Spatio-temporal structures in broad-area VCSELs
VCSELs are very short, typically the inner spacer layer is only one wavelength long (about 200-250 nm) and the effective cavity length is slightly larger than one micrometer. This has the advantage that VCSELs operate intrinsically in single longitudinal mode. On the other hand, this implies that VCSELs have a rather large Fresnel number, i.e. their longitudinal dimension is considerably smaller than the transverse size (about 10-20 µm for typical commercial lasers and up to about 200 µm for prototypes investigated for high-power applications as free space communication, sensors, printing and laser pumping). Hence the spatial and temporal coherence and/or the available output power are limited by spatial instabilities, i.e. a very strong tendency for the excitation of transverse modes (potentially of very high order). These spatial instabilities can be regarded also as a manifestation of self-organization, i.e. spontaneous pattern formation.
Hence, in this project the formation and characteristics of spatial structures in broad-area VCSELs are studied and control strategies are developed in order to stabilize and to steer their output in a well defined emission state. For this, we consider the injection of an external field and spatially and frequency selective feedback.
Injection and feedback are a well known, powerful tools to control the emission of a laser. However, in most cases its application is limited
to a control of the spatial fundamental mode. Here the controlled excitation of more general patterns is demonstrated and their
properties characterized. One example is the search for highly nonlinear excitations as dissipative solitons: bright spots on a homogeneous background which are considerably smaller than the active zone and which can exist anywhere in the transverse plane. These soliton-like states are also referred to as localized states, spatial
solitons or cavity solitons. They were recently predicted and observed in semiconductor microcavities
[7,11]
and are
discussed as "bits" for massively parallel, all-optical information storage and processing.
The experimental investigations are done in collaboration with J. R. Tredicce (Institut Non Linéaire de Nice, Sophia-Antipolis, France), F. Marino and S. Balle (IMEDEA, Palma de Mallorca, Spain), the theoretical ones with N. A. Loiko and I. Babushkin (Academy of Sciences of Belarus, Minsk, Belarus) and J. R. Moloney (ACMS, University of Tucson, Tucson AZ, USA).
 Publications
|
