Download A Ph.D PROPOSAL ON

A Ph.D PROPOSAL ON
1. Title: Fibre Non-Linearity Dispersion and Performance of RZ, NRZ and Duo
binary Modulation Formats in WDM Optical Network
BY
EKEMEZIE, CHIDIEBERE FIDELIS
2. Brief Background of The Study:
In today’s IT environment, many elements like high speed internet, streaming video, social
networking, mobile devices, government regulations, virtualization, network based security,
building automation and collaboration are all driving an explosion in information content that
needs to be processed and stored. This ever increasing acceleration in information being
generated, processed and stored is at the highest point in history. This trend is shifting the
dynamics of how networks are being designed and implemented. One of the major shifts,
especially in the data centre space, is the ever increasing migration to fibre optic
infrastructure to accommodate the thirst for higher bandwidths, densities and application
support. For years, fibre optic media has been utilized in the IT space, however, its presence
and role within the data centre space is rapidly changing.
Optical fibre is a physical transmission medium applied for high speed data communications.
Optical networks are adopted for efficient accommodation of traffic. Information is send
from one place to another in the form of light pulses. Today’s fibre optic data systems are
very complex, expensive and lossy. Increasing demand of communication requires robust and
efficient optical system.
Telecommunications service providers have to face continuously growing bandwidth
demands in all networks areas, from long-haul to access. Because installing new
communication links would require huge Investments, telecommunications carriers prefer to
increase the capacity of their existing fibre links by using possible expandable method which
means introducing wavelength division multiplex thereby bringing in dispersion into the
system. The major problem of the wave length division multiplex (WDM) is how to avoid
the interference/ distortion that normally arises from transmitting the signals belonging to
different operators into one fibre as this will lead to over lapping bearing in mind that this
will cause signal broaden (chromatic dispersion) in the channel. Due to possibility of high
transmission capacity, WDM system is progressing. Multiple data signals of light wavelength
are transmitted by WDM systems. WDM is the most popular method to increase the capacity
of a single strand of fibre. Traditionally, only one colour of light was used in a single strand
of fibre to carry the information such as 1550nm light [5]. However, starting from the early
1990s, the internet boom pushed service providers to find a method to increase the capacity
of their network, which is when WDM devices were invented [3], [4]. In a WDM system
many different coloured lights are combined by a WDM multiplexer and put into a single
strand of fibre, each colour is a separate channel. At the receiver, each colour is separated
into its own channel by a WDM de-multiplexer device. The diagram is depicted in figure 1.0
Figure 1: WDM System
Optic fibre transmission uses wavelength that are in the near infrared portion of the spectrum
just above the visible spectrum and are undetectable to the unaided eye. Optical transmission
falls within the range of 850nm, 1310nm and 1550nm. Laser and LEDs are used to transmit
light through optic fibre. Lasers are usually for 1310nm or 1550nm single mode application,
while LEDs are used for 850nm or 1300nm multimode applications. Recently, the optic fibre
carrying capacity has been greatly improved by introduction of Dense Wave Length Division
Multiplex (DWDM) where different fibre modes operate on different ranges of wavelengths
spaced 100 GHz apart and commonly called the ITU-T grid, each operating range is termed
WINDOW. The window operating medium ranges are as shown in table 1.0
Table1.0: Wavelength Operating Window Available for Utilization Depending on the
Distance.
WINDOW
OPERATING
WAVELENGTH (λ)
800-900nm
850nm
1250-1350nm 1310nm
1500-1600nm 1550nm
These wavelengths were chosen because they lie in the ranges of least attenuation and thus
allows signal to travel longer distances. As DWDM is used to transmit different wavelength
down the optical fibre cable, the signals begin to spread into one another or converge until
they have become completely distorted due to chromatic dispersion (CD) thereby limiting the
bandwidth and the distance the fibre can transmit data.
At high bit rates, the modulation format, type of dispersion compensation scheme, and
channel power become important issues for optimum system design.
The main drawbacks of physical medium are non linear effects, dispersion and loss. For long
haul, optical fibre communication system performance is influenced by fibre non-linearity
which accumulates along the length of optical fibre. Non linear effects occur where
interaction of signal at different wavelengths is possible. Nonlinearities result in distortion,
attenuation and interference in optical system which degrades system performance [2]. The
most important non-linear effects are Four-wave mixing (FWM), Stimulated Raman
Scattering (SRS), Self Phase Modulation (SPM) and Cross Phase Modulation (XPM) [1].
Phase of the signal is affected by SPM and XPM which causes spectral broadening which in
turn increases dispersion. In fibre optic channel, the widening of pulse duration leads to
dispersion which limits transmission rate and bit spacing.
3. Aim and Objective/ Purpose:
The main aim of this dissertation is to develop an optimization model that will solve
the problem of Fibre Nonlinearity Dispersion in WDM Optical Communication Network and
the performance of RZ, NRZ and Duo Binary Modulation Format in WDM Optical
Communication Network. The said objective is to be realized by pursuing the following subobjectives:
(a) To investigate the main causes of interference, cross talk, signal broadening etc in the
network (Worldscope Media and Telecoms Ltd)
(b) To develop a Scheme, modeling and simulation of WDM Optical Communication System
for Fibre Nonlinearity Dispersion using Optsim ver. 5.2 software. To analyze the
problems arising from WDM optical communication system and provide possible
solutions. Also, to develop chromatic dispersion compensation scheme to fine tune the
effect of chromatic dispersion on optical signal.
(c) To design a Hybrid Network via Fibre Optic for the Anambra State University campuses
and its environs (Igbariam Campus and Uli Campus) in line with Fibre Optic Association
(FOA) standard and Engineering Best Practices, stating the routes and nodes for existing
test beds comparative analysis. Reducing the chromatic dispersion resulting from the
overlapping of wavelength by testing the optic fibre to know the correct solution to apply
in order to eliminate the problem.
(d) To deduce the problems associated with deployment of different modulation format used
to create the optical pulses, in optimizing the network.
(e) To develop a computational model in MATLAB to investigate how FWM which is the
Dominating effect of WDM system affects the performance of an optical communication
network using split step algorithm. Finally, to analyze the challenges of QoS in a typical
fibre optic communication link using a Hybrid Case study Methodology to solving the
problem. The results obtained from the analysis will be comparing with the standards set
by Fibre Optics Association (FOA) and the certificates of conformance of manufacture.
4. Methodology:
Methodology is a recommended set of methods or procedures for collecting data, analysing
data and also has a standard for the validation of findings. Hybrid Research Methodology
will be implemented in this work considering an active environment as well as the stated
approaches. The approach used in the actualization of optimum performance in this project, is
based on the principles of fibre optics using the Optsim Version 5.2 Block oriented
simulation package. In this regard, this work will be carried out in an industrial setting within
an action research methodology oriented manner complemented by case study methodology;
so as to evolve the proposed concepts presented in this thesis and to obtain validity in an
industrial environment. The triangulation method of case study methodology will be used to
obtain and collate data from measurements carried out on the faulty installed optic fibre
cables as stipulated in the various FOTP standards of measurement using OTDR etc.
5. Expected Outcomes
The effects of fibre nonlinearity and modulation formats on WDM optical network may be
optimized by choosing appropriate values of different parameters in optical fibre
communication systems. The steps taken to mitigate the effects of Fibre Nonlinearity via
optimized models developed on Optsim platform version 5.2 will be depicted. The effect of
chromatic dispersion on optical signal can be minimised by developing an enhanced scheme
(either in MATLAB or Optsim) for compensation and criterion for selecting a suitable
modulation format to enhance the performance of optical signal
References:
[1] Jing Liang,Student Member and Katsushi Iwashita,”FWM compensation in DPSK
transmission by reducing detectors with digital coherent detection using backward
propagation ,” International Journal of Information and Electronics Engineering, Vol. 1, No.
1, July 2011.
[2] Kyo Inoue, “Four-Wave Mixing in an Optical Fiber in the Zero-Dispersion Wavelength
Region,” Journal of lightwave technology, Vol. 10, No. 11, November 1992 1553 .
[3] Y. Miyamoto, A. Hirano, K. Yonenaga, A. Sano, H. Toba, K. Murata, O Mitomi, “320
Gbit/s (8 × 40 Gbit/s WDM transmission over 367 km with 120 km repeater spacing using
carrier-suppressed return-to-zero format”,Electron Lett , vol 35, pp 2041- 2042, 1999.
[4] S P Majumder, A Azhari and F. M. Abbou, “Impact of fibre chromatic dispersion on the
BER performance of an optical CDMA IM/DD transmission system” IEEE Photon Technol
Lett , vol 17, pp. 1340–1342, 2005.
[5] Zheng, X , Liu, F. and Jeppesen ,P., “Receiver optimization for 4Gb/s optical duobinary
signal”, IEEE Photonics Technol Lett , 2001, 13,(7)