Enhancement of vertical emission in photonic crystal nanolasers

Photonic crystal nanolasers have a drawback of weak vertical emission, which degrades the detection efficiency from above. We show that the vertical emission is enhanced greatly by introducing asymmetry to the cavity, so that Fourier components around the Brillouin zone boundary are shifted to the zone center. When the light output is collected from above by an objective lens with a numerical aperture of 0.42, the efficiency for the optimized devices, with and without nanoslot, are calculated to be 26 and 153 times that of the original structure. We confirm the experimental and calculated results to be in good agreement.