Experimental and theoretical study of the passively mode-locked ytterbium-doped double-clad fiber laser

Abstract

We consider an Yb-doped double-clad fiber laser in a unidirectional ring cavity containing a polarizer placed between two half-wave plates. Depending on the orientation of the phase plates, the laser operates in continuous, Qswitch, mode-lock or unstable self-pulsing regime. An experimental study of the stability of the mode locking regime is realized versus the orientation of the half-wave plates. A model for the stability of self-mode-locking and cw operation is developed starting from two coupled nonlinear Schrödinger equations in a gain medium. The model is reduced to a master equation in which the coefficients are explicitly dependent on the orientation angles of the phase plates. Analytical solutions are given together with their stability versus the angles.

Stability calculations for the ytterbium-doped fibre laser passively mode-locked through nonlinear polarization rotation

“…In the framework of the eigenaxis of the fiber moving at the group velocity, the propagation equations for the two polarization components of the amplitude of the electric field are [12,24,25] i ∂u ∂z − Ku − β 2 2…”

“…Following our analysis of reference [12], we assume that the effects of the GVD β 2 , the nonlinear effect γ, and the gain filtering ρ = g/ω 2 g are small over one round-trip of the cavity. A perturbative approach can be used.…”

“…We introduce a small parameter ε and replace the quantities β 2 , γ and ρ by εβ 2 , εγ and ερ. Let (u(0), v(0)) the electric field components at the entrance of the ytterbium-doped fiber, and (u(L), v(L)) the components at the exit of the fiber of length L. A first order perturbative calculation leads to [12,22] …”

“…In this paper we are interested in mode-locking through nonlinear polarization rotation. This technique has been successfully used to obtain short pulse generation in different rare-earth doped fiber lasers [3]- [5], [12]- [15] and is self-starting. The laser configuration is a unidirectional fiber ring cavity containing a polarizer placed between two polarization controllers.…”

“…On the other hand, many numerical simulations have been done to complete analytic approaches [18]- [20]. We have recently investigated experimentally and theoretically the mode-locking properties of an Yb-doped double clad fiber laser passively mode-locked through nonlinear polarization rotation [12,21]. The optical configuration was a unidirectional ring cavity containing an optical isolator placed between two halfwave plates.…”