Communications network with switching distributed among a centra

Details Communications network with switching distributed among a centra Communications network with switching distributed among a centra

1991-08-05

1993-08-31

Coles, Sr., Edward L.

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

359117, 359139, H04J 1402

Patent

active

052414094

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to communications networks, and in particular to networks in which the transmitters of two or more sub-networks of transmitters are connectable to receivers of two or more sub-networks of receivers by means of a central switching node.


BACKGROUND OF THE INVENTION

In a known implementation of such a network, the transmitters and receivers are linked to the input and output ports of the central switching node by means of dedicated electrical communications links, the node having sufficient switching power to be able to interconnect a desired number of ports.
Passive optical networks are emerging as a promising means of providing customers with broadband services, and are economically attractive for providing telephony and low data-rate services to customers requiring just a few lines. The telephony passive optical network (TPON) shares customer access costs by means of a passive splitting architecture to multiplex up to 128 customers, with current technologies, onto a single fibre at the exchange. With such a network in place, broadband services could easily be provided by the addition of more operating wavelengths. The first step towards a broadband passive optical network (EPON) would probably be to add just a few wavelengths, each allocated to a particular service such as broadcast TV, video library and ATN services, with each wavelength electronically multiplexed to provide sufficient numbers of channels. In the longer term, spectrally-controlled sources such as DFB lasers would allow extensive wavelength multiplexing, and the possibility of allocating wavelengths to individual customers or connections, to provide wavelength switching across the network.
It has therefore been proposed to link the sub-networks of transmitters and receivers to the central switching node by means of such passive optical networks, each transmitter of a sub-network transmitting information optically on an optical carrier of a fixed, distinct wavelength, and the various transmitted signals being passively multiplexed onto a single optical fibre for transmission to the central switching node. A demultiplexer at the central switching node would separate the signals according to wavelength, and convert each into an electrical signal. In this way, each transmitter is permanently linked to a distinct, input port of the central switching node. Similarly, the outgoing connections from the output ports of the central switching node to the optical receivers can be in the form of a passive optical network. The outgoing signal from each output port of the central switching node is converted to an optical signal of a wavelength corresponding to that which the receiver associated with that output port is configured to receive. These optical signals for the receivers of the sub-network are multiplexed onto a single outgoing optical fibre, which multiplex is passively split to each receiver. Each receiver selects the wavelength corresponding to it by the use, for example, of an optical filter or a coherent optical receiver. Such a network, employing passive optical sub-networks, requires a central node of the same switching power as that using dedicated electrical connections for the same interconnect power.
Another known interconnection arrangement uses wavelength switching or routing which is a simple but powerful technique for providing both one-to-one and broadcast connections between customers. One-to-one connections simply require each customer to have a tunable light source connected by a wavelength division multiplexer. Light can be directed from any transmitter to any receiver by tuning to an appropriate wavelength. A fast connection time of 2 nsec, has been demonstrated using a cleaved coupled cavity laser. Broadcast or distributed connections are naturally provided by a star coupler arrangement shown, for example, in patent specification EP-A-2,043,240. A star coupler splits the optical power from each input port to every output port so that, by using sources of fixed, distinct wav

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patent: 5091905 (1992-02-01), Amada
Patent abstract of Japan, vol. 7, No. 284 (E-217)(1429), Dec. 17, 1983 and JP,A,58161486 (Nippon Denki K.K.) Sep. 1983.
Patent abstract of Japan, vol. 4, No. 44 (E-5)(526), p164 E 5 and JP, A5516584 (Nippon Denshin Denwa Kosha) Feb. 5, 1980.

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