Quantum cascade lasers with integrated plasmonic antenna-array collimators

We demonstrated in simulations and experiments that by defining a properly designed two-dimensional metallic aperture-grating structure on the facet of quantum cascade lasers, a small beam divergence angle can be achieved in directions both perpendicular and parallel to the laser waveguide layers (denoted as theta(perpendicular to) and theta(parallel to), respectively). Beam divergence angles as small as theta(perpendicular to)=2.7 degrees and theta(parallel to)=3.7 degrees have been demonstrated. This is a reduction by a factor of similar to 30 and similar to 10, respectively, compared to those of the original lasers emitting at a wavelength of 8.06 mu m. The devices preserve good room temperature performance with output power as high as similar to 55% of that of the original unpatterned lasers. We studied in detail the trade-off between beam divergence and power throughput for the fabricated devices. We demonstrated plasmonic collimation for buried heterostructure lasers and ridge lasers; devices with different waveguide structures but with the same plasmonic collimator design showed similar performance. We also studied a device patterned with a spider's web pattern, which gives us insight into the distribution of surface plasmons on the laser facet. (C) 2008 Optical Society of America