Optical Fiber Labs
ECEn 466 Introduction to Optical Engineering
This lab is broken up into 3 separate labs. These labs must all be done before the end of
the semester but they can be accomplished in any order. Each lab will have its own set of
equipment. We will be using this arrangement to use the equipment efficiently. Do not
expect each laboratory portion to take the same amount of time.
Refer to http://www.et.byu.edu/groups/ece466/equipment/equipment.html for
information and operating instructions on the various pieces of equipment.
Always inspect each connector and clean it if necessary before connecting it!
Fiber Alignment and Fusion Splicing
Required Equipment: Laser source, optical detector, fusion splicer, fiber cleaver
Introduction
Optical fibers are the principal means for carrying nearly all long distance voice and data
traffic. In the near future optical fiber will play an increasingly important role in local
area networks. Long-haul systems use single mode fibers while some local networks use
multimode fibers. This laboratory exercise demonstrates some of the key issues in fiber
loss and alignment.
Laboratory objective
Explore the alignment sensitivity of optical fiber connections. In addition, the students
learn how to create a fusion splice to connect two fibers.
Safety and Equipment care
Be sure to be cognizant of all eye-safe procedures from the prior lab.
Take extra care in following all the instructions associated with the fusion splicer.
Checking a connector
To see if a connector is clean, insert connector end into bottom. Look into lens. Push red
button.
Fiber Cleaning
When cleaning the end of the connector, slide across the cleaning paper once with slight
rotational movements. Do not rub on paper more than is necessary.
Always inspect each connector and clean it if necessary before connecting it!
Preliminary
The mode-field diameter is essentially the diameter of the optical mode, where the mode
diameter is measured at point where the power drops to e-2 of it maximum power.
1. Draw the refractive index profile for the single-mode optical fiber (SMF-28). Be sure
to list the dimension.
2. List the mode-field diameter at a wavelength of =1550nm for the single-mode
optical fiber (SMF-28).
3. Draw the refractive index profile for the multi-mode optical fiber (62.5/125). Be sure
to list the dimension. (The mode-field diameter of the multi-mode fiber is close to the
diameter of the fiber.)
Fiber alignment and fusion splicing** (see endnote)
Part 1: Single Mode Fiber Preparation
 Strip the fiber jacket
o Insert fiber into clamp with 2 – 2.5 cm sticking out of the end.
Always inspect each connector and clean it if necessary before connecting it!
o Clear debris from the stripper.
o Insert clamp (with fiber inside) into the left part of the stripper. Plug the
stripper in and turn it on.
Always inspect each connector and clean it if necessary before connecting it!
o Lower the tops down.
o When the red light (ready) turns to yellow, press on the top (where it says
press), and pull the left slider to its limit.
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o Your fiber is now stripped. Remove it from the stripper, and unplug it.
Handle your stripped fiber with care as it is now more brittle, and the oils
from your fingers could affect your fiber.
o Clean up the jacket debris.
Cleave the fiber (the lab TA will show you how this is done)
Always inspect each connector and clean it if necessary before connecting it!
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Insert the fiber into the fusion splicer according to instructions given in the lab.
Pay attention to the fiber profile as seen in the fusion splicer viewer. If the cleave is
not flat and smooth repeat the prior steps.
Repeat the above procedures for a second half-fiber.
Part 2: Single Mode Fiber alignment tolerances
 With both fibers in the viewer connect one to a source and the other to a detector. (Be
sure to inspect any fiber connector before connecting it.)
 Note the power changes for different lateral and longitudinal displacements of the
fibers.
 Quantify your observations by taking data and using MATLAB or other similar
program to plot coupling power vs. lateral and longitudinal alignment. (You will need
to estimate distances using the fiber dimensions as a reference.)
Part 3: Single Mode Fiber Fusion splicing
 Using the fusion spice viewer, move the cleaved ends of both fibers in close
proximity to each other, without touching.
 Place the fusion splice in auto mode and follow the machine instruction to perform
the splice.
 Estimate the excess loss at the fusion splice.
o Compare a single short optical fiber patch cord to your new fusion spliced
connector.
o Calculate the loss in dB.
 Bend the fiber near the splice location. The splice should break. Notice how the
fusion splice is weaker than the rest of the fiber.
Part 4: Multi-Mode Fiber preparation
 Select a multi-mode optical fiber having a connector on only one end.
 Use stripping tool to remove the plastic jacket from the glass fiber.
 Cleave the fiber.
 Insert the fiber into the fusion splicer.
 Pay attention to the fiber profile as seen in the fusion splicer viewer. If the cleave is
not flat and smooth repeat the prior steps.
 Repeat the above procedures for a second half-fiber.
Part 5: Multi-Mode Fiber alignment tolerances
 With both fibers in the viewer connect one to a source and the other to a detector. (Be
sure to inspect any fiber connector before connecting it.)
 Note the power changes for different lateral and longitudinal displacements of the
fibers.
 Quantify your observations by taking data and using MATLAB or other similar
program to plot coupling power vs. lateral and longitudinal alignment. (You will need
to estimate distances using the fiber dimensions as a reference.)
Part 7: Multi-Mode Fiber Fusion splicing
Always inspect each connector and clean it if necessary before connecting it!
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Splice a single-mode optical fiber to a multi-mode optical fiber. With the singlemode optical fiber connected to the laser and the multi-mode optical fiber connected
to the detector.
Measure the power through the spliced fiber.
Now connect the multi-mode optical fiber to the laser and the single-mode optical
fiber to the detector. Comment on any differences from the previous step.
Conclusion
Make some general observations about optical fiber connections and splices from your
experience with this laboratory exercise.
** Fusion splicer hint: Strip just enough plastic jacket to allow the glass portion of the
fiber to be guided by the groove, while leaving enough jacket to be held by the clamp.
Note: Because the fusion splicer is designed for a different fiber diameter then we will be
using, a kluge is needed to put the thing working. The fusion splicer must simultaneously
perform two actions. The first is to guide the fibers through the little grooves. If the
fibers stay in the grooves, then they will line up enough at the junction to be able to see
both fibers (in both viewing modes) in the view window. While maintaining the fibers in
the grooves, the fusion splicer must also clamp down on the fibers to keep them from
slipping, particularly when using the splicer to move the fibers or when someone clumsy
bumps into the machine. This second duty is where we have trouble -- our fibers are too
thin for the splicer's clamps to hold the fiber. Here is a solution to the problem: Trim
back all the protective coatings so that enough fiber is exposed to allow most of the fiber
to lie in the grooves, from where the fibers will join clear back until the clamping base in
the fuser (the little black thing on each side that looks like a rear rifle sight). You would
do this anyway. The trick is to leave just a little piece of clear plastic jacket on the fiber
so that the clamp (rifle sight) is actually holding on to the jacket instead of the thin fiber.
It takes some good estimating, but this will allow the fibers to stay in the grooves and the
clamp to do its job at the same time. Happy splicing!
Always inspect each connector and clean it if necessary before connecting it!
Source Characterization
Required Equipment: Optical spectrum analyzer, HeNe laser, semiconductor laser,
optical detector, pattern generator (You have to share this with another lab)
Introduction
This laboratory exercise introduces the student to a variety of optical sources and
detectors used in optical systems.
Laboratory objective
The student should gain an understanding of how to use an optical spectrum analyzer and
how to think about detector sensitivity.
Safety and Equipment Care:
The same safety precautions should be used in this lab as in prior labs. Laser beams must
always be confined inside of cables and test equipment. Great care should be taken to
avoid scratching, fouling, or otherwise damaging the equipment.
Preliminary
The mode-field diameter is essentially the diameter of the optical mode, where the mode
diameter is measured at point where the power drops to e-2 of it maximum power.
1. Provide a description of the following.
a. Optical fiber mode field diameter.
b. Optical time domain reflectometer
2. Look up the following parameters from the specification sheets. (These are on the
class web site.)
a. Attenuation of SMF-28 at =1550nm and =1310nm.
b. Mode field diameter of SMF-28 at =1550nm and =1310nm.
c. Attenuation of graded index multi-mode optical fiber at =1550nm and
=1310nm.
d. Mode field diameter of graded index multi-mode optical fiber.
Part 1: Optical Time Domain Reflectometer (OTDR)
 Connect the long section of single mode optical fiber to the OTDR and determine the
following.
o Length
o Total loss at =1550nm
o Total loss at =1310nm
o Attenuation at =1550nm
o Attenuation at =1310nm
 Compare the loss of the optical fiber to the specification sheet
 Connect the SMF-28 spool to a long patch cord and measure the following at
=1550nm.
o Length of each fiber
o Total loss
o Loss of the connection
Always inspect each connector and clean it if necessary before connecting it!

Calculate the transmission length using the following.
o Received power 10 W
o Laser transmission power 10mW
o Fiber spool length measured earlier
o Spools connected with FC connectors. Loss measure earlier
Part 6: Pattern generator laser wavelength spectrum
 Measure the wavelength spectrum of the following. Make sure that the power is less
than 100W before connecting any fiber to the OSA.
o The OC-48 laser from the ST2400 pattern generator without modulation
o The OC-48 laser from the ST2400 pattern generator with modulation
o The OC-3 laser from the ST2400 pattern generator without modulation
Part 7: Laser focusing and HeNe laser wavelength spectrum
 Take a section of single mode optical fiber with only one end connectorized.
 Strip off part of the yellow jacket if necessary.
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Feed the white plastic coated fiber through the brass fiber chuck.
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Strip off part of the plastic jacket.
Always inspect each connector and clean it if necessary before connecting it!
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Cleave the fiber by scoring the optical fiber (gently slide the blade along the fiber)
and then bending the fiber away from the score.
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Insert the fiber chuck into the fiber alignment mount.
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Focus the HeNe laser light into the fiber.
o Use a small piece of paper to determine where the laser beam is going
Always inspect each connector and clean it if necessary before connecting it!
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o Look at the far end of the fiber to focus the light in. Don’t worry this laser is
not bright enough to hurt your eyes. Go side to side until you get a maximum
and then up and down. After this lateral alignment is accomplished change
the focal position.
o Once the light is bright enough continue focusing using the detector.
Measure the wavelength spectrum of the HeNe laser using the OSA.
Follow a similar process to that explained in order to focus light into a section of
multi-mode optical fiber. Are you able to focus mode light into the multi-mode
optical fiber?
Discuss the differences between the wavelength spectra of the different optical sources.
Always inspect each connector and clean it if necessary before connecting it!
Optical Communications
Required Equipment: Optical pattern generator (shared with a different lab), optical
attenuator, optical receiver, optical transmitter
Preliminary
1. A pattern generator creates a pseudo-random set of digital data. When this pseudorandom data is measured on an oscilloscope it will appear as if both a ‘1’ and a ‘0’ are
sent. If these random scans are recorded it will create a pattern that is called an eye
diagram. Explain the details of an eye diagram.
(http://www.complextoreal.com/chapters/eye.pdf)?
2. With respect to optical communications what does OC-48 mean
(http://www.ee.byu.edu/cleanroom/FiberStandards.parts/DataRates.phtml)?
3. What are the OC designations for data rates of 155Mbps and 622 Mbps?
Safety and Equipment Care:
The same safety precautions should be used in this lab as in prior labs. Laser beams must
always be confined inside of cables and test equipment. Great care should be taken to
avoid scratching, fouling, or otherwise damaging the equipment.
Procedures
1. Measure an eye diagram for the OC-48 pattern coming directly out of the pattern
generator. The basic connection is shown in Figure 1.
a. Measure the bit rate, noise, the signal to noise ratio, etc.
Figure 1: Unconditioned OC-48.
2. Measure an eye diagram for the reconditioned OC-48 pattern. The basic connection
is shown in Figure 2.
a. Measure the bit rate, noise, the signal to noise ratio, etc.
b. What is the different between this configuration and the previous one?
Always inspect each connector and clean it if necessary before connecting it!
Figure 2: Re-conditioned OC-48.
Always inspect each connector and clean it if necessary before connecting it!