WDM systems and methods

A WDM optical system includes first and second WDM's including an optical link therebetween. Each WDM includes circuitry for linking multiplexer and demultiplexer circuitry to a plurality of modular elements. The modular elements include a first set of modules for converting between native protocol media signals and common format signals. A second set of modules converts between the common format signals and optical signals at separate wavelengths for communication with the multiplexers and demultiplexers. A dual path transmit and receive optical link is provided between near and far end WDM's.

FIELD OF THE INVENTION

The present invention relates to wavelength division multiplexed optical networks.

BACKGROUND OF THE INVENTION

Wavelength division multiplexed (WDM) optical networks are known where light of multiple wavelengths is spacially dispersed such that each wavelength of light is spacially separated from every other wavelength of light. A plurality of signals having wavelengths of different lengths can be combined for transmission over a single fiber optic cable. For optical transmission systems such as in a backbone network with a great demand for communication, a further increase in capacity has been found by reducing the optical frequency spacing of a plurality of signal channels to increase the degree of multiplexing. WDM processing with a higher degree of multiplexing is called dense wavelength division multiplexing (DWDM). Also, it is known in optical transmission systems where there is not a large demand for communication, the degree of multiplexing can be decreased by increasing the optical frequency spacing of a plurality of signal channels. This has the effect of reducing costs for the system components. WDM processing with a lower degree of multiplexing is called coarse wavelength division multiplexing (CWDM). In a CWDM system, inexpensive optical components can be used.

In WDM systems, and in particular CWDM systems, a variety of different media signals may be handled including coaxial, twisted pair (shielded and unshielded), and optical. WDM's including CWDM's are utilized to process these signals for transmission over fiber networks. In the case of multimode signals on fiber optic cables, WDM's can be used to process the signals for transmission on a multiplexed single cable system including a single mode fiber.

There is a need for conversion circuitry associated with the WDM's to convert the native protocol media signal (coaxial, twisted pair, multimode optical), into an appropriate signal for multichannel transmission on a single fiber optic cable. There is a further need to modularize such system components. In particular, there is a need to modularize the components of the system to address concerns that arise during initial setup, and modifications and upkeep of the system over time.

SUMMARY OF THE INVENTION

The present invention concerns a WDM optical system and method including first and second WDM's including an optical link therebetween. Preferably, the optical link includes both a transmit signal path and a receive signal path. Each WDM includes circuitry for linking a multiplexer and demultiplexer to a plurality of modular elements. The modular elements include a first set of modules for converting between native protocol media signals and common format signals, and a second set of modules for converting between the common format signals and optical signals at separate wavelengths for communication with the multiplexers and demultiplexers.

In one preferred embodiment, a WDM chassis includes a backplane including an input power port, a control signal port, and a plurality of optical interface ports for interfacing with an optical to electrical conversion module or card. Each optical interface port includes a power port, a control signal port, and at least one optical port. Each optical to electrical card includes a backplane interface portion for mating with the power port, the control signal port, and the at least one optical port of the optical interface port of the backplane. The optical to electrical cards include optical to electrical conversion circuitry for converting between common format signals and optical signals. Each optical to electrical card includes an electrical interface port including a power port, a control signal port, and at least one electrical port. The electrical interface port interfaces with an electrical to electrical conversion module or card. Each electrical to electrical card includes electrical to electrical conversion circuitry for converting between native protocol media signals and common format signals. Each electrical to electrical card includes a media interface port including at least one main signal port.

The WDM chassis includes optical signal splitters for splitting or combining of the multiplexed output and input optical signals. The splitters provide dual pathway protection between near and far ends of the optical system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now toFIG. 1, a first embodiment of a WDM system10is shown. A plurality of channels of native optical or copper media20are linked to a plurality of channels of native optical or copper media40across a multiplexed/demultiplexed optical link30over a single optical path. Near end individual channels22(represented by 16 different channels in the present embodiment,221through2216) communicate with far end channels42(represented by channels421through4216) over optical pathways36,38. As shown, pathways36,38define transmit and receive signal pathways. Near and far end WDM's32,34are used to multiplex/demultiplex the optical signals. As will be described below, WDM's32,34include modular elements utilized during assembly and also useable at later points in time for further system modification or repair.

Referring now toFIG. 2, a modified WDM system12is shown including a multiplexed/demultiplexed optical link50with dual path protection. WDM's52,54include splitting and combining functions which create dual pathways for communication between WDM's52,54. Such dual pathways are useful in case one pathway is disrupted, such as when one pathway is inadvertently severed in an underground placement. Generally, WDM's52,54are similar to WDM's32,34, except WDM's32,34do not include any splitting function.

Referring now toFIG. 3, WDM52includes circuitry for converting between native protocol media signals on channels22and the combined multiplexed optical signals on pathways56,57,58,59. WDM52includes multiplexing/demultiplexing circuitry60, hereinafter referred to as mux/demux circuitry60. Mux/demux circuitry60multiplexes the separate channels of optical signals into one signal for transmission to far end equipment. Mux/demux circuitry60also demultiplexes the one signal received from far end equipment into separate channels of optical signals. WDM52includes optical to electrical conversion circuitry90which interfaces with mux/demux circuitry60. WDM52further includes electrical to electrical conversion circuitry100which interfaces with optical to electrical conversion circuitry90. The conversion circuitry90,100converts between native protocol media circuitry and the optical signals transmitted by mux/demux circuitry60. WRDM54includes similar features, allowing for two-way communication.

In the preferred embodiment, electrical to electrical conversion circuitry100is removably connectable to mux/demux circuitry60. Further, in the preferred embodiment, optical to electrical conversion circuitry90is removably connectable to mux/demux circuitry60. In addition, it is preferred that optical to electrical conversion circuitry90is removably connectable to electrical to electrical conversion circuitry100. It is anticipated that a variety of different protocol media signals may be desired for handling by mux/demux circuitry60. Appropriate conversion circuitry is selected for communicating between electrical to electrical conversion circuitry100and optical to electrical conversion circuitry90, and also optical to electrical conversion circuitry90and mux/demux circuitry60.

One result of the removable connections between components of WDM52is that a variety of native protocol media signals can be handled with a reduced number of components. In particular, the electrical to electrical conversion circuitry100can be selected for the native protocol media signals which are anticipated for WDM52. The native protocol media signals can be converted into a common format signal such as NRZI digital format. An optical transceiver associated with optical to electrical conversion circuitry90uses the NRZI format signal to modulate a laser associated with each channel. Each laser associated with optical to electrical conversion circuitry90operates at a different wavelength. Receivers associated with the optical to electrical conversion circuitry90receive optical signals from mux/demux circuitry60and produce an NRZI format output signal which is transmitted to the electrical to electrical conversion circuitry100.

By separating the optical to electrical conversion circuitry90from the electrical to electrical conversion circuitry100, different grades of optical devices (i.e., data rates, launch power, and wavelength) can be employed as desired. Therefore, in low end applications like DS3, OC3, 10/100 M b/s Ethernet, lower cost components can be used.

Mux/demux circuitry60includes a power input port62which provides electrical power to a backplane64. Backplane64can be constructed from a circuit board including appropriate circuit paths to link power from input power62to each O/E converter card92. Backplane64includes optical couplers or interfaces66,68(such as adapters) for each O/E converter card92. Optical interfaces66,68communicate through optical signal pathways70,72to the multiplexer element74including multiplexer76or demultiplexer78. From multiplexer76and demultiplexer78, one by two splitters84,86are provided at splitter circuitry82for creating the dual optical pathways. Optical pathways77,79link multiplexer76, and demultiplexer78to the respective splitters84,86. Preferably, optical pathways36,38,56,57,58,59are single mode optical pathways.

Each O/E converter module or card92includes an optical link96,98(such as connectors) for linking to optical interfaces66,68of backplane64. An electrical interface80provides for an electrical link from backplane64to each O/E converter card92, such as for any necessary power needed by each O/E converter card92. Also, electrical interface80can link control signals handled by backplane64and communicated to each O/E converter card92.

Each E/E converter module or card102includes an electrical link106,108for communicating electrical signals with each O/E converter card92which are then converted into optical signals for transmission through mux/demux circuitry60. Each E/E converter card102includes pathways120,122for communicating native protocol media signals on channels22. An electrical link104connects between each E/E converter card102and the mated O/E converter cards92for conveying any power needed by E/E converter cards102, and for any control signals to be communicated to the E/E converter cards102.

Referring now toFIG. 4, backplane64is shown as including a card edge connector130which connects to an edge contact132of O/E converter card92. Together card edge connector130and edge contact132form the electrical link80ofFIG. 3. Fiber optic connectors134,136connect to optical interfaces66,68of back plane64wherein O/E converter card92is connectable and disconnectable with backplane64, as desired. O/E converter card92includes a circuit board140including circuitry142for converting electrical signals from E/E converter card102into optical signals for transmission at fiber optic connectors134,136. For example, DFB lasers are used on O/E converter cards92. Circuitry142of circuit board140further includes circuit pathways and elements for control and for converting any necessary power needed on O/E converter card92for signal conversion. Also, circuit pathways and elements are provided on circuit board140for linking edge contact132with card edge connector144.

Card edge connector144on O/E converter card92links to E/E converter card102by connecting to an edge contact148on E/E converter card102. E/E converter card102includes one or more connectors124for connecting to native protocol media signals. E/E converter card102includes a circuit board150including circuitry152for converting signals from the native protocol media format into the common format, such as NRZI, between connectors124and edge contact148. In the present system, it is anticipated that native protocol media signals include coaxial and twisted pair (shielded and unshielded). Also, it is anticipated that native protocol media signals include optical signals, such as multimode. Circuitry152of circuit board150also includes circuit pathways and elements for power conversion for use in signal conversion between connectors124and edge contact148. Also, circuit pathways and elements are provided on circuit board150for receipt and processing of control signals received from backplane64.

Referring now toFIG. 5, two optical to electrical converter cards92are shown removed from a chassis construction270. Each converter card92operates at a different wavelength. Chassis construction270includes a housing280for holding the circuit cards and components of system10. Housing280includes an open front282and internal guides284for guiding the circuit cards. Adjacent to a back286of chassis construction270is backplane64. Chassis construction270can be rack mounted or mounted to other system cabinets or frames.

Both optical to electrical converter cards92slide into open front282of chassis construction270. A rear end94of each optical to electrical converter card92includes edge contact132and fiber optic connectors134,136for interfacing with perpendicularly arranged backplane64. At a front end95of optical to electrical converter card92, card edge connector144is positioned for interfacing with electrical to electrical converter card102arranged in a parallel manner. Adjacent to a back end104of E/E converter card102edge contact148is positioned for interfacing with card edge connector144. At a front end105of E/E converter card102is positioned connectors124. When both O/E converter card92and E/E converter card102are fully inserted into chassis construction270, connectors124are presented along a front face288of chassis construction270and are linked with backplane64for signal transmission to other system components, including a far end WDM54.

FIG. 5illustrates a second embodiment of an E/E converter card190for use in handling signals of a different native protocol format. Connectors124of E/E converter card102are coaxial, such as for handling coaxial signals or HDTV signals. E/E converter card190includes a front port252for connecting to twisted pair cables. Specifically, port252is constructed as an RJ style jack. Circuitry on board250links port252with edge contact148.

Chassis construction270further includes a CPU card300with ports304,306,308for connecting to other system components. CPU card300includes a rear interface (not shown onFIG. 5) similar to edge contact148for connecting to backplane64, such as with a card edge connector, like card edge connector130. CPU control signals are linked from CPU card300to each O/E converter card92and E/E converter card102through backplane64. CPU card300sends command and control signals to each O/E converter card92, and each E/E converter card102. Also CPU card300can communicate with other system components including far end WDM's54.

FIG. 5also shows a splitter card350which shows four optical ports352,354,356,358. The optical ports provide for the dual path optical signal transmission to other system components, including a far end WDM54. A rear of splitter card350includes optical connections to circuit paths56,57,58,59, noted above.

Referring now toFIG. 6, an alternative arrangement for a WDM452is shown. A similar backplane464is provided as noted above for WDM52including a card edge connector530and optical interfaces66,68. Similar mux/demux circuitry60is provided for multiplexing and demultiplexing the optical signals for transmission to far end equipment. One difference with WDM452is that the input and output native protocol signals are through backplane464, instead of adjacent to a front of WDM452. E/E converter card502receives input signals and provides output signals for the native protocol format at native pathways560,562. Distal ends define connectors564,566and are connected to cables, such as 75 ohm coaxial cables. Proximal ends568,570define interface structure for mating with coaxial connectors572,574of E/E converter card502. Converter card502also communicates with backplane464through an edge contact532received in card edge connector530. Any power needed for signal conversion on E/E converter card502is provided through edge contact532. Also, all control signals can also be processed through edge contact532. E/E converter card502includes circuitry550for converting native protocol media signals into common signal format, such as NRZI format. Also, circuitry550includes any necessary links between edge contact532, and O/E converter card492, such as for power or control. E/E converter card502includes an edge contact548for interfacing with the card edge connector544of O/E converter card492. O/E converter card498includes conversion circuitry498for converting between common format signals and optical signals for communicating with mux/demux circuitry60. Fiber optic connectors534,536interface with optical interfaces66,68to optically connect to mux/demux circuitry60.

E/E converter card502includes access circuitry580for test or patch access to the native protocol media signals. Such test access may include a splitter function where a portion of the signal is tapped off, such for monitoring. In the case of patch access, switches can be included, such as switching jacks, for completely removing connectors572,574from the circuit paths. In this manner, signals to or from card502can alternatively be to a second location, instead of through backplane464.

The electrical interface80preferably includes an identification feature which will identify a code on O/E converter card92so that only an appropriate wavelength output will be accepted for each interface80. For example, a bit position could be hardwired on to the card edge connection circuitry. In this manner, only the desired O/E converter card92with the desired wavelength for the overall system can be inserted and used. CPU card300can be employed to run queries of each card92. With such a system, cards92at the wrong wavelength cannot be inserted into backplane64and used to cause system communication failures.

Preferably, power input port62is Telco power, and any different power needed by either O/E converter cards92or E/E converter cards102can be accomplished through isolated power converters on each of the cards.

While WDM52is shown as including 16 channels of signals (16 wavelengths), greater or fewer channels can be handled by appropriately selected conversion circuitry and mux/demux circuitry. In one preferred implementation, an 18 channel system can be provided wherein at least one channel is reserved for interconnecting local and remote CPUs for management and control. WDM's52,54are considered CWDM's in the preferred embodiment. There would be a 20 nm optical separation between each laser. Systems with 2, 4, 8, 16, 20, and 48+ channels can be implemented with appropriate O/E cards92.

Path protection is accomplished by using a one by two splitter on the output of the WDM mux/demux circuitry60. A one by two splitter will typically reduce the power level on each output fiber by 50%. Preferably, each laser associated with the O/E converter cards has a sufficiently high optical launch power that allows this system to use splitters for path protection instead of optical switches. This has particular application for short haul applications.

With the above systems, a variety of native protocol media signal formats can be supported using an appropriately selected E/E converter card102. Optical inputs can also be supported wherein the E/E converter card102converts the optical signal into an electrical signal, such as in the common format signal, wherein that signal is then converted back into an appropriate optical signal in the O/E converter card92for communication with the mux/demux circuitry60. By splitting the converting functions between O/E cards and E/E cards, the number of line cards needed to populate a given chassis is reduced.

The E/E converter cards102and the O/E converter cards92can be added over time as systems grow. A chassis construction270can be sold partially populated, and then as system needs increase, additional cards can be added. Also, upgrades can be easily added with only replacing one of the O/E converter cards92or the E/E converter cards102, depending on the upgraded elements. In the case of field replaceability, only that component needing replacement needs to be removed and replaced. The modular O/E convert cards allow for lower cost optics to be used for less demanding applications (i.e., less than 155 Mb/s).

Systems10,12are protocol independent. E/E converter cards102are selected for the given native protocol. O/E converter cards92are provided with the desired laser and optical performance. Such systems are advantageous during manufacture and during maintenance and upkeep over time.

While preferred systems include both transmit and receive pathways, other systems may only need transmit or receive on each respective near and far end WDM's52,54. For example, one way video does not need both transmit and receive functions at each end. In this system, the corresponding multiplexer or demultiplexer components and pathways can be removed to further save cost.