Physics and Computer Science Department
Winter Term, 2009
PC237 Fibre Optics Lab
INSTRUCTOR:Dr.Hasan Shodiev
Office : N2086 Science Building
Phone: (519)884-0710 ext.2461
OFFICE HOURS:by appointment
E-mail: hshodiev@wlu.ca
TEXTBOOK: Introduction to Optics, by Frank L. Pedrotti, Leno M. Petrotti and Leno
S.Pedrotti, Third edition, Prentice Hall, 2007
3. Instrument Manuals
4. Laboratory Notes
Web: http Lab: http://denethor.wlu.ca/pc237/index.html
General Description:
This course is designed to familiarize students with the Wave properties of light or classical
optics in a hands-on environment. Total of 9 experiments will be required. During the first lab
you should form a lab group of two three students. Every next week is due date for each previous
lab work. Te lab report should be handed in before the lab starts. This will allow some time to
repeat certain parts of the lab that you are unsure of or wish to check. At the end of the PC237
lab there will be lab test – quiz
Labs schedule:
Section 1: Mon, 12:30 –2:20pm, N2088
Section 2: Thu, 4:00 – 5:50pm, N2088
February 16 week is Reading Week
1. Michelson Interferometer
The purpose of this lab is to use the Micheleson interferometer to detect small differences
in index of refraction.
2. Malus’ law
The purpose of this lab is study polarization
3. Newton’s ring
The purpose of this lab is to investigate interference in thin films
4. The lenses
In this experiment we measure the focal lengths of two thin converging lenses, observe
real and virtual images in lenses, build a simple telescope, and make use of the simple
lens formula.
5. Reflection and Refraction of Light
This exercise is designed for the demonstration of the law of reflection of light from a
mirror surface and the location of the image of the object formed by a mirror. Further, the
law of refraction of light is demonstrated and the path of light rays through a glass prism
is studied. The index of refraction for the glass used is measured as wel
6. Microscope.Refraction Index Measurement
The purpose of this exercise is to study working principles of Microscopes and telescopes
and determine refractive index of a glass slide
7. Difftraction Grating
To determine the wavelength of diffracted light by means of a transmission rating and slit
separation distance of this diffraction grating
8. Numeric Aperture in Fiber Optics
The purpose of this experiment is to study propagation of light in optical fibres, measure
numerical aperture (NA) of a plastic multimode fiber by different methods
9. Brewster angle
The purpose of this lab is to investigate polarization by reflection and the Brewster angle.
PC 237 Schedule
Date
Topics Covered
To be handed in (questions, reports) or get
checked off (tasks)
January 12
Introduction.
Exercise on Generalized Least
Squares Fitting
Exercise, in-lab questions and tasks
January 19
Michelson Interferometer
Experiment, pre-lab questions
January 26
Malus Law
Experiment, pre-lab questions and previous
week lab report
February 2
Newton's Ring
Experiment, pre-lab questions, previous
week's lab report
February 9
..
The Lenses
Experiment, pre-lab questions and previous
week lab report
February 16
Reading week
No-labs
.
February 23
Reflection and Refraction of Light
Experiment, pre-lab questions, previous
week's lab report
March 2
Microscope.Refraction Index
Measurement
Experiment, pre-lab questions, previous
week's lab report
March 9
Difftraction Grating
Experiment, pre-lab questions, previous
week's lab report
March 16
Numeric Aperture in Fiber Optics
Experiment, pre-lab questions, previous
week's lab reportt
March 23
Brewster Angle
Experiment, pre-lab questions and previous
week lab report
March 30
Lab Evaluation and Lab test
Final Marks
Lab Safety
No Food or Drink is permitted in the lab.
Enrolled students for course only allowed in lab.
The laser will start about 10 second after it is switched on. _
DO NOT LOOK AT DOWN DIRECT LASER BEAM FOR ANY REASON
Block beam with supplied black safety screen to prevent stray beams round laboratory.
Remove watches, rings and pendant jewelry when working with direct beam; they may reflect a
beam into your eye.
Do not unplug laser head from power supply even when switched off. Lasers operate are very
high voltage and contain large capacitors which are dangerous even when disconnect from the
main supply.
The lab should be kept tidy at all times. Please read and submit the Department Laboratory
Safety Form
General Description:
The labs are the hands-on portion of the course. This course is designed to familiarize
students with the Wave properties of light or classical optics in a hands-on environment. Total of
9 experiments will be required. You must be prepared to discuss and demonstrate your
experiment before leaving the lab. When leaving the laboratory, ensure that you switch off and
unplug all equipment and that your work area is left tidy and clean. Any changes will be posted
on the lab web page. Please check the exact details on the lab website each week. Students will
work individually.
Attendance: It is expected that you will attend every class. Please be prompt. If you anticipate
an absence, please let your lab instructor know immediately. If you miss a class, it is YOUR
responsibility to come in during open lab hours to make up the laboratory experiment. Absence
from class DOES NOT alter the deadlines for turning in labs. For safety reason no food or drinks
are allowed in the lab.
Every next week is due date for each previous lab work. Te lab report should be handed
in before the lab starts. This will allow some time to repeat certain parts of the lab that you are
unsure of or wish to check. At the end of the PC237 lab there will be lab test – quiz.
Lab Evaluation:
Lab Performance (attendance, participation, etc.): 2%
Lab reports: 18%
Each lab will be evaluated according following scheme:
Pre-lab question: 10%
Introduction: 10%
Result:data analysis: uncertainty calculation, graphing and least squire fitting:50%
Discussion/Conclusion: 30%
Total: 20%
Always be on time!!
John Doe
OPSE 301 Section 001.Lab Partner:
Lab 7 : Detection of Light
I. Objective
The purpose of this experiment is the following:
to introduce to the student a method of quantitatively measuring light from a laser light source. You will
use two methods: An optical power meter and a photodetector.
to illustrate the need of operating a light detector in the “linear” range. In the linear range, the voltage
output of the photodetector is proportional to the incident light power.
II. Introduction
Various types of light sources are used extensively in today’s research environments. This includes
everything from x-rays, ultraviolet, infrared and visible light sources. However, the most sophisticated
light source is of little use to any researcher or scientist if it cannot be measured or manipulated to suit the
users needs. In this experiment, a Helium-Neon laser or a diode laser will be used as the light source. The
student will become familiar with Neutral Density filters and how they can be used to alter the power of
the light source. Finally, this lab will examine the method of quantitatively measuring the light from the
He-Ne laser using a power meter. The power meter will be used to calibrate a more sensitive
Photodetector.
Operation of Neutral Density Filters
A Neutral Density Filter (NDF) is used to attenuate or reduce the power in an optical beam. Darker filters
attenuate more light then less-dark filters. The NDF is characterized by its ND value according to the
following formula:
P  Po 10 ND (1)
Where Po is the incident power on the filter and P is the transmitted power, and ND is the neutral density
value of the filter. As an example an ND=1 filter attenuates the power by a factor of 10. An ND=2 filter
attenuates the power by a factor of 100. The ND=0.3 filter is very useful for calibration purposes because
it attenuates the power 50.12% or by nearly a factor of two. Some of the ND filters are labeled by part
number. Use the following table to identify the corresponding ND value.
ORIEL ND FILTER PART NUMBERS:
Model #
50490
50500
ND value
0.1
0.2
Model #
50530
50532
ND value
0.5
0.6
Model #
50540
50545
ND value
1.0
1.5
50510
0.3
50534
0.7
50550
2.0
50520
0.4
0.8
50560
3.0
50536
Operation of a Photodetector
The photodetectors that are used in this lab convert the TOTAL light power incident on the detector to a
corresponding voltage. The voltage can be measured using a voltmeter, oscilloscope, or some other
device that can convert the voltage into a number to be used in calculations.
Operation of an Oscilloscope
An oscilloscope is an instrument that produces a graphical plot of a measured voltage as a function of
time. For this lab, the measured voltages will be constant and therefore not depend on time. If you are
unfamiliar with the operation of the oscilloscope, ask your instructor for a quick lesson. The simplest
method for reading the voltages on the oscilloscope is to use the “Measure Voltage” button on the
Oscilloscope’s front panel. Under the collection of “MEASURE” buttons on the front panel, push
“Voltage”. On the buttons below the Oscilloscope screen choose “V average” and a text line should
appear on the bottom of the screen that displays a numeric value of the voltage.
III. Procedure
The apparatus must be completely set up according to the attached schematic diagram in order to perform
the following experiments. The purpose of the two mirrors is to adjust the height and direction of the laser
beam. Rather than manipulating the laser mount to adjust the height and direction of the beam, you can
use the fine adjustment knobs on the mirror mounts.
The NDF mount is a semicircular holder. The photodetector (PD) should be connected to the oscilloscope
Channel 1 using a co-axial cable.
Figure 1: Experimental Setup.
Measuring PD voltage using an oscilloscope. Does Background light affect the measurement?
Place the PD on the table with the diode facing the lights on the ceiling. Trigger the scope on auto with a
timebase of roughly 20 msec/division. Make sure to DC couple the input. You should observe a small DC
signal. If you do not observe any detectable signal, please ask for help. Observed signal is 15mV.
Cover the PD with your hand and observe any changes. What is the observed change in the detected
signal due to? Signal changes to 2mV because……
Place the PD on the table in a mount. Do no direct the laser light onto the PD yet. Increase the sensitivity
of the oscilloscope until you observe a non-zero voltage response from the detector. Can you still observe
the DC signal observed in Part 1 above? I can not observe the signal because….
Determine Optical Power of laser
Using the Optical Power Meter, determine the power of the laser beam (in mW) AFTER the two mirrors.
There are only two power meters in the lab, so if one is not available right now, go on to the next task and
measure the power sometime later. The power is 12mW
Determine the Linearity of the Diode
At this point, you can use your calibration from III.B to determine the optical power on the photodetector
for different ND filters. Before EACH measurement with the detector, you should adjust the mount to
maximize the signal. This optimization of the detector position is necessary because any small deviation
of the laser beam will change the apparent reading from the photo diode.
It is most likely that the direct light from the laser will saturate the detector (i.e. the detector becomes
“sunblind”- it does not measure the “true” intensity of the light). However, it may not. The result of
saturating a detector is that is does not operate in a linear fashion. ie. The voltage produced by the
detector is not proportional to the power of incident light. Therefore it is necessary to determine what
Neutral Density (ND) filter(s) (if any) should be placed before the photodetector so that the detector
responds linearly to detected light. You can quickly determine if the detector is linear by placing a 0.3 ND
filter between in from of the detector, the output signal from the detector should drop by 50% (not 10%,
20% etc.). With no ND filters in the laser path, record the voltage from the detector. Next place the 0.3
ND filter in front of the detector. Record the new voltage from the detector. Compare the two voltages
that you just measured. Is the second 50% of the first value? Is the detector is linear. Is it linear? Why do
you conclude so?
The voltage without the ND filter is 100mV. The voltage with the 0.3ND filter is 50mV. The second value
is 50% of the first value. Therefore……
Remove the 0.3 ND filter. Choose an assortment of ND filters to calibrate of the Detector. Be sure to
include the 3.0 ND filter and cover the range from 0 ND (ie. no filter) to 3 ND. For example, you could
use the 0.1, 0.3, 0.5 and 1.0 ND filters. Then use the 1.0 AND the 0.3 ND filters together for an effective
attenuation of 1.3 ND. For each ND filter or combination of filters, record the corresponding voltage
from the oscilloscope. See data table in summary of results.
You should also make a measurement by blocking the laser light completely. NOTE YOU WILL
MEAURE A NON-ZERO VOLTAGE when you block the laser light. This is a CONSTANT offset value
that you will use to develop a calibration curve. The measured voltage is 1.2mV.
IV. Summary of Results
Develop a calibration curve for the photodetector voltage (volts) as a function of Power (milliwatts). To
calculate the voltage at a particular power level, make sure that you subtract the BACKGROUND voltage
that you measured in Part III.4 from each voltage value.
Indicent Power
(mW)
5
5
5
5
5
5
5
5
5
ND filter
0
0.1
0.3
0.5
1
1.5
2
2.5
infinite
Power on
Detector (mW)
5
3.971641
2.505936
1.581139
0.5
0.158114
0.05
0.015811
0
Measured
Voltage (mV)
26
26
25
20
10
3
0.98
0.031
0.0005
Corrected Voltage
(mV)
25.9995
25.9995
24.9995
19.9995
9.9995
2.9995
0.9795
0.0305
0
Corrected Detector
Voltage (mV)
30
25
20
15
10
5
Experimental
Points
0
0
2
4
6
Power on Detector (mW)
Below what power level is the photo diode linear? Below 1mW the detector is linear because…..
Plotting only the data identified as being in the linear range from your answer to 2 above, fit your data
(using EXCEL for example) to a linear trend and determine the sensitivity (Volts per mW) of your
detector. Below is plotted the linear portion of the data (square symbols). The solid line is the linear fit to
the data. The slope of the line is 20.191. The sensitivity of the detector is approximately 20.2 Volts/mW.
Corrected Detector Voltage (mV)
12
y = 20.191x - 0.1165
R2 = 0.9993
10
8
6
4
Data Points
2
Linear (Data Points)
0
0
0.1
0.2
0.3
0.4
0.5
0.6
Power on Detector (mW)
Using your calibration curve, determine if a ND filter is required to enable the photodetector to operate
linearly. If a filter is required, state what value of filter would be required and why. Based on the data in
figure???, a ND filter value of 1.7 is required to make the detector linear.
Does room light generally affect your measurement of the photodetector calibrate curve? Why? Light did
affect the measurements under the following conditions….
Does room light affect the calibration point for the 3.0 ND filter? Why? This did affect the calibration
point because….. something with the oscilloscope ….. something with light intensity….
Assuming that a 1.0 ND filter is required to make the photodetector linear, where in
Figure 1 relative to the photodetector, should the filter be optimally placed. Why? I would place the filter
next to ???? because……
Required equipment:
He-Ne or Diode Laser with mount
Mirrors (2) with mounts
ND filter holder with mount
ND filter set
Photodetector with mount
Oscilloscope
Discussion.
Conclussion.
Any suggestion leading to improvements in the laboratory work are most welcome!
Important Dates 2008/2009
September 5: Final day to cancel Fall Term and Fall/Winter session registration with no tuition
charge (cancellation fee applies)
September 8: Fall Term and Fall/Winter Term sessions begin.
September 12: Final day to drop 12-week and Fall/Winter courses with no charge.
September 19: Final day to add Fall and two-term courses and final day to drop Fall courses @
10% charge.
November 3: Final day to drop Fall courses at 55% charge and without penalty of failure.
December 1: Fall term classes end.
Dec. 4 to 18: Fall Term Final Exam Period.
Final day to cancel Winter Term registration with no tuition charge (Cancellation
January 2:
fee applies).
January 5:
Winter Term Begins.
Final day to drop 12-week winter course(s) but remain registered with no tuition
January 9:
charge.
January 16: Final day to add Winter courses and last day to drop at 10% charge.
Feb. 16 to 20 Reading Week
March 6:
Final day to drop Winter and Fall/Winter courses at 55% charge.
April 3:
Winter term and Fall/Winter classes end.
April 8 to 29: Winter and F/W Final Examination Period.
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