WDM – Wavelength-division Multiplexing

The starting point of wide-area optical networking was the introduction of the optical amplifier in the early 1990s. Amplifiers enabled both optical transport over longer distances and the ability to compensate for the losses in the optical multiplexer and de-multiplexer units that were needed to create multi-channel systems. WDM systems enabled telecommunications companies to expand the capacity of their networks without laying additional fiber.

The first WDM systems were two-channel ones that used 1310 nanometer (nm) and 1550 nm wavelengths. Shortly afterward came multi-channel systems that used the 1550 nm region, where the fiber attenuation is lowest. Depending on their wavelength patterns, WDM systems are typically divided into coarse wavelength-division multiplexing (CWDM) and dense wavelength-division multiplexing (DWDM).

Infinera’s founding vision is to enable an infinite pool of intelligent bandwidth that the next communications infrastructure is built upon, and the company is well-recognized in the technology segments of optical WDM transport and packet optical transport network (OTN) switching. Infinera pioneered a new approach for networks with photonic integration, which provides massive WDM capacity in a small power and space footprint to handle growing bandwidth needs.

Coarse wavelength-division multiplexing – cost-efficient transport in short-distance optical networks

CWDM is the technology of choice for cost-efficiently transporting large amounts of data traffic in telecom or enterprise networks. Optical networking and especially the use of CWDM technology has proven to be the most cost-efficient way of addressing this requirement.

CWDM typically has the capability to transport up to 16 channels (wavelengths) in the spectrum grid from 1270 nm to 1610 nm with 20 nm channel spacing. Each channel can operate at either 2.5, 4 or 10 gigabits per second (Gb/s). CWDM cannot be amplified as most of the channels are outside the operating window of the erbium-doped fiber amplifier (EDFA) used in DWDM systems. This results in a shorter overall system reach of approximately 100 kilometers (km). However, due to the broader channel spacing in CWDM, less sophisticated transceiver designs can be used, giving a cost advantage over DWDM systems.

Infinera uses both CWDM and DWDM technologies as a means of transporting different types of services, e.g. Ethernet, Synchronous Digital Hierarchy (SDH)/Synchronous Optical Networking (SONET), and Fibre Channel (FC) in metro networks. CWDM is the more cost-efficient of the two WDM variants, but has limitations in the distance over which the traffic is transported and in total channel count. Infinera’s XTM Series is CWDM- and DWDM-agnostic. This means a CWDM network can initially be deployed with either product series and when required, the network can be simply upgraded to a hybrid CWDM/DWDM network using common cards and pluggable optics. Therefore, by deploying Infinera’s CWDM- or DWDM-based solutions, the lowest possible day one cost is enabled without sacrificing the scalability of the network.

Dense wavelength-division multiplexing – efficient transport in metro and long-haul optical networks

DWDM is the technology of choice for transporting extremely large amounts of data traffic over metro or long distances in telecom networks. Optical networking and especially the use of DWDM technology has proven to be the optimal way of combining cost-efficient transport with advanced functionality that can cope with the bandwidth explosion from the access network.

DWDM puts data from different sources together on an optical fiber, with each signal carried at the same time on its own separate light wavelength. Using DWDM, 80 (and more) separate wavelengths or channels of data can be multiplexed into a light stream transmitted on a single optical fiber. Since each channel is demultiplexed at the end of the transmission back into the original source, different data formats being transmitted at different data rates can be transmitted together. Specifically, Internet (IP) data, SONET and Ethernet data can all be traveling at the same time within the optical fiber. A super-channel is an evolution in DWDM in which several optical carriers are combined to create a composite line-side signal of the desired capacity, and which is provisioned in one operational cycle. This multi-carrier approach to building a DWDM network delivers scalability to terabits and beyond.

Infinera DWDM line systems have the capability to transport 128 channels (wavelengths) across the extended C-band channel spectrum over thousands of kilometers (typically 4000 km). With core network traffic increasing at about 40 percent per year, service providers need a long-haul transmission technology that will deliver scalable, cost-effective capacity without compromising on optical reach. The DWDM industry is now aligned on the fact that multi-carrier super-channels are the way to quickly access the spectral capacity that coherent transmission delivers in a way that will scale WDM without scaling operations. Today, the Infinera Intelligent Transport Network delivers 500 Gb/s FlexCoherent™ super-channels and is designed to support terabits in the future, powered by large-scale photonic integrated circuits (PIC).