Experiment:
Objective: V-I Characteristics of LED (E - O converter).
Equipments Required:
●
Scientech 2502A Training platform with Power Supply cord.
●
Optical Fiber cable.
●
Connecting probes.
●
Optical power meter.
Connection Diagram:
Theory:
LED’s and LASER diodes are the commonly used sources in optical communication
systems, whether the system transmits digital or analog signal. It is therefore, often
necessary to use linear electrical to optical converter to allow its use in intensity
modulation & high quality analog transmission systems. LED's have a linear optical
output with relation to the forward current over a certain region of operation.
Procedure:
●
Power supply is given to the kit.
●
Emitter 1 block is kept in Digital Mode and connections are made as given above.
●
●
●
●
Voltage bias of comparator 1 is given to the emitter 1 input.
One DMM is connected between input of emitter 1 and ground to read the input bias
voltage.
DMM is connected between +12V supply and input of emitter LED thus it reads the
bias voltage. Vin = (DVM reading)-12
DMM is connected between top of the input of emitter LED and ground thus it reads
the forward voltage (Vf).
If = Vf /1000 mA
Then we vary the bias voltage, so as to vary the forward voltage note the
corresponding forward voltage.
We will connect power meter to output of emitter 1, to read power(in dBm).
Record the values of V, Vfand P.
0
●
●
●
Observations:
Forward
Vin(V) bias
voltage (V)
Forward
current
(mA)
Power
(dBm)
Power (mW)
Graphs:
Conclusion:
Experiment:
Objective: Measurement of Numerical Aperture of optical fiber.
Equipments Required:
●
Scientech 2502A Training platform with Power Supply cord.
●
Optical Fiber cable.
●
Numerical Aperture measurement Jig.
Theory:
Numerical aperture of any optical system is a measure of how much light can be
collected by the optical system. It is the product of the refractive index of the incident
medium and the sine of the maximum ray angle.
NA = ni * Sinθmax (ni for air is 1)
Hence, NA = sinθmax
For a step-index fiber, as in the present case, the numerical aperture is given by
N= (ncore2-ncladding2)
Connection Diagram:
Procedure:
●
Connect the Power Supply cord to Scientech 2502.
●
Connect the frequency generator's 1 KHz, 1Vpp sine wave output to input of
emitter 1 circuit. Adjust its amplitude.
●
Connect one end of fiber 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.
●
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.
●
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.
𝑊
𝑁𝐴 = √𝑊 2


+4𝐿2
The distance from the screen is varied accordingly and coincided with one of the concentric
circles and the distance is noted.
We further tabulate the various distances and diameters on the white screen to compute the
numerical aperture from the aforementioned formula.
Observations:
Width (mm)
Conclusion:
Length(cm)
Numerical Aperture
(NA)
Acceptance angle
(θA)
Experiment:
Objective: Study of Bending Loss.
Equipments Required:
●
Scientech 2502A Training platform with Power Supply cord.
●
Optical Fiber cable.
●
Digital storage oscilloscope with necessary connecting probe.
●
Mandrel (Cylindrical material).
Connection Diagram:
Procedure:
 Scientech 2502A is powered ON using power supply cord.
 Make the circuit connections as follows:
o Sinusoidal signal of 1KHz is generated using the function generator and given as input
to the emitter block.
o Optic Fiber Cable is connected between emitter output and detector input.
o Detector Output is connected to AC Amplifier input.
 Take measurement of amplitude of the output signal at zero turns, 1 turn, 2 turns and 3 turns
of the optic fiber wrapped around the mandrel using the DSO which should gradually be
reducing, showing loss due to macrobends.
Observations:
No. of turns
Graphs:
Vin (V)
Vout (V)
% Bending loss
Conclusion:
Experiment:
Objective: Characteristics of Photo Detector (E - O converter).
Equipments Required:
●
Scientech 2502A Training platform with Power Supply cord.
●
Optical Fiber cable.
●
Connecting probes.
Connection Diagram:
Theory:
Photo Transistors and Photo Diodes are the commonly used detectors in optical
communication systems, whether the system receives digital or analog signal. It is
therefore, often necessary to use linear optical to electrical converter to allow its use in
intensity demodulation & high quality analog receiving systems. Photo Diodes have a
linear electrical output with relation to the light intensity over a certain region of
operation.
Procedure:
 The power supply is to be connected to the board.
 Emitter Block is set to digital mode.
 Make connections as given below:
o The digital bias input is connected to the emitter 1 block.
o Fiber optic is connected between emitter output and detector input




DMM is connected between ground and the input of emitter LED to read the forward
voltage (Vf)
Voltage drop is measured across the 75 ohm resistor by connecting DMM between the
output of Photo-Transistor and Ground. The detector current is given by the following:
id = (DVM reading)/75 mA
Bias 1 is varied so as to vary the forward voltage and the corresponding forward
currents are measured.
The measurements for the above parameters are recorded and plotted.
Observations:
Vin(V)
Graph:
Vout(V)
I(mA)
Conclusion:
Experiment:
Objective: To study Frequency Modulation System through analog fiber optic link.
Equipments Required:
●
Scientech 2502A Training platform with Power Supply cord
●
Optical Fiber cable
●
Digital storage oscilloscope with necessary connecting probe
Connection Diagram:
Theory:
Frequency modulation (FM) is a technique used to encode data on an alternating digital or
analog signal. In this modulation scheme, the frequency of the carrier wave changes as per
the amplitude of message signal.
The voltage controlled oscillator (VCO) is a device whose frequency changes linearly
with the input voltage. It is used to perform direct frequency modulation on signals.
In PLL, the input FM signal and the output of the VCO is applied to the phase detector
circuit.When deviation in carrier frequency occurs (that means modulation occurs), the
VCO frequency follows the input signal in order to keep the loop in lock.
Procedure:
 Power Supply Cord is to be connected to Scientech 2502A
 The following connections are made as shown in the figure above.
o 1 KHz sinusoidal signal is supplied using Function Generator as input to the
Frequency Modulator.
o
o
o

Emitter 1 Input is connected to output of Frequency Modulator.
We further connect the optic fiber between emitter 1 output and detector 1 input.
Connect the detector 1 output to comparator 1 input and further to the PLL
detector input
o The PLL Detector output to LPF1 input which is to be connected to AC
Amplifier 1 input.
Now, we monitor the output at various points of the circuit block namely at the function
generator block, the FM block, Emitter & Detector blocks, Comparator block, PLL
block, LPF block and finally at the output of the AC Amplifier block.
Observations:
Graphs:
Conclusion
Experiment:
Objective: To study Pulse Width Modulation through analog fiber optic link.
Equipments Required:
●
Scientech 2502A Training platform with Power Supply cord.
●
Optical Fiber cable.
●
Digital storage oscilloscope with necessary connecting probe.
Connection Diagram:
Theory:
PWM works by pulsating DC current, and varying the amount of time that each pulse stays on to control
the amount of current that flows to a device such as an LED. PWM is digital, which means that it has two
states: on and off (which correspond to 1 and 0 in the binary). The longer each pulse is on, the brighter
the LED will be. Due to the fact that the interval between pulses is so brief, the LED doesn’t actually turn
off.
Procedure:
 Power Supply Cord is to be connected to Scientech 2502A
 The following connections are made as shown in the figure above.
o 1 KHz sinusoidal signal is supplied using Function Generator as input to the Pulse Width
Modulator.
o Emitter 1 Input is connected to output of Pulse Width Modulator.
o We further connect the optic fiber between emitter 1 output and detector 1 input.
o Connect the detector 1 output to comparator 1 input and further to LPF1 input which is to be
connected to AC Amplifier 1 input.
 Now, we monitor the output at various points of the circuit block namely at the function generator
block, the PWM block, Emitter & Detector blocks, Comparator block, LPF block and finally at the
output of the AC Amplifier block.
Observations:
Graphs:
Conclusion:
Experiment:
Aim: Analyzing the effect of dispersion compensation on single channel fiber optic
communication link using Opti-system Software.
Required software: Opti-System Software.
Theory: The optical fiber consists of three main elements: Transmitter: An electric signal is
applied to the optical transmitter. The optical transmitter consists of driver circuit, light source
and fiber flylead. Driver circuit drives the light source. Light source converts electrical signal
to optical signal. Fiber flylead is used to connect optical signal to optical fiber. Transmission
channel: It consists of a cable that provides mechanical and environmental protection to the
optical fibers contained inside. Each optical fiber acts as an individual channel.
Figure 1: Optical communication system
Optical splice is used to permanently join two individual optical fibers. Optical connector is for
temporary non-fixed joints between two individual optical fibers. Optical coupler or splitter
provides signal to other devices. Repeater converts the optical signal into electrical signal using
optical receiver and passes it to electronic circuit where it is reshaped and amplified as it gets
attenuated and distorted with increasing distance because of scattering, absorption and
dispersion in waveguides, and this signal is then again converted into optical signal by the
optical transmitter
Receiver: Optical signal is applied to the optical receiver. It consists of photo detector, amplifier
and signal restorer. Photo detector converts the optical signal to electrical signal. Signal
restorers and amplifiers are used to improve signal to noise ratio of the signal as there are
chances of noise to be introduced in the signal due to the use of photo detectors. For short
distance communication only main elements are required. Source- LED Fiber- Multimode step
index fiber .Detector- PIN detector .For long distance communication along with the main
elements there is need for couplers, beam splitters, repeaters, optical amplifiers. SourceLASER diode. Fiber- single mode fiber. Detector- Avalanche photo diode (APD).
Dispersion is the spreading out of a light pulse in time as it propagates down the fiber.
Dispersion in optical fiber includes model dispersion, material dispersion and waveguide
dispersion. Dispersion will cause pulse broadening, results in the limit of the communication
capacity (product of BL) of communication system, which will ultimately affect the quality of
the signal transmission. forward many kinds of dispersion compensation technics. Finally the
dispersion compensation fiber(DCF) is applied widely because of advantages such as the
relatively matured technics, suitable for long distance compensation with controllable
dispersion compensation amount, large bandwidth and transparent for transmission formats and
bit rate. The method of dispersion compensation fiber is to add dispersion compensation fiber
into optical fiber link, to make the total dispersion nearly zero, to decrease the influence of
Group Velocity Dispersion (GVD) atleast.
Layout design:
Fig. 2: Layout design.
Procedure:
1) From the opti-system’s default library design the transmitter and receiver end of the fiber
optic communicationlink.
2)In the transmitter end ,by using pseudo-random pulse generator we are generating the
message signal (bit rate=5Gbps) and the converting it into light signal using NRZ pulse
generator.
3) Continuous wave LASER is used as a carrier for the message signal and the modulator used
is Mach-zehndermodulator.
4)The fiber used is single mode optical fiber with attenuation 0.2 dB/kms and we are varying
the length from 10km to 80km and wavelength1550nm.
5)In the receiver end, PIN photo detector is used to change optical signal into electrical signal
and following filter which is used for better resolution LOW PASS BESSEL FILTER(cutoff
frequency =0.75*BITrate).
6)For analysing the optical output at various stages, we used optical spectrum analyser and to
compare the output signals we used EYE diagramanalyzer.
7)For dispersion compensator, the dispersion compensation provided is -200ps/nm-km.
8)Thus, we have noted down the BER by changing the length of optical fiber from 10 to 80 km
(with and withoutcompensation).
Observations:
(a) BeforeCompensation:
Length(km)
BER
(b) AfterCompensation:
Length(km)
Plot:
Conclusion:
BER
Experiment:
Objective:
Study the characteristics of LASER Diodes
(i) Optical Power (Po) of LASER Diode vs LASER Diode Forward Current(I F).
(ii) Monitor photodiode current (IM) vs LASER Optical Power Output(Po).
Equipments needed:
1. Digital Multi-meters.
Basic principles and definitions:
LEDs and LASER Diodes are the commonly used sources in optical communication systems,
whether the system transmits digital or analogue signals. LASER Diodes are used in telecom, data
com and video communication applications involving high speeds and long hauls. All single mode
optical fiber communication systems use LASERs in the 1300nm and 1550 nm windows. LASERs
with very small line widths also facilitate realization of wavelength division multiplexing (WDM)
for high density communication over a single fiber. The inherent properties of LASER diodes that
make them suitable for such applications are high coupled optical power into the fiber (Typically
greater than 1 mW), high stability of optical intensity, small line-widths (less than 0.05 nm in
special devices), high speed (several GHz) and high linearity (over a specified region suitable for
analogue transmission). Special LASERs also provide for generation/ amplification of, optical
signals within an optical fiber. These fibers are known as erbium doped fiber amplifiers; LASER
diodes for communication applications are available in the wavelength regions 650nm, 780nm,
850nm, 980nm, 1300nm and 1550nm.
A LASER diode has a built inphoto detector, which one can employ to monitor the optical intensity
of the LASER at a specified forward current. This device is also effectively utilized in designing
an optical negative feedback control loop, to stabilize the optical power of a LASER in the steep
lasing region. The electronic circuit scheme that employs the monitor photodiode to provide a
negative feedback for stabilization of optical power is known as the Automatic Power Control
Mode (APC). If a closed loop employs current control alone to set optical power than this mode is
called the Automatic Current Control Mode(ACC).
The disadvantage of ACC scheme is that the optical power output may not stable at a given current
due to the fact that small shifts in the lasing characteristics occur with temperature changes and
ageing. The disadvantage of the APC is that the optical feedback loop may cause oscillations, if
not designed properly.
Fig. 1:Schematic of a LASER diode Operation (ACC Mode)
Procedure for Po vs IF characteristics:
The schematic diagram for study of the laser diode P o as a function of laser diode forward current
IF is shown below:
Fig 2: Setup for IF v/s Po






Place Laser transmitter port in line of sight to the RX Unit with minimal length of separation.
Set DMM to the mV range and connect Po point to multimeter.
Po = (DMM reading)/10dBm.
On the Tx Unit, connect VL to a DMM and observe readings of VL from here.
Switch on the power supply and observe it.
By varying VL, observe the change in Po. Take the readings at some intervals.
IF = VL/100 mA.
Plot IF v/s Po. Repeat the above procedure by changing the distance between Tx and Rx units
and maintaining the line of sight.
Procedure for Im vs Po characteristics:

Place Laser transmitter port in line of sight to the RX Unit with minimal length of separation.

Set DMM to the mV range and connect Po point to multimeter.
Po = (DMM reading)/10dBm.

On the Tx Unit, connect VM to a DMM and observe the readings of VM from here.



Switch on the power supply and observe it.
By varying VM, observe the change in Po. Take the readings at some intervals.
IM = VM/100K mA.
Plot IM v/s Po. Repeat the above procedure by changing the distance between Tx and Rx units
and maintaining the line of sight.
Results:
1. IF vs Po characteristics:
VL(V)
IF(mA)
Po (dBm)
Po (mW)
Graph:
1. Po vs IM characteristics:
VM (V)
Graph:
Conclusion:
IM(mA)
Po (dBm)
Po (mW)
Experiment:
Objective: To Measure Bit Error Rate and observe Eye Pattern.
Apparatus Required:

Eye Pattern and BER MeasurementModule.

Scientech Optical Fiber Communicationplatform.

PatchCords

Optical FiberCable
●
500 mAAdapter

CRO
Theory:
In telecommunication transmission, the bit error rate (BER) is a Ratio of bits that have errors relative
to the total number of bits received in a transmission. The BER is an indication of how often a packet
or other data unit has to be retransmitted because of an error. Too high a BER may indicate that a
slower data rate would actually improve overall transmission time for a given amount of transmitted
data since the BER might be reduced, lowering the number of packets that had to be resent.
Connection Diagram:
Fig. 1: Set up to observe BER count
Fig. 2: Set up to observe eye pattern.
Procedure:
This Eye Pattern and BER Measurement Module is to be used with Optical Fiber communication
kit.

Connect power supply to optical fiber communication kit.

Give bias voltage to input of emitter circuit and connect the fiber optic cable between emitter
output and detectorinput.

Connect 500 mA adapter to theboard.

Make the connections as shown in abovefigure:

Clock frequency of 64 KHzfrom clock generator is connected to clkin of data generator.

Data out of data generator is connected to the data in of opticallink.

Now, connect a patch cord from data in of optical link of kit toinput of emitter of optical fiber
communication kit.

Then, connect a patch cord from detector output of optical fiber communication kit to data
out of optical linkmodule.

Data out of optical link is connected to signal in of noisegenerator.

Keep toggle switch towards bit errorcounter.

Switch ON the power of Trainer andModule.

Initially keep noise level at zero and observe the bit error count on 7-Segment display of
counter by using the start/ stop switch for 10sec of time duration.

Adjust noise level for medium and maximum position and thus observe effects of variable

noise on the bit error errorcount.
Later on, we will observe the eye pattern too, by toggling the switch to eye pattern side and
thus observe different eye patterns for for different noise levels by connecting clock in to
external trigger of CRO and eye pattern to channel 1 of CRO.
Observations:
Conclusion:
Experiment:
Objective: To setup a digital fiber optic link and study Pulse Width Modulation through the
digital fiber optic link.
Equipments Required:
●
Scientech 2502A Training platform with Power Supply cord.
●
Optical Fiber cable.
●
Digital storage oscilloscope with necessary connecting probe.
Theory:
PWM works by pulsating DC current, and varying the amount of time that each pulse stays on
to control the amount of current that flows to a device such as an LED. PWM is digital, which
means that it has two states: on and off (which correspond to 1 and 0 in the binary). The longer
each pulse is on, the brighter the LED will be. Due to the fact that the interval between pulses is
so brief, the LED doesn’t actually turn off.
Procedure:
Setup of basic digital fiber optic link:
● Power Supply Cord is to be connected to Scientech 2502A
● The following connections are made as shown in the figure above.
o 1 KHz sinusoidal Digital Signal is supplied using Function Generator as input to the
Emitter block
o We now connect the optic fiber between emitter 1 output and detector 1 input.
o Connect the detector 1 output to comparator 1 input which is to be connected to AC
Amplifier 1 input.
● Now, we monitor the output at various points of the circuit block namely at the function
generator block, Emitter & Detector blocks, Comparator block, and finally at the output of
the AC Amplifier block.
Setup and study of Pulse Width Modulation through the digital fiber optic link:
● Power Supply Cord is to be connected to Scientech 2502A
● The following connections are made as shown in the figure above.
o 1 KHz sinusoidal Digital Signal is supplied using Function Generator as input to the
Pulse Width Modulator.
o Emitter 1 Input is connected to output of Pulse Width Modulator.
o We further connect the optic fiber between emitter 1 output and detector 1 input.
o Connect the detector 1 output to comparator 1 input which is to be connected to AC
Amplifier 1 input.
● Now, we monitor the output at various points of the circuit block namely at the function
generator block, the PWM block, Emitter & Detector blocks, Comparator block, and finally
at the output of the AC Amplifier block.
Connection Diagram:
Fig 1: Setup of basic digital fiber optic link
Fig 2: Setup and study of Pulse Width Modulation through the digital fiber optic link
Observations:
Setup of basic digital fiber optic link
Setup and study of Pulse Width Modulation through the digital fiber optic link:
Conclusion: