Reti in fibra ottica
Exercises on Transmission System Design
Exercise 1
A single span optical transmission system operates at 2.5 Gbps. The transmitter generates
rectangular pulses:
p (t )
PTX (t )  2 PTX

a
n 
n
p(t  nT )
1
0
T
where T is the bit time.
The transmission takes place on a fiber link which is characterized by 60 km length, a connector
every 2 km and a splice every 500 m. The structure of the receiver is showed in the following
figure.
MAX3267
PRX (t )
photodiode
Transimpedance
amplifier
low-pass
filter
The photodiode responsivity is 0.9 A/W. The MAXIM 3267 has the following parameters:
transimpedance gain 1.9 k, -3 dB bandwidth 1.9 GHz. The receiver sensitivity (@ BER=10-9)
is equal to –24 dBm.
Do the following:
1. Evaluate the amplitude of the receiver output voltage if the received power PRX is equal
to –15dBm.
2. Evaluate the optical average power that must be emitted by the transmitter in order to
obtain a BER smaller than 10-9. Assume an attenuation of 0.2 dB/km due to the fiber, 0.2
dB for a pair of connectors and 0.05 dB for each splice. Consider an extra fiber
attenuation equal to 1 dB due to the cable bends and a system margin equal to 3 dB.
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Exercise 2
A single span optical transmission system operates at 10 Gbps. The transmitter generates
rectangular pulses:
p (t )
PT (t )  2 PTX


n 
1
an p (t  nT )
T
0
where T is the bit time.
The transmission takes place on a fiber link which is characterized by a connector every 2 km
and a splice every 500 m. The structure of the receiver is showed in the following figure.
MAX3970
PRX (t )
Transimpedance
amplifier
photodiode
low-pass
filter
The photodiode responsivity is 0.9 A/W. The MAXIM 3970 has the following parameters:
transimpedance gain 590 , -3 dB bandwidth 9 GHz. The receiver sensitivity (@ BER=10-9) is
equal to –18 dBm.
Do the following:
1. Evaluate the received power PRX (t ) if the amplitude of the output voltage is equal to 100
mVpp.
2. Evaluate the maximum length of the fiber link if the transmitted power is equal to 3
dBm. Assume an attenuation of 0.2 dB/km due to the fiber, 0.2 dB for a pair of
connectors and 0.05 dB for each splice. Consider an extra fiber attenuation equal to 1 dB
due to the cable bends and a system margin equal to 3 dB.
Exercise 3
A single span optical transmission system operates at 10 Gbps. The structure of the receiver is
depicted in the following figure.
electrical
amplifier
(noise)
optical
band-pass filter
PRX (t )
optical amplifier
(ASE noise)
Pph (t )
low-pass
filter
vout (t )
photodiode
2
An Optical Spectrum Analyzer (OSA) measures the OSNR at the input of the optical filter. The
resolution bandwidth is 0.1 nm and the measured OSNR is equal to 12 dB. Evaluate:
1. The BER assuming that the optical band-pass filter is matched to the incoming pulse
2. The BER assuming that the optical band-pass filter is an order-2 supergaussian with
Bopt=100 GHz and the electrical filter is a 5-pole Bessel with BW=0.7RB.
Exercise 4
A single span optical transmission system operates at 10 Gbps. The transmission takes place on
a fiber link which is characterized by 150 km length, a connector every 10 km and a splice every
1 km. The structure of the receiver is showed in the following figure.
electrical
amplifier
(noise)
optical
band-pass filter
low-pass
filter
Pph (t )
PRX (t )
optical amplifier
(ASE noise)
vout (t )
photodiode
The optical amplifier has the following parameters: gain G=20 dB, noise figure F=5 dB. The
bandwidth of the optical band-pass filter is equal to 100 GHz. The electrical filter has a
bandwidth equal to 0.7RB.
Evaluate the average power that must be emitted by the transmitter in order to obtain a
BER<10-9. Assume an attenuation of 0.2 dB/km due to the fiber, 0.2 dB for a pair of connectors
and 0.05 dB for each splice. Consider an extra fiber attenuation equal to 2 dB due to the cable
bends and a system margin equal to 3 dB.
Exercise 5
A single span optical transmission system operates at 10 Gbps. The transmitter emits 7 dBm of
power. The transmission takes place on a fiber link which is characterized by 160 km length, a
connector every 10 km and a splice every 1 km. Assume an attenuation of 0.2 dB/km due to the
fiber, 0.2 dB for a pair of connectors and 0.05 dB for each splice. Consider an extra fiber
attenuation equal to 3 dB due to the cable bends. The structure of the receiver is showed in the
following figure.
electrical
amplifier
(noise)
optical
band-pass filter
PRX (t )
optical amplifier
(ASE noise)
Pph (t )
low-pass
filter
vout (t )
photodiode
3
The optical amplifier has the following parameters: gain G=20 dB, noise figure F=5 dB. The
bandwidth of the optical band-pass filter is equal to 80 GHz. The electrical filter has a
bandwidth equal to 0.7RB. Evaluate the BER.
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