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China Communications December200554

Feature Articles: Optical Fiber Communications

ABSTRACT

According to the requirement of large information

transport, 40Gb/s (STM-256) SDH optical commu-

nication system is the very useful technology for

national information infrastructure. In this paper, the

development progress has been introduced in terms

of the key technologies of 40Gb/s equipment and

system, and some test results have been showed.

Key words: 40Gb/s, STM-256, SDH, optical

communication, dispersion, PMD

I. INTRODUCTION

The total length of installed optical cable is

more than 3.38M km in China, including 646 K

km of core network and 2.73M km of local

network. But the microwave line length is only

190 K km. So we can see almost 95% of the total

information is transported through optical trans-

port network in China. On the other hand, there

are a total of 700M telephone subscribers (340M

POTS subscribers and 360M mobile phone users)

in China. This is the largest telecommunication

network in the world. Thus, more information

transportation is needed.

In this paper the development status of 40Gb/s

(STM-256) SDH optical communication system

in China is described based on the "10th five year

plan of Na tional Key Technologies R&D

Programme (NKTRDP)".

II. 40GB/S (STM-256) SDH OPTICAL

COMMUNICATION SYSTEM

TDM is the basic technology to increase the

system's capacity or bit-rate. The highest level

of SDH hierarchy is STM-256, i.e. 40Gb/s. In

the world, there are only a few companies can

provide such equipment. In 2002, Wuhan Re-

search Institute of P&T, China (WRI) initial-

ized the STM-256 optical communication sys-

tem R&D project, or the NKTRDP project.

The final target of this project is to establish a

40Gb/s optical transmission field trial and provide

commercial use in the future. The trial system

consists of two terminal equipment and five optical

repeaters (i.e. optical amplifiers) for a linear link

system or three ADM nodes for ring systems, which

are shown in Fig 1.

This project was implemented at the end of

2004, and it was checked and accepted by MII of

China in June, 2005.

Development Progress of 40

Gb/s (STM-256) SDH Optical

System in China

Mao Qian

Professor, Wuhan Research Institute of P&T. Wuhan, Hubei, China

FEATURE ARTICLES


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China Communications December2005 55


III. KEY TECHNOLOGIES IN40GB/S SYSTEM

There are several key technologies in the 40Gb/

s sys tem, such as chromat ic d i sper s ion

compensation, Polarization Mode Dispersion

(PMD) compensation, nonlinear control, opti-

cal amplifier technology, OSNR control and so

on. All of such problems have been well re-

solved in this system by theoretic studies, com-

puter simulations and pract ical experiments.

For example, the chromatic dispersion in

optical fiber could cause a pulse to pread out

progressively as it travels along the f iber. This

spreading leads to interference between adja-

cent pulses (called inter-symbol interference),

which limits the distance of system signal. The

limited distance calculation is as following

formula:

(1)

Where, L is the maximum transported distance,

C is the velocity of light,

D is the dispersion coefficient of used optical

fiber,

is the operating wavelength,

B is the bit rate of transported signal.

Table 1 shows the calculation results for trans-

ported signal from 2.5Gb/s to 40Gb/s.

So, to send the 40Gb/s signals over hundreds of

kilometers in G.652 and G.655 fiber operating at

1550nm, we must use dispersion compensation tech-

nologies to reduce the dispersion effects. Our meth-

ods combine the use of Dispersion Compensation

Fiber (DCF), tunable dispersion compensator and

chirp fiber grating. Thus system dispersion could be

compensated exactly.

Another example is PMD effect. PMD results

from the fact that light signal energy at the operating

wavelength in the fiber actually occupies two or-

thogonal polarization states or modes. The resulting

difference in propagation time between the two

(b) STM ring(b) STM ring(b) STM ring(b) STM ring(b) STM ring

Fig (a) STM Linear linkFig (a) STM Linear linkFig (a) STM Linear linkFig (a) STM Linear linkFig (a) STM Linear link

Bit rate 1550nm(G.652) 1550nm(G.655) 1310nm(G.652)

2.5Gb/s 928km 4528km 6400km

10Gb/s 58km 283km 400km

40Gb/s 3.6km 18km 25km

Table.1 Limited distances for transported

signal from 2.5Gb/s to 40Gb/s.


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orthogonal polarization states will result in pulse

spreading. So, high bit rate signal could not be

transported to long distance due to the PMD effect.

The limited distance could be calculated using

formula (2)

(2)

Where: L is the maximum transported distance,

B is the bit rate of transported signal,

DPMD

is the

PMD coefficient of

used opti-

cal fiber.

Fig.2 shows the

calculation results

for different bit rate

signals and PMD

coefficients.

We can see only

25km could be trans-

ported for 40Gb/s

signal in G.652A and

G.655A fiber from

Fig.2. But right now,

almost all of the

fiber's PMD coeffi-

cients are very small,

typically less than 0.

05ps/km1/2. So, the

limited distance of

40Gb/s signal could

reach to 2 500km, even there is no PMD compensa-

tion work needed in the general project.

For nonlinear effect, we could reduce its influence

by incidence optical power control. According to

our theoretic calculation and computer simulation, -

1~+3dBm (for G.655 fiber) and 0~+2 dBm (for G.

652 fiber) is the optimum incidence optical power in

our system.

Due to the fact that the noise figure of Raman

optical amplifier is less than 0 dB, so we use EDFA

plus Raman optical amplifier in the line system to

ensure that the OSNR could be more than 25dB at

system sink end.

All of those technologies mentioned above have

been applied in our 40Gb/s optical communica-

tion system, and the experiment results couldshow the coherence between theoretic calculation

and practical system test.

IV. TEST RESULTS OF

40GB/S TRIAL SYSTEM

We have implemented the 40Gb/s STM-256 optical

transmission system trial using NRZ line code, with-

out FEC, without PMD compensation and without

electrical regenerator over 560km (7 80km

ba sed on Fi g. 1a ) in G.652 and G.655 fi be r

respectively. Table 2 shows the test results of

major objectives of STM-256 trial system.

Fig. 4 shows the optical signal eye pattern at

transmitter end and receiver end after 560km

transmission respectively. We could see a very

clear eye open and there are more margins in the

Fig The limited transport distances for different bit rate signals and PMDFig The limited transport distances for different bit rate signals and PMDFig The limited transport distances for different bit rate signals and PMDFig The limited transport distances for different bit rate signals and PMDFig The limited transport distances for different bit rate signals and PMD

coefficientscoefficientscoefficientscoefficientscoefficients


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China Communications December2005 57


Parameter Unit Objective

Application code I.256-2, L.256-2, L.256-3

Operating wavelength range nm 1530~1565

Max. -20dB spectral wide nm 0.52

Side mode suppression ratio dB 45.2

Mean launched power dBm +1.5

Min. return loss at S point dB 36

Min. extinction ratio dB 11.9

Eye pattern mask Compliance with Fig.3 and Table 3

Receiver Min. sensitivity dBm - 20.1

Receiver Min. overload 0

Max. Reflectance at R point dB - 42

S-R path penalty dB 1.8

Max. non-congestion cross Cap. Gb/s 320

Tributary signal level STM16, 64, GE

Table.2 Major objectives of STM-256 trial system

receiver end eye pattern, so it is possible to extend

more transmission distance.

We have done the trial test for 40Gb/s system trans-

mission pass through 480km in G.655 fiber over 30

days. The error performance is as follows:B1 error: 0

B2 error: 0

B3 error: better than 2 10-18

V. CONCLUSION

This 40Gb/s STM-256 SDH optical transmission

system is the first one in China. A transmission

distance of 560km without electrical regenera-

tors is the longest record for the single channel

40Gb/s STM-256 system in China, and even in

the world.

Another important project program is the " 863

Hi-tech Research and Development Program of

China " ( 863 in short). There is a "80 40Gb/s

DWDM transmission system" in 863 programs, which has been completed by Wuhan Research Institute of

P&T in June 2005. The longest transmission distance of 8040Gb/s DWDM signal is more than 300km both

in G652 and G655 fibers.

STM-256X1/X4

X2/X3

X3-X2 0.2

Y1/Y2 0.30/0.70

Y3/Y4 0.25/0.25

Table.3 Parameters of eye pattern mask

Fig Eye pattern maskFig Eye pattern maskFig Eye pattern maskFig Eye pattern maskFig Eye pattern mask


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Both the single channel and the DWDM system based

on 40Gb/s will be applied in commercial telecommuni-

cation network in the near future in China.

REFERENCES

[1] ITU-T Rec. G.707/Y.1322 (10/00) " N e t -

work node interface for the synchronous digital

hierarchy (SDH)"

[2] ITU-T Rec. G.783 (10/00)

"Characteristics of synchronous digital hierarchy

(SDH) equipment functional blocks"

[3] ITU-T Rec. G.959.1 (12/03) "Optical trans-

port network physical layer interface"

BIOGRAPHY

Mr. Mao Qian, Graduated from Wuhan Posts and

Telecommunications Institute in 1964. Received Master

degree from Wuhan Research Institute of posts and

telecommunications in 1982. He is mainly engaged in R

& D on optical fiber communication equipment, systems,

optical transport networks, digital communications and

data communications and science & technologies

managements. He received national and ministerial or

province level Science & Technology Progress Award

several times. At present he works as Professor, vice

president and chief engineer of Wuhan Research Insti-

tute of posts and telecommunicationspresident of

FiberHome Technologies Institute, director of Quality

Supervision & Inspect Center of optical communication

products of MII. He is the professor of Huazhong

University of Sciences and Technologies and Dalian

University of Technologies. He is national level expert

and enjoyed special government subsidy. He is ITU-T

Study Group 15 membercouncil member and vice

chairman of transport network & access network tech-

nical committee of China communication standards

association. Also, he is the director of optical communi-

cation committee, vice director of science working

committee of China Institute of Communications, coun-

cil vice chairman and director of optical communication

committee of Communication Institute of Hubei province,

council vice chairman and director of communication

transmission

committee of

Electronics In-

stitute of Hubei

province. He

has published

three books

and more than

one hundred

papers in na-

tional & inter-

national con-

ferences and

magazines.

(a) (b)

Fig Optical signal eye pattern: (a) Transmitter end (b) Receiver end after km transmissionFig Optical signal eye pattern: (a) Transmitter end (b) Receiver end after km transmissionFig Optical signal eye pattern: (a) Transmitter end (b) Receiver end after km transmissionFig Optical signal eye pattern: (a) Transmitter end (b) Receiver end after km transmissionFig Optical signal eye pattern: (a) Transmitter end (b) Receiver end after km transmission

built sdh fiber optic in china

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