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Local area network

  • US 4,641,375 A
  • Filed: 03/07/1985
  • Issued: 02/03/1987
  • Est. Priority Date: 03/08/1984
  • Status: Expired due to Fees
First Claim
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1. An optical fibre transmission system, which includes optical transceiver stations each having its transmitter coupled via a length of optical fibre to a star coupler and its receiver coupled via another length of optical fibre to the star coupler, so that with n stations there are 2n lengths of optical fibre coupled to the star coupler, wherein each said station includes means to generate a pilot signal specific to that station, which pilot signal is transmitted at a level which is low compared with the level used for data transmission, and wherein means in each said station receives its said pilot signal after it has passed from the station'"'"'s transmitter via one length of optical fibre to the star coupler and from that star coupler via another length of optical fibre to the station'"'"'s receiver, the level of the pilot signal being monitored on reception so that the attenuation to which signals conveyed via the system is monitored, wherein the pilot signal is a tone which is transmitted at a level which is low compared with that of data signals, e.g. of an amplitude 0.5% of a data signal, and wherein each said station connected to the star coupler is allocated its own tone frequency, further comprising:

  • a reference signal generator coupled by optical fibres to the star coupler which includes means, responsive to a calibration request from a said station sending a first reference signal, for emitting a signal at twice the frequency of the signal which it received, andmeans at the said station to measure the signal level, and to adjust the station, on the basis of that level.

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