Abstract
We experimentally demonstrate spatial beam self-cleaning in an Yb-doped graded-index multimode fiber taper, both in passive and active configurations. The input laser beam at 1064 nm was injected for propagation from the small to the large core side of the taper, with laser diode pumping in a counterdirectional configuration. The Kerr effect permits to obtain high-beam quality amplification with no accompanying frequency conversions. As a result, our nonlinear taper amplifier may provide an important building block for multimode fiber lasers and amplifiers.
Highlights
Multimode optical fibers (MMFs) are currently the subject of renewed research interest, for their potential application in different optical technologies
Fiber lasers provide the most promising field of application of MMFs: the nonlinear transmission of a short span of graded-index (GRIN) MMF between singlemode fibers leads to an ultrafast saturable absorber mechanism with high damage threshold [5], [6]
We experimentally studied the dependence of the output beam quality and the occurrence of beam self-cleaning in the T-YD MMF as a function of the peak power of the injected signal pulses
Summary
Multimode optical fibers (MMFs) are currently the subject of renewed research interest, for their potential application in different optical technologies. In order to use the T-YD MMF in a high power fiber laser, any frequency conversion should be avoided, so that the signal must necessarily propagate from the smaller to the larger diameter, similar to conventional T-YDF amplifiers [21], [24]–[26] In this configuration, which decreases the fiber nonlinearity as the pulse get amplified, it remains an open issue whether any beneficial Kerr-induced beam self-cleaning may still be achieved. We observed self-cleaning with its associated beam quality improvement in the active configuration, that is in the presence of gain (induced by the pump laser diode), but even in a lossy configuration (i.e., with no pump laser diode)
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