Abstract
The mode discrimination criterion for single mode operation, usually considered in fiber amplifiers designed for high power operation, has been investigated and tested on three different fiber designs, a large pitch fiber and two symmetry free photonic crystal fibers. To have a significant collection of results, parameters like pump configuration, pump power, and amplifier length have been varied. The analysis has been carried out through the use of a custom numerical tool provided with efficient thermal and spatial amplification models. From the obtained results, it is possible to observe that the mode discrimination criterion is helpful but not strictly necessary to pledge an effective single mode operation through differential amplification. This fact extends the possibility for the study, as well as for the optimization, of different fiber designs. The use of advanced numerical analysis, which takes into consideration amplification along with thermally influenced modes guidance, becomes extremely useful for an effective fiber design.
Highlights
Without any doubt, fiber laser research and technology have experienced great improvements in the last decade
In this paper the range of validity of mode discrimination criterion for effective single mode operation induced by differential amplification has been investigated
The behavior of the doped fibers under investigation has been simulated through the use of a custom software provided with a spatial amplification model which takes in consideration the guidance changes induced by thermal effects
Summary
Fiber laser research and technology have experienced great improvements in the last decade. Rare-earth doped fiber lasers offer clear advantages with respect to their counterparts based on active materials like semiconductors, crystals or gases These advantages can be justified by several reasons, such as: the efficient heat dissipation of the fiber medium; the superior emission quality, thanks to the possibility to finely control the modal content of the amplified signal; and the capability to obtain a remarkable output power in the continuous wave regime or high energy short pulses in the pulsed one [1, 2]. The second is the use of Double Cladding (DC) micro-structured fibers, which enhances pump absorption and permits to deliver higher power while preserving Single Mode (SM) operation and avoiding detrimental non-linear effects Focusing on the latter key point, the introduction of Photonic Crystal Fibers (PCFs) and, more generally, of micro-structured fibers, has opened a new chapter in the field of photonics and fiber lasers technology [4]. On one hand, this abundance of degrees of freedom has originated several fiber designs, such as: Large Pitch Fibers (LPFs), Distributed Mode Filtering fibers (DMFs), Leakage Channel Fibers (LCFs), and Chirally Coupled Core fibers (CCCs) [7,8,9,10], on the other hnad, fiber design has become much more complicated, requiring advanced numerical analysis tools [11, 12]
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