InGaAs/AlInAs quantum cascade laser sources based on intra-cavity second harmonic generation emitting in 2.6-3.6 micron range M.A. Belkin a* , M. Jang a , R.W. Adams a , J. X. Chen b , W. O. Charles b , C. Gmachl b , L. W. Cheng c , F.- S. Choa c , X. Wang d , M. Troccoli d , A. Vizbaras e , M. Anders e , C. Grasse e , and M.-C. Amann e a Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX 78758 b Deptartment of Electrical Engineering and MIRTHE, Princeton University, Princeton, NJ 08544 c Department of Computer Science and Electrical Engineering, University of Maryland Baltimore County, Baltimore, MD 21250 d Adtech Optics, Inc., 18007 Cortney Court, City of Industry, CA91748 e Walter Schottky Institut, Technische Universität München, Garching 85748, Germany *E-mail: mbelkin@ece.utexas.edu ABSTRACT We discuss the design and performance of quantum cascade laser sources based on intra-cavity second harmonic generation operating in at wavelengths shorter than 3.7μm. A passive heterostructure tailored for giant optical nonlinearity is integrated on top of an active region and patterned for quasi-phasematching. We demonstrate operation of λ≈3.6μm, λ≈3.0μm, and λ≈2.6μm devices based on lattice-matched and strain-compensated InGaAs/AlInAs/InP materials. Threshold current densities of typical devices with nonlinear sections are only 10-20% higher than that of the reference lasers without the nonlinear section. Our best devices have threshold current density of 2.2kA/cm 2 and provide approximately 35μW of second-harmonic output at 2.95μm at room temperature. The second-harmonic conversion efficiency is approximately 100μW/W 2 . Up to two orders of magnitude higher conversion efficiencies are expected in fully-optimized devices. Keywords: quantum cascade lasers, second harmonic generation, short wavelength, room temperature, intersubband, giant nonlinear susceptibility, quasi-phase matching 1. INTRODUCTION InGaAs/AlInAs/InP quantum cascade lasers (QCL) have recently been developed into reliable high-power sources that operate continuous-wave (CW) at room-temperature (RT) in the spectral range 3.7-12μm [1]. Their growth and fabrication process is compatible with telecommunication diode lasers production lines which makes manufacturing cost efficient. The spectral range 2.5-12μm is called ‘molecular fingerprint region’; it contains a large number of molecular absorption lines and is highly important for chemical sensing. Widely-tunable QCL sources have been developed to address spectroscopic needs in this region. Examples include an external-cavity QCL tunable between 7.6μm and 11.4μm reported in Ref. [2] and a QCL source based on an array of distributed-feedback (DFB) devices with frequency output variable between 8μm and 9.8μm [3]. A 2.5-3.7μm portion of the ‘molecular fingerprint region’ contains a number of absorption lines important for chemical sensing and spectroscopy. Ideally, one would want to have a device that can provide spectral coverage of the whole ‘molecular fingerprint region’. However, the operation of InGaAs/AlInAs/InP QCLs at 2.5-3.7μm spectral range suffers from inter-valley scattering, even when highly strained heterostructures are used [4]. Diode lasers [5] and interband cascade lasers [6] can operate CW at λ=2.5-3.7μm but they cannot operate at RT at longer wavelengths. In addition, their growth and fabrication process is not compatible with that of telecommunication diode lasers. Heterostructures based on InAs/AlSb [7] and GaInAs/AlAsSb/InP [8] materials may be used to extend the operation of QCLs to the wavelengths shorter than 3.7 μm, but these devices are yet to demonstrate CW operation at RT and their fabrication is also not compatible with that of telecommunication diode lasers. We note that most spectroscopic application require a narrowband CW laser source with only about a milliwatt of output power. Invited Paper Novel In-Plane Semiconductor Lasers X, edited by Alexey A. Belyanin, Peter M. Smowton, Proc. of SPIE Vol. 7953, 795315 · © 2011 SPIE · CCC code: 0277-786X/11/$18 · doi: 10.1117/12.879232 Proc. of SPIE Vol. 7953 795315-1 Downloaded from SPIE Digital Library on 28 Mar 2011 to 128.62.81.150. Terms of Use: http://spiedl.org/terms