Nonlinear beam self-cleaning in a coupled cavity composite laser based on multimode fiber.

R Guenard,A Desfarges-Berthelemot,K Krupa,V Kermene,A Bendahmane,A Tonello,A Barthélémy,R Dupiol,G Millot,V Couderc,M Fabert,J L Auguste,S Wabnitz

doi:10.1364/oe.25.022219

Abstract

We study a coupled cavity laser configuration where a passively Q-switched Nd:YAG microchip laser is combined with an extended cavity, including a doped multimode fiber. For appropriate coupling levels with the extended cavity, we observed that beam self-cleaning was induced in the multimode fiber thanks to nonlinear modal coupling, leading to a quasi-single mode laser output. In the regime of beam self-cleaning, laser pulse duration was reduced from 525 to 225 ps. We also observed a Q-switched mode-locked operation, where spatial self-cleaning was accompanied by far-detuned nonlinear frequency conversion in the active multimode fiber.

Highlights

Multimode optical fibers (MMFs) may provide an interesting alternative to large mode area (LMA) single mode fibers for the fiber-based delivery of high peak power pulses, and for fabricating high-power fiber amplifiers and lasers [1,2,3]
We study a coupled cavity laser configuration where a passively Q-switched Nd:YAG microchip laser is combined with an extended cavity, including a doped multimode fiber
The main obstacle with the use of MMFs is their inherent degradation of the spatial beam quality leading to modal noise, and, in the short pulse regime, temporal broadening from modal dispersion

Summary

Introduction

Multimode optical fibers (MMFs) may provide an interesting alternative to large mode area (LMA) single mode fibers for the fiber-based delivery of high peak power pulses, and for fabricating high-power fiber amplifiers and lasers [1,2,3]. Spatial filtering and differential diffraction losses, differential bending losses [1], resonant coupling with a surrounding structure [5], long-period Bragg gratings, tailoring of the doping area [6], and gain guiding [7], to mention a few Another approach involves adaptive input wavefront shaping by electrooptic phase control in order to properly shape the output beam in spite of the highly multimode propagation environment [8]. We obtained intra-cavity nonlinear beam self-cleaning in the active MMF section under appropriate settings of its gain, and of the coupling between short and long cavities We achieved both Q-switched and Q-switched mode-locked operations, in combination with spatial beam cleaning in the MMF amplifier

Coupled cavity composite laser based on a multimode fiber

Findings

Conclusion