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A super-channel is an evolution in Dense Wavelength Division Multiplexing (DWDM) in which multiple, coherent optical carriers are combined to create a unified channel of a higher data rate, and which is brought into service in a single operational cycle.

Background
From around the year 2010, coherent optical transmission at 40Gb/s, and later at 100Gb/s began to be deployed in long haul optical networks around the world. Coherent technology enables higher data rates to be sent over long haul (typically >2,000km) optical transmission networks, compared to the historical modulation and detection technique, Intensity Modulation with Direct Detection (sometimes referred to as Non-Return to Zero, NRZ or On/Off Keying, OOK), which has been widely used for several decades.

However, a coherent detector requires that the incoming phase modulation information is digitized before being sent to a high performance Digital signal processor (DSP). Within the DSP, optical impairments such as Chromatic dispersion and Polarization mode dispersion can be compensated for. Digitizing the received signal requires an extremely high speed Analog-to-digital converter (ADC) capability, and it is generally expected that increases in serial ADC sampling may make it increasingly difficult to implement single-wavelength coherent detection at data rates above 100Gb/s in the near future.

Rather than a single wavelength line card of >100Gb/s data rates, a super-channel creates a multi-wavelength signal in which each wavelength will operate at the maximum data rate permitted by commercially available ADC components.

The primary advantages of a super-channel approach are increased spectral efficiency (a consequence of coherent detection), and operational scalability (the ability to bring larger units of long haul optical capacity into service for a given operational effort).

Examples of super-channels
Early work on DWDM super-channels included attempts using multiple laser sources, and wavelength combs generated from a single source – a form of optical Orthogonal frequency-division multiplexing (Optical OFDM).

The approach being brought to market by companies such as Infinera, Alcatel-Lucent, Huawei and Ciena makes use of multiple laser sources. Infinera is making use of their large scale photonic integrated circuit (PIC) technology, while the other system vendors are building super-channel line cards using predominantly discrete optical components.

The Infinera super-channel solution was first deployed in mid-2012, and consists of a ten-carrier, 500Gb/s Polarization Multiplexed Quadrature Phase Shift Keying (PM-QPSK) super-channel implemented on a single line card. Infinera has also demonstrated a ten-carrier PM-16QAM super-channel solution that is intended to fit in the same form factor as the current 500Gb/s product. Infinera claims over twenty customer deployments of this technology worldwide.

Alcatel-Lucent, Ciena and Huawei have all announced dual carrier, 200Gb/s PM-QPSK super-channel designs that can also operate at 400Gb/s using a shorter optical reach PM-16QAM modulation. As of March 2012 it is not clear if these 200Gb/s super-channel solutions are commercially available, but Alcatel-Lucent has announced at least one customer trial with the RENATER research network in France.

Notes and references

 * Govind P. Agrawal : “Fiber-Optic Communication Systems, 4th Edition.” ISBN: 978-0-470-50511-3 (2010).
 * Gabriella Bosco et al.: “On the Performance of Nyquist-WDM Terabit Superchannels Based on PM BPSK, PM-QPSK, PM-8QAM or PM-16QAM Subcarriers”. Journal of Lightwave Technology, Vol. 29, No. 1, January 1, 2011.
 * Light Reading: “Infinera Claims Top 100G Share”. http://www.lightreading.com/long-haul-wdm-equipment/infinera-claims-top-100g-share/240143572
 * Light Reading: "Huawei Unveils New WDM Prototype". http://www.lightreading.com/optical-equipment/huawei-unveils-new-wdm-prototype/240140353
 * Light Reading: "AlcaLu Claims 400G is Hot". http://www.lightreading.com/optical-equipment/alcalu-claims-400g-is-hot/240140479
 * Light Reading: "Beyond 100G: Optical Vendors Push for 400G". http://www.lightreading.com/beyond-100g-optical-vendors-push-for-400g/240145009

Category:Photonics