basic knowledge about wdm principle-a

HUAWEI TECHNOLOGIES Co., Ltd.

www.huawei.com

HUAWEI Confidential

Security Level: Internal Use Only April 8, 2023

Basic Knowledge About WDM PrincipleOptical Network Technical Service Dept.

Yang Mingzhang (ID: 42198)

HUAWEI TECHNOLOGIES CO., LTD. HUAWEI Confidential

• Know the basic concept, basic principle and

structure of WDM.

• Know the transmission media in WDM systems.

• Master key technologies of DWDM.

• Master limitations of DWDM systems and relevant

solutions.

• Know typical networking with Huawei WDM

products.

ObjectivesObjectives

After learning this course, you will:


Contents

Chapter 1 Overview of WDM

Chapter 2 Transmission Media in WDM Systems

Chapter 3 Key Technologies of DWDM

Chapter 4 Limitations of WDM Systems

Chapter 5 Signaling Flow in Typical Networking


Background of WDMBackground of WDM

With SDM technology, new multiple-core optical cables can be laid (time and cost must be considered).

With TDM technology, the bit rate is increased. The bit rate ranges from STM-1 to STM-64.

Multiple signals are transmitted through one optical fiber.

With

the

boom

of v

ario

us n

ew s

ervi

ces,

mor

e an

d m

ore

band

wid

th is

nee

ded.

How to improve transmission capacity?


Expressway

Gas station

Patrol car

What Is WDM?What Is WDM?

Car/Signal Expressway/Optical fiber Gas station/Optical amplifier Patrol car/Supervisory channel

2.5G

10G

GE


Optical signals of different wavelengths are transmitted through one

optical fiber, which is called Wavelength Division Multiplexing (WDM).

Concept of WDMConcept of WDM

1

2

┋

1 2 n

┉

Coarse Wavelength Division Multiplexing (CWDM): Wavelength interval is bigger, usually 20 nm.

Dense Wavelength Division Multiplexing (DWDM): Wavelength interval is smaller, usually less than or equal to 0.8 nm.


Requirements for Wavelengths in WDMRequirements for Wavelengths in WDM

From the perspective of technical implementationVendors can choose any wavelength in WDM.

From the perspective of technical compatibility Optical wavelengths in WDM systems should be specified.

ITU-T specifications for optical wavelengths in WDM systemsG.692, G.694.1 and G.694.2 =====> Wavelength and Frequency Allocation Table

Optical wavelengths in WDM systems must strictly comply with the Wavelength and Frequency Allocation Table.


Typical Model of WDMTypical Model of WDM

Rx1

Rxn

Rx2

Tx1

Tx2

Txn

MUX

OA

DEMUX

OSC OSC OSC OSC


In a two-fiber unidirectional WDM system, two optical fibers are used and each optical fiber transmits optical signals in only one direction.

Two-Fiber Unidirectional WDMTwo-Fiber Unidirectional WDM

Optical source 1

Optical source N

Detector 1

Detector N

WDM

WDM

WDM

WDM

Optical source N

Optical source 1

Detector N

Detector 1


In a single fiber bidirectional WDM system, one optical fiber is used to transmit

optical signals in both directions, but the signals in the two directions must be of

different wavelengths.

Single Fiber Bidirectional WDMSingle Fiber Bidirectional WDM

…

λ１

λ２

λＮ

λ１

λ２

λＮ

…

Op

tical d

em

ultip

lexe

r un

it

Op

tical m

ultip

lexe

r un

it

Booster amplifier/Pre-amplifier

/Booster amplifier/Pre-amplifier

Optical line amplification

… … … …

Eastern1-NWestern1-N

Red bandEDFA

1547.5–1560.5 nm

Blue bandEDFA

1527.5–1542.5 nm

WDM

Coupler

WDM

Coupler

OSC1510 nm

OSC 1625 nm


Mainstream

Classification of WDM SystemsClassification of WDM Systems

Open WDM system

The system supports optical interface conversion in WDM terminal equipment and can interconnect with SDH equipment from any vendor.

Integrated WDM system

The system does not support optical interface conversion in WDM terminal equipment.

The performance of optical transponder units (OTUs) in SDH equipment must meet the following requirements of the WDM system:

Wavelength accuracy, spectral characteristics, transmit optical power and so on.

Semi-open WDM system

The system supports optical interface conversion at the TX end in WDM terminal equipment and can interconnect with SDH equipment from any vendor.

Open WDM system

The system supports optical interface conversion in WDM terminal equipment and can interconnect with SDH equipment from any vendor.

Integrated WDM system

The system does not support optical interface conversion in WDM terminal equipment.

The performance of optical transponder units (OTUs) in SDH equipment must meet the following requirements of the WDM system:

Wavelength accuracy, spectral characteristics, transmit optical power and so on.

Semi-open WDM system

The system supports optical interface conversion at the TX end in WDM terminal equipment and can interconnect with SDH equipment from any vendor.


Optical transponder unit (OTU): converts the optical signals of non-standard wavelengths into optical signals of standard wavelengths that meet G.694.1(2).

OM/OD: multiplexes and demultiplexes optical signals of fixed wavelengths that meet G.694.1(2). Optical amplifier (OA):

Booster amplifier (BA): raises the output optical power of optical signals of different wavelengths by raising the power of multiplexed optical signals. Pre-amplifier (PA): raises receiver sensitivity for optical signals of different wavelengths by raising the optical power of input multiplexed optical signals.Line amplifier (LA): regenerates and amplifies multiplexed optical signals.

Optical supervisory channel (OSC): supervises data transmission over the whole network, usually in 1510 nm and 1625 nm (later, with the use of ESC and OTU, optical signals can directly carry supervisory data. In the ESC technology, the OSC is unnecessary but the OTU should support ESC).

Structure of the Open WDM System

OTU

OTU

PA1

n

Optica

l mu

ltiplexe

r (OM

)

OTU

OTU

1

n

OTMOLA OTM

BA

OTU OM OA OD

Optica

l dem

ultip

lexe

r (OD

)

OSC OSC OSC

OSC

OTU OTU

LA

Clie

nt

Clie

nt


Summary

Concept of WDM

Requirements for wavelengths in WDM

Classification of WDM systems

Structure of the open WDM system and the role of each part


Contents







Principle of Optical Transmission Through Optical FibersPrinciple of Optical Transmission Through Optical Fibers

N 2

N 1

N 1 > N 2

2

1

N1Sin 1 = N2Sin 2

Sinc = N2/N1

1 >= c

Refraction law and total reflection law


Structure of an optical fiber

Structure of an Optical FiberStructure of an Optical Fiber

Which is bigger, the refractive index n1 of the core or the refractive index n2 of the cladding?

Coating

Cladding

Core

Coating

Cladding


Single-Mode and Multi-Mode Optical FibersSingle-Mode and Multi-Mode Optical Fibers

The number of transmission modes in optical fibers varies with diameters of fiber

cores. So optical fibers can be classified into single-mode optical fibers and multi-

mode optical fibers according to the number of transmission modes: When the diameter of an optical core is much bigger than the optical

wavelength, the optical fiber supports dozens of transmission modes or more.

This kind of optical fiber is a multi-mode one. The core diameter of a multi-

mode optical fiber is relatively big, usually about 50 um. When the diameter of an optical core is near to the optical wavelength, the

optical fiber supports only one transmission mode. This kind of optical fiber is

a single-mode one. The core diameter of a single-mode optical fiber is

relatively small, usually 5–10 um. The above two kinds of optical fibers have little difference in appearance. The

diameter of an optical fiber with a plastic jacket is less than 1 mm.

Only single-mode optical fibers are used in WDM systems.


Attenuation of Optical FibersAttenuation of Optical Fibers

Attenuation or loss in an optical fiber is an important factor that restricts the

propagation of optical signals and limits the optical transmission distance. Optical

loss includes absorption loss, scattering loss and bending loss. Absorption loss is caused by the optical fiber material, mainly including

ultraviolet absorption, infrared absorption and contamination absorption. Uneven density of material within an optical fiber causes light to scatter, which

is called Raileigh scattering. This kind of loss is the intrinsic property of the

fiber material — silicon dioxide. The bending of an optical fiber causes radiation loss.

The optical fiber attenuation constant is mainly determined by absorption loss and

scattering loss.


Variable Curve of Optical Attenuation and Wavelength

Attenuation varies with wavelengths. The attenuation around 1380 nm goes up sharply due to absorption by hydroxyl ions. This is generally called "water

peak". According to ITU-T, the bands over 1260 nm in a single-mode optical fiber are classified into six bands: O, E, S, C, L and

U. As we can see, the attenuation in C band and F band is the lowest.

900 1300 1400 1500 1600 1700Wavelength: nm

Attenuation

dB/km

2

3

1

4

5

1200

Multi-m

ode op

tical fibers (85

0–900 n

m)

O band E band S C L U

OH-


Wavelength Ranges in WDM

Band Description Range (nm) Bandwidth (nm)

O band Original 1260–1360 100

E band Extension 1360–1460 100

S band Short 1460–1525 65

C band Normal 1525–1565 40

L band Long 1565–1625 60

U band Ultra-long 1625–1675 50

In a DWDM system, C band and L band are used because the attenuation in the two bands is the lowest.

In a CWDM system, multiple bands are used, ranging from 1311 to 1611 nm, because attenuation is not a major restrictive factor in short-distance transmission.


Dispersion of Optical Fibers Dispersion of Optical Fibers

The group velocities of optical pulses of different frequencies or modes are different in optical fibers.

Therefore, the arrival time of these pulses at the fiber end is different, which causes pulse broadening.

This is the dispersion in optical fibers.

pulse

λ 1λ2λ3. . .

pulse

λ1λ2λ3. . .

Fiber coreFiber core

Fiber cladding

Fiber cladding

Dispersion in optical fibers is classified into mode dispersion, chromatic dispersion (CD) and

polarization mode dispersion (PMD): Mode dispersion is also called inter-mode dispersion. It occurs mainly in multi-mode optical fibers.

CD is also called intra-mode dispersion. It includes material dispersion and waveguide dispersion.

PMD occurs when optical signals in two orthogonal polarizations travel at different speeds in optical

fibers. PMD occurs randomly, so it is a random variable and hard to compensate for.

CD coefficient specifies the arrival time delay that would be included per 1 km of the transmission

line if the wavelength deviates by 1 nm. CD coefficient is indicated by D and the unit is ps/(nm.km).

PMD coefficient is indicated by PMDQ and the unit is ps/kmⁿ (n = ½).


Impact of CDIn terms of TDM, CD will cause intersymbol interference.In terms of TDM, CD will cause intersymbol interference.

λ 3 λ 1 λ 3 λ 1 λ 3 λ 3λ 1 λ 1

T

T+Δ T

The intensity of the optical signals output by an optical source of non-zero spectral width is modulated by The intensity of the optical signals output by an optical source of non-zero spectral width is modulated by

electrical pulses. The modulated signals contain all wavelengths of the optical source.electrical pulses. The modulated signals contain all wavelengths of the optical source. Due to the difference in arrival time of various wavelengths, optical pulses become longer (T + ΔT), which Due to the difference in arrival time of various wavelengths, optical pulses become longer (T + ΔT), which

is called pulse broadening. The bigger the transmission distance of optical pulses, the greater the pulse is called pulse broadening. The bigger the transmission distance of optical pulses, the greater the pulse

broadening. Pulse broadening causes different optical pulses to overlap, which is called intersymbol broadening. Pulse broadening causes different optical pulses to overlap, which is called intersymbol

interference. Intersymbol interference will cause bit errors, thus limiting the symbol rate and transmission interference. Intersymbol interference will cause bit errors, thus limiting the symbol rate and transmission

distance.distance. But in terms of WDM, CD helps prevent inter-channel interference caused by nonlinearityBut in terms of WDM, CD helps prevent inter-channel interference caused by nonlinearity of optical fibers, of optical fibers,

such as FWM and XPM. such as FWM and XPM. We should look at the impact of CD based on dialectics.We should look at the impact of CD based on dialectics.


PMD

PMD occurs when optical signals in two orthogonal polarizations travel at different speeds in optical fibers. PMD is one of critical parameters related to optical fibers.

PMD occurs randomly. So it is a random variable.

PMD has the same impact as CD has: resulting in pulse broadening.


Cut-Off Wavelength

Cut-off wavelength: the minimum wavelength of optical signals that can be transmitted in a Cut-off wavelength: the minimum wavelength of optical signals that can be transmitted in a

single mode through a single-mode optical fiber.single mode through a single-mode optical fiber. When the actual wavelength is smaller than the cut-off wavelength, optical signals in When the actual wavelength is smaller than the cut-off wavelength, optical signals in

multiple modes are transmitted through an optical fiber and take on a multi-mode feature.multiple modes are transmitted through an optical fiber and take on a multi-mode feature. To avoid modal noise and mode dispersion, the cut-off wavelength in the shortest optical To avoid modal noise and mode dispersion, the cut-off wavelength in the shortest optical

cable should be smaller than the operating wavelength of the system. The cut-off cable should be smaller than the operating wavelength of the system. The cut-off

wavelength can ensure the single-mode transmission through the shortest optical cable and wavelength can ensure the single-mode transmission through the shortest optical cable and

prevent the generation of high order modes or reduce noise power to an insignificant prevent the generation of high order modes or reduce noise power to an insignificant

amount. amount. The cut-off wavelength in G.652 fibers is equal to or less than 1260 nm in a 22 m optical The cut-off wavelength in G.652 fibers is equal to or less than 1260 nm in a 22 m optical

cable, equal to or less than 1260 nm in a 2–20 m optical patch cord and equal to or less cable, equal to or less than 1260 nm in a 2–20 m optical patch cord and equal to or less

than 1250 nm in an optical patch cord less than 2 m.than 1250 nm in an optical patch cord less than 2 m. The cut-off wavelength in G.655 fibers is equal to or less than 1480 nm in a 22 m optical The cut-off wavelength in G.655 fibers is equal to or less than 1480 nm in a 22 m optical

cable, equal to or less than 1480 nm in a 2–20 m optical patch cord and is equal to or less cable, equal to or less than 1480 nm in a 2–20 m optical patch cord and is equal to or less

than 1470 nm in fibers with primary coating in an optical cable less than 2 m.than 1470 nm in fibers with primary coating in an optical cable less than 2 m.


Mode Field Diameter (MFD)

In an optical fiber, not all light is transmitted within the optical core. Instead, some In an optical fiber, not all light is transmitted within the optical core. Instead, some light is transmitted through cladding. The core diameter cannot reflect the distribution light is transmitted through cladding. The core diameter cannot reflect the distribution of light. So the concept of MFD is put forward.of light. So the concept of MFD is put forward.

MFD is a parameter describing the centralization degree MFD is a parameter describing the centralization degree of light in a single-mode optical fiber.of light in a single-mode optical fiber.

The smaller the MFD, the greater energy density through The smaller the MFD, the greater energy density through the cross section of an optical fiber. Excessive density will the cross section of an optical fiber. Excessive density will bring about non-linear effects in the fiber and cause bring about non-linear effects in the fiber and cause optical signal-to-noise ratio to decrease. This will affect optical signal-to-noise ratio to decrease. This will affect the performance of the system significantly. the performance of the system significantly.

Question: Which is better, a bigger MFD or a smaller Question: Which is better, a bigger MFD or a smaller one?one?

光纤纤芯

MFD

光纤纤芯

MFD

Optical core


In essence, all media are non-linear, but the non-linear feature is generally insignificant In essence, all media are non-linear, but the non-linear feature is generally insignificant and hard to manifest. When the fiber input power is low, the fiber takes on a linear feature. and hard to manifest. When the fiber input power is low, the fiber takes on a linear feature. When optical amplifiers and high-power lasers are used in optical communication When optical amplifiers and high-power lasers are used in optical communication systems, the non-linear feature of fibers becomes more significant. systems, the non-linear feature of fibers becomes more significant.

Non-linear effects of single-mode optical fibers are generally as follows:Non-linear effects of single-mode optical fibers are generally as follows: Stimulated non-flexible scattering: stimulated Raman scattering (SRS) and stimulated Stimulated non-flexible scattering: stimulated Raman scattering (SRS) and stimulated

Brillouin scattering (SBS)Brillouin scattering (SBS) Kerr-effect: self-phase modulation (SPM), cross-phase modulation (XPM) and four Kerr-effect: self-phase modulation (SPM), cross-phase modulation (XPM) and four

wave mixing (FWM)wave mixing (FWM)

Note: Non-linear effects cannot be eliminated or compensated for. So they should be restricted

as much as possible!

The use of optical fibers with large MFD can reduce the power density on the fibers and MFD can reduce the power density on the fibers and

suppress the non-linear effects.suppress the non-linear effects. We can prevent non-linear effects by reducing fiber input power or using fibers with large effective area. Non-linear effects are related to dispersion, but that does not mean the less dispersion, the better.

Non-Linear Effects of Single-Mode Optical FibersNon-Linear Effects of Single-Mode Optical FibersNon-Linear Effects of Single-Mode Optical FibersNon-Linear Effects of Single-Mode Optical Fibers


According to ITU-T, three types of single-mode optical fibers are defined in G.652, G.653, and G.655 respectively. The differences between them are shown in the following table:

Type Definition Scope Main Specifications

G.652

The standard single-mode fiber (SMF) refers to the fiber whose zero-dispersion point (the zero-dispersion wavelength) is near to 1310 nm.

Used in both SDH system and DWDM system

Attenuation: The attenuation value of the 1310 nm band is 0.3––0.4 dB/km and the typical value is 0.35 dB/km. The attenuation value of the 1550 nm band is 0.17––0.25 dB/km and the typical value is 0.20 dB/km.Dispersion: The allowed value of the zero-dispersion wavelength is 1300––1324 nm. The dispersion coefficient of the 1550 nm band is positive and the typical value of the dispersion coefficient D is 17 ps/(nm.km). The maximum value is not more than 20 ps/(nm.km).

G.653

Dispersion-shifted fiber (DSF) refers to the fiber whose zero-dispersion point is near to 1550 nm. Compared with G.652 SMF, the zero-dispersion point of G.653 DSF shifts.

Used in the SDH system but not in the DWDM system

Attenuation: The attenuation value of the 1310 nm band is less than 0.55 dB/km and the typical value has not been confirmed. The attenuation value of the 1550 nm band is less than 0.35 dB/km and the typical value is 0.19––0.25 dB/km.Dispersion: The wavelengths in the G.653 DSF are near to 1550 nm, usually 1525––1575 nm. The maximum dispersion coefficient is 3.5 ps/(nm.km). The dispersion coefficient in the DSF is too small or may be 0 for 1550 nm bands, especially C band.

G.655

Non-zero dispersion-shifted fiber (NZDSF) refers to the fiber whose zero-dispersion point is shifted away from 1550 nm and not within the DWDM operating wavelength range near to 1550 nm.

Used in both SDH system and DWDM system, but more applicable to the DWDM system

Attenuation: The attenuation value of the 1310 nm band is not specified in ITU-T. The attenuation value of the 1550 nm band is less than 0.35 dB/km, usually 0.19––0.25 dB/km.Dispersion: If 1530 nm < < 1565 nm, 0.1 ps/(nm.km) < |D(λ)| < 6.0 ps/(nm.km). The typical value of the dispersion coefficient of the G.655 NZDSF varies with vendors and needs to be confirmed based on actual situations, usually 4.5 ps/(nm.km) and 6 ps/(nm.km).

G.652/G.653/G.655 Single-Mode Optical FibersG.652/G.653/G.655 Single-Mode Optical FibersG.652/G.653/G.655 Single-Mode Optical FibersG.652/G.653/G.655 Single-Mode Optical Fibers


Characteristics of G.652/G.653/G.655 FibersCharacteristics of G.652/G.653/G.655 FibersCharacteristics of G.652/G.653/G.655 FibersCharacteristics of G.652/G.653/G.655 Fibers

Dispersion coefficient ps/(nm·km)

Positive dispersion coefficient of G.655 NZDSF

Wavelength (nm)15501310

17

1.The minimum dispersion and attenuation in the 1550 nm band, applicable to the DWDM system and able to transmit signals at a high speed.2.Applications: TrueWave fibers (SPM effects in the positive dispersion area facilitate transmission) and LEAF-large effective area fibers (non-linear effects are weakened)

G.652 SMF: large-scale laying, high-speed transmission and dispersion compensation

G.653 DSF: serious frequency mixture in the 1550 nm band and not applicable to the DWDM system

Negative dispersion coefficient of G.655 NZDSF

G.654Similar to G.653 DSF but different in cut-off wavelengths. The cut-off wavelength in G.654 fiber is 1530 nm.

Full wavelength fiber

Eliminating the "water peak" gain at 1380 nm.


Summary

Are multi-mode fibers or single-mode fibers used in WDM systems?

In what wavelength ranges, is the attenuation the least in single-mode fibers?

What problems may occur when optical signals are transmitted in single-mode fibers?

What are the characteristics of G.652/653/655 fibers?

Is less dispersion better?


Contents







Key Technologies in the DWDM SystemKey Technologies in the DWDM System

Optical amplifier

光监控技术

Optical source/Optoelectrical detector

Supervisory channelWavelength multiplexing

and demultiplexing


Optical Source Technologies in the DWDM SystemOptical Source Technologies in the DWDM System

The optical sources in the DWDM system have two distinctive characteristics:

1. Relatively big dispersion tolerance values

2. Standard and stable wavelengths

Therefore, diode lasers (DLs) are used as optical sources in the DWDM system. The DLs

used in the high-speed optical communication system include multi-longitudinal mode

lasers (MLM) and single-longitudinal mode lasers (SLM).

MLM SLM

Amplitude

Primary mode

Secondary mode

Wavelength Wavelength

Secondary mode

Primary mode


b. Mach-Zehnder modulation (M-Z)

1. Direct modulation of optical sources

a. Electro-absorption modulation (EA)

Laser Modulation MethodsLaser Modulation Methods

2. Indirect modulation of optical sources


Advantage: simple technologies and low costs

Disadvantage: Due to frequency changes between "1" and "0", chirp cannot be

avoided, which broadens the bandwidth of spectrums from lasers and degrades

spectral characteristics. This restricts transmission speed and distance. So direct

modulation is applicable to short-distance transmission.

Direct Modulation of Optical SourcesDirect Modulation of Optical Sources

Direct modulation is to use electrical signals "1" and "0" to enable and disable a laser and use lightwaves of specified wavelengths to carry electrical signals.

LD


Indirect Modulation of Optical Sources

Indirect modulation is to modulate lightwaves by adding a modulator in the lightwave transmission channel of the optical source instead of modulating the optical source directly. Actually, the modulator serves as a switch.

A constant optical source is very stable and continuously provides fixed wavelengths and power. The optical source is not affected by electrical modulation signals. So chirp can be avoided and the bandwidth of the spectrum is minimum.The optical modulator processes the stable lightwaves emitted by the constant optical source by allowing or forbidding lightwaves to pass according to electrical modulation signals, without exerting any impact on spectral characteristics, thus ensuring the spectrum quality. So indirect modulation is applicable to high-speed and long-distance transmission.The common indirect modulations are EA and M-Z.

Constant optical source

Optical modulator

Optical signal output


Advantage: low frequency chirp and long dispersion limited distance

Disadvantage: complex technologies

EAEA

LD EA


Advantage: insignificant frequency chirp and very long dispersion limited distance

Disadvantage: very complex technologies and difficult integration

M-ZM-Z

LD


Comparison Among Three Types of Optical Sources

In WDM, EA modulated and directly modulated optical sources are often used.

Directly Modulated

Optical Source

EA Modulated Optical Source

M-Z Modulated Optical Source

Maximum dispersion (ps/nm)

1200~2400 7200~12800 > 12800

Cost Moderate High Very high

Wavelength stability Fairly good Good Excellent


Optoelectrical DetectorOptoelectrical Detector

An optoelectrical detector is used to convert received optical signals into electrical signals. Semiconductor optoelectrical detectors include positive intrinsic negative (PIN) and avalanche photo diode (APD).

PIN: lower sensitivity (usually about -20 dBm) and higher overload point (usually about 0 dBm); applicable to short-distance transmission

APD: higher sensitivity (usually about -28 dBm) and lower overload point (usually about -9 dBm); applicable to long-distance transmissionBoth high reverse bias and strong input optical signals may cause excessive bias current, which will break down the APD. So operate on site according to relevant specifications:

1. When measuring an optical channel by using devices such as an optical time domain reflectometer (OTDR) that can output high-power optical signals, disconnect the peer communication device from the optical channel to protect the receiver from being damaged by strong lightwaves.

2. Ensure the input optical power does not exceed the allowed maximum power in devices. Add proper attenuators to self-loop boards.

3. Do not loosen optical connectors to substitute for optical attenuators.


Semiconductoroptical amplifier (SOA)

Semiconductoroptical amplifier (SOA)

Fiber Raman amplifier (FRA)Fiber Raman amplifier (FRA)

Erbium-doped fiber amplifier (EDFA)Erbium-doped fiber amplifier (EDFA)

AmplifierAmplifier


Structure and Principle of EDFA

Output power of an EDFA is related to the following factors:

Input light intensity

Erbium fiber length

Pump light intensity

Amplified spontaneous emission (ASE) noise


Gain control methods:

1. Dope metal elements 2. Customize EDFAs by gain flattening filters (GFF)

EDFA Gain Flatness ControlEDFA Gain Flatness Control

Cascading amplification with uneven amplifier gain

Cascading amplification with flat amplifier gain

Gain

1525–1565 nm EDFA without aluminum 1525–1565 nm aluminum-doped EDFA

Gain


Gain Flatness Technology — GFF

G

Wavelength1530 nm

EDFA gain spectrum curve

Gain flattening filter (GFF)

GFF

IL

Wavelength

Flatten output

Requirement:Gain flatness < 2 dB

1560 nm

Gain fluctuation


Common EDFA Control Mode

Automatic gain control (AGC)

Output varies with input while gain remains unchanged. AGC is the most common control mode in the WDM system. AGC is also called gain locking mode. There are multiple solutions to AGC and the most common one is electrical control pump technology, as shown below:

Automatic power control (APC)No matter how input power is changed, output power remains unchanged. In this case, the gain is changed. APC is used for adjustable gains.

The actual gain is calculated based on output power and input power. Output power changes with pump power, thus keeping the actual gain at the target value.

APC changes the pump power by detecting output power and comparing it with the target value, thus keeping actual output power at the target value.

Non-linear control


Why to Use AGC

When other conditions remain unchanged, wavelength multiplexing/demultiplexing through an EDFA bring the following problems to a WDM system:

When more lightwaves enter the EDFA, input power becomes higher and pump optical power contributes less to the lightwaves, which causes optical power of each lightwave to decrease suddenly. If the optical power is lower than the minimum optical power acceptable to the receiver, transient loss of signals will occur and the gains of lightwaves will decrease more or less.

When less lightwaves enter the EDFA, input power becomes lower and extra pump optical

power contributes to the remaining channels, which causes optical power of each ligthwave to rise suddenly. If the optical power is higher than the maximum optical power acceptable to the receiver, that will overshoot the receiver and the gains of lightwaves will rise more or less.

Therefore, AGC technology is necessary for amplifiers in the WDM system.

Pump

PoutPin

EDF


ASE is the primary source of EDFA noises and the main factor contributing to the

degrading of optical signal-to-noise ratio of the system. See the following figure:

ASE noise power generated by an amplifier is: PASE = -58 + NF + G (dBm)

where, NF is the noise figure of an optical amplifier (unit: dB) and G is the gain of the

optical amplifier (unit: dB).

EDFA NoisesEDFA Noises

OSNR

Span

LA LABA PA

DCM DCM DCM DCM


Working current is also called bias current. It determines the output optical power of

an amplifier board. Normally, the output power of the board is stable. Working

current should remain relatively stable. Refrigerating current is related to the adjustment of refrigerating circuits. On the

amplifier board, refrigerating current varies with the temperature of the pump laser.

Pay attention to the meaning of positive and negative symbols (the negative symbol

indicates heating). Back facet current is a performance parameter related to the amplifier board. Back

facet current is related to power detection, so we can know the output power of a

laser from back facet current. Generally, we can judge the quality of a pump laser

from back facet current.

Understanding the following parameters will facilitate fault location in maintenance:

Major Performance Parameters Related to EDFA — 3 IMajor Performance Parameters Related to EDFA — 3 I

3 I


If a weak signal and a strong pump lightwave are transmitted in an optical fiber at the same time and the wavelength of the weak signal is kept within the Raman gain bandwidth (GB) of the pump lightwave, the weak signal will be amplified. The optical amplifier based on the SRS mechanism is called FRA.

PUMP1 PUMP3

70~100nm

30nm

GAIN

PUMP2PUMP1 PUMP3

70~100nm

30nm

GAIN

PUMP2

Three characteristics: Gain wavelengths depend on pump wavelengths. Theoretically, any wavelength

can be amplified so long as the pump wavelength is proper. Optical fibers serve as gain media. So the FRA can amplify optical signals within

optical fibers, which is distributed amplification. Long-distance transmission without trunks and remote pumps can be achieved.

The noise figure of the FRA is small. So the combination of the FRA and EDFA can reduce the noise figure significantly and increase transmission span.

Principle of an FRAPrinciple of an FRA


Principle of an FRA

The following is an example of using non-linear effects of optical fibers skillfully: • SRS: Incident photon energy is transferred to low-frequency lightwaves (frequency

shifts down by 13.2 THz).• A photon of frequency f1 enters an optical fiber. If the photon power is high enough

to cause SRS, the photon will transfer its energy to the photon of frequency f1-13.2 THz and then disappear in the molecular vibration way.

• SRS requires very strong light. This is why FRAs are very powerful but dangerous.

An FRA can work in ordinary optical fibers without any restriction on bands. Theoretically, any wavelength can be amplified.

FRA gain spectrum curve


Principle of an FRA

Amplification rangePump source

The amplification range of a pump source is limited. So choose multiple wavelengths

according to actual situations and add them to amplify any wavelength. To amplify the wavelength corresponding to frequency f2, choose the incident pump

source corresponding to f2 + 13.2 THz.

Schematic drawing of an FRA:

Optical fiber

Optical signal

Pump1 Pump2

FRA


Gain of an Amplifier (G)

Power meterFRAOptical signal

Gain of an EDFA (G) = Pout - Pin

P1 indicates the test result when the pump source in an FRA is off.P2 indicates the test result when the pump source in an FRA is on.

Gon-off = P2 - P1

EDFA

P1 P2

G = P2 - P1

P1

P2

In an FRA, G refers to on-off gain. The definition and test of G are different from those for an EDFA:

Note: In an FRA, P1 and P2 indicate output optical power.

Optical signal


Comparison Between EDFA and FRA

Item EDFA FRA

Amplification principleStimulates emission by semiconductors

A kind of non-linear effect: SRS

Amplification mediaErbium-doped optical fibers (within amplifiers)

Common optical fibers (line optical fibers)

Pump source 980/1480 nm

The pump source can be chosen according to the amplification objective. The RPC of Huawei corresponds to 1427/1457 nm.

Requirement for optical power of pumps

Ordinary High (SRS threshold is high.)

Bandwidth C band and L bandTheoretically, there are no restrictions on bandwidth and bandwidth depends on pump combination.

Noise High Low

Gain test Common gain On-off gain


Optical Multiplexer and DemultiplexerOptical Multiplexer and Demultiplexer

OM OD

OD

OM


Currently, the most common components are fiber coupler, dielectric film and arrayed waveguide grating (AWG).

Optical Multiplexer and DemultiplexerOptical Multiplexer and Demultiplexer

Fiber coupler

Dielectric film

AWG

Coupling length (L)

Input waveguide

Planar coupled waveguide

Arrayed waveguide

Output waveguide

Arrayed waveguide

Auto-focus len

Filter

Glass

Filter


Supervisory TechnologySupervisory Technology

The requirements for supervisory channels in DWDM systems are as follows:

Optical supervisory channels do not impose restrictions on pump wavelengths in

optical amplifiers.

Optical supervisory channels do not impose restrictions on the distance between

two optical amplifiers.

Optical supervisory channels do not impose restrictions on the future services on

the 1310 nm wavelength.

Optical supervisory channels are available even if amplifiers fail.


Typical Frame Structure of OSC DataTypical Frame Structure of OSC Data

The 2 Mbit/s interfaces of optical supervisory channels (OSCs) should comply with

the requirements in G.703. The frame structure and bit rate should comply with the

requirements in G.704:

0 Frame alignment signal

02 Byte F1

17 Byte F2

19 Byte E2

20 Byte APE

01 Byte E1

3~15 Byte D1–D12

18 Byte F3

14 Byte ALC

Others Reserved


ESC Technology

• In earlier WDM systems, dedicated OSCs are used for operations, administration and

maintenance of network elements (NEs) . With the development of technologies,

considering product costs, people came up with the idea of using overhead bytes in

fixed frame structure for data communications channels (DCC) and realizing

communications between NEs through interconnections of OTUs. This is electrical

supervisory channel (ESC) technology. • The associated mode is adopted in ESC technology. That is, supervisory data is

transmitted along with main service signals and then separated from the latter at the

peer end. In this mode, supervisory data does not need to occupy extra wavelengths. • In terms of board realization principles, ESCs include fixed frame structure DCCs

and pilot tone modulation DCCs. • Fixed frame structure DCCs further include fixed SDH frame structure DCCs and

GCCs based on G.709 frame structure.

Cost-effective solution


Summary

Which optical sources are used in the WDM system? What are the

characteristics of these optical sources?

What kind of receivers are used in the WDM system? What are the

main differences between these receivers?

What is the principle of an EDFA and what is the noise source?

What are AGC, gain flatness and 3I of an EDFA?

What types of OM and OD are mentioned? Which type is currently

used by Huawei?

What are the requirements for OSCs in the DWDM system?


Contents







Accumulated noises caused by ASE and

degrading OSNR

System performance

CD

PMDNon-linear effects in

optical fibersSPM/XPM/…

Limitations of DWDM Systems

Four limiting factors: attenuation, dispersion (CD and PMD), OSNR and non-linearity. Four limiting factors: attenuation, dispersion (CD and PMD), OSNR and non-linearity. Attenuation is not a major problem because it can be solved through amplifiers. Attenuation is not a major problem because it can be solved through amplifiers.

The 40G DWDM system puts higher requirements for optical transmission. Compared The 40G DWDM system puts higher requirements for optical transmission. Compared with the 10G DWDM system under the same physical conditions, the limiting factors to with the 10G DWDM system under the same physical conditions, the limiting factors to the 40G DWDM system are as follows:the 40G DWDM system are as follows: OSNR is degraded by four times (6 dB), CD tolerance is reduced by 16 times and OSNR is degraded by four times (6 dB), CD tolerance is reduced by 16 times and

PMD is degraded by four times and non-linear effects become more obvious.PMD is degraded by four times and non-linear effects become more obvious.


Calculation of OSNR

As a key parameter related to optical amplifiers, NF describes the value of ASE As a key parameter related to optical amplifiers, NF describes the value of ASE noise generated by optical amplifiers:noise generated by optical amplifiers:

(dB)58(dBm)(dB)

5.12,11

GPNF

GHzh

P

GNF

ASE

ASE

Noise generated by one amplifier: Noise generated by one amplifier: Pase = -58 + NF + G (dBm)Pase = -58 + NF + G (dBm)

G1 G2 G3 Gi GnL1 L2 Li Ln-1 A

Usually, OSNR refers to that of the output end of the last amplifier. For output end A, Usually, OSNR refers to that of the output end of the last amplifier. For output end A, OSNR = Ps(A)/Pase(A).OSNR = Ps(A)/Pase(A).

where, Ps (A) indicates signal power at A and Pase (A) indicates noise power at A. where, Ps (A) indicates signal power at A and Pase (A) indicates noise power at A. Pase (A) is equal to the accumulated noise power at A of all amplifiers.Pase (A) is equal to the accumulated noise power at A of all amplifiers.


Example of OSNR Calculation

WBA02WBA02 WBA02WBA02 WPA02WPA02WPA02WPA02

＋＋ 5530dB30dB

-25-25 -2-2 -18-18 +5+537dB37dB

-32-32 OSNROSNR

#1#1 #2#2 #3#3 #4#4

ASE noise generated by each amplifier is (NF = 5 dB):ASE noise generated by each amplifier is (NF = 5 dB):

Pase1 = Pase2 = Pase3 = Pase4 = -Pase1 = Pase2 = Pase3 = Pase4 = -58 + 5 + 23 = -30 (dB) = 1E-3 (mw)58 + 5 + 23 = -30 (dB) = 1E-3 (mw)

The total noise power at the output end of the last amplifier is:The total noise power at the output end of the last amplifier is:

Pase = (Pase = (Pase1 - L1 + G2 - L2 + G3 - L4 + G4) Pase1 - L1 + G2 - L2 + G3 - L4 + G4) + (+ (Pase2 - L2 + G3 - L4 + G4) Pase2 - L2 + G3 - L4 + G4) + (+ (Pase3 - L4 + G4) Pase3 - L4 + G4) + + Pase4 Pase4 = 1E (-3 -3 + 2.3 - 2 + 2.3 - 3.7 + 2.3) + 1E (-3 -2 = 1E (-3 -3 + 2.3 - 2 + 2.3 - 3.7 + 2.3) + 1E (-3 -2 + 2.3 - 3.7 + 2.3) + 1E (-3 - 3.7 + 2.3) + 1E (-3) = 0.00001589 + 0.00007943 + + 2.3 - 3.7 + 2.3) + 1E (-3 - 3.7 + 2.3) + 1E (-3) = 0.00001589 + 0.00007943 + 0.00003981 + 0.001 = 0.00113513 (mw) = -29.45 (dBm)0.00003981 + 0.001 = 0.00113513 (mw) = -29.45 (dBm)

OSNR at the output end of the last amplifierOSNR at the output end of the last amplifier is: OSNR = Ps(mw)/Paseh(mw) = is: OSNR = Ps(mw)/Paseh(mw) = Ps(dB) – Pase(dB) = -9 - (-29.45) = Ps(dB) – Pase(dB) = -9 - (-29.45) = 20.45 dB 20.45 dB > 20 dB> 20 dB

The OSNR calculated above meets the requirements of the system.The OSNR calculated above meets the requirements of the system.


Example of OSNR Calculation

The OSNR calculated by the above tool is 19.93 dB, which is near to the value 20.45 dB The OSNR calculated by the above tool is 19.93 dB, which is near to the value 20.45 dB obtained in the formula. If the OSNR calculated by using CAS.EXE meets relevant obtained in the formula. If the OSNR calculated by using CAS.EXE meets relevant requirements, the actual OSNR is desirable. requirements, the actual OSNR is desirable.

Note: This tool is saved in the CD-ROM 7.0. The path is: \Chinese data CD-ROM 7.0\ 05-Note: This tool is saved in the CD-ROM 7.0. The path is: \Chinese data CD-ROM 7.0\ 05-WDM product data\01-WDM public\03-Functions and characteristics\02-Tools\01-Rough WDM product data\01-WDM public\03-Functions and characteristics\02-Tools\01-Rough calculator of OSNR.calculator of OSNR.


To improve the OSNR of the system:

1. Combine low-noise pre-amplifiers and high-gain amplifiers.

2. Combine FRAs and EDFAs to reduce the NF.

To reduce the OSNR tolerance:

1. Use forward error correction technologies — forward error correction (FEC), enhanced forward error correction (EFEC) or adaptive forward error correction (AFEC).

2. Use special coding technologies.

How to Improve OSNR MarginHow to Improve OSNR Margin


Signal Coding Technologies

NRZ

RZ

1 1 11 11 1 00

Smaller duty cycleSmaller duty cycle

Larger Q factor margin under the same OSNR conditionsLarger Q factor margin under the same OSNR conditions

Stronger capability to resist optical dispersion and non-linear distortionStronger capability to resist optical dispersion and non-linear distortion

Stronger capability to resist received eye pattern distortion caused by polarization Stronger capability to resist received eye pattern distortion caused by polarization division multiplexing (PDM)division multiplexing (PDM)


Signal Code Technologies

2000 Tbit/s x km2000 Tbit/s x km

SuperDRZSuperDRZ

Capacity x distanceCapacity x distance



ALLRAMAN systems

RZRZ

CSRZCSRZ

SuperCRZSuperCRZODBODB BL-PSBTBL-PSBTDMSDMS

Comparison among coding technologies

Code Modulation Technologies

Non-LinearityDispersion Tolerance

Spectrum Efficiency

Remarks

RZ

RZ Good Normal 50 GHz

CSRZ Good Normal 50 GHz

DMS Very excellent Good 50 GHzIn engineering implementation, FRAs are necessary.

SuperCRZ Very excellent Normal 50 GHz

SuperDRZ Excellent Good 25 GHzAchieve the best balance among non-linearity, dispersion and spectrum efficiency.

SuperWDM technology


SuperDRZ Technology

0 0 0 1 1 1 1 1 0 0 1 1 0 1 0 0 1 0 0 0 0 0 1 0 1 0 1 1 1 0 1 1 0

SuperDRZ

0 0 0 1 1 1 1 1 0 0 1 1 0 1 0 0 1 0 0 0 0 0 1 0 1 0 1 1 1 0 1 1 0

SuperDRZ

SuperDRZ pulse sequence before entering the optical fiber (the phase difference between red pulses and blue pulses is 180 degrees)

Due to opposite phases between two adjacent pulses "1", the signal indicating optical power is equal to 0 is received by the receiver.

In SuperDRZ, the transmitter converts input differential signals to positive and negative pulses to drive MZ modulators. The phase difference between adjacent codes "1" in modulated optical pulse sequences (SuperDRZ coding) is 180 degrees (opposite phases).

As optical signals are transmitted in the optical fiber, optical pulses are broadened. But due to opposite phases between adjacent codes "1", light intensity is approximate to 0 despite overlapping codes "1".

SuperDRZ pulse sequence after optical transmission for some time (the phase difference between red pulses and blue pulses is 180 degrees)


SuperDRZ Reduces Intersymbol Interference

Eye patterns of signals after optical transmission over different distances

Compared with RZ, SuperDRZ has larger dispersion tolerance and can reduce

intersymbol interference.

SuperDRZ has larger PMD tolerance than RZ.

General RZ

SuperDRZ


Excellent Non-Linear Tolerance of SuperDRZ

DRZ inherits the advantage of SuperWDM in non-linear tolerance through controllable chirp modulation.

Special frequency modulation can reduce non-linear effects such as SPM, FWM, SRS and SBS.


FEC Technology

FEC includes inband FEC and outband FEC. The main FEC technology used for FEC includes inband FEC and outband FEC. The main FEC technology used for

DWDM boards is outband FEC. Outband FEC is supported by ITU-T G.975/709.DWDM boards is outband FEC. Outband FEC is supported by ITU-T G.975/709.

Signal payload Signal payload FECFEC

codingcoding

As specified in ITU-T G.975, FEC coding/decoding are done for SDH signals directlyAs specified in ITU-T G.975, FEC coding/decoding are done for SDH signals directly through RS(255, 239) codes.through RS(255, 239) codes.

ITU-T G.709 describes the structure of optical transmission networks (OTN). In this ITU-T G.709 describes the structure of optical transmission networks (OTN). In this standard, the FEC overhead belongs to the OTUk layer in an OTN.standard, the FEC overhead belongs to the OTUk layer in an OTN.

Comparison of theoretic BERs before and after RS(255, 239) FECComparison of theoretic BERs before and after RS(255, 239) FEC

BER Before FEC BER After FEC

1.0E-3 8.6E-8

2.0E-4 2.0E-12

1.0E-4 5.0E-15

1.0E-5 6.3E-24

1.0E-6 6.4E-33


FEC Technology

• FEC and extended FEC in the ITU-T G.709 standard:

Figure 1 Standard OTUk frame structure

Figure 3 OTUk frame structure — FEC overhead size extension

Figure 2 OTUk frame structure — FEC coding type extension


FEC Technology

Coding Coding Algorithm Coding Gain Line Speed Standard

Out-band FEC RS(255, 239) 5–7 dB 10.7 Gbps G.709

Enhanced-FECRS(255, 238)RS(245, 210)

7–9 dB 12.5 Gbps No

Advanced-FEC RS(255, 238)

BCH(900, 860)BCH(500, 491)

7–9 dB 10.7 Gbps G.709

The line speed in AFEC is equal to that in

outband FEC but coding gain in AFEC is higher. The coding gain in AFEC is near to that in

EFEC, but the line speed is lower in AFEC. So

bandwidth costs in AFEC are lower. AFEC complies with the frame structure defined

in ITU-T G.709.


WithoutFEC

Inband FEC

Out-bandFEC

AFECAFEC

OSNR > 25 dBOSNR > 25 dB

OSNR > 23.5 dBOSNR > 23.5 dB

OSNR > 20 dB OSNR > 20 dB


WithoutFEC

Out-bandFEC


OSNR > OSNR > 14 14 dBdB

1010G:G:

2.52.5G:G:

Requirements for OSNR in FECRequirements for OSNR in FEC


Currently, CD effects are reduced mainly by using dispersion compensation

modules (DCMs) to compensate for accumulated dispersion in optical fibers. There

are mainly two kinds of chromatic dispersion compensation technologies:

1. Dispersion compensation fiber (DCF)

2. Dispersion compensation grating, that is, chirped fiber grating (CFG)

In the current DWDM system, the main dispersion compensation technology is

DCF.

Dispersion Compensation TechnologyDispersion Compensation Technology


The difference between DCF and general fibers lies in that the dispersion coefficient at 1550 nm is negative. This kind of negative dispersion fibers are connected to the G652 optical system to offset the positive dispersion in G652 fibers.

The typical value of the dispersion coefficient of DCF is -90 ps/(nm.km). So DCF can make dispersion value in the total link approximate to 0 only by occupying 1/5 of the total G.652 fiber.

DCFDCF

Dispersion coefficient

Wavelength

General DCF

Dispersion slope compensation fiber (DSCF)


Dispersion limit = (Dispersion tolerance / Dispersion coefficient) + DCM compensation - (10–30)

(The system should have 10–30 km redundant length.)

The dispersion tolerance of a 10G optical wavelength conversion unit is 700 ps/nm. In the G.652 fibers, the dispersion coefficient is 17 ps/(nm.km). Considering the redundant length is 10–30 km, the longest transmission distance without compensation is: L = 700/17 - (10–30) = 10–30 km. That is, when the transmission distance exceeds 30 km, DCM must be used for compensation. Similarly, in the G.655 fibers, the dispersion coefficient is 4.5 ps/(nm.km). The longest transmission distance without compensation is: L = 700 / 4.5 = 155 km. That is, when the transmission distance exceeds 100 km, DCM must be used for compensation. In G.652 optical fibers, the calculation formula is: DCM ≥ L - [(Dispersion tolerance / Dispersion coefficient) - (10–30)] = L - [(700 / 17) - (10–30)]

= L - (10–30) In G.655 optical fibers, the calculation formula is: DCM ≥ L x (4.5 / 17) - (10–30) = Lx - (10–30)

Note: Convert the length of a G.655 fiber to that of a G.652 optical fiber: Lx = L x (4.5 ps / 17 ps)

Calculation of DCM Dispersion Compensation SpecificationsCalculation of DCM Dispersion Compensation Specifications


CFG

CFG is formed due to etching by ultraviolet rays that are sent to optical fibers through the CFG is formed due to etching by ultraviolet rays that are sent to optical fibers through the template, which makes the refractive index of the optical fibers change periodically. template, which makes the refractive index of the optical fibers change periodically. Lightwaves of different frequencies in input pulses are reflected by different parts of the Lightwaves of different frequencies in input pulses are reflected by different parts of the grating and coupled between two counter-propagation mode fields. Adjust reflection delay to grating and coupled between two counter-propagation mode fields. Adjust reflection delay to make it equal to that of optical transmission but in opposite directions.make it equal to that of optical transmission but in opposite directions.

Optical circulator

1 2

3

Input signal

Output signal

CFG

Long wavelength

Short wavelength


Key Technologies in 40G Transmission

Code modulation technologiesODB, CS-RZ, RZ-DPSK, DQPSKCode modulation technologiesODB, CS-RZ, RZ-DPSK, DQPSK

FECAFECFEC

AFEC

Dispersion management

ADC, EDC

Dispersion management

ADC, EDC

Distributed Raman amplification

Distributed Raman amplification

OSNR tolerance is raised by 6 dB.

OSNR tolerance is raised by 6 dB.

Dispersion tolerance is decreased by 16 times

(60 ps/nm).

Dispersion tolerance is decreased by 16 times

(60 ps/nm).

PMD effects are increased by four

times.

PMD effects are increased by four

times.

More danger is caused by non-linear effects.

More danger is caused by non-linear effects.

Under the same physical conditions, the 40G DWDM system should meet the following requirements to Under the same physical conditions, the 40G DWDM system should meet the following requirements to compete with the current 10G DWDM system in performance:compete with the current 10G DWDM system in performance: AFEC can improve the white noise correction capability and lower system OSNR tolerance by 6 dB.AFEC can improve the white noise correction capability and lower system OSNR tolerance by 6 dB. Use advanced code modulation technology and improve transmission performance in a Use advanced code modulation technology and improve transmission performance in a

comprehensive way and reduce restrictions on OSNR, PMD, non-linearity and dispersion.comprehensive way and reduce restrictions on OSNR, PMD, non-linearity and dispersion. Use new dispersion management technology such as ADC, improve dispersion tolerance and reduce Use new dispersion management technology such as ADC, improve dispersion tolerance and reduce

non-linearity.non-linearity.


Summary

What are the main limiting factors to the WDM system?

What kind of technology is used by Huawei for CD?

What measures can be taken to improve the OSNR?


Contents







Types of Huawei WDM NEs

According to the usage, Huawei WDM NEs include:

Optical terminal multiplexer (OTM)

Optical line amplifier (OLA)

Optical add/drop multiplexer (OADM)

REG

Take the BWS 1600G for example to illustrate networking signaling flows.


Networking Types

SDHOTM OLA OLA OTM SDH

STM-16s16

OTM16/16

120 km

STM-16s16

STM-16sEightOTM16/16

120 km

OADM16/8

Chain networking:

Point-to-point networking:


Networking Types

Ring networking:

OADM

OADM OADM

OADM

1–8

1–8

1–8 1–8


Schematic Drawing of Networking for the BWS 1600G

D

M

X

D

M

X

D

M

X

D

M

X

OTUL

OTUL

OTU

OTU C

M

U

X

M

U

X

M

U

X

OTU

L OTU

C

OTU

OTU

SC1

ITL

ITL

ITL

SC1 SC2 SC2

OADM

OADM

F

I

U

OTMOLA OADMOTM

C

L

F

I

U

F

I

U

F

I

U

F

I

U

F

I

U

C

M

U

XITL

L band moduleC band module

50GHz 50GHz

50GHz 50GHz

C/L band module

D

M

X

D

M

X

D

M

X

D

M

X

OTUL

OTUL

OTU

OTU C

M

U

X

M

U

X

M

U

X

OTU

L OTU

C

OTU

OTU

SC1

ITL

ITL

ITL

SC1 SC2 SC2

OADM

OADM

F

I

U

OTMOLA OADMOTM

C

L

F

I

U

F

I

U

F

I

U

F

I

U

F

I

U

C

M

U

XITL

D

M

X

D

M

XOTU

OTU C

M

U

X

C

OTU

OTU

SC1

ITL

SC1 SC2 SC2

OADM

F

I

U

OTMOLA OADMOTM

C F

I

U

F

I

U

F

I

U

F

I

U

F

I

U

C

M

U

XITL

M

U

X

C

OTU

OTU

C

M

U

X

ITL

ITLD

M

X

D

M

XOTU

OTU C

C

ITL

ITL

50 GHz25 GHz

50 GHz

50 GHz25 GHz

In the new system structure, only C band modules are used; expensive L band components have been removed; modular upgrade is supported; the Interleaver supporting 25 GHz wavelength interval is added.


Evolution of Networking for the BWS 1600G

OTM REG REG OTM

OADM

Phase 1: Point-to-point networking 600 km transmission without electrical

regenerators

OADM

ROADM

Phase 2:

Ring networking 2000–3000 km transmission without

electrical regenerators— reducing optical-electrical-optical (OEO) conversion costs

Phase 3: Ring/Mesh networking Supporting dynamic networks based on

reconfigurable optical add/drop multiplexing (ROADM) technology

4000–5000 km transmission without electrical generators

OADM OADM


Diversified Fixed Optical Add/Drop Multiplexer (FOADM)

Low costs

Simple structure

Maximum of 16 wavelengths

FOADM I

Multiple-layer dielectric film technologySerial OADMs

FOADM II

AWG technologyParallel OADMs

Supporting online upgrade

100% wavelength add/drop

Direct pass-through without electrical regenerators

Extension capability from 2D to 3D

The purpose of using OADM is to lower wavelength converter costs in DWDM.The purpose of using OADM is to lower wavelength converter costs in DWDM.

EREG


Example of FOADM Networking

ADMOTU

ADMOTUOTU

ADMADMADM

OTU

FOADM I FOADM II

3: pass-through at each OADM node and no need for electrical regenerators

2: pass-through at FOADM I nodes and add/drop at FOADM II nodes

1: add/drop at each OADM node

• Flexible FOADM configuration according to wavelength add/drop scale at each node• FOADM suitable for middle and small nodes (≤ 16) and FOADM suitable for large nodes (>

16)


2D ROADM

Splitter /Drop filters

Add filters /Combiner

WB module

ROADM II (Wavelength selective switch)

Suitable for 2D nodes

Supporting dynamic wavelength add/drop and pass-through

100% wavelength add/drop

Built-in optical balance

Coupler

1 x 9 switch

Multi-port Mux/Demux

WSS module

Tunable laser for colorless add

Broadband receiver for colorless drop

ROADM I (Waveblocker)

Colorless add/drop

Easier upgrade

2D-4D-8D lossless extension capability

Supporting mesh networking

40 switches


Multi-D ROADM

Colorless drop and multi-degree update ports

OA1*9 WSS

SOA

E

OA

EOA

S

OAN

OAW

OA

WOA

N

M32 D32

1*9 WSS

1*9 WSS

1*9 WSS

1*9 WSS

1*9 WSS

1*9 WSS

Add local trafficAdd local traffic Drop local trafficDrop local traffic

Coupler Coupler

1*9 WSS

Ring1Ring1

Ring2Ring2

Major hub nodes

• Flexible optical layer cross-connect — automatic wavelength connection through cross-ring networking, thus eliminating manual optical patch cord between hub nodes.

• Online upgrade from 2D to multi-D (a maximum of 8D is supported)• Reducing regenerators through optical layer pass-through — reducing high costs caused by

expensive electrical regenerator cascading


Flexible ROADM Networking

Regional convergence nodes

• 2D nodes• Low wavelength

add/drop rate• Local termination of

add/drop services • Basically no need for

rebuilding

ROADM (WSS)

OADM/ROADM (WB)

Regional core nodes• Low wavelength

add/drop rate• Connecting with 3–5

nodes• Need for remote

rebuilding and management

Core nodes• High wavelength

add/drop rate• Possible need for

rebuilding• Connecting with multiple

nodes


Summary

• What types of ROADMs are mentioned?

Thank You

www.huawei.com

basic knowledge about wdm principle-a

Documents