PERFORMANCE COMPARISON OF DISPERSION COMPENSATING FIBER … · compensation method and optical phase conjugation are the effective dispersion compensation techniques which limit the

International Journal of Research in Engineering, Technology and Science, Volume VII,

Special Issue, Feb 2017

www.ijrets.com, [email protected], ISSN 2454-1915

Tushar Kant Panda, Krishna Chandra Patra, Nalinikant Barapanda and Padmini Mishra 1

PERFORMANCE COMPARISON OF DISPERSION COMPENSATING

FIBER IN 40 GBPS WDM NETWORK USING PRE, POST AND

SYMMETRICAL COMPENSATION SCHEMES Mr.TusharKantPanda1 , Dr. Krishna Chandra Patra2,Dr.Nalinikant Barapanda3 and Mrs.

Padmini Mishra4

1Research scholar, Sambalpur University Institute of Information Technology, Sambalpur 2Asst. Professor, Sambalpur University Institute of Information Technology, Sambalpur

2Reader, Sambalpur University, Sambalpur 3Asst. Professor, Gandhi Institute of Engineering and Technology, Gunupur

Abstract-Fiber optics communication has become a widespread adopted method for data transmission. The miraculous idea of using light as carrier to carry the message across the distance allured a lot of researchers towards itself. The major advantage offered by the fiber optic communication is its high bandwidth. In order to make the optimum use of this bandwidth we must transmit many signals through single fiber. WDM Network permits multiple channels to be routed through single fiber at different wavelength. However it does face some challenges and Dispersion being the major limiting factor among all. Dispersion causes pulse distortion and spreading of pulses in time domain. In this paper, we have used the very basic technique of using dispersion compensating fibers (DCF) to compensate the positive dispersion in a WDM network. Three schemes of dispersion compensation (pre, post and symmetrical) with DCF are proposed in this paper by using Optisystem 7.0 simulator. The results obtained from the respective schemes are compared in terms of Q-factor, BER, Eye height and Threshold value and it is found that the symmetrical compensation method is superior to pre- and post-compensation methods. Thus by using these comparisons one can achieve a cost effective, propitious system with high spectral efficiency and good flexibility. Keywords –Dispersion compensating Fiber, Bit error rate (BER), Q-factor, Eye height, MZM (Mach Zender Modulator), Optisystem Software version 7.0. 1. INTRODUCTION

From past few years, the number of internet users is

increasing day by day, hence, the internet business is

increasing too. Therefore, primary requirement of

people are more capacity and better network system

[1]. In order to get better and effective performance

while transmitting the data from transmitter side to

receiver side, WDM network is being used [2]. The key

parameters which is responsible for effective

performance in Wavelength Division Multiplexing

(WDM) optical network is high data rate, high capacity

and high bandwidth. Different signals are being used

as input signal at transmitter side and are multiplexed

using WDM network [3]. After multiplexing, signals

are sent through a single fiber. While transmissionof

signal, there is degradation in light intensity while

travelling through fiber. Though WDM network is one

of the effective techniques for data transmission, still it

suffers from performance limiting factors like

dispersion and nonlinear effects. Here dispersion is the

main performance limiting factor which responsible for

limiting the information capacity at high data rate [4].

In order to compensate dispersion, different dispersion

compensation techniques are being used. Dispersion

compensating fiber, fiber Bragg grating, electrical

compensation method and optical phase conjugation

are the effective dispersion compensation techniques

which limit the performance limiting factor

(dispersion).

2. DISPERSION

The main performance limiting factor in the world

of optical communication is dispersion [5]. When

light pulses of different wavelength are

transmitted through optical fiber, due to the

variation in refractive index with wavelength,

pulses travels with different speed. After travelling

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PERFORMANCE COMPARISON OF DISPERSION COMPENSATING FIBER IN 40 GBPS WDM

NETWORK USING PRE, POST AND SYMMETRICAL COMPENSATION SCHEMES

TusharKantPanda, Krishna Chandra Patra, Nalinikant Barapanda and Padmini Mishra 2

certain distance, these pulses spreads and

broadening of pulses are observed. These pulse

broadening in optical fiber is referred as

dispersion. Dispersion is also responsible for

inter symbol interference (ISI) [6]. In ISI, the

pulses goes on broadening and hence overlap

each other. Due to this overlapping, the

pulses can’t be distinguished at receiver end.

Dispersion can be classified into following

categories.

Fig 1: CLASSIFICATION OF DISPERSION

Material Dispersion: This type of dispersion arises

due to the variation in refractive index of material

used during transmission of data from transmitter

side to receiver side. Because of the change in

refractive index in the material of the fiber, the

rays travels with different speed and also get

refracted differently and hence dispersion arises.

Waveguide Dispersion: This type of dispersion

arises due to the refractive index profile of core

and cladding of optical fiber used. Since core

refractive index is different as compared to

cladding refractive index, the ray of light will travel

with different speed which results to cause

dispersion.

Modal Dispersion: This type of dispersion arises

because of the use of multimode fiber in optical

communication. When a beam of light travels

through multimode fiber then at the receiver end,

the rays which comprises the beam of light reaches

at different time. This results in pulse broadening

and hence, dispersion is observed.

Polarization Mode Dispersion: This type of

dispersion arises because the light pulses of

different polarization state travels with different

group velocities which results in pulse width

spreading and hence, dispersion is observed.

As dispersion increases, ISI also increases due to

which there is reduction in effective bandwidth

which leads to an incresing BER. So to eliminate

dispersion, different dispersion compensation

techniques are used. Some of the dispersion

compensation techniques which are commonly

used are dispersion compensating fiber, Fiber

Bragg grating, electrical compensation method

and optical phase conjugation [7]. Among these

compensation technique, dispersion compensating

fiber is the most suited one.

3. DISPERSION COMPENSATING FIBER

In order to tackle the performance limiting factor

(dispersion) in optical communication and

maximizing the overall system performance,

dispersion compensating fiber commonly known as

DCF is used.

DCF was introduced to the world in the year 1980.

The idea of DCF became viral and started to spread

with a higher rate, in this way DCF gained the

attention and became a field to study about. Due

to the higher stability of DCF and resistance to

temperature, it is being used to compensate

dispersion and has been studied in large scale all

over the world.

The range of dispersion in DCF ranges from -70 to -

90 ps/nm km [8]. Due to the negative value of

dispersion, DCF can be used to compensate

dispersion efficiently. WDM system is mostly

affected by dispersion and nonlinearity. The system

performance depends upon the following:

(a) Power at the input of different fiber.

(b) Position of DCF.

(c) The Value of dispersion used.

When the DCF is placed before or after the SMF

then the average dispersion values comes down to

zero [9].

D= Dispersion of fiber

L= Length of fiber

According to the positioning of DCF, dispersion

compensation can be done in following three

ways:

Pre-Compensation: In this type of

compensation method, DCF is placed just

before SMF in order to compensate

dispersion.

Post-Compensation: In this type of

compensation method, DCF is placed just

after the SMF to compensate dispersion.

Symmetric-compensation: In this type of

compensation method, two DCF are used.

One is placed just before and another just

after optical fiber [10].

4. SIMULATION SETUP:





A SMF is standardized by using a dispersion

compensating scheme In a Wavelength Division

Multiplexing (WDM) network in order to achieve

high data rate and high capacity .There exists some

of the most effective compensating schemes such

as FBG, DCF, electrical dispersion compensation

and optical phase conjugation method etc. In this

experimental setup, simulation is carried out by

using WDM technique in which the data rate used

is 4×10=40Gbps . Here DCF is used to compensate

dispersion. There exist three compensation

schemes if DCF technique is considered. The

schemes are Pre-Compensation, Post-

Compensation and Symmetric-Compensation.

Symmetric compensation technique which is also

known as mix compensation technique is

considered to be the best among all three and in

our experiment we got the results which prove the

same.

FIG (2) is a block diagram representation of our

experimental setup of optical communication

network using WDM for multiple transmission and

DCF to compensate the dispersion caused in SMF

during transmission. The setup comprises of

transmitter, fibers and receiver. In the transmitter

side we have Pseudo random bit generator which

generates random sequences of pulse which is

given to NRZ pulse generator for line coding, CW

Laser is used to convert the electrical signal into

optical signal that is fed to an optical modulator

i.e. Mach Zehnder Modulator. The transmitted

signal is then sent to WDM network which

multiplexes these signals. Once the signal is

multiplexed it is sent through SMF. EDFA present

after the SMF amplifies the signal that it receives

from SMF and thus helps to overcome attenuation.

The amplified signal is then passed to DCF where

the compensation of dispersion takes place. Once

the dispersion has been compensated, the

compensated signal is again amplified by using

another EDFA having different optical

amplification gain as compared to the EDFA used

before. After the amplification of the signal, the

amplified signal is sent to WDM DEMUX where de-

multiplexing takes place. It converts the serial data

in parallel data. As soon as the signal is de-

multiplexed, the receiver that consist of

photodetector decodes the information and

converts the signal back to its electrical form and

the filter used at end filters any noises that may

have been left and at last we receive the signal

without any kind of loss.

Fig 2: POST COMPENSATION SCHEME

Fig3.1: OPTISYSTEM 7.0 SIMULATION SETUP(POST)






Fig3.2: OPTISYSTEM 7.0 SIMULATION SETUP(MIX)

Fig3.3: OPTISYSTEM 7.0 SIMULATION SETUP(PRE)

Simulation parameters used in this piece of work to get

an effective result is given in the Table no.1.

TABLE NO 1. : Simulation parameters

Parameters Values

LENGTH of SMF 150Km(pre,post), 80km(symmetric)

REFERENCE WAVELENGTH in SMF

1550 nm

ATTENUATION in SMF 0.2dB/Km

DISPERSION coefficient in SMF

17 ps/nm/Km

DISPERSION SLOPE in SMF 0.08 ps/nm^2/Km

DIFFERENTIATION GROUP DELAY in SMF

3 ps/Km

Dispersion coefficient in DCF -85ps/nm/Km(pre, post), -68ps/nm/Km (symmetric)

Length of DCF 30Km(pre, post) , 20km(symmetric)

Gain of EDFA 20 dB

Gain of EDFA 4 dB

In this simulation, transmitter consist of 4 pseudo random bit

sequence generator each operating at a bit rate of 10

GBits/s. Pseudo random bit sequence generator generates a

random code consisting of 0’s and 1’s. This sequence of 0’s

and 1’s are then converted into electrical pulses which are

fed in the Mach Zehnder Modulator. There exist 4 pairs of

CW Laser and Mach Zehnder Modulator. The work of Mach

Zehnder modulator is to modulate the signal from the CW

Laser. The frequency range of CW Laser

used is 193.1THz to 193.4THz. The band width of WDM MUX

used at the transmitter side is 80 GHz. The SMF used for the

transmission of data is 150 Km long for pre and post

compensation and 160 km long for symmetrical

compensation and the reference wavelength at which it

operate is considered to be 1550 nm with 0.2 dB/km of

attenuation. Dispersion value taken for SMF is 17 ps/nm/Km

and its dispersion slope is taken to be 0.08 ps/nm2/Km. The

value Differential group delay of SMF is 3ps/Km. The EDFA

used just prior to the DCF is having an optical amplifier gain

of 20 dB and the one used just after the DCF is having an

optical amplifier gain of 4dB. DCF used to compensate

dispersion is 30 Km long for pre and post compensation and

20 km long for symmetrical compensation. The dispersion

value of DCF used to compensate dispersion is taken to be -

85 ps/nm/Km. at receiver side there is a WDM DEMUX

whose channel band width is same as the channel band

width of WDM MUX used in the transmitter side. PIN

Photodiode is used here to retrieve the optical signal and

convert it into electrical signal. The electrical signal is passed

through low pass filter. LPF filters the high frequency noises

and transfer the filtered signal to BER analyzer to determine

the parameters like eye height, BER and Q-Factor.

5. RESULT:

5.1 Post compensation method:

Fig1: First channelFig2: Second channel

Fig3: Third channel Fig4: Fourth channel

5.2 Pre compensation method:

Fig1: First channelFig2: Second channel





Fig3: Third channelFig4: Fourth channel

5.3 Symmetric compensation method:

Fig1: First channelFig2:Second channel

Fig3: Third channel Fig4: Fourth channel

Table 2.3: Comparison of three dispersion compensation schemes:

Pre-compensati

on

Post-compensati

on

Symmetrical-

compensation

Average Q-factor

(dB) 11.521925 9.0804325 7.959815

Average BER

10488831572e-026

1.837630753e-016

9.49928761e-014

Average Eye

2.913e-005 2.723995e-

005 0.00550149

height

Average Threshold value

1.7346e-005 1.563695e-

005 0.005724132

5

6. CONCLUSION

For any system to work effectively it must have the

Q factor that determines the quality of service of that system

about 7dB and the next factor which is very crucial for the

system is it’s eye height value, the wider the eye opening the

better the system gets.

Comparing above obtained results we can very

well observe that symmetric compensation has the best eye

height and it also has satisfactory value for the Q factor and

hence it is the best technique compared to post and pre.

7. REFERECES:

[1] Mochida Y, Yamaguchi N, Ishikawa G, "Technology-

oriented review and vision of 40Gb/s-based optical transport

Networks", Journal of light-wave technology.PP. 2272-228,

12002, 20(12).

[2] Dispersion compensation in 40 gb/s wdm network using dispersion compensating fiber 1 mr. Gaurang.h.patel, 2prof. Rohit.b. Patel, 3 prof. Sweta.j.patel, journal of information, knowledge and research in electronics and communication engineering, issn: 0975 – 6779| nov 12 to oct 13 | volume – 02, issue - 02

[3] WDM-OTDM based spectral efficient hybridmultiplexing technique inherent with properties of bandwidth elasticity and scalability Gousiaa, G.M.Rathera, AjayK.Sharmab.ELSEVIERwww.elsevier.de/ijleo ,Received 5 August 2008; accepted 16 December 2008

[4] Zou X Y, Hayee M I, H wang S M, et al. Limitations in 10Gb/s WDM optical-fiber transmission when using a variety of fiber types to manage dispersion and nonlinearities[J]. Light wave Technol., PP: 1144-1152,June,1996

[5] WuQiang,Yu Chong Xiu, "Analysis on dispersion compensation with DCF", semiconductor optoelectronics,Vol.24 No.3 pp.186-196.June 2003

[6] Bo-Ning HU, Wang Jing, Wang Wei, Rui-Mei Zhao, Analysis on Dispersion Compensation with DCF based on Optisystem, 2ndInternational Conference on Industrial and Information Systems 2010, 40-43

[7] Jianjun Yu, Bojun Yang,"Dispersion-allacated soliton technology with long amplifier spacing and long distance," IEEEphotontechnollett, vol 9, pp. 952-954,No.7, 1997:



http://www.elsevier.de/ijleo




[8] Bo-ningHU, Wang Jing, Wang Wei and Rui-mei Zhao1, “Analysis on Dispersion Compensation with DCF based on Optisystem”, IEEE 2nd International Conference on Industrial and Information Systems, 2010

[9] ZhouZhiQiang, TangYuLiang, "Optimmum schemes of dispersion compensation transmission systems using

dispersion compensation fibers",laser technology, VoI.24,No.5,pp.265-269 Oct.2000.

[10] R.S.Kaler, Ajay K Sharma, and T.S.Kamal, Comparison of pre-,post- and symmetrical- dispersion compensation schemes for 10Gb/s NRZ links using standard and dispersion compensated fibers, Elsevier Optics Communication 209 2002, 107-123

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PERFORMANCE COMPARISON OF DISPERSION COMPENSATING FIBER … · compensation method and optical phase conjugation are the effective dispersion compensation techniques which limit the