Learning

White Papers and Presentations

A little bit of Raman makes the Repeater go a long way
Xtera’s Stuart Barnes, Wayne Pelouch and Nigel Taylor share a rare insight into a Regional System. From the analysis of comprehensive system data, the long-term economic benefits of low NF Raman techniques become abundantly clear.

When Should You Consider An Unrepeatered Solution
With the increasing popularity of Space Division Multiplexing (SDM) on repeatered systems, and with new high fiber count transoceanic cables being contracted every month, it is worth reviewing how all this traffic is carried within regions.  Traditionally a mixture of small repeatered systems, unrepeatered festoons and point to point links have been used, but how do we determine which design makes the most economic sense and over what distances should we opt for one solution over another?

Generalized SNR for Submarine Systems. Calculating performance in repeatered open line systems

Xtera has developed an Open System architecture to allow the sharing of bandwidth and/or fibers while allowing multiple SLTE vendors access to the line system gateway. With potentially different channel plans and line cards on the repeatered system, a method to calculate channel independent performance is required. In this White Paper, we show how the GN model can be used to separate the line system performance from the SLTE, allowing simple calculations for various channel spacing and baud rates.

How to make a simple supply contract in a complex world

The subsea industry has always battled with conflicting pressures in the process of getting a system into the water. Even if the very first systems in the mid 1800’s were, astonishingly, private ventures, the need for cross-border risk and cost sharing led to the consortium approach and to an inevitable complexity in management structures and decision making. This in turn slowed down and impeded the projects, through all their phases – conception, contract forming, management and exploitation, including backhauling and eventual upgrading.

SubOptic 2019 | Electrical power – greener solutions with minimal compromise

This paper examines ways to reduce the power consumption of submarine cable, showing that this is nearly always good for the environment and often has financial and other benefits.

SubOptic 2019 | Artificial Intelligence or Real Engineer, Which Is Better?

Artificial Intelligence (AI) has found applications in many areas, but does it have a future in subsea communications? Current generations of subsea amplifiers are extending bandwidth from the C-band into the L-band, employing either hybrid Raman-EDFA or dual-EDFA solutions, and branching units are offering flexible wavelength routing. The extra capacity and flexibility, however, comes with extra complexity which risks increasing the difficulty of both initial commissioning and long-term operation.

SubOptic 2019 | Masterclass 4: Updates to Transmission Technology

Updates to Transmission Technology Masterclass presented at SubOptic 2019 by Tony Frisch, Masaaki Hirano and Ronald Freund.

Options for Increasing Capacity in Subsea Systems

Drawing on his early career work on fibre and cable design, Stuart Barnes shares his perspective on the drive for more bandwidth in submarine links. This white paper looks to debunk what can and cannot be done as we approach the Shannon Limit.

91nm Bandwidth Low-noise Amplifiers Enable 120Tbit/s on a Single Fibre

During the last few months Xtera and University College London (UCL) have worked together to explore how large capacities can be achieved based on technology which can be industrialised. Using hybrid EDFA / Distributed Raman Amplifiers, the result is a record breaking capacity of 120 Terabit/s on a single fibre, over 9 spans of 70 km. To ensure that the design could be industrialised the amplifiers used were based on the hybrid Raman-EDFA design that Xtera currently uses for subsea amplifiers, with the bandwidth increased by adding extra Raman pumps.

Open and Extended Systems

The following presentation on Open and Extended Systems was given by Xtera’s CTO Tony Frisch at the Subsea Connect Americas Conference in December 2017. Tony discusses the variety of different flavours that Open Systems come in, and addresses some of the problems and their solutions.

Current Trends in Unrepeatered Systems

Unrepeatered (UR) transmission systems are characterized by an extremely long fiber span with no in-line electrically powered elements between the terminals and are typically deployed in submarine environments. The relative performance of UR links is constrained by four main factors: fiber properties, transponder technology, Raman amplification, and remote optically-pumped amplifier (ROPA) design and location [1], [2].

Optical Amplifier Options for Wideband Submarine Systems

Submarine systems have enjoyed the tremendous advances in coherent transmission brought about by high DSP technology over the last few years. These techniques have brought us remarkably close to the Shannon limit. Increasing the transmission capacity further is achievable by selecting improved system parameters such as a smaller fibre attenuation coefficient and a lower nonlinear coefficient.

Raman Amplification: An Enabling Technology for Long-Haul Coherent Transmission Systems

The past 15 years have seen an incredible increase in data rates of optical transponders and, more recently, a move to multi-level phase modulated formats and coherent digital signal processing at the receiver. However, the fiber optic transport system has not changed much over this time and is dominated by C-band erbium-doped fiber amplifiers (EDFAs). These am- plifiers are the main building blocks of the transport system that define the performance characteristics of the optical net- work independent of the transponders.

Maximising the Capacity of Ultra-Long Haul Submarine Systems

The capacity of ultra-long haul (ULH) submarine systems is ultimately limited by the electrical power that can be delivered to the submerged amplifiers within the repeaters. An excessive power feed voltage will cause damage to the cable and joints and so the system should be designed to maximize the power available per repeater using the available voltage.

15 Tb/s Unrepeatered Transmission over 409.6 km using Distributed Raman Amplification and ROPA

Larger network bandwidth to meet ever increasing traffic demand requires higher transport capacity. For unrepeatered applications, several reports have already been published on both high capacity and long reach unrepeatered transmission [1-8]. However, these results often require either a mix of fiber types in the span [2, 4-7], very strong (> 5W) high-order Raman pumping [1, 4, 7], or offline-channel processing [3, 6], which are less practical in real deployments.

557-km Unrepeatered 100G Transmission with Commercial Raman DWDM System, Enhanced ROPA, and Cabled Large Aeef Ultra-Low Loss Fiber in OSP Environment

Many applications would benefit from very-long, “skinny” (low-capacity) unrepeatered systems. One such application is terrestrial routes in remote and hostile areas (tropical forest, desert…) for which the use of unrepeatered transmission alleviates the need for intermediate amplification sites (and associated operational expenses).

150 x 120 Gb/s Unrepeatered Transmission over 333.6 km and 389.6 km (with ROPA) G.652 Fiber

Unrepeatered transmission systems provide a cost-effective solution in submarine networks to communicate between coastal population centers or in terrestrial networks to connect remote areas where service access is difficult. One of the main goals of unrepeatered systems is to achieve the longest reach without any inline active elements.

Invited Paper: Advanced Technologies for Unrepeatered Transmission Systems and Their Applications

Unrepeatered transmission systems provide cost effective solution for:

  • communication between islands or main-lands
  • communication for oil platforms (for oil and gas company)
  • skipping intermediate sites in hostile areas (tropical forest, desert etc.)

Electrical Power, a Potential Limit to Cable Capacity

One of the factors limiting the potential capacity of a long submarine cable is the need to power the optical amplifiers which compensate for fibre loss. This paper shows how a number of routes to higher capacity all result in higher power requirements and uses the Shannon formula to assess upper limits on capacity. The results suggest that a promising, and practical, route to raising the limit would be to improve the powering of the optical amplifiers.

Field Deployment of Advanced Photonic Technologies for Ultra-High Bit Rate and Ultra-Long Reach Terrestrial WDM Transmission in Brazil

The insatiable quest for higher capacity in the optical backbone networks, fueled by video, cloud and other high capacity services, applies to both mature and emerging countries worldwide and in any geographical areas as well.  Installation of new, high data rate backbone networks continues apace as a key driver for economic advancement in developing regions of the world.

Introduction of Spectrally and Spatially Flexible Optical Networks

Given the introduction of coherent 100G systems has provided enough fiber capacity to meet data traffic growth in the near term, enhancing network efficiency will be service providers’ high priority. Adding flexibility at the optical layer is a key step to increasing network efficiency, and both spectral and spatial functionality will be considered in next generation optical networks along with advanced network management to effectively harness the new capabilities.

Performance Scaling Rules for Raman Amplification in Coherent Transmission Systems

It is well known that Raman amplification can improve system performance, but by what amount? I recently have written a review article on Raman amplification [1] based on an Invited Tutorial presented at OFC 2015 [2]. This article provides a good overview on how Raman amplification works in real systems and describes a method to calculate the nonlinear transmission penalties in coherent links. It also describes the implementation and control of Raman modules.

Raman Amplification for Ultra-Large Bandwidth and Ultra-High Bit Rate Submarine and Terrestrial Long-Haul WDM Transmission

Insatiable capacity growth and lower cost per transported bit are part of the main challenges any long-haul optical transmission infrastructure needs to cope with. The advent at the beginning of this decade of 100G channel rate, with PM-QPSK modulation format associated with digital coherent detection [1], offered a 10-fold capacity increase compared to networks based on 10G waves.

Transmission of 400G PM-16QAM Channels over LongHaul Distance with Commercial All-Distributed Raman Amplification System and Aged Standard SMF in Field

PM-QPSK has become the standard long-haul transmission modulation format for practical carrier networks while PM-16QAM has been considered for practical metro and regional networks [1, 2]. Since much higher SNR is required for 16QAM signals compared with QPSK signals it has not been considered so far to run 16QAM signals for long-haul distance in a real field environment with lossy and aged fiber.

16QAM Reach Performance with Xtera’s Wise RamanTM

In the past few years, we have seen a tremendous surge in fiber capacity enabled by 100G optical channels built upon PM-QPSK (Polarization Multiplexing Quadrature Phase Shift Keying) modulation format.  The quest for extreme bandwidth in optical backbone networks, however, seems never ending.

30 Gbaud Opto-Electronics and Raman Technologies for New Subsea Optical Communications

30 Gbaud opto-electronics and Raman technologies have quickly become the new standards for terrestrial backbone networks.  Today, the different subsea market segments take benefit from these new technologies as well.

200G and Raman Technologies for Long-Haul Data Center Interconnect

This insatiable demand for more bandwidth in optical backbone networks is fueled not only by increases in the number of users, the access methods and rates, but also the increased importance of data centers, cloud and the number of services (such as mobile, social media, and video in general).

Frequent 10G Adds/Drops in a Long-Haul 100G Network

Network operators who want to have frequent low bitrate client add/drop points on a long-haul 100G DWDM route have three legitimate options. They can 1) use a second pair of fibers for a parallel 10G DWDM system, 2) share the optical spectrum by adding 10G wavelength in with the 100G wavelengths on the same system, or 3) drop a 100G channl and mux/demux the lower rate clients from it at every add/drop point. Xtera can support three options.

Line Monitoring and Control in Subsea Networks

Until recently the main purpose of line monitoring, or supervisory, was to monitor the repeater status, detect system degradation and locate faults. As systems become more complex the submerged equipment may need, however, to be controlled as well as monitored.  The Branching Unit (BU) is a good example: while electrical switching can be controlled by power-feed currents, several suppliers have used supervisory signaling as a way of addressing some of the issues that this can create.

Recovering and Re-laying Cables for Building New Subsea Systems

Below the water, laid on the sea floor, numerous high-capacity submarine cables connect countries and continents. Today, optical subsea cable systems carry more than 95% of the world’s international voice and data traffic. This figure clearly shows that very little international traffic is carried by satellite, which is still a popular misconception.

Relationship between SMP, ASON, GMPLS and SDN

Traditional networks consist of two operating planes: the management plane and the transport or data plane. In this architecture, the data plane carries the user data. It consists of various network equipment, such as interface cards, switching equipment, and the fiber plant. Network operating information is managed by the management plane consisting of the Element Management System (EMS), the Network Management System (NMS) and the Operation Support System (OSS).

Shared Mesh Protection (SMP): What It Is and Where It Fits

For the world’s complex infrastructure of information and communications technologies, industry standards are critical to the interoperability of all networks regardless of whether they are for voice, data or video.  Industry standards allow these networks to “speak the same language,” and be able to exchange information among them.

Complimentary Fiber and Active Equipment Technologies that Deliver Extended Reach for High Data Rate Transmission in Long-Haul Networks

Installation of new, high data rate backbone networks continues apace as a key for economic advancement in developing regions of the world. Providing a reliable infrastructure for the movement of large volumes of telecoms data are as important for the economic development of a country as road network is for transporting physical goods.

Wise RamanTM: Integrated Design for Operational Simplicity

From its inception, Xtera’s objective was to develop a Raman-centric solution that brings together operational excellence and simplicity, as well as outstanding reach and capacity in optical transmission performances, in field conditions. Unlike competitive offerings where integrating optical Raman amplifiers with EDFAs is an afterthought, Xtera designed its optical networking platform from the ground up to combine different optical amplification flavors, ranging from simple EDFA to all-distributed Raman amplification.

XWDM Solution for 64 Terabit Optical Networking

Continuous capacity growth – fueled by video and cloud services – and lower cost per transported bit are part of the main challenges any long-haul optical transmission infrastructure needs to cope with. The advent at the beginning of this decade of 100G channel rate, associated with digital coherent detection, offered a 10-fold capacity increase compared to networks based on 10G waves.

Raman Amplification: An Enabling Technology for Long-Haul Coherent Transmission Systems

HE past 15 years have seen an incredible increase in data rates of optical transponders and, more recently, a move to multi-level phase modulated formats and coherent digital signal processing at the receiver. However, the fiber optic transport system has not changed much over this time and is dominated by C-band erbium-doped fiber amplifiers (EDFAs). These am- plifiers are the main building blocks of the transport system that define the performance characteristics of the optical net- work independent of the transponders.

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