Hybrid DWDM/CWDM Optical NetworksCost-effective capacity growth and investment protection with WaveReady hybrid systems.WaveReady™ Hybrid CWDM-DWDM Optical NetworksJDS Uniphase WaveReady 3000 series optical modules offer a simple, plug-and-play option for creatinghybrid systems of DWDM channels interleaved with existing CWDM channel plans. Support for hybridconfigurations is a key value of the WaveReady product family.CWDM is an excellent, cost-effective, first step solution for scaling metro networks. Low cost WaveReadyCWDM transport can support up to eight channels at 2.5 Gb/s. This is sufficient for many networks in themetro space.If capacity needs grow beyond eight channels, WaveReady products can be used to merge DWDM andCWDM traffic seamlessly at the optical layer. This allows carriers to add many channels to networksoriginally designed for the more limited CWDM capacity and reach. Hybrid networks deliver true pay-as-you-grow capacity growth and investment protection.For carriers, the major advantages of hybrid CWDM/DWDM are: • Reduced cost: CWDM has a significant cost advantage over DWDM due to the lower cost of lasers and the filters used in CWDM modules. Coarse channel spacing allows more tolerance for channel deviations or wavelength deviations. Therefore, CWDM transmitters and filters are easier, and cheaper, to manufacture. This cost saving becomes quite significant for large deployments. • Pay-as-you-grow: Adding new channels one at a time allows for on-demand service introduction with minimal initial investment, a critical feature in times of reduced OPEX and CAPEX spending • Investment protection: Although 8 channels may be enough in an initial deployment, it’s important to have an upgrade path to avoid a forklift upgrade to DWDM when growth in demand finally requires significant new capacity. Given the unique WaveReady upgrade capability, carriers no longer have to choose between CWDM and DWDM—both options can be deployed simultaneously or as part of a planned future, or incremental, upgrade. WaveReady 3000 series CWDM/DWDM modules can be used in either the WaveReady 3500, usually in central offices, or in the WaveReady 3100, usually on customer premises. Current capital investment can always be used in the upgraded network.
Hybrid DWDM/CWDM Optical Networks | 2Theory of CWDM/DWDM HybridizationThe CWDM frequency grid consists of 16 channels spaced at 20 nm intervals. The eight most commonlyused channels are: 1470 nm, 1490 nm, 1510 nm, 1530 nm, 1550 nm 1570 nm, 1590 nm and 1610 nm.Within the pass band of these channels there exists the capacity to add 25 100 GHz spaced channelsunder the 1530 nm envelope and 25 more under the 1550 nm envelope if the filter is properly designed.For example, in the 1530 nm window there is a total theoretical pass band of ±10 nm on either side of thenominal center frequency. Therefore, one can, theoretically, concatenate multiple WDM filters to addanother 25 channels within the pass-band. Looking at the ITU grid in Table 1 one can easily pick outthese channels.Table 1: Theoretical Availability of Channels in the 1530 nm and 1550 nm Pass-band 1521.02 1540.56 1521.79 1541.35 1522.56 1542.14 1523.34 1542.94 1524.11 1543.73 1524.89 1544.53 1525.66 1545.32 1526.44 1546.12 1527.22 1546.92 1527.99 1547.72 1530 nm ± 20 nm 1550 nm ± 20 nm 1528.77 1548.51 1529.55 1549.32 1530.33 1550.12 1531.12 1550.92 1531.90 1551.72 1532.68 1552.52 1533.47 1553.33 1534.25 1554.13 1535.04 1554.94 1535.82 1555.75 1536.61 1556.55 1537.40 1557.36 1538.19 1558.17 1538.98 1558.98 1539.77 1559.79
Hybrid DWDM/CWDM Optical Networks | 3Practical Application of CWDM/DWDM HybridizationIn practice, adding another 25 channels in the pass-band of both the 1530 nm and 1550 nm CWDMchannels is not achievable because the optical filters are not perfect square functions. The actual filterprofile affects the number of channels which can be accommodated. However, actual JDS UniphaseDWDM filter technology does allow 38 additional channels to clear the CWDM archway as shown inTable 2.Table 2: Actual Availability of Channels in the 1530 nm and 1550 nm Pass-band 1521.02 1540.56 1521.79 1541.35 1522.56 1542.14 1523.34 1542.94 1524.11 1543.73 1524.89 1544.53 1525.66 1545.32 1526.44 1546.12 1527.22 1546.92 1527.99 1547.72 1550 nm ±20 nm 1530 nm ±20 nm 1528.77 1548.51 1529.55 1549.32 1530.33 1550.12 1531.12 1550.92 1531.90 1551.72 1532.68 1552.52 1533.47 1553.33 1534.25 1554.13 1535.04 1554.94 1535.82 1555.75 1536.61 1556.55 1537.40 1557.36 1538.19 1558.17 1538.98 1558.98 1539.77 1559.79
Hybrid DWDM/CWDM Optical Networks | 4The system impact to adding these channels is equivalent to adding the component in line with existingCWDM equipment. The insertion losses add linearly.Figure 1 shows the infrastructure in a fully populated CWDM system. MUX DeMUX TX1 1470 RX1 TX2 1490 RX2 CWDM 8 CWDM 8 TX3 1510 RX3 TX4 1530 RX4 TX5 1550 RX5 TX6 1570 RX6 TX7 1590 RX7 TX8 1610 RX8To add more channels to MUX side of this network, one would plug in a DWDM MUX with theappropriate channels to fall under the pass-band of the existing CWDM filters. Figure 2 shows theinfrastructure of Figure 1 upgraded with 38 additional 100 GHz spaced channels.Figure 2: Forty Four Channel Hybrid CWDM/DWDM System MUX DeMUX D TX1 1470 RX1 D 19 W WDWDM TX2 1490 RX2 D D CWDM 8 CWDM 8 TXs M TX3 1510 RX3 M 1530 1550 TX6 1570 RX6 D D 19 W TX7 1590 RX7 WDWDM D D TXs TX8 1610 RX8 M MThe number of channels present in Figure 2 is 38 DWDM channels plus the existing six CWDM channelsfor a total of 44. The equipment required to go from the first architecture to the second are 2 DWDMmultiplexers and demultiplexers, as well as the additional transmitter and receiver pairs required. Theadditional loss incurred by the upgrade is equal to the additional loss of the DWDM elements and theadditional connection points.Several network types could take advantage of the architecture shown in Figure 2. For example onecould increase the capacity of an existing ring, by deploying all of the elements above at each node. Or,one could allow DWDM traffic to overlay an existing CWDM network at a pre-determined crossover point.
Hybrid DWDM/CWDM Optical Networks | 5Figure 3: Hybrid CWDM/DWDM Rings DWDM Metro CWDM Core RING RINGThe two networks would be configured in such a way to allow the DWDM traffic to travel across theCWDM ring. All of the nodes where the DWDM traffic would travel on the CWDM ring would require theDWDM multiplexer and demultiplexer pairs.Another application for the DWDM channels is for long reach links in CWDM rings. If a certain spanexists in a CWDM network with a large distance between regenerators, say 100 km, DWDM channelscan be used in place of CWDM ones to overcome this distance. CWDM NODE MIXED NODE 1470 RX 1490 RX 1510 RX 1530 RX 1550 RX 1570 RX 1590 RX 1610 RX 1470 RX 1490 RX DWDM NODE 1510 RX 1570 RX 1590 RX 1610 RX
Hybrid DWDM/CWDM Optical Networks | 6System ImpactThe added components on the CWDM ring will decrease the link budget for each span by the amount ofinsertion loss for each new component. The use of high isolation optical filters for the DWDM channelswill ensure that cross talk is minimized between closely spaced channels. In the case of very highchannel counts, non-linear effects should be taken into consideration. These include self phasemodulation and four wave mixing.The lasers used in DWDM networks have a much narrower line width than lasers used in CWDM. As aresult the DWDM signals will typically have farther reach, and will undergo less pulse broadening due tochromatic dispersion. However they also lie within the operating range of erbium doped fiber amplifiers.This means that DWDM signals can go un-regenerated for large distances. This limit is reached at thetransmitter’s dispersion limit.Receiver technology is independent of the optical signal present. The same receiver can be used toresolve a CWDM signal as well as a DWDM signal. The InGaAs material used to convert the opticalsignal into an electrical one has an operating range that includes both wavelength schemes. In the caseof a 3R receiver, the receiver should be chosen such that it is compatible with the transmitter’s data rate.GlossaryDCF – Dispersion Compensating FiberDWDM – Dense Wavelength Division MultiplexingEDFA – Erbium-Doped Fiber AmplifierIEEE – Institute of Electrical and Electronics Engineers, Inc.ITU-T – International Telecommunication Union – Telecommunication Standardization SectionSONET – Synchronous Optical NetworksFeatured ProductsDescriptionWaveReady 3000 Bi-directional 1310 nm to CWDM transponder (WSH 500)WaveReady 3000 Bi-directional 850 nm to CWDM transponder (WSH 510)WaveReady 3000 Bi-directional 1310 nm to DWDM transponder (WSH 413)WaveReady 3000 Bi-directional 850 nm to DWDM transponder (WSH 400)WaveReady 3000 Communications Module 100WaveReady 3500 Shelf Mounting Solution (DenseMount Shelf)Additional InformationFor more information on WaveReady™ or other products and their availability, please contact your localJDS Uniphase account manager or JDS Uniphase directly at 1-800-498-JDSU (5378) in North Americaand +800-5378-JDSU worldwide or via e-mail at email@example.com.WaveReady and JDS Uniphase are registered trademarks of JDS Uniphase Corporation.