Modal Behaviour of Passive, Stable Microcavities

Tunable active and passive components for wavelength division multiplex (WDM) systems like vertical cavity surface emitting lasers (VCSELs) and filters show advanced optical performance at reduced production costs if the cavity structure is of stable, half symmetric type. In this paper we report about the mathematical modelling of the power of sidemodes which appear if beam and cavity geometry do not match. We present experimental data which show that the sidemodes are filtered out up to a certain degree by the fiber coupling optics. A limit for the sidemode suppression even for perfect cavity and beam geometry match was also observed. These aspects raise the question on the influence of spherical aberrations on the performance of fiber coupled devices.