Optical waveguides – With optical coupler – Plural
Patent
1995-01-26
1997-04-22
Ullah, Akm E.
Optical waveguides
With optical coupler
Plural
359126, G02B 628
Patent
active
056235658
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical communication system particularly suitable for use in gathering data from a number of sensors. Sensors of the type the present invention is concerned with are used, for example, in industry for process control, pollution monitoring and chemical/biological analyses. The system might also be used with domestic sensors, such as smoke detectors or burglar alarms.
The use of optical rather than non-optical wired networks for such sensors potentially offers a number of advantages, including immunity from sparking in a flammable environment, and immunity to electro-magnetic interference (EMI). However because of their characteristics of more or less continual data output at low data rates, sensors are not generally suitable for connecting directly to conventional optical telecommunications networks. It would be desirable to provide a network particularly suitable for sensor data but which also carries diverse other types of traffic.
2. Related Art
It has previously been proposed to provide a system using an optical fibre network having a bus-type topology to communicate data from a plurality of sensors to a head-end station. Each branch of the network is connected to the bus by a wavelength selective tap, so that each sensor communicates data on a different characteristic wavelength. Such a system is disclosed in "Wavelength Division Multiplexing in Optical Fibre Sensor Systems and Networks", J. M. Senior et al, OPTICS AND LASER TECHNOLOGY, Vol. 22, No. 1, 1st Apr. 1990. This network is primarily designed for one-way traffic from sensors to the head-end station. There are however situations where it would be desirable to provide two-way data communication on the network. In many systems for use in industrial processes, there will be associated with each sensor an actuator, such as a valve, switch or other control device, which is responsive to control signals received over the network so as to provide a control loop from the sensor via the head-end to the actuator. These control signals may be processed by a local computer at the actuator. In the context of the present specification, the term "actuator" also encompasses any other device responsive to optical signals received over the network, including the receive side of a telephone, where the two-way system is used to integrate, e.g. voice telephony with the carrying of sensor data.
EP-A-0206901 discloses a network in which a demultiplexer splits a broadband optical signal into different wavelength components and outputs each component on a different optical fibre going to a respective sensing or control device.
SUMMARY OF THE INVENTION
According to the present invention an optical communications system comprises: local to and associated with a respective one of the plurality of sensors, the sensors being arranged to communicate data via the network at a plurality of different wavelengths characteristic of different respective sensors and actuators; by the sensors and returned via the network to the head-end station; optical signals and means for outputting the resulting modulated signals onto the network for transmission to the actuators; and narrowband components and arranged to output outgoing data to the optical modulators.
Preferably, the optical source includes a broadband source and outputs a broadband signal onto the network, and the head-end station includes wavelength division means for splitting a signal from a broadband source into a plurality of narrowband components for modulation by the optical modulator means.
The optical modulators may take any convenient form such as magneto-optic or acousto-optic devices, but preferably are electro-optic modulators.
Preferably the network has a star topology and includes a first path for carrying optical signals between the head-end station and a first node, a plurality of branches extending from the node to respective sensors and a second path carrying optical signals from the head-end station to a second no
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Blair Loudon T.
Cassidy Stephen A.
Millar Colin A.
Urquhart Paul
British Telecommunications public limited company
Ullah Akm E.
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