Verizon plans coherent-optimised routes
"Next-gen lines will be coherent only"
Glenn Wellbrock, Verizon Business
Muxponders at 40Gbps
Given the expense of OC-768 very short reach transponders, Verizon is a keen proponent of 4x10Gbps muxponders. Instead of using the OC-768 client side interface, Verizon uses 4x10Gbps pluggables which are multiplexed into the 40Gbps line-side interface. The muxponder approach is even more attractive with compared to 40Gbps IP core router interfaces which are considerable more expensive than 4x10Gbps pluggables.
DQPSK will be deployed this year
Verizon has been selective in its use of differential phase-shift keying (DPSK) based 40Gbps transmission within its network. It must measure the polarisation mode dispersion (PMD) on a proposed 40Gbps route and its variable nature means that impairment issues can arise over time. For this reason Verizon favours differential quadrature phase-shift keying (DQPSK) modulation.
According to Wellbrock, DPSK has a typical PMD tolerance of 4 ps while DQPSK is closer to 8 ps. In contrast, 10Gbps DWDM systems have around 12 ps. “That [8 ps of DQPSK] is the right ballpark figure,” he says, pointing out that a measuring a route's PMD must still be done.
Verizon is testing the technology in its labs and Wellbrock says Verizon will deploy 40Gbps DQPSK technology this year.
Cost of 100Gbps
Verizon Business has already deployed Nortel’s 100Gbps dual- polarization quadrature phase-shift keying (DP-QSPK) coherent system in Europe, connecting Frankfurt and Paris. However, given 100Gbps is at the very early stages of development it will take time to meet the goal of costing 2x 40Gbps.
That said, Verizon expects at least one other system vendor to have a 100Gbps system available for deployment this year. And around mid-2011, at least three 300-pin module makers will likely have products. It will be the advent of 100Gbps modules and the additional 100Gbps systems they will enable that will reduce the price of 100Gbps. This has already happened with 40Gbps line side transponders; with 100Gbps the advent of 300-pin MSAs will happen far much quickly, says Wellbrock.
Next-gen routes coherent only
When Verizon starts deploying its next-generation fibre routes they will be optimised for 100Gbps coherent systems. This means that there will be no dispersion compensation fibre used on the links, depending on the 100Gbps receiver’s electronics to execute the dispersion compensation instead.
The routes will accommodate 40Gbps transmission but only if the systems use coherent detection. Moreover, much care will be needed in how these links are architected since they will need to comply with future higher-speed optical transmission schemes.
Verizon expects to start such routes in 2011 and “certainly” in 2012.
OFC/NFOEC 2010: Technical paper highlights
Here is a sample of some of the noteworthy papers.
Optical transmission
Nortel’s Next Generation Transmission Fiber for Coherent Systems details how various fibre parameters impact coherent system performance. This is important for existing 40 and 100Gbps systems and for future ones based on even higher data rates.
In 40G and 100G Deployment on 10G Infrastructure: Market Overview and Trends, Coherent Versus Conventional Technology, Alcatel-Lucent discusses 40G and 100G deployment strategies over 10G infrastructures based on a trial using live commercial traffic.
Two papers demonstrate possible future optical modulation steps.
In Ultra-High Spectral Efficiency Transmission, Bell Labs Alcatel-Lucent details the generation, transmission and coherent detection of 14-Gbaud polarization-division multiplexed, 16-ary quadrature-amplitude-modulation (16-QAM) signals achieving spectral efficiencies as high as 6.2 b/s/Hz.
Meanwhile, NEC Labs America and AT&T Labs address 112.8-Gb/s PM-RZ-64QAM Optical Signal Generation and Transmission on a 12.5GHz WDM Grid. The optical signal was sent over 2x40km using an 8-channel WDM using 12.5GHz grid spacing.
Photonic integration
In High Performance Photonic Integrated Circuits for Coherent Fiber Communication, Chris Doerr of Bell Labs, Alcatel-Lucent presents how photonic integration can benefit high-speed transmission. In particular, how optical integration can be used to tackle the complex circuitry needed for coherent systems to reduce the area, cost, and power consumption of optical coherent transceivers.
Another photonic integration development is the CMOS-Integrated Low-Noise Germanium Waveguide Avalanche Photodetector Operating at 40Gbps from IBM T.J. Watson Research Center. The avalanche photodiode has a gain-bandwidth-product above 350GHz operating at 3V. The avalanche photodetector is monolithically integrated into CMOS.
Optical access
An update will be given on the EU’s Seventh Framework programme for WDM-PON, dubbed Sardana - Scalable Advanced Ring-based passive Dense Access Network Architecture. The paper, Results from EU Project SARDANA on 10G Extended Reach WDM PONs, details the integration of WDM metro and PON access technologies to implement ring protection, 100km reach and up to 1024 users served at 10Gbps using a passive infrastructure.
In 44-Gb/s/λ Upstream OFDMA-PON Transmission with Polarization-Insensitive Source-Free ONUs, NEC Labs America details its work on colourless 44-Gb/s/λ upstream OFDMA-PON transmission using polarization-insensitive, source-free ONUs.
Green telecom and datacom
There are other, more subtle developments at OFC/NFOEC. Two papers from Japan have ‘Green’ in the title, highlighting how power consumption is increasingly a concern.
High Performance “Green” VCSELs for Data Centers from Furukawa Electric Co. Ltd details how careful design can achieve a 62% power conversion efficiency in the 1060nm VCSEL.
The second paper tackles power consumption in access networks. Key Roles of Green Technology for Access Network Systems from NTT Labs in Japan addresses the ITU-T’s standardisation activities. Optics for flow and interconnect
In Optical Flow Switching, Vincent Chan of MIT will discuss 'optical flow switching' that promises significant growth, power-efficiency and cost-effective scalability of next-generation networks.
Meanwhile Bell Labs, Lucent Technologies has a paper entitled Photonic Terabit Routers: The IRIS Project, detailing the results of the DARPA-MTO funded program to develop a router with an all-optical data plane and a total capacity of more than 100 Tbps.
Another important topic is optical interconnect. Low Power and High Density Optical Interconnects for Future Supercomputers from IBM Research reviews the status and prospects of technologies required to build low power, high density board and chip level interconnects needed to meet future supercomputers requirements.
NFOEC papers
There are also some noteworthy NFOEC papers bound to stir interest:
- Google reviews the optical communication technologies required to support data center operations and warehouse-scale computing.
- Verizon shares lessons learned during the five years of Verizon’s FiOS and the need to continually evolve product and service offerings.
- AT&T details the key decisions required in defining its new 100G backbone.
There is a comprehensive OFC/NFOEC preview in the February issue of IEEE Communications magazine, click on the "conference preview" tab.
