GB2191645A

GB2191645A - Optical telecommunication system

Info

Publication number: GB2191645A
Application number: GB8614403A
Authority: GB
Inventors: Isobel Jennifer Goddard
Original assignee: STC PLC
Current assignee: STC PLC
Priority date: 1986-06-13
Filing date: 1986-06-13
Publication date: 1987-12-16
Anticipated expiration: 2006-06-13
Also published as: GB2191645B; GB8614403D0

Abstract

In an optical transmission system, e.g. of the ring or bus type, the same optical transmission path is used to convey both wavelength-division- multiplexed (WDM) light and light for point-to-point links. In one example the WDM light is centred on a wavelength of 1.5 mu m, and the point-to-point links use light at 1.3 mu m. At the nodes wavelength-selective optical couplers (1,2,3,4) are used to couple or connect the receivers and the transmitters to the transmission paths. <IMAGE>

Description

SPECIFICATION Optical telecommunication system The present invention relates to optical fibre transmission systems such as used in telecommunication systems of the ring of bus types.

These may be of the optical fibre type butthe invention is applicable to other optical systems.

The transmission capacity of an optical fibre network can be increased by wavelength division multiplexing (WDM) ofthetrafficto be handled. Ndte that WDM is also frequently referred to as frequency division multiplexing (FDM). Optical couplers may be used to distribute the light conveying the traffic, e.g. bythe use of multiportcouplers in a star-like configuration, orbythe use of 2 x2 couplers in a ring or bustype system. In all of these arrangements the Iightfrom any one node of the system may be received at all other nodes. It is also possible to distribute the traffic by other means, e.g. on a point-to-point basis.

An object ofthe invention is to extend the traffic handling capacity of a ring or bus type optical transmission system.

According to its broadest aspect, the invention provides an optical transmission system, in which the same optical transmission path is used to convey intelligence using a defined range ofwavelengths and further intelligence using a wavelength or wavelengths outside said defined range, in which at each node of the system wavelength-selective optical couplers are used to route the intelligence from the transmission path to the appropriate receiving means and to route intelligence from respective transmitting means onto the transmission path.

According to the invention, there is also provided an optical transmission system, in which the same optical transmission path is used to convey wavelength division multiplexed (WDM) intelligence using a defined range of light wavelengths and point-to-point intelligence using a wavelength or wavelengths outside said defined range, in which at each node ofthe system wavelength-selective optical couplers are used to route the intelligence from the transmission path to the appropriate receiving means and to route intelligence from respective transmitting means onto the transmission path.

Embodiments ofthe invention will now be described with reference to the accompanying highly schematic Figures 1 to 4.

In the arrangements to the described herein, the two basically differenttransmission techniques referred to above are combined onto the same transmission path, using wavelength selective couplers, i.e. ones which pass different ratios of poweratthe different wavelengths to the output ports. TheWDM traffic is transmitted in one wavelength region, e.g. 1.45 to 1.55clam, i.e. around 1 Sum, and the traffic sent on point-to-point links is transmitted at a different wavelength outside that region, e.g. 1 .3Am. By using fourwavelength selective couplers, as shown at 1,2,3,4 in Figure 1, the intelligence sent in the two wavelength regions behave differently.

In the example of Figure 1, and with the wavelengths referred to above, some ofthe 1 .51lem light is split off from the main transmission path MTP by coupler 1, and passed via coupler 3 to a receiver for 1 .5pm light. The light from the transmitter at 1.5m passes via coupler 4 and some of it is coupled on to the main transmission path MTP via coupier2.

At 1.3m, coupler 1 couples all, orsubstantiallyall, light off the main transmission path MTP and that light is coupled via coupler3 to another receiverfor 1 .3,ubm. Coupler4 couples all, or substantially all, 1.3 m lightfrom the transmitterto coupler 2, which in turn couples ali, or su bsta ntial Iy al I light at 1 .3pm onto the main transmission path MTP.

Thus it will be seen that couplers 1 and 2couple mostofthe 1 .5pm light past the couplers, and a small proportion ofthat light is coupled across the coupler 1,while coupling all (orsubstantiallyall) 1.3m light across the coupler 1. Couplers3 and4 couple all the 1 .5m light past the couplers, and each couples all the 1 .3 > m I light across the respective couplers. Thus couplers 3 and 4 have the effect that atthe node'stransmit portthe light atthetwo wavelengths is combined for coupling onto the main transmission path, and at the node's receive port of splitting the light for reception by two separate receivers.Note that there is light at 1 .5ym travelling between the couplers 1 and 2, but little orno light at 1 .3m passing between the couplers 1 and 2, which gives the required point-to-point links.

Figure 2 shows an arrangementsimilartothat shown in Figure 1, as used in a ring-type system, but with a fibre CRTP for transmission in the opposite direction at 1 .3film, with additional receiver and transmftter. This will be referred to again later.

Another node configuration, known as "stretched" is shown in Figure 3; this can be modified to enable both WDM and point-to-point links to be provided on the same network. The connection uses a passive 2 x 2 optical couplerOC, andthe coupleroutputwhich does not connect into the trunk ring is connected to another ring,the local ring,whichtakesthelightto the adjacent node. Figure 4shows howto provide this, using four identical wavelength-selective 2 x 2 couplers 5,6,7,8. The wavelengths conveyed bythe transmission paths are indicated by the figures given adjacent thereto.

The arrangement includes "counter-rotating" rings MTPA and MTPB for 1 .3pm point-to-point links.

The WDM and the 1.3um lighttravel in the same direction in the local ring MTPA,whilethetrunklink MTPB the 1 .3 > m light travels in the opposite direction to the WDM light. Thusthe ringswhich carry the 1 .3 m light "counter-rotate", and there are transmit and receive ports on each ring. The Americal National Standards Institute (ANSI) Fibre Distributed Data Interface (FDDI) standard requires these two features, so FDDI operationally-compatible equipment could be used with the arrangement just described, without having to install anothertransmission path. The addition of the second ring to the first arrangement described herein, as in Figure 2, enables that arrangement to be used with such equipment.

In the preceding description the emphasis is on the use ofthe present invention in ring type systems, but the invention can also be used with bus-type systems. In addition, the specific arrangements described use optical fibre as the transmission media, although other forms of optical transmission path may be used.

Claims

1. An optical transmission system, in which the same optical transmission path is used to convey intelligence using a defined range ofwavelengths and further intelligence using a wavelength or wavelengths outside said defined range, in which at each node of the system wavelength-selective optical couplers are used to route the intelligence from the transmission path to the appropriate receiving means and to route intelligence from respective transmitting means onto thetransmission path.

2. An optical transmission system, in which the same optical transmission path is used to convey wavelength division multiplexed (WDM) intelligence using a defined range of light wavelengths and point-to-point intelligence using a wavelength or wavelengths outside said defined range, in which at each node of the system wavelength-selective optical couplers are used to route the intelligence from the transmission path to the appropriate receiving means and to route intelligence from respective transmitting means onto the transmission path.

3. A system as claimed in claim 2, in which to route the lightfrom the transmission path to the receiving means a first said optical coupler couples substantially all ofthe point-to-point light and a proportion of the WDM light to another optical transmission path which extends via anothersaid optical coupler to receiving means forthe WDM light, and in which said second optical coupler couples the point-to-point lightto receiving means for the point-to-point light.

4. A system as claimed in claim 3, in which the outputfromtransmitting meansfortheWDM light is applied via a third said optical couplerwhich couples it to the transmission path, and in which the output from transmitting means forthe point-to-point light is applied to the third coupler which couples it to the transmission path from that coupler to the fourth coupler where it also is coupled to the transmission path.

5. A system as claimed in claim 2, 3 or 4, and which includes a second optical transmission path on which intelligence is conveyed in the opposite direction to that used on the first said path, and in which each said node has additional receiving and transmitting means for light conveyed over said second transmission path.

6. Asystem as claimed in claim 2, in which the transmission path is coupled at said node via a first wavelength selective optical couplertotwo receiving means, one for WDM lightand one for point-to-point light, in which transmitting means for WDM light at the node is connected to a second wavelength selective optical couplerwhich couples some of the lightto a second optical transmission path on which WDM light is conveyed in the same direction as that used on thefirst-mentioned transmission path, in which the light which passes through said last-mentioned coupler passes via a third wavelength selective coupler to the first-mentioned transmission path, in which the output of a transmitting means for point-to-point light is coupled via said wavelength selective coupler to said first-mentioned transmission path, and in whichfurthertransmitting and receiving means for point-to-point light are coupled via further wavelength selective optical couplers to the second mentioned transmission path on which point-to-point light is conveyed in the opposite direction to that used on the first-mentioned transmission path and to the WDM light on the second-mentioned transmission path.

7. A node for use in an optical transmission system as claimed in claim 1,2,3,4,5 or6.

8. A node for an optical transmission system, in which system the same optical transmission system is used to convey wavelength division multiplexed (WDM) intelligence using a defined range of light wavelengths and point-to-point intelligence using a wavelength outside said defined range, in which the node has a set offourwavelength selective optical couplers, in which a first of said couplers couples substantially all ofthe point-to-point light from the transmission path to another optical transmission path which extends to a second of said couplers, in which said first coupler also couples a proportion of the WDM light onto said optical transmission path, in which the second of said couplers has two outputs via which the WDM light and the point-to-point light are applied respectively to two receivers, in which the third of said couplers has two inputtransmission paths onefrom a transmitter of WDM light and one from a transmitter of point-to-point light, said third couplercouplingtheoutputfromsaidtransmittervia a further optical transmission path to a fourth of said optical couplers, in which said fourth coupler couples intelligence from both said transmitters to the transmission path, and in which said first coupler while coupling substantially all ofthe point-to-point lightoffthetrunktransmission path onlycouplesa proportion oftheWDM lightoffthetrunk transmission path.

9. A node for an optical transmission system which has first and second optical transmission paths both serving the node, in which the transmission paths are both used to convey wavelength-distributed (WDM) intelligence using a defined range ofwavelengths and point-to-point intelligence using a wavelength or wavelengths outside said defined range, theWDM and the point-to-point light being conveyed in the same direction in the first of said paths and in opposite directions in the second of said paths, and in which at the node; (a) said firsttransmission path which conveys both said WDM and said point-to-point light in the same direction is coupled via a first wavelength selective optical couplerto separate receivers for said types of light;; (b) a transmitterforthe WDM light is connectedto the outgoing fibre of said first optical transmission path, which path extends via a second optical couplerwhichcouplessomeofthatlightontothe second of said optical fibre transmission paths; (c) a transmitterfor said point-to-point light is coupled via a third wavelength-selective optical coupler to the said first transmission path; (d) anothertransmitterfor said point-to-point light is coupled via a fourth wavelength-selective optical coupler to the second optical transmission path; and (e) the second optical fibre transmission path is coupled via a fifth wavelength-selective optical coupler to another receiver for said point-to-point light.

10. A system ora node as claimed in anyone of the preceding claims, in which the WDM intelligence is conveyed using light whose wavelength is centred on 1.Sym,while the point-to-point intelligence is conveyed using light at a wavelength of 1 .3cm.

11. An optical transmission system substantially as described with reference to Figures 1,2 or4 ofthe accompanying drawings.

12. A node for an optical transmission system substantially as described with reference to Figures 1,2 or4 ofthe accompanying drawings.

Amendments to the claims have been filed, and have the following effect: (b) New ortextuallyamended claims have been filed asfollows: Claims 13-14.

13. An optical transmission system, in which the same optical transmission path which serves a numberof nodes is used to convey intelligence using multiple wavelengths in a defined range and further intelligence using a wavelength or wavelengths outside said defined range, in which at each node of the system wavelength-selective optical couplers are used to route a proportion ofthe intelligence from the transmission path to the appropriate receiving means, the remainder of said intelligence continuing on to other nodes in the system, and in which at each node of the system wavelength-selective optical couplers are used to route intelligence from respective transmission means onto the transmission path.

14. An optical transmission system, in which the same optical transmission path which serves a number of nodes is used to convey intelligence using multiple wavelengths in a defined range and further intelligence using a wavelength or wavelengths outside said defined range, in which at each node of the system wavelength-selective optical couplers are used to route a proportion ofthe intelligence from the transmission path to the appropriate receiving means, the remainder of said intelligence continuing on to the other nodes in the system, and in which at each node in the system wavelength-selective optical couplers are used to route a proportion of the intel I igence from respective transmitting means onto the transmission path.