CWDM, DWDM & ROADM

In a typical fiber optic network, the data signal is transmitted using single light pulse at either 1310 nm or 1550 nm wavelengths.  Historically, the way to increase the capacity of a single fiber is to increase the bit rate of the signal (1 Mbps to 10 Mbps to 100 Mbps).  Throughout the last 30 years, optical systems have increased their capacity regularly, allowing for bandwidth upgrades that outpaced the growth in bandwidth demands.

Primarily driven by Ethernet and packet-based services, the need for bandwidth has exploded. Even mid-sized network operators are demanding multiple 10 Gbps pipes to accommodate large increases for growing and diverse applications such as surveillance, ITV, and data-center connections. This growth requires transport that is flexible and scalable.

Wavelength division multiplexing (WDM) is now a cost-effective, flexible and scalable technology for increasing capacity of a fiber network. WDM architecture is based a simple concept – instead of transmitting a single signal on a single wavelength, transmit multiple signals, each with a different wavelength. Each remains a separate data signal, at any bit rate with any protocol, unaffected by other signal on the fiber.

                                                         Wave Division Multiplexing

CWDM and DWDM

There are two types of WDM: Coarse and Dense Wavelength Division Multiplexing (CWDM and DWDM).

CWDM uses a wide spectrum and accommodates eight channels.  This wide spacing of channels allows for the use of moderately priced optics, but limits capacity.  CWDM is typically used for lower-cost, lower-capacity, shorter-distance applications where cost is the paramount decision criteria.

DWDM systems pack 16 or more channels into a narrow spectrum window very near the 1550 nm local attenuation minimum.  Decreasing channel spacing requires the use of more precise and costly optics, but allows for significantly more scalability.  Typical DWDM systems provide 1-44 channels of capacity, with some new systems, offering up to 80-160 channels. DWDM is typically used where high capacity is needed over a limited fiber resource or where it is cost prohibitive to deploy more fiber.

ROADM and FOADM

As with most transport systems, there are requirements to add and drop traffic along ring and tapered networks.  WDM systems support two types of add/drop Fixed and Reconfigurable Optical Add/Drop Multiplexers (FOADM and ROADM).

FOADMs are based on simple static fibers that permit add/drop of predefined wavelengths. These systems are fully integrated and manageable and provide a fine balance of features and cost.

ROADMs add the ability to remotely switch traffic from a WDM system at the wavelength layer. While more expensive than FOADMs, ROADMs are used in application where traffic patterns are not fully known or change frequently.

The key features and benefits of WDM include:

• Protocol and Bit Rate Agnostic – wavelengths can accept virtually any services
• Fiber Capacity Expansion – WDM adds up to 160X bandwidth to a single fiber
• Hi Cap/Long Haul and Lo Cap/Short Haul Applications – CWDM and DWDM provide price performance for virtually any network
• Remotely Provisionable – ROADMs provide the flexibility to change with changing network requirements
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