WO2000057583A1

WO2000057583A1 - Optical matrix protection system

Info

Publication number: WO2000057583A1
Application number: PCT/US2000/007967
Authority: WO
Inventors: Krishna Bala; John Gamelin; W. John Tomlinson
Original assignee: Tellium, Inc.
Priority date: 1999-03-24
Filing date: 2000-03-24
Publication date: 2000-09-28
Also published as: US6307653B1

Abstract

An optical matrix protection system (200) is described. Optical signals that are cross-connected by a NxN matrix switch (100) are routed through alternative protection paths (210, 212) using an optical matrix protection system (200). The optical matrix protection system (200) includes a Nx1 optical switch (110-1 to 110-N) and a 1xN optical switch (120-1 to 120-N). An input port of the 1xN optical switch is coupled to an output port of the Nx1 optical switch. Input ports of the Nx1 optical switch are connected to a plurality of 2x1 optical switches (220-1 to 220-N), which selectively switch input optical signals to either the NxN matrix switch or to the Nx1 optical switch. Output ports of the 1xN optical switch (120-1 to 120-N) are connected to a plurality of 2x1 (230-1 to 230-N), which selectively switch optical signals from wether the NxN matrix switch or the 1xN optical switch to an output line.

Description

OPTICAL MATRIX PROTECTION SYSTEM

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to optical matrix switches, and more

specifically, to protection mechanisms for optical matrix switches.

Discussion of the Related Art

Fiber optic technology has continued to expand across today's data

communication networks. Having replaced many of the long-haul connections and

other inter-office facilities, fiber optics technology has begun to replace transmission

facilities and network elements used in intra-office communication. One of the

primary network elements used in intra-office communication is the digital cross-

connect. Generally, digital cross-connects link any of several incoming lines to any of

several outgoing lines. Today's digital cross-connects switch digital signals on the

electrical level. Thus, a fiber optic terminal that receives an optical signal must

convert the optical signal to an electrical signal before it sends it to the digital cross- connect.

Optical cross-connects are envisioned as the replacement for the conventional

digital cross-connect. Optical cross-connects switch signals at the optical level and

therefore obviate the need for optical-to-electrical conversions. The elimination of

unnecessary components can lower the overall cost of the network while also

increasing the reliability of the network. Reliability is a paramount concern to

network planners and bandwidth providers. For optical cross-connects to be considered as viable replacements for digital cross-connects, the optical cross-

connects must meet reasonable reliability expectations.

SUMMARY OF THE INVENTION

The present invention addresses the reliability concerns of optical matrix

switches by providing an optical matrix protection system that enables a failed path in

an optical matrix switch to be re-routed. The optical matrix protection system of the

present invention includes a Nxl optical switch and a lxN optical switch, wherein an

input port of the lxN optical switch is coupled to an output port of the Nxl optical

switch.

The inputs to the Nxl optical switch are provided by output ports of a plurality

of 1x2 optical switches. The 1x2 optical switches are positioned such that an input

port of a 1x2 optical switch is coupled to an input line carrying an optical signal, a

first output port of the 1x2 optical switch is coupled to one of N input ports of a NxN

switch, and a second output port of the 1x2 optical switch is coupled to one of N input

ports of the Nxl optical switch.

The N outputs of the lxN optical switch are coupled to input ports of a

plurality of 2x1 optical switches. The 2x1 optical switches are positioned such that an

output port of a 2x1 optical switch is coupled to an output line, a first input port of the

2x1 optical switch is coupled to one of N output ports of the NxN switch, and a

second input port of the 2x1 optical switch is coupled to one of N output ports of the

lxN optical switch. Upon a failure in a path connecting an optical input port and an optical output

port of the NxN switch, the failed path is re-routed through the Nxl optical switch and

the lxN optical switch using one of the plurality of 1x2 optical switches and one of

the plurality of 2x1 optical switches.

It is to be understood that both the foregoing general description and the

following detailed description are exemplary and explanatory and are intended to

provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS

The accompanying drawings, which are included to provide a further

understanding of the invention and are incorporated in and constitute a part of this

specification, illustrate embodiments of the invention that together with the

description serve to explain the principles of the invention.

In the drawings:

.Figure 1 illustrates an embodiment of an optical matrix switch; and

Figure 2 illustrates an optical matrix protection system according to the

present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of the

present invention, examples of which are illustrated in the accompanying drawings.

Optical matrix switches will have a valuable role in the continuing evolution

of today's communication networks. The replacement of conventional electrical digital cross-connects with optical cross-connects will eliminate some of the

unnecessary complexity in connectivity of network elements in an intra-office

network. By enabling the switching of signals at the optical level, optical cross-

connects will eliminate the need for back-to-back optical-to-electrical and electrical-

to-optical conversions. The elimination of these unnecessary functions will

significantly lower the overall cost of the network.

One example of an optical matrix switch is illustrated in Fig. 1. Optical matrix

switch 100 is operative to selectively connect any one of N input ports to any one of N

output ports. Optical matrix switch 100 includes N IxN optical switches 110-1 to

110-N and N Nxl optical switches 120-1 to 120-N. The N input ports are connected

to the N IxN optical switches and the N output ports are connected to the N Nxl

optical switches. As illustrated in part, input port 1 is connected to IxN optical switch

110-1, input port 2 is connected to IxN optical switch 110-2, and input port N is

connected to IxN optical switch 110-3. Similarly, output port 1 is connected to Nxl

optical switch 120-1, output port 2 is connected to Nxl optical switch 120-2, and

output port N is connected to Nxl optical switch 120-N.

Generally the IxN and Nxl optical switches are mechanically activated optical

switches. These mechanically activated optical switches are programmable and

designed to repeatedly connect a single input (output) port to any of N (e.g., 16)

output (input) ports. In one embodiment, the IxN (Nxl) optical switches select

input/output channels by aligning a common input (output) port with one of the N

output (input) ports. The use of collimating lenses improves the insertion loss and

repeatability of the optical switch. Control of the IxN and Nxl optical switches is effected through an electronic interface. An example of a IxN switch is the SN Series

Programmable lxΝ Optical Fiber Switch manufactured by JDS Fitel, Inc.

Individual output ports of a lxΝ optical switch are connected to one of the

Νxl switches. For example, output port 1 of lxΝ optical switch 110-1 is connected to

input port 1 of Νxl optical switch 120-1, output port 2 of lxΝ optical switch 110-1 is

connected to input port 1 of Νxl optical switch 120-2, and output port Ν of lxΝ

optical switch 110-1 is connected to input port 1 of Νxl optical switch 120-Ν.

Similarly, output port 1 of IxN optical switch 110-2 is connected to input port 2 of

Nxl optical switch 120-1, output port 2 of IxN optical switch 110-2 is connected to

input port 2 of Nxl optical switch 120-2, and output port N of IxN optical switch

110-2 is connected to input port 2 of Nxl optical switch 120-3.

By using N IxN optical switches and N Nxl optical switches, it is possible to

achieve a NxN switch in which the complexity of the switch is not strongly dependent

on N. Since any signal goes through just two optical switches, optical losses for the

signal passing through the NxN optical switch can be attractively low. The fiber

connectivity, on the other hand, is strongly dependent upon N as N² fibers are

required to connect the N IxN optical switches and the N Nxl optical switches. Thus

for a 16x16 switch having 16 1x16 optical switches and 16 16x1 optical switches, 256

fibers are required to implement the NxN optical switch.

One major concern of optical switch 100 is the reliability of the mechanical

actuators that are used to control the switching of the IxN and Nxl optical switches.

Although the IxN and Nxl optical switches are designed for frequent changes in

connectivity, each of the IxN and Nxl optical switches represent a single point of failure that can disrupt a significant amount of bandwidth traffic. For example,

assume that input port 2 of NxN switch 100 is desired to be connected to output port 1

of NxN switch 100. To implement this connection, IxN optical switch 120 would

connect its input port to output port 1 and Nxl optical switch 112 would connect its

output port to input port 2. If the mechanical actuator in either IxN optical switch

110-2 or Nxl optical switch 120-1 fails, the connection between input port 2 and

output port 1 of NxN switch 100 will fail.

The consequence of these single points of failures is often unacceptably large.

Any single optical fiber can carry bandwidth in the gigabit range. The downtime

caused while repair of any one of the IxN and Nxl optical switches can result in

serious consequence in the relationship between a service provider and their

bandwidth customers.

The present invention provides a protection system for a NxN switch that

enables a service provider to repair a failed element within an optical switch without

incurring substantial downtime in an affected connection. The optical matrix

protection system of the present invention is illustrated in Fig. 2 and is applied to the

optical matrix switch 100 described above with reference to Fig. 1.

Optical matrix protection system 200 includes optical matrix switch 100. In

addition to the N IxN optical switches 110-1 to 110-N and the N Nxl optical switches

120-1 to 120-N, optical matrix protection system 200 also includes 1x2 optical

switches 220-1 to 220-N, 2x1 optical switches 230-1 to 230-N, Nxl optical switch

210, and IxN optical switch 212. As will be described below, optical matrix protection system 200 enables an optical signal to be re-routed upon a failure in any

one of the optical switches within optical matrix switch 100.

As illustrated, 1x2 optical switches 220-1 to 220-N are connected to the input

ports of optical matrix switch 100, while 2x1 optical switches 230-1 to 230-N are

connected to the output ports of optical matrix switch 100. More specifically, 1x2

optical switches 220-1 to 220-N are used to selectively connect an input signal to

either an input port of optical matrix switch 100 or to an input port of Nxl optical

switch 210. In this manner, input signals that are ordinarily sent to an input port of

optical matrix switch 100 can be re-routed to Nxl optical switch 210.

Nxl optical switch 210 selectively connects one of its N input ports to the

single output port. This single output port is connected to the single input port of IxN

optical switch 212. IxN optical switch 212 selectively connects its single input port

to one of the N output ports. Each of these N output ports are connected to one of the

2x1 optical switches 230-1 to 230-N. 2x1 optical switches 230-1 to 230-N are used to

selectively connect one of either an output port of optical matrix switch 100 or an

output port of IxN optical switch 220 to its output port. The output ports of 2x1

optical switches 230-1 to 230-N represent the intended output of optical matrix switch

100.

The following example illustrates the operation of optical matrix protection

system 200. In case of a failure on a single path from input port i to output porty of

optical matrix switch 100, the 1x2 optical switch connected to input port /^' and the 2x1

optical switch connected to output port/ are switched to re-route the optical signal.

The re-routed signal is then carried through input port i of Nxl optical switch 210 and output port j of IxN optical switch 212. Thus, the optical signal is re-routed from

input port / to output port j, bypassing the failed path through optical matrix switch

100.

The provision of a protection path enables a service provider to repair failed

optical switch elements in optical matrix switch 100 without incurring substantial

downtime. This increase in the reliability of the optical matrix switch 100 is critical

in altering the perception of those that are considering inclusion of an optical matrix

switch within their network.

It should be noted that the optical matrix protection system of the present

invention can also be used in connection with a cross-connect having optical

input/output ports and an electrical switch matrix. Although the internal switch

matrix would be distinct from the optical matrix switch 100 illustrated in Fig. 1, the

provision of a protection path using the optical matrix protection system 200 would be

identical.

In addition to providing an alternate protection path for an optical matrix

switch, the optical matrix protection system 200 of the present features has additional

advantageous features in connection with the maintenance and repair process. First,

the 1x2 optical switches 220-1 to 220-N can serve as dumps to prevent signals from

being sent to incorrect output ports during switch reconfiguration. Second, the 2x1

optical switches 230-1 to 230-N can be replaced by 2x2 optical switches to effect a

detection scheme. The additional output port of the 2x2 optical switches can be used

to monitor signal levels before putting a signal on the intended output line. Finally, it should be noted that the 1x2 optical switches 220-1 to 220-N and

2x1 optical switches 230-1 to 230-N can also be replaced by optical splitters and

combiners. As noted, an advantage of optical matrix switch 100 is that the passage of

an optical signal through only two optical switches (i.e., IxN and Nxl) results in low

losses. The inclusion of two additional switches (i.e., 1x2 and 2x1) to effect the

optical matrix protection system of the present invention results in additional signal

loss. This signal loss should be acceptable. However, although the loss

characteristics are favorable, the 1x2 optical switches 220-1 to 220-N and 2x1 optical

switches 230-1 to 230-N do represent single points of failure. These single points of

failure can be reduced using passive optical elements (i.e., optical splitters and

combiners) which are not driven by mechanical actuators. Since passive optical

elements have greater loss as compared to 1x2 and 2x1 optical switches, there is a

tradeoff between reliability and loss characteristics.

The decision to replace 1x2 optical switches 220-1 to 220-N with optical

splitters and the decision to replace 2x1 optical switches 230-1 to 230-N with optical

combiners are independent decisions. For example, optical switches can be used on

one side of optical matrix switch 100 and passive optical components on the other

side. If passive components are used on both sides of optical matrix switch 100, the

protection path could potentially send signals to incorrect output ports during

reconfiguration. Accordingly, in one embodiment, an optical blocking switch is

included in the path between Nxl optical switch 210 and IxN optical switch 212 to

block any incorrect signals during reconfiguration. While the invention has been described in detail and with reference to specific

embodiments thereof, it will be apparent to one skilled in the art that various changes

and modifications can be made therein without departing from the spirit and scope

thereof. Thus, it is intended that the present invention cover the modifications and

variations of this invention provided they come within the scope of the appended

claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. An optical matrix protection system, comprising:

a Nxl optical switch;

a IxN optical switch, an input port of said IxN optical switch being coupled to

an output port of said Nxl optical switch;

a first plurality of optical elements, wherein an i'^h one of said first plurality of

optical elements has an input port coupled to an i'^h one of a plurality of input lines, a

first output port of said i'^h one of said first plurality of optical elements being coupled

to input port i of a NxN switch, a second output port of said i'^h one of said first

plurality of optical elements being coupled to input port i of said Nxl optical switch;

and

a second plurality of optical elements, wherein af^h one of said second

plurality of optical switches has an output port coupled to aj'^h one of a plurality of

output lines, a first input port of said/* one of said second plurality of optical

elements being coupled to output port/ of said NxN switch, a second input port of

said ^Λ one of said second plurality of optical elements being coupled to output port/

of said IxN optical switch,

wherein upon a failure in a path connecting an optical input port and an optical

output port of said NxN switch, said path is rerouted through said Nxl optical switch

and said IxN optical switch using one of said first plurality of optical elements and

one of said second plurality of optical elements.

2. The optical matrix protection system of claim 1 , wherein said first

plurality of optical elements comprises a plurality of 1x2 optical switches, wherein an

i'^h one of said plurality of 1x2 optical switches has an input port coupled to an i'^h one

of said plurality of input lines, a first output port of said i'^h one of said plurality of 1x2

optical switches being coupled to input port i of said NxN switch, a second output

port of said i'^h one of said plurality of 1x2 optical switches being coupled to input port

of said Nxl optical switch.

3. The optical matrix protection system of claim 1 , wherein said first

plurality of optical elements comprises a plurality of optical splitters, wherein an i'^h

one of said plurality of optical splitters has an input port coupled to an /'* one of said

plurality of input lines, a first output port of said '* one of said plurality optical

splitters being coupled to input port i of a NxN switch, a second output port of said i'^h

one of said plurality of optical splitters being coupled to input port i of said Nxl

optical switch.

4. The optical matrix protection system of claim 1 , wherein said second

plurality of optical elements comprises a plurality of 2xP optical switches, wherein a

j"¹ one of said plurality of 2xP optical switches has an output port coupled to a/^Λ one

of said plurality of output lines, a first input port of said/^Λ one of said plurality of 2xP

optical switches being coupled to output port/ of said NxN switch, a second input

port of said/"¹ one of said plurality of 2xP optical switches being coupled to output

port/ of said IxN optical switch.

5. The optical matrix protection system of claim 1 , wherein said second

plurality of optical elements comprises a plurality of optical combiners, wherein a/^Λ

one of said plurality of optical combiners has an output port coupled to a/^A one of

said plurality of output lines, a first input port of said/" one of said plurality of optical

combiners being coupled to output port/ of said NxN switch, a second input port of

said/" one of said plurality of optical combiners being coupled to output port/ of said

IxN optical switch.

6. The optical matrix protection system of claim 2, wherein said second

/'" one of said plurality of 2xP optical switches has an output port coupled to a/" one

of said plurality of output lines, a first input port of said/" one of said plurality of 2xP

port of said/" one of said plurality of 2xP optical switches being coupled to output

port/ of said IxN optical switch.

7. The optical matrix protection system of claim 2, wherein said second

plurality of optical elements comprises a plurality of optical combiners, wherein a/"

one of said plurality of optical combiners has an output port coupled to a/" one of

IxN optical switch.

8. The optical matrix protection system of claim 3, wherein said second

/" one of said plurality of 2xP optical switches has an output port coupled to a/" one

port/ of said IxN optical switch.

9. The optical matrix protection system of claim 3, wherein said second

IxN optical switch.

10. The optical matrix protection system of claim 1 , wherein said NxN

switch is a NxN optical matrix switch.

11. The optical matrix protection system of claim 10, wherein said NxN

optical matrix switch comprises N IxN optical switches and N Nxl optical switches,

wherein output ports of said IxN optical switches are coupled to input ports of said

Nxl optical switches.

12. The optical matrix protection system of claim 1 , wherein said NxN

switch is an electrical switch having optical input and output ports.

13. The optical matrix protection system of claim 4, wherein said 2xP

optical matrix switches are 2x1 optical matrix switches.

14. The optical matrix protection system of claim 4, wherein said 2xP

optical matrix switches are 2x2 optical matrix switches, wherein a second output port

of a 2x2 optical matrix switch is coupled to a signal detector.

15. The optical matrix protection system of claim 7, further comprising a

blocking switch positioned between said Nxl optical switch and said IxN optical

switch.

16. A telecommunications network, comprising:

a first plurality of network elements, said first plurality of network elements

generating a first plurality of optical signals on a plurality of input lines;

a second plurality of network elements, said second plurality of network

elements operative to receive said first plurality of optical signals on a plurality of

output lines; and

an optical matrix protection system that provides connectivity between said

first plurality of network elements and said second plurality of network elements, said

optical matrix protection system including a Nxl optical switch;

a IxN optical switch, an input port of said IxN optical switch being

coupled to an output port of said Nxl optical switch;

a first plurality of optical elements, wherein an /'" one of said first

plurality of optical elements has an input port coupled to an /'" one of a

plurality of input lines, a first output port of said i"¹ one of said first plurality of

optical elements being coupled to input port i of a NxN switch, a second

output port of said i'^h one of said first plurality of optical elements being

coupled to input port i of said Nxl optical switch; and

a second plurality of optical elements, wherein a/" one of said second

plurality of optical switches has an output port coupled to a/" one of a

plurality of output lines, a first input port of said/" one of said second

plurality of optical elements being coupled to output port/ of said NxN switch,

a second input port of said/" one of said second plurality of optical elements

being coupled to output port/ of said IxN optical switch,

wherein upon a failure in a path connecting an optical input port and an

optical output port of said NxN switch, said path is rerouted through said Nxl

optical switch and said IxN optical switch using one of said first plurality of

optical elements and one of said second plurality of optical elements.

17. The telecommunications network of claim 16, wherein said first

/'" one of said plurality of 1x2 optical switches has an input port coupled to an i"' one of said plurality of input lines, a first output port of said /'" one of said plurality of 1x2

port of said /'" one of said plurality of 1x2 optical switches being coupled to input port

i of said Nxl optical switch.

18. The telecommunications network of claim 16, wherein said first

one of said plurality of optical splitters has an input port coupled to an i'^h one of said

plurality of input lines, a first output port of said i'^h one of said plurality optical

splitters being coupled to input port i of a NxN switch, a second output port of said /'"

optical switch.

19. The telecommunications network of claim 16, wherein said second

port/ of said IxN optical switch.

20. The telecommunications network of claim 16, wherein said second

plurality of optical elements comprises a plurality of optical combiners, wherein a/" one of said plurality of optical combiners has an output port coupled to a/" one of

said plurality of output lines, a first input port of said/'" one of said plurality of optical

IxN optical switch.

21. The telecommunications network of claim 17, wherein said second

port/ of said IxN optical switch.

22. The telecommunications network of claim 17, wherein said second

plurality of optical elements comprises a plurality of optical combiners, wherein a/"'

said/'" one of said plurality of optical combiners being coupled to output port/ of said

IxN optical switch.

23. The telecommunications network of claim 18, wherein said second

of said plurality of output lines, a first input port of said/'" one of said plurality of 2xP

port of said/'" one of said plurality of 2xP optical switches being coupled to output

port/ of said IxN optical switch.

24. The telecommunications network of claim 18, wherein said second

IxN optical switch.

25. The telecommunications network of claim 16, wherein said NxN

switch is a NxN optical matrix switch.

26. The telecommunications network of claim 25, wherein said NxN

Nxl optical switches.

27. The telecommunications network of claim 16, wherein said NxN

switch is an electrical switch having optical input and output ports.

28. The telecommunications network of claim 19, wherein said 2xP optical

matrix switches are 2x1 optical matrix switches.

29. The telecommunications network of claim 19, wherein said 2xP optical

matrix switches are 2x2 optical matrix switches, wherein a second output port of a

2x2 optical matrix switch is coupled to a signal detector.

30. The telecommunications network of claim 22, further comprising a

blocking switch positioned between said Nxl optical switch and said IxN optical

switch.