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Coherent optics and 100G - Top wireline technologies in 2013

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What is it? Coherent optics, which reduces the need for amplification of a signal and increases the distance it can be sent while reducing chromatic dispersion, has been combined with 100G technology to ease carrier network upgrades.

As service providers face the problem of supporting increasingly heavy bandwidth demands on their wireline and wireless networks, combining 100G and coherent optics provides a foundation to serve those needs.

Although there's no common definition of what DWDM coherent detection is, there is a consensus among vendors and service providers that it would consist of four major elements: high order amplitude/phase modulation, polarization multiplexing, coherent detection using a local oscillator laser in the receiver, and high-speed ADCs and sophisticated digital signal processing in the receiver.

What has made coherent technology a good fit with 100G is that unlike initial DWDM systems that used the Intensity Modulation with Direct Detection (IMDD) modulation technique is it can overcome various fiber impairments, such as chromatic dispersion (CD) and polarization mode dispersion (PMD), as data rates increase beyond 10 Gbps.   

Following some initial trials in 2009 and 2010, a growing base of service providers--including domestic telcos like CenturyLink (NYSE: CTL) and Verizon (NYSE: VZ), cable operators including Comcast (Nasdaq: CMCSA), CLECs such as XO Communications, European providers like BTFrance Telecom-Orange and P&T Luxembourg, and R&E networks including Internet2--are in the process of deploying 100G on parts of or throughout their respective networks.

From a vendor perspective, the race has been led by Alcatel-Lucent (NYSE: ALU) and Ciena (Nasdaq: CIEN). But Infinera (Nasdaq: INFN) has been gaining traction in recent quarters, having won a spot on CenturyLink's 100G supplier list and completing Ericsson's OSMINE process.

Why is it important? Despite being a hot research topic during the formative years of the optical communications market throughout the 1970s and 1980s, coherent optics was overtaken by optical amplifiers to overcome signal attenuation in fibers, an issue that can limit the reach of an optical system. However, coherent optics reduces the need for amplification and increases the distance, in addition to reducing chromatic dispersion, meaning a service provider can have wavelengths set closer together with fewer sub channels.

The advent of 100G technology coupled with coherent optics means that service providers can more easily upgrade their backbone, core and edge networks with the right amount of bandwidth to ensure that the user gets a consistent experience.

A recent Dell'Oro report said that 100G wavelength shipments will experience 75 percent CAGR over the next five years. The firm forecasts that by 2017, about 60 percent of the WDM capacity shipments will be with 100 Gbps wavelengths.

But even as 100G gains momentum, the IEEE and the Optical Internetworking Forum are looking what lies ahead. The IEEE is developing a Terabit Ethernet standard, while the OIF's Multi-Link Gearbox 2.0 project addresses how to process link technology with optical interfaces as bandwidth grows to 400G.