An erbium-doped fibre nonlinear coupler with coupling ratios controlled by pump power

We fabricate a 3 dB nonlinear coupler for a signal at 1550 nm by fusing together two single-mode Er3+-doped fibres. Pump light at 980 nm passes through one of the two fibres, changing the coupling ratios of the coupler. Our experiment shows that when the pump power increases from 0 to 20 mW, the bar coupling ratio changes by 40%. Using the coupled mode equations and resonant nonlinear polarization theory, we obtain the relationship between the coupling ratio and the pump power. The theoretical curve agrees well with the experimental data.