Fiber core mode leakage induced by refractive index variation in high-power fiber laser

Abstract

This paper presents an investigation of specific optical fiber core mode leakage behavior that occurs in high-power double-clad fiber lasers as a result of thermally-induced refractive index variations. A model of the power transfer between the core modes and the cladding modes during thermally-induced refractive index variations is established based on the mode coupling theory. The results of numerical simulations based on actual laser parameters are presented. Experimental measurements were also carried out, the results showed good agreement with the corresponding simulation results.

Theoretical Study of the Thermal Distribution in Yb-Doped Double-Clad Fiber Laser by Considering Different Heat Sources

“…By considering a value for the reflectivity of the output coupler at the pump wavelength (R 3 ), this symmetry will disappear [44]. The variation of the normalized ground and upper state of dopant densities N 1 /N , and N 2 /N with σ a p = 6.64 × 10 −25 m 2 Pump emission cross-section [74] σ e p = 4 × 10 −26 m 2 Input pump power, FWP, BDP P p = 500, 250 mW Input pump power, BWP, BDP P p = 500, 250 mW Pump background loss [33] α P = 3 dB/km power filling factor 0.0025 If there are no reflectors at the ends of the fiber, similar to the fiber amplifiers, the maximum value of the normalized density of each level must be unity [32]. So the reflectivity of the mirrors at the signal and pump wavelengths determine the shape of the graph.…”

“…For the signal (laser) wavelength R i = R co and for the pump power R i = R cl1 . For the signal power with the Gaussian pulse envelope, the profile variation is proportional to |E x | 2 and can approximate as ψ i (r, ω i ) = exp(−r 2 /ω 2 i )/πω 2 i by integration, and the overlap factor will be [29,33,34]:…”

“…The thermal distribution in the DCFL can be described by the thermal conduction equation in the cylindrical coordinate [33,51].…”

Contribution of different factors in heat production in Yb3+-doped fiber laser: a review

“…The heat distribution equation in the core and clads region of the double-clad FL are described by the thermal conduction equation in the cylindrical coordinates 58 , 59 1r∂∂r(r∂Tcore(r,z)∂r)=−Q(z)K1,(0≤r≤∈a),1r∂∂r(r∂Tclads(r,z)∂r)=0,(a≤r≤c),where Q(r,z) is the heat density per unit of volume (W/m3). In this paper, it is assumed that the generated heat from the QD, PD, and background loss vary as follows: 23 QT(z)=QQD(z)+QPDP(z)<...…”

“…The heat distribution equation in the core and clads region of the double-clad FL are described by the thermal conduction equation in the cylindrical coordinates 58,59 E Q -T A R G E T ; t e m p : i n t r a l i n k -; e 0 0 9 ; 1 1 6 ; 3 2 6 1 r…”