Directional single mode quantum cascade laser emission using second-order metal grating coupler

We report on the design and experimental demonstration of a substrate emitting quantum cascade laser (QCL) with low beam divergence in the two directions. A low-loss, index-coupled, distributed feedback laser is coupled to a monolithic extraction area. Both functions are performed with a top metal grating spatially differentiated for improving the divergence of the QCL in the two directions. Spectrally single-mode InGaAs/AlInAs QCL emitting at a wavelength of 5.65 mu m with a low beam divergence, represented by a full width at half maximum of 2.3 degrees and 4 degrees, is demonstrated at room temperature with a threshold current of 2.1 kA/cm(2). (C) 2011 American Institute of Physics. {[}doi:10.1063/1.3535610]