COMMUNICATIONS APPARATUS COMPRISING OPTICAL AMPLIFIER

Abstract: An optical communications apparatus, comprising: (a) at least one pump laser support, on which is located at least one pump laser which provides pump light energy suitable for one or more optical amplifiers; (b) a splitter support, on which is located an optical splitter, the splitter having at least one inlet and a plurality of outlets; and (c) at least one optical waveguide which optically connects the pump laser(s) to the inlet(s) of the optical splitter such that pump light energy transmitted from the pump laser(s) is split into a plurality of separate portions before leaving the apparatus; the pump laser support, the splitter support and the optical waveguide constituting a single discrete apparatus which is able to provide pump light energy for a plurality of optical amplifiers, each optically connected, in use, to a respective outlet of the splitter.

Description: COMMUNICATIONS APPARATUS COMPRISING OPTICAL AMPLIFIER The present invention relates to optical communications, and in particular to the optical amplification of optical signals. Optical amplifiers are well known, and are often an important part of an optical communications network, particularly where the network extends over large distances. Doped fibre amplifiers, in particular rare-earth element doped fibre amplifiers, for example erbium doped fibre amplifiers (EDFAs), are widely regarded as important for all-optical communications systems. Doped fibre amplifiers are described in United States Patent No. 4955025, for example. One advantage of doped fibre amplifiers is that they may be optically pumped from a remote location. This means, for example, that an amplifier situated in a network a large distance from the central office may be optically pumped by means of a pump laser located in the central office. Remote pumping of optical amplifiers is described in several published patent specifications. For example, United Stated Patent No. 5039199 describes a lightwave transmission system in which a plurality of short lengths of rare-earth doped silica-based fibres and a corresponding plurality of long lengths of substantially un-doped silica-based fibres are interleaved to form a fibre span having alternating sections of compensated and uncompensated lightwave transmission media. Pumping of the amplifying fibre sections is performed remotely from either end of the fibre span. United States Patent No. 5321707 describes the remote pumping of optical amplifiers and other active optical components by a common pump laser. United States Patent No. 5323474 describes a lossless optical signal splitter which includes a remotely pumped optical amplifier. European Patent Application No. 0717516 Al describes bidirectional optical transmission over a single fibre. The transmission system incorporates an optical circulator in customer premises equipment together with an optical fibre amplifier and a narrow band filter. The central office has a star coupler and at least one pump laser connected to the star coupler for remotely pumping the fibre amplifier. According to a first aspect, the present invention provides an optical communications apparatus, comprising: (a) at least one pump laser support, on which is located at least one pump laser which provides pump light energy suitable for one or more optical amplifiers; (b) a splitter support, on which is located an optical splitter, the splitter having at least one inlet and a plurality of outlets; and (c) at least one optical waveguide which optically connects the pump laser(s) to the inlet(s) of the optical splitter such that pump light energy transmitted from the pump laser(s) is split into a plurality of separate portions before leaving the apparatus; the pump laser support, the splitter support and the optical waveguide constituting a single discrete apparatus which is able to provide pump light energy for a plurality of optical amplifiers, each optically connected, in use, to a respective outlet of the splitter. (It is to be understood that in this specification "optical connection" includes the possibility of indirect optical connection, i.e. with one or more intervening optical elements.) One advantage of this aspect of the invention is that because the pump light is split into a plurality of separate portions before it leaves the apparatus, the power of each separate portion (i.e. for each individual amplifier) is lower than the total light power output of the pump laser(s), and therefore the supply of the pump light energy to the amplifiers is safer than would be the case if all of the pump light energy were transmitted down a single fibre. Furthermore, this relatively safe supply of pump light energy is provided by means of a single discrete apparatus which provides the possibility of compactness, modularity and a high degree of fibre management and organization. In preferred embodiments of the invention, the or each optical waveguide comprises at least one optical fibre, designated an inlet optical fibre. Preferably, the or each inlet optical fibre actually comprises two optical fibres spliced together, therefore there is preferably a splice in the or each inlet optical fibre. Advantageously, the apparatus includes at least one inlet optical fibre splice storage tray which store(s) the splice(s) in the inlet optical fibre(s). The apparatus also preferably includes a plurality of optical fibres, designated outlet optical fibres, each of which is optically connected to a respective outlet of the splitter. Advantageously, the apparatus may include one or more outlet optical fibre storage tray(s) arranged to store splices between the outlet optical fibres and optical fibres of an external optical communications network. Most preferably, there are a plurality of outlet optical fibre splice storage trays, each of which is arranged individually to store the splice between a respective outlet optical fibre and an optical fibre of an optical communications network. The apparatus of the invention thus preferably provides single fibre management. In some particularly preferred embodiments of the invention, the apparatus includes a plurality of pump lasers, each of which is optically connected to the optical splitter. Preferably, therefore, the splitter comprises an optical coupler, i.e. it has a plurality of inlets as well as a plurality of outlets. Advantageously, each pump laser may be optically connected to a respective inlet of the splitter/coupler. Alternatively, the apparatus may include an optical energy combiner optically connected between the pump lasers and the optical splitter, to combine the pump light from each of the pump lasers prior to its entry into the splitter. The apparatus preferably includes active electronics which control the or each pump laser, the active electronics preferably being located on the or each pump laser support. Advantageously, the active electronics may be able to switch each of the pump lasers on or off, thereby providing pump laser redundancy, for example in case of pump laser malfunction. According to a second aspect, the invention provides an optical communications apparatus, comprising: (a) a plurality of pump lasers which provide pump light energy suitable for one or more optical amplifiers; (b) an optical coupler and/or an optical energy combiner, the coupler and/or combiner having a plurality of inlets and at least one outlet, the or each outlet having at least one optical amplifier optically connected thereto in use; (c) a plurality of optical waveguides, each of which optically connects a respective pump laser to a respective inlet of the coupler or the combiner; and (d) active electronics which are able to switch each of the pump lasers on or off, thereby providing pump laser redundancy. (It is to be understood that any or all of the components of this aspect of the invention may be the same as the corresponding components of the first aspect of the invention.) This aspect of the invention has the advantage that because the apparatus includes more than one pump laser, an optical coupler and/or an optical energy combiner, and active electronics to switch between the pump lasers, it provides pump laser redundancy, for example in case of pump laser malfunction. If the apparatus includes two or more pump lasers which are optically connected to respective inlets of a coupler, one of the pump lasers may function as the primary pump laser and the or each other may function as a back-up pump laser, for example. Therefore, if the primary pump laser malfunctions, the active electronics may switch (preferably automatically) to the (or one of the) back-up pump laser(s). Furthermore, instead of (or in addition to) such switching between pump lasers being carried out in the event of malfunction, it may be carried out in order to change the pump power output as and when required. In this case, the (or at least some of the) pump lasers may have different power outputs. These advantages are also obtained when an optical energy combiner is used. In this case however, more than one pump laser may be in operation at the same time, which has the advantage of enhancing the reliability of the pump light energy source. One reason for this is that the reliability of a laser is generally strongly dependent upon its optical power output, therefore the generation of a given optical power output by means of more than one lower power laser will normally be more reliable than generating the same power output by means of a single higher power laser. Furthermore, the effect on the total pump power generation of the failure of one laser out of several lasers, will normally be small, and may be negligible. The optical energy combiner is preferably a prism combiner. For example, the combiner may comprise an assembly of laser diode chips, optical elements, and prisms which combine the light beams. Alternatively, the optical energy combiner may comprise an NxM optical splitter. In some embodiments of either aspect of the invention, the apparatus may include an optical energy combiner optically connected between the pump lasers and the optical splitter or coupler. Embodiments of the invention which include more than one pump laser preferably include a plurality of pump laser supports, on each of which is located at least one pump laser. Advantageously, the or each pump laser support may comprise a heat sink to dissipate heat generated by the active electronics. Preferably, the or each pump laser support is formed at least partially from metal, preferably aluminium, the metal of the support constituting at least part of the heat sink. The apparatus preferably includes a thermal barrier situated between the or each pump laser support and the splitter or coupler support, to reduce the amount of heat received by the splitter or coupler support from the active electronics of the pump laser support(s). Advantageously, the thermal barrier may comprise at least one tray, preferably containing one or more heat-dissipating vents. The or each pump laser support and/or the splitter support preferably each comprise a tray. The pump laser tray(s) is/are preferably fabricated from metal. The pump laser(s) of the apparatus preferably supply(s) pump light energy to remotely located amplifiers. However, in some embodiments of the invention, the apparatus may include at least one doped fibre amplifier which is optically pumped by at least one pump laser of the apparatus. Preferably, the or each such doped fibre amplifier is located on a tray. The apparatus preferably includes a mounting structure, e.g. a base, especially one in the form of a plate, on which each support and/or tray is mounted, preferably pivotally mounted. The mounting structure may also guide the optical fibres between respective components of the apparatus, for example in grooves formed in the mounting structure. The invention will now be described, by way of example, with reference to the accompanying drawings, of which: Figure 1 is a schematic diagram showing the function of one type of apparatus according to the invention; Figure 2 is a schematic diagram showing the function of another type of apparatus according to the invention; Figure 3 is a schematic illustration of a pump laser support of an apparatus according to the invention; Figure 4 is a schematic illustration of a series of trays pivotally mounted on a mounting structure in accordance with the invention; Figure 5 is an illustration of a series of four pivotally mounted optical fibre splice storage trays of an apparatus according to the invention; and Figure 6 is an illustration of a series of trays pivotally mounted on a mounting structure according to the invention. Figure 1 is a schematic diagram showing the function of one type of apparatus according to the invention. It shows, schematically, that the driving electronics (the active electronics) control the pump laser, and that the pump light energy transmitted from the laser is split into N separate portions before leaving the apparatus. Optically connected to the N outlets of the 1 :N optical splitter are N optical amplifiers, preferably doped fibre amplifiers. The doped fibre amplifiers are preferably remote from the apparatus, in the network. However, in some embodiments the doped fibre amplifiers may be part of the apparatus. Advantageously, each amplifier can be connected, disconnected and reconnected to the apparatus by means of the optical fibre management capabilities of the apparatus. The apparatus is preferably located in a central office. Figure 2 is a schematic diagram showing the function of another type of apparatus according to the invention. In this case, the splitter is a 2:N splitter, i.e. a coupler, and there are two pump lasers, each of which is optically connected to a respective inlet of the splitter. The apparatus therefore has the advantage of pump laser redundancy, e.g. in case of malfunction of one of the pump lasers. In normal use, only one of the pump lasers will be in operation. If this first laser malfunctions (and this may be detected by the active electronics, for example), the active electronics will switch it off and switch on the second laser. Figure 3 is a schematic illustration of a pump laser support of an apparatus according to the invention. The support comprises a tray 1 which has a pump laser 3 and active control electronics 5 (on a printed circuit board) located on it. An optical fibre 7 extends from the pump laser 3. An electrical cable 9 extends onto the tray 1 to power the electronics 5. The tray has hinge members 11 for pivotally mounting the tray on a mounting structure. The wavelength of the pump light emitted by the pump laser is preferably 1480nm or 980nm. Figure 4 is a schematic illustration of a series of trays pivotally mounted on a mounting structure 13 in accordance with the invention. The mounting structure 13 is in the form of a plate which preferably includes optical fibre guide means, for example as shown in Figure 6. Pivotally mounted on the mounting structure 13 in a series are a pump laser tray 1 , an inlet optical fibre splice storage tray 15, an optical splitter tray 17 (for a 1 :4 splitter), and four outlet optical fibre splice storage trays 19. An optical fibre (not shown) which is optically connected to the pump laser is routed from the pump laser tray 1 , onto the mounting structure 13 and then onto the inlet splice tray 15, where it is spliced to another optical fibre. This optical fibre is similarly routed onto the splitter tray 17, where its is optically connected to the inlet of the splitter. Four other optical fibres are optically connected to respective outlets of the splitter, and routed to respective individual outlet splice trays 19. External optical fibres from a communications network may be spliced to the outlet optical fibres on the outlet trays. Remotely located doped fibre amplifiers are preferably optically connected to these external optical fibres. Figure 5 shows a series of four outlet optical fibre splice storage trays 19. The trays are pivotally mounted to intermediate mounting structures 2 1. These intermediate mounting structures 21 are attachable to a plate-like mounting structure 13 as shown in in Figure 6. The mounting structure 13 includes optical fibre guide means in the form of grooves 23 and protrusions 25. These guide means are for guiding optical fibres onto and off the mounting structure, and between the trays. Each tray may be accessed in turn by pivoting adjacent trays. The adjacent trays may be temporarily secured in position by a wedge device 27 inserted between the tray being accessed and the pivoted trays.

Claims: Claims 1. An optical communications apparatus, comprising: (a) at least one pump laser support, on which is located at least one pump laser which provides pump light energy suitable for one or more optical amplifiers; (b) a splitter support, on which is located an optical splitter, the splitter having at least one inlet and a plurality of outlets; and (c) at least one optical waveguide which optically connects the pump laser(s) to the inlet(s) of the optical splitter such that pump light energy transmitted from the pump laser(s) is split into a plurality of separate portions before leaving the apparatus; the pump laser support, the splitter support and the optical waveguide constituting a single discrete apparatus which is able to provide pump light energy for a plurality of optical amplifiers, each optically connected, in use, to a respective outlet of the splitter. 2. An apparatus according to Claim 1, in which the or each optical waveguide comprisesat least one (inlet) optical fibre. 3. An apparatus according to Claim 2, further comprising a splice in the or each inlet optical fibre. 4. An apparatus according to Claim 3, further comprising at least one inlet optical fibre splice storage tray which store(s) the or each splice in the or each inlet optical fibre. 5. An apparatus according to any preceding claim, further comprising a plurality of (outlet) optical fibres, each of which is optically connected to a respective outlet of the splitter. 6. An apparatus according to Claim 5, further comprising one or more outlet optical fibre splice storage tray(s) arranged to store splices between the outlet optical fibres and optical fibres of an optical communications network. 7. An apparatus according to Claim 6, in which there are a plurality of outlet optical fibre splice storage trays, each of which is arranged individually to store the splice between a respective said outlet optical fibre and an optical fibre of an optical communications network. 8. An apparatus according to any preceding claim, in which the apparatus includes a plurality of pump lasers, each of which is optically connected to the optical splitter. 9. An apparatus according to Claim 8, in which the apparatus includes a plurality of pump laser supports, on each of which is located at least one pump laser. 10. An apparatus according to Claim 8 or Claim 9, further comprising an optical energy combiner optically connected between the pump lasers and the optical splitter. 11. An apparatus according to any one of claims 8 to 10, further comprising active electronics which control the or each pump laser, the active electronics preferably being located on the or each pump laser support. 12. An apparatus according to Claim 11, in which the active electronics are able to switch each of the pump lasers on or off, thereby providing pump laser redundancy. 13. An apparatus according to Claim 12, in which the or each pump laser support comprises a heat sink to dissipate heat generated by the active electronics. 14. An apparatus according to Claim 13, in which the or each pump laser support is formed at least partially from metal, preferably aluminium, the metal of the support constituting at least part of the heat sink. 15. An apparatus according to any one of claims 11 to 14, further comprising a thermal barrier situated between the or each pump laser support and the splitter support, to reduce the amount of heat received by the splitter support from the pump laser support(s). 16. An apparatus according to Claim 15, in which the thermal barrier comprises at least, one tray, preferably containing one or more heat-dissipating vents. 17. An apparatus according to any preceding claim, in which the or each pump laser support and/or the splitter support each comprise a tray. 18. An apparatus according to any preceding claim, further comprising at least one doped fibre amplifier which is optically pumped by at least one said pump laser. 19. An apparatus according to Claim 18, in which the or each doped fibre amplifier is located on a tray. 20. An apparatus according to any preceding claim, further comprising a mounting structure on which each support and/or tray is pivotally mounted. 21. An optical communications apparatus, comprising: (a) a plurality of pump lasers which provide pump light energy suitable for one or more optical amplifiers; (b) an optical coupler and/or an optical energy combiner, the coupler and/or combiner having a plurality of inlets and at least one outlet, the or each outlet having at least one optical amplifier optically connected thereto in use; (c) a plurality of optical waveguides, each of which optically connects a respective pump laser to a respective inlet of the coupler or the combiner; and (d) active electronics which are able to switch each of the pump lasers on or off, thereby providing pump laser redundancy.

Inventors: CONWAY BRUCE, DELLINGES STEVEN, JEAN FABRICE, MAURER GREGORY SCOTT, CONWAY, BRUCE, DELLINGES, STEVEN, JEAN, FABRICE, MAURER, GREGORY, SCOTT
Applicants: CONWAY BRUCE, DELLINGES STEVEN, JEAN FABRICE, MAURER GREGORY SCOTT, RAYCHEM LTD, RAYCHEM SA NV, CONWAY, BRUCE, DELLINGES, STEVEN, JEAN, FABRICE, MAURER, GREGORY, SCOTT, N.V. RAYCHEM S.A., RAYCHEM LIMITED
Application year: 1998
Main classification: H04B10
IPC codes: H01S3, H04B10