We propose and demonstrate all-optical clock recovery (CR) from nonretu-to-zero differential phase-shift-keying (NRZ-DPSK) signals at different bit rates theoretically and experimentally.By pre-processing with a single optical filter,clock component can be enhanced significantly and thus clock signal can be extracted from the preprocessed signals,by cascading a CR unit with a semiconductor optical amplifier based fibre ring laser.Compared with the previous preprocessing schemes,the single filter is simple and suitable for different bit rates.The clock signals can be achieved with extinction ratio over 10 dB and rms timing fitter of 0.86 and 0.9 at 10 and 20 Gb/s,respectively.The output performances related to the bandwidth and the detuning of the filter are analysed.By simply using a filter with larger bandwidth,much higher operation can be achieved easily.