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Title: Photonic Trends in Future Networks
Kurosh Bozorgebrahimi,
UNINETT, Abels gate 5, 7030 Trondheim, Norway
e-mail: [email protected]
Josef Vojtěch
CESNET, Zikova 4, Praha, Czech Republic
e-mail: [email protected]
Pavel Škoda
CESNET, Zikova 4, Praha, Czech Republic
e-mail: [email protected]
Paper type
Future Networks
Abstract
The aim of this presentation is to give a general overview of new trends in optical networking. The presentation
will cover the new movements and directions in fibre industry, coding technique, ROADM evolution and optical
based switching technologies.
Keywords
Optical networking, Transport network
1. Introduction
The developments of optical transport networking have been driven by need for higher and higher capacity in the
core networks, in addition to bring more flexibility and manageability to the network. Higher capacities have
been achieved by DWDM technology and by using higher bit rate per channel, using shorter channel spacing and
extending the optical transmissions band. A mix and match of these factors in addition to need for maximum
reach have been important factors in order to design a specific DWDM system.
We still face the increased demand for data transmission, but the focus is turned to channel bit rate rather than
total system capacity. It is probably caused by fact that mature all optical amplification doesn’t exist for other
bands than C (1530 nm - 1565 nm) and L (1565 nm – 1625 nm) and narrower channel spacing is in direct
conflict with higher bit rates per channel. Development of 40GbE and 100GbE accelerate this need, and the
market expectation about development of 400GbE and 1TbE will force the system vendors to spend their
development resource to develop systems which can handle 1Tbit/s channel bit rate even more than before.
In the short term view commercial operators are focusing on wide usage of Wavelength Selective Switch (WSS),
Optical Transport Network (OTN) and Multiprotocol Label Switching-Transport Profile (MPLS-TP) in the
backbone area. The short term strategy is to replace traditional circuit switched technologies like SDH with
packet oriented transport protocols like OTN (ODU switching) and MPLS-TP. Based on type and the size of
connection will wavelength switching, ODU switching and switching based on MPLS-TP be provided. We will
see a general deployment of OTN and MPLS-TP as switching engines beside the wavelength switching in the
backbone in the next 1-5 years. Regarding deployment of 100G, operators have a little bit different views.
Verizon already has a commercial 100G line in Europe (890km, Frankfurt-Paris), and is going to deploy more
100G lines. But some other operators, as Telefonica and France telecom, don’t see any immediate need for 100G
and will continue to use 40G until prices for 100G drops to a level closer to 40G prices. It is important to notice
that Verizon use the 100G line capacity as 10x10G in the client side due to lack of 100G supports on routers.
2. Three “M technologies”
The three “M technologies” are considered to be the second innovation wave in optical communication
technology which will achieve three orders increase in capacity (The first innovation wave was the invention of
EDFA and WDM) [1]. Ultramulti-level coherent transmission (Multi-level modulation formats), new optical
fibre technologies (Multi-core fibres) and mode division multiplexing (Multi-mode control with Multiple-input
and multiple-output (MIMO)) will be the key technologies in the second innovation wave (achieving peta
bit/s/fiber) within 2020.
Quadrature amplitude modulation (QAM) coherent transmission (256 QAM, 1024 QAM) is seen as a possible
successor of today 10G technology. The trade-off for transmission of multiple bytes in one symbol of ultra-high
multilevel QAM is higher required OSNR. Below are two examples of recent achievements with multilevel
modulation (QAM):
-
69.1 Tbit/s (432x171 Gbit/s), Polarization Division Multiplexed (PDM) 16QAM transmission over 240
km (polarization multiplexed 16-state quadrature amplitude modulation), ECOC2010
64 Tbit/s (640x107 Gbit/s), PDM-36QAM transmission over 320 km, ECOC2010, PDPB9 (Show the
figure below)
Multicore fiber: High optical power can cause “fiber fuse” in the core where fiber core could partially melt, and
the result is damaged fiber. In order to carry more power per fiber, the solution could be Multi-Core Fiber (MCF,
figures below). The development of such a fiber is although in its early stages. The industry needs to develop
MCF splice technique, MCF connectors and MCF amplifiers before it could be used in the field. In short term
perspective the pure silica core fibers [2] are considered again to solve some issues of these advanced
modulations. Their excellently low loss coefficient (< 0.15 dB/km) and high effective area can improve the
OSNR and reduce the non-linear effects.
Mode division multiplexing (MDM): The idea is to use each mode in a multi mode fiber as carrier. This can
again multiply transmission capacity of fiber, maybe not in long haul transmission systems, but it could be used
in other application areas. The picture below shows MDM using MIMO technique to improve the performance.
Additionally the polarization multiplexing allows doubling of bit rates today, especially in case of 100G. We
therefore see the potential increase of bit rates in combination of polarization multiplexing together with mode
division multiplexing. Nowadays the polarization mode multiplexing in 40G and 100G transmission is the key
technology for higher bit rate transmission systems.
Multicarrier and super-channel: Super-channel: Using Orthogonal frequency-division multiplexing (OFDM)
technology and sending “n” number of carrier within a fixed optical band. This technique removes the guardbands and sends multicarrier in one band that consists of more than one channel. For example, one 1.2 Tbit/s
demonstrated on super-channel consists of 24-carriers spaced 12.5-GHz, each carrying 50-Gb/s data via 12.5Gbaud PDM-QPSK. The super-channel has better spectral efficiency by using carrier overlap in the sender side
and filtering and detection in the Rx side. Deployment of multicarrier and super-channels will require
bandwidth-flexible DWDM systems.
Digital Signal Processing: DSP is getting more and more important in optical transmission systems. In the “inline dispersion compensation free” systems DSP does the Chromatic dispersion (CD) and Polarization Mode
Dispersion (PMD) compensating at receiver side. The figure below shows the block diagram for the receiver
based signal processing device [3].
3. Next Generation Reconfigurable Optical Add and Drop Multiplexer
NG-ROADM: Toward Colorless, directionless, Contentionless and gridless(Flexigrid) ROADMs
Colorless (uses any wavelength) and directionless (connects to any direction or degree) ROADM are widely in
use today. The next step is contentionless (utilizes any wavelength channel independent of all other channels in
action) functionality which add a new level of flexibility in the network. Colorless is achieved by tunable lasers
at transponders. Directionless is got by introducing another level of WSS in connection with transponders.
Contentionless in one direction is reached by adding another level of WSS and space switching devices in the
required A/D module. The full contentionless is achieved by NxM cross connect where N is number of ROADM
degree and M number of colorless A/D ports required.
Above mentioned bandwidth-flexible DWDM systems can be delivered by flexigrid functionality which enables
dynamic control of channel center frequency and channel bandwidth. Developing flexigrid capable WSS
technology is the first step toward Flexigrid ROADMs. Finistar demonstrate for the first time a Flexigrid WSS
technology (Finisar to Demonstrate Flexgrid(TM) WSS Technology at ECOC 2010).
References
[1] Masataka Nakazawa, Giant Leaps in Optical Communication Technologies Towards 2030 and Beyond,
ECOC 2010
[2] Nagayama Katsuya et al, Ultra Low Loss (0.1484 dB/km) Pure Silica Core Fiber, SEI technical review, 2004
[3] Chris R S Fludger et al, Digital Signal Processing: from Simulation to Silicon(Tu.5.A.1) , ECOC21010
Acknowledgements
The research leading to these results has received funding from the European Community¹s Seventh Framework
Programme (FP7/2007-2013) under grant agreement nº 238875 (GÉANT).
Biographies
Kurosh Bozorgebrahimi had been working with the Telenor ‘Transport Network’ and ‘Innovation Group’ from
1996 to 2006 before he joined UNINETT. He has participated in and managed various research and development
projects within xDSL, Ethernet/NG-SDH and optical networking for Telenor Networks. In 2003 he joined the
‘Network Strategy Group’, where he was participating in defining Telenor’s fixed network strategy. In 2006 he
joined UNNNETT and has the technical responsibility for UNINETT’s optical networks rollouts. His main fields
of interest are access and optical networks. Kurosh received his Masters degree in Physical Electronics (Optical
Communication) from the Norwegian University of Science and Technology in 1995.
Josef Vojtěch joined Research and Development Department of CESNET, a.l.e., in 2002, where he is active in
applied research in the area of photonic networking. He received the M.Sc. degree in Electrical Engineering and
B.Sc. degree in Pedagogy from the Czech Technical University, Prague, in 2001 and 2003, respectively. In 2009
he defended his Doctoral thesis “All-optical networking” at the Czech Technical University in Prague. In
Scopus, 24 records have been found with 29 citations, h-factor was 3.
Pavel Škoda graduated in 2008 at the faculty of electrical engineering at the Czech technical university in
Prague. Already at university started Pavel the collaboration with the Institute of Photonics and Electronics at the
Academy of Sciences of Czech Republic and joined the project “Components for high transmission rate alloptical networks”. After graduation went Pavel to the Tyndall National Institute in Ireland to study the dynamics
of mutually coupled laser system. From 2009 is Pavel working at Optical networks activity in CESNET z.s.p.o.
in Prague. In 2010 started Pavel the Ph.D. study at the Czech technical university in Prague.