Wavelength-scale deformed microdisk lasers

Abstract

We investigate lasing and output directionality of limaçon-shaped microdisk lasers of dimensions comparable to the emission wavelength. The far-field patterns are shown to differ between lasing modes, unlike in large cavities where lasing modes exhibit universal emission directionality determined by chaotic ray dynamics. Unidirectional emission is obtained for certain modes in the wavelength-scale cavities. It results from weak coupling of nearly isotropic high-quality resonances to anisotropic low-quality resonances, combined with chiral symmetry breaking of clockwise and counterclockwise propagating waves. The latter is described by an extended ray dynamics which includes the Goos-Hänchen shift and the Fresnel filtering. Mode hybridization and wave effects in open cavities make it possible to control the output properties of individual lasing modes in wavelength-scale lasers.

Dielectric microcavities: Model systems for wave chaos and non-Hermitian physics

“…Consequently, the triangle orbit is broken into two distinct CW and CCW periodic pseudo-orbits. This split is confirmed by direct calculation of periodic orbits with the extended ray dynamics that incorporates the beam shifts (Song et al, 2011). Figure 41 plots the CW and CCW orbits of period 3 that correspond to the LQM.…”

“…Because of this the extended ray dynamics violates time-reversal symmetry (Altmann et al, 2008). One consequence is that time-reversal periodic orbit partners of the conventional ray dynamics are distorted differently by the FF and therefore split (Altmann et al, 2008;Redding et al, 2012b;Shim et al, 2012;Song et al, 2011).…”

“…Moreover, the output directionality is no longer universal, it varies from mode to mode, in contrast to the prediction of the ray model. Nevertheless, unidirectional emission can still be generated from such small cavities by coupling an isotropic HQM to an anisotropic low-Q mode (LQM) (Song et al, , 2011. As an example, let us consider a cavity of shape similar to the limaçon cavity discussed in Section VII.D.…”

“…The Husimi function on the classical Poincaré SOS reveals that the LQM is concentrated on a periodic orbit of triangle shape with three bounces from the cavity boundary. The beam shifts, i.e., the GHS and the FF, are evident in the incident and emergent Husimi functions (Song et al, , 2011. Consequently, the triangle orbit is broken into two distinct CW and CCW periodic pseudo-orbits.…”

“…The beam shifts, which are significant for the LQM and makes its emission directional, are negligible for the HQM, which is concentrated on a period-4 orbit with larger angle of incidence (Song et al, , 2011. Hence, directional output for a HQM can only be obtained by accidental coupling to a LQM.…”