Coupled clocks are a classic example of a synchronization system leading to periodic collective oscillations. This phenomenon already attracted the attention of Christian Huygens back in 1665, who described it as a kind of "sympathy" among oscillators. In this work we describe the formation of two types of laser frequency combs as a system of oscillators coupled through the beating of the lasing modes. We experimentally show two completely different types of synchronizations in a quantum dot laser -in-phase and splay states. Both states can be generated in the same device, just by varying the damping losses of the system. This effectively modifies the coupling among the oscillators. The temporal output of the laser is characterized using both linear and quadratic autocorrelation techniques. Our results show that both pulses and frequency-modulated states can be generated on demand. These findings allow to connect laser frequency combs produced by amplitude-modulated and frequency-modulated lasers, and link these to pattern formation in coupled systems such as Josephson-junction arrays.

Mode-locked InAs/InGaAs quantum dot lasers emitting optical frequency combs centered at 1310 nm are promising sources for high-speed and high-capacity communication applications. We report on the stable optical pulse train generation by a monolithic passively mode-locked edge-emitting two-section quantum dot laser based on a five-stack InAs/InGaAs dots-in-a-well structure directly grown on an on-axis (001) silicon substrate by solid-source molecular beam epitaxy. Optical pulses as short as 1.7 ps at a pulse repetition rate or intermode beat frequency of 9.4 GHz are obtained. A minimum pulse-to-pulse timing jitter of 9 fs, corresponding to a repetition rate line width of 400 Hz, is demonstrated. The generated optical frequency combs yield exceptional low amplitude jitter performance and comb widths exceed 5.5 nm at a −3 dB criteria, containing more than 100 comb carriers.

The pulse repetition rate (RR) tuning and locking range (LR) as well as the pulse train timing stability of passively mode-locked quantum-well (QW) semiconductor lasers (SCLs) subject to single-cavity optical self-feedback (OFB) are investigated experimentally and by simulations. A simple and universal stochastic time-domain model confirms the experimentally observed RR control and LR as well as timing jitter (TJ) improvement in QW SCLs subject to very long OFB cavities with lengths up to 73.1 m. In particular, the model allows predicting control potential and limits of the RR tuning, locking and TJ improvement depending on the choice of OFB delay length for time-delay modelocked semiconductor laser stabilisation experiments.

Sudden cardiac death due to ventricular arrhythmias often caused by action potential duration (APD) prolongation is a common mode of death in heart failure (HF). microRNAs, noncoding RNAs that fine tune gene expression, are frequently dysregulated during HF, suggesting a potential involvement in the electrical remodeling process accompanying HF progression. Here, we identified miR-19b as an important regulator of heart function. Zebrafish lacking miR-19b developed severe bradycardia and reduced cardiac contractility. miR-19b deficient fish displayed increased sensitivity to AV-block, a characteristic feature of long QT syndrome in zebrafish. Patch clamp experiments from whole hearts showed that miR-19b deficient zebrafish exhibit significantly prolonged ventricular APD caused by impaired repolarization. We found that miR-19b directly and indirectly regulates the expression of crucial modulatory subunits of cardiac ion channels, and thereby modulates AP duration and shape. Interestingly, miR-19b knockdown mediated APD prolongation can rescue a genetically induced short QT phenotype. Thus, miR-19b might represent a crucial modifier of the cardiac electrical activity, and our work establishes miR-19b as a potential candidate for human long QT syndrome.