Small divergence substrate emitting quantum cascade laser by subwavelength metallic grating

Metallic periodic structure in subwavelength scale offers an exciting way to couple light into surface plasmons (SPs), thus manipulating the properties of near-field optics. We show that subwavelength metallic grating (SMG) defined on the substrate side of substrate emitting quantum cascade lasers enables far-field improvement in mid-infrared spectrum. The SMG is designed to tailor the interaction of SPs with single mode transverse magnetic light. The experiment results are in good agreement with the simulated model. A far-field full width at half maximum (FWHM) divergence angle of 3.9 ° in the direction perpendicular to the laser waveguide layers is obtained, improved by a factor of 8.5 compared with traditional surface emitting device.