Eitan Ronen

Controlling synchronization in large laser networks.

Synchronization in large laser networks with both homogeneous and heterogeneous coupling delay times is examined. The number of synchronized clusters of lasers is established to equal the greatest common divisor of network loops. We experimentally demonstrate up to 16 multicluster phase synchronization scenarios within unidirectional coupled laser networks, whereby synchronization in heterogeneous networks is deduced by mapping to an equivalent homogeneous network. The synchronization in large laser networks is controlled by means of tunable coupling and self-coupling.

Phase locking of two coupled lasers with many longitudinal modes.

Detailed experimental and theoretical investigations of two coupled fiber lasers, each with many longitudinal modes, reveal that the behavior of the longitudinal modes depends on both the coupling strength and the detuning between them. For low to moderate coupling strength only longitudinal modes that are common for both lasers phase lock, while those that are not common gradually disappear. For larger coupling strengths, the longitudinal modes that are not common reappear and phase lock. When the coupling strength approaches unity the coupled lasers behave as a single long cavity with correspondingly denser longitudinal modes. Finally, we show that the gradual increase in phase locking as a function of the coupling strength results from competition between phase-locked and non-phase-locked longitudinal modes.

Phase locking of two fiber lasers with time-delayed coupling

Two coupled fiber laser arrangements demonstrating isochronal and achronal phase locking with long-time-delayed coupling are presented. Experimental results show that stable phase locking with coupling delay lines as long as 4 km can be obtained and that phase locking can be invariant to the time delay.

Phase locking a fiber laser array via diffractive coupling

We demonstrate phase locking of a linear array of seven fiber lasers via diffractive coupling. Coupling between the lasers is achieved by a common output coupler positioned at a quarter Talbot distance from the lasers. The output beams are anti-phase locked with a measured far-field fringe contrast of 82%, and their total output power is higher than that obtained when the lasers operate individually. We measure an exponential phase decorrelation between distant lasers in the array, and discuss its fundamental limitation on scalability of this and similar local coupling methods.

Phase locking of lasers with intracavity polarization elements.

New configurations for phase locking several laser beams with intracavity polarization elements are presented. With this configuration we demonstrated efficient phase lock of up to 24 ND:YAG laser beams with only two polarization beam displacers.

Conversion of out-of-phase to in-phase order in coupled laser arrays with second harmonics

A novel method for converting an array of out-of-phase lasers into one of in-phase lasers that can be tightly focused is presented. The method exploits second harmonic generation and can be adapted for different laser arrays geometries. Experimental and calculated results, presented for negatively coupled lasers formed in a square, honeycomb, and triangular geometries are in good agreement.

Recent developments in passive phase locking and coherent combining of lasers

Selections from our recent developments in passive phase locking and coherent combining of lasers are presented. These include the principles of our approaches, lasers configurations, experimental procedures and results with solid state lasers and fiber lasers.

Phase Clusters Induced by Degeneracy in a Phase Locked Fiber Laser Array

We investigate phase-locking of seven fiber lasers coupled in a Talbot configuration. We show that phase clustering occurs in the array whereby the array separates into two different phase-locked clusters. Further, theoretical analysis and experimental measurements show that these clusters result from an incoherent superposition of the in-phase and out-of-phase supermodes of the array. By inserting selective loss in the resonator, we manage to demonstrate operation in a nearly single pure in-phase supermode.

Frequency, phase, and polarization locking of evanescently coupled lasers

Coherent lasing of two lasers can be achieved passively by intracavity exchange of light between the lasers. Full coherence of the lasers typically implies synchronization in three parameters: frequency, phase, and polarization. Here we investigate a simple laser system in which exchange of light can cause a variety of states: full coherent lasing, only polarization-locked lasing, frequency-locked lasing without phase locking, and independent incoherent lasing. We demonstrate these states experimentally with evanescently coupled fiber lasers, and propose a simple model that offers a simple explanation for these intriguing observations.

Phase Locking Large Arrays of Lasers via a Single Degenerate Cavity

Experimental realization for phase-locking large arrays of lasers arranged in a variety of 2D geometries is presented. Using our degenerate-cavity coupling between lasers is easily controlled giving rise to a variety of intriguing phase structures.