System for dealing with faults in an optical link

• US 6,545,779 B1
• Filed: 07/26/2000
• Issued: 04/08/2003
• Est. Priority Date: 10/29/1996
• Status: Expired due to Fees

• Current Assignee: EC-Optics Technology Inc.
• Original Assignee: Chorum Technologies, Inc.
• Inventors: Liu, Jian-Yu, Wu, Kuang-Yi
• Primary Examiner(s): PASCAL, LESLIE C
• Application Number:
  US09/625,780
• Time in Patent Office: 986 Days
• Field of Search: 359/110, 359/124, 359/127, 359/161, 370/227, 370/228
• US Class Current: 398/14
• CPC Class Codes: G02B 6/272 comprising polarisation means for beam splitting and combining
• CPC Class Codes: G02B 6/29302 based on birefringence or polarisation, e.g. wavelength dependent birefringence, polarisation 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 6/29395 configurable, e.g. tunable or reconfigurable switching G02B6/35
• CPC Class Codes: G02B 6/29397 Polarisation insensitivity
• CPC Class Codes: G02F 1/31 Digital deflection, i.e. optical switchingG02F1/33 takes precedence
• CPC Class Codes: H04B 10/032 using working and protection systems H04J14/0287 takes precedence
• CPC Class Codes: H04J 14/0208 Interleaved arrangements
• CPC Class Codes: H04J 14/0209 Multi-stage arrangements, e.g. by cascading multiplexers or demultiplexers
• CPC Class Codes: H04J 14/0212 using optical switches or wavelength selective switches [WSS]
• CPC Class Codes: H04J 14/0213 Groups of channels or wave bands arrangements
• CPC Class Codes: H04J 14/0279 WDM point-to-point architectures
• CPC Class Codes: H04J 14/0283 WDM ring architectures
• CPC Class Codes: H04J 14/0289 Optical multiplex section protection
• CPC Class Codes: H04J 14/0291 Shared protection at the optical multiplex section (1:1, n:m)
• CPC Class Codes: H04Q 11/0003 Details
• CPC Class Codes: H04Q 11/0005 Switch and router aspects
• CPC Class Codes: H04Q 2011/0026 using free space propagation (e.g. lenses, mirrors)
• CPC Class Codes: H04Q 2011/0032 using static wavelength routers (e.g. arrayed waveguide grating router [AWGR] )
• CPC Class Codes: H04Q 2011/0035 using miscellaneous components, e.g. circulator, polarisation, acousto/thermo optical

Abstract

A system for dealing with faults in wavelength division multiplexed (WDM) optical communications between two terminals connected by at least two optical fibers monitors the status of communications over both optical fibers. If both optical fibers are operating normally, a first set of channels is routed over the first optical fiber and a second set of channels (which is mutually exclusive of the first set of channels) is routed over the second optical fiber. However, if a fault is detected in either optical fiber, the first terminal combines the first and second sets of channels and routes the combined channels over the remaining optical fiber to the second terminal. The second terminal separates the combined channels to recreate the first and second sets of channels. Wavelength slicers can be used to multiplex and demultiplex the channels at both terminals. This architecture allows the first and second sets of channels to be interdigitally spaced.

Claims

1. An optical communications system for communicating wavelength division multiplexed (WDM) signals containing a first set of channels and a second set of channels, the system comprising:

a first terminal coupled to at least a first optical fiber and a second optical fiber, the first terminal operable to;

receive the first and second sets of channels;

route the first set of channels to the first optical fiber in a normal state and a first fault state, wherein the normal state defines a condition in which both the first and second optical fibers are operating normally and the first fault state defines a condition in which the second optical fiber has a fault;

route the first set of channels to the second optical fiber in a second fault state, wherein the second fault state defines a condition in which the first fiber has a fault;

route the second set of channels to the second optical fiber in the normal state and the second fault state; and

route the second set of channels to the first optical fiber in the first fault state; and

a second terminal coupled to at least the first optical fiber and the second optical fiber, and operable to receive the first and second sets of channels.

2. The system of claim 1, wherein the first terminal comprises:

a first multiplexer operable to combine optical signals from a first input port and a second input port, wherein the first input port receives the first set of channels;

a second multiplexer operable to combine optical signals from a first input port and a second input port, wherein the second input port receives the second set of channels;

a first optical switch operable to selectively route the combined optical signals from the first multiplexer to the first optical fiber in the normal state and the first fault state, and to the first input port of the second multiplexer in the second fault state; and

a second optical switch operable to selectively route the combined optical signals from the second multiplexer to the second optical fiber in the normal state and the second fault state, and to the second input port of the first multiplexer in the first fault state.

3. The system of claim 1, wherein the second terminal comprises:

a first demultiplexer operable to separate optical signals from an input port into a first set of channels at a first output port and a second set of channels at a second output port;

a second demultiplexer operable to separate optical signals from an input port into a first set of channels at a first output port and a second set of channels at a second output port;

a third optical switch operable to selectively route the channels from the first optical fiber to the input port of the first demultiplexer in the normal state and the first fault state, and selectively routing the first set of channels from the first output port of the second demultiplexer to the input port of the first demultiplexer in the second fault state; and

a fourth optical switch operable to selectively route the channels from the second optical fiber to the input port of the second demultiplexer in the normal state and the second fault state, and selectively routing the second set of channels from the second output port of the first demultiplexer to the input port of the second demultiplexer in the first fault state.

4. The system of claim 1, further comprising a controller operable to monitor the status of the first and second optical fibers, the controller defining the normal state, the first fault state, and the second fault state.

5. An optical communications terminal, comprising:

a first multiplexer comprising a first input port and a second input port;

a second multiplexer comprising a first input port and a second input port;

a first optical switch operable to selectively route optical signals received from the first multiplexer to a first optical fiber in a normal state and a first fault state, and to the first input port of the second multiplexer in a second fault state, wherein;

the normal state defines a condition in which the first optical fiber and a second optical fiber are operating normally;

the first fault state defines a condition in which the second optical fiber has a fault; and

the second fault state defines a condition in which the first optical fiber has a fault; and

a second optical switch operable to selectively route optical signals received from the second multiplexer to the second optical fiber in the normal state and the second fault state, and to the second input port of the first multiplexer in the first fault state.

6. The terminal of claim 5, wherein at least one of the first multiplexer and the second multiplexer comprise a wavelength slicer.

7. The terminal of claim 6, wherein the wavelength slicer comprises:

a first polarization-dependent routing element spatially separating an input beam containing a plurality of channels into a pair of orthogonally-polarized beams;

a polarization rotator for rotating the polarization of at least one of the pair of orthogonally-polarized beams to create first and second beams having the same polarization;

a wavelength filter coupled to receive the first and second beams from the polarization rotator, the wavelength filter having a polarization-dependent optical transmission function such that the first beam decomposes into third and fourth beams with their polarizations orthogonal to each other, and the second beam decomposes into fifth and sixth beams with their polarizations orthogonal to each other, wherein the third and fifth beams carry the first set of channels at a first polarization and the fourth and-sixth beams carry the second set of channels at a second polarization, wherein the first and second polarizations are orthogonal; and

a second polarization-dependent routing element spatially routing the third and fifth beams carrying the first set of channels along a first optical path and the fourth and sixth beams carrying the second set of channels along a second optical path based on their polarizations.

8. The terminal of claim 7, wherein the wavelength filter comprises a stacked plurality of birefringent waveplates with each waveplate oriented in a predetermined direction.

9. The terminal of claim 5, wherein the first multiplexer combines optical signals from the first input port and the second input port of the first multiplexer in the first fault state.

10. The terminal of claim 5, wherein the second multiplexer combines optical signals from the first input port and the second input port of the second multiplexer in the second fault state.

11. An optical communications system providing optical communications from a first terminal to a second terminal over a first optical fiber and a second optical fiber carrying wavelength division multiplexed (WDM) signals containing a first set of channels and a second set of channels that are interdigitally spaced between said first set of channels;

said optical communications system comprising;

a controller monitoring the status of said first and second optical fibers, said controller defining a normal state in which both of said first and second optical fibers are operating normally, a first fault state in which the first optical fiber has a fault, and a second fault state in which the second optical fiber has a fault;

said first terminal comprising;

(a) a first wavelength slicer combining optical signals from a first input port and a second input port, wherein said first input port receives said first set of channels;

(b) a second wavelength- slicer combining optical signals from a first input port and a second input port, wherein said second input port receives said second set of channels;

(c) a first optical switch selectively routing the combined optical signals from said first wavelength slicer to said first optical fiber in the normal state and the second fault state, and to said first input port of said second wavelength slicer in the first fault state; and

(d) a second optical switch selectively routing the combined optical signals from said second wavelength slicer to said second optical fiber in the normal state and the first fault state, and to said second input port of said first wavelength slicer in the second fault state; and

said second terminal having;

(a) a third wavelength slicer separating optical signals from an input port into a first set of channels at a first output port and a second set of channels at a second output port;

(b) a fourth wavelength slicer separating optical signals from an input port into a first set of channels at a first output port and a second set of channels at a second output port;

(c) a third optical switch selectively routing the channels from the first optical fiber to said input port of said third wavelength slicer in the normal state and the second fault state, and selectively routing said first set. of channels from said first output port of said fourth wavelength slicer to said input port of said third wavelength slicer in the first fault state; and

(d) a fourth optical switch selectively routing the channels from the second optical fiber to said input port of said fourth wavelength slicer in the normal state and the first fault state, and selectively routing said second set of channels from said second output port of said third wavelength slicer to said input port of said fourth wavelength slicer in said second fault state;

wherein at least one of said wavelength slicers comprises;

(a) a first polarization-dependent routing element spatially separating an input beam containing a plurality of channels into a pair of orthogonally-polarized beams;

(b) a polarization rotator for rotating the polarization of at least one of said pair of orthogonally-polarized beams to create first and second beams having the same polarization;

(c) a wavelength filter coupled to receive said first and second beams from said polarization rotator, said wavelength filter operable to process the first and second beams to generate third, fourth, fifth, and sixth beams, wherein said third and fifth beams carry said first set of channels at a first polarization and said fourth and sixth beams carry said second set of channels at a second polarization, wherein said first and second polarizations are orthogonal; and

(d) a second polarization-dependent routing element spatially routing said third and fifth beams carrying said first set of channels along a first optical path and said fourth and sixth beams carrying said second set of channels along a second optical path based on their polarizations.