Using an optical network to transmit radiofrequency signals (radio over fibre) naturally leads to implementation functions, such as frequency mixing, directly in the optical layer. Proposed is an all-optical sampling method based on a SOA-MZI to frequency upconvert an electrical subcarrier at 1 GHz up to 38 GHz. The optical pulsed source used to sample the electrical subcarrier generates 21 ps-width pulses at a repetition rate of 7.8 GHz. Although the SOA-MZI bandwidth is limited to 7 GHz, frequency upconversions up to five times the 7.8 GHz sampling rate have been evaluated through the conversion gain. Its value lies between 14.4 to -20.3 dB depending on the frequency to be reached.