Optical waveguides – With optical coupler – Plural
Patent
1997-10-31
1999-12-21
Ngo, Hung N.
Optical waveguides
With optical coupler
Plural
G02B 626
Patent
active
060059966
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a branching unit for an optical fibre transmission system which permits powering by electrical power provided from either direction on a trunk but which permits selective isolation of cable sections which are coupled via the branching units.
In the operation of optical fibre communication systems over long distances where there are a number of branches problems can arise due to a trunk cable fault or breakage which results in failure of transmission between terminals at opposite sides of the fault or break. Under such fault conditions it is still possible to communicate between terminals on the same side of the break and electrical power can be supplied to branching units from a trunk end on the appropriate side of the break. A difficulty which arises is in repairing the fault or break which normally requires the system power to be switched off to isolate the brake which requires the whole system to be out of action. The present invention is concerned with the provision of means for isolating a section of cable from the power supply to permit repair whilst still permitting the remainder of the system to be operational.
According to the invention there is provided a branching unit for an optical fibre transmission system having a pair of inputs/outputs for receiving an end of a different section of trunk cable of the type having an electrical conductor and one or more pairs of optical fibres, wherein a switching circuit is effective to selectively route power between the electrical conductors of each trunk section or via an earth return in response to a supervisory signal provided on the trunk.
The switching circuit may have a latching function effective once switched to maintain the routing via the earth return until power is removed. The switching circuit may comprise a relay. The relay may be a latching relay which is effective once switched to maintain the routing via the earth return until power is removed. The switching circuit may also comprise a transistor switch coupled to the relay coil which transistor switch is driven by a control circuit in response to the supervisory signal.
The branching unit may include a diode bridge circuit, comprising two parallel arms each having a pair of diodes connected in series anode to cathode the ends of which arms are cross coupled to anode to anode and cathode to cathode, wherein a connection for individual electrical conductors, of different trunk cable sections is provided at the junction between diodes of each pair of arms, and the transistor and relay coil switching arrangement is coupled between the ends of the arms. A refinement of the branching unit is wherein there is provided a further parallel arm having a pair of diodes connected in series anode to cathode is connected in the same sense between the cross coupled ends of the two parallel arms and the junction between the diodes of the further parallel arm is coupled to earth via normally closed relay contacts. A Zener diode may be connected between the cross coupled ends of the parallel arms to regulate the voltage for the transistor and relay coil circuit.
The earth return may be a sea earth.
The switching circuit may be responsive to an optical supervisory signal provided over one of the optical fibres. Alternatively the switching circuit may be responsive to an electrical supervisory signal provided over the electrical conductor.
The invention also includes an optical transmission system comprising a trunk cable provided with two or more spaced branching units as previously defined, wherein the switching circuit in each branching unit is responsive to a different supervisory signal thereby to permit selective coupling of power between adjacent branching units or to earth in response to a supervisory signal provided from at least one cable end to permit isolation of power feed to a trunk section.
In order that the invention and its various other preferred features may be understood more easily, some embodiments thereof will now be described, by way of example only, with refe
REFERENCES:
patent: 4879762 (1989-11-01), Hanyuda et al.
patent: 5214312 (1993-05-01), Inoue
patent: 5717796 (1998-02-01), Clendening
Alcatel
Ngo Hung N.
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