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Self-pulsing and dual-mode lasing in a square microcavity semiconductor laser are studied experimentally. Self-sustained pulses originating from undamped relaxation oscillation induced by a two-mode interaction are obtained, as the injection current is slightly above the laser threshold. A repetition frequency of 4.4 GHz and a pulse width of 30-40 ps are obtained at a current of 8 mA. The laser switches to continuous-wave operation when the injection current is higher than a certain value, and dual-mode lasing with 30.7 GHz at 16 mA and 10.7 GHz at 27 mA are observed in the lasing spectra. Furthermore, the relative intensity noise spectra are presented to reveal the relationship between the lasing states and the dynamics induced by relaxation oscillation and mode beating.

A tri-mode micro-square laser under optical feedback is proposed and demonstrated to generate chaos with the broadband flat microwave spectrum. By adjusting lasing mode intensities, frequency intervals, and optical feedback strength, we can enhance the chaotic bandwidth significantly. The existence of two mode-beating peaks makes the flat bandwidth much larger than the relaxation oscillation frequency. Effective bandwidth of 35.3 GHz is experimentally achieved with the flatness of 8.3 dB from the chaotic output spectrum of the tri-mode mode laser under optical feedback.

We propose and demonstrate a circular-side octagonal microcavity (COM) semiconductor laser with a spatially distributed current injection for manipulating the lasing modes. There are two types of high-quality-factor whispering-gallery (WG) modes with distinct field patterns in a COM: the four-bounced quadrilateral modes and the eight-bounced octagonal modes. By designing two separated p-electrodes, the COM laser is divided into two regions that are pumped independently to select specific modes for lasing. The two types of WG modes lase simultaneously when the two regions are injected with equivalent currents. Degeneracy removal of the quadrilateral modes is observed in both simulation and experiment when the two regions are injected with inequivalent currents. The quadrilateral modes are suppressed when one of the two regions is un-injected or biased with a negative current, and single-octagonal-mode lasing is realized. The results show that the lasing modes can be efficiently manipulated with the spatially distributed current injection considering the distinct field patterns of different WG modes in the microcavities, which can promote the practical application of the microcavity lasers.

All-optical switch and multiple logic gates have been demonstrated using a hybrid-cavity semiconductor laser composed of a square microcavity and a Fabry-Perot cavity experimentally. In this paper, two-section tri-mode rate equations with optical injection terms are proposed and applied to study all-optical logic gates of NOT, NOR, and NAND operations utilizing the hybrid-cavity laser. Steady-state and dynamical characteristics of all-optical multiple logic gates are simulated, taking into account the influence of mode frequency detuning, gain suppression coefficients, mode Q factor, injection energy, and biasing current. All-optical logic NOT, NOR, and NAND gates up to 20, 15, and 20 Gbit/s are obtained numerically with dynamic extinction ratios of over 20, 20, and 10 dB, respectively, which are potential response speeds of the all-optical logic gates based on the hybrid-cavity semiconductor lasers.

In this Letter, we design and realize a hybrid-cavity laser with single- or dual-mode lasing states and study the nonlinear states of the laser under external optical feedback (EOF). The laser at a dual-mode state easily and directly enters the chaotic state without periodic oscillation states and display chaos for a much wider range of the EOF magnitude than the laser at a single-mode state. A flat chaotic signal is obtained for the laser at a dual-mode lasing state under a weak EOF benefitting from the low-frequency energy enhancement caused by mode competition between the dual modes.

We theoretically and numerically study optical modes in regular-polygonal microcavities with non-uniform gain and loss, where high quality (Q) whispering-gallery-like modes typically appear as superscar states. High Q superscar modes can be described by the propagating plane waves in an effective rectangle formed by unfolding the periodic orbits and exhibit regular and predictable spatial field distributions and transverse-mode spectra. With non-uniform gain and loss, anti-Hermitian coupling between the transverse modes with close frequencies occurs according to the mode coupling theory, which results in novel mode properties such as modified mode spectra and field patterns, and the appearance of exceptional points. Numerical simulation results are in good agreement with the theoretical analyses, and such analyses are also suitable for other kinds of high Q microcavities with non-uniform gain and loss. These results will be highly useful for studying non-Hermitian physics in optical microcavities and advancing the practical applications of microcavity devices.