Dense WDM optical multiplexer and demultiplexer

• US 6,281,997 B1
• Filed: 09/11/1997
• Issued: 08/28/2001
• Est. Priority Date: 09/11/1997
• Status: Expired due to Term

• Current Assignee: Ciena Corporation
• Original Assignee: Ciena Corporation
• Inventors: Alexander, Stephen B., Archambault, Jean-Luc, Mizrahi, Victor, Yaffe, Henry H.
• Primary Examiner(s): Pascal, Leslie
• Assistant Examiner(s): Phan, Hanh
• Application Number:
  US08/927,781
• Time in Patent Office: 1,447 Days
• Field of Search: 359/124, 359/127, 359/130
• US Class Current: 398/87
• CPC Class Codes: G02B 6/12019 characterised by the optical interconnection to or from the AWG devices, e.g. integration or coupling with lasers or photodiodes coupling integrated waveguide to fibre G02B6/30, to optoelectronic element G02B6/42; monolithic integration of integrated waveguides with other optical elements G02B6/12004
• CPC Class Codes: G02B 6/29317 Light guides of the optical fibre type
• CPC Class Codes: G02B 6/29355 Cascade arrangement of interferometers
• CPC Class Codes: G02B 6/29361 Interference filters, e.g. multilayer coatings, thin film filters, dichroic splitters or mirrors based on multilayers, WDM filters
• CPC Class Codes: G02B 6/2938 for multiplexing or demultiplexing, i.e. combining or separating wavelengths, e.g. 1xN, NxM
• CPC Class Codes: H04J 14/02 Wavelength-division multiplex systems
• CPC Class Codes: H04J 14/0204 Broadcast and select arrangements, e.g. with an optical splitter at the input before adding or dropping
• CPC Class Codes: H04J 14/0209 Multi-stage arrangements, e.g. by cascading multiplexers or demultiplexers
• CPC Class Codes: H04J 14/0213 Groups of channels or wave bands arrangements

Abstract

In accordance with the present invention, optical channels to be demultiplexed are supplied to first and second fibers via an optical splitter. Low loss interference filters, for example, coupled to the first and second optical fibers, select respective groups of channels. Each group of channels is next demultiplexed with sub-demultiplexers into individual channels, each of which is then sensed with a corresponding photodetector. Although the optical splitter introduces an optical power loss at the input to the demutiplexer, the interference filters and sub-demultiplexer create little additional loss. As a result, the total power loss associated with the present invention is significantly less than that obtained with a conventional n channel demultiplexer based on a 1×n splitter. Accordingly, large numbers of channels, e. g., in excess of forty can be readily demultiplexed and detected.

Claims

1. An optical device, comprising:

an optical splitter having an input and first and second outputs, said input for coupling to an input optical path, said input optical path carrying a plurality of optical channels, each of said plurality of optical channels having a respective wavelength, said first output being coupled to a first output optical path, and said second output being coupled to a second output optical path, said first and second output optical paths carrying said plurality of optical channels;

a first plurality of optical filtering elements coupled to said first output optical path, said first plurality of optical filtering elements respectively selecting first groups of said plurality of optical channels, each of said first groups of optical channels being supplied on a corresponding one of a first plurality of common outputs, each of said first plurality of common outputs being associated with a respective one of said first plurality of optical filtering elements;

a second plurality of optical filtering elements coupled to said second output optical path, said second plurality of optical filtering elements respectively selecting second groups of said plurality of optical channels, said firs- groups of optical channels being different than said second groups of optical channels, each of said second groups of optical channels being supplied on a corresponding one of a second plurality of common outputs, each of said second plurality of common outputs being associated with a respective one of said second plurality of optical filtering elements;

a first plurality of sub-demultiplexers respectively coupled to each of said first plurality of common outputs associated with each of said first plurality of filtering elements, each of said first plurality of sub-demultiplexers having a plurality of outputs, each presenting a respective channel associated with a corresponding one of said first groups of said plurality of channels; and

a second plurality of sub-demultiplexers respectively coupled to each of said second plurality of common outputs associated with each of said second plurality of filtering elements, each of said second plurality of sub-demultiplexers having a plurality of outputs, each presenting a respective channel associated with a corresponding one of said second groups of plurality of channels.

2. An optical device in accordance with claim 1, wherein said optical splitter comprises a waveguide doped with an optically active material.

3. An optical device in accordance with claim 1, wherein said splitter is a first splitter and at least one of said first optical filtering elements has an output port for outputting one of said first groups of said plurality of optical channels, at least one of said first plurality of sub-demultiplexers comprising:

a second splitter having an input coupled to said output port and a plurality of outputs; and

a plurality of optical selectors, each respectively coupled to a corresponding one of said plurality of outputs of said second splitter, each optical selector outputting at least a corresponding one of optical channels within said one of said first groups of said plurality of optical channels.

4. An optical device in accordance with claim 3, wherein said second splitter comprises an optical waveguide doped with an optically active material.

5. An optical device in accordance with claim 3, wherein each of said plurality of optical selectors comprises:

an optical circulator having a first port coupled to a corresponding one of said plurality of outputs of said second splitter, a second port, and a third port, said one of said first groups of said plurality of optical channels being received at said first port and being directed toward said second port;

a Bragg grating coupled to said second port having a first reflectivity at a wavelength associated with an optical channel within said one of said first groups of said plurality of optical channels greater than a second reflectivity associated with remaining optical channels of said one of said first groups of said plurality of optical channels, said one of said first groups of said plurality of optical channels being output from said second port and supplied to said Bragg grating, said Bragg grating substantially reflecting said optical channel back to said second port while substantially transmitting said remaining channels of said one of said first groups of said plurality of optical channels; and

a photodetector coupled to said third port, said one of said first group of channels being directed from said second port to said third port, said photodetector sensing said optical channel output from said third port.

6. An optical device in accordance with claim 5, wherein each of said plurality of optical selectors comprises a feedback circuit coupled to said Bragg grating for adjusting said in-Bragg grating to have a peak reflectivity at said one of said first group of channels.

7. An optical device in accordance with claim 1, wherein at least one of said first plurality of optical sub-demultiplexers further comprising a plurality of selectors, each of which is respectively coupled to a corresponding one of said plurality of outputs of said first plurality of optical filtering elements, each of said plurality of selectors comprising:

an optical coupler having a first port coupled to said corresponding one of said plurality of outputs of said at least one of said first plurality of optical sub-demultiplexers, a second port and a third port;

a Bragg grating coupled to said second port of said optical coupler, said Bragg grating receiving one of said first groups of said plurality of optical channels via said first and second ports and reflecting an optical channel within said one of said first groups of said plurality of optical channels back to said second port of said optical coupler; and

a photodetector coupled to said third port of said optical coupler, said optical coupler transmitting said corresponding one of said first groups of said plurality of optical channels through said third port to said photodetector, said photodetector sensing said optical channel.

8. An optical device in accordance with claim 7, wherein each of said plurality of selectors comprises a feedback circuit coupled to said Bragg grating for adjusting said Bragg grating to have a peak reflectivity at a wavelength associated with said optical channel.

9. An optical device in accordance with claim 3, wherein said second optical filtering element having an output port for outputting said second group of channels, said second optical sub-demultiplexer comprising:

a third splitter having an input coupled to said output port of said second optical filtering element, and a plurality of outputs corresponding in number to said second group of channels; and

another plurality of optical selectors, each respectively coupled to a corresponding one of said plurality of outputs of said third splitter, each optical selector selecting a corresponding one of said another group of channels.

10. An optical device in accordance with claim 1, wherein said first and second output optical paths are configured to accommodate additional filtering elements.

11. An optical device in accordance with claim 1, wherein said first and second pluralities of filtering elements comprise interference filters.

12. An optical device in accordance with claim 1, wherein said first and second pluralities of filtering elements comprise a plurality of optical circulators each respectively coupled to a corresponding one of a plurality of Bragg gratings.

13. An optical device in accordance with claim 1, further comprising an optical amplifier coupled to said input of said optical splitter.

14. An optical device in accordance with claim 1, wherein said first and second pluralities of sub-demultiplexers include a plurality of cascaded Mach-Zehnder interferometers.

15. An optical device in accordance with claim 1, wherein said first and second pluralities of sub-demultiplexers include a plurality of arrayed waveguide gratings.

16. An optical device in accordance with claim 1, wherein said first and second pluralities of sub-demultiplexers include a plurality of fiber optic couplers.

17. An optical device in accordance with claim 1, wherein said first groups alternate with said second groups.

18. An optical device, comprising:

an arrayed waveguide grating (AWG) having an input and a plurality of outputs, said input being configured to be coupled to an optical communication path carrying a plurality of first optical channels, each at a respective wavelength, said arrayed waveguide grating supplying a respective one of a plurality of second optical channels selected from said plurality of first optical channels, and undesired optical signals at each of said plurality of outputs; and

a plurality of filtering elements each having an input port coupled to a respective one of said plurality of outputs of said arrayed waveguide grating and an output port, each of said plurality of filtering elements supplying said respective one of said plurality of second optical channels at said output port while reducing said undesired optical signals

wherein each said plurality of filtering elements comprises;

an optical coupler having a first port coupled to said input port, a second port and a third port;

an in-fiber Bragg grating coupled to said second port of said optical coupler, said in-fiber Bragg grating receiving said respective one of said plurality of second optical channels via said first and second ports and reflecting said respective one of said plurality of second optical channels back to said second port of said optical coupler for output through said third port of said optical coupler; and

a feedback circuit coupled to said in-fiber Bragg grating for adjusting said in-fiber Bragg grating to have a peak reflectivity at said respective one of said plurality of second optical channels.

19. An expandable optical channel demultiplexer, comprising:

an optical splitter having an input and first and second outputs, said input for coupling to an input optical path, said input optical path carrying a plurality of optical channels, each of said plurality of optical channels having a respective wavelength, said first output being coupled to a first output optical path, and said second output being coupled to a second output optical path, said first and second output optical paths carrying said plurality of optical channels;

a first plurality of optical filtering elements coupled to said first output optical path, said first plurality of optical filtering elements respectively selecting first groups of said plurality of optical channels, each of said first groups of optical channels being supplied on a corresponding one of a first plurality of common outputs, each of said first plurality of common outputs being associated with a respective one of said first plurality of optical filtering elements;

a second plurality of optical filtering elements coupled to said second output optical path, said second plurality of optical filtering elements respectively selecting second groups of said plurality of optical channels, each of said second groups of optical channels being supplied on a corresponding one of a second plurality of common outputs, each of said second plurality of common outputs being associated with a respective one of said second plurality of optical filtering elements, said first groups of optical channels being different than said second groups of optical channels, said first and second output optical paths being configured to accommodate coupling to a plurality of additional optical filtering elements;

a first plurality of sub-demultiplexers respectively coupled to each of said plurality of first common outputs associated with each of said first plurality of filtering elements, each of said first plurality of sub-demultiplexers having a plurality of outputs, each presenting a respective channel associated with a corresponding one of said first groups of said plurality of channels; and

a second plurality of sub-demultiplexers respectively coupled to each of said plurality of second common outputs associated with each of said second plurality of filtering elements, each of said second plurality of sub-demultiplexers having a plurality of outputs, each presenting a respective channel associated with a corresponding one of said second groups of plurality of channels.

20. An optical device comprising:

a plurality of input lines, each carrying a respective channel at a unique wavelength;

a first optical combiner coupled to first selected ones of said plurality of input lines, said first optical combiner supplying a first group of channels on a first output line, said first group of channels corresponding to channels carried by said first selected ones of said plurality of input lines;

a second optical combiner coupled to second selected ones of said plurality of input lines, said second optical combiner supplying a second group of channels on a second output line, said second group of channels corresponding to channels carried by said second selected ones of said plurality of input lines;

a filtering element having inputs coupled to said first and second output lines and an output carrying said first and second groups of channels; and

a coupling element having a first input coupled to said output of said filtering element and receiving said first and second groups of channels, a second input receiving a third group of channels, and an output supplying said first, second and third groups of channels.