Abstract
Power scaling of fiber laser systems requires the development of innovative
active fibers, capable of providing high pump absorption, ultralarge effective
area, high-order mode suppression, and resilience to thermal effects. Thermally
induced refractive index change has been recently appointed as one major limitation
to the achievable power, causing degradation of the modal properties and preventing
to obtain stable diffraction-limited output beam. In this paper, the effects
of thermally induced refractive index change on the guiding properties of
a double-cladding distributed modal filtering rod-type photonic crystal fiber,
which exploits resonant coupling with high-index elements to suppress high-order
modes, are thoroughly investigated. A computationally efficient model has
been developed to calculate the refractive index change due to the thermo-optical
effect, and it has been integrated into a full-vector modal solver based on
the finite-element method to obtain the guided modes, considering different
heating conditions. Results have shown that the single-mode regime of the
distributed modal filtering fiber is less sensitive to thermal effects with
respect to index-guiding fibers with the same effective area. In fact, as
the pump power is increased, their single-mode regime is preserved, being
only blue-shifted in wavelength.
© 2012 IEEE
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