A double loop optical buffer (DLOB) cascaded scheme based on collinear 3×3 coupler is proposed and the buffer principle and method of reading-out or writing-in operation of single-stage and cascade structure is analysed. Through analyzing the noise characteristics of the semiconductor optical amplifier (SOA), a conclusion is achieved that the output performance is determined by the control light power and the current injected into the SOA during writing and reading. And the possibility of multiple circulations buffering in one-stage buffer unit and buffering in the cascaded units is proposed. A cascaded experimental system consisting of two buffer units was set up. The experiment demonstrated that, when the optical packets traversing in two units of the cascaded buffer exceeded 9 circles respectively, the peak-peak value of output power did not decrease compared to the input optical signals, and signal-to-noise ratio (SNR) declined by less than 4 dB. The result of theoretical analysis and experiment both prove that cascaded optical buffer can provide a buffer from nanosecond to microsecond, which would meet the demand of optical packets switch (OPS) development in the future.