Abstract
The transmission matrix of an ytterbium doped multimode fiber with gain was measured. It was shown to vary owing to the pump power level. Amplified beam focusing, beam steering and shaping were demonstrated using the measured matrix for input wavefront shaping, with an efficiency similar to the case of a passive fiber. The impact of weak gain saturation was lastly investigated.
Highlights
Multimode fibers (MMF) share some analogies with the disordered media, because of mode coupling which scatters light fields among the different guided modes [1]
We show that laser beam focusing and shaping through an amplifying multimode fiber can be efficiently achieved by measuring its transmission matrix (TM) under pumping
We have carried out measurement of the transmission matrix of a step-index Yb-doped multimode fiber in amplification regime
Summary
Multimode fibers (MMF) share some analogies with the disordered media, because of mode coupling which scatters light fields among the different guided modes [1]. Pioneering works showed that the spatial pattern of a laser beam transmitted by a scattering media can be controlled by shaping the wavefront of the input signal [7]. They rely for instance on digital optical phase conjugation [9], or on transmission matrix (TM) measurement [10] or on deep learning [11] or on correlations [12]. Laser beam shaping by an iterative adaptive control of the input wavefront feeding an amplifying multimode fiber was demonstrated to be a potential option [25]. The shaping capabilities offered by the TM were assessed here in the linear gain regime and in the early stage of the gain saturation regime
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