Laser amplification mechanism in an Nd3+-doped polymer optical fibre

The Judd-Ofelt theory was applied to optical-absorption transitions in an Nd3+-doped polymer optical fibre to obtain the intensity parameters (Omega (2) = 0.83 x 10(-20) cm(2), Omega (4) = 1.64 x 10(-20) cm(2), Omega (6) = 4.04 x 10(-20) cm(2)), the radiative lifetime (371 mus) and the quantum efficiency (0.73) of the (4)G(5/2)level, from which we found that the transition probability from (4)G(5/2) to I-4(9/2) (A(ij) = 1995.7s(-1)) is higher than others. Thus, in the polymer system, the traditional four-level laser system for Nd3+ was substituted by a three-level system. Furthermore, we have calculated the emission cross section (sigma (e)(ij) = 2.45 x 10(-21) cm(2)), and solved the differential equations of the single-pass gain. In comparison with inorganic optical fibres, an increased saturated intensity is observed.