paper 150205064404

Abstract

Optical microdisk laser provide a promising alternative to the well-known Fabry- Perot lasers as well as to VCSELs as the size of optical devices is further reduced to the scale of few micrometers. Whereas high Q-modes are available through whispering-gallery-type resonances that are trapped by total internal reflection inside the resonator, it remains a challenge to achieve directional emission by suitably breaking the rotational symmetry of the devices. In a previous work (J. Wiersig and M. Hentschel, Phys. Rev. Lett., Vol. 100, 033901, 2008.) [6] we have shown that the so-called Limaçon-shape provides a robust possibility to combine directional far-field emission with high Q-factors. In detail, the far-field characteristic is determined by the unstable manifold of the cavity, a quantity well-known in the field of dynamical systems and quantum chaos. It implies that ray-based calculations, wave-simulations and experiments yield practically the same result. In particular, the easy-to-implement ray-optics methods are an appropriate tool to predict the far-field of microdisk lasers. A long-standing problem is to understand the role of boundary imperfections. Presumably these are responsible for the reduction of the Q- factors observed in experiments in comparison to the theoretical predictions. Here, we consider exemplarily the reflection of a Gaussian beam at a surface that was equipped with sharp and rounded cusps of wavelength size. We find that this changes the properties of the reflected beam considerably. We conclude that in practice, such imperfections will reduce the cavity Q-factors and will influence the far-field emission properties of microdisk lasers.

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Martina Hentschel

Jakob Kreismann

Kazuhiro Kubo

Pia Stockschlader