Static modal energy transfer in high power, polarization maintaining fiber laser systems

Impact of mode instability on polarization extinction ratio in backward pumped fiber amplifiers

“…Therefore, for forward pumped PM fiber amplifier, due to the fiber coiling, the HOMs would be leaked into the cladding, and a small part of the cladding signal light can reinject into the active core during propagating along the fiber. The polarization state of the reinjected signal light is random due to the scramble of the cladding, and reinjected signal light was amplified by the Yb-ions and in the process of amplifying in PM fiber amplifier, and the polarization state is maintained [26], which results to the degradation of the PER. For backward pump schemes, the HOMs is mainly generated at the output end, which results to that the leaking and reinjecting process happens in passive fiber.…”

Polarization instability in high power fiber amplifiers

“…This model accounts for the simultaneous propagation of the FM and of a HOM (the LP11 in this case) in both main polarization axes of the fiber. More details of the model can be found elsewhere 4 . Using this model, we have simulated a 1m long, 80µm core rodtype fiber with a cladding diameter of 280 µm.…”

“…Additionally, the drift accelerates the closer the power gets to the TMI threshold. The main reason for this behavior is the quasi-static energy transfer induced in PM fibers 4 . As mentioned above, this is a phenomenon that results in the thermally-induced grating created by the MIP of one polarization inducing energy transfer between the FM and the HOM in the other polarization.…”

“…the one resulting after the overlap of the MIP from each polarization axis) if the seed is coupled with a polarization that is oriented at 45° with respect to the main polarization axes 3 . On the other hand, it has also been shown that the refractive index grating (RIG) generated by the MIP of the light polarized parallel to one of the axes of the PM fiber can induce a quasi-static energy transfer in the orthogonally polarized light components 4 .…”