Optical waveguides – With optical coupler – Plural
Reexamination Certificate
2002-06-24
2004-09-21
Patel, Tulsidas C. (Department: 2839)
Optical waveguides
With optical coupler
Plural
Reexamination Certificate
active
06795609
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to optical networks and more particularly relates to a virtual bi-directional connection system for connecting unidirectional devices to other bi-directional devices.
BACKGROUND OF THE INVENTION
Optical communication systems are becoming increasingly widespread due mainly to the very large bandwidths they offer for carrying information. The growth and diversity of lightwave networks, such as Wavelength Division Multiplexed (WDM) and Dense WDM (DWDM) networks are placing new demands on all aspects of optical networks including, for example, capacity management and provisioning, maintenance, and reliable and robust operation.
Currently, high capacity optical networks are constructed as rings and use WDM technology to achieve high bandwidth capacities. For example, WDM ring networks are in commonly used in metropolitan area network (MAN) applications but can also be used in LANs and WANs.
Wavelength division multiplexed (WDM) optical networks are particularly desirable because of their restoration capabilities and suitability for minimizing the number of optical fibers for the interconnection of system nodes. A typical WDM optical ring network includes network elements with optical add/drop multiplexers (OADMs), whereby some optical channels are dropped, some are added and/or other channels are expressed or passed through.
In a ring topology, each ring node is connected to exactly two other ring nodes. The OADMs are used to construct a ring network whereby adjacent OADMs are connected pair wise while the network nodes are adapted to form a ring. In a ring network, any node can be reached from any other node using two physically separate paths, i.e. one traveling clockwise and one counter clockwise. This is used for providing protection against route failures. The use of at least two parallel fibers with traffic flowing in opposite directions provides restoration capabilities in the event of a fiber cut.
An Optical Add/Drop Multiplexer (OADM) functions to filter or drop one or more wavelengths transiting on the ring. The optical technologies usable for producing an OADM can be placed in two main categories, namely: (1) those using fixed filtering, whereby an OADM is produced for dropping and adding a fixed wavelength, and (2) those using tunable filtering, whereby an external control determines the wavelength of the dropped and added channel.
Normally, only a single wavelength of light is used to carry optical signals from one node to another. To increase the communications bandwidth of the network, however, it is common to transmit light signals having multiple wavelengths. Additional signal channels can be added using well-known DWDM techniques wherein each channel corresponds to a different wavelength of light.
As is common practice in DWDM optical networks, OADMs are used to drop, add or express one or more optical channels. The OADM comprises a drop module adapted to generate a drop channel from the multi-wavelength input signal and an add module adapted to add a channel to the multi-wavelength output signal.
Many of the optical based devices and components used to construct optical networks function to process an input optical signal to generate an output optical signal. Both input and output optical signals (i.e. ingress and egress signals) comprise separate signals for both transmit and receive directions. A diagram of an example prior art optical networking rack having a plurality of optical networking cards is shown in FIG.
1
. The optical card cage, generally referenced
10
, comprises a plurality of slots for optical circuit cards. Two are shown to illustrate the typical connections that occur between processing cards. Bi-directional processing cards
12
,
14
, labeled circuit card A and circuit card B, comprise input ports
16
and output ports
22
. The input port comprises individual transmit (Tx)
18
and receive (Rx)
20
ports. Similarly, the output port
22
comprises individual transmit
24
and receive
26
ports.
To connect one processing card to another, a pair of cables
28
,
30
is used to connect the transmit and receive ports from the output port of one card to the input port of the card in the downstream processing path. More particularly, one cable
28
functions to connect the output transmit port of one card to the input receive port of the downstream card. The second cable
30
functions to connect the output receive port of one card to the input transmit port of the downstream card. In this manner, the various bi-directional optical processing cards are connected together.
One way to connect the ports from one card to another is to use individual optical fiber cables for each pair of connections. Great care must be given to connecting each cable to the correct port An alternative is to use a special paired cable that is keyed on each end. A diagram of a prior art bi-directional optical cable including keyed transmit and receive optical fiber connections is shown in FIG.
2
. The cable, generally referenced
40
, comprises keyed connectors
44
on each end of a pair of optical fiber cables
46
,
48
. The cables are crossed to insure that a transmit port is connected to a receive port and vice versa. A key
44
comprising a tab or other keying mechanism is used to guarantee that the orientation of the cable is correct when a user connects the cable to the port
A block diagram of example prior art bi-directional optical circuit cards connected together via a keyed cable comprising transmit and receive fibers is shown in FIG.
3
. The example system, generally referenced
50
, comprises two optical circuit cards
52
, labeled circuit card A and circuit card B, connected via keyed optical pair cable
60
. Each circuit card is a bi-directional processing circuit card having a processing circuit
56
, an input port
54
and output port
58
. Each port further comprises transmit and receive connections. During installation of the cards, a user manually connects the output port of circuit card A to the input port of circuit card B. To insure the correct orientation of the connections, the keyed cable is used which forces the user to properly connect the ports together. As long as a keyed cable is used, the transmit port of one card will always be connected to the receive port of the other card. Likewise, the receive port of one card will always be connected to the receive port of the other card.
A problem arises, however, when connecting unidirectional processing cards to other processing cards in the system. The problem is that unidirectional cards only process signals in one direction. These types of cards only have a single input and output which force the user to apply great care when connecting them in a system. This problem is illustrated in
FIG. 4
which shows a block diagram of several prior art optical circuit cards that include both bi-directional and unidirectional devices.
The system, generally referenced
70
, comprises two bi-directional processing cards
72
, labeled circuit card A and circuit card B, connected to a unidirectional processing card
80
. Circuit cards A and B comprise a processing circuit
78
and input ports
74
and output ports
76
, each comprising transmit and receive connections. The unidirectional card in this example is an amplifier card having only an input receive port
84
connected to the output transmit port of circuit card A via optical cable
88
and an output transmit port
86
connected to the input receive port of circuit card B via optical cable
90
.
Since the amplifier card functions to only process the signal output of card A the input transmit signal from circuit card B is connected directly to the output receive port of circuit card A via optical cable
92
. Thus, cable
92
is connected so as to bypass the amplifier card altogether. A problem with this arrangement, however, is that standard keyed optical cables cannot be used since the amplifier card does not process optical signals in both directions. Thus, great care must be exercise
Hendell Erik
Lichtman Eyal
Atrica Ireland Limited
Patel Tulsidas C.
Zaretsky Howard
Zaretsky & Associates PC
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