A new all-optical broadband phase modulator of subcarrier in radio over fiber (RoF) system has been
proposed. This modulator is based on cross phase modulation (XPM) in fiber. In this approach the
stability of the subcarrier modulation is improved significantly as most of the disturbance introduced
by environment variance can be cancelled when the lightwaves interfere in PD. A proof-of-concept
experiment demonstrates the feasibility of the modulator.