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Mar 05 2012

The 400G Photonic Service Engine

The next-generation Photonic Service Engine (PSE) sets new benchmarks in electro-optics, enabling the industry’s first 400G transmissions and superior performance at 100G.

A next-generation electro-optics engine

Growing demands and new opportunities are pushing service providers to take optical networks to the next levels of capacity, performance and speed. A new Photonic Service Engine developed by Alcatel-Lucent combines innovations in optics and silicon to give service providers the capabilities they need to evolve optical networks.

The advantages of in-house innovation

Designing new chips in-house allows us to give service providers faster access to the latest advances in optical and silicon technologies. And by leveraging our real-world experience, we can custom-design chips that meet service providers’ specific needs. We don’t need to wait for mass-market, off-the-shelf chips to become available. Bell Labs’ innovations have been recognized with 7 Nobel Prizes in Physics shared by 13 scientists. It is one of the only in-house organizations with the scientific research, technical expertise and experience needed to custom-design advanced silicon solutions for service providers.

The PSE is a line interface ASIC, or chip, for the line cards in switched optical networks. Built with expertise from Bell Labs and from Alcatel-Lucent design and development centers around the globe, the PSE enables 400G line speeds and improves performance at 100G. It determines the capabilities and the evolution potential for the optical platforms it supports. Such major advances in optical chips set the stage for significant differentiation in a highly competitive market. With its capabilities and performance, the 400G PSE brings service providers several advantages, including higher capacity and scalability, faster time to market and lower cost per bit.

The new state-of-the-art 400G PSE

Compared to today’s 100G chips , the 400G PSE delivers:

  • 4 times the line rate
  • more than 2.6 times the spectral efficiency
  • more than 4 times the density
  • more than 1.5 times the reach and performance
  • 33% lower power consumption
  • 25% better tolerance to fiber impairments

With higher speeds, longer reach and improved performance, service providers are in a better position to:

  • Expand and upgrade core networks
  • Meet growing demand for high-bandwidth services, such as mobile video
  • Take advantage of new opportunities, such as storage area networks, cloud computing and data center interconnection
  • Increase capacity at lower cost per bit

Table 1 summarizes the new benchmarks set by the 400G PSE.

Designed for throughput and efficiency

The 400G PSE is designed to help service providers get more from their 100G networks while smoothly evolving to 400G. It integrates the analog to digital converter (ADC), digital to analog converter (DAC) and digital signal processor (DSP) functions into the same chip for unparalleled throughput and efficiency. As a result, the 400G PSE is the market’s fastest silicon for integrated digital signal processing in high-speed telecom applications. Figure 1 illustrates the ASIC architecture in the PSE.

Key innovations in the 400G PSE include:

  • Soft Decision Forward Error Correction (SD-FEC) with enhanced algorithms to improve transmission performance
  • Integrated wave-shaping, pre-compensation and enhanced optical signal to noise ratio (OSNR) performance, enabling very high tolerance to fiber non-linearities
  • Support for multiple programmable modulation formats, including PDM-BSPK, PDM-QPSK and PDM-16QAM to optimize reach and capacity.
  • Support for flexible grids to maximize capacity
  • Support for 50 GHz spacing at 400G for full compatibility with reconfigurable optical add-drop multiplexer (ROADM) networks
  • Plug-and-play compatibility with both existing and new network equipment
  • High configurability of optical parameters to achieve optimal performance according to network conditions.

Reach with no sacrifices in performance

The PSE extends reach at 100G from 2000 km to greater than 3000 km in real-world optical networks without the need for regeneration, delivering the highest performance per wavelength available today in the market. To ensure the highest possible performance is maintained at all times, the PSE includes SD-FEC capabilities that are enhanced with Bell Labs digital signal processing algorithms. This combination:

  • Increases performance in the range of 50%
  • Improves tolerance to non-linear impairments by 25% or more
  • Takes advantage of the versatile architecture to provide SD-FEC for all supported modulation formats

In addition, several lab experiments have led to new implementations in which phase slips —also known as cycle slips — are addressed using a unique technique that does not incur any OSNR penalties. Phase slips are a phenomenon known for decades. They can cause burst errors, traffic interruptions and outages in phase modulated systems. In networked applications, zero-penalty cycle slips mean:

  • No increase in spectral width
  • No increase in filtering penalties
  • No reduction in the number of cascaded ROADMs
  • No sacrifices in reach or performance

The 400G PSE also integrates wave-shaping capabilities at the optical transmitter level. This advanced feature can be used to extend reach in a cost-effective way for specific applications. The transmit (TX) DSP wave-shaper in the PSE can shape the transmit spectrum into any given shape based on filter configuration. This capability allows service providers to make trade-offs between spectral efficiency and non-linearity tolerance. The PSE can optimize the overall spectral content of the signal, offering a higher degree of tolerance to noise. It can also minimize cross-talk effects whenever the signal traverses multiple cascaded ROADM Wavelength Selective Switches. The PSE reduces the bandwidth of the optical signal, allowing denser channel spacing and increased capacity when flexible grids are employed. To extend reach with no sacrifices in performance, the PSE also:

  • Includes new algorithms that enhance chromatic dispersion (CD) and polarization mode dispersion (PMD) compensation capabilities. These enhancements enable 100G transmissions over lesser quality links and over longer uncompensated distances.
  • Allows dynamic opto-electronic chromatic dispersion mapping adjustments at the transmitter. This offsets the compensation that is built into existing photonic lines to improve non-linear tolerance.
  • Improves transponder synchronization time. This improves restoration times in Generalized Multi-Protocol Label Switching (GMPLS) networks.
  • Allows tuning of the TX DSP to minimize the effects of electrical and radio frequency (RF) noise in the PSE

Multiple modulation formats

With the optical technology available today, service providers must choose a specific modulation format for each signal speed. For example, at 100G, single-carrier quaternary phase-shift keying (QPSK) is the modulation format that meets service providers’ needs in terms of reach, capacity and tolerance to linear and non-linear transmission impairments. The 400G PSE forms the basis for software-defined flexible bit-rate line interfaces. A transponder based on this next-generation ASIC can generate a number of spectrally engineered modulation formats. This gives service providers the flexibility to choose the optimal modulation format for their distance and spectral efficiency requirements by:

  • Using the binary phase shift keying (BPSK) modulation format allows super, ultra long-haul systems to be covered at 40G or 100G per carrier
  • Using the quadrature phase shift keying (QPSK) modulation format increases capacity while keeping long-haul reach at 100G
  • Using the more advanced 16-state quadrature amplitude modulation (16QAM) format doubles spectral efficiency compared to current 100G solutions. 16QAM combines Bell Labs innovations with advanced DSP techniques to enable full 400G support. It also improves density and increases power efficiency.

Each of these modulation formats uses advanced SD-FEC to maximize transmission reach. Service providers’ ability to choose the modulation format that is best suited to their requirements allows them to optimize both performance and cost per route. For example, they can use one modulation format for a short-haul application at 400G in a metro or regional network and another format for a longer haul application at 100G.

Flexible grids and spectral efficiency

Most optical networks today are based on a channel grid that uses 50 GHz spacing. Support for 50 GHz spacing allows service providers to use the PSE at 400G with all currently deployed systems. It also allows service providers to seamlessly upgrade from 10G to 40G, 100G and 400G with scalability to terabit optical channels.

Plug-and-play architecture

The new 400G PSE will be supported on next-generation line cards in the Alcatel-Lucent 1830 Photonic Service Switch. With the capabilities of the PSE, this dense wave division multiplexing (DWDM) platform is uniquely positioned to reinforce its leadership in high-speed coherent optical transmission. The PSE chip will be built into line cards which are backward compatible with the two existing generations of single-carrier 100G electro-optics engines. This allows service providers to simply add PSE-based line cards to existing network switches when they become available. They can also share common spares with 100G wavelengths that are already in service. This approach gives service providers the flexibility to concurrently run:

  • Legacy 2.5G, 10G and 40G wavelength services
  • 100G wavelength services using current generation line cards
  • Enhanced performance 100G wavelength services using PSE-powered line cards
  • 400G wavelength services using PSE-powered line cards

As competitive pressure mounts, more and more service providers will need higher performance 100G channels. And they will look to 400G channels to help build their competitive advantage. The ability of the PSE to deliver higher speeds, better performance and lower cost per bit within the existing infrastructure will help service providers address their challenges and make the most of new opportunities. Read our 400G PSE whitepaper to learn more about Alcatel-Lucent's Photonic Service Engine. To contact the authors or request additional information, please send an e-mail to networks.nokia_news@nokia.com.

About Sam Bucci

Sam Bucci heads the Optical Networking Business Unit for Nokia’s IP/Optical Networks Business Group. Sam spends an inordinate amount of time on airplanes working with customers around the world. It is the insight he gains on his travels combined with his deep knowledge of photonic networks which makes him a recognized expert and visionary in the optical field.

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