Optical waveguides – With optical coupler – Plural
Patent
1992-07-09
1994-06-21
Bovernick, Rodney B.
Optical waveguides
With optical coupler
Plural
372 6, 385141, G02B 628
Patent
active
053234740
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an optical coupler for incorporation in an optical fibre communications network.
Throughout this specification, the term "optical" is intended to refer to that part of the electromagnetic spectrum which is generally known as the visible region, together with those parts of the infra red and ultra violet regions which are capable of being transmitted by dielectric waveguides such as optical fibres.
An optical fibre communications network is used to distribute information (optical signals) from one or more transmitting stations to one or more receiving stations. For telecommunications purposes, passive optical networks, such as TPON (telephone by passive optical networks), are advantageous in that they permit telecommunications over a network using a single transmitter (a laser located at an exchange connected to the network). The main advantage of TPON is that no electric components are required in the field. A disadvantage of TPON is that it requires the use of optical splitters to pass optical signals from a transmitter (exchange) to a plurality of receiving stations (customers' telephones). TPON is, therefore, limited by the loss at the splitters (typically a TPON system will service only 32 customers per laser). One way to increase this ratio would be to incorporate optical amplifiers into the system. This could be achieved by amplifying the optical signals by means of optical amplifiers at one or more positions along the network, for example by using a power amplifier at the transmitter, repeater amplifiers along the network paths, or pre-amplifiers at the receiving stations. In this connection, it should be noted that safety considerations limit the maximum power which can be delivered by the head end (exchange) laser.
A known type of optical amplifier employs an electric regenerator for boosting power to compensate for splitter losses. The disadvantages of electric regenerators are that they are expensive, directional and are not data transparent. Another known type of optical amplifier (the semiconductor laser amplifier) overcomes some of the disadvantages of using electric regenerators, in that a semiconductor laser amplifier is bi-directional and data transparent. Unfortunately, however, a semiconductor laser amplifier requires an electrical power source, and this detracts from the main advantage of TPON, namely having only passive components in the field.
The present invention provides an optical coupler having an input and a plurality of outputs, the optical component comprising a splitter portion and an amplifier portion upstream of the splitter portion, wherein the amplifier portion includes an optical amplifier for amplifying optical signals received by the input, the optical amplifier being provided with input optical wave guiding means via which the optical amplifier is optically pumpable by a remote pump laser, and wherein the optical amplifier has a gain which is at least equal to the loss of the splitter portion.
In a preferred embodiment, the optical amplifier is a doped fibre amplifier constituted by a length of Er.sup.3+ doped fibre. Preferably, the input optical waveguiding means is connected to the doped fibre amplifier via a first WDM, and the first WDM is upstream of the doped fibre amplifier. In this case, the input may be connected to the first WDM, the doped fibre amplifier may be connected to the output via a second WDM, and the component may further comprise a filter downstream of the second WDM.
The invention also provides an optical system comprising an optical source, an optical coupler and a pump laser, the optical coupler being as defined above, the optical source being connected to the input of the optical coupler, and the pump laser being connected to the input optical wave guiding means.
Advantageously, the system further comprises an agc unit, the agc unit and pump laser being connected to the input optical wave guiding means by means of a further WDM. In the case where the input is connected to the first WDM, the input optical wave guiding
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Optical Communication (ECOC '89), Sep. 10-14, 1989, vol. 3, pp. 29-32, Nishi et al.: "1.8Gb/s 310 km Fiber Transmission Without Outdoor Repeater Equipment Using a Remotely Pumped In-Line Er-Doped Fiber Amplifier in an IM/Direct-Detection System".
Optical Communication (ECOC '89), Sep. 10-14, 1989, vol. 3, pp. 33-36, "Non-Regenerative Optical Transmission Experiment Using 12 Er-Doped Fibre Amplifiers," by Edagawa et al.
Hornung Stephen
Rowe Christopher
Bovernick Rodney B.
British Telecommunications PLC
Ngo John
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