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Huawei OptiX BWS 1600G. Technical Description - part 8

3 System Configuration

3.4 REG

3.4.1 Signal Flow

We have already discussed that the OLA can extend the optical transmission

distance without regeneration. However, when the distance is longer, such factors

as dispersion, optical noise, non-linear effect, or PMD will affect the transmission

performance. In this case, we need to regenerate the original signals. An REG

implements the 3R function, that is, reshaping, re-timing and regenerating, to

improve the signal quality and extend the transmission distance.

An REG station contains:

„ Optical transponder unit (OTU)

„ Optical multiplexer (OM)

„ Optical demultiplexer (OD)

„ Optical amplifier (OA)

„ Optical supervisory channel unit or supervisory channel and timing

transporting unit (OSC/OTC)

„ Fibre interface unit (FIU)

„ Multi-channel spectrum analyser unit (MCA)

„ System control & communication unit (SCC)

„ Power backup unit (PBU)

Figure 3-22 shows the block diagram of the REG signal flow.

DCM

λ01

DCM

OTU01

λ02

OTU02

OA

OM

OD

OA

λn

OTU n

F

F

OSC/OTC

I

I

U

U

λ01

OTU01

λ02

OTU02

OA

OM

OA

OD

λn

DCM

OTU n

DCM

MCA

Figure 3-22 REG signal flow

The signal flow of the REG is similar to that of back-to-back OTMs, except that no

signal is added/dropped. Signals are regenerated through the regenerating OTU.

3.4.2 Structure

For the REG of the six system types, each functional unit and the board(s)

contained are shown in Table 3-1.

3-29

3 System Configuration

„ Optical supervisory channel unit or supervisory channel and timing

transporting unit (OSC/OTC)

„ Fibre interface unit (FIU)

„ Multi-channel spectrum analyser unit (MCA)

„ System control & communication unit (SCC)

Figure 3-23 shows the signal flow of the optical power equaliser.

OA

OPE

OA

F

F

OSC/OTC

I

I

U

U

OA

OPE

OA

MCA

Figure 3-23 Signal flow of optical power equaliser.

(2) Dispersion equaliser

It consists of:

„ Dispersion equaliser (DE)

„ Optical amplifier (OA)

„ Optical supervisory channel unit or supervisory channel and timing

transporting unit (OSC/OTC)

„ Fibre interface unit (FIU)

„ Dispersion compensation module (DCM)

„ Multi-channel spectrum analyser unit (MCA)

„ System control & communication unit (SCC)

Figure 3-24 shows the signal flow of dispersion equaliser.

OA

DE

OA

F

F

OSC/OTC

I

I

U

U

OA

DE

OA

MCA

Figure 3-24 The signal flow of dispersion equaliser

3-31

3 System Configuration

The dispersion equaliser and the optical power equaliser can be placed in the same

station.

The dispersion equaliser is often placed at the receive end of the OTM for

dispersion equalization, as shown in Figure 3-25 . It is recommended to place it at

the receive end of the last station in the optical multiplexing section.

λ01

DE

OTU01

λ02

OTU02

OD

OA

RPU

λn

OTU n

F

Client

OSC/OTC

I

side

λ01

U

OTU01

λ02

OTU02

OA

OM

λn

OTU n

DCM

MCA

Figure 3-25 Signal flow of dispersion equaliser in OTM

3.5.2 Structure

„ Optical power equaliser

Two solutions are available: use of the dynamic gain equaliser unit (DGE) and use

of the VMUX unit, as shown in Figure 3-26 and Figure 3-27.

C-EVEN

OAU

F

F

I

DGE+DCM

I

DGE+DCM

U

U

C-EVEN

OAU

SC2/TC2

MCA-C

DGE: Dynamic gain equaliser unit

OAU: Optical amplifier unit

DCM: Dispersion compensation module

FIU: Fibre interface unit

SC2: Bidirectional optical supervising channel unit

Figure 3-26 Optical power equalization through the DGE

As shown in Figure 3-26, the optical power equaliser unit consists of the DGE and

DCM. The DGE realises optical power equilibrium of each channel by adjusting

insertion loss spectrum of the DGE board. The DCM is used to realise dispersion

compensation of the system.

3-32

3 System Configuration

This solution has all the functions of the OLA. In addition, optical power

equilibrium is implemented to make the multiplexed signals meet the requirement

for optical power flatness, and to extend the transmission distance without

regeneration.

Note

For DGE solution, note whether the power margin of the OAU meets the insertion

loss requirement of the DCM and the DGE. If the margin cannot meet the

requirement, OAU+OBU should be adopted. DCM and DGE are placed between

two amplifiers.

C-EVEN

OAU

D40

V40

OBU

F

F

I

SC2

I

U

U

C-EVEN

OBU

V40

D40

OAU

V40: 40-channel multiplexing unit with VOA

D40: 40-channel demultiplexing unit

OBU: Optical booster unit

FIU: Fibre interface unit

SC2: Bidirectional optical supervisory channel unit

OAU: Optical amplifier unit

Figure 3-27 Optical power equalization through the VMUX (the V40 board)

In Figure 3-27, the VMUX is adopted. The V40 is used as the VMUX unit to adjust

optical power of each channel, so as to equalize optical power.

The user can select one of the solutions according to the actual requirement.

„

Dispersion equaliser

The dispersion equaliser realises equalised compensation of dispersion for

multiplexed signals, as shown in Figure 3-28.

3-33

3 System Configuration

DCM

OAU

DSE

OBU

F

F

I

SC2

I

U

U

OBU

DSE

OAU

DCM

DSE: Dispersion slope equaliser unit

OAU: Optical amplifier unit

OBU: Optical booster unit

SC2: Bidirectional optical supervising channel unit

FIU: Fibre interface u nit

DCM: Dispersion compensation module

Figure 3-28 Composition of dispersion equaliser

Through the dispersion slope equaliser (DSE), the system sends the multiplexed

signals to the DCM for equalised compensation for dispersion.

Note

In ultra-long haul transmission, the configuration of the optical equaliser should

follow the principles below.

1. In the case of "8 ≤ number of optical amplification sections ≤ 12", and without

configuration of the OEQ, the VMUX must be configured at the transmit end for

equalisation.

2. In the case of "number of optical amplification sections ≥ 12", the OEQ must be

configured. The subsequent optical amplification sections will be configured

differently according to OEQ solution.

(a) D40+V40 solution: An OEQ is added when 8 optical amplification sections are

added.

(b) DGE solution: An OEQ is added when 5 optical amplification sections are

added.

If the optical fibre length of multiplexing section is equal to or greater than 1000 km,

a dispersion equaliser is required.

3.5.3 Typical Configuration

Figure 3-29 shows the configuration of the optical equaliser in the type III system.

Figure 3-30 shows the configuration of the dispersion equaliser in the type III

system.

3-34

3 System Configuration

Power

Power

M

S

V

D

M

S

D

V

C

C

4

4

C

C

4

4

A

E

0

0

A

E

0

0

(C)

(C)

O

D

F

T

S

F

D

O

O

O

F

T

S

F

O

O

A

G

I

C

C

I

G

A

A

B

I

C

C

I

B

A

U

E

U

2

C

U

E

U

U

U

U

2

C

U

U

U

(C)

(C)

(C)

(C)

(C)

(C)

DCM

DCM

HUB

HUB

Solution 1: DGE

Solution 2: V40+D40

Note: The "(C)" indicates the C band.

Figure 3-29 Configuration of OEQ

3-35

3 System Configuration

Power

F

S

F

M

I

C

I

C

U

E

U

A

(C)

O

O

D

T

S

D

O

O

A

B

S

C

C

S

B

A

U

U

E

2

C

E

U

U

(C)

(C)

(C)

(C)

DCM

HUB

Note: The "(C)" indicates the C band.

Figure 3-30 Configuration of dispersion equaliser

3.5.4 Configuration Principle

The configuration principle of the OEQ is the same as that of the OLA.

The OEQ (DGE and DSE) is inserted following "west on the left and right on the

east".

3-36

4 Networking and System Applications

OLA

OLA

OLA

(＃1)

(＃2)

(＃n-1)

Client

OTM

OTM

Client

1～160

mdB

1～160

n×m dB

Point-to-point network

ADD

Client

OTM

OLA

OADM

OLA

OEQ

REG

OTM

Client

1～160

1～160

DROP

Chain network

λ

1

λ 160

Back-to-back

OTM

λ

1

λ

1

OADM

OADM

λ

λ

80

80

Back-to-back

OTM

λ

1

λ 160

OTM：Optical terminal multiplexer

OLA：Optical line amplifier

OADM：Optical add/drop multiplexer

Ring network

OEQ：Optical equalizer

REG：Regenerator

Figure 4-1 OptiX BWS 1600G networking diagram

„ Point-to-point

The point-to-point network, composed of OTM and OLA, is the most prevalent

networking mode adopted by the OptiX BWS 1600G.

„ Chain

The chain network is frequently used in a national DWDM backbone network that

is of high capacity and long distance. A chain network may comprise OTM, OLA,

OADM, REG and OEQ, and can be regarded as the extension of a point-to-point

network.

„ Ring

The ring network is largely used in regional networks. It may comprise OADMs or

back-to-back OTMs depending on the practical situation. In practice, one OADM

in the DWDM ring network may be composed of back-to-back OTMs to remove

the accumulated noise caused by the amplifier.

4-2

4 Networking and System Applications

4.1.1 Type I system

The type I system, adopting non return to zero (NRZ) encoding, is applied in G.652

or G.655 optical fibers. Table 4-1 shows its networking capability.

Table 4-1 Networking capability of the type I system (160-channel, NRZ)

Classification

Specification

Typical distance

With FEC

1 × 28 dB

1 × 101 km (101 km)

2 × 24 dB

2 × 87 km (174 km)

5 × 20 dB

5 × 72 km (360 km)

The span attenuation is the actual attenuation of fibers, not including the loss of any optical

components.

Note

In section 4.1

, the span attenuation is the actual attenuation of the fiber, that is, the

difference between the output optical power of the local station and the input

optical power of the downstream station, not including the attenuation of the FIU

board.

In section 4.1

, the typical distances in the networking specification are calculated

on condition that the fiber attenuation coefficient is 0.275 dB/km.

The Raman amplifier can suppress OSNR from deteriorating to support more spans,

and to transmit signals longer. With Raman amplification, the type I system

supports a transmission distance of 640 km without a regenerator.

If the type I system uses out-band AFEC, it can support longer transmission without

REG.

4.1.2 Type II system

The type II system supports C+L 800G and C 800G.

C+L 800G

The C+L 800G system, adopting NRZ encoding, is applied in G.652 or G.655

optical fibers. Table 4-2 shows its networking capability.

4-3

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