Advances in Optical Fiber Communication System Using DWDM by Reducing PMD.

Mr. H.V.Rajurkar1, Mr.A.M.Agarkar2

SSGMCE Shegaon - 444203,Maharashtra.

harish529@rediffmail.com1,ajayagarkar@rediffmail.com2

1. ABSTRACT:

One inherent challenge to provide higher data rate communication is managing dispersion effect on the fiber optics system. There are various methods that can be used to increase the data rate of the fiber system .One of them is wavelength division multiplexing (WDM). But for any optical fiber system increase in the bit rate will cause increase in the dispersion effect on the system leading to pulse broadening causing incorrect reception of data at the receiver.

This paper presents the importance of DWDM and impact of PMD on system performance by considering some factor.

2. KEYWORDS:

Optical fiber communication, Polarization Mode Dispersion, Wavelength division multiplexing, DWDM

3. INTRODUCTION:

Polarization mode dispersion (PMD) is one of the main limiting factors of high-speed long distance all optical network. PMD can be a serious limitation on certain fiber links operating at 10 Gb/s. As network data rates rise, it is becoming increasingly important to understand PMD and its potential impact on your network.

Fiber optic networks continue to improve when using DWDM (Dense Wavelength Division Multiplexing). Optical fiber integrated with DWDM can increase throughput. The development of DWDM (Dense Wavelength Division Multiplexing) is a key innovation that allows for more bandwidth without installing additional, cost-prohibitive cabling. The emergence of DWDM is one of the most recent and important phenomena in the development of Fiber optic transmission technology.

Importance of PMD for High Data Rate Transmission Systems

The continuous growth of Internet traffic is driving transmission system engineers to use higher and higher data rates in all segments of communication networks.. At the present moment 10 Gb/s SONET/SDH systems are most commonly deployed in long-haul networks but we are now at the advent of frequent 40 Gb/s deployments heralded by the recent announcements of the introduction of 40 Gb/s equipment to networks in Western Europe (Deutsche Telkom), the US (MCI) and Asia (CERNET). At the same time Ethernet and Fiber Channel (FC) transmission protocols that are used in Local Area Networks (LAN) and in Metropolitan Area Networks (MAN) have reached 10 Gb/s data rates.

It is widely recognized that 40 Gb/s data transmission rates impose very strict requirements on the fiber plant and transmission systems deployed in the field.

However, data rates of 10 Gb/s also impose similar significant performance requirements. In particular, Polarization Mode Dispersion (PMD) can be a serious limitation on certain fiber links operating at 10 Gb/s, particularly on links in older legacy networks. Recent papers written on the topic argue that even fibers made and deployed in the 1998-2001 time frame may be unusable for 10 Gb/s and higher data rate transmission, due to the challenges presented by PMD. As network data rates continue to rise, it is becoming increasingly important to

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understand PMD and its potential impact on your network. The subject of PMD presents many challenges, including understanding the inconsistent terminology and the statistical nature of PMD and also comprehending the background to the advanced measurements techniques employed to calculate PMD. The purpose of this paper is to provide an introduction to the topic of PMD. This paper will explain the origin and nature of PMD, will clarify the terminology and statistical nature of PMD, and will examine the impact of PMD on high-speed transmission systems. [3,5]

Fig 1. PMD

DWDM Technology

The emergence of DWDM is one of the most recent and important phenomena in the development of fiber optic transmission technology. DWDM is a core technology in an optical transport network. The system performs the following main functions:

Fig 2. Basic DWDM system blocks

PMD and DWDM:

From the above discussion we had a brief review on PMD and DWDM. It is clear that the increase in bit rate is one of the most important specifications of any communication system. There is no dought that by using optical fiber system more data rates can be possible. But as seen from the discussion on PMD it is clear that PMD will be more serious at higher bit rates. For the optical system operationg at 10 Gb/s PMD will have less effect as compare to the system at 40 Gb/s . It is because as the bit rates are increases the time duration between the optical pulses will also increases Because of which the effect of pulse broadening (Intersymbol interference) will be more hence the probability of correct data reception at the receiver will be less.

Correcting for PMD

The research centering on polarization mode dispersion is currently focused on reducing it in order to increase the rate at which data can be transferred using optical fibers. It is difficult to correct PMD, since it is time varying, and therefore changing constantly. There are two main methods for correcting the PMD in a fiber; one utilizes optical methods, the other electrical methods.[1,2]

The optical method of reducing the PMD uses a polarizer at the output of the fiber. This splits the light so that only light of one polarization at a time gets through. With this method of correction it is possible to see as much

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as 62% improvement in the distortion of the signal [6], [5].

Also PMD caused by change in the non-circularity or ellipticity of the core in a single mode fiber are simulated .PMD and Birefringence are found that they are proportional to the non-circularity or ellipticity of the core, also they are proportional to the difference between the core and cladding refractive index, young’s modulus and photo elastic constant.

4. SIMULATION RESULTS:

EMBED PBrush

Fig 3. (For bending radius of 4, 10,20 mm respectively)

5. OBSERVATIONS & FINDINGS

PMD caused by change in the bending radius of the core in a single mode fiber are simulated .PMD and Birefringence are found that they are proportional to the bending radius of core, Form the graph shown in figure 3 it is found that,

Sr.

No

Bending

Radius (mm)

PMD

(ps)

Sr.

No

Bending

Radius (mm)

PMD

(ps)

1 2 79.82 5 20 0.73

2 3 35.68 6 25 0.427

3 4 19.30 7 30 0.28

4 10 3.30 8 100 0.019

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6.CONCLUSION

From above values of PMD it is clear that, PMD is dependant on the bending radius. From the further more values of radius it is seen that if the bending radius is too small then PMD effect is more causing more dispersion. But if the values of bending radius are increased further then after some values of bending radius the PMD is almost constant i.e. for larger values of bending radius the PMD values is very less causing a very low dispersion of the pulses and hence will not affect the system data carrying capacity much leading to faster data transfer through the fiber. So it is very necessary to maintain proper bending radii during fiber installation, which further may affect the performance of DWDM system.

By using DWDM technology higher bit rate are possible but at the same time it is very important to pay more attention towards PMD, which may affect the system performance. So to compensate these effects of PMD that are responsible for affecting the DWDM system performance is very necessary to minimize the PMD effects by proper bending radii, maintaining the non-circularity of the core.

7.REFERENCES:

1] J. Sakai, and T. Kimura, “Birefringence Caused by Thermal Stress in Elliptically Deformed Core Optical Fibers”, IEEE Journal of Quantum Electronics, vol. QE-18, no. 11, pp 1899-1909, November 1982.

2] A.Stein , S.Vorbeck,E.Voges .Polarizationn mode dispertion and polarization dependant loss in optical fiber system .University of Dortmund Germany www.photos.com

3] B.W.Hakki. Polarization mode dispertion in a single mode fiber .IEEE J.Lightwave technology Vol.14. No.10, Octomber 1996

4] I.P.Kaminow. Polarization in Optical fiber. IEEE J.Quantom electronics, Vol QE-17, No.1, January 1981

5] S.Ten, M. Edwards .An introduction to the fundamentals of PMD in fibers. White paper www.corning.com

6] Geard Keiser. Optical fiber communication, McGraw Hill Int. Editions.

7] www.optifiber.com

8] Software: optiwave Photonic Design software

9] G. J. Foschini and C. D. Poole, “Statistical Theory of Polarization Dispersion in Single-Mode Fibers”, Journal of Lightwave Technology, vol. LT-9, no. 11, pp 1439-1456, November 1991.

10] R. Scott. University ofArizona.College of optical sciences Polarization mode dispertion www.erizona.edu

11] www.cisco.com/univercd/cc/td/doc/product/mels/dwdm/dwdm_fns.htm - 47k -

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