GB2365238A

GB2365238A - Arrayed waveguide optical router with wavelength converters

Info

Publication number: GB2365238A
Application number: GB0018380A
Authority: GB
Inventors: Anna Tzanakaki
Original assignee: ILOTRON Ltd; Ditech Networks Inc
Current assignee: ILOTRON Ltd; Ditech Networks Inc
Priority date: 2000-07-26
Filing date: 2000-07-26
Publication date: 2002-02-13
Also published as: GB0018380D0

Abstract

In the present invention, an arrayed waveguide (AWG) type optical router incorporates an output wavelength conversion stage that enables flexible virtual wavelength path provisioning and eliminates the crosstalk introduced by the AWG, thereby suppressing the overall power penalty. In particular, an output stage of the AWG includes a plurality of wavelength converters connected to a respective one of each of the output ports of the AWG device.

Description

<Desc/Clms Page number 1> AN OPTICAL ROUTER Field of the Invention The present invention relates to an optical router, and in particular an optical cross connect (OXC) architecture that incorporates an arrayed waveguide grating (AWG). Background to the Invention An OXC architecture incorporating an AWG has been reported (A. Tzanakaki, K. M. Guild, D. Simeonidou and M. J. O'Mahony, "Penalty-free concatenation of 25 Optical Cross-Connects Performing Reconfigurable Wavelength Routing", ECOC'99, Nice, vol. 1, pp. 1-254-1-255, Sept. 1999) and this is shown in Figure 1. However, it has since been recognised that this architecture suffers from unacceptable crosstalk.

The wavelength conversion stage in Figure 1 is mainly used to facilitate wavelength routing of the input channels to the required output ports through the AWG. The number of crosstalk components at the output of the configuration illustrated in Figure 1 depends on the number of input/output ports of the OXC and the number of wavelengths per port. In the case of an NxN OXC with m number of wavelengths per input port, the size of the AWG required to perform wavelength routing is (mxN)x(mxN). Due to the imperfections of the device, crosstalk elements originating from every input port appear at each output port of the AWG. Since m of the output ports of the AWG are coupled together for the recombination of the WDM channels at the output of the OXC there are mxN-1 intraband (same wavelength) crosstalk interferers for every WDM channel at each output port of the node.

The power penalty can be calculated as a function of the number of crosstalk components for different levels of crosstalk, and this is illustrated in Figure 2. It was assumed that the interferometric crosstalk noise is of Gaussian distribution and that the receiver's decision threshold is optimised. For an OXC supporting 4 input WDM signals (3 input fibres plus inserted local traffic) with 4 WDM channels per fibre the number of intraband crosstalk components can be as high as 15. In this case, the penalty due to the interferometric crosstalk for crosstalk values of -30 can be very severe (>3 dB), as shown in Figure 2. It should be noted that the typical value of crosstalk for a 16xl6 AWG with 100 GHz (0.8 nm) channel spacing is less than -30 dB. It is clear that the introduced power penalty increases with the number of input ports and wavelength channels as the number of crosstalk interferes will increase accordingly. If this AWG based OXC architecture is to be used in a WDM communications network then it is important that the issue of unacceptable levels of crosstalk is addressed. Summary of the Invention According to one aspect of the present invention, an optical router comprises an arrayed waveguide (AWG) device having a plurality of input ports and a plurality of output ports, wherein an optical signal at an input port is coupled to an output port in dependence on the wavelength of the optical signal, and an output stage having a plurality of wavelength converters connected to a respective one of each of the output ports of the AWG device.

According to another aspect of the present invention, an optical node comprise an optical router in accordance with the one aspect of the invention.

According to yet another aspect of the present invention, an optical communications network comprises an optical node in accordance with the other aspect of the invention.

In the present invention, an AWG type optical router incorporates an output wavelength conversion stage that enables flexible virtual wavelength path provisioning and eliminates the crosstalk introduced by the AWG, thereby suppressing the overall power penalty. The proposed configuration is also suitable for packet switching applications.

Preferably, the optical router further comprises an input stage having a plurality of wavelength converters connected to a respective one of each of the input ports of the AWG device.

Preferably, the output stage of the optical router comprises means for recombining optical signals output from the wavelength converters. This may be a number of optical couplers or a number of multiplexers. Preferably, the input stage of the optical router comprises a number of demultiplexers for splitting one or more optical signals into their constituent wavelengths, each of which is coupled to a respective input port of the AWG device.

The wavelength converters may be fixed wavelength or tuneable wavelength devices. Suitable devices include semiconductor optical amplifiers, which act as cross-gain modulators, or interferometric devices, which act as cross-phase modulators.

The present invention provides an optical cross connect architecture design that enables full and dynamic configuration of the WDM traffic, virtual wavelength path provisioning and significant crosstalk reduction.

Brief Description of the Drawings An example of the present invention will now be described in detail with reference to the accompanying drawings, in which: Figure 1 shows an example of a known OXC architecture incorporating an AWG; Figure 2 is a graph showing the power penalty caused by the effects of crosstalk within the AWG of Figure l; Figure 3 is an example of an OXC in accordance with the present invention;and, Figure 4 is an example of an optical node for a WDM optical communications network incorporating the OXC of Figure 3.

Detailed Description Figure 3 shows an example of an OXC in accordance with the present invention. The device comprises an input stage of tuneable wavelength converters followed by an AWG wavelength router and an output tuneable wavelength conversion stage. The input tuneable wavelength converter translates the incoming channel to the appropriate wavelength so that it can be routed to the desired output port of the AWG. Following the AWG, the signal is converted again through the second wavelength

conversion stage, which can be either fixed or tuneable, to one of the transmission wavelengths and it recombines with the rest of the WDM channels at the output couplers.

This architecture overcomes the penalty limitations arising from the crosstalk performance of the AWG shown in Figure 1 by the use of a dual wavelength conversion scheme. By employing the output wavelength conversion stage, the functionality of the OXC is enhanced in terms of virtual wavelength path provisioning and the crosstalk originating from the AWG is eliminated through the second wavelength conversion stage.

Figure 4 illustrates an example of an optical routing node. Traffic arriving at a number of input fibres can be routed to a number of output fibres: this is referred to as an OXC function. This part of the node includes an OXC architecture assembled using a number of the AWG based optical routers described above with reference to Figure 3. Furthermore, the optical routing node incorporates an optical add/drop multiplexing (OADM) function that provides flexible traffic management at the interface with local clients. The OADM enables a variety of protocols to be transported across a network in a transparent manner.

In operation, some traffic arriving at the input fibres of the optical routing node will traverse the node through the AWG of the OXC without being dropped to local clients. This is termed "through traffic". The remainder is directed through the OADM, as "drop traffic". Traffic that originates from a local client is termed "add traffic", and is routed through the OADM to the output fibres of the OXC.

Claims

CLAIMS: 1. An optical router comprising an arrayed waveguide (AWG) device having a plurality of input ports and a plurality of output ports, wherein an optical signal at an input port is coupled to an output port in dependence on the wavelength of the optical signal, and an output stage having a plurality of wavelength converters connected to a respective one of each of the output ports of the AWG device.
2. An optical router according to claim 1, further comprising an input stage having a plurality of wavelength converters connected to a respective one of each of the input ports of the AWG device.
3. An optical router according to claim 1 or 2, in which the output stage of the optical muter comprises means for recombining optical signals output from the wavelength converters.
4. An optical router according to claim 3, in which the recombining means comprises a number of optical couplers or a number of multiplexers.
5. An optical router according to any preceding claim, in which the input stage of the optical router comprises a number of demultiplexers for splitting one or more optical signals into their constituent wavelengths, each of which is coupled to a respective input port of the AWG device.

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6. An optical router according to any preceding claim, in which the wavelength converters are tuneable wavelength devices.
7. An optical router according to any preceding claim, in which the wavelength converters include semiconductor optical amplifiers, which act as cross-gain modulators, and/or interferometric devices, which act as cross-phase modulators.
8. An optical node comprising an optical router according to any preceding claim.
9. An optical communications network comprising an optical node according to claim 8.
10. An optical router substantially as shown in and/or described with reference to any of Figures 3 and 4 of the accompanying drawings