| 摘要 |
PCT No. PCT/GB92/00524 Sec. 371 Date Sep. 20, 1993 Sec. 102(e) Date Sep. 20, 1993 PCT Filed Mar. 23, 1992 PCT Pub. No. WO92/17008 PCT Pub. Date Oct. 1, 1992.This invention relates to photonic amplifiers, e.g., fibre amplifiers, which are specially suitable for use in long distance telecommunications optical linkages. The amplifier includes an optical transmitter, which is adapted to provide to the output of the amplifier a default signal which is digitally modulated and the digital modulation includes the identity of the amplifier. The default condition is constituted when the traffic signals fall below a preset level, e.g., in the case of a cable break when the signal falls to zero. In a preferred embodiment, the traffic signals are modulated with a control tone which is used to control the AGC's of the telecommunications link. In this system, the default condition is constituted when the level of control tone falls below a predetermined level, and the default signals also contain control tone, so that subsequent amplifiers are held out of default state.
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