| 摘要 |
To transmit digital information in a secure manner in an optical fibre, the same information is modulated (M1, M2, M3) via different delays ( tau 1, tau 2, tau 3) on to lasers (L1, L2, L3) running at different wavelengths. The delays are so chosen with respect to the group velocity differences in the optical fibre that the pulses are superimposed at the output. However, due to the velocity differences and the relative weakness of the individual components the pulses are scrambled between the input to the fibre and the output therefrom. Then a high degree of security is attained. Tapping is readily detectable because the individual lasers run at powers lower than the detector's sensitivity so if power is tapped out at an intermediate point the loss of power at the output is readily detectable. <IMAGE> |
