Optical add/drop multiplexer/demultiplexer

• US 5,959,749 A
• Filed: 05/20/1997
• Issued: 09/28/1999
• Est. Priority Date: 05/20/1998
• Status: Expired due to Term

• Current Assignee: Ciena Corporation
• Original Assignee: Nortel Networks Corporation
• Inventors: Hardcastle, Ian, Bordogna, Giuseppe, O'Sullivan, Maurice S., Patel, Bipin, Baker, Nigel, Solheim, Alan G., Danagher, David John, Roberts, Kim Byron, Harley, James St. Leger, Habel, Richard A., Hadjifotiou, Takis, Forbes, Duncan John
• Primary Examiner(s): NEGASH, KINFE MICHAEL
• Application Number:
  US09/081,666
• Time in Patent Office: 861 Days
• Field of Search: 359/124, 359/128, 359/130, 359/118, 385/24
• US Class Current: 398/83
• CPC Class Codes: H04J 14/0212 using optical switches or wavelength selective switches [WSS]
• CPC Class Codes: H04J 14/0221 Power control, e.g. to keep the total optical power constant
• CPC Class Codes: H04Q 11/0005 Switch and router aspects
• CPC Class Codes: H04Q 2011/0016 using wavelength multiplexing or demultiplexing
• CPC Class Codes: H04Q 2011/0024 using space switching
• CPC Class Codes: H04Q 2011/0039 Electrical control
• CPC Class Codes: H04Q 2011/0069 using dedicated optical channels

Abstract

An add/drop multiplexer/demultiplexer (ADM) for switching, modulating and attenuating optical signals in a fiber optic network employing wavelength division multiplexing (WDM) is disclosed. The ADM is equipped an optical multiplexer for splitting an input WDM signal into individual optical signals, leading to respective 2×2 switches. Each switch has another input originating from a plurality of "add lines", and selects one of its inputs to be dropped and the other to continue along a main signal path. The retained signals may be modulated and attenuated prior to being tapped and finally multiplexed together by a WDM multiplexer. The tapped signals are optoelectronically converted and fed back to a controller, preferably a digital signal processor running a software algorithm, which controls the switching, modulation and attenuation. This permits remote control of the ADM functions by encoding instructions for the controller into a low-frequency dither signal that is embedded within the individual optical signals. The ADM can accordingly be instructed to reroute traffic, dynamically equalize or otherwise change optical channel power levels, and add or remove dither, all in real time. A specific optical channel may be reserved for control purposes, allowing a network administrator to "log in" to the ADM to override the controller software algorithm. Optionally, the optical signals can be tapped upon entry to the ADM. A bidirectional ADM can be constructed from two unidirectional ADMs, and may share the same controller. Also, a single, general multi-input multi-output switch can be used to provide an arbitrary mapping between individual input and output optical signals.

Claims

1. An add/drop multiplexer/demultiplexer (ADM) for connection in a fiber optic network adapted to carry WDM optical signals, the ADM comprising:

first and second optical ports for connection to the network;

a wavelength demultiplexer connected to the first port and a wavelength multiplexer connected to the second port;

a plurality of optical signal lines extending between the demultiplexer and the multiplexer for carrying respective demultiplexed optical signals;

a plurality of optical switches connected respectively to the plurality of optical signals lines, each switch also being connected to a respective one of a plurality of add signal lines and to a respective one of a plurality of drop signal lines;

a plurality of optoelectronic converters respectively connected to the plurality of optical signal lines;

a controller electronically connected to the optoelectronic converters and the optical switches for detecting dither signals in the demultiplexed optical signals and controlling the optical switches according to instructions encoded in the detected dither signals.

2. An add/drop multiplexer/demultiplexer (ADM) for connection in a fiber optic network adapted to carry wavelength division multiplexed (WDM) optical signals, the ADM comprising:

a wavelength demultiplexer having an input port for connection to the network and a plurality of output ports respectively connected to a plurality of optical input signal lines for carrying respective demultiplexed optical input signals;

a wavelength multiplexer having an output port for connection to the network and a plurality of input ports respectively connected to a plurality of optical output signal lines for carrying respective demultiplexed optical output signals;

a plurality of controllable optical switches, each having a first input connected to a respective one of the plurality of optical input signal lines, a first output connected to a respective one of the plurality of optical output signal lines, a second input connected to a respective one of a plurality of add signal lines and a second output connected to a respective one of a plurality of drop signal lines;

a plurality of optoelectronic converters respectively intercepting the plurality of optical output signal lines; and

a controller electronically connected to the optoelectronic converters and to the optical switches, for detecting dither signals contained in the demultiplexed optical output signals and controlling the optical switches according to instructions encoded in the detected dither signals.

3. An ADM according to claim 2, further comprising a further plurality of optoelectronic converters respectively intercepting the plurality of optical input signal lines and electronically connected to the controller, wherein the controller further controls the optical switches according to instructions encoded in dither signals embedded in the demultiplexed optical input signals.

4. An ADM according to claim 2, further comprising a plurality of controllable optical modulators respectively intercepting the plurality of optical output signal lines and electronically connected to the controller, wherein a controllable amount of dither may be added to or removed from a demultiplexed optical output signal by the respective optical modulator under control of the controller.

5. An ADM according to claim 2, further comprising a plurality of controllable optical attenuators respectively intercepting the plurality of optical output signal lines and electronically connected to the controller, wherein a controllable amount of attenuation may be applied to a demultiplexed optical output signal by the respective optical attenuator under control of the controller.

6. An ADM according to claim 2, wherein at least one of the optical input signal lines is reserved as a control channel for controlling the controller.

7. An ADM according to claim 6, wherein at least one of the optical output signal lines is used for providing ADM status and maintenance information to the network.

8. An ADM according to claim 2, wherein the controller is a digital signal processor running software.

9. An add/drop multiplexer/demultiplexer (ADM) for connection in a fiber optic network adapted to carry wavelength division multiplexed (WDM) optical signals, the ADM comprising:

a first wavelength demultiplexer having an input port for connection to the network and a plurality of output ports respectively connected to a first plurality of optical input signal lines for carrying respective first demultiplexed optical input signals;

a second wavelength demultiplexer having an input port for connection to the network and a plurality of output ports respectively connected to a second plurality of optical input signal lines for carrying respective second demultiplexed optical input signals;

a first wavelength multiplexer having an output port for connection to the network and a plurality of input ports respectively connected to a first plurality of optical output signal lines for carrying respective first demultiplexed optical output signals;

a second wavelength multiplexer having an output port for connection to the network and a plurality of input ports respectively connected to a second plurality of optical output signal lines for carrying respective second demultiplexed optical output signals;

a first plurality of controllable optical switches, each having an input connected to a respective one of the first plurality of optical input signal lines;

an output connected to a respective one of the first plurality of optical output signal lines;

an input connected to a respective one of a first plurality of add signal lines; and

an output connected to a respective one of a first plurality of drop signal lines;

a second plurality of controllable optical switches, each having an input connected to a respective one of the second plurality of optical input signal lines;

an output connected to a respective one of the second plurality of optical output signal lines;

an input connected to a respective one of a second plurality of add signal lines; and

an output connected to a respective one of a second plurality of drop signal lines;

a first plurality of optoelectronic converters respectively intercepting the first plurality of optical output signal lines;

a second plurality of optoelectronic converters respectively intercepting the second plurality of optical output signal lines; and

a controller electronically connected to the optoelectronic converters and to the optical switches, for detecting dither signals contained in the demultiplexed optical output signals and controlling the optical switches according to instructions encoded in the detected dither signals.

10. An ADM according to claim 9, further comprising further first and second pluralities of optoelectronic converters respectively intercepting the first and second pluralities of optical input signal lines and electronically connected to the controller, wherein the controller further controls the optical switches according to instructions encoded in dither signals embedded in the demultiplexed optical input signals.

11. An ADM according to claim 9, further comprising first and second pluralities of controllable optical modulators respectively intercepting the first and second pluralities of optical output signal lines and electronically connected to the controller, wherein a controllable amount of dither may be added to or removed from a demultiplexed optical output signal by the respective optical modulator under control of the controller.

12. An ADM according to claim 9, further comprising first and second pluralities of controllable optical attenuators respectively intercepting the first and second pluralities of optical output signal lines and electronically connected to the controller, wherein a controllable amount of attenuation may be applied to a demultiplexed optical output signal by the respective optical attenuator under control of the controller.

13. An ADM according to claim 9, wherein at least one of the optical input signal lines is reserved as a control channel for controlling the controller.

14. An ADM according to claim 13, wherein at least one of the optical output signal lines is used for providing ADM status and maintenance information to the network.

15. An ADM according to claim 9, wherein the controller is a digital signal processor running software.

16. An ADM according to claim 9, wherein the first wavelength demultiplexer and the second wavelength multiplexer are integral parts of a first bidirectional wavelength multiplexer/demultiplexer, and wherein the second wavelength demultiplexer and the first wavelength multiplexer are integral parts of a second bidirectional wavelength multiplexer/demultiplexer.

17. An optical router for use in a fiber optic network adapted to carry wavelength division multiplexed (WDM) optical signals, the router comprising:

a plurality of input ports for connection to the network and for carrying respective optical input signals;

a plurality of output ports for connection to the network and for carrying respective optical output signals;

demultiplexing means for separating the optical input signals into respective sets of demultiplexed optical input signals;

multiplexing means for forming the output WDM optical signals from respective sets of demultiplexed optical output signals;

switch means for selectively interconnecting the demultiplexed optical input signals to the demultiplexed optical output signals; and

control means for controlling the switch according to instructions provided by dither signals embedded within the demultiplexed optical input or output signals.

18. An optical ADM (OADM) for a node of an optical WDM network, comprising:

an optical switch operable in a straight-through mapping for connecting an input fiber with an output fiber, and in a cross-over mapping for connecting said input fiber with a drop fiber and an add fiber with said output fiber;

first opto-electronic conversion means for converting a fraction of an incoming optical signal present on said input fiber into an input electrical signal; and

a control unit connected to the first opto-electronic conversion means, for extracting an input control signal comprising at least routing instructions from said input electrical signal and for operating said optical switch according to said routing instructions.

19. An OADM as claimed in claim 18, further comprising second opto-electronic conversion means for converting a fraction of an outgoing optical signal present on said output fiber into an output electrical signal;

wherein the control unit is further connected to the second opto-electronic conversion means and is operable to extract an output control signal comprising at least routing instructions from said output electrical signal and operate said optical switch according to the routing instructions in the output control signal.

20. An OADM as claimed in claim 19, further comprising a modulator connected between said optical switch and said second opto-electronic conversion means, for amplitude modulating said outgoing optical signal with an additional control signal, on instructions from said control unit, wherein said control unit sets the modulation depth for said additional control signal.

21. An OADM as claimed in claim 19, further comprising a modulator for amplitude modulating said outgoing optical signal with a phase inverted variant of said input control signal on instructions from said control unit, thereby to obtain a de-modulated variant of said outgoing optical signal.

22. An optical ADM (OADM) for a node of an optical WDM network, comprising:

an optical switch operable in a straight-through mapping for connecting an input fiber with an output fiber, and in a cross-over mapping for connecting said input fiber with a drop fiber and an add fiber with said output fiber;

first opto-electronic conversion means for converting a fraction of an incoming optical signal present on said input fiber into an input electrical signal; and

a control unit connected to the first opto-electronic conversion means, for measuring the power of the input electrical signal and for operating said optical switch according to the measured power.

23. A node for an optical dense WDM network comprising:

an optical demultiplexer for separating a multi-channel incoming signal into a plurality of incoming optical signals, each associated with an input fiber;

an optical multiplexer for combining a like plurality of corresponding outgoing optical signals, each associated with an output fiber, into a multi-channel outgoing signal;

for each respective pair of incoming-outgoing signals, an optical switch operable in a straight-through mapping for connecting said associated input fiber with said associated output fiber, and in a cross-over mapping for connecting said associated input fiber with a drop fiber and an add fiber with said associated output fiber;

first opto-electronic conversion means for converting a fraction of an incoming optical signal present on said associated input fiber into an input electrical signal; and

a control unit connected to the first opto-electronic conversion means, for extracting an input control signal comprising at least routing instructions from said input electrical signal and for operating said optical switch according to said routing instructions.