Double Loop Optical Buffer With Vertical 8-Figure Structure Based on a Collinear 3 $\times$ 3 Coupler

A double loop optical buffer (DLOB) with vertical eight-figure structure based on a collinear 3 3 coupler is proposed. Unlike the DLOB with a horizontal eight-figure structure proposed by Aiming Liu in 2004, our structure can overcome leak power effectively and raise the extinction ratio by realizing the different nonlinear phase shifts of and achieving consistency of the gains of counterpropagating probe beams. Moreover, the buffer depth can reach up to 1, thus improving the use efficiency of the fiber ring, because two interferential probe beams transmit along different optical paths. The experimental results buffered five and ten cycles that are consistent with theoretical analysis.