Abstract

We present a simple semianalytical model of thermally induced mode coupling in multimode rare-earth doped fiber amplifiers. The model predicts that power can be transferred from the fundamental mode to a higher-order mode when the operating power exceeds a certain threshold, and thus provides an explanation of recently reported mode instability in such fiber amplifiers under high average-power operation. We apply our model to a simple step-index fiber design, and investigate how the power threshold depends on various design parameters of the fiber.

© 2012 Optical Society of America

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References

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  1. T. Eidam, C. Wirth, C. Jauregui, F. Stutzki, F. Jansen, H. Otto, O. Schmidt, T. Schreiber, J. Limpert, and A. Tünnermann, Opt. Express 19, 13218 (2011).
  2. C. Jauregui, T. Eidam, J. Limpert, and A. Tünnermann, Opt. Express 19, 3258 (2011).
    [CrossRef]
  3. K. R. Hansen, T. T. Alkeskjold, J. Broeng, and J. Lægsgaard, Opt. Express 19, 23965 (2011).
    [CrossRef]
  4. A. V. Smith and J. J. Smith, Opt. Express 19, 10180 (2011).
  5. K. D. Cole and P. E. Crittenden, J. Heat Transfer 131, 091301 (2009).
  6. R. G. Smith, Appl. Opt. 11, 2489 (1972).
    [CrossRef]

2011 (4)

2009 (1)

K. D. Cole and P. E. Crittenden, J. Heat Transfer 131, 091301 (2009).

1972 (1)

Alkeskjold, T. T.

Broeng, J.

Cole, K. D.

K. D. Cole and P. E. Crittenden, J. Heat Transfer 131, 091301 (2009).

Crittenden, P. E.

K. D. Cole and P. E. Crittenden, J. Heat Transfer 131, 091301 (2009).

Eidam, T.

Hansen, K. R.

Jansen, F.

Jauregui, C.

Lægsgaard, J.

Limpert, J.

Otto, H.

Schmidt, O.

Schreiber, T.

Smith, A. V.

Smith, J. J.

Smith, R. G.

Stutzki, F.

Tünnermann, A.

Wirth, C.

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Figures (3)

Fig. 1.
Fig. 1.

Coupling constant χ for LP01LP11 coupling as a function of Δf for varying Rc and V=3.

Fig. 2.
Fig. 2.

Coupling constant χ for LP01LP11 coupling as a function of Δf for varying V and Rc=20μm.

Fig. 3.
Fig. 3.

Coupling constant χ for LP01LP11 coupling as a function of Δf for varying RYb and Rc=20μm, V=3.

Tables (1)

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Table 1. Power Threshold

Equations (14)

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E=a1(z)ψ1ei(β1zω1t)+a2(z)ψ2ei(β2zω2t)+c.c.,
ε(r,t)=εf(r)ig(r)εfk+Δε(r,t),
ρCΔTtκ2ΔT(r,t)=Q(r,t),
Q(r,t)=(λsλp1)g(r)I(r,t),
2ΔT˜(r,ω)q(ω)ΔT˜(r,ω)=Q˜(r,ω)κ,
ΔT˜(r,ω)=1κG[r,r,q(ω)]Q˜(r,ω)d2r.
P1z=χ1(Δω)g(z)P2P1+Γ1g(z)P1,
P2z=χ2(Δω)g(z)P2P1+Γ2g(z)P2,
χ1,2(Δω)=ηk2κβ1,2Im[A(Δω)](1λsλp).
A=ψ1(r)ψ2(r)×ΩdG(r,r,Δω)ψ1(r)ψ2(r)d2rd2r,
Γi=kβiΩdεf(r)ψi(r)2d2r,
P2(L)P(L)P2(0)P1(0)exp(χ(Δω)Γ1ΔPΔΓgavL),
xoeΔΓgavLP1(0)ωexp(ΔPΓ1χ(ω1ω))dω.
xoω12πΓ1|χ(ω0)|P(L)(Γ2Γ132)P1(0)Γ2Γ1exp(χ0Γ1P(L)),

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