Excited-state absorption and ion pairs as sources of nonlinear losses in heavily doped Erbium silica fiber and Erbium fiber laser

Abstract

We report an experimental and theoretical investigation of the nonlinear transmission coefficient of a heavily doped (2300 ppm) Erbium silica fiber at continuous-wave pumping at the wavelength 1560 nm. It is shown that the fiber transmission is essentially deteriorated by the nonlinear losses, which are caused by the excited-state absorption (ESA) and Erbium ion pairs (IP) presented in the fiber. These phenomena inevitably result in worsening of the amplifying and lasing potential of the heavily doped Erbium fiber. We demonstrate the latter on the example of an Erbium fiber laser (wavelength, lambda= 1560 nm) under IR (wavelength, lambda= 978 nm) pumping, where the heavily doped Erbium fiber is used as an active medium. The developed theory, addressing both the nonlinear transmission coefficient of the fiber at the 1560-nm pumping and the generation characteristics of the Erbium fiber laser, takes into account the additional losses and non-radiative relaxation factors stemming from the ESA- and IP-effects and allows getting a good agreement between the modeling and experimental results.

Excited-state absorption in erbium-doped silica fiber with simultaneous excitation at 977 and 1531 nm

“…11,17,18 So, the results discussed below are almost free from the pairs' effect, so the nonlinearity occurring in the EDF transmission coefficient and UCE stem both solely from ESA. The first experiment was focused on the demonstration of the presence of ESA in the EDF, when it is pumped simultaneously at p = 977 nm ͑through 4 Experimentally, an EDF piece was pumped, using a wavelength division multiplexer ͑WDM͒ supporting up to 1 W of optical power, by the pump and signal beams from the same fiber side.…”

“…11,20 The main difference that stems from the use of the five-level scheme is a substantial ͑11%-12%͒ populating of level "3" ͑see Fig. 6͒ from where a pump-ESA starts.…”

“…One can point out their relatively low efficiency comparing to ytterbium ͑Yb 3+ ͒-doped fiber lasers and amplifiers, and the tendency to possess a relatively high-level noise or even self-pulsing. [6][7][8][9][10] One of the selfpulsing sources in EDFL, as it stems from a series of previous works, [11][12][13][14][15][16][17] is the presence of excited-state absorption ͑ESA͒ in Er 3+ . ESA is immanent to the Er 3+ system while an Er 3+ -doped silica fiber ͑EDF͒ is pumped through its groundstate absorption ͑GSA͒ bands, centered at ϳ977 and ϳ1531 nm.…”

“…ESA is immanent to the Er 3+ system while an Er 3+ -doped silica fiber ͑EDF͒ is pumped through its groundstate absorption ͑GSA͒ bands, centered at ϳ977 and ϳ1531 nm. 11,12 ESA appears immediately after populating the excited states 4 I 13/2 ͑"2"͒ and 4 I 13/2 ͑"3"͒ of Er 3+ through the GSA transitions "1 " → "2" ͑ϳ1480-1590 nm:…”

Experimental study of a symmetrically-pumped distributed feed-back Erbium-doped fiber laser with a tunable phase shift

“…The active fiber was pumped symmetrically from the opposite sides at the wavelength 980 nm with the light launched from a standard fibered semiconductor laser (JDSU) through a 50/50 fused fiber coupler. The symmetric pumping scheme provided the conditions of a quasi-homogeneous interaction of the pump wave with the DFB structure [25], that allowed us to avoid possible influence of inhomogeneous heating of the active fiber and, thereafter, to diminish inhomogeneities in the refractive index distribution (this heating stems from the Stokes loss, the excited-state absorption at both the pump and laser wavelengths, and the Auger upconversion in Erbium-doped fiber [26,27]). …”