Single-mode output by controlling the spatiotemporal nonlinearities in mode-locked femtosecond multimode fiber lasers

Abstract

The performance of fiber mode-locked lasers is limited due to the high nonlinearity induced by the spatial confinement of the single-mode fiber core. To massively increase the pulse energy of the femtosecond pulses, amplification is performed outside the oscillator. Recently, spatiotemporal mode-locking has been proposed as a new path to fiber lasers. However, the beam quality was highly multimode, and the calculated threshold pulse energy (>100 nJ) for nonlinear beam self-cleaning was challenging to realize. We present an approach to reach high energy per pulse directly in the mode-locked multimode fiber oscillator with a near single-mode output beam. Our approach relies on spatial beam self-cleaning via the nonlinear Kerr effect, and we demonstrate a multimode fiber oscillator with M 2 < 1.13 beam profile, up to 24 nJ energy, and sub-100 fs compressed duration. Nonlinear beam self-cleaning is verified both numerically and experimentally for the first time in a mode-locked multimode laser cavity. The reported approach is further power scalable with larger core sized fibers up to a certain level of modal dispersion and could benefit applications that require high-power ultrashort lasers with commercially available optical fibers.

Scalable optical learning operator

“…Graded-index multimode fibers (GRIN MMFs) in particular have become the subject of considerable interest for telecommunications, imaging and nonlinear optics studies due to their unique properties such as relatively low modal dispersion and periodic self-imaging. With spatiotemporal pulse propagation in GRIN MMFs, nonlinear beam cleaning 22 , spatiotemporal mode-locking [23][24][25] and various nonlinear frequency generation dynamics [26][27][28][29][30] have been realized in recent years. Moreover, learning and controlling nonlinear optical dynamics in GRIN MMFs was demonstrated by modifying the spatial properties of the intense pump pulse with a SLM or deformable mirror device 31,32 .…”

Spatiotemporal beam self-cleaning for high-resolution nonlinear fluorescence imaging with multimode fiber

“…Besides their relevance as a test-bed for fundamental research, MMFs have recently attracted a strong attention for their technological applications. For instance, MMFs may provide a solution to the data capacity bottleneck of optical communication links via spatial-division-multiplexing 1 , 2 , and scale-up the output energy of fiber lasers sources 3 – 6 . Linear and nonlinear imaging in microscopy and endoscopy configurations 7 , 8 also provide an interesting application of MMFs.…”

Reusability report: Predicting spatiotemporal nonlinear dynamics in multimode fibre optics with a recurrent neural network

“…In recent years, various interesting nonlinear dynamics such as spatiotemporal instability 3,4 , dispersive wave generation 5 , graded-index solitons 6,7 , self-beam cleaning 8 , nonlinear pulse compression 9 , and supercontinuum generation 10,11 have been reported. In addition to the aforementioned single-pass dynamics, spatiotemporal mode-locked lasers [12][13][14] have been realized, thanks to the low-modal-dispersion pulse propagation in graded-index multimode fibres. Using a spatial light modulator, learning and controlling nonlinear optical dynamics in graded-index multimode fibres was demonstrated by modifying the spatial properties of the intense pump pulse 15,16 .…”