Abstract

In recent years, laser arrays were extensively studied to create high power sources. Coherent combining techniques were developed to improve the brightness of such laser sources. Passive techniques in particular were widely investigated because of their simple operation based on self-organization of the laser. Nevertheless, phase-locking laser array of large size remains challenging because it leads to a decrease of the combined beam stability and efficiency [1]. Recently, we proposed a multiple feedback architecture including a phase contrast filtering and resonant non-linearity to overcome these limitations [2]. In such self-organized laser, we add a new degree of freedom by the phase contrast filtering which encodes the phase deviations between the multiple laser beams in intensity fluctuations. Resonant refractive index non-linearity, due to the gain saturation in the different amplifiers, performs an inverse transformation (amplitude/phase encoding) and compensates for residual phase deviations. After a first proof of principle with a four element laser [3], we will report new results with the successful phase-locking of arrays of 3×3 and then 4×4 Yb doped fiber lasers (with one laser missing). Far field patterns and laser optical spectra were recorded and compared to the ones measured with a standard cavity configuration. The combined power detected in the far field was observed to be significantly more stable in the former case than in the latter. This improved stability can be explained by the cooperative effects between phase contrast filtering and resonant non-linearity. The new architecture also offers extra opportunity for cavity resonance so that new frequencies may appear in the laser spectrum as it was noticed in the laser modeling. Recorded spectra attested the increased number of oscillating wavelengths with the phase contrast configuration. These new laser lines improved the robustness of the system against environmental perturbations. The far field pattern of the 15 coupled lasers, the temporal evolution of its combined power and the output laser spectrum are shown Figure 1.

© 2013 IEEE