Nu-Wave ES

The Nu-Wave ES is a next generation optical line system that is designed to significantly lower the cost of a highly scalable optical network. Its unique architecture makes it ideal for next generation communication providers that will start out with lower capacities, but will ultimately require the high capacity needed by today’s emerging bandwidth-intensive applications. The design of the optical line system enables next generation networks through the introduction of the latest technologies, supporting multi-degree nodes, optical protection, tunable lasers, and higher bit-rate (40 Gb/s and 100 Gb/s) services.

Raman amplification overview

A Raman optical amplifier is based on a different physical principle than conventional optical (rare-earth doped) amplifiers. In a Distributed Raman Amplifier (DRA), pump lasers are connected to the line fiber and transmit optical energy down the length of the line fiber. As it passes along the fiber this extra energy interacts with the optical signal  increasing its strength. Since the amplification is distributed along the length of the fiber Raman amplifiers have some significant advantages. First, the distances between amplifiers can be stretched further even when pumped from one end of the fiber. Where extra distance is required the fiber can be pumped from both ends, further increasing the distance. Secondly the distributed amplification provides a much improved Optical Signal to Noise Ratio (OSNR) performace compared to conventional optical amplifiers. This makes it possible to increase the number of cascaded amplifiers enabling very long links (3000 km) without the need for regeneration. In a Discrete (or Lumped) Raman Amplifier (LRA), gain is provided in Dispersion Compensating Fiber (DCF). So, as an added benefit, an all-Raman amplifier (which combines DRA & LRA) not only provides gain but also provides dispersion compensation, thus limiting the need for external Dispersion Compensation. Finally the optical bandwidth of a Raman amplifier can be increased by adding extra pump lasers at different wavelengths. This makes it possible to transmit many more optical signals (up to 240 wavelengths) on a single fiber than a typica EDFA-based l system (80-90 wavelengths). As a significant side benefit, the multiplicity of pump lasers results in a more robust amplifier (a defectice pump laser could be overcome by its neighbors), leading to higher system reliability and thus network availability.

Nu-Wave ES and Nu-Wave CXR

The Nu-Wave ES platform differs from the Nu-Wave CXR only in the amplifier. Whereas the Nu-Wave CXR amplifier provides a bandwidth of 100nm day-1 (240 waves, spaced 50GHz apart), the modular design of the Nu-Wave ES amplifier provides, in its simplest configuration (“core”), a bandwidth limited to 25nm (60 waves spaced, 50GHz apart), resulting in a lower day-1 capital investment for the carrier.

The bandwidth of the core amplifier can be increased to 60nm by adding a Capacity Expansion Module (CEM), in service – thus not affecting the existing channels – when a capacity in excess of 60 channels is required. The incremental capital investment is thus required only at the 61st channel. The continuous 60nm bandwidth provides a max capacity of 150 waves (spaced 50GHz apart).

The Nu-Wave ES amplifier (with or without the CEM) can bridge spans with an average loss of 21dB, with 0dB net gain. For higher-loss spans, a Span Extension Module (SEM) can be added to the core amplifier, allowing spans with up to 33dB of loss to be bridged with 0dB net gain.

The design of each link can therefore be optimized on a per span basis, adding SEM and CEM only when required, resulting in considerable savings.

The Nu-Wave ES amplifier with a SEM and a CEM occupies the same volume (4 RU high) as the Nu-Wave CXR amplifier.

Another distinction of the Nu-Wave ES platform compared to the Nu-Wave CXR platform is the number of different amplifiers needed in the line system. For the Nu-Wave CXR, different amplifiers are used:

• as boosters at transmit terminals
• as line amplifiers at repeater and OADM sites, and
• as sub-band amplifiers at receive terminals and OADMs.

In comparison, the same Nu-Wave ES amplifier can be used in all 3 positions, reducing the number of amplifier types needed and thus drastically reducing the cost of sparing.

Key features of the Nu-Wave ES:

All Raman performance

• All Raman amplification results in superior noise performance when compared to EDFA based systems. Superior noise performance translates to networking flexibility that can be used to bridge longer amplifier spans and longer all-optical transmission paths, and support higher capacity. For network operators, this means fewer network elements and in many cases, the complete elimination of intermediate regeneration sites.
• Scalable capacity expansion, in service
• Optimized link design
• 10G and 40G support; 100G ready
• All fiber types supported
• R(OADM) / Multi-degree node
• Optical protection
• Wide range of client interfaces

Nu-Wave ES implementation

Nu-Wave ES optical bandwidth

Deployment on all fiber types

A side benefit of the wide spectral range of all-Raman amplification is the maximisation of the existing fiber infrastructure. Indeed, all-Raman amplification allows flexible channel wavelength allocation that dramatically improves the capacity of older generation fibers whose design was not optimized for DWDM systems.

Scalability

The bandwidth of the core amplifier can be increased to 60nm by adding a Capacity Expansion Module (CEM), in service – thus not affecting the existing channels – when a capacity in excess of 60 channels is required.

In addition to cost-effective scalability in terms of capacity, the Nu-Wave ES offers transmission power scalability by using Span Extension Modules. These modules are used during the initial network deployment to provide just the right amount of optical gain for each span. This additional degree of scalability eliminates the over engineering of moderate length spans that often occurs when deploying high gain EDFA amplifiers.