Dispersion is pulse broadening as a result of wave propagation in fibers, leading to intersymbol interference. This document simulates a 40 Gbps dense wavelength division multiplexing (DWDM) system using numerical modeling to optimize performance. Dispersion compensation is achieved through the use of dispersion compensating fiber with negative dispersion placed in the link. Results show the system can transmit over 480km with a bit error rate less than 10-5 by optimizing optical and electrical filters and compensating for dispersion.

1. Dispersion AnalysisDWDM Transmission Systems B.Eng (Hons.) Electronic and Communications Engineering University of Nottingham

2. Prologue Dispersion is the pulse broadening as a result of wave propagation in fibers leading to Inter Symbol Interference (ISI)[1]. 40 Gbps DWDM Systems have been studied by numerical simulation to optimize their performance. A LucentTRUEWAVE_1550 single mode fiber and the most popular modulation format, NRZ, is used for the study.

3. Dispersion Adapted from [2]

4. Dispersion Compensation This is one dispersion compensation mechanism that is totally fiber based. Suitable for long haul networks Fabricated with a negative dispersion slope [3] Adapted from [4]

5. System Architecture

6. TX NRZ DRIVER - This component converts the logical input signal into an electrical signal. A Non Return to Zero is a modulation technique in which if a “1” is input, the output signal is at the low level during the entire bit interval and if a “0” was fed into the driver, the output will be at the high level again during the entire bit interval. DATA SOURCE - simulates either a pseudo-random or deterministic output that is synchronized to the baud rate. Plots Eye diagrams – with potential to approximate the q-factor, eye opening, eye closure, jitter and BER values. Sin2 MODULATOR - All comm systems transmit data using a sinusoidal carrier waveform which is modulated so as to increases the distance, allows transmission at lower power levels and the choice of the carrier frequency also enables the placement of signal in arbitrary part of spectrum. CW LASER SOURCE- this model implements a simplified continuous wave (CW) laser. A continuous wave is an electromagnetic or optical wave that has a constant amplitude and frequency and it exists over an infinite time period

7. Link Two duplicates of link consisting of 200 KM span of LucentTRUEWAVE_1550 fiber with dispersion of 16 [ps/nm/km] and 40 KM of Dispersion Compensating fiber with dispersion of -80 [ps/nm/km]. Lengths derived from dispersion equation D1L1 +D2L2 = O Pre – amp (6dBm) SPLITTER / DEMUX COMBINER / MUX – joins n number of signals at differing λ’s Post - amp EDFA’s used for post amplification the values of which depend on received power. OPTICAL POWER METER- evaluates the power, defined as the mean square value, @ Tx side. OPTICAL POWER METER- evaluates the power, defined as the mean square value, @ Rx side.

8. Rx In the PIN photo-diode, detection process depends on the input optical power and on the dark current. Total current = Electrical 5 pole Bessel Filter Optical Filter - Multiple-stage CW Lorentzian- a 4 stage BAND PASS is used Electrical Scope The acceptable received power range lies between -10dBm to approximately - 30dBm [3]

9. RESULTS & ANALYSIS Without DCF With DCF

10. BER and Q VALUE Q Value Vs. Rx Power BER Vs. Rx Power

11. Power Spectrum Plot Delta X – Channel Spacing = 100Ghz Delta Y – Power Penalty by system

12. Eye Diagram

13. Summary It is shown that the standard single mode fiber can transmit optical signals over 480km (BER < 10'5) by optimizing optical and electrical filter characteristics at the receiver and by compensation of dispersion.

14. Industrial Research According to an article on Light reading.com, Ciena, Infiniera, Nortel, and Opvista are currently deploying and testing out 100 Gbps DWDM systems in various locations. Back here at the Kenyan frontier, the much awaited fiber by SEACOM is already here and launched. Anticipation is high for the arrival of Essay and TEAMS cables.

15. References [1] Govind P. Agrawal, “Fiber Optic Communication Systems”, Third edition, Wiley & Sons, 2002. [2] Jong-Hyung Lee, Dae-Wyun Han, Jeom-Young Ahn, “Simulation of 4OGbps WDM Systems using Single Mode Fiber” KOR 115, 2005. [3] OptSim Models Reference, Volume I Sample Mode, 1989 – 2007 RSoft Design Group. [4] J.J. Yu, Kejian Guan, and Bojun Yang. “The Effects of Dispersion Compensation Ratio on the Performance of WDM Systems with Long Amplifier Spacing”. Beijing University of Posts and Telecommunications, 1997.