Optical waveguides – With optical coupler – Particular coupling function
Patent
1998-09-02
2000-09-19
Palmer, Phan T. H.
Optical waveguides
With optical coupler
Particular coupling function
385 16, 385 24, 385 37, 385 47, 359128, 359130, 359139, G02B 626
Patent
active
061224189
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
1. Field of the Invention
The present invention relates to a structure for dispersion compensating a wavelength division multiplexed (WDM) signal in an optical network.
2. Background Art
The most efficient use of the available optical communication bandwidth can be achieved by multiplexing a number of different optical communication channels over a single optical fibre. One of the most promising multiplexing schemes is WDM in which channels have different wavelengths. In addition to increasing the capacity on any individual point to point communication link, it is known that such optical multiplexing offers many potential advantages in the provision of coarse traffic routing, simplified switching architectures and advanced restoration facilities. In high speed WDM optical networks using embedded standard fibre, chromatic dispersion is a key limiting factor. A number of techniques for compensating chromatic dispersion are known. In one conventional technique, fibre gratings are used to perform dispersion compensation. Other techniques include the use of dispersion compensating fibre or dispersion tolerant transmission formats.
Optical multiplexers/demultiplexers are provided in WDM networks to drop or insert one or more wavelengths at a node. Again, it is known that fibre gratings may be used to perform this drop and insert function.
At present, dispersion compensation and drop and insert functions in WDM networks are carried out separately. Furthermore, any flexibility in routing is provided by a further functional block including electro-optic switches or electro-mechanical optical switches. Accordingly, at present at least three functional blocks are required in a given system.
The document U.S. Pat. No. 5,048,909 discloses a chromatic dispersion compensating device having a chirped fibre grating for selectively dropping and dispersion compensating one channel within a WDM optical signal.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, a chromatic dispersion compensating node for connection to a transmission medium carrying a wavelength division multiplexed optical signal having N channels corresponding to N different wavelengths, comprises: selective dispersion compensating elements, each of which is tuned to a respective one of the N wavelengths, to one of the drop port and the output port, the node thereby selectively dropping one or more of the N channels and dispersion compensating all of the N channels.
According to a second aspect of the present invention, an optical communication network comprises a number of chromatic dispersion compensating nodes in accordance with the first aspect of the present invention.
In the present invention, wavelength division multiplexed transmission functions of chromatic dispersion compensation and channel drop are performed by a node having a number of wavelength selective dispersion compensating elements and switching means. The switching means is arranged to select or bypass each wavelength selective dispersion compensating element. If a wavelength selective dispersion compensating element is selected, the corresponding channel is dispersion compensated and reflected to one of a number of drop ports. Any remaining channels are circulated by the switching means to the remaining dispersion compensating elements where they are dispersion compensated and reflected to the optical output.
Preferably, the node includes an insert port to allow multiplexing of additional channels. This allows the node to perform both drop and insert functions in addition to dispersion compensation and so forms a dispersion compensating drop and insert node.
Preferably, the wavelength selective compensating elements are chirped fibre gratings. These fibre gratings are reflective and may be tuned to a desired wavelength corresponding to one of the N channels. As each of the chirped fibre gratings is independent, characteristics of the fibre gratings can be tailored to suit particular transmission formats of that channel. Thus each channel m
REFERENCES:
patent: 5048909 (1991-09-01), Henry
patent: 5701188 (1997-12-01), Shigematsu et al.
patent: 5943151 (1999-08-01), Grasso et al.
Electronics Letters, vol. 31, No. 11, May 25, 1995, pp. 899-901, Quellette et al., "Broadband and WDM Dispersion Compensation Using Chirped Sampled Fibre Bragg Gratings".
British Telecommunications
Palmer Phan T. H.
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