Introduction to Optical Networks

T. Zami, D. Chiaroni, L. Noirie, O. Audouin Nokia Centre Villarceaux, Route de Villejust, 91620 NOZAY E-mail : [email protected]

January 2017 This course includes contributions from many Nokia colleagues Slide n°1

Illustration des enjeux "techniques" des télécoms Acteur

Son client

Ses besoins pour gagner des parts de marché

Utilisateur final

Ses requêtes auprès des fournisseurs + de services accessibles avec le meilleur rapport "qualité de service/prix"

(particulier, entreprise) Opérateur télécom/ Opérateurs de centre de données (Data Center)

Utilisateur final

Équipementier télécom

Opérateur

Fabricant de composant ou de sous-système

Opérateur et Équipementier

(particulier, entreprise)

(privée, publique)

Trouver les éléments pour fournir de nouveaux services ou des services améliorés en appliquant de la qualité de service différenciée à des prix compatibles avec la grande diffusion

Réduction des coût

Associer efficacement les techniques disponibles (si possible de façon propriétaire) pour optimiser la fourniture des services (ex : éviter les changements inutiles de couche réseau)

Réduction des coûts

Standardisation pour une meilleure interopérabilité Meilleures perfs. avec une qualité de service maintenue (voire améliorée)

Amélioration des perfs. (intégration, consommation, impact sur le signal optique, augmenter la capacité transmise)

Innovation et réactivité

Slide n°2

1

Introduction to Optical Networking 1. Introduction : transport networks today 1.1. Some examples of transport networks 1.2. Hierarchical networks 1.3. SDH/OTN networks 1.4. Optics in today’s network 1.5. New trend in optical networking (beyond the scope of this course)

2. Optical routing : principles and definitions 3. Building blocks : optical technologies 4. Towards “all” optical networks : limitations 5. Illustration of experimental assessment of an optical core network 6. Node architecture : Why now "Less" is better

Slide n°3

Introduction : transport networks today Example of an optical U.S Backbone network Network nodes

Seattle

wavelength routing Optical Cross-Connects (OXC)

Portland Detroit Denver

SF LA San Diego

Chigago

NYC DC

Las Vegas Phoenix

Optical fiber transmission links

Atlanta

Dallas

San Antonio

New Orleans

Orlando

Houston

Miami

• Of course the population distribution impacts the topology : • Dense network (shorter links) on east and west coasts • Longer transmission links in the center of the country Slide n°4

2

Introduction : transport networks today The protection and the restoration concepts Seattle

Restoration connection

Portland

Working connection

Denver

Detroit Chigago

SF

DC

LA

Protection connection

NYC

Las Vegas

San Diego

Phoenix

Dallas

Atlanta New Orleans

Orlando

Houston

San Antonio

Miami

• Connection from Los-Angeles to New-York • In case of protection, the working connection (red) and the protection one (orange)

transport the same information simultaneously. In case of failure, the destination node automatically switches very quickly from the working connection to the protection one. The “protection” service level agreement requires less than 50 ms connection recovery time

• In that respect, the working and the protection connections should not go through any common transmission link or network node

• Since the restoration path (blue) is calculated when the failure occurs, this process is slower than protection. It only avoids the failing network element but it can reuse the other parts of the previous working path Slide n°5

Introduction : transport networks today Possible Blocking issues for protection in the networks • For a protected connection from A to F, is the working path A-C-D-F appropriate?

A

C

working

E

• No because totally disjoint protection path is not possible

• So when disjoint protection is demanded, the working paths A-C-E-F or A-B-D-F should be preferred

B protection

F

D

• This basic example illustrates one of the issues when implementing the "protection" feature in real WDM networks

• Other constrains may exist such as: • Other conditions of path separation (not only between the working/protection pair of paths of the allocated service)

• Optimize as far as possible the balance of transmission distances between working and the protection paths to avoid too different transmission performances

• Management of different protection types: optical line interfaces shared or not shared

• The global optimization of the associated routing through the network is a NP-complex problem the ultimate solution of which cannot be determined in a reasonable range of time as soon as the number of network nodes exceeds 30 Slide n°6

3

Introduction : transport networks today France Telecom network • France Telecom

backbone network

• terrestrial fibre links in Europe

• with sub-marine fibre links towards/from other continents

http://www.francetelecom.com/ en 2001 Slide n°7

Introduction : transport networks today Global trans-oceanic internet fiber routes (1)

Interactive map from http://submarinecablemap.com/ Active and planned (the gray ones) submarine cable systems and their landing stations, with a maximum upgradeable capacity of at least 5 Gbps. Slide n°8

4

Introduction : transport networks today Global trans-oceanic internet fiber routes (2)

504.5 Gbit/s

181.4Gbit/s 66.3Gbit/s

Status mid-2004, 5Gbit/s minimum 2004 data source: www.telegeography.com Slide n°9

Introduction : transport networks today Hierarchical networks • Hierarchical Telecommunication Networks WAN : World Area Networks

~ 1000 km

~ 10 km

bit-rate, aggregation

distances

~ 100 km

=> backbone network

« RAN » : Regional Area Networks

MAN : Metropolitan Area Networks

~ 1 km

LAN : Local Area Networks Client A

=> access network Client B Slide n°10

5

Multi-layer network layout (as an early illustration) IP/MPLS Clients • Complete transparency for clients in flexible containers • ODU container sizes wellsuited for Ethernet transport

Clear Channel Clients

• ODU Termination (G.709 OAM) guarantees a clear demarcation • Intermediate Monitoring can be electronic and/or photonic

LO-ODU

LO-ODU

LO-ODU

• HO-ODU networking used when

client throughput does not need further aggregation within a  • LO-ODU networking used when sub- multiplexing is needed (no stranded BW)

LO-ODU

Sub- level networking

• Switching can be electronic

HO-ODU

and/or photonic

HO-ODU

HO-ODU

Electrical cross-connect Wavelength cross-connect

HO-ODU

HO-ODU

HO-ODU

 level networking

HO-ODU

NE “B” sub- switch

NE “A”  switch

Slide n°11

Introduction : transport networks today SDH/SONET/OTN routing nodes - issues • Optical transmission, but electronic nodes • Opto-electronic conversion, time demultiplexing, low rate switching, time multiplexing, optical transmitter, whereas a lot of traffic is transit • Synchronisation and node size issues to increase bit rate

2.5 GBit/s

Sync. Demux

SDH electronic Crossconnect

155 MBit/s

155 MBit/s

Fiber

STM-16

O/E

E/O

STM-1

Fiber

Sync. Mux

Sync. Demux

STM-1

O/E

STM-16

Fiber

Sync. Demux

E/O

Fiber

2.5 GBit/s

Slide n°12

6

Introduction : transport networks today SDH/SONET networks • SDH/SONET : • SDH : Synchronous Digital Hierarchy • SONET : American name…  Synchronous Optical NETwork • Primary technology for telecommunication transport networks before 2010

• What SDH/SONET is : a telecommunication standard (not datacom) • see ITU-T standards (main for SDH: G.707) • some normalized bit-rates (see next slide) • a way to aggregate low bit-rate to higher bit-rate

 "hierarchy"

• transmission format => framing • overhead in the frame => signalling and monitoring of networks • management of networks • standardisation of interfaces • Multi-vendors (Alcatel-Lucent, Huawei, Nokia-Siemens, Ciena, NEC, Fujitsu, etc…) Slide n°13

Introduction : transport networks today SDH/SONET bit-rates • The SDH/SONET normalized bit-rates are : SDH

SONET

155 Mbit/s

STM-1

OC-3

622 Mbit/s

STM-4

OC-12

2.5 Gbit/s

STM-16

OC-48

10 Gbit/s

STM-64

OC-192

40 Gbit/s

STM-256

OC-768

SDH => STM : Synchronous Transmission Module SONET => OC : Optical Channel

• How many voice communications in STM-N ? (1 voice channel = 64 kbit/s) • • • • •

155 Mbit/s : 1890 622 Mbit/s : 7560 2.5 Gbit/s : 30240 10 Gbit/s : 120960 40 Gbit/s : 483840

Note : some part of the bit-rate is used for signalling and can not be used for voice channels (1890*64 kbit/s = 120.960 Mbit/s < 155 Mbit/s …)

Slide n°14

7

Optical Transport Network - OTN Flexible and Efficient Protocol-Agnostic Transport – Defined in G.709 While SDH has been mainly designed to transport "telephone" communications, OTN is more suitable to transport any kind of data traffic thanks to a higher smallest switching granularity (1.25 Gb/s instead of 155 Mbit/s more convenient for 1 Gb/s Ethernet) SONET/SDH

ETHERNET

OTN/DWDM

OC-n/STM-n

1GE, 10GE, 40GE, 100GE

2.5G, 10G, 40G, 100G

Optical Transport Hierarchy (OTH) Client Signal

Client

•Optical Payload Unit

OPU OH

OPU

Optical Data Unit

ODU OH

ODU

ODU-n ODU0 = 1.25G ODU1 = 2.5G ODU2 = 10G ODU3 = 40G ODU4 = 100G

OTN “Digital Wrapper”

Optical Channel

Optical Transport Unit

OTU

Optical Channel

OTU OH

OCh

Optical Multiplex Unit

OMU

Optical Transport Module

OTM

OSC

Slide n°15

Introduction : transport networks today Optics in today’s networks

• Optical Transmission: • Use of the Wavelength Division Multiplexing (WDM) technique : several

wavelengths, each one carrying one signal, are transmitted in the same fibre

• Use of EDFAs for optical amplification => longer distances • Transmission capacity : • Commercial: 96 x 100 Gbit/s over 3000 km (9.6 Tb/s total capacity) • Laboratories record at the conference ECOC'2016 (Sept. 2016): • 65 Tb/s over 6600km (C+L amplification, Th.3.C.4, Nokia)

• Optical Routing: • Combining electronic routers (for the smallest switched granularities) and optical nodes to directly route optical channels carrying bigger granularities

• Even if the current optical networks are not regularly reconfigured on the optical

layer, the operators ask for automatic reconfiguration, in particular to enable fast restoration

Slide n°16

8

Introduction : transport networks today difference between circuit routing and packet switching • Circuit routing (initially mainly for voice communication) • All the corresponding physical resources are allocated in advance along the light path • Hence the quality of service is very good at the expense of a would-be over-provisioning of resource if the channel capacity is not fully occupied from the source network node to the destination network node.

• Packet switching (IP (Internet Protocol ), Ethernet, ATM, etc…) • The data to transmit is divided in small packets • Each packet goes with a "header" part that carries the associated important information such as the identification of the destination network node

• In the network node, the routing configuration is established only during the duration of the

packet crossing according to the destinations of all the packets that go through the node at a given moment. To achieve this task the node should have a very fast global scheduler

• Hence the routing matrix can be time-multiplexed and the utilization of the physical resources can be optimized

• Because of the very small packet durations (less than few ms at 10 Gb/s), the optical packet switching is very demanding in terms of switching speed and signal processing. It is the reason why optical packet switching is mainly still at the research level

• This course mainly focuses on optical circuit routing Slide n°17

Introduction : the new trend "data center networking" (1) Alan Benner (IBM), Paper OTu2B4, conference OFC'2012

Slide n°18

9

Introduction : the new trend "data center networking" (2) • Optics for data center networking:

• "Data center" intra-connection -> data center networks with instant connections with very low latency

• "Data center" interconnection • Printed Circuit Board (PCB) interconnection (chip/chip or card/card or rack/rack) • Pressure on cost and footprint

Current hierarchical non-blocking multistage data center topology

Can some of these switches become optical ?

Slide n°19

Introduction to Optical Networking 1. Introduction : transport networks today 2. Optical routing : principles and definitions 2.1. Network topologies 2.2. Main concepts of optical WDM networks 2.3. Node architecture

3. Building blocks : optical technologies 4. Towards “all” optical networks : limitations 5. Illustration of experimental assessment of an optical core network 6. Node architecture : Why now "Less" is better

Slide n°20

10

Optical routing : principles and definitions Mesh topology • Mesh topology : • Node connectivity  2

A

• Advantages : Working path

• short paths : depends on connectivity

Protection path 1

• typically ~N hops

• several solutions for protection • efficient use of resources

• Drawbacks :

Protection path 2

• nodes a bit more complex • management more complex

B

• protection schemes more complex

• Adapted for large networks (large number N of nodes) Slide n°21

Optical routing : principles and definitions Ring topology • Node connectivity : • connectivity = number of neighbour nodes

Protection path

• for Ring topology : Node connectivity = 2

• Advantages :

A

• simplicity of nodes • simplicity of protection schemes • simplicity of management

• Drawbacks : • long paths : up to ~N hops for N nodes

Working path B

• inefficient use of resources : • lot of transit & long paths for protection

• Adapted for small networks (small number N of nodes) Slide n°22

11

Optical routing : principles and definitions Interconnected ring topology • Ring interconnection • the network is made of several rings which are interconnected

Example : I21 network from http://www.interoute.com/ in 2001 A

• another way to make mesh topology • for protection issues : one ring is at least interconnected to the other rings by two nodes

• Advantages (vs. mesh) : • management by ring : simpler mgt, simpler protection, simpler structure

• Drawbacks (vs. mesh) : • inefficient use of resources

amplificateur optique B

nœud de routage nœud d’interconnexion

• Adapted for networks with large number N of nodes

Slide n°23

Optical routing : principles and definitions Other topologies • Bus • Two terminal nodes (connectivity = 1) are linked together with some intermediate nodes (with connectivity = 2) Terminal 1

Terminal 2

• Used for several sub-marine links • Protection issues : generally, another separate link between the two terminals

• Tree • One main node distributes/broadcasts the signals to all the other nodes • May be used for example for access networks

Hub

Access node

Slide n°24

12

Principle of the Wavelength Division Multiplexing (WDM) Mono-channel transmission at D Gbit/s

Optical fibre

Tx

Rx

Mono-channel transmission at 4xD Gb/s (time multiplexing) Tx

Rx 4 mono-channel transmissions at D Gb/s (overall rate : 4xD Gb/s) (spatial multiplexing)

Tx Tx Tx Tx

Tx

Rx Rx Rx Rx Wavelength multiplexing (WDM) at 4xD Gb/s

Rx

Tx Tx

Rx

Optical amplifier

Tx

Rx Rx

EDFA

Wavelength Multiplexer (mux/demux)

Slide n°25

The backbone networks and the corresponding Optical Cross-Connects (OXC) Granularity IP/MPLS (routed data bit-rate) Clients Capacity (sum of the data rates of all the input ports) Clear Channel

Wavelength Cross-connect

fibre

fibre

fibre

fibre

fibre

fibre

Clients

LO-ODU

LO-ODU

LO-ODU

Addition from local electronic router

LO-ODU

Sub- level networking HO-ODU

HO-ODU

HO-ODU

 level networking

HO-ODU

HO-ODU

NE “B” sub- switch

Optical Spatial switch

Dropping to local electronic router

HO-ODU

HO-ODU

NE “A”  switch

Backbone network (national or continental scale) Slide n°26

13

Optical routing : principles and definitions Hierarchical networks • As all networks, Optical Networks will be hierarchically organised ~ 1000 km

bit-rate, aggregation

distances

~ 10 km

Optical Migration

~ 100 km

WAN

« RAN »

MAN

~ 1 km

LAN Client A

Client B Slide n°27

Optical routing : principles and definitions Optical nodes • Depends on the connectivity of the node : • connectivity = number of neighbour nodes • connectivity = 1 : Terminal • connectivity = 2 : Optical Add-Drop Multiplexer (OADM) • connectivity >2 : Optical Cross-Connect (OXC)

• In some networks, there may be some specific nodes different of the other ones : the hubs • example : metropolitan networks (MAN) • a lot of traffic goes to / comes from the backbone network • one node can be dedicated to this operation : it will be concerned by the biggest part of the traffic  that’s what we call a “hub”

• Hub can be generally found in LAN, MAN and “RAN” • In backbone networks (WAN), there is generally no hub, all the nodes are “identical” Slide n°28

14

Main components for WDM optical routing A

i

B

Wavelength Demultiplexing

i

Space Switching : • Point to point (A) • Broadcast (B)

•Connectivity properties :



• point-to-point : • One input can be cross-connected to one output



 i Wavelength Filtering 

   

i

• broadcast/point-to-multipoint



• One input can be cross-connected to several outputs

Optical coupler

• cf. bridging for protection Slide n°29

Optical routing : principles and definitions WDM Terminal • Terminals : • connectivity = 1

Tx

• 1 input and 1 output fibre

Tx

• optical demultiplexing/multiplexing

Tx

• Transmitters / Receivers

Tx

• no switching

Rx Rx

• Use of Terminals : • bus networks • End points of mesh networks • Hubs (no switching)

Rx

WDM optical Multiplexer Output fibre WDM optical Demultiplexer Input fibre

Rx

Terminal Slide n°30

15

Optical routing : principles and definitions Optical or electronic switching ? • Electronic switching

Rx

• the input/output of the switching matrix are optical

O/E/O Electronic switching

Rx

• the switching inside the matrix is made by

Rx

electronic technologies

Rx

• some adaptation interfaces are required: • Receiver (Rx => O/E) at the input • Transmitter (Tx => E/O) at the output • we call it O/E/O (E=Electronic)

Tx Tx Tx Tx WDM multiplexer

WDM demultiplexer O/O/O Optical switching

• Optical switching : • the input/output of the switching matrix are optical • the switching inside the matrix leverages optical technologies • we call it O/O/O (O=Optical) • In this course we more focus on O/O/O switching • => transparent to bit-rate, less transponders ...

Rx

Electronic switching

Rx

Tx Tx

Slide n°31

Optical routing : principles and definitions Reconfigurable Optical Add-Drop Multiplexer (ROADM) •Optical Add-Drop Multiplexer:

Add/Drop

•connectivity = 2

Tx

•1-2 input / output fibres

2x2

•optical demultiplexing/multiplexing

In W

2x2

•conversion / regeneration (generally no)

2x2

•Transmitters / Receivers on Add/Drops

Switching matrix (typ. 2x2 arrays)

•optical switching matrix inside •if no wavelength conversion : array of cross-bar switches (2X2)

2x2

Out W

2x2

•bus networks

WDM multiplexer In E

2x2

•Use of OADMs : •ring networks

Out E

2x2

•wavelength adaptation if required

•can also be O/E/O switching

Rx

WDM demultiplexer

2x2 OADM

Rx

Tx

Slide n°32

16

Optical routing : principles and definitions WDM Optical Cross-Connect (OXC) OXC Tx Tx

• Optical Cross-Connect (OXC) :

Rx Rx

Wavelength converter

• connectivity > 2 • several input / output fibres

• optical demultiplexing/multiplexing • wavelength adaptation if required to solve wavelength contention • conversion / regeneration

Optical Switching Matrix

• Transmitters / Receivers on Add/Drops • optical switching matrix inside • can also be electronical switching with transponders

WDM multiplexer

WDM demultiplexer

• Use of OXCs : • mesh networks • interconnection of rings

Slide n°33

Optical routing : principles and definitions Switched-wavelength routing • A signal, carried by a wavelength, is routed through a network, possibly with wavelength conversion along its path :

TU1

1

3

2 5

TU

5

5

4

5 5

TU2

TU

TU : Terminal Unit Routing Node

Path from TU1 to TU2 on 1-2-3-4 : (VIRTUAL) WAVELENGTH PATH: (V) WP

Slide n°34

17

Optical routing : principles and definitions  conversion : wavelength number reduction • Helps to reduce the number of wavelengths needed in the network: • If no conversion in B, a 4th wavelength is needed for A-to-C connection

Node A

B

? 3

2 1 •

C

With conversion at B : wavelength reuse C A B

3

2 1

1

3

4 required wavelengths

Only 3 wavelengths needed

Slide n°35

Optical routing : principles and definitions Wavelength allocation • Wavelength allocation methods impact the dimensioning of the network. It takes into account the following parameters : • number of wavelengths and fibres needed • nodes equipment cost (number of transit lines, splitting losses, wavelengths used) • number of nodes on a path, physical impairments along light-paths • blocking probability

• Wavelength allocation is a complex problem that has no optimised solution • We use Heuristics : • Proceeding by successive evaluations and provisional hypotheses • Research methods based on progressive approach of the problem

Slide n°36

18

Optical routing : principles and definitions OXC : switching matrix functionality • Blocking properties : • Non-blocking • we can always find a state of the switching matrix to have the required connection status for all the input/output ports

• Rearrangeable non-blocking • non-blocking, but when we want to add a new connection some other connection must be disconnected and reconnected in a different way

• Strictly non-blocking • non-blocking, and when we want to add a new connection the other connections are not disturbed.

• For circuit routing Strictly non-blocking is mandatory while Rearrangeable non-blocking is sometimes suitable for packet switching

Slide n°37

Optical routing : principles and definitions OXC : single-stage architecture • Single-stage architecture : • N inputs Inputs

• M outputs • Switching elements : cross-bar

Cross state

Bar state

• Number of X-bars / cross-point : MN

Outputs

• M=N  N2 cross-bars • “digital”

c.f. MEMS “2D” => AT&T, OMM ...

Slide n°38

19

Optical routing : principles and definitions OXC : 2-stage architecture • 2-stage architecture : • N inputs

1xM

• M outputs • Switching elements : 1xM, Nx1 switches Inputs

1xM

Nx1

1xM Nx1

• The 1xN switches may also be "wavelength selective" (see the remainder)

1xM

• M=N  2N “1xN” switches

1xM

Outputs

• One of the stages of 1xN switches may be replaced by one stage of 1xN splitters but with more losses

Nx1

Nx1

• “analogue” or “digital” depending on 1xN structure (single-block / tree) : single-block

tree

c.f. MEMS “3D” => CrossFiber, Calient, ...

Slide n°39

Optical routing : principles and definitions OXC : 3-stage Clos architecture N = p.n port 1

p “n x 2n” “n x 2n” Module A-1

2n “p x p” 2N links p “2n x n”

2N links

“p x p”

“2n x n”

Module B-1

Module C-1

port 1

strictly non-blocking

 low number of links between modules

 maximum size of submatrix is max(2n,p)

 outputs of 1st stages, port In(i,e)

“n x 2n” Module A-i

“p x p” Module B-j

“2n x n”

port Out(k,s)

Module C-k

inputs of 3rd stages & 2nd-stages are protected (1:2n)

 modules of different types “n x 2n” port N

Module A-p

“p x p” Module B-2n

“2n x n” Module C-p

 optimised if p=2n=2N port N

=> N=2n2

 complexity : 42.NN

Unlike in the electronic domain, up to now these multi-stage layouts are rare in the WDM layer because their "complexity" implies too many switching elements Slide n°40

20

Optical routing : principles and definitions Network requirements • Connection establishment without disturbing already existing traffic • strictly non-blocking switching matrices

• Different quality of service, with possible traffic protection • dedicated protection (1+1) or shared protection (1:N) • short protection time (generally < 50 ms)

• To be “transparent” to the transported traffic • different protocols (IP, ATM, SDH, GigabitEthernet, …) • different classes of services (best effort, premium, …)

• Upgradability : small capacity increase of the network without too much extra hardware • Scalability : to be able to double (to scale) the capacity of the network without changing all the hardware of the network • Reconfiguration ability : optimized resources sharing (for instance the pool of transponders should be shared among several ports of the optical cross-connect) • Operators ask now for fast restoration (finding out and establishment of a new light-path should take less than 20 seconds) Slide n°41

Introduction to Optical Networking 1. Introduction : transport networks today

2. Optical routing : principles and definitions 3. Building blocks : optical technologies 3.1. Optical fibre 3.2. Optical amplification 3.3. Lasers, modulation schemes 3.4. (Elastic) transponders 3.5. Couplers, Optical filtering 3.6. Optical switching & mixed switching/filtering 3.7. Wavelength converters & regeneration 3.8. Technologies for optical packet and optical access

4. Towards “all” optical networks : limitations 5. Illustration of experimental assessment of an optical core network

6. Node architecture : Why now "Less" is better Slide n°42

21

Power and attenuation

•Power • P : power in Watt • PdBm = 10.Log10(P/(1 mW)), power in dBm

•Gain & Attenuation (insertion loss) • Pin : input power in Watt • Pout : output power in Watt • Gain in dB = 10.Log10(Pout/Pin) = PoutdBm – PindBm when >0 • Attenuation or Loss in dB = 10.Log10(Pout/Pin) = PoutdBm – PindBm when +25 dBm • issue : gain flattening...

• Semiconductor optical amplifiers (SOAs) • all windows possible (C-band, L-band, 1310 nm…), 35 nm bandwidth • bad noise factor, typically F=8-9 dB • low Pout, typ. equivalent noise factor < 0 dB !!!

• Others : EDWA (Erbium Doped Waveguide Amplifiers), ... Slide n°45

Building blocks : optical technologies Semiconductor Optical Amplifiers (SOA) • classical SOA • drawback : saturation power => gain depends on input power (more recent setup based on MQW significantly mitigate this downside) • NF not as good as EDFA => EDFA still preferred in real products

• Clamped-Gain SOA (CG-SOA) • internal laser mode at wavelength out of the WDM transmission window thanks to Bragg Grating => constant gain for a large input power range SOA

CG-SOA

Slide n°46

23

Building blocks : optical technologies Laser sources • Laser

CW laser

• Continuous Wave laser (CW) • Integrated Laser Modulator (ILM) • on the same chip wavelength source plus 2.5 or 10 Gbit/s modulation compatible with DWDM transmission

• Tunable laser : wavelength can be tuned continuously or step-by-step

ILM

Slide n°47

Building blocks : optical technologies External modulators : The Mach-Zehnder modulator each arms that is translated in an intensity variation thank to the interference at the Ei output of the Mach-Zehnder interferometer

• Illustration of the sinusoidal intensity

transfer function of the Mach-Zehnder modulator to carry out Amplitude Shift Keying (ASK) modulation

• The "Push-Pull" configuration (V1=-V2)

allows an intensity modulation without phase variation (no chirp) that is desirable to optimize the transmission

NRZ or RZ Complex constellation

V1(t) Eo V2(t)



 V ( t )V ( t )   i .   .  .e 2 EO  Ei .Cos  . 1  2.V  

V1 ( t )V2 ( t )   2.V

 

1

Normalized Transmission In intensity

• V1(t) and V2(t) induce a phase variation in

0

V 2.V 3.V 4.V V1-V2 (driving voltage) Slide n°48

24

Building blocks : optical technologies The Phase Shift Keying modulation Pre-coder

CW laser

DPSK Complex constellation

Pre-coder

• Differential Phase Shift Keying (DSPK) signal is obtained simply by modulating its phase between 0 and 

• The differential characteristic implies a pre-coding a make the signal more tolerant to non-linear effects of the propagation

• It is also possible to combine two MZ modulators to get 4 different

DQPSK Complex constellation

phase levels instead of only 2. This modulation scheme is called Differential Quadrature Phase Shift Keying (DQPSK). As 4=22, it allows 2 bits/symbol instead of only 1 bit/symbol in case of DPSK

• Next step…….. 16 QAM :

16=24 so 4 bits/symbol

Slide n°49

Typical data waveforms (here for 40Gbit/s systems) and their spectral occupancy 80GHz Freq.

Power (dB)

Phase-Shaped Binary Transm. (PSBT) 40GHz

Freq.

Power (dB)

Differential Phase Shift Keying (DPSK) 80GHz Freq.

Power (dB)

Quadrature Phase Shift Keying (QPSK) 40GHz Freq.

Power (dB)

Polarization Division Mux(PDM)-QPSK 20GHz Freq.

Increasing transmitter and receiver complexity

Power (dB)

Non Return to Zero (NRZ)

• Of course the new PDM modulation formats received by coherent detection are of interest for the optical transmission since they enable higher transmitted capacity • Moreover, they are also attractive for optical networking because the beatings with the local oscillator makes the detection more tolerant to optical crosstalk (see further part of this presentation) created by the adjacent WDM channels. Hence, in case of coherent detection only partial optical filtering is needed before detection. This can contribute to reduce the cost of the optical node

Slide n°50

25

Building blocks : optical technologies Receiver of Amplitude or Phase modulated channels Receiver for an "Amplitude Shift Keying" (ASK) modulated channel (NRZ or RZ) +V Photodiode

Optical signal

Electrical amplifier

Optical filter

Binary electrical signal

Decision Flip-flop

Clock recovery

resistance

Decision threshold

Low-pass filter

Decision time

Receiver for a "Differential Phase Shift Keying" (DPSK) modulated channel

• The simple photodiode is replaced by a differential system where Tb is a delay corresponding to the duration of a bit • The MZ interferometer changes the phase modulation into an amplitude modulation detected by the photodiodes

Tb

• Such detection scheme is more tolerant to optical noise and non- MZ interferometer linear effects of the transmission Slide n°51

Building blocks : optical technologies Reception in coherent mode • For 40 Gb/s and 100 Gb/s transmission, the coherent detection method associated to advanced electronic processing is of high interest because :

• The signal interferes with a local oscillator at the same wavelength so that Analogical-to-Digital converters can measure data related to its phase and its amplitude

• This additional information (as compared to a simple quadratic receiver) is very helpful to totally compensate for linear physical impairments such as PMD and CD

• It can handle polarization division multiplexed (PDM) channels and so the capacity per channel is

ADC ADC

3 4

PD3

ADC ADC

DSP DSP DSP DSP

j

BER & Q²

PD3

BER & Q²

Polarization Beam Splitter

Half mirror

j

Polarization Demultiplexing and Equalization

? /4

ADC ADC

Digital Clock Recovery

Incoming signal

2

ADC ADC PD2

CD comp.

1

CD comp.

PD1

Symbol identification

DSP - ASIC

Half mirror

Resampling --

? /4

Sampling Scope SamplingScope

Local oscillator

Symbol identification

3dB

Frequency Frequency and Carrier and Carrier Phase recovery Phase recovery

doubled as compared to simple PSK detection for a given symbol duration

Slide n°52

26

Elastic optical transponder (EOT) – Part 1 • An EOT is a transponder of WDM signal than can change capacity with a relatively small granularity (for instance with 100 Gb/s or 50 Gb/s step) and/or that can change nearly continuously its optical frequency. In Addition, it can also modify its FEC overhead.

• The channel data rate is adjusted via its Baud rate (32, 44, 56, or 61 GBaud) or via its constellation of modulation (QPSK, 8QAM, 16QAM, etc….)

• The first basic EOT’s became commercially available in 2014 with 100 Gb/s

and 200 Gb/s modulations. the much more versatile 2nd generation has been released in 2016 with up to 7 different modulation modes ( see next slide). EOT with more than 10 modulations modes are expected in 2017.

• The main goal of this evolution is to better fit the spectral efficiency of the

transported service to the actual (and possibly dynamic) quality of the light path that it follows though the network.

• This evolution also makes the network planning much more complex with the requirement to manage WDM network featuring various channel spacings (this could induce detrimental spectral fragmentation) Slide n°53

Elastic optical transponder (EOT) – Part 2

Slide n°54

27

Usual telecommunication WDM transponder – D5X500 • One shelf can be equipped with different types

of cards, like transponders, amplifiers, filters, Client Line etc…. ports ports

• Each shelf exhibits about 20 available slots

• The finer the card (in terms of slots), the larger the number of cards per shelf, and so the more complex the subsystems that one shelf can hold

• Some shelves also has extra

electric back panel connection between the cards Slide n°55

Photonic Integrated Circuit (PIC) Technology with the use of semiconductor manufacturing processes (with InP) This approach is mainly advocated by the Infinera company claiming that PIC Txs/Rxs can be significantly more cost effective than sets of single Txs/Rxs PIC combining 10x10.7 Gb/s NRZ transponders has been commercially available for several years The electronic DSP-ASIC is not part of this PIC. It should be added externally

Slide n°56

28

Silicon Photonic Integration

(Paper Th5C.1, OFC’2014)

Emitted modulated signal Local oscillator Received signal

CFP2 module dimensions 41.5x107x12.4 mm Slide n°57

Introduction : the Data Center Interconnect (DCI) boxes Example of the new compact and modular “DCI-box” transponder

CORIANT GROOVE G30 DCI platform • 1,6Tb/s (4 x 400Gb/s) • 4 independent slices of 400Gb/s each • Low power consumption: 45W/(100Gb/s) 1RU • each slice based on an hot swappable Field Replaceable Unit (FRU) card containing:

• 2 x CFP2-ACO (FRU) • 4 x QSFP+/QSFP28 client 2 x CFP2-ACO (32GBaud) enabled by silicon photonic integration

4 x QSFP28 (100GE) or 4 x QSFP+ (4x10GE/40GE)

400Gb/s capacity (1 sled) 400 Gb/s client+400 Gb/s line

400G ASIC (used as a framer) • Low power consumption • Low latency • QPSK 100G, 8QAM 150G, 16QAM 200G • DC compensation up to 280 ns/nm for QPSK and 45 ns/nm for 8QAM/16QAM Slide n°58

29

Equipment vendors bypassed by some of the GAFAM’s • The new networking trends initiated by the most powerful cloud players (Google-AmazonFacebook-Apple-Microsoft) are changing the “game” in the WDM domain

• They act now in the WDM domain like they have been acting in the domain of server blades for

several years, by specifying their own products. Indeed, to reduce capital as well as operational expenditures and so to only pay for the features they need, they can directly discuss with vendors of WDM sub-modules (bypassing equipment vendors like Nokia) to specify the WDM network elements (transponder) they want.

• The sizes of the data centers they operate are so large that they can order about 100000 items.

This huge growing capacity to invest explains their raising influence on the WDM market direction

Facebook’s Voyager DCI-box announced in November 2016 Ethernet router accommodating twelve 100Gbps QSFP28 input client interfaces and four 200-Gbps coherent optical output modules

• Microsoft teamed with Inphi for first 100 Gb/s QSPF28 for Data Center Interconnect • 50 Gb/s PAM4 per lambda and 2 lambdas per 100 Gb/s used • Connect data centers nearly 80km apart • Tentative availability: 2017 Slide n°59

Next step of Coherent CFP2 modules CFP2-DCO integrating ASIC-DSP

http://acacia-inc.com/products/cfp2dco-product-family/

From “Juniper Networks IP & Optical Update” presentation

twitter.com/junipernetworks/status /740287302140858368

CFP2-ACO socket Next Generation CFP2-DCO

Same form factor Slide n°60

30

Building blocks : optical technologies Passive couplers • Different kind of couplers :

Loss (dB) = 10.LogN • splitter 1:N => power diffusion • N:1 combiner => multiplexing • N:N star coupler => multiplexing + power diffusion

P

1:N

P/N

1

P/N

2

P/N

3

/N N:1

1

/N

2

/N

3

P/N Splitter

P/N a% b%

N

Combiner

+ Excess Loss

N

N:N Nx1 Star coupler

/N /N /N

Loss (dB) = -10.Log(a/100) + Excess Loss Loss (dB) = -10.Log(b/100) + Excess Loss

• tap coupler = 2:2 with specific coupling ratio => monitoring Slide n°61

Building blocks : optical technologies Optical filters • Different functions : • • • • • •

single wavelength filter : to filter a fixed wavelength waveband filter : to filter a group of wavelengths mux / demux : to demultiplex a fibre into s or group of s interleavers : to select 1 wavelength each N wavelength on a regular grid wavelength routers : fixed wavelength routing tunable filter : to be able to select a wavelength

• Different technologies & techniques : • • • • • • •

Fabry-Perrot thin films AWGs : Array Waveguide Gratings interferometers MEMS/MOEMS : Micro-(Opto)-Electronic-Mechanical Systems Fibre Bragg-Gratings ...

Slide n°62

31

Building blocks : optical technologies Optical mux / demux • Mux/Demux :

Tx 1

• to multiplex the wavelengths in the fibre • to demultiplex the wavelengths from the fibre



Tx 2 Tx 3 Tx 4 Tx 5 Tx 6

M U X

D E M U X



Tx 7 Tx 8

Diffraction grating

Arrayed-waveguide grating

Splitter and filters

1

 8

RWA

DATA OUT

RWA

DATA OUT

RWA RWA

DATA OUT DATA OUT DATA OUT DATA OUT

RWA RWA RWA RWA

DATA OUT DATA OUT

Interference filters

 

1 2 3 4 5 6 7 8

1

8



1

Thin film

8

Slide n°63

Building blocks : optical technologies Optical switches : technologies • Opto-mechanical : • Mechanically activated, low insertion loss, low PDL (polarisation dependent loss), very good port-to-port crosstalk, long switching time (~100 ms)

• Micromechanical switches (MOEMs) : • same as opto-mechanical but very small ones (example : micro-mirrors => < 1 mm mirror size) => compact and faster (~1 ms)

• Lithium niobate (LiNbO3) directional couplers : • High loss, high driving voltages (poor integration), high PDL, switching speed up to several tens of GHz (10 ps), bad crosstalk (~20 dB)

• Indium phosphide (InP) digital optical switches (DOS) : • High loss, high integration possible, high PDL, switching speed up to 100 MHz (10 ns), bad crosstalk (~15 dB)

• semiconductor optical amplifier based : • Loss partly compensated by gate gain, good integration potential, switching speed > GHz (55 dB

optical losses < 1 dB (1525-1565 nm) return losses > 50 dB switching time < 400 µs

Slide n°66

33

Building blocks : optical technologies 1xN / Nx1 optical switches • 1xN switch use :

1x4

4x1

• shared 1:N network element protection

1x4

4x1

• NxN switch in association with Nx1 switches

1x4

4x1

1x4

4x1

• Nx1 switch use : • shared 1:N network element protection • NxN switch in association with 1xN switches • monitoring : to share monitoring device between different elements

• Technologies :

4x4 switch with : - 1x4 switches (4) - 4x1 switches (4)

Tap couplers transmission fibres 4x1

Spectrum analyser

Optical Spectrum Monitoring :

• Opto-Mechanical, MEMS, thermo-optic, Liquid Crystal, ... Slide n°67

Building blocks : optical technologies 1xN / Nx1 optical switch example • 8x1 switch (MOEMS) • 3 cascaded stages of basic 2x1 switches :

• Basic 2x1 switching stage: • Electro-mechanical switch using CEA-LETI SiO2/Si technology

8 fibers ribbon input

SMF output

8x1 switching module basic stage

• deflection by cantilever beam

 driving voltage = 70 V  full size = 115 x 25 mm2 "A 8x8 optical space-switch based on a novel 8x1 MOEMS switching module", J.-P. Faure et al., OFC'01

Slide n°68

34

Building blocks : optical technologies NxN & NxM optical switches • Functionality : • at least point to point strictly non blocking • sometimes multicast / broadcast capability

• Use : • optical switching matrix • or part of an optical switching matrix (ex: Clos architecture …)

• Technologies : • Opto-mechanical, micromechanical switches (MOEMs), thermo-optic, Liquid Crystal, “bubble switch”, ...

Slide n°69

Building blocks : optical technologies NxN 2D MOEMS switch • MOEMS 8x8 switch : • “Free-space micromachined optical crossconnects: routes to enhanced portcount and reduced loss”, L.Y.Lin et al, AT&T, OFC´99, FH1 • Information : • 8x8 switch => 16x16 (4 “8x8”) • mirrors 300 mm diameters, waist 100 mm, 8x8 in 1 cm2 (step : 1.25 mm)

• Architecture : • Plane (2D) with • N input fibres on one side • N output fibres on the other side

• N2 mirrors 0° / 90° • thus N2 electrical commands (ON/OFF)

Slide n°70

35

Building blocks : optical technologies NxN 3D micromechanical switch • See for example : • “Performances of a 576x576 Optical Cross-Connect”, H.Laor and al., Astarte / Texas Instrument, LEOS´99, L.Y.Lin et al, AT&T, OFC´99, FH1

• Architecture (Astarte) :

Moving mirror

• Space (3D) with • N input fibres on one side • N output fibres on the same side • fixed Mirror

• only 2N mirrors

Fixed mirror

• 2N electrical commands (“analogic”)

• See also Lucent MOEMS based switches Slide n°71

Building blocks : optical technologies High-speed, 128x128 3D-MEMS OXC switch Input/output fiber array Roof-type Retro-reflector

Input/output m-lens array

Input/output MEMS mirror array

Folded configuration with roof-type retro-reflector by a factor of 1/2 of flat-reflector (Lucent)

Features -Large scale: 128 x 128 channels -Switching time: 1ms -Low power consumption: 22W -Small size: 430 x 131 x 400mm Slide n°72

36

Comparison of optical node architecture on a "insertion loss" point of view (Part 1) • 2 basic elements : 1xn optical coupler

1xn optical spatial switch

• The insertion loss of the coupler is by far higher than the one of the spatial switch (above all when n>2) • For instance 11 dB for a coupler 1x8 and less than 3 dB for a optical spatial switch 1x8 • These information should be accounted for, among others considerations such as the total cost, when searching the best node architecture

Slide n°73

Comparison of optical node architecture on a "insertion loss" point of view (Part 2) • How to achieve an 4x4 optical spatial router with : • Coupler 1x4 (insertion loss : 7 dB) • Optical spatial switch 1x2 (insertion loss : 2 dB) • Optical spatial switch 1x4 (insertion loss : 3 dB)

• Examples

Insertion loss : 11 dB

Insertion loss : 10 dB

Insertion loss : 6 dB Slide n°74

37

Building blocks : optical technologies 16-channel monolithic wavelength selector on InP 4.2 mm 10

4.6 mm

Fibre-to-fibre gain (dB)

0 SOA1 SOA2 SOA3 SOA4 SOA7 SOA8 SOA9 SOA10 SOA11 SOA12 SOA13 SOA14 SOA15 SOA16

-10 -20 -30 -40 -50 -60 0

10

20

30

40

50

60

70

80

90

100

Current (mA)

R. Mestric et al., OFC’2000 S. Khalfallah et al., ECOC’2001

• Zero loss @50mA for all channels • Good homogeneity: 1.9±1.6dB @50mA • PDL < 3.5dB on all channels

Slide n°75

Building blocks : optical technologies Wavelength Blockers and Wavelength Selective Switches • Component suppliers are now making optical switching devices integrating the filtering function (mux/demux) • Optical switch part : MOEMs, Liquid Crystal • Optical filtering part : AWGs, free space grating

• Wavelength Blockers (WB) • Demux + array of "ON/OFF" switches + Mux • power equalisation functionality when the "ON/OFF" switches are indeed variable optical attenuators

• Wavelength Selective Switches (WSS) • 1 Demux + array of 1xN switches + N Muxes • Or N Demuxes + array of NxN switches + N Muxes • Possible integration of power equalisation like in WBs

WB

1x1 1x1 1x1 1x1

variable optical attenuators WSS 1xN 1xN 1xN 1xN

Slide n°76

38

Building blocks : optical technologies WSS layout attenuator 1xN switch

output ports

Common port

optical demultiplexer

Achieved with only one array of bi-axial MEMs

optical multiplexers

Future WSS with more output/input ports, less insertion loss, broadcast ability or adjustable bandwidth (the same WSS can process 100-GHz or 50-GHz spaced channels) Slide n°77

Liquid Crystal on Silicon (LCOS)-based 1xN WSS Matrix Matrix of of 1920x1080 1920x1080 LCoS LCoS pixels pixels making making vertical vertical phase gratings Array ofphase MEMsgratings One MEM per channel With Withirregular regular spectral spectral spacing spacing

• Schematic diagram (from FINISAR) exemplifying optical beam steering in LCoS WSS • Unlike MEMs-based WSS, there is no single MEM dedicated to each WDM channel • LCoS is highly software programmable enabling, for instance, reconfiguration of the

frequency grid from 50 GHz to 100 GHz (Flexgrid/Mixgrid) or even less than 50 GHz

• Max size of commercial WSS: 1x32, max size achieved by research lab: 1x95 Slide n°78

39

Functional diagram of a “all-in-one” OXC line card Example of the 20-Port Cisco NCS 2000 line card

This layout corresponds to a single pack gathering all the elements of one WDM direction (ingress amplifier and WSS, egress amplifier and WSS, internal monitoring photodiodes) Slide n°79

10x10 WSS by JDSU (Paper AF4E.1, ACP'2013) Simplified optical block diagram for MxN WSS

Photograph of prototype Twin 10x10 WSS

• In the switching plane, imaging optics collimate light from an array of fibers and transform fiber height at the input to angle of incidence at the LCoS switching engine

• The high definition LCoS switching engine is used as a programmable phase grating, steering light in the first diffraction order from input port to a selected output port

• LCoS configured to steer light from input 1 to output 2 for one wavelength channel (solid line) and input 1 to output 1 for another (dashed line)

• 2 sets of "twin" input/output ports (only one appears on the leftmost figure) are steered to different regions of the LCoS, so that they can be switched independently

• Only one instance of each wavelength can go at once through this 10x10 WSS Slide n°80

40

8x8 contentionless WSS prototype by Huaweï (Paper P4.4, ECOC'2014)

Functional view

Picture of assembled module

• 8x8 WSS that can handle simultaneously up to 8 instances of the same wavelength in between 8 distinct pairs of ingress/egress ports

• So far physical performance not good enough for practical application • From 12 dB to 20 dB insertion loss, 16 dB typical value (Zong et al., JOCN, Vol. 8, n°7, July 2016)

• Worst optical crosstalk: higher than -25 dB, that will degrade when attenuating the channel power for power leveling (Zong et al., PTL, Vol. 27, n°24, December 2015) Slide n°81

Current WSS-based optical node architectures • These architectures are now standard, used by most of the optical telecommunication vendors broadcast & select architecture

Select & combine architecture

Route & select architecture

Optical splitters

WSSs WSSs

WSSs

WSSs

Optical combiner

Slide n°82

41

Building blocks : optical technologies Other • Photodiodes : for receivers • PIN, APD

• Modulators : associated with lasers => for transmitters • external modulators : LiNbO3, Electro-Absorption, ...

• Attenuators : optical power adjustment • single attenuator => VOA : Variable Optical Attenuator • Dynamic Gain (/Power) Equaliser (DGE)

• Chromatic Dispersion management : • Dispersion Compensation Modules (based on DCF), FBGs

• Optical connections : • fibre connectors, ribbon connectors • shuffles…

• Others…(Optical regenerator)

Slide n°83

Towards more efficient optical networks : example From circuits

To packets

(N-1) TRX

(N-1) TRX N(N-1)/2 wavelengths

(N-1) TRX

1 TRX

1 TRX

1 wavelength

1 TRX

Time multiplexing to optimize the resource allocation and provide full connectivity with a minimum of transponders and wavelengths when the filling ratio of each channel between each pair of ring nodes is low Slide n°84

42

Building blocks : optical technologies Principles of optical packet one optical packet : up to few ms header

guard-band (10 to 20 ns) to switch if necessary

header of next optical packet

payload

time

• The header • At predefined bit rate with synchronisation sequence for fast clock recovery

• Contains identification, source and destination read and sometimes modified in the packet switch fabrics to perform the routing

• The Payload • Contains the real data to be transmitted • Fixed (ATM, 48 bytes) or variable (Ethernet, IP) size

• The Guard-band • Absorbs the switching time and the processing time of the header Slide n°85

Key Technology: Fast tunable laser 50

4

45

SG-DBR

Gain

Phase

SG-DBR

Back Current (mA)

40

34

35 30 25 20 15 10

18

5 62

0 0

Wavelocker

Jesse Simsarian, Bell Labs

Gain Source

Laser

50 mm

TEC Control

5

10

15

20

25

Front Current (mA)

SGDBR device for fast switching demonstration made to switch from any to any of 64 channels in 6000km

QPSK

8PSK

50 Gb/s per polarization Transmission reach on SMF=3200km 64QAM 16QAM

8QAM

75 Gb/s per polarization Transmission reach on SMF=1400km

100 Gb/s per polarization Transmission reach on SMF=650km

150 Gb/s per polarization Transmission reach on SMF