e. up to 100 /spl mu/W/W/sup 2/. Full theoretical treatment of nonlinear light generation in QC lasers is given, and excellent agreement with the experimental results is obtained. For the best structure, a second-order nonlinear susceptibility of 4.7/spl times/10/sup -5/ esu (2/spl times/10/sup 4/pm/V) is calculated, about two orders of magnitude above conventional nonlinear optical materials and bulk III-V semiconductors.