Prezentace aplikace PowerPoint · 2011. 12. 9. · Title: Prezentace aplikace PowerPoint Author:...

Josef Vojtěch (FIT ČVUT) Optical Networks

Optical Networks

Josef Vojtěch josef.vojtech/at/cesnet.cz

Katedra počítačových systémů FIT České vysoké učení technické v Praze

© Josef Vojtěch, 2011

MI-MTI, ZS2011/12, Předn. 12 https://edux.fit.cvut.cz/MI-MTI/

Evropský sociální fond Praha & EU: Investujeme do vaší budoucnosti

MI-MTI, 2011, L. 12

Josef Vojtěch (FIT ČVUT) Optical Networks MI-MTI, 2011, L. 12 2

Optical Networks

Outline

History

Typical Transmission Fibers

Impairments (CD, PMD, non-linearities)

WDM Transmission (WDM, DWDM, CWDM)

Amplifiers

Doped fiber – EDFA, PrDFA

Raman

SOA

SDH, OTN

Present and Future Transmission Systems

Conclusion


Back to Antiquity (mirrors, fire beacons, smoke signals) [1]

Till the end 18th century with lamps, flags

1792 – Claude Chappe with mechanical „optical“ telegraph

1830 – the advent of telegraphy

1866 – the first transatlantic cable went into operation

1876 – the invention of telephone (A.G.Bell, U.S. Patent No. 174 465)

1940 – massive increase of pairs installed - 3 MHz coax-cable system (repeater spacing 1 km), high freq. dependent loss

1948 – 4 GHz microwave system

1960 – the invention of laser (suitable transmission medium?)

1960s – optical fibre (1000 dB/km)

Optical Networks

A Little Bit of History (1)


Evolution of optical communication systems

850 nm, 1310 nm, 1550 nm

1st generation GaAs lasers 850nm, 10km regeneration

1980 – 45 Mb/s (1st generation) multi-mode fibres

2nd generation 1310 nm

1980s – 1310 nm, 1 dB/km, 100 Mb/s, multi-mode fibres

Late 1980s – 2 Gb/s, single mode fibres, repeater spacing 50 km (2nd generation)

3rd generation 1550 nm

1990s – 1550 nm (problem with lasers, dispersion of fibres, typical repeater spacing 60 -70km), 2.5 Gb/s or 10 Gb/s (3rd generation)

Optical Networks



4th generation 1550 nm – WDM - DWDM, CWDM

Optical amplification, EDFAs developed late 1980s

1990s - DWDM, optical amplification (4th generation)

Today – 10, 40 and 100G waves, 160 channels ie x Tb/s, thousands of kilometers

Optical Networks



All electromagnetic phenomena are described by Maxwell‘s equations

An optical fibre (silica or non-silica) is a nonconducting, non magnetic medium without free charges: ρ=0, J=0, M=0

Optical Networks

A Little Bit of Theory

t

BE

t

DH

0 D

0 B

PED 0

HB 0

E, H: electric/magnetic fields vectors

D, B: electric/magnetic flux densities

P: induced electric polarization

M: induced magnetic polarization

ε 0: the vacuum permittivity

μ 0: the vacuum permeability

rot

rot

div

div

Josef Vojtěch (FIT ČVUT) Optical Networks MI-MTI, 2011, L 12 7

Optical Networks

Optical Fibres

core: n1

cladding: n2

jacket: n0

n1 > n2 > n0

θi θr

Φ

1

2csin

n

n

Total internal reflection (discovered 1854)

Numerical aperture NA, the maximum angle of the incident ray to remain inside the core

Core: MM: 50 μm/62,5 μm, SM: 8,6 μm – 9,5 μm

Cladding: 125 μm

NAcossin ci 10 22

21 nnnn


1970: 20 dB/km (Kapron, Keck, Maurer), silica fibres

Multimode (MM) and singlemode (SM) fibres

Multimode: step-index (SI) or graded index (GI)

MM SI: modal dispersion: different rays disperse in time because of the shortest (L) and longest (L/sinΦC) paths

MM SI: 10 Mb/s

MM GI: parabolic index, lower modal dispersion, higher bit rates, 100 Mb/s

Plastic MM GI, for 1 GE (or even 10 Gb/s)

Attenuation: 1 – 4 dB/km, <10 dB/km for plastic

Optical Networks

Optical Fibres - MM


Optical Networks

Optical Fibres


Single mode (SM, Standard SMF, G.652) fibres

Supports only one so called „the fundamental mode of the fibre“, all higher modes are cut off @ the operating wavelength

An optical mode refers to a specific solution of the wave equation (satisfies boundary conditions, spatial distribution is constant as light travels along a fibre)

The cutoff wavelength is specified in ITU G.650, SM@1310 nm and 1550 nm, cutoff approx. 1200 nm

0,2 dB/km@1550 nm, 0,4 dB/km@1310 nm

Optical Networks

Optical Fibres - SM


PTx = 1 mW

PTx = 0 dBm

PRx = ??

PRx = -6 dBm

Optical Networks

Optical Powers

Tx Rx

P [dBm] = 10 log P[mW]

A = 6 dB

Attenuation coefficient

α [dB/km] = A / l


MM: Intermodal dispersion (pulse broadening, the most important limiting factor)

SM: Intermodal dispersion is absent, pulse broadening is present still because of Intramodal dispersion (or Group-velocity dispersion CD), even laser pulses have finite spectral width and pulses are modulated

CD: different spectral components of the pulse travel at different speeds

Increases as the square of the bit rate

Optical Networks

Optical Fibres – CD


D = DM + DW

Material dispersion

Waveguide dispersion

Optical Networks



G.652 (SSMF): Zero dispersion at 1310 nm

G.653 (DSF): Zero dispersion at 1550 nm

G.655 (NZDSF): Small dispersion at 1550 nm, positive/negative

Dispersion-flattened fibre (DFF), positive/negative

Dispersion Compensating fibres (DCF)

Optical Networks



Optical Networks Chromatic Dispersion Compensation

Typical values (receivers can have different tolerance to CD!)

Bit rate (Gbit/s)

Maximum length of G.652 link (km)

2,5 1280

10 80

40 5


Dispersion compensating fibres (DCF)

A special kind of fibre, compensates all wavelengths (the only solution for „grey“ transmitters)

Adds link loss (and money), especially for long-haul applications

Stronger non-linear effects (due to a smaller core diameter)

Fibre Bragg gratings (FBG)

Typically narrow-band elements – a stabilized DWDM laser is a must

„Wide-band“ FBGs available today (for 50 ITU DWDM channels)

Signal filtering, spectrum shaping, tuneable compensators

Cost effective solution

Electronic post and pre compensation, GTE, VIPA, MZI

Tunable

Optical Networks

Chromatic Dispersion Compensation


Optical nNtworks

Chromatic Dispersion Compensation

Chirped FBG


Optical Networks

Chromatic Dispersion Compensation (FBG)


Optical Networks

Chromatic Dispersion Compensation (FBG)


Polarization Mode Dispersion (PMD)

The stochastic phenomenon

Fibre stress, temperature, imperfections

The fundamental mode has two orthogonally polarized modes

The two components with different propagating speeds disperse along the fiber

The difference between the two propagation times is known as the Differential Group Delay (DGD)

PMD is a wavelength averaged value of DGD

Optical Networks

Optical Fibres – PMD


Optical Networks


Bit rate (Gb/s)

Maximum PMD (ps)

PMD coefficient for 400 km fibre (ps/(km)1/2)

2,5 40 2,0

10 10 0,5

40 2,5 0,125

ITU proposed PMD values


PMD is measured and quoted in ps for a particular span and discrete components but its coefficient is in ps/(km)1/2

PMD accumulates as the square root of distance of a link

A single span with high PMD dominates the total PMD for the whole network

A big issue for older fibres (late 1980s, 80 000 000 km) and higher bit rates (10 Gb/s and more)

Modern fibres have PMD of less than 0,5 ps/(km)1/2

Difficult to compensate

Optical Networks



Optical Networks

Nonlinear Optical Effects

When an intesity of elektromagnetic fields becomes too high, the response of materials becomes nonlinear

For optical systems, nonlinear effects can be both advantageous (Raman amplification) and degrading (Four Wave Mixing, Self Phase Modulation)


Optical Networks

Nonlinear Optical Effects - SRS

Stimulated Raman Scattering (SRS)

A signal is scattered by molecular vibrations of fibre – optical phonons

Can occur both in forward and backward directions

Shifted to longer wavelengths (lower energy) by 10 to 15 THz in the 1550 nm window

Wide bandwidth of about 7 THz (55 nm)

Maybe used for amplification (Raman fibre lasers), so called counter directionally pumping schemes

In DWDM systems: transfer of power from shorter wavelengths to longer ones


Optical Networks

Nonlinear Optical Effects - SBS

Stimulated Brillouin Scattering (SBS)

A signal is scattered by sound waves – acoustic phonons

Shifted to longer wavelengths (lower energy) by 11 GHz in the 1550 nm window

Narrow bandwidth of about 30 MHz

A problem for monochromatic unmodulated signals


Optical Networks


Self-Phase Modulation (SPM)

When the intensity of the signal becomes too high, the signal can modulate its own phase

The refractive index is no longer a constant

Significant for fibres with small effective areas (G.655, DCF)

Higher bit rates (10 Gb/s and higher)


Optical Networks

Nonlinear Optical Effects (SPM1)

Pin = 16,5 dBm


Optical Networks


Pin = 22,7 dBm

Josef Vojtěch (FIT ČVUT) Optical Networks MI-MTI, 2011, L12 29

Optical Networks


Pin = 25,8 dBm


Optical Networks Nonlinear Optical Effects (SPM4)

Pin = 30,1 dBm


Optical Networks


Cross-Phase Modulation (CPM)

A signal modulates the phases of adjacent channels


Optical Networks


Four Wave Mixing (FWM)

New „ghost“ signals appear in the transmission spectral range

Depends on several factors like launched powers, the CD, the refractive index, the fibre length

Severe limitations for G.653 fibres and DWDM transmissions in the 1550 nm window (C band)

Solution to this problem is to deploy L band DWDM systems (1565 nm – 1625 nm), where CD is high enough


Optical Networks

Nonlinear Optical Effects (FWM1)

Pin = 20 dBm

83 km, G.652


Optical Networks


Pin = 25 dBm

83 km, G.652


Optical Networks


Pin = 27 dBm

83 km, G.652


Optical Networks


Pin = 30 dBm

83 km, G.652


Optical Networks

Wavelength Division Multiplex System

Basic passive principle for 2 channels over MM fibre

Still used, typically 1310+1550 nm over SMF

[11]


Optical Networks

Dense WDM = DWDM

200 GHz

100 GHz ~ 0,8 nm (C band ~ 40 channels)

50 GHz becoming standard

33 GHz submarine

[11]


Optical Networks

Transmission Systems C(coarse)WDM

+ passive, non thermally stabilized lower power consumption, less space, cheaper lasers and filters

- Limited number of channels, limited reach

Typically in MAN


Optical Networks

DWDM vs. CWDM

Parameter CWDM DWDM

Wavelength spacing 20 nm 1.6 nm (200 GHz)

0.8 nm (100 GHz)

0.4 nm (50 GHz)

The number of wavelengths 18 (G.694.2) 16-32 (metro)

40-80 (long distance)

Laser technology Uncooled DFB Cooled DFB

Bands O+E+S+C+L C+L

Filter technology Thin film Thin film, Grating, AWG


Optical Networks

Optical Amplifiers

Dopped fibre, Semiconductor (SOA), Raman

Erbium Doped Fibre Amplifiers (EDFA)

Really began a revolution in the telecommunications industry

Late 1980s, Payne and Kaming (University of Southampton)

OAs can directly amplify many optical signals

Protocol, bit-rate transparent

EDFAs working in the 1550 nm window (C band and later L band)


Optical Networks

Optical Amplifiers EDFA

Low energy level

High energy level, 1 μs

Metastable energy level, 10ms

980 nm 1480 nm

Er atoms

Amplified signal

Light Amplification by Stimulated Emission


Optical Networks


WDM WDM

PUMP PUMP

SIGNAL SIGNAL

Forward, backward pumping

Forward: lowest noise

Backward: highest output power

980 nm: low noise

1480 nm: stronger pump sources (req. longer Er fibres)

1480 nm & backward; 980 nm & forward

Single or dual stage (for DCF)

Er doped fibre, 10 m – 100 m


Optical Networks


Output powers (5 Watts or more)

Gain (30 dB), is not uniform across C (L) band

Input power (- 36 dBm)

Noise Figure (NF): theoretical minimum 3 dB

ASE

For L band: long Er fibres (> 100 m)

Booster, in-line, preamplifiers


Optical Networks

Optical Amplifiers - experiments


Optical Networks

Other Optical Dopped Fibre Amplifiers

Praseodymium Doped Fluoride Fibre Amplifier (PDFA)

1310 nm, not as energy efficient compared to EDFA, higher NF

Problems with fluoride fibres, not very widespread

Thulium DFFA (TDFA)

1460 nm, 1650 nm

the lifetime problems

Neodymium DFA

1310 nm, fluoride fibre


Optical Networks

Semiconductor Optical Amplifiers

Based on conventional laser principles

Active medium (waveguide) between N and P regions

+ InGaAsP – small and compact components

+ Cost effective solutions, especially for O and S bands

+ High gain (up to 25 dB)

- Low output powers (15 dBm)

+Wide bandwidth

- High noise figure (8 dB)

-- Very short life time - cross gain effects

Josef Vojtěch (FIT ČVUT) Optical Networks MI-MTI, 2010, Př. 3 48

Optical Networks

Semiconductor Optical Amplifiers


Optical Networks

Raman Amplification

Both discrete and distributed amplifier

Stimulated Raman scattering effect

Distributed amplification, a communication fibre itself is a gain medium

Can add 40 km to increase a maximum transmitter-receiver distance

Upgrading of existing links to add more channels

A quite weak effect in silica fibre – very high powers have to be used

Safety problems (automatic laser shutdown - ALS)


Optical Networks

Raman Amplification

Counter-directionally pumping schemes


SDH(the world)/SONET(the U.S.) – ANSI, Telcordia, ITU Synchronous Digital Hierarchy/Synchronous Optical NETwork

Different terminology but the same in principle

Synchronous – TDM with input clocks synchronized to output clocks, byte-interleaved multiplexing

Distribution of accurate frequency only, not accurate time of the day!

For channelized voice traffic, circuit-switched technology (i.e. guaranteed bandwidth)

Excellent tools for trouble monitoring, detection, isolation

Next Gen: Generic Framing Procedure - ITU With two new protocols: VCAT Virtual Concatenation and LCAS Link Capacity

Adjustment Scheme

Efficient mapping of any client signals, dynamic bandwidth allocation, better granularity

Up to 40 Gb/s, 160 Gb/s will not be deployed, 100 G and beyond - OTN

Optical Networks

SDH/SONET


Optical Transport Networks - ITU

Similar to SDH/SONET concepts but not the same Layered structure, performance monitoring, protection etc.

New features added, like managing optical channels without need for OEO conversions (all optical approach)

FEC standard to enable longer optical spans

100 G interfaces defined (OTU 4) for 100 GE

„Transport for all digital payloads with superior performance and support for the next generation of dynamic services with operational efficiencies not expected from current optical wavelength division multiplexing (WDM) transport solutions.“

Architecture, Framing & Interfaces, Equipment Functions, Network Management and more… http://www.itu.int/itudoc/gs/promo/tsb/78799.pdf

Optical Networks

OTN


Common 50/100 GHz systems, C band, approx. 80/40 channels, C+L band approx. 160 channels

Commercially available 25 GHz systems and e.g. undersea 33 GHz systems

Why not ultra broadband? - Bandwidth demand satisfied by serial speed growth

10->40G transition

40G NRZ tolerance very weak CD 50ps/nm (equals to 3km of G.652 fibre), PMD 2,5 ps

ODB, DPSK proposed, but more strict design rules compared to 10G DQPSK NRZ ODB DPSK DQPSK

Optical Networks Present Transmission Systems


100G coherent DP-DQPSK (25GBaud) solves some issues

+ Works over 50 GHz grid

+ Design rules almost 10G; CD, PMD electronic compensation

- Sensitive to non-linearities, FWM->DCFs removal->coexistence with present 10G channels?

- Cost of complicated modulation format (TX+RX) + necessity of powerful DSPs and ADCs

Proposed alternative modulation formats: 16 QAM, OFDM, 3ASK-PSK,…


TE TM



TE TM


Profits from integration

Source: www.oiforum.com



„Digital“ DWDM system

Profits from photonic integration – photonic integrated circuits (PIC)

Do not use optical processing (DCM) but massive OEO regeneration in nodes

DWDM system on chip, source: Infinera



Working on 400 Gb/s and 1Tb/s per one serial lambda

DP-DQPSK

High channel bandwidth

ROADM + WSS have to support „flexi grid“

OFDM, 16 or 32 or 64-QAM with or without DP

High OSNR

Raman amplification

Decrease spacing of inline amplifier huts

Optical Networks Future Transmission


Optical Networks Future Transmission - Hero

Experiments



New Fibers

[Jun Sakaguchi, Proc. OFCNFOEC2011, OWJ2]

Multicore fibers

Issues:

Amplification – experimental EDFA, Raman

Cross-talk - MIMO

Splices ?

Connectors ?

New fibers instalation



New Fibers Few mode fibers - FMF

[OFCNFOEC2011,PDPB9]

Josef Vojtěch (FIT ČVUT) Optical Networks MI-MTI, 2011, L1 2 62

Optical Networks

Conclusions

Till now, “long fat pipes”

High granularity (= lambda) routing exist today

ROADMs, WSS

Dynamics still limited

OTN functionality

Sub-lambda capacity switching (from SDH)

Done in electrical domain

Possibilities of electronic processing are limited

Optical Burst or Optical Packet Switching – still experiments only


[1] Agrawal G.P., „Fiber-Optic Comminications Systems“, 2002.

[2] Kartalopoulos S.V., „DWDM Networks, Devices and Technology“, 2003.

[3] Ramaswami R., Sivarijan K.N., „Optical Networks“, 2nd edition, 2002.

[4] Radil, J. - Karásek, M., „Experiments with 10 GE long-haul transmissions in academic and research networks.“, In: I2 member meeting, Arlington, VA, 2004.

[5] Vojtěch J., „CzechLight and CzechLight amplifiers“. In: 17th TF-NGN meeting, Zurych, Switzerland, April 2005.

[6] Vojtěch J., Karásek M., Radil J., „Extending the Reach of 10GE at 1310 nm “. In: ICTON 2005 meeting, Barcelona, Spain, 2005.

Optical Networks

References 1


[7] www.seefire.org, Deliverables

[8] czechligh.cesnet.cz, Publications

[9] ECOC 2004 , 2005 proceedings

[10] OFC 2004 , 2005 proceedings

[11]http://www.cisco.com/univercd/cc/td/doc/product/mels/cm1500/dwdm/dwdm_ovr.htm

Optical Networks

References 2


Optical networks

Thank you for your attention!


Optical networks

Laboratory experiments

1GE NIL

300 km G.652 (EDFA only)

325 km G.652 (EDFA + Raman)

10GE NIL

2x10G+2x1G WDM 202km G.652 (EDFA + DCF)

2x10G WDM 250km G.652 (EDFA + Raman + DCF)

10G DWDM 302 km G.655+652 (EDFA + Raman)

8x10G DWDM 250km G.652 (EDFA + FBG)

10GE NIL bidirectional (single fibre) transmission

2x4x10G 210km G.652 (EDFA + FBGs)


Optical networks


Tx1

MUX

Tx8

.

.

EDFA 1 EDFA 2

FBG

Rx1

Rx8

.

.

250 km G.652

DEMUX


Optical networks


Bidirectional transmission over single fibre

Tx1

MUX 1

Tx4

EDFA 1 EDFA 2 Tx5

Tx8

210 km G.652

MUX 2

FBG 1 FBG 2

Rx1 Rx8 Rx5 Rx4

EDFA 3 EDFA 4

DEMUX 2 DEMUX 1

λ1+λ2+λ3+λ4

λ5+λ6+λ7+λ8

λ5+λ6+λ7+λ8

λ5+λ6+λ7+λ8

λ1+λ2+λ3+λ4

λ1+λ2+λ3+λ4


Optical networks

Real deployments


Optical networks

Real deployments

OSA (One Side Amplification) – all components are located at

one place, for star topologies


Optical networks

PDFAs/SOAs and Ramans for 1310 nm

Configuration Reach (km)

Guaranteed 10

In lab, no amps 30

Booster 85

Booster and preamp 120

Dual booster and Raman 135


Optical networks

PDFAs/SOAs 1310 nm

Eye diagram after preamp, l = 100 km


Optical networks PDFAs/SOAs for 1310 nm

Eye diagram after preamp, l = 120 km


Optical networks

PDFAs/SOAs for 1310 nm

Eye diagram after preamp and optical filter, l = 120 km

Date post:	28-Feb-2021
Category:	Documents
Upload:	others
View:	2 times
Download:	0 times

Prezentace aplikace PowerPoint · 2011. 12. 9. · Title: Prezentace aplikace PowerPoint Author:...

Documents