OPTICAL COMMUNICATION LAB
LAB MANUALS
EXPERIMENT 1(a)
AIM:
To setup Fiber Optic Analog link.
APPARATUS REQUIRED:
ST2502 Or 2501 optical fiber trainer kit, Oscilloscope 20MHz Dual Trace, Optical fiber cable,
Microphone, Headphone.
THEORY:
Fiber optic links can be used for transmission of digital as well as analog signals. Basically a fiber
optic link contains three main elements transmitter and optical fiber & a receiver. The transmitter
module takes the input signal in electrical form and then transforms it into optical (light) energy
containing the same information. The optical fiber is the medium, which carries this energy to the
receiver. At the receiver, Light is converted back into electrical form with the same pattern as
originally fed to the transmitter.
Transmitter:Fiber optic transmitters are typically composed of a buffer driver and optical source. The
buffer provides both an electrical connection and isolation between the transmitters and the
electrical system supplying the data. The driver provides electrical power to optical source. Finally
the optical source converts the electrical current to the light energy with the same pattern.
Commonly used optical source are LED and a laser beam.
The transmitter section comprises of:
1. Function Generator:- The function generator generates the input signals that are going to
be used as information to transmit through the fiber optic link. Output voltage available
is 1 KHz sinusoidal signal of adjustable amplitude and fixed amplitude of 1 KHz square
wave signal.
2. Frequency Modulator & Pulse width modulator:- The modulator section accepts the
information signal and converts it into suitable form for transmission through the fiber
optic link.
Fiber optic link:
Emitter and detector circuit on board form the fiber optic link. This section provides the
light source for the optic fiber and the light detector at the far end of the fiber optic links. The
optical fiber connectors provided in this part of the board for two separate links.
The receiver:The comparator circuit, low pass filter, phase locked loop, AC amplifier circuit jointly
forms the receiver circuit on the board. It is able to demodulate in order to recover the original
information signal. In this experiment the trainer board is used to illustrate one-way
communication between digital transmitter and receiver circuits.
Function
Generator
(analog
signal or
audio
input)
Emitter
Circuit
(LED)
OFC
Detector
Circuit
(Phototransis
tor)
Amplifier
CRO or
Audio
output
PROCEDURE:
1. Connect the power supply to the board.
2. Ensure that all switch faults are off.
3. Make the following Connections:
a) Connect the function generator 1 KHz sine wave to emitter’s input.
b) Connect the optical fiber cable between emitter and detector’s input.
c) Detector’s to Amplifier input.
4. Switch emitter driver to Analog mode.
5. Switch ON the power supply.
6. Observe the input to emitter block with the output from amplifier and note that the two
signals are same.
7. Switch OFF the power supply.
8. Disconnect the emitter’s input to 1 KHz Sine wave socket and make the following
additional connections.
a) Microphone to Audio input block.
b) Connect the output of audio input block to emitter input.
c) A.C. Amplifier to input of audio block.
9. Switch ON the power supply.
10. Observe that same audio output is available on the speaker as fed to the microphone.
RESULT:
CONCLUSION:
EXPERIMENT 1(b)
AIM:
To set up Fiber Optic Digital link.
APPARATUS REQUIRED:
ST2502 Or 2501 optical fiber trainer kit, Oscilloscope 20MHz Dual Trace, Optical fiber cable,
Microphone, Headphone.
THEORY:
Fiber optic links can be used for transmission of digital as well as analog signals. Basically a fiber
optic link contains three main elements transmitter and optical fiber & a receiver. The transmitter
module takes the input signal in electrical form and then transforms it into optical (light) energy
containing the same information. The optical fiber is the medium, which carries this energy to the
receiver. At the receiver, Light is converted back into electrical form with the same pattern as
originally fed to the transmitter.
Transmitter:Fiber optic transmitters are typically composed of a buffer driver and optical source. The
buffer provides both an electrical connection and isolation between the transmitters and the
electrical system supplying the data. The driver provides electrical power to optical source. Finally
the optical source converts the electrical current to the light energy with the same pattern.
Commonly used optical source are LED and a laser beam.
The transmitter section comprises of:
3. Function Generator:- The function generator generates the input signals that are going to
be used as information to transmit through the fiber optic link. Output voltage available
is 1 KHz sinusoidal signal of adjustable amplitude and fixed amplitude of 1 KHz square
wave signal.
4. Frequency Modulator & Pulse width modulator:- The modulator section accepts the
information signal and converts it into suitable form for transmission through the fiber
optic link.
Fiber optic link:
Emitter and detector circuit on board form the fiber optic link. This section provides the
light source for the optic fiber and the light detector at the far end of the fiber optic links. The
optical fiber connectors provided in this part of the board for two separate links.
The receiver:The comparator circuit, low pass filter, phase locked loop, AC amplifier circuit jointly
forms the receiver circuit on the board. It is able to demodulate in order to recover the original
information signal. In this experiment the trainer board is used to illustrate one-way
communication between digital transmitter and receiver circuits.
Function
Generator
(analog
signal or
audio
input)
Emitter
Circuit
(LED)
OFC
Detector
Circuit
(Phototransis
tor)
Amplifier
&
Demodulat
or
CRO or
Audio
output
PROCEDURE:
1.
2.
3.
4.
5.
6.
7.
8.
Make the following connections (as shown in the diagram).
Connect the FG 1 KHz square wave output to emitter 1’s input.
Connect the fiber optic link cable between emitter output and detector 1’s input.
Detector 1’s output to comparator 1’s input.
Comparator 1’s output to amplifier 1’s input.
Switch emitter 1’s driver to digital mode.
Switch ON the power.
Monitor both the inputs to comparator 1 (t.p. 13 & t.p. 14). Slowly adjust the comparators
bias preset, until DC level on the input (t.p. 13) lies mid way between the high and low
level of the signal on the positive input (t.p. 14).
9. Observe the input to the emitter 1 with the output from amplifier 1 and note two signals are
same.
RESULT:
CONCLUSION:
Experiment 2 (a)
AIM:
Measurement of propagation loss.
APPARATUS:
Fiber optic kit ST2501, CRO 20 MHz, Signal generator, 1m plastic fiber.
THEORY:
Optical fibers are available in different materials they are selected by considering the absorption
characteristics for different wavelengths of light. Losses are introduced in the fiber due to a variety
of reasons. As light propagates from one end of the fiber to other end, part of it absorbed in the
material exhibiting absorption loss. Part of the light is reflected back or in some other direction
from the impurity loss of the signal at the other end of the fiber. This phenomenon is called
propagation loss. Whenever the condition for angle of incidence of the incident light is violated,
the losses are introduced due to refraction of light. This occurs when fiber is subjected for bending
PROCEDURE:
1. Set up the analog link as shown in the block diagram.
2. Use an optical fiber link of length 1 meter and note down the output voltage V1 Volts.
3. Use an optical fiber link of length 3 meters and note down the output voltage say V2 Volts.
4. If α is the attenuation of the fiber,
P1/P2 = V1/V2 = e[-α(L1+L2)]
Where α= nepers/meter
L1=fiber length V1
L2=fiber length for V2
CONCLUSION:
Experiment 2(b)
AIM:
Measurement of Numerical Aperture.
APPARATUS:
Fiber optic kit, CRO, Signal generator, 1m &3m plastic fiber.
THEORY:
Numerical aperture refers to the maximum angle at a light incident on the fiber end is totally
internally reflected and is transmitted properly along with the fiber. The cone found by the rotation
of this angle along with the axis of the fiber is the cone of acceptance of the fiber. The light ray
should strike the fiber end within its cone of acceptance; else it is reflected out of the fiber core.
Consideration in measurement:1. It is a very important that the source should be properly aligned with the cable & the distance
from the launched point & the cable be properly selected to ensure that the maximum amount of
optical power is transferred to the cable.
2. This experiment is best performed in a less illuminated room.
Function
Generator
Emitter
Circuit
(LED)
PROCEDURE:
1. Connect power supply to the board.
2. Connect the frequency generator’s 1 KHz sine wave output to input of emitter 1 Circuit.
Adjust its amplitude at 5V p-p.
3. Connect one end of fiber optic cable to the output socket of emitter 1 circuit and the
other end to the numerical aperture measurement jig. Hold the white screen facing the
fiber such that its cut face is perpendicular to the axis of the fiber.
4. Hold the white screen with 4 concentric circles (10, 15, 20 & 25mm diameter) vertically
at a suitable distance to make the red spot from the fiber coincide with 10mm circle.
5. Record the distances of screen from the fiber end L and note the diameter W of the spot.
6. Compute the numerical aperture from the formula given below:
N.A. = W/(√4L2+W2) = sin θmax(acceptance angle)
7. Vary the distance between the screen and fiber optic cable and make it coincide with one
of the concentric circles and note its distance.
8. Tabulate the various distances and diameters of the circles made on white screen and
compute the numerical aperture from the formula.
 The N.A. recorded in the manufacturers datasheet is 0.5.
RESULT:
CONCLUSION:-
Experiment 3
AIM:
Measurement of optical power bending loss in a plastic optical fiber.
APPARATUS:
Fiber optic kit, CRO, Signal generator, mandrel, 1m & 3m plastic fiber.
THEORY:
Numerical aperture refers to the maximum angle at a light incident on the fiber end is totally
internally reflected and is transmitted properly along with the fiber. The cone found by the rotation
of this angle along with the axis of the fiber is the cone of acceptance of the fiber. The light ray
should strike the fiber end within its cone of acceptance; else it is reflected out of the fiber core.
Consideration in measurement:1. It is a very important that the source should be properly aligned with the cable & the
distance from the launched point & the cable be properly selected to ensure that the
maximum
amount
of
optical
power
is
transferred
to
the
cable.
PROCEDURE:
1. Connect power supply cord to the main power plug & to trainer kit.
2. Make the connections as shown in figure above
a) Function Generator 1 KHz sine wave output to input socket of emitter Circuit via 4 mm lead.
b) Connect 0.5 m optic fiber between emitter output and detectors input.
c) Connect Detector output to amplifier input socket via 4 mm lead.
3. Switch ‘On’ the power supply of the trainer and oscilloscope.
4. Set the Oscilloscope channel 1 to 0.5 V/ Div and adjust 4-6 div amplitude by using X 1 probe
with the help of variable pot in function generator Block at input of Emitter.
5. Observe the output signal from detector (TP8) on CRO.
6. Adjust the amplitude of the received signal as that of transmitted one with the help of gain
adjusts potentiometer in AC amplifier block. Note this amplitude and name it V 1.
7.Wind the fiber optic cable on the mandrel and observe the corresponding AC amplifier output on
CRO, it will be gradually reducing, showing loss due to bends.
Observations
S.No
1
2
3
4
RESULT:
CONCLUSION:-
No. of Turns
No Bending
Output Voltage
EXPERIMENT 4 (a)
AIM:
Study and measure characteristics of fiber optic LED.
APPARATUS REQUIRED:
ST2502 Or 2501 optical fiber trainer kit, Oscilloscope 20MHz Dual Trace, Optical fiber cable,
Optical power meter: INFOS, Model # M100, Two laboratory jacks, Two digital multimeters, Infrared LED(GaAs Infrared Emitter, Siemens: LD 271L),Power supply, Resistor 1K ohm, Rotational stage
with adapter plate, Cleaved 62.5 µm GI optical fiber (2-5 meters long, Gray Color).
THEORY:
The LED is an important element in fiber optics communication systems. It is used as a light
source in multimode optical fibers. It is inexpensive and has a relatively fast response. The LED
can be regarded as an ordinary diode, with the exception that it emits light which is generally
proportional to the input current. The LED symbol is shown in Figure 1, which is identical to the
symbol of the ordinary LED. The diode voltage Vd is defined with + polarity on the p terminal and
the diode current Id is defined to flow through the diode from the p to the n terminal, which is
identical to the standard definitions of the voltage and current of the ordinary diode.
Figure 1. Symbol of the LED, Showing Definition of the Current and Voltage.
The LED must be forward biased in order for it to emit light energy. The light power Po emitted
by the LED is generally proportional to current Id ( P0 Id ), provided Id . The center
wavelength of the LED light emission depends on the bandgap energy of the material used in the
fabrication of the LED. The diode used in this experiment emits in the infrared region of the
spectrum, so you will not be able to see the emitted light without some aid.
Fiber optic transmitters are typically composed of a buffer driver and optical source. The
buffer provides both an electrical connection and isolation between the transmitters and the
electrical system supplying the data. The driver provides electrical power to optical source. Finally
the optical source converts the electrical current to the light energy with the same pattern.
Commonly used optical source are LED and a laser beam.
The experimental setup used in this experiment is capable only of measuring part of the emitted
optical power (see Figure 2). Because we are interested in measuring the diode linearity with
respect to the diode current, then we need only to detect a fraction of the emitted power, which is
obviously proportional to the total power emitted, provide we fix the location of the optical power
meter relative to the LED. It is thus important in this experiment not to move either the power
meter or the LED after we start measurements.
Figure 2.Setup for Measuring Part of the Optical Power Emitted by the LED.
PROCEDURE:
LED IV Characteristic and Linearity.
1- Connect the circuit shown in Figure 3. The ammeter should be connected in series with the 1
Kilohms resistor in order to directly measure the diode current Id and the voltmeter should be
connected across the diode to directly measure the diode voltage Vd. .
2- Set the power supply voltage to Vs= 5V .
3- Verify that the LED actually emits optical power. [A mobile phone with camera can be used to
view the light emitted by infrared LED’s].
4- Turn on the optical power meter and set it to dBm and 𝞴= 0.85µm.
5- Bring the optical power meter as close as possible to the LED and observe the meter’s reading.
Try to obtain as much power as you could. [Do not remove the optical power meter cover].
6- Set the supply voltage to Vs= 0 V . Record the values of Id and Vd. the optical power meter’s
readings in table 1.
7- Slowly increase until Vs =0.1 V. In table 1, record Id , Vd and the optical power meter reading.
[There is no need to measure and record the value of Vs in this step].
8- Repeat step 7 for Vd =0.2 V, 0.3 V , …., up to 1.0 V . [Do not record the value of Vs at this
point. Also, be careful that Id is initially very small (in the µA range)].
9- Now, set the supply voltage to Vs =2 V . Record the measured values of Id , Vd , the optical
power meter reading and Vs in table 1.
10- Repeat step 9 for Vs= 2.5,3.0,3.5,4.0,4.5,5.0,6.0,.....9.0,9.5,10.0 [Note the change in the step
size of Vs ].
11- Covert the measured optical power in dBm (fourth column of table 1) to mW and record the
value in column 5 of the same table. Calculate the normalized power PN and record the values in
column 6 of table 1.
12- Plot PN versus Id
13- On the same graph, plot a straight line (you may need more than one separate straight line to
fit with the experimental graph) that best fits the experimental graph.
Comment on the linearity of the output optical power versus diode current and the range of
linearity.
14- Plot the LED IV characteristic ( Id versus Vd ).
15- Comment on the resulting curve.
16- Estimate the turn-on voltage VT (forward voltage) and compare it with the typical LED
specification.
17- Discuss the overall experimental results for this part of the experiment and write some
conclusions.
Vs (Volts)
(Vd) V
0
0.0
0.1
0.2
0.8
0.9
0.95
1.0
2.0
2.5
3
10
Id(mA)
P(dBm)
P(mW)
PN
EXPERIMENT 4 (b)
AIM:
Study and measure characteristics of fiber optic Laser Diode (LD)
APPARATUS REQUIRED:
ST2502 Or 2501 optical fiber trainer kit, Oscilloscope 20MHz Dual Trace, Optical fiber cable,
Optical power meter: INFOS, Model # M100, Two laboratory jacks, Two digital multimeters,
Benchmark 650 nm LD unit (or) 1300nm (or) 1550nm LD unit, Benchmark LD driver module with its
accessories, Benchmark Fiber Optic Power meter with ST adaptor, Mounting Posts for 650nm LD unit
(or) ST-ST Patch cord for 1300nm LD unit or SC-ST patch cord for 1550nm LD unit
THEORY:
LD characteristics such as the threshold current can be studied using the benchmark LD module.
The injection current through a LD (in 650nm LD unit or in 1330nm LD unit or in 1550nm LD
unit) is varied and thereby its characteristics are studied. This current is varied using a multi-turn
potentiometer, which enables the user to have a precise control over it. The LD driver is shown
.The LD driver unit needs its own external DC power supply to operate. The LD driver unit is
provided with appropriate monitoring posts for taking the necessary measurements. A selfexplanatory basic circuit is printed over the module for easy understanding. Benchmark LD
module can also be used to setup a Point-to-Point link and the link characteristics may be
observed.
PROCEDURE:
1. Setup the LD driver module.
2. Keep the pot at the minimum position. Turn ON the power to the module.
3. Measure the voltage V1 across the resistor R1 (where R1 is 68 ohms) and calculate the
current ILD through the LD which is given as
ILD = V1 / R1
4. Measure the voltage VLD across the LD.
5. Now without changing any voltage or the multi-turn pot position, measure the optical
power output P of the LD.
Calculate the power in mW which gives as
6.
Po = 10p/10
7. Increase the current through LD by turning the multi-turn pot clockwise direction slightly
towards the maximum. Repeat the steps 2 to 5 and tabulate them.
Sample Graphs:
Observation Table:
S.No
Results:
CONCLUSION:
V1
(in Volts)
ILD
(in mA)
VLD
(in Volts)
P
(dBm)
Po
(mW)
EXPERIMENT 5
AIM:
OTDR Measurement of Fiber length, Attenuation and Dispersion Loss.
APPARATUS REQUIRED:
ST2502 Or 2501 optical fiber trainer kit, Oscilloscope 20MHz Dual Trace, OTDR: Agilent
Technologies E6000 Mini OTDR Main Frame with E6005A Module (850/1300 nm High
Performance Multimode Module), Unknown length of two different types of fibers connected
together with three splices (two fusion splices and one mechanical splice). The fiber types are: 50
m multimode GI (orange) and 62.5 m multimode GI (gray).
THEORY:
The Figure 1 shows an imaginary OTDR trace of an optical fiber link in which three different
types of fibers are connected together to form the entire link. This arrangement is not very
common in practice, but some existing links use more than one fiber type. The reason we know
that three different types of fibers exist in the link (whose OTDR scan is shown in Figure 1) is
because there are three distinct straight lines (due to Rayleigh scatter) with different slopes. The
first line segment has a slightly larger slope than the second straight line segment. This means fiber
1 is slightly lossier than fiber 2. Therefore, they must be different types of fibers.
From the trace, we also know that the lengths of fibers 1, 2 and 3 are L1, L2- L1 and L3-L2,
respectively. We already know how to find the fiber’s attenuation in dB per unit length by finding
the slope of each straight line segment. The splice between fibers 1 and 2, located at z=L1, is nonreflective because of the sudden decrease in the reflected power without a spike. Non-reflective
event can be due to either a good splice, fiber break or fiber bends. We can find the loss of this
splice, simply by calculating the difference in the power levels before and after the splice (i.e. P1P1’)
The joint between fibers 2 and 3, located at z=L2, is reflective because of the sudden increase (with
a spike) in the reflected power (if the sudden increase has no spike, then it must be interpreted as a
non-reflective event). The joint between fibers 2 and 3 could be due to either a poor splice or a
connector. The loss due to this joint can be calculated as before (i.e. P2-P2’). The trace also shows a
reflective fiber’s end at z=L3. This is due to light reflection at the glass/air interface (Fresnel
reflection) at the fiber’s end. If desired, the fiber’s end can be made non-reflected. This can be
done by immersing the fiber’s end into an index-matched fluid (a fluid that has the same refractive
index as glass) to minimize Fresnel reflection. Alternatively, it is also possible to wrap the fiber’s
end several times around a tight bend to produce a non-reflective end. The tight bend causes large
power loss, without reflection. In this manner, the light reaching the un-terminated fiber’s end
becomes too weak to detect.
Figure1 An Imaginary OTDR Trace of an Optical Fiber Link Consisting of Three Different Fiber
Types Spliced Together. The OTDR Trace Shows the Locations of the Reflective Events, the NonReflective Events and the Link’s End.
The OTDR trace shown in Figure 1 assumes that the three fibers used in the link have the same
Rayleigh scattering coefficients. Rayleigh scattering coefficient is related to the fraction of power
scattered due to Rayleigh scatter. For instance, suppose fiber 2 has a significantly higher Rayleigh
scattering coefficient than fibers 1 and 3, then the OTDR scan of Figure 1 may be modified to the
one shown in Figure 2. The OTDR trace due to Rayleigh scatter from fiber 2 appears as power
gain. In this link, it is impossible to have optical power gain, because the system does not have
optical amplifiers. The sudden rise in power is simply due to the higher percentage of power
scattered from fiber 2. In reality the optical power in fiber 2 is less than the optical power in fiber
1.
Figure2. Sudden Rise in the Scattered Power when Fiber 2 has a higher Rayleigh Scattering
Coefficient than Fiber 1 and Fiber 3.
When two fibers with different Rayleigh scattering coefficients are joined together, the joint loss
cannot be calculated using the difference in power P1- P1’and P2- P2’. The only way to compute the
joint loss in this case is by first knowing the Rayleigh scattering coefficient of the two fibers.
Unfortunately, we do not know the values of the Rayleigh scattering coefficients for the fiber types
used in the experimental link. To summarize: when two different fiber types are joined together,
the joint loss cannot be computed from the OTDR trace, unless the Rayleigh scattering coefficients
of the two fibers are known.
The optical fiber link that you are going to examine in this experiment consists of two fiber types
joined together using three joints. The first and second joints are fusion splices between two
dissimilar fibers. The last joint is a homemade mechanical splice between two identical fibers.
Thus, only the loss of this third joint can be computed, because it connects two identical fibers. In
addition, because this splice is mechanical, its dB loss is expected to be relatively high
PROCEDURE:
[The test fiber should be connected by the laboratory instructor or the laboratory technician. Do
not remove the fiber from the OTDR. DO NOT LOOK DIRECTLY AT THE OUTPUT END OF
THE FIBER]
.INVESTIGATING A FIBER OPTIC LINK.
1-Read the fiber reel letter (e.g. A, B, C, etc.) and record it in the top row of table 1.
2-Turn the OTDR on and wait for the self -test to end.
3-Select  855 nm from the SETTINGS menu.
4-Select AUTO.
5-Press the RUN/STOP to generate an OTDR trace and wait for the averaging to end or the trace
to be free of noise.
6-Print the trace.[The printed trace should be included in your experimental report. The printed
trace must show the correct wavelength].
7-Find the distance from the fiber’s start to the first splice (splice 1). Record the distance in table 1.
8-Zoom around splice 1 until you see it clearly and print the magnified OTDR trace. [Change both
the horizontal and vertical scales to see the details. Include the magnified trace in your report].
9-Determine if the splice is reflective or non-reflective and record the result in table 1.
10-Repeat steps 7 -9 for the second splice.
11-Repeat steps 7 -9 for the third splice. In addition, compute the splice loss and record it in table
1.
12-Find the total link length and record it in table 1.
13-Find the total link loss in dB and record it in table 1. The total link loss can be found by finding
the difference in dB just to the right of the fiber’s start and just to the left of the fiber’s end.
14-Find the loss in dB/Km for the first link segment and record it in table 1 (Determine the slope
of the straight line segment from just to the right of the fiber’s start till the very beginning of splice
1, i.e. the left hand side edge).
15. Repeat step 14 for link segments 2, 3 and 4.
16-Repeat steps 3-15 at 1310 nm.Record the result in table 2.
17-Compare the fiber lengths measured at 855 nm and 1310 nm Discuss.
18-Compare the losses (in dB/Km) of the four fiber segments at 855 nm and indicate if the four
segments are made of the same fiber type or different fiber types.
19-Compare the fiber losses (in dB/Km) and at 855 nm and 1310 nm. Are those losses
expected to be dependent or independent of ? Discuss.
20-Compare the measured loss of the third splice at 855 nm and 1310 nm.
21-Discuss the overall experimental results and make appropriate comments and conclusions.
Observations:
Table 1. Summary of OTDR Measurements at 𝞴= 855nm
Location of splice 1 (m)
Type of splice 1 (Reflective/Non Reflective)
Location of splice 2 (m)
Type of splice 2 (Reflective/Non Reflective)
Location of splice 3 (m)
Loss of splice 3 (dB)
Type of splice 3 (Reflective/Non Reflective)
Total link length (m)
Total Link Loss (dB) [Including splice loss]
dB Loss/Km of segment 1
dB Loss/Km of segment 2
dB Loss/Km of segment 3
dB Loss/Km of segment 4
Table 2. Summary of OTDR Measurements at 𝞴= 1310 nm
Location of splice 1 (m)
Type of splice 1 (Reflective/Non Reflective)
Location of splice 2 (m)
Type of splice 2 (Reflective/Non Reflective)
Location of splice 3 (m)
Loss of splice 3 (dB)
Type of splice 3 (Reflective/Non Reflective)
Total link length (m)
Total Link Loss (dB) [Including splice loss]
dB Loss/Km of segment 1
dB Loss/Km of segment 2
dB Loss/Km of segment 3
dB Loss/Km of segment 4
Result:
Conclusion:
EXPERIMENT 6
AIM:
Design and simulate of single and multimode transmission in optical fiber design.
APPARATUS REQUIRED:
S.NO
1
2
3
4
5
COMPONENTS
OFT
Two channel oscilloscope
Function generator
Fiber alignment unit
BNC Cables
RANGE
20MHz
1 Hz – 10 Hz
-
QUANTITY
1
1
1
1
3
THEORY:
The fiber used in OFT is multimode plastic fiber with 1000 µm core diameter. Unlike its
Glass-Glass Plastic Coated Silica fiber counterparts, this fiber has very high attenuation. It is useful
mainly for short links such as in Local Area Network, especially where there could be serious EMI
problems. This fiber has been selected for the OFT because of the ease of handling it affords.
While the loss in plastic fiber is high for all wavelength regions, the loss at 850 nm is such
higher than at 650 nm.
Apart from the above propagation loss in a fiber, bending of fiber, connectors, splices and
couplers may all contribute significantly to the losses in a fiber optic communication link.
An optical fiber is a circular wave guide. A small in a fiber will not significantly affect the
propagation characteristics and therefore the losses in the fiber. However, if the fiber is bent with a
radius of curvature smaller than a certain value (usually about a centimeter), the propagating signal
may suffer significant bending loss.
Two optical fibers are joined using either a connector or a splice. The alignment of the cores
of two fibers is critical in both the situations, as even the minutest misalignment or gap between the
fibers may cause significant coupling losses.
PROCEDURE:
1. The connections are made as per the block diagram.
2. Set the switch SW8 to the ANALOG position. Ensure that the shorting plug to the jumper
JP2 is across the posts B&A1 (for PD1 selection). Remove the shorting plugs from coded
data shorting links S6 in the Manchester coder block and S26 in the decoder & clock
recovery block.
3. Take the 1m fiber and set up an analog link using LD1 in the Optical Tx1 block and
detector PD1 in the optical Rx1 block [850 nm link]. Drive a 1Vp-p 10 KHz sinusoidal
signal with zero D.C. at P11. Observe the signal at P31 on the oscilloscope. Use the BNC
I/Os for feeding in and observing signals as described. Adjust the GAIN such that the
received signal is not saturated.
TABULATION:
ATTENUATION LOSS:
Length of the cable
Input signal
Output signal
Amplitude (v)
Amplitude (v)
Attenuation (dB/m)
BENDING LOSS:
Diameter (cm)
Radius (cm)
Output voltage (mV)
4. Note the peak value of the signal received at P31 and designate it as V1. Replace the
1m fiber by the 3m fiber between LD1 and PD1. Again note the peak value of the
received signal and designate it as V3. If α is the attenuation in the fiber and l1 and l3
are the exact length of the 1m and 3m fibers in meters respectively, we have
P3
P1
=
V3
=exp [-α (l1 - l3)]
V1
Where α is in neperism/m, and P1 and P3 are the received optical power with 1m and
3m respectively.
Compute α’ in dB/m for 850 nm wavelength using α’ =4.343 α where α is in
nepers/m.
5. Set up the 850 nm analog link using the 1m fiber. Drive a 1Vp-psinusoidal signal of
10 KHz with zero D.C. at P11 and observe the received signal P31 on the
oscilloscope. Now bend the fiber in a loop. Reduce the diameter of the loop slowly
and observe the reduction of the received signal at P31. Keep reducing the diameter
of the loop to about 2 cm and plot the amplitude of the received signal versus the
diameter of the loop.
6. Connect one end of the 1m fiber to LD2 and the other end to the detector PD1. Drive
the LD with a 10 KHz TTL signal at post B of S6. Note the peak signal received at
P31 and designate it as V1 [ensure that the GAIN is low to prevent saturation]. Now
disconnect the fiber from the detector. Take the 3m fiber and connect one end to the
detector PD1. The optical signal can be seen emerging from the other end of the 1m
fiber. Bring the free ends of the two fibers as close as possible and align them using
the Fiber Alignment Unit. Observe that the received signal P31 varies as the free
ends of the fibers are brought closer and moved apart. Note the received signal level
with the best possible alignment and designate it as V4. Using the attenuation
constant obtained in step 4, compute the coupling loss associated with the above
coupling of the two fibers using
η= -10 log (V4 / V1)- α’(l1 + l3)
RESULT:
EXPERIMENT 7
AIM:
Show and simulate the optical system performance analysis using Eye diagram and measure the
value of Q-factor & BER of optical signals.
APPARATUS REQUIRED:
S.NO
1
2
3
4
5
COMPONENTS
OFT
Two channel oscilloscope
Function generator
EMI unit
Patch cord [supplied with OFT]
RANGE
QUANTITY
20MHz
1 Hz – 10 Hz
40 cm
1
1
1
1
1
THEORY:
While optical fiber has established itself as the medium for long-haul wide-bandwidth
communications, it has also made a significant impact in other application where neither the link
nor the bandwidth requirement is large. This is because optical fiber is a dielectric medium, i.e.
totally non-metallic. The signal propagating is optical and does not have any associated voltage or
current. In many environments today, Electromagnetic Interference [EMI] and Radio Frequency
Interference [RFI] have become a serious problem affecting even low bit-rate communication over
short distances. Optical fiber, being totally dielectric, has immunity to EMI/RFI and is finding
widespread application in such situation.
PROCEDURE:
1. Set up the digital link using optical fiber.
2. Remove the shorting plugs of shorting links S6 in the Manchester coder block and
S26 in the decoder & clock recovery block.
3. Reconnect the shorting plug at S6 and S26. Remove the fiber. Connect P12 in the
electrical o/p block and P32 in optical Rx1 block using the 40cm patch cord supplied
with OFT. Adjust GAIN to ensure that the multiplexer / demultiplexer is working.
The shorting of P12and P32 establishes an analog link between the Tx and the Rx
side on copper cable.
4. Using the signal at S7 as the external trigger for the oscilloscope, observe the signal at
P31. The Rx data observed at the oscilloscope now starts with the digitized voice data
in slot1. Increase the time scale to observe only on roe two bits on the scope
5. Disconnect the patch cord at P12, insert it through the coil tube in the EMI unit
supplied for interference generation, and reconnect it at P12 with the coil now
around the wire. Connect the interference coil to a function generator and excite it
with a sinusoidal signal of around 100 KHz at around 5V p-p, with zero D.C. Observe
the signal P31.
6. As the interference on the incoming signal increases the EYE opening decreases.
7. With the frequency of the interfering sinusoidal signal fixed [say at 500 KHz],
increase its amplitude without disturbing the coil.
8. Repeat steps 6 and 7 for several frequencies between 500 KHz and 1 MHz and note
the voltages required for the interference to affect the working of the multiplexer.
9. Remove the patch cord containing P12 and P32. Put the interfering coil around a 1m
optical fiber and set up the optical link at 850 nm.
Parameter Sweeps – BER x Input power
Step
1
2
Action
From the Main toolbar, select File > Open.
The Open dialog box appears.
From your C: drive, select Program Files > Optiwave
Software > OptiSystem 9 > samples > Introductory tutorials > “Lesson4
Parameter Sweeps – BER x Input power.osd”.
The sample file appears (see Figure 1).
Selecting the parameter to iterate using the Sweep mode
Step
1
Action
Double-click the CW Laser.
The CW Laser Properties dialog box appears (see Figure 2).
2
In the Power row, click the Mode cell.
A drop-down list appears.
3
4
Select Sweep.
To save the settings, click OK.
The CW Laser Properties dialog box closes.
Changing the number of sweep iterations
Step
1
Action
From the Layout menu, select Set Total Sweep Iterations.
The Total Parameter Sweep Iterations dialog box appears (see Figure 3).
2
In the Total Iterations, type:
10
3
To set the value and return to the Main layout, click OK.
Changing the values of sweep iterations
Step
1
2
3
4
5
6
7
Action
From the Layout menu, select Parameter Sweeps.
The Parameter Sweeps dialog box appears.
Select the Power column (all cells).
The selected cells are highlighted.
Under Spread Tools, click Linear.
The Parameter Iteration Spread dialog box appears (see Figure 4).
In Start Value, type:
–10
In End Value, type:
10
To set the values, click OK.
The Parameter Iteration Spread dialog box closes.
To return to the Main layout, click OK.
The Parameter Sweeps dialog box closes.
Running the simulation
Step
1
2
Action
Click Calculate
Click the Run button.
The calculation progress appears in the Calculations dialog box window.
Obtaining results using the Report Page
Step
1
2
3
4
Action
Select the Report tab in the Project layout window.
The Report window appears.
Click the Opti2DGraph button on the Report toolbar and draw a 2D
graph in the report window.
The 2D graph appears in the Report window.
In the Project Browser, select the parameter Power from the CW Laser,
and drag it to the 2D graph X-axis (a grey triangle appears in the graph in
the bottom right corner).
The graph appears in the Report window.
In the Project Browser, select the Min. log of BER result from the BER
Analyzer component, and drag it into the Y-axis of the graph (the grey
triangle appears in the top left corner).
The result is plotted in the graph.
Browsing parameter sweep iterations
Step
1
2
3
RESULT:
Action
In the Main layout, double-click the BER Analyzer.
The BER Analyzer graph opens.
Select the Show Eye Diagram check box.
The graph changes to display the Eye Diagram.
In the toolbar, change the Sweep iteration (see Figure 6).
Note: You obtain different results for each iteration, one for each input
power value.
EXPERIMENT 8
AIM:
Study and simulate the linear and parabolic waveguide structure use in optical fiber
communication.
SIMULATION:
Drawing Linear Waveguide
Step
1
2
Action
From the Draw menu, select Linear Waveguide.
Draw the waveguide in the center of the wafer and covering the length of
the wafer
Inserting the Input Plane
Step
1
2
3
Action
From the Draw menu, select Input Plane.
Click in the layout and position the Input Plane at 10 microns
Double-click the Input Plane. The Input Plane dialog box appears.
4
Click the Input Fields 2D tab, and then click Edit. The Input Field dialog
box appears.
5
Click All to move the waveguide for input from the Waveguides window
to the Fields window
6
7
To save the setting and return to the Input Plane dialog box, click OK.
To return to the main layout, click OK.
To select the Single Waveguide module
1
2
File > New.
In the New dialog box, click Single Waveguide.
To open the Single Waveguide dialog box
1
2
In the Gratings box, click the Fiber/Waveguide Parameters button.
In the Single Waveguide dialog box, you can define the following options:
RESULT:
EXPERIMENT 9
AIM:
Design and simulate the Dispersion compensators for fiber optic communication.
THEORY:
The pulse broadening effect of chromatic dispersion causes the signals in the adjacent bit periods
to overlap. This is called inter symbol interference (ISI). Broadening is a function of distance as
well as dispersion parameter D. The dispersion parameter is given in ps/nm/km and changes from
fiber to fiber. It is also a function of wavelength. D is usually about 17 ps/nm/km in the 1.55 μm
wavelength range for a standard single mode fiber (SMF). It is at a maximum of 3.3 ps/nm/km in
the same window for a dispersion-shifted fiber (DSF). Nonzero dispersion fiber (NDF) has a
chromatic dispersion between 1 and 6 ps/nm/km or -1 and -6 ps/nm/km.
For externally modulated sources, transmission distance limited by chromatic dispersion
When D=16 ps/(km-nm) and at 2.5 Gbps, L ≈ 500km, whereas it drops to 30 km at 10 Gbps bit
rate.
Several techniques, including Dispersion Compensating Fiber or Fiber Bragg Grating, can be used
to compensate the accumulated dispersion in the fiber. In the following example we will show
three different schemes, pre-, post-, and symmetrical compensation, to compensate the fiber
dispersion. First we will use dispersion compensating fibers (DCFs). We will then show how the
amount of accumulated dispersion from the dispersion compensator affects the performance. In
this case, we will use an ideal dispersion compensating module (DCM) as the dispersion
compensator to show the idea.
Pre-, post-, and symmetrical-compensation by using DCF
Pre-, post-, and symmetrical compensation configurations are shown in Figure 1, Figure 2, and
Figure 3. In our simulations, we have used optical amplifiers after each fiber to compensate for the
span loss. The dispersion parameter of SMF is 120 km long and 16 ps /nm-km. Therefore, total
accumulated dispersion is 16×120 = 1920 ps /nm. This much dispersion can be compensated by
using a 24 km long DCF with -80 ps /km-nm dispersion. Total transmission distance is 120×2
=240 km for each cases. In the post-compensation case, DCF is placed after SMF. In the
symmetrical compensation case, fiber placement follows the sequence of SMF, DCF, DCF, and
SMF.
For these three cases, the project is found in the following file: Dispersion compensation pre post
symmetrical.osd. In these simulations, we have used NRZ modulation formats. Receiver sensitivity
is -28 dBm for 2.5 Gbps and -25 dBm for 10 Gbps. (Thermal noise of the PIN is 2.048e -23W/Hz.)
Simulation results are shown in Figure 4 and Figure 5. Figure 4 shows Q factor of received signal
versus transmitted signal power for these three schemes at 2.5 Gbps bit rate. Figure 5 shows the
same graph for the 10 Gbps bit rate. To simulate the designs in 10 Gbps, you need to set the global
parameter bit rate to 10 Gbps. From these figures, we can conclude that the best performance is
obtained by using symmetrical dispersion compensation. The worst case is dispersion precompensation. This can also be seen from the eye diagrams given in Figure 5.
RESULT:
EXPERIMENT 10
AIM:
Design and calculate the power budget for optical communication link.
THEORY:
The purpose of power budget is to ensure that enough power will reach the receiver to maintain
reliable performance during the entire system lifetime. The minimum average power required by
the receiver is the receiver sensitivity. The average launch power is generally specified for each
transmitter with optical powers expressed in dBm.
In order to estimate the maximum fiber length we should specify the output power of the
transmitter and the receiver sensitivity. We can also specify a system margin. The purpose of the
system margin is to allocate a certain amount of power to additional sources of power penalty that
may develop during the system lifetime.
System Design – Power Budget.osd (see Figure 4) shows a system designed using a receiver with 30 dBm sensitivity and an external modulated transmitter with output power of -3 dBm.
Using a system margin of 0 dB the total loss allocated for the channel will be:
•
Channel Loss = System Margin + Receiver Sensitivity + Transmitter power
•
Channel Loss = 30 – 3 = 27 dB
For a typical fiber attenuation of 0.25 dB/km, the maximum distance we can propagate in this
system is 108 km. In this case, we are not including dispersion effects that will limit the system
performance.
RESULT:
EXPERIMENT 11
AIM:
Design and simulate the DWDM and WDM techniques use in optical communication.
APPRATUS REQUIRED:
S.NO
1
COMPONENTS
LD modulator with accessories
RANGE
-
QUANTITY
1
2
3
4
5
1550nm LD unit
1310nm LD unit
FORX-500 receiver
Benchmark power meter(FOPM102)
-
1
1
1
1
6
7
8
9
WDM 13-15 coupler
SC/PC to SC/APC patch cord
SC/APC to SC/PC adaptor
1310nm & 1510nm fixed optical
attenuator
SC/APC to ST Single-mode patchcord
TTL Gen
-
1
2
2
1-each
-
1
-
1
10
11
THEORY:
A method of combining several wavelength of light into a single fiber at the transmitting
end and then separating them at the receiving end such that the bandwidth available in a
fiber can be utilized effectively. Several 10s of Gbps signals are combined like this to utilize
the vast bandwidth of fiber.
Facilities to realize complex fiber optic communication setup to meet the growing demands
of today’s communication
- Add-Drop Mux within the entire length of fiber such that data can be injected or extracted
at several points
-EDFA to increase the distance further
TYPES OF WDM:
- CWDM - Coarse Wavelength Division Multiplexing
-DWDM - Dense Wavelength Division Multiplexing
MODEL GRAPH:
TABULATION:
S.NO
AMPLITUDE(V)
TIME PERIOD(µS)
PROCEDURE:
1. Make the connection as shown in block diagram
2. Set the waveform pattern to wave2 in TTL Gen using wave switch.
3. Observe the AMP output FORX-500.
WDM Multiplexing:
4. Block diagram shows the data corresponding to each wave length and the output of
FORX-500.
5. The optical power seen by the photo detector to start with is due to 1550nm
wavelength corresponding to logic 1 data and hence the output of FORX-500 is at a
level marked by level1 till the point marked as A is reached.
6. When the point A is reached the photo detector sees an additional optical power due
to 1310nm wavelength corresponding to logic1.
WDM Demultiplexing:
7. The multiplexed wavelengths is separated using another WDM13-15 coupler
(WDM2) and connected to receivers.
8. 1550nm optical signal is now available at the arm marked 1550nm in WDM2
9. Similarly 1310nm optical signal is now available at the arm marked 1310nm in WDM2
10. The photo detector in the receiver FORX-500 is now seeing the optical power
corresponding to only one wavelength and converts it to appropriate electrical signal
DEMULTIPLEXING of WDM:
RESULT: