In order to reduce the bitrate of high-speed optical signal, a novel all-optical serial-to-parallel converter is proposed, which is based on the cascaded Semiconductor Laser Amplifier in a Loop Mirror(SLALOM), to be used to convert high speed serial optical signal to multi-output low-speed parallel optical signal. The converter adopts the structure of the cascaded SLALOMs, the output of the previous SLALOM connects to the input of the next one with the optical propagation delay time between them equaling to the bit period of the input optical pulse signal. Morever, the particular timing of optical control and signal pulses is designed to guarantee appropriate outputs. The feasibility is verified by converting 80 Gb/s serial optical signal to ten 8 Gb/s parallel outputs by using the designed 1×10 all-optical serial-to-parallel converter. The device parameters are optimized including the optical power of control / signal pulse and the time offset of them. The difference of the receive sensitivity values of all output ports is less than 10 dB. Comparing with the traditional parrallel structure, the proposed converter has the advantage of lower optical power loss, and it′s easier to extend parallel port numbers, which is available for the applications including high-speed demultiplexing, optical information processing and optical switching system.