Wavelength-division multiplexing (WDM) technology combines multiple wavelengths into a single optical fiber. This technique enables better fiber utilization, as it increases fiber capacity by a factor of 16-96 and enables building effective optical networks.

DWDM System

In WDM technology, each channel is transparent to the speed and type of data. Any mix of Ethernet, SAN, OTN, SONET/SDH and native video services can be transmitted simultaneously over a single fiber or fiber pair. There are two types of WDM technologies: DWDM - dense wavelength division multiplexing, and CWDM - coarse wavelength division multiplexing. Each technology has characteristics that suite different environments, networks and user requirements.

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DWDM Solutions for Metro, Long Haul and High Capacity DCI Networks

DWDM C-band spectrum supports up to 96 wavelengths, spaced at the standard ITU grid of 50GHz, 64 wavelengths, spaced at the standard ITU grid of 75GHz, and 48 wavelengths, spaced at the standard ITU grid of 100GHz. DWDM also supports flex-grid in which flexible bandwidth spectrum slices are allocated to the optical signals.

The dense division multiplexing architecture enables the fitting multiple wavelengths on a single fiber and supports long haul, metro and DCI applications with capacities of 10G/100G/200G/400G per wavelength (see Figure 1).

DWDM Technology

Figure 1: DWDM Network with Mux/Demux and EDFAs

One of the biggest advantages of DWDM is the use of optical amplifiers, which can amplify the entire DWDM spectrum and overcome long spans of attenuation and fiber loss, enabling cost-effective transmission over long distance. The optical amplifiers are managed and configured as part of the optical network and have adjustable gain and operation modes. There are several types of amplifiers which are used a according to the link design such as booster/inline/mid-stage/pre-amp EDFA, and Raman. When boosted by Erbium-doped-fiber amplifiers (EDFAs), the DWDM systems can support ultra-long haul applications of thousands of kilometers without the need for regenerators.

DWDM pluggable optical transceivers support wavelength tunability, which reduces the part numbers needed and enables faster delivery time while also reducing spare parts. The 10G/100G/200G/400G transceivers connect to the front panel and easily increase capacity for pay-as-you-grow network architecture.

The need for high speed, more capacity and longer distances has made DWDM the technology of choice for greenfield installations, for upgrading existing networks, and is compulsory for transmission of 100G and above.

The optical multiplexer/demultiplexer (mux/demux) supports 4 to 96 DWDM channels in the fiber, with 50GHz, 75GHz and 100GHz spacing, according to the output standards.

As bandwidth requirements grow rapidly, optical network operators are challenged with extending and modifying their WDM networks by adding new wavelengths and changing the wavelength path within the network. The reconfigurable optical add/drop multiplexer (ROADM) enables dynamic and flexible wavelength routing capabilities suitable for mesh, ring, linear add/drop, core and edge DWDM network topologies, by provisioning of wavelengths from a remote management system without major network changes or redesign. The ROADM supports colorless, directionless features, 50GHz/75GHz/100GHz and flex-grid, and enables automatic power balancing of the wavelengths across the network, which is critical especially for links with many EDFAs and multiple channels.

PacketLight provides the full optical layer transport solution, including ROADM, optical amplifiers, transponders, muxponders, OTN layer, and network management (see Figure 2).

Optical Layer Transport Solutions DWDM OTN

Figure 2: Optical Transport Layer Building Blocks

DWDM over CWDM

CWDM used to be the popular choice in low capacity, short distance and low rate (up to 10G per wavelength) applications, as well as in networks where the initial requirement does not exceed 8 wavelengths. In addition, low cost entry point and the difference in economic scale make CWDM ideal for initial network set up. However, CWDM is limited as it cannot be amplified and does not support tunable DWDM 100G/200G/400G wavelengths. As the need for capacity grows, so does the demand to increase capacity by adding DWDM onto existing CWDM infrastructure. For more details, see DWDM over CWDM Network.

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