Optical waveguides – With optical coupler – Plural
Reexamination Certificate
1999-04-06
2001-03-20
Spyrou, Cassandra (Department: 2874)
Optical waveguides
With optical coupler
Plural
C385S037000, C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06205269
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to the field of wavelength division multiplexed optical communication systems and, more particularly, to an add-drop multiplexer for transferring selected optical channels between transmission paths within a wavelength division multiplexed optical communication system.
BACKGROUND OF THE INVENTION
Wavelength Division Multiplexing (WDM) techniques have been utilized to significantly enhance the signal capacity of optical communication systems. WDM systems simultaneously transmit multiple information signals on a single waveguide medium at different wavelengths or channels. Examples of such communication systems include, telecommunications systems, cable television systems, local area networks (LANs) and wide area networks (WANs). In a WDM system, optical signals are generated and multiplexed onto a plurality of optical channels, transmitted over a single optical waveguide, and demultiplexed at one or more destination terminals. Dense WDM (DWDM) systems are characterized by relatively close spacings between the respective channels.
WDM or DWDM communication systems may carry signals over many miles, with the system having a number of different origination and destination terminals or nodes. In many of these systems, channels are added/dropped from the WDM signal corresponding to one or more different origination/destination nodes. This form of optical signal routing is generally referred to as “add/drop multiplexing.”A number of different devices and configurations have been employed as add/drop multiplexers. One approach is explored in Giles and Mizrahi,
“Low
-
Loss ADD/DROP Multiplexers for WDM Lightwave Networks,
” IOOC Technical Digest, (The Chinese University Press, Hong Kong) c. 1996, pp. 65-67, the disclosure of which is incorporated herein by reference. In this paper, an add-drop multiplexer is proposed which uses two three-port optical circulators with a fiber grating positioned therebetween. Using this configuration, an optical signal to be dropped from multiplexed optical signals is reflected by the fiber grating and exits through a drop port of the first optical circulator. All other input signals exit via a through port of the first optical circulator. Similarly, an optical signal to be added which has a wavelength nominally identical to the optical signal being dropped from the optical transmission path is input to an add port of the second circulator. The signal to be added to the optical transmission path is reflected towards a through port of the second circulator by the same fiber grating disposed between the first and second circulators used for signal dropping.
A disadvantage associated with this type of add/drop multiplexer is the loss associated with the grating and, more significantly, the loss contributed by each of the two circulators. These loss values have a negative effect on the overall system loss budget, i.e. the total amount of optical loss that a given optical link can tolerate while maintaining signal integrity. Moreover, this loss may accumulate over a plurality of nodes each including one or more add/drop multiplexers.
Accordingly, it would be advantageous to provide an optical add/drop multiplexer with reduced optical loss adaptable for use with an optical communication system employing wavelength division multiplexing. Other and further objectives will be apparent from the following detailed description and the appended claims.
SUMMARY OF THE INVENTION
The present invention provides an optical add/drop multiplexer for use in optical communication systems which includes an optical waveguide capable of carrying one or more optical input signals on one or more optical input channels. A first optical fiber grating having an associated stop-band and positioned along the waveguide reflects a particular channel corresponding to the optical channel to be added to the input signals. An optical circulator with four ports optically communicates with the waveguide. The optical input signals not dropped by the first fiber grating, pass through the first grating to a first one of the input/output ports of the optical circulator. The circulator passes the optical input signals to a second input/output port. The second input/output port is connected to a second optical fiber grating. The second optical fiber grating reflects those optical input signals having wavelengths within an associated stop-band, while other optical signals, outside the stop-band, pass through the grating. The optical signals reflected by the second grating exit the circulator through a drop port. In another aspect, an optical circulator receives an optical add signal at an add port and passes the optical add signal to the second input/output port, while preventing the optical add signal from passing to the drop port.
REFERENCES:
patent: 5712717 (1998-01-01), Hamel
patent: 5717798 (1998-02-01), Strasser
patent: 5748349 (1998-05-01), Mizrahi
patent: 5748350 (1998-05-01), Pan
patent: 5822095 (1998-10-01), Taga
patent: 5982518 (1999-11-01), Mizrahi
patent: 6041152 (2000-03-01), Clark
patent: 6067389 (2000-05-01), Fatehi
patent: 0794629A2 (1997-09-01), None
patent: 0857988A1 (1998-08-01), None
Boutsikaris Leo
Ciena Corporation
Daisak Daniel N.
Soltz David L.
Spyrou Cassandra
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