Comparative Performance Analysis of DCF and FBG for Dispersion Compensation in Optical Fiber Communi

IJSRD - International Journal for Scientific Research & Development| Vol. 4, Issue 04, 2016 | ISSN (online): 2321-0613

Comparative Performance Analysis of DCF and FBG for Dispersion Compensation in Optical Fiber Communication Gobinder Singh1 Shivinder Devra2 Karamdeep Singh3 1 Student 2,3Assistant Professor 1,2,3 Guru Nanak Dev University, Amritsar Abstract— Dispersion compensation is the essential feature of an optical transmission system. Two widely used dispersion compensation techniques i.e. Fiber Bragg Grating (FBG) and Dispersion Compensation Fiber (DCF) has been discussed. There will be the review of basic principle, Definition of figure, merits and conditions for dispersion compensation. There will be also discussion on how dispersion is compensated in Wavelength Division Multiplex (WDM) System using different techniques like FBG, DCF, Digital Filters and MLSE. Design techniques and implementation of FBG and DCF has been discussed.

Key words: Wave Division multiplexed (WDM) System, Dispersion Compensating fiber (DCF), Fiber Bragg Grating (FBG), Maximum Likelihood Sequence Estimation (MLSE) I. INTRODUCTION Since the invention of telephone the copper wires have been used for the data transmission. But due to the demand of data transmission increasing day by day, the use of copper wire is continuously reduced due to different reasons such as short transmission distance, low bandwidth, inefficiency etc.[1] To overcome the all these problem optical fiber is introduced as a new medium, in which information (such as voice, data and video) is transmitted through a fiber cable, in form of light pulses. But the main problem in a optical communication system is the dispersion. When optical signals are supposed to be transmitted over the optical links, different wavelength components of the signals will experience different propagation time due to transport medium has different refractive indices for different wavelength over a medium. [2] Dispersion is the main problem which affects the performance of optical transmission at high bit rate. It is the pulse broadening which may be caused by different elements such as core diameter, refractive index profile, wavelength, numerical aperture, and laser line width of a fiber cable. It may lead the signal to distortion and overlapping of pulse which is also known as Inter Symbol Interference (ISI). [3] Dispersion is mainly of two different types: 1) Nonlinear Dispersion 2) Chromatic Dispersion Chromatic Dispersion occurs when wavelength may travel at different speeds through a fiber cable. An optical source emits a specific wave length within a range of a Dense Wave Division Multiplexing System and when these wavelengths travel through a fiber, each signal wavelength arrives at different time and speed, which leads to the signal distortion as shown in fig 1(a) and 1(b).

Fig. 1: Broadening of pulse due to chromatic dispersion and different shapes of light pulse [4] The Rest of paper is organized in following manner:  In Section II there will be discussion on the literatures of various authors.  Section III will through ample light on the various compensation techniques.  Section IV will show the tools used to compensate dispersion.  In Section V the results of the experiments which are simulate by us are discuss.  Section VI will discuss on the conclusion of the paper.

II. LITERATURE SURVEY H. M. Foisel et al [4] in 1999 investigated that RZ versus NRZ Modulation Format for Dispersion Compensation SMF based 10 GB/s Transmission. They discover that by independently varying the power at the different types of fiber input and compensation ratio, the post compensation performs better than pre compensation. They also show that by introducing pre distortion the performance of both pre compensation and post compensation schemes can be significantly improved.

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Comparative Performance Analysis of DCF and FBG for Dispersion Compensation in Optical Fiber Communication (IJSRD/Vol. 4/Issue 04/2016/280)

Zhou Zhi Qiang et al[5] in 2000 investigated in his paper “ Optimum scheme of dispersion compensation transmission system using dispersion compensation fibers laser technology� . He found that a device itself requires only a Bragg Grating and a taped thin metal film coating to shift and chirp the FBG wavelength by changing the applied current throught the film which optimize time varying dispersion maps and can reduce power penalty associated with non-linear transmission impairments and other variation.

Zhang Hongb et al [6] in 2001 demonstrated on the basis of analyzed the three system simulation result. The attenuation of Dispersion compensation fiber is not null.

Therefore the attenuation of DCF will produce impairment to signal quality as well as that of SMF. Mix compensation scheme can greatly reduce the fiber nonlinear effect.

M. Weiming demonstrated dispersion compensation over 50 km of standard single mode fiber using chirped fiber grating [7]. Chirped fiber grating is a passive device with low insertion loss that is compatible with the transmission system and CFG dispersion can be easily adjusted. For optimum results CFG should be located in-line [8].

Y. Aiying concluded that, the increased interaction of SPM and anomalous dispersion in CFG can be used to extend the transmission distance in point-to-point system [9].

M. J. Islam analyzed that FBG can also be used to compensate GVD, based on BER. The numerical results indicated that the BER performance can be improved significantly depending on the fiber length [10].

Cascaded grating was implemented in WDM system to compensate GVD [11]. Chirped FBG (CFBG) is more preferred technique over LDF and DCF because of its advantages including small footprints and dispersion slope compensation and negligible non-linear effects over others [12].

S. Devra et al [13] in 2011 discussed in his paper “Different Compensation Techniques To Compensate Chromatic Dispersion In Fiber Optics� that dispersion compensation is most challenging as well as important aspect to maintain signal to noise ratio in an optical communication. He discussed that Dispersion Compensation Fiber (DCF) is a reliable technology but it also gives high insertion loss as well as introduce some nonlinear distortion when there is high input power. Other dispersion techniques such as electronics dispersion Compensation (EDC), Fiber Bragg Grating (FBG) and Digital Filters are discussed by him.

Ravi Parkash Shukla et al [14] in 2012 suggested Dispersion Compensation is necessary to reduce losses and coast of the system and can be done through two different methods i.e DCF and FBG. III. VARIOUS COMPENSATION TECHNIQUES

3) Maximum Likelihood Sequence Estimation (MLSE) 4) Digital Filters 5) In this paper we briefly discuss the working and principle of DCF and FBG. A. Dispersion Compensation Fiber (DCF) DCF is a loop of fiber cable with an opposite dispersion as that of original fiber cable in the link and can be introduced before or after the fiber cable, accordingly and it is referred as pre-compensation or post-compensation technique. [13] We can also use a thirt option in which we can use DCF at both ends of fiber cable as shown in fig.

Fig. 2: Pre and Post Compensation techniques using DCF [13] B. Fiber Bragg Grating (FBG) FBG is very efficient in compensation of dispersion broadening in long haul communication. The basic principle behind the operation of FBG is Fresnel Reflection. In which the light travels between media of different refractive indices which may reflect as well as refract at interface. It is also used as optical filter to block certain wavelengths. The Reflected index will be possible over a particular wavelength.[15] The reflected wavelength (đ?œ†đ??ľ ), called as Bragg wavelength, given by: đ?œ†đ??ľ = 2đ?‘›đ?‘’ đ?›Ź (1) Here đ?‘›đ?‘’ is the effective refractive index Λ is grating period đ?‘›đ?‘’ depends on wavelengths as well as on the mode of propagated light. So that it is also known as modal index.

The wavelength spacing between minima or bandwidth is given by: 2δn Ρ âˆ†Îť = [ 0 ]đ?œ†đ??ľ (2) Ď€ Where δn0 are variations in refractive index. Ρ fraction of power in core.

In order to reduce the spreading of light pulses, Dispersion Compensation is the most important feature in optical communication system. The most commonly utilized techniques for the compensation of dispersion are as follows: 1) Dispersion Compensation Fiber (DCF) 2) Fiber Bragg Grating (FBG)

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Comparative Performance Analysis of DCF and FBG for Dispersion Compensation in Optical Fiber Communication (IJSRD/Vol. 4/Issue 04/2016/280)

involves attenuation. This problem is to be solved by using observation r(t) to create a good estimation of x(t).[16] This estimation of x(t) is defined to be sequence of value which maximize the function.

L(x) = p(r | x) (3) Where p(r | x) denotes the conditional joint probability density function of r (t) D. Digital Filters When digital filters used with Digital Signal Processing (DSP) can compensate the chromatic dispersion. They can provide fix as well as tunable dispersion compensation for WDM System. All Pass Filters (APF) are used often for dispersion compensation as Digital Filters.[13] IV. TOOL USED

Fig. 3: working principle of FBG[15] C. Maximum Likelihood Sequence Estimation (MLSE) It is mathematical algorithm which is used to extract the important data from the noisy data stream. To detect the optimized digital signal, it should do a best estimation of transmitted data having least number of errors.

Let us consider there is a signal x(t), of which an observed signal r(t) is available. The observed signal r is related to x by transformation which can be non linear and

Optisystem 7.0 is used to compare the performances of DCF and FBG. Optisystem 7.0 provides the each and essential tool which are used in the optical communication system. In this experiment we use a WDM system with 8 channels with 8 transmitting and 8 receiving channels which are connected with each other by 8X1 multiplexer and 1X8 demultiplexer for both DCF and FBG. We have established two setups to perform the dispersion compensation one is with DCF which is shown in fig. and another is with FBG as shown in fig.

Fig. 4: Simulation setup with DCF

Fig. 5: Simulation setup with FBG The following are different parameters which are fiber Table 2: Parameters of optical fiber cable, CW laser Source, DCF, and FBG: DCF Parameters Value Value Reference wavelength 1550 nm CW Laser Length 10 km Power 0db Attenuation 0.2 db/km Frequency 1550-1557nm Dispersion -80 ps/nm/km Table 1: Parameters of CW laser Source Dispersion slope 0.075 ps/��²/km Value PMD coefficient 0.5 ps/km Fiber Parameter Differential group delay 0.2 ps/km Reference wavelength 1550 nm Table 3: Parameters of DCF Length 10-100 km FBG Parameters Value Attenuation 0.2 db/km Frequency 1550-1557 nm Dispersion 16.75 ps/nm/km Effective index 3.45 Dispersion slope 0.075 ps/��²/km length 6mm PMD coefficient 0.5 ps/km Table 4: Parameters of FBG Differential group delay 0.2 ps/km

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Comparative Performance Analysis of DCF and FBG for Dispersion Compensation in Optical Fiber Communication (IJSRD/Vol. 4/Issue 04/2016/280)

V. RESULTS

100

In this section we will analyze the results and graph of the readings which we get from the optisystem 7.0 and the graphs are plotted using these reading in MatLab. The graps with are shown below it is only for the one channel. The following results are on the bases of quality factor and BER are shown in the tables.

Without With Without With Length(km) DCF DCF FBG FBG 10 5.01 8.10 6.04 11.40 50 4.19 8.06 4.94 9.90

2.22 2.57 2.64 4.12 Table 5: Result of channel 1 for Q Factor Without With Without With Length(km) DCF DCF FBG FBG 2.27x10 4.88x10 1.24x10 10 2.03x10-7 8 10 32 50 100

1.10x10-5

3.61x1010

4.94x10-7

1.8x10-23

0.004 0.005 0.003 Table 6: Result of channel 1 for BER

0.014

Fig 4 (a): Mat Lab graph using DCF

Fig 4 (b): Mat Lab graph using FBG system using a WDM system 8 channels using DCF and VI. CONCLUSION FBG by varying the length of optical fiber from 10 km to 100 km and analyzed that both the techniques are good at 10 In this paper we have analyzed two different methods for gbps and increased almost doubles the quality factor of the dispersion compensation in an optical communication

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Comparative Performance Analysis of DCF and FBG for Dispersion Compensation in Optical Fiber Communication (IJSRD/Vol. 4/Issue 04/2016/280)

system. As FBG shows higher quality factor than DCF but it will be more cost effective as we have to use 8 FBGs at different frequencies at the receiver end varying from 1550 nm to 1557 nm and on the other hand we are using only one DCF with high negative dispersion of -80 ps/nm/km. So both the techniques are good in their own respect and the used as per the users’ requirement.

REFERENCES [1] J C Palais ,” Fiber Optic Communications”, 2nd Edition, PHI [2] J.M. Senior, “Optical Fiber Communications Principles and Practice” Harlow Pearson 2005, Prentice Hall International Series in Optoelectronics, second edition, no. 3, 2005.

[3] N. K. Kahlon, Various Dispersion Compensation Techniques for Optical System: A Survey, open journal of communications and software Volume 1, Number 1, MAY 2014 [4] C. Cooper, H.M. Foisel RZ VERSUS NRZ Modulation Format for Despersion compensated SMF Based 10GB/s Transmission with more than 100 km Amplifier spacing.

[5] Zhou Qiang, Tang, "Optimum schemes of dispersion compensation transmission systems using dispersion compensation fibers", laser technology, voI.24, no.5,pp.265 -269 Oct.2000 [6] Weiming, S. Chengcheng, “Dispersion compensation of 50 km smf optical transmission systems with a linearly chirped fiber grating,” Tsinghua Science and Technology, vol. 4, no. 4, pp. 1624–1627, 1999.

[7] Zhang Hongb “ Emulation of characterstics of optical fiber transmission for 10 G/s single channel situation”, acta photonica sinica 2001 vol.30 no.6 715-720 [8] C. Sun, J. Cao, and C. Li, “Dispersion compensation of 180-km 10-gb/s transmission system using chirped fiber grating,” Tsinghua Science and Technology, vol. 7, no.

3, pp. 305–308, 2002.

[9] A. Yang, Z.Wang, Z. Zhang, Z. Chen, and D.Wu, “Dispersion compensation cfbg in 100km 10gbit/s recirculating systems,” Journal of Electronics (China), vol. 20, no. 6, pp. 461–466, 2003.

[10] J. Islam and R. Islam, “The ber performance improvement of optical cdma using fbg-based compensator,” Procedia Engineering, vol. 30, pp. 821– 827, 2012.

[11] N. M. Litchinitser, B. J. Eggleton, and G. P. Agrawal, “Dispersion of cascaded fiber gratings in wdm lightwave systems,” Journal of lightwave technology, vol. 16, no. 8, pp. 1523–1529, 1998.

[12] M. Guy, F. Tr´epanier, A. Doyle, Y. Painchaud, and R. L. Lachance, “Novel applications of fiber bragg grating components for next-generation wdm systems,” in Annales des t´el´ecommunications, vol. 58, pp. 1275– 1306, Springer, 2003 [13] Shivinder Devra, Gurmeet Kaur, “Different Compensation Techniques to Compensate Chromatic Dispersion in Fiber Optics”, International Journal of Engineering and Information Technology, vol. 3, no. 1, pp. 1-4, 2011 (ISSN 0975-5292 (Print), ISSN 09760253 (Online)).

[14] Ravi Parkash Shukla, “ Performance Analysis of Dispersion compensation in optical communication link using DCF”, ISSN: 2277-3878, Volume- I, Issue- 2, June 2012 [15] Gobinder Singh, “Performance Evaluation of DCF and FBG in a WDM system with eight channels in term of quality factor”, ISSN: 2277-9655, Volume- 5, Issue- 5, May 2012 [16] https://en.wikipedia.org/wiki/Maximum_likelihood_seq uence_estimatio.

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