2 Channel Wavelength Division Multiplexing Systems
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Transcript of 2 Channel Wavelength Division Multiplexing Systems
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2 CHANNEL WAVELENGTH DIVISION
MULTIPLEXING SYSTEMS
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Aim:
simulating two 2- channel WDM System and
compute Bit error rate in different scenarios
Software used:
Optsim
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Wavelength division multiplexing (WDM)
is a fiber-optic transmission technique that
employs light wavelengths to transmit data
parallel-by-bit or serial-by-character.
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WAVELENGTH DIVISION MULTIPLEXING
COARSE WDM (C-WDM) DENSE WDM (D-WDM)
Both CWDM and DWDM are enhanced versions of WDM -
they support more channels than legacy WDM. But they are still WDM.
CWDM allows 8 channels.
DWDM allows 16 and above
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LINEAR AND NON LINEAR EFFECTS SEEN
IN WDM
Two general types of dispersion affect DWDM systems.
1. Chromatic Dispersion, is linear2. Polarization Mode Dispersion (PMD), is nonlinear.
Linear effects such as attenuation and dispersion can be
compensated, but nonlinear effectsaccumulate.
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2-CHANNEL WDM :10 Gbps link FOR 10km
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Specificatons:1) Data source generate data of Bit rate 10 Gbps.
2) Two Direct modulated lasers modulated binary modulation
format like NRZ
DM laser 1 have central emission frequency at 1550nm,
optical power 3dBm & FWHM line width 10 MHz.DM Laser 2 have central emission frequency at 1310 nm,
optcal power 3dBm & FWHM line width 10 MHz.
3) Multiplexer is used to combine the signals.
4) single mode optical fiber of 10 km long is used.
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5) Two Gaussian filters are used after the fiber.
Optical filter 1 is centered at 1550nm,-3dB,and BW of 10 GHz.
Optical filter 2 is centered at 1310nm,-3dB,and BW of 10 GHz.6) Optical Power Normalisers are used which average the
optical power and send it to the Compound receiver.7) Compound receiver consists of photodetectors,
pre-amplifiers,filters.Photodetectors are used at receiver side to convert opticalsignal into electrical signal.Bessel electrical filter is used in the compound receiver.Bessel electrical filter is low pass type, having number ofpoles 5,bandwidth as 10 GHz.
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RESULTS AND ANALYSIS
EYE DIAGRAM AFTER 10km FOR 10 Gbps LINKFOR UPPER CHANNEL AT 1550 nm
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EYE DIAGRAM AFTER 10km FOR 10 Gbps LINK
FOR LOWER CHANNEL AT 1310 nm
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FOR THE ABOVE SIMULATED SYSTEM,BER IS
COMPUTED.THE RESULTS ARE SHOWN IN THE
FOLLOWING TABLE.
S.NO DISTANCE TYPE OF
LASER
DATA
RATE
OPERATING
WAVELENGTH
BIT ERROR RATE(BER)
1. 10km DM 10Gbps 1550nm 9.8125x10-7
2. 10km DM 10Gbps 1310nm 5.4654x10-11
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From the table it is seen that at 1310nm,the BER
is better than the BER at 1550nm.This means thatlower channel transmits signal with lessattenuation than the upper channel which hassuffered from distortion effects like dispersion, and
non linear effects like SRS, SBS,FWM,etc and sohigher bit rate.
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. 2-CHANNEL WDM :10 Gbps link FOR 40km
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Specificatons:1) Data source generate data of Bit rate 10 Gbps.
2) Two Continuous Wave (CW)semiconductor lasers externally
modulated by binary modulation format like NRZ
CW laser 1 have central emission frequency at 1550nm,
optical power 3dBm & FWHM line width 10 MHz.
CW Laser 2 have central emission frequency at 1310 nm,
optical power 3dBm & FWHM line width 10 MHz.
Here external modulation is carried out by amplitude Dual arm
Mach Zehnder modulator .Mach Zehnder modulator has
maximumtransmissivity ,offset voltage of 0.5V & extinction ratio of 20dB
3) Multiplexer is used to combine the signals.
4) single mode optical fiber of 40 km long is used.
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5) Two Gaussian filters are used after the fiber.
Optical filter 1 is centered at 1550nm,-3dB,and BW of 10 GHz.
Optical filter 2 is centered at 1310nm,-3dB,and BW of 10 GHz.6) Optical Power Normalisers are used which average the
optical power and send it to the Compound receiver.7) Compound receiver consists of photodetectors,
pre-amplifiers,filters.Photodetectors are used at receiver side to convert opticalsignal into electrical signal.Bessel electrical filter is used in the compound receiver.Bessel electrical filter is low pass type, having number ofpoles 5,bandwidth as 10 GHz.
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RESULTS AND ANALYSIS
S.NO DISTANCE TYPE OF
LASER
DATA RATE OPERATING
WAVELENGTH
BIT ERROR
RATE(BER)
1. 40km CW,EXTERNALMODULATION
10Gbps 1550nm 5.3190x10-35
2. 40km CW,EXTERNAL
MODULATION
10Gbps 1310nm 8.8691x10-25
From the table it is seen that at 1550nm,the BER is better than theBER at 1310nm.Hence, the upper channel performs better.
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. 2-CHANNEL WDM :10 Gbps link FOR
100km
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RESULTS AND ANALYSIS
EYE DIAGRAM AFTER 100km FOR 10 Gbps LINKFOR UPPER CHANNEL AT 1550 nm
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EYE DIAGRAM AFTER 100km FOR 10 Gbps LINKFOR LOWER CHANNEL AT 1310 nm
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FOR THE ABOVE SIMULATED SYSTEM,BER IS COMPUTED.THERESULTS ARE SHOWN IN THE FOLLOWING TABLE.
S.NO DISTANCE TYPE OF
LASER
DATA
RATE
OPERATING
WAVELENGTH
BIT ERROR
RATE(BER)
1. 100km CW,EXTERNAL
MODULATION
10Gbps 1550nm 2.322x10-2
2. 100km CW,EXTERNAL
MODULATION
10Gbps 1310nm 6.6208x10-2
From the table it is seen that at 1550nm and at 1310nm, the BER is very very poor
and it is an inefficient transmission. The signal is attenuated and affected by the
non linear effects which are clearly visible from eye diagram where the eye is
poorly open.The performance can be improved if optical power boosters like
EDFA are used.
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CONCLUSION
The principle of WDM, development of WDM
technology, its advantages and the linear and
non linear effects seen in WDM systems are
discussed briefly. Thus the two channel WDM
systems are designed intuitively and the
simulations are carried out and the
performance of the systems are analyzed with
the eye diagrams and with the obtained BER.
