We investigate cluster synchronization in experiments with a multilayer network of electronic Colpitts oscillators, specifically a network with two interaction layers. We observe and analytically characterize the appearance of several cluster states as we change coupling in the layers. In this study, we innovatively combine bifurcation analysis and the computation of transverse Lyapunov exponents. We observe four kinds of synchronized states, from fully synchronous to a clustered quasiperiodic state-the first experimental observation of the latter state. Our work is the first to study fundamentally dissimilar kinds of coupling within an experimental multilayer network.

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Injection locking is an effective technique for synchronization of oscillator networks and controlling the phase and frequency of individual oscillators. As such, exploring new mechanisms for injection locking of emerging oscillators is important for their usage in various systems. Here, we present the first demonstration of injection locking of a radiation pressure driven optomechanical oscillator (OMO) via acoustic waves. As opposed to previously reported techniques (based on pump modulation or direct application of a modulated electrostatic force), injection locking of OMO via acoustic waves does not require optical power modulation or physical contact with the OMO and it can be easily implemented on various platforms to lock different types of OMOs independent of their size and structure. Using this approach we have locked the phase and frequency of two distinct modes of a microtoroidal silica OMO to a piezoelectric transducer (PZT). We have characterized the behavior of the injection locked OMO with three acoustic excitation configurations and showed that even without proper acoustic impedance, matching the OMO can be locked to the PZT and tuned over 17 kHz with only -30 dBm of RF power fed to the PZT. The high efficiency, simplicity, and scalability of the proposed approach paves the road toward a new class of photonic systems that rely on synchronization of several OMOs to a single or multiple RF oscillators with applications in optical communication, metrology, and sensing. Beyond its practical applications, injection locking via acoustic waves can be used in fundamental studies in quantum optomechanics where thermal and optical isolation of the OMO are critical.

We demonstrate a simple and effective technique for stabilizing the oscillation amplitude of a radiation pressure driven RF optomechanical oscillator (OMO). By controlling the optomechanical gain through a feedback loop that uses the oscillation amplitude itself as the feedback parameter, we have been able to suppress the amplitude fluctuations and drift. In contrast to more complex techniques that only lock the relative wavelength detuning, the proposed technique isolates the oscillation amplitude not only from laser wavelength variations, but also from laser power variations, ambient temperature variations, and coupling gap variations. The amplitude stabilization also improves the stability of the oscillation frequency (compared to free-running OMOs).

With both radiation effects and thermal effects taken into consideration, a multiphysics thermal model concerning high-power Yb-doped fiber lasers operated with post-irradiated active fibers is established. Radiation-related parameters, including propagation losses, refractive indexes and lifetime, are considered. And, with the temperature profile of the active fiber, temperature-dependent parameters, including absorption and emission cross-sections, refractive indexes and lifetime, are updated every loop to simulate the output parameters. Simulation results show that radiation induces great changes to the thermal profiles of the active fiber. And severe performance degradation of high-power Yb-doped fiber lasers are recorded, featuring a remarkable drop in output power and an even steeper decline in the transverse mode instability threshold, which is a predominant limitation at high radiation doses. With a deposited radiation of 100 Gy, an output decline of about 50% and a mode instability threshold drop over 85% are observed. And it’s shown that, with the exploited active fiber, it’s hardly possible for the investigated fiber laser to generate stable single-mode output at kilowatt levels with accumulated radiation doses beyond 50 Gy. At low radiation doses within 20 Gy, to maintain safe and stable single-mode operation of the laser system, longer active fibers with lower absorption coefficients are preferred despite a small rollover of the output power.