  We investigate the dynamic mechanisms for low frequency fluctuations in
semiconductor lasers subject to delayed optical feedback, using the
Lang-Kobayashi model. This system of delay differential equations displays
pronounced envelope dynamics, ranging from erratic, so called low frequency
fluctuations to regular pulse packages, if the time scales of fast oscillations
and envelope dynamics are well separated. We investigate the parameter regions
where low frequency fluctuations occur and compute their Lyapunov spectrum.
Using geometric singular perturbation theory, we study this intermittent
chaotic behavior and characterize these solutions as bursting slow-fast
oscillations.
