Periodic Pump Modulation Research Articles

Reconfigurable high-order exceptional points in coupled optical parametric oscillators for enhanced sensing

Non-Hermitian systems around exceptional points (EPs) demonstrate increased sensitivity as the EP order increases. We propose a protocol for constructing a reconfigurable non-Hermitian system consisting of three coupled optical parametric oscillators (OPOs) and demonstrate its enhanced sensitivity around EPs. The coupled OPO system exhibits reconfigurable high-order EPs and corresponding-order enhanced sensitivity (i.e. fourth and sixth order) when it is subjected to pump modulation. Furthermore, the coupled OPO system can synthesize directly a Floquet non-Hermitian system by introducing periodic pump modulation, and can achieve a tunable second-order Floquet EP without periodic modulation of the coupling rates. The convenient flexibility of the coupled OPO system allows it to operate at EPs of different orders and customize a Floquet EP by manipulating the pump parameters. Our protocol can thus contribute to the development of high-performance sensors and precision measurement devices by exploring the unique features of non-Hermitian systems around various EPs.

Reconfigurable dynamics of optical soliton molecular complexes in an ultrafast thulium fiber laser

Dissipative optical solitons of particle-like structures can form soliton molecules with striking molecule-like interactions. However, the experimental investigation of soliton molecules in ultrafast lasers is still largely confined to bound states of only two solitons and is far from being explored for soliton molecular complexes. Here, the reconfigurable switching of soliton molecular complexes originating from the binding of two soliton-pair molecules was demonstrated around 2 μm, simultaneously opening an emerging window in the longer wavelength. The periodic switching of soliton molecules with dual-stability can be resolved. Moreover, the single and multiple successively switching of soliton molecules can be triggered by the collision of drifting soliton or control over saturable absorption parameters. Further, the consecutive reversible switching with high fidelity is verified in soliton molecules with periodic pump modulation. These results unveil the dynamical soliton interaction and motivate potential applications in ultrafast spectroscopy, information encoding, and computations.

Breathing Dissipative Soliton Molecule Switching in a Bidirectional Mode‐Locked Fiber Laser

Breathing optical solitons propagating in a dissipative nonlinear system can interact and bind stably, forming an optical soliton molecule that presents striking molecule‐like dynamics. To date, the breathing soliton pair has been mainly observed in the microcavity platform, and the peculiar dynamic evolution of breathing soliton molecules (BSMs) remains largely unexplored in mode‐locked fiber lasers. Herein, the transient switching dynamics of BSMs in a bidirectional ultrafast fiber laser is revealed, specifically triggered at different parameter spaces of saturable absorption with manipulation polarizations that maintain constant pulse separation or undergo strong repulsion and kink after switching. All‐optical switching of breather molecules and significantly increasing multiple soliton molecules’ switching of two or three solitons between states with different binding separations by applying a strong stimulus with periodic pump modulation is demonstrated. The instantaneous pulse breakup can be induced by the collision of bidirectional breathing solitons in each switching, which is characteristic of the breathing solitons in a bidirectional fiber laser and further corroborated by numerical simulation. The study unveils new perspectives into the ultrafast transient process of BSMs in various dissipative systems.

Synchronisation and desynchronisation of self-modulation oscillations in a ring chip laser under the action of a periodic signal and noise

The effect of pump noise on the synchronisation of self-modulation oscillations in a solid-state ring laser with periodic pump modulation is studied numerically and experimentally. It is found that, in contrast to desynchronisation that usually occurs under action of noise in the case of 1/1 synchronisation of self-oscillations by a periodic signal, the effect of noise on 1/2 synchronisation may be positive, namely, at a sufficiently low intensity, pump noise is favourable for synchronisation of self-oscillations, for narrowing of their spectrum, and for increasing the signal-to-noise ratio.

Parametric excitation of relaxation oscillations at the subharmonic of the external modulating signal in a ring Nd : YAG laser

The dynamics of solid-state ring laser (SSRL) radiation with periodic pump modulation is studied experimentally and simulated numerically in the case of parametric excitation of relaxationoscillations at the subharmonic of a modulating signal. Parametric processes are investigated by modulating the pump in two regimes of the SSRL operation: steady-state regime of unidirectionallasing and self-modulation regime of the first kind. Significant differences in the dynamics of radiation for these regimes are found. It is established that when the laser operates in the self-modulation regime, a first-order parametric instability can result in the appearance of the dynamic chaos regime.

Bistable vertical cavity laser with periodic pump modulation as a random bits generator

It is experimentally demonstrated that the semiconductor vertical cavity laser with the pump current modulation, operating in the regime of polarization bistability, can be an effective source of true random bits with the rate of generation up to several Mbps, which is determined by the modulation frequency. The generated sequences are characterized by the low bias and low correlations between generated bits.

Experimental study of noise-induced phase synchronization in vertical-cavity lasers.

We report the experimental evidence of noise-induced phase synchronization in a vertical-cavity laser. The polarized laser emission is entrained with the input periodic pump modulation when an optimal amount of white, Gaussian noise is applied. We characterize the phenomenon, evaluating the average frequency of the output signal and the diffusion coefficient of the phase difference variable. Their values are roughly independent of the different wave forms of periodic input, provided that a simple condition for the amplitudes is satisfied. The experimental results are compared with numerical simulations of a Langevin model.

Chaotic synchronization and evolution of optical phase in a bidirectional solid-state ring laser.

We present results on experimental and theoretical studies of chaos in a solid-state ring laser with periodic pump modulation. We show that the synchronized chaos in the counter-propagating waves is observed for the values of pump modulation frequency fp satisfying the inequality f1 < fp < f2. The boundaries of this region, f1 and f2, depend on the pump-modulation depth. Inside the region of synchronized chaos we study not only dynamics of amplitudes of the counter-propagating waves but also the optical phases of them by mixing the fields of the counter-propagating waves and recording the intensity of the mixed signal. We demonstrate experimentally that in the regime of synchronized chaos the regular phase jumps appear during intervals between adjacent chaotic pulses. We improve the standard semi-classical model of a SSRL and consider an effect of spontaneous emission noise on the temporal evolution of intensities and phase dynamics in the regime of synchronized chaos. It is shown that at the parameters of the experimentally studied laser the noise strongly affects the temporal dependence of amplitudes of the counter-propagating waves.

Phase dynamics of radiation in chaotic lasing regimes of a solid-state ring laser

The radiation phase dynamics of a solid-state ring laser with a periodic pump modulation operating in a dynamic chaotic regime is studied theoretically and experimentally. It is found that, in the regime of synchronised dynamic chaos, the optical phases of counterpropagating waves change by π in intervals between two adjacent chaotic radiation pulses. It is shown that spontaneous radiation has a significant effect on the chaotic dynamics of the counterpropagating wave intensities, but its effect on the phase dynamics in a solid-state ring laser is negligible.

New periodic and chaotic regimes in a solid-state ring laser with an optical phase nonreciprocity

Dynamics of a solid-state ring laser with periodic pump modulation was investigated experimentally in the presence of a phase nonreciprocity of its cavity. New lasing regimes were discovered: periodic antiphase pulsed modulation of counterpropagating waves and synchronisation of chaotic intensities of counterpropagating waves, differing from the perfect synchronisation investigated earlier because the difference between the intensities of chaotic pulses travelling in opposite directions was a periodic function of time. The phase nonreciprocity reduced the range of existence of dynamic chaos in a ring solid-state laser.

Parametric processes and multistability in a ring chip laser with periodic pump modulation

The first detailed experimental and theoretical investigation is reported of the influence of periodic pump modulation on a type 1 self-modulation in a ring Nd:YAG chip laser pumped by a semiconductor laser diode. It is shown that the excitation of relaxation oscillations as a result of parametric processes and direct resonant action of pump modulation has a significant influence on the lasing regimes, on the temporal and spectral characteristics of the output radiation, and on the scenario of a transition to chaos. It is shown that for the same laser parameters there may be two coexistent lasing regimes, including quasiperiodic operation of two types. The lasing regimes are classified and the ranges of their stability are investigated for varying modulation frequency and depth.

Transient and modulation dynamics of a multimode Fabry-Pérot laser

The two-mode rate equations for a laser in a Fabry-Pérot cavity are studied, taking into account the dynamics of spatial holeburning. We prove analytically that each mode intensity has a transient behavior characterized by two damped oscillation frequencies, while the total intensity displays a domain where only the largest oscillation frequency remains; this domain appears to display antiphase dynamics. These results are generalized to N lasing modes. We then analyze the response of the two-mode laser to a periodic pump modulation. For small modulation depth, the two oscillation frequencies are clearly displayed as resonances on the response curve. For deeper modulation depth, the beating of the modulation frequency and the largest internal oscillation frequency produces a subharmonic sequence to chaos. This chaotic domain disappears in a crisis when it collides with the branch of stable periodic oscillations associated with the smaller oscillation frequency which coexists with the subharmonic cascade.

On the dynamics of a two-mode laser with periodically modulated parameter

The results for a numerical simulation of a two-mode homogeneously-broadened laser due to a periodic pump modulation are presented. The region with the parameters for the complicated periodic and chaotic laser-intensities pulsation to be observed has also been defined. Complex bifurcation diagram versus modulation frequency with the periodic and chaotic regimes alternation is presented.

Bifurcation structure of a laser with pump modulation

The nonlinear phenomena that occur in the laser rate equations with periodic pump modulation are studied numerically. The gross bifurcation structure of the system covering a large range of the parameters can be classified through the concept of nonlinear resonances and torsion numbers, which have already been used to great advantage in other nonlinear oscillatory systems. The pump-modulated laser rate equations are closely related to the Toda oscillator.