Download ULTRA splice ,fiber , cleaver, blade, general rubbing alcohol, tex

ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
AIM:
To Study the VI characteristic of the FO-LED
APPARATUS: Trainer kit, CRO, Patch chord
THEORY:
Preparatory Information:
Light source for fiber optics act as light transmitters and, consequently , must
meet certain requirements if they are to be acceptable for the purpose.
First, their light must be as nearly monochromatic (Single frequency) as
possible. Most light source are not single frequency, but emit light at several
frequencies over a band or portion of the spectrum, which may be quite broad.
A few sources such as gas ionization lamps, light emitting diodes, and lasers
emit light over a much narrower portion of the spectrum.
The light emitting diodes find a prominent place in fiber communication
because of the following advantages:
1. Simpler Fabrication
2. Cost
3. Reliability
4. Generally less temperature dependence
5. Simpler drive circuitry
6. Linearity
The LEDs for use with fibers are typically made using a solid solution of
gallium arsenide (GaAs) as the semiconductor base, with various doping
elements such as phosphorous (P), indium (In) and aluminum (Al) used to form
the p-and n-regions.
The FO LED operates on the principle of spontaneous emission of radiation in
the visible and infrared regions of the spectrum from a forward biased p-n
junction. The normally empty conduction band of the semiconductor is
populated by electronics injected into it by the forward current through the
junction and light is generated when these electrons recombine with holes in the
valence band to emit a photon (light).
PROCEDURE :
1. Connect 0-2V range DC voltmeter between B3-B2
2. Connect 0-200 mA range DC Ammeter between B1-B2
3. Initially adjust FO-LED current to minimum. Turn VR6 to extreme
clockwise
4. Push the MEASURE switch SW1. Note the ammeter and voltmeter
5. Slightly increase FO-LED current by varying VR6. Note the ammeter and
voltmeter reading by pushing switch SW1.
6. Repeat the procedure 3 in steps till FO-LED current in maximum.
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
7. Plot the I-V graph
OBSERVATION :
S No.
FO-LED Voltage
FO-LED Current
1mA
25mA
RESULT: V-I characteristics of given FO-LED was plotted.
PRECAUTIONS:
1) Do connections properly.
2) Reading should be taken carefully.
3) When trainer kit is not in use switch off the mains.
FREQUENTLY ASKED’S QUESTION :
1.What kind of optical source is suitable for multimode fibres?
2. Give a comparison of LED and LASER Diodes.
3. What is the function of measure switch in this experiment?
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
AIM:
To install and use ULTRA splice.
APPARATUS REQUIRED:
ULTRA splice ,fiber , cleaver, blade, general rubbing alcohol, tex wipe pad .
THEORY:
SPLICE: A fiber splice is a permanent or semi permanent joint between two fibers. These are
typically used to create long optical links or in situations where frequent connections or
disconnections are not needed
ULTRA splice : That is being used in this experiment is a high performance , low cost , easy
to install , fully mechanical Fiber optic splice. It employs a visible glass capillary alignment
member which is pre loaded with index matching gel . The user can inspect the fiber location
during fiber installation. The splice is tunable and reusable. Major problem with ULTRA
splices’ installation procedure is that it keeps breaking into the splice, reason being that the
gray locking nut on the splice is being twisted out too far during the installation process.
FEATURES & BENEFITS of ULTRA splice
 It limits the amount the gray locking nut can be rotated.
 Reduces the fiber breakage.
 Automatic setting for 900m buffers.
Specification: Length –51.5mm , Height - 9mm , Width –6mm , Colour – light grey.
Construction of ULTRA splice:
main body
Splice housing
Fiber
Collet
Locking nut
Blue tube
The body of the module has a cradle that holds the splice’s main body and there are slots at
either ends of the module on which the collet rests. This design limits the amount by which the
gray locking nut can be twisted /opened .Thus operator cannot twist the locking nut too far
thereby limiting chances of any fiber breakage.
Gray locking nut and collet have same mechanical workings as an ordinary hand drill.
When gray locking nut is twisted in the counter clockwise direction(left) , the internal collet
opens in order for larger diameter buffer sizes to be accommodated. When twisting the gray
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
locking nut towards the clockwise direction , (right) , it closes the internal collet onto the
buffer. This action grabs the buffer.
PROCEDURE:
Preparation, cleaning and cleaving the fiber :
1.
2.
3.
4.
5.
6.
7.
For this we use an adjustable cleaver for cleaving the fiber. The fiber should be cleaved
to about a seven (7) millimeter length. Any longer (more than 9 millimeters) the fiber will
pass through the glass capillary, and the other side will not be able to be inserted.
After cleaving we clean both ends of the fiber we intend to use with general rubbing
alcohol and a Tex Wipe Pad, then cleave the end(s) to the proper length of about 7
millimeters. Now we place prepared fiber(s) in a safe location, away from unsanitary
conditions.
The ULTRA splice comes pre-adjusted for 250 micron buffers.
a) If working with 250 micron buffers, we do not twist the gray locking nut at all, the
ULTRA splice has been set to accommodate the buffer size during factory
assembly.
b) If working with over 500 micron buffers, we proceed as follows:
i) The Blue Tube is removed
ii) Gray Locking Nut is opened In the counter clockwise direction until the“bone
colored” insert slightly moves back and forth. This action assures that the
Collet (bone colored insert) is completely open, and is ready to accept the
larger diameter buffer.
The gray locking nut and collet have the same mechanical workings as an ordinary hand
drill. When the gray locking nut is twisted in the counter clockwise direction (left), the
internal collet “opens” in order for larger diameter buffer sizes to be accommodated.
When twisting the gray locking nut towards the clockwise direction (right), it “closes” the
internal collet onto the buffer, this action “grabs” the buffer.
Now that fiber end (s) are cleaved, and the ULTRA splice is set to accommodate
required buffer size (if 250 micron are being used, no adjustment should have been
necessary) the ULTRA splice can now be installed.
Now the ULTRAsplice is held with the Visible Glass Capillary (in the middle of the
splice) facing toward us. The previously cleaved fiber is retrieve, and we begin to insert it
into the splice by placing the fiber into the Blue Tube (If UNDER 500 micron buffer is
used) OR the “bone colored” Collet (if OVER 500 micron buffer used). We gently insert
the fiber through the hole of the Collet (or Blue Tube) , such that we should be able to
feel the buffer being “grabbed”. Once we get a feelof the buffer being grabbed, the fiber
end is close to the entrance of the glass capillary. We should be able to see the visible
glass capillary.
If cleaved to the proper length of 7 millimeters, the buffer stops “ automatically THE
FIBER SHOULD BE IN THE MIDDLE OF THE GLASS CAPILLARY or close as
possible to the center. Once the FIBER is in the middle, the gray locking nut is twisted
closed (clockwise direction) until the gray locking nut is hand tight. We proceed to the
other end. Now we start inserting the other fiber end in the same manner as the first end,
however, careful attention is given to the following:
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
a) The pre-loaded index matching get act like a Hydraulic Piston when the other fiber
is being inserted, therefore, we insert the second fiber carefully, giving the gel
enough time to “mold” itself around the fiber.
b) The fiber should stop automatically, however, depending on the accuracy of the
cleave length, the fiber could be too long, and possibly break if pushed too hard. So
we WATCH THE FIBER BUTT UP TO THE OTHER FIBER END. Through the
visible capillary.
Once we have inserted the second fiber to our satisfaction, the gray locking nut is
twisted closed (clockwise direction) and the ULTRAsplice installation is now
complete.
8. Tuning
If loss is occuring, we can simply “Tune” the ULTRA splice as follows :
a) We twist ONE END OPEN (counter clockwise direction)- Not more than ½
turn.
b) Gently pull back (slightly) and twist the buffer, possibly even pushing it closer to the
other fiber, until an achieved loss is obtained. If we open both ends, and push the
fibers together (back and forth), we can possibly damage your cleave. It is
recommended that only one end is loosened while tuning.
c) Twist the Gray Locking nut closed (clockwise direction until hand tight)
PRECAUTIONS :
1. An adjustable cleaver is used for cleaving the fiber. The fiber should be cleaved to
about a seven (7) millimeter length. Any longer (more than 9 millimeters) the fiber
will pass through the glass capillary, and the other side will not be able to be
inserted.
2. After cleaving clean both ends of the fiber we intend to use wipe with general
rubbing alcohol and a Tex Wipe Pad, then cleave the end(s) to the proper length of
about 7 millimeters. Now prepared fiber(s) in a safe location, away from unsanitary
conditions.
a) ULTRA splice must not catch any dirt or be contaminated
c) If working with 250 micron buffers, do not twist the gray locking nut at all, the
ULTRA splice has been set to accommodate the buffer size during factory
assembly.
d) If working with over 500 micron buffers, proceed as follows:
i) Remove the Blue Tube
ii) Open the Gray Locking Nut In the counter clockwise direction until the “bone
colored” insert slightly moves back and forth. This action assures that the Collet
(bone colored insert) is completely open, and is ready to accept the larger
diameter buffer.
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
FREQUENTLY ASKED QUESTION
Q1
At what places in a fiber optic link are fiber interconnection required?
Q2
What factors need to be considered in making or evaluating such splices.
Q3
Name the various splicing methods used.
Q4
Name the splicing technique you used in this experiment.
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
AIM :
To Study Time Division Multiplexing (TDM) with fiber communication system
APPARATUS USED : TDM Trainer Kit, CRO, patch chords, multimeter.
THEORY:
The given fiber optic communication system also supports Time division
Multiplexed signal where the TDM output of three different frequency analog
signals.
Since the signals are bipolar and the optical source can respond to only bipolar
signals they are first level shifted in a DC level shifter where the bipolar signals are
converted to unipolar. The TDM signal is then intensity modulated and then
conveyed on the optical fiber. At the receiver end, a photo detector detects the
signal from the light falling on it in the form current .
A Current–Voltage (I-V) Amplifier converts the current signals to voltage and
amplifies them. This is then fed to a Demultiplexer where the individual signals are
obtained.
PROCEDURE :
1. Connect TDM (A5) to FO-LED (A)
2. Connect Photo Transistor output (C) to the input of the I-V Amplifier (D2)
3. Terminate the fiber optic cable both at the source and the detector.
4. Adjust the amplitudes of all source DC,250 Hz, 500 Hz and 1 KHz to minimum
OBSERVATION:
1. Observe the waveforms at TDM out (A5) and I-V Amplifier input (D2)
2. It can be observed that (D2) duplicating (A5), except FO reduced amplitude and
rounding off rise times.
3. Observe the demultiplexed waveform at the output of Demultiplexer. The
Demultiplexer output will be Sample and Hold version of input source.
4. Observe the reconstructed signal at the output of Low Pass Filters at CH0,CH1
5. CH2 and CH3.
RESULT:
Time division multiplexing was accomplished on the given fiber communication
system and waveforms at various points as mentioned were observed.
PRECAUTIONS:
1) Always make connection properly in breadboard
2) All connections should be tight.
FAQ’S
1. Explain TDM with diagram.
2. Differentiate between TDM & FDM
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
AIM :
Measurement of Numerical Aperture
THEORY :
Numerical Aperture refers to the maximum angle a which the light incident on the
fiber end is totally internally reflected and is transmitted properly along the fiber . The
cone formed by the rotation of this angle along 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 refracted out of the fiber.
Consideration in NA measurement
(1) It is very important that the optical source should be properly aligned
with the cable and the distance from the launched point & cable be
properly selected to ensure that the maximum amount of optical power is
transferred to the cable.
Equipments
(1) Numerical Aperture measurement Jig.
PROCEDURE:
(1)
(2)
(3)
(4)
(5)
(6)
Connect power supply to the board
Connect the frequency generator’s 1 KHz sine wave output to input of
emitter 1 circuit . Adjust its amplitude at 5V p-p
Connect one end of fiber cable to the output socket of emitter 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.
Hold the white screen with 4 concentric circles (10,15,20 & 25 mm
diameter) vertically at a suitable distance to make the red spot from the
fiber coincide with 10 mm circle.
Record the distance of screen from the fiber end L and note the diameter
W of the spot.
Compute the numerical aperture from the formula given below
N.A =
W___
√4L2 +W2
= Sin θ max
(7) Vary the distance between in screen and fiber optic cable and make it
coincide with one of the concentric circles. Note its distance
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
(8) Tabulate the various distance and diameter of the circles made on the
screen and compute the numerical aperture from the formula given above
Inferences
The N.A recorded in the manufacturer’s data sheet is 0.5 typical the variation in the
observation is due to fiber being under filled the Acceptance Angle is given by 2
Sin θ max.
The deviation from the Data sheet is again due to fiber being filled.
OBSERVATION TABLE :
S no.
Distance
of spot
center
from fiber
d (cm)
Vertical
diameter
r (cm)=
Horizontal
diameter
(MR+PN)
4
NA =
r
(r +d2)1/2
2
MR (cm)
PN (cm)
RESULT:
Study of numerical aperture was done using 660 nm wavelength
of radiation and it was found to be--------------PRECAUTIONS:
1. Check to see that all jumper settings have been made before
starting the experiment
2. Ensure that fibre is screwed neither too tight nor too loose in the
jig.
3. Make precise measurement of d & r.
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
FAQ’S:
Q.1 Define NA
Q.2 What happens as distance d of spot center from fiber tip
is increased
Q.3 What are the practical limits of NA.
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
AIM :
Study of pulse width modulation & demodulation.
OBJECTIVE :
The objective of this experiment is to study the circuit action of pulse width
modulation and demodulation over fiber optic digital link.
EQUIPMENT:
Kit fiber link –A
20MHz dual channel oscilloscope
1MHz function generator
1meter fiber cable
THEORY:
PULSE WIDTH MODULATION
This technique of modulation controls the variation of duty cycle of the square
wave (with some fundamental freq.) according to the input modulating signal.
Here the amplitude variation of the modulating signal is reflected into ON period
variation of square wave. Hence it is also called as technique of V to T
conversion.
The circuit is divided into two stages. First one is the circuit built around OP-AMP
741.This is unity gain non inverting amplifier designed as level shifter. When there is
no input signal the output of the amplifier simply follows the voltage at inverting input
terminal, with inverted polarity. This is necessary because PWM chip requires only
positive polarity signal. Now the input signal fed to non-inverting terminal overrides
this shifted voltage.
This signal is now fed to second part of the circuit. This is specialized for
regulating PWM. This primarily consist of one fixed frequency oscillator whose freq. is
decided by timing register Rt & capacitor Ct. The regulation is given by the formula
F=1.18/(Rt* Ct)
Here F is in KHz ,R is in Kohm ,C is in μF.
Also an error amplifier comparator and flip-flop are important
functioning parts internal to the IC. When no input signal is given to the error amplifier
the output oscillates with the same frequency decided by the external RC network.
When input is given to the error amplifier a linear charging of the Ct results in a linear
voltage ramp, which is then fed to the comparator. This provides the linear control of
the output of the pulse width. The amplified output is compared with the linear
charging voltage at Ct, resulting in the modulated pulse at the output of the high gain
comparator. Thus we get the PWM. For more details please refer to the SG 3524 data
sheet.
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
PULSE WIDTH DEMODULATION
The input signal is PWM, so the ON time of the signal is changing according to the
modulating signal. In this demodulation technique , during the on time of PWM signal
one counter is enabled. At the end of ON time, counter outputs a particular count,
which directly corresponds to the amplitude of input signal. Then this count is fed to a
DAC. The output of DAC corresponds to the amplitude of input signal. Thus train of
varying pulse widths gives varying count values and accordingly DAC gives outputs,
which is directly proportional to amplitude of input signal. This is then filtered to get
original signal. Thus at the output we get original modulating signal extracted from
PWM wave.
PROCEDURE :
1.
Slightly unscrew the cap of IR LED SFH 450V.Do not remove the cap
from the connector. Once the cap is loosened, insert the fiber into cap and
assure that the fiber is properly fixed. Now tighten the cap by screwing it
back. Keep pot P3 at minimum.
2.
Make the jumper connections as shown in jumper block diagram. Connect
the power supply cables with proper polarity to kit. While connecting this,
ensure that the power supply is off. Remove the JP7 & JP8.
3.
Connect the signal generator between the AMP I/P and GND posts or
SINE wave output to AMP I/P to feed the analog signal to the pre
amplifier.
4.
Connect the signal generator between the PWM I/P and GND posts.
5.
Keep the signal generator in sine wave mode & select the frequency of
1-10 Hz with amplitude of 1.5V p-p {max} for proper observation
of
phenomena.
6.
Switch on power supply & signal generator.
7. Observe PWM signal at PWM O/P post. Variation in width of square wave
is kept very low. If the frequency is high then due to persistence of vision
only blurred band in the waveform will be observed. If the signal
generator is OFF, only square wave of fundamental frequency and fixed
ON time will be observed and no width variation is present
8.
Short the following posts with the links provided.
PPM O/P and BUF I/P BUF O/P and Tx I/P
9. Connect the other end of the fiber to detector SFH551V very carefully as per
the Instructions in step1.
10. Observe the received signal over fiber at TTL O/P. It should be exactly
similarly to the signal available at PWM O/P post.
11. Short TTL. O/P post to DEMOD I/P (PPM) post.
12. Vary I/P frequency (not more than 4 Khz) & observe the demodulated
signal at DEMOD. O/P post.
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
13. Short DEMOD o/p to FILTER I/P post & observe o/p post.
OBSERVATION :
Observe the output at the following posts and draw the waveforms.
Input signal
PWM output
TTL output
DEMOD output
FILTER output
RESULT: Pulse width modulation and de modulation was studied.
PRECAUTIONS :
1. Do not switch ON the power supply until all the connections
have been made.
2.Check that all the jumper settings have been done before starting
the experiment
FAQ’S:
1. Study the PWM circuit given in the manual understanding the
functions of respective components.
2. Try to see the effect of increasing the signal frequency beyond 10
HZ
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
AIM:
Study of bending loss & measurement of Propagation(or attemuation) Loss in given
Optical Fiber on Fiber optic Trainer ST 2502.
APPARATUS USED:
Fiber optic trainer ST 2502, C.R.O, C. R.O Probes, optical fiber
THEORY
:
STUDY OF BENDING LOSS
When ever the condition for angle of incidence light is violated the
losses are introduced due to refraction of light . This occurs when fiber is
subjected to bending . Lower the radius of curvature more is the loss.
PROCEDURE :
1. Connect power supply to board
2. Make the following connection as shown in Diagram.
(b) Function Generators 1 KHz sine wave output to Input 1 socket of
emitter 1 circuit via 4mm lead.
(c) Connect Detector 1 output to amplifier 1 input Socket via 4mm
lead.
3.Switch ON the power supply
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 1 of
Emitter 1
5.
Observe the output signal from detector t.p. 10 on CRO
6.
Adjust the amplitude of the received signal as that of transmitted one with the help
of gain adjust pot AC Amplifier block. Note this amplitude and name it V1.
7.
Wind the FO cable on the mandrel and observe the corresponding AC
amplifier on CRO. It will be gradually reducing showing loss due to bends.
8.
Again observe the output at t.p. 10 as you go on increasing the number of
turns on the mandrel.
OBSERVATION:
Output at detector without bending
S.No No. of turns
Output Voltage
---------Volts
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
RESULT:
Bending losses were observed by changing the radius of curvature of fiber
PRECAUTIONS:
1 Do not the fiber too much to cause a breakage.
2 Count the number of turns carefully.
3 The fiber must be fixed properly.
FAQ’S:
Q1 Differentiate between Macrobending and Microbending losses.
Q2 What is the effect of increasing the radius of curvature of fiber.
Q3 What is mode splitting?
THEORY :
MEASUREMENT OF PROPAGATION(OR ATTEMUATION) LOSS
IN GIVEN OPTICAL FIBER ON FIBER OPTIC TRAINER ST 2502.
Attenuation is loss of power. During transit, light pulses loses
some of their photons, thus reducing their amplitude. Attenuation for a fiber
is usually specified in decibels per kilometer. For commercially available fibers
attenuation ranges from 1 db/km for premium small-core glass fibers to over
2000 db/km for a large core plastic fiber. Loss is by definition sign. The basic
measurement for loss in a fiber is made by taking the logarithmic of the input
power (P1) to the output power (Po).
 (dB) = 10 log 10 P1 /Po
Where  is loss in dB / Meter
PROCEDURE :
2. Connect power supply to board
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
3. Make the following connection as shown in Diagram .
(a) Function Generators 1 KHz sine wave output to Input 1 socket of
emitter 1 circuit via 4mm lead.
(b) Connect Detector 1 output to amplifier 1 input Socket via 4mm
lead.
4. Switch ON the power supply
5. 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 in put 1 of Emitter 1
6. Observe the output signal from detector t.p. 10 on CRO
7. Adjust the amplitude of the received signal as that of transmitted one with
the help of gain adjust pot AC Amplifier bloch. Note this amplitude and
name it V1.
8. Now replace the previous F.O cable with 1 m cable without disturbing any
previous setting.
9. Measure the amplitude at the receiver side again at output of amplifier 1
socket t.p 28 . Note this value end name it V2 .
V1 / V2 = e- (L1 + L2)
Where  is loss in nepers / meter
1 neper = 8.686 dB
L1 = length of shorter cable (0.5m)
L2 = Length of longer cable (1 m)
OBSERVATION:
Voltage at tp10 with 0.5 m cable-------- volts.
Voltage at tp10 with 1.0 m cable-------- volts\
CALCULATION:
Determine value of  using V1 / V2 = e- (L1 + L2)
RESULT:
Propagation (or attenuation ) losses were measured for the given optical
fiber and was found to be-----------nepers/meter.
PRECAUTIONS:
1 Fix the fiber properly.
2 Amplitude of received signal at tp 10 must be properly adjusted on CRO
to be the same as transmitted one.
3 Calculations must be done accurately.
4 Optical fiber must be handled carefully.
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
FREQUENTLY ASKED QUESTION’S:
Q1 What are the causes of attenuation in the fiber?
Q2 Name the various types of losses occurring in an optical fiber.
Q3 What is the amount of attenuation offered by 1300 nm fibers?
Q4 What is the gain offered by gain adjust pot on in AC amplifier block of the kit
you are using?
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
AIM : Setting up 650 nm Fiber Optic Digital Link using Fiber optic Trainer ST 2502.
APPARATUS USED:
Fiber optic trainer ST2502 , C.R.O, C. R.O Probes ., optical fiber.
THEORY
:
Digital signal can be transmitted over fiber optic cable and can be
reproduced at the receiving end . The same LED, Detector and fiber of the
kit can be configured for digital application to transmit binary data over
fiber. Thus basic elements of the link remain the same for digital
applications.
Vcc
LED
Vin
Above Fig 1show a simple drive circuit for binary digital transmission consisting
a common emitter saturating switch.
PROCEDURE :
1) Connect the power supply to the board.
2) Ensure that all switch faults are off.
3) Make the following connections.(as shown in Diagram )
a. Connect the Function Generator 1 KHz square wave output to emitter 1’s
input
b. Connect the Fiber optic Cable between emitter output and detectors input
c. Detector 1’s output to comparator 1’s input
d. Comparator 1’s output to A.C Amplifier 1’s input
4) On the board, switch emitter 1’s driver to Digital mode.
5) Switch ON the power
6) Monitor both the inputs to comparator 1 (tp 13 & 14). Slowly adjust the
comparators bias preset, until DC level on the input (tp. 13) lies mid way between
the high and low level of the signal on the positive input (tp.14)
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
7) Observe the input to emitter 1 (t.p 5) with the output from A.C Amplifier 1 (tp.28)
and note that the two signals are same.
OBSERVATION:
Observe the waveforms at following test points.
tp 13
tp 14
tp 5
tp 28
Draw the observations made and the input supplied.
RESULT:
Fiber optic digital link was set up using 650 nm fiber.
PRECAUTIONS:
1 Fix the fiber properly.
2 Check that emitter 1’s input is 1 KHz square wave.
3 Handle the fiber with care.
4 Adjust comparators bias preset carefully.
FREQUENTLY ASKED QUESTION’S:
Q1 Why do you call the given link as a digital link.
Q2 Should there be a difference between transmitted and received
signal?
Q3 What are the advantages of a digital link?
Q4 Should the transmitted signal be a TTL signal necessarily?
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION
SUB : OPTICAL COMMUNICATION
AIM`:- Preparation and application of ST (Straight Tip) connector
APPARATUS USED:Cable Stripper, Fiber Stripper (No-Nik Red), Scissors, Scribe Tool, Polishing
Puck, Polishing Plate, Microscope, Epoxy Mixer, Hand crimping tools, Polishing
pad, Epoxy Applicator, Epoxy, 5-m Polishing Film, 1-m Polishing Film, 0.3-m
Polishing Film, Isopropyl Alcohol, Tissue Pads, Cotton Swabs
THEORY:
Demountable fiber connectors are more difficult to achieve than optical
fiber splices . This is because they must maintain similar tolerance requirements to
splices in order to couple light more efficiently , but they must accomplish this in a
removable fashion.
Connector design must allow for repeated connection and disconnection
without problems of fiber alignment which may lead to fiber degradation in the
performance of the transmission line at the joint.
Connectors are used in:
(a)
Fiber termination (to protect and locate fiber end)
(b)
Fiber end alignment to provide optimum optical couplig.
The outer shell (that maintains fiber connection and alignment, protects fiber
ends from environment and gives adequate strength at joint) ST (Straight tip )
connector is a type of cylindrical sleeve ferrule connector used commercially for
both multimode and single mode fiber termination. An ST series multimode fiber
exhibits an optimized cylindrical sleeve with a cross section designed to expand
uniformly when the ferrules are inserted. Hence the constant circumferential
pressure provides accurate alignment, even when the ferrule diameters slightly
differ.
Figure 1 shows the ST connector which consists of connector body, strain-relief
boot, crimp eyelet, and dust cover. PVC tubing (option) is used only with cable
having a Jacket diameter of 2.5 mm (1 in) or less. The connector can be used with
125 m or 140 m glass fiber cable with a cable diameter ranging from 2.0 to 3.0
mm (0.08 to 12 in.)
PROCEDURE:
An ST connector preparation involves the following steps.
1
Preparation of fiber
2
Preparation of epoxy
3
Termination procedure
4
Crimping
5
Polishing of fiber
6
Inspection of fiber
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1. PREPARING FIBER
Jacketed Cable
Slide the strain-relief boot(small end first) over the cable. See figure 1. Slide the
crimp Eyelet onto the cable(rolled end first) see figure I. Mark the cable jacket at
the ‘X’ dimension shown in figure 2A , then using Cable Stripper strip the cable.
Trim the strength members as close as possible, with scissors to the end of the cable
Jacket at the ‘X’ dimension. Mark and strip the cable jacket to the ‘Y’ dimension.
The correct length of strength members (approximately 6.6mm[2.6 in]) will now be
exposed. See figure 2A. Mark and strip the fiber buffer to the dimension shown in
figure 2A. It is recommended to use No-Nik tool. Evenly “fan out” strength
members from the buffer. Clean the fiber thoroughly using alcohol-soaked pad.
Buffered Cable.
Slide the strain-relief boot, crimp eyelet, and the clear (900-m) or blue (250 m)
small tubing onto the fiber before stripping buffer from the fiber. See figure 1.
NOTE
It might be more convenient to insert the tubing into the eyelet before placing the
individual components onto the fiber. Mark and strip the fiber to the dimensions shown in
figure 2B.
2. PREPARING EPOXY
Solid Epoxy is easy to work with because it comes in packs with pre measured
components. It will cure in 24 hours at 25o C [77o F]; or with the use of Epoxy
curing Oven, it will cure in 2 hours at 65o C [150o F) or 10 minutes at 43o C[110o
F].
Liquid Epoxy are ready to use directly & cure fast.
Preparing Solid Epoxy
Remove the separating clip from the epoxy package and mix the epoxy
thoroughly for 20 to 30 seconds. Use of Epoxy Mixer is recommended for through
mixing of the components.
Install the needle tip on Epoxy Applicator (syringe). Make sure it is secure.
Remove the plunger.
Cut the epoxy packet open and squeeze the epoxy into the back of the
applicator. Replace the plunger. Hold the applicator vertically with the needle
pointing up and slowly push on the plunger until the entrapped air escapes and a
head of epoxy appears at the tip.
NOTE
An alternative method is using the epoxy is to remove the tip of the epoxy
applicator by twisting it one-quarter turn and pulling it away fro the body of the
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applicator. Put the open end of applicator into epoxy and pull back on plunger to draw
epoxy into the applicator. See Figure 3. Put the tip on the applicator make sure it is firmly
secured. Hold the applicator vertically and slowly push on plunger until a bead of epoxy
appears at the tip.
3. TERMINATION PROCEDURE
Hold connector with knurled end up. Insert the tip of the epoxy applicator until
it bottoms Against the ferrule. See Figure 4A.
Inject epoxy until a small bead, approximately .76mm[0.30 in] in diameter,
appears at the ferrule end. Do not let the bead get too large or smear.
Withdraw the applicator while simultaneously injecting epoxy into the bore until it
is approximately three-quarters full.
Apply a small drop of epoxy to the outside(knurl) of the body, (see Figure 4B)
Do not get
any epoxy on the nut/spring area.
Using a rotating motion, gently push the connector onto the fiber until it
bottoms. Do not force the fiber. When it is located correctly, the fiber will enter the
connector freely. The fiber must extend out the front of the connector. See Figure
4C.
Twist the connector and move it back and forth axially about 1.25mm [0.60 in]
to distribute the epoxy.
Slide the crimp eyelet toward the connector until it contacts the connector
shoulder, trapping the strength members against the knurl. If PVC tubing is used, or
the small tube with plastic fiber, slide it under the crimp eyelet until the tubing
bottoms.
Termination procedure (Liquid Epoxy)
The Primer bottle is without needle.
Remove white cap of epoxy bottle and replace with needle cap provided.
Apply Epoxy with needle inside the connector and ferrule.
Dip the fiber only in the primer and keep dry for 30 seconds.
Insert the cable as per earlier procedure. (solid epoxy)
4. CRIMPING
CAUTION
Be sure to crimp the connector before the epoxy cures. Install the die assembly
in hand tool. (Already done in your case) Squeeze the handless until the ratchet
releases. Open the tool FULLY. Place the Connector in the appropriate position in
the dies. See Figure 5
If terminating buffered cable, slide the eyelet over the connector and small
tubing before Crimping. Crimp the eyelet by squeezing the tool handles until the
ratchet releases. Allow the tool handles to open FULLY, then remove the connector
from the tool.
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NOTE
When using clear tubing, rotate connector 90o and crimp again. After
terminating buffered fiber, slide the strain-relief boot over the tubing and onto the
Connector. Clean unwanted epoxy from the hand tool and die assembly.
Applying the Strain Relief Boot
If using the strain-relief boot, slide the boot over the eyelet and connector
shoulder. Make Sure the strain relief boot slides over the connector shoulder and
snaps into place.
Curing
Hang the connector vertically with the tip down and cure it.
5. POLISHING THE FIBER
Polishing may be done by hand polishing puck.
Scribing
Carefully remove the protective sleeve from the connector.
Firmly support the connector assembly.
Lightly scribe the fiber with the beveled edge of Scribe. After scribing, pull the fiber
straight away from the connector. See Figure 6.
Insert the connector into the polishing puck see Figure 7.
Polishing Procedure.
Place the 5-m polishing film on top of the polishing pad.
CAUTION
Always place the polishing bushing on a clean area of the polishing film. Never
start polishing on or across a dirty section of the film.
Holding the polishing bushing, not the connector, start polishing very lightly.
Polish in an elongated figure-8 pattern. See figure 8. Initially a small amount of
exposed fiber will be worn away. This is indicated by a narrow white trace on the
film. As the exposed fiber wears away, the trace will widen and darken, indicating
that epoxy is being removed. At this point a slight download force may be applied
while polishing. Check the tip often and stop polishing on the 5-m film when the
epoxy is medium blue and about one-third the ceramic diameter in size.
CAUTION
When polishing ceramic tip connectors, it is essential that not all of the epoxy is
removed when using the 5-m film. Polishing on 5-m film must stop when the
epoxy changes to light blue color or rubbed sufficiently.
lean the polishing bushing and connector assembly with an alcohol-dampened
tissue.
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Using the 1-m film on the polishing pad polish the connector until only a
very light blue trace of epoxy remains. Clean the polish bushing and connector
assembly with an alcohol-dampend tissue. For end finish, using the 0.3-m film on
the polishing pad, polish the connector until all the epoxy is gone. Use only a light
force on the polishing bushing. Do not over polish. Use a magnifier to examine the
tip. Stop polishing as soon as all the proxy has been removed.
6. INSPECTING THE FIBER.
DANGER
Never inspect or look into the end of a fiber when optical power is applied to
the fiber. The infrared light used, although it cannot be seen, can cause injury to the
eyes.
Inspect the polished ceramic tip with the microscope. See figure 9. Check for
the following:
Scratches on the fiber indicate a need for further polishing with 1 or .3 m
polishing film.
Small pits in the outer rim of the fiber are permissible. Large chips, or chips in
the center of the fiber mean either that further polishing is needed or the termination
is unaccepted and the fiber must be re-terminated.
Small chips in the outer rim of the fiber are permissible. A large fracture at the
edge indicates the fiber was broken below the surface of the capillary during
scribing or initial polishing.
Place the dust cover over the connector if the connector is not going to be used
immediately.
RESULT:
The ST connector for given fiber (125m or 140m )was prepared using various
steps as mentioned in the procedure
PRECAUTIONS:
1
2
3
4
Always wear safety glasses when working with optical fibers
carefully dispose fiber ends because the fibers create silvers that easily
puncture the skin and cause irritation.
Never inspect or look into the end of a fiber when optical power is applied to
the fiber. The infrared light used, although it cannot be seen, can cause injury to
the eyes.
When connector is not in use, place dust cover over the connector.
FREQUENTLY ASKED QUESTION ’s
Q1 What is the difference between splice and a connector?
Q2 What are the various basic types of fiber connectors?
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Q3 What is the purpose of index matching material/gel in the connector?
Q4 What do you understand by expanded beam connectors?
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AIM :
To study the setting up fiber optic Analog Link.(ST2502)
OBJECTIVE :
The objective of this experiment is to study an 650nm fiber optic link. In
this experiment you will study the relationship between the input signal and
received signal.
APPARATUS REQUIRED:
Fiber optic trainer kits, C.R.O, C. R.O Probe.
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, a transmitter,
an optical fiber and 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 takes the 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 transmitter & the electrical system supplying the data . The driver
provides electrical power to the optical source . Finally, the optical source
converts the electrical current to the light energy with the same pattern.
Commonly used optical source are light emitting diodes (L E D s) and Laser
beam. Simple L E D circuits, for digital and analog transmission are shown
below.
Fig. 18 show Trans conductance drive circuits for analog transmission –
common emitter configuration. The transmitter section comprises of
(1)
Function Generator
(2)
Frequency modulator &
(3)
Pulse width modulator block.
The function generator generates the input signals that are going
to be used as information to transmit through the fiber optic link. The output
voltage available are 1Khz sinusoidal signal of adjustable amplitude, and fixed
amplitude 1 KHz square wave signal. The modulator section accepts the
information signal and converts it into suitable form for transmission through the
fiber optic link.
THE 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
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the far end of the fiber optic links. The optic fiber plugs into the connectors
provided in this part of the board. Two separate links are provided.
THE RECEIVER:
The Comparator circuit, Low Pas Filter , Phase Locked Loop,
AC Amplifier Circuits form receiver on the board. It is able to undo the
modulation process 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.
PROCEDURE :
1) Connect the power supply to the board.
2) Ensure that all switched faults are off.
3) Make the following connections.(as shown in Diagram)
(a) Connect the Function Generator 1 KHz sine wave output to emitter 1’s input
(b) Connect the Fiber optic Cable between emitter output and detectors input
(c) Detector 1’s output to AC Amplifier 1 input
4) On the board, switch emitter 1’s driver to Analog mode.
5) Switch ON the power
6) Observe the input to emitter 1 (t.p 5) with the output from A.C Amplifier 1
(t.p.28) and note that the two signals are same.
RESULT : Fibre optic analog link was set up
PRECAUTION :
1) Before starting the experiment check to see that all jumper settings have
been made.
.2) Do not turn on the power supply until all connection have been made.
FAQ’S
1) What does gain frequency plot resembles a HPF or BPF.
2) Identify the type of detector used.
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EXPERIMENT
AIM :
Computer to Computer communication using RS232 interface via Fiber Optic Link.
APPARATUS REQURIRD:
1. Two PC’s 2. Fiber Optic Kit
THEORY :
There are 2 Fiber optic Links provided on ST2502 trainer .We shall utilize these two link
to communicate from one PC to other & via-versa. That means it is Duplex system of
communication using fiber optic link. The Software developed by Scientech will help to
transmit & receive messages from the computers . This software is supplied with trainer
and is self explanatory and hardly need any practice. The Directory is FIBCOMM &
command is fibcomm.
You will need the following:
1. Personal Computer –2No.
486 or Pentium
DOS 6.0 or onwards
3.5 Floppy Drive
2. RS232 cables for connecting PC’s to Trainer –2 Nos.
PROCEDURE :
1. Keep one PC towards left and another towards right ST2502.
2. Load the software in PC1 & PC2 , with the help of the floppy disc supplied.
3. Keep one of the COM port free on each of PC to connect the RS232 cables. Keep
baud rate of both equal, say 57600
4. Switch OFF both the PC’s
5. Make the following connections on the ST2502 trainer.
a. Connect Fiber Link on CH1 (emitter to Detector)
b. Connect Fiber Link on CH2 (emitter to Detector)
c. Connect output of Detector 1 to comparator input
d. Connect output of Detector 1 to comparator input
e. Connect 1khz square wave to input of CH1 (emitter)
f. Keep mode switch of both channels to Digital and all Switched Faults in
OFF position
g. Switch ON the Trainer .Observe input to emitter 1 and output of
comparator 1. Adjust bias of comparator 1 for sq. wave output.
h. Switch 1Khz Sq. wave from the input of CH1 to input of CH2 (emitter)
and adjust comparator 2 bias for square wave output. Switch OFF the
Trainer.
i. Make connections shown in Diagram and Switch ON Trainer. Now your
ST2502 is ready for connection to PC’S . Switch OFF the Trainer.
j. Connect PC1 & PC2 to D type connectors.(Any to any one). Switch on the
PC’s and the Trainers & start working (Directory is FIBCOM & command
is fibcomm.)
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Whatever you type in PC1 will also be received in the receive column of
PC1
And will also be received in the receive column of PC2 simultaneously &
vice versa.
k. Remove any one fiber link. The transmit & receive of that link is
disconnected.
l. Change baud rate of any one PC & you will find that data is not transmitted
. Keep the baud rate same.
m. Reduce the baud rat of Both PC’s & you will see that transmit rate is lower
.Switch OFF the Trainer and PC’s
RESULT:
PC to PC
communication.
communication
was
established
using
RS232-C
serial
PRECAUTIONS :
1. Do not switch ON the power supply until all the connections have been made.
2. Check that all the jumper settings have been done before starting
the experiment.
FEEQUENTLY ASKED QUESTION’S :
1. Explain RS232 serial communication interface.
2. Modify the programs in BASIC to transmit alphabets rather than numerals
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AIM : To study the transfer characteristics between DECTECTOR & SOURCE with simplex
cable
APPARATUS REQURIED : DCLT trainer , patch coeds, CRO
THEORY :
The supplies the required optical energy for modulating the signal to be transmitted
through the fiber optic cable. At the receiver there should be a device on detector whose
function is to convert the received optical signal into an electrical signal. Which is then
amplified before further processing. The role of detector places demands that it must satisfy
very stringent requirements for performance and compatibility.
The following criteria define the importance performance and compatibility requirements for
detectors:
High sensitivity at the operating wavelengths
High fidelity
 Large electrical response
 Short response time to obtain a suitable bandwidth
 A minimum noise introduced by the detector
 Stability of performance characteristic
 Small size, low cost & high reliability
 Low bias voltages
The photo transistor detector has an advantage over the photo diodes since it can provide
internal gain of the optical current . This is achieved through transistor action rather than
avalanche multiplication .
The fig. Below show a symbolic representation of the npn transistor If differs from the
convention bipolar transistor in that base is unconnected , the base collector junction being
photosensitive to act as a light gathering multiplication of primary photo current through the
device


PROCEDURE :
1. Connect 0-20 mA DC ammeter between B5 –B6
2. Connect 0-200 mA DC ammeter between B1 –B2
3. Initially adjust FO_ LED current to minimum, turn VR6. to extreme clock wise.
4. Push the measurement switch SW1 . Note the ammeter readings.
5. Slightly increase FO_LED current by varing VR6 . Note the ammeter & voltmeter
reading by pushing SW1
6. Repeat the procedure 3 insteps till FO-LED current is maximum
7. Plot the graph between photo transistor current and FO-LED current
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OBSERVATION :
S NO.
Photo transistor current
FO-LED current (mA)
1 mA
25 mA
RESULT:
VI characteristics of given FO-LED was plotted
PRECAUTIONS:
1. Do connections properly
2. Reading should be taken carefully
3. When trainer kit is not in use switch off the same.
FREQUENTLY ASKED QUESTION :
1.Is there a difference between transfer characteristic of an ordinary PN junction
diode and that of transfer characteristics of FOLED.
2.Define Responsivity.
2.What is the gain of photo transistor used?