Abstract An optical frequency-hopping scheme using phase modulator-embedded optical loop mirror (PME-OLM) is proposed, analyzed and demonstrated to achieve long distance secure communications. In the proposed system, the data from every user are separated into small data segments in time domain and carried by different wavelength carriers instead of being fixed on one carrier all the time. The segments from different users occupy different wavelengths at different time according to the hopping pattern, which can be regarded as encryption key. Therefore, any particular user data are interference to data from other users. The feasibility and performance of the frequency-hopping scheme has been investigated through simulation by VPI transmission Maker. A 4-frequency-hopping system demonstration was designed to support a 20 Gb/s non-return-to-zero (NRZ) data error-free transmission through 8-km dispersion compensated fiber (DCF) and 32-km single mode fiber (SMF). And an analysis based on a theoretical model was established to evaluate the security performance of the frequency-hopping communication system.