A synchronous error equation for semiconductor lasers injected with external light is presented.Two chaotic systems with distributed feedback semiconductor lasers injected with external light at 1.31μm can be synchronized with little synchronous error.The chaotic synchronous system has been successfully stimulated in a long propagation distance optical fiber.The synchronous error increases with the fiber length.The synchronization is limited by the self-phase modulation in the fiber.The influences of intensity and phase noises on the synchronous error are studied in different propagation distances.Both analog and digital secure communications with the system are studied by numerical simulations in the long propagating distances.It is found that the information is hidden in the chaotic signal very well both in time-domain and frequency-domain and the system shows the good ability of robust security and anti-uncoverage.