We study symmetries in multi-transverse-mode near-fields of circular vertical cavity surface emitting lasers (VCSELs). The 0 • polarized component of the near-field always has circular or high-order rotational symmetry, indicating that all significant optical properties of the laser are isotropic for light of that polarization. In contrast, the simultaneously present 90 • polarized part of the same near-field is always symmetrical only upon reflection. This is evidenced by sequences of near-field images of increasing complexity for increasing pump current. The presence of a preferred direction of the symmetry axis is evidence for a symmetry-breaking anisotropy. We attribute this anisotropy to birefringence, which is induced into any electrically pumped VCSEL by the applied vertical electrical field via the linear electro-optic effect. Thus, the optical index becomes a function of the transverse component of the k-vector of light inside the cavity, which corresponds to an angular dependent index. As the functional dependence on the emission angle is of different strength for orthogonal polarizations, the circular symmetry of the laser is broken only for 90 • polarized light, while the effect on the 0 • polarization is too small to affect the near-field. The highly symmetrical near-field of the unaffected polarization shows remarkable similarities to another physical system of circular symmetry, the static patterns in cellular flames. Our analysis of the symmetry properties of the near-fields has implications for the design of VCSELs as well as for future modelling activities.

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We present theoretical and experimental results of nonlinear amplification and propagation of short optical pulses in Fabry-Perot semiconductor lasers. The theoretical description is based on spatially resolved Maxwell-Bloch-Langevin equations that take into account the spatially varying light-field dynamics including counterpropagation, diffraction, self-focusing, and the microscopic carrier dynamics including carrier heating and carrier relaxation. Femtosecond pump-probe measurements using upconversion and femtosecondresolved pump-probe measurements and frequency-resolved optical gating on a Fabry-Perot laser allow a combined analysis of the transmitted pulses in real time and the spectral domain. The experimental results are compared with the microscopically calculated gain and index distributions, pulse shapes, and optical spectra. In order to assess the full potential of semiconductor lasers and amplifiers, a quantitative measurement and understanding of amplitude and phase dynamics is required. The computer simulations of the ultrashort dynamics of semiconductor waveguides with optical injection of light pulses provide insight into the dynamic spectral gain and index changes responsible for frequency drifts and self-phase modulation, visualization of propagation effects, and a time-and frequency-resolved analysis of the amplified light pulses.

We report on the observation of spatiotemporal dynamics on picosecond time scales for an antireflection-coated ridge waveguide laser diode that is only 5 m wide. Depending on the applied current, three dynamic regimes can be distinguished, showing the transition from regular to irregular spatiotemporal emission. We discuss the underlying mechanisms and develop a comprehensive understanding of this dynamic behavior. First, for moderate pumping, we find a typical relaxation oscillation behavior of the fundamental lateral mode. Second, at intermediate current levels, we observe lateral high-frequency switching of the output intensity between the left-hand and the right-hand parts of the active region. The switching frequency increases linearly with the excitation current and is of the order of 10 GHz. We give evidence that this switching behavior results from the coexistence and interaction of fundamental and first-order lateral modes that belong to different longitudinal mode families. The observed dependence of the switching frequency on the bias current can be attributed to a change in the width of the emission profile. Third, at high pumping levels, irregular spatiotemporal dynamics with the coexistence of low-and high-frequency spatial switching and temporal pulsations can be found. Finally, the influence of waveguide design and consequences for applications are considered and discussed.

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