TESTING
MTP ® /MPOASSEMBLIES:S E T U P S , T R O U B L E S H O OT I N G& W H AT TO E X P E C T

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ALL RIGHTS RESERVEDPRINTED IN THE UNITED STATES OF AMERICA
EB-101 Rev.B 10/13/20
MTP®/MPO

online resources

OVERVIEW
T E S T ING M T P ® / MPO A SSEMBLIE S

MTP®/MPO connectors and patchcords
are prevalent in fiber networks andtheir quantities continue to growas demand for greater capacity andefficiency increases. These multifiberconnectors present unique challenges
when it comes to assessing their quality
and performance. OptoTest is proud topresent this complete guide to MTP®/
MPO testing. In this guide, you will learn
all there is to know about the different
test methods, equipment options,troubleshooting, and best maintenancepractices to ensure that you have thebest testing experience.

CONTENT

06
08

Measurement Methods
Why use a pulse-based method?

Instrument Selection
08

Automated Solutions

10

Instrument Selection

16

Typical System Reference Setups
16
Reference Cord Setups
18
12 and 24 Fiber Testing20

Launch/Reference Cords
20
Jacketed and Bare MTP® Cords
21
Multimode 50μm Reference

22

Reference Process22
Insertion Loss Reference
23
Return Loss Reference
24
General Rules for Referencing

25
27
29
43
45

Cleaning and Inspection
25
Cleaning and Inspection Guidance

Polarity
27

How Fibers are Routed

28

Polarity Verification

Measurement processes
29
Insertion & Return Loss
30

Dealing with Genders

35

Unidirectional method

38

Fanouts

Troubleshooting

General Rules

TESTING
MTP ® /MPOASSEMBLIES:S E T U P S , T R O U B L E S H O OT I N G& W H AT TO E X P E C T

MEASUREMENT METHODS
Return Loss Measurement Methods- Why Use A Pulse-Based Method?

The two main methods to measure return loss (RL) on fiber optic cable
assemblies are the continuous wave (CW) method and the OTDR pulsebased method. While the CWRL test equipment is less expensive thanits pulse based cournterpart, it is more time consuming and requires
more steps for testing MPO assemblies. With the CW method, toproperly measure RL, it is necessary to reduce stray reflections causedby subsequent connectors and fiber contributions. This additional step
typically means that insertion loss (IL) and RL must be measured as
separate steps: one step with the device under test (DUT) connected to
the OPM to measure IL and one step with the DUT mandrel wrapped or
terminated to measure RL.
To reduce the additional reflections on a fiber optic cabling assembly,
the operator can wrap the cable around a mandrel or press the open
connector into a matching block. For bend-insensitive cabling, mandrel
wrapping is not an option as the cable cannot be bent tight enough toreduce the stray reflections. Using a matching block is also not an ideal
solution, especially for MTP®/MPO connectors. Matching blocks cancollect debris if left exposed in a production environment, which canthen transfer onto the connector and cause damage. For male (pinned)
MTP®/MPO connectors, the pins will damage the block and the matching
substance can adhere to the pins and prevent proper mating.

Figure 1 - Mandrel wrapping and using a matching block are
not recommended for MTP®/MPO connectors.

6 of 48

MEASUREMENT METHODS- Why Use A Pulse-Based Method?
The pulse-based (OTDR) method of measuring RL allows the operator
to measure IL and RL in the same test step. With a pulse-based
measurement system there is no need to terminate the back connector
in order to isolate the measurement to the front connector. The diagram
below shows how the front connector is measured independently of theback connector.

Figure 2 - OTDR method can measure the front connector
independent of the back connector.

7 of 48

INSTRUMENT SELECTION
Automated Solutions
The MPO test process involves many different steps and generates a lotof data during referencing and measurement. For instance, a 12 fiber
MPO assembly has 12 ports on each side for a total of 24 ports to test.
The typical IL and RL test is performed at two separate wavelengths.
That is 96 total measurements for the 12 fiber MPO assembly! A
software package is highly recommended to automate the test process
and manage all this data. The software guides the instrument and user
through the referencing and measurement processes efficiently andstores data to ensure there are no errors and to generate reports.
For multifiber connectors such as MPO assemblies, it is beneficial toinclude an optical switch in the setup that has at least as many channels
as the DUT has fibers. This allows the user to perform one connectionof the DUT per test, which limits the amount of times it can be damaged.
A simplex system would require the technician to perform many
more connect/disconnects adding uncertainty and inaccuracy to themeasurement.
A switch-based instrument setup coupled with automation software
allows for easy testing and data management. The software guides
the instrument from channel to channel, performs the corresponding
measurements, and records them to the proper location.

Figure 3 - OptoTest offers a number of automation
solutions ideal for multifiber testing.

8 of 48

Automated Solutions

Figure 4 - OPL-CLX automates the MPO test process.



Focus on switch-based multichannel testing• MPO testing just too difficult with a simplex setup

Software package to automate the process• Automated from one channel to the next
• Data management controlled by software and not the technician

9 of 48

INSTRUMENT SELECTION
Immediate and Future Needs
When investing in MPO test equipment, it is best to understand current
needs and anticipate future needs of your cable production. Expanding
the channel count capabilities of an existing system typically includes
upgrade cost and opportunity cost as the equipment is unavailable foruse during the upgrade. In addition, some equipment cannot be upgradedor the cost to do so is comparable to a new system. For instance, notevery power meter capable of testing 12 fiber MPO connectors can do thejob for 16 fiber connectors. When preparing a production floor to meetcurrent and future needs, it is important to weigh the pros and cons ofmaking a higher initial investment and the hidden costs of failing to do so.

12f

16f

24f

32f

Figure 5 - 12, 16, 24 & 32F MPO Connectors.

Prior to purchasing equipment, first, understand the immediate andfuture needs
Expandability? If current requirement calls for 12f, is there a futureneed for 24, 16, 32, etc.?

10 of 48

INSTRUMENT SELECTION
Optical Power Meter
When selecting a system for testing MPO assemblies, one needs to pay
careful attention to the optical power meter. Choosing the wrong OPM
may reduce accuracy and limit expandability if it cannot accommodate
larger channel counts. This is a problem with MPOs due to the spacing
between the outermost fibers.
For 12/24 fiber MPOs this distance is 2.75mm and for 16/32 fibers it is
3.75mm. A detector that does not provide full coverage will not capture
light from the outermost fibers, and a detector that works for the 12/24
fiber connector may not for 16/32 fibers (see figure 5).

Figure 6 - 12/24 fibers with different size detectors.

Figure 7 - The same detector captures light from 12/24 fibers but not 16/32.

Given the wide pitch of fibers in MPO assemblies, an integrating spherewith a large aperture or a large area detector (5mm or 10mm) is necessary.
InGaAs is recommended for standard telcom wavelengths (1310, 1550, etc.).
For 850nm only applications (OM2 and up) an inexpensive Silicon detector
can be used.
11 of 48

INSTRUMENT SELECTION— OPTICAL POWER METEROPM Form Factor

Remote Head Vs. Panel Mount Detector
There are two housings that a detector can come in. They come as either aremote head or a panel mount detector.
Panel mount detectors are mounted on the front panel of the instrument


Requires the user to connect the back end of their test assembly to thepanel of the instrument every time
Sometimes this can be very cumbersome especially with rigid cabling

Figure 8 - Panel Mount Detector.

A remote head detector has the detector in a small semi-portablehousing.
Tethered to the instrument
Allows for a wide range of movement
For stiff assemblies or hard-to-route assemblies, the detector can bebrought to the DUT

Figure 9 - Remote Head.
12 of 48

INSTRUMENT SELECTIONILRL SOURCE MODULE

Creating a Multichannel ILRL System- Method 1: Simplex ILRL System and External optical switch
There are three options to achieve a multichannel insertion loss andreturn loss test setup.
The first option for a multichannel IL and RL test setup is pairing a single
channel ILRL meter with an external switch to increase the channel count(Figure 9). Multiple switches can increase channel counts further by
cascading (Figure 10). It is important to note that these setups can leadto a crowded work space due to the volume of equipment and cables
required. Optical switches are also not accounted for during the standard
calibration of the ILRL meter which can impact the test accuracy.

Pros:



Expandable by adding more switches (figure 10)
The ILRL meter can function alone for simplex testing and pair with theswitch for MPO testing.

Cons:



Complicated setup
Possibly affects calibration due to additional external losses in the switch

Figure 10 - 24 Channel ILRL System with a Simplex
OP940 cascaded through a 24Ch switch.

13 of 48

INSTRUMENT SELECTION–ILRL SOURCE MODULE- Method 1: Continued

Figure 11 - 48 Channel test setup using a 1x2 switch
cascaded through two 1x24 switches.

- Method 2: ILRL System with Internal Switch
The second method is a multichannel ILRL meter, combining the elementsof the first method in one machine. The all-in-one system allows fora simplified test setup with a smaller footprint than a multi-unit setup
requires. Since the optical switch is integrated into the system, the added
loss is accounted for during calibration. On the other hand, this also
makes the use of external switches for expandability more complicated.

Figure 12 - 24 Channel all-in-one ILRL test set.

Pros:




All-in-one
Easier to manage
Optical switch is included in the unit calibration

Cons:


Adding external switches makes the setup more complicated
14 of 48

INSTRUMENT SELECTION– SOURCE MODULE

Method 3: Compact Dedicated MTP® Test System
The third system is a compact, dedicated MPO test system. This option
is great if the system will be used for MPO assembly testing only. The
OP940-CSW has a compact footprint, and the MTP® connector at thefront panel makes cable management minimal by eliminating the needfor fanout cables. However, expandability is difficult since an external
switch cannot be cascaded. This system is also the least flexible with nosingle fiber connectors for more varied applications.

Figure 13 - CSW compact MPO test setup.

Pros:


Small footprintSimple cabling

Cons:


Expandability is difficult

Not optimized for simplex testingFanouts are complicated with such a set

15 of 48

TYPICAL SYSTEM REFERENCE SETUP
Reference Cord Setups- Equipment cord:
When setting up an MPO testing station, pay careful attention to thereference cord setup.
An equipment cord connects directly to the instrument and is intended to
not be replaced often. It is typically a fanout cord that combines simplex
connectors into a single MPO connector. These cables are relatively
expensive and as such should be treated with care.
Typically, a fanout type cord to take multiple simplex connectors androute into a single MTP®



Expensive assembly and difficult to replace

Stays attached to equipment

Equipment cord
Figure 14 - 12f fanout cords connected to a 24 channel ILRL test set.

16 of 48

TYPICAL SYSTEM REFERENCE SETUP
Reference cord setups- Launch Cord:

A launch cord interfaces directly with the DUT. It is connected to the MPO
connector of the equipment cord via a mating adapter. The open connectorof the launch cord will be mated to the DUT. This open connector isconsidered the reference connector and as such should be maintained andcleaned routinely.
Note, for typical MPO assembly test setups it is recommended to keep all
equipment and launch cords as type A cords as well as all mating adaptersshould be type A. Type A mating adapters are key up to key down and are
typically black in color. Gray adapters are typically B type adapters. Using atype A setup maintains 1 to 1 mapping, which keeps maintaining results simple.
Intermediate connections such as the connection between the equipment
cord and launch cord need to have low insertion loss and high return loss.
This maintains a high level of accuracy on the DUT measurements. Whenconnecting the launch cord to the equipment cord, the IL and RL should beverified. Not verifying this connection could result in inaccurate measurements.

Equipment cord

Launch cord

Figure 15 - two launch cords connected to the equipment cords of a system.

17 of 48

TYPICAL SYSTEM REFERENCE SETUP
12 and 24 Fiber Setups
When using the same test setup for testing both single and dual row
MPOs, such as 12 vs 24 fiber, we recommend using two fanout cords as
the equipment cords. This allows for easy transitioning between single
row testing and dual row testing.

Figure 16 - Two 12f equipment cord connected to a 24 channel OP940.



Use two 12f fanout cords to allow for easy transitions between 12 and24f testing.

Figure 17 - Two 12f launch cords connected to the 2 12f equipment cords.

For single row assembly testing, attach a single row launch cord to theequipment cord.

18 of 48

TYPICAL SYSTEM REFERENCE SETUP
12 and 24 Fiber Setups
For dual row connectors (24 or 32) use a secondary fanout cord to convert
from two single row connectors to 1 dual row connector. This cableenables the ability to test dual row cable assemblies. Figure 18 shows anexample of a 24f setup employing 2 12f MPOs to 1 24f MPO.

Figure 18 - A dual 12f fanout to single 24f cable is connected to the equipment cords.

For dual row assembly testing, use a fanout that has two single row
connectors combined into 1 dual row connectors.

19 of 48LAUNCH/REFERENCE CORDS
When setting up the testing space, use reference cords that match yourrequirements. There are space constraints as well as handling requirements.
Your reference cords need to be able to withstand normal handling practices
in the manufacturing environment.
A jacketed cord is rugged and durable, but does not allow for easy genderchanging. A bare ribbon cord allows for easy gender swapping, but it isfragile and the binding material can break causing the cable to fray. An MTP®
Pro cord is the best of both worlds. It allows for gender swapping and it isrugged and able to withstand rough handling.

Jacketed cord

Rugged and durable
Gender not changeable

Bare ribbon cord

Easily change genderRibbon fiber fragile so needs to be handled accordingly

MTP® Pro cordRugged and durable
Gender swappable
Best of both worlds

Figure 19 - Pictured is a gender-swapping tool for MPO
assemblies. This tool is best used on ribbon fiber.

20 of 48LAUNCH/REFERENCE CORDS
Multimode 50µm Reference CablesMultimode reference cords throughout, should be constructed of non bend
insensitive fiber (Non-BIMMF).​ Non bend insensitive fiber allows for launch
conditions to be better maintained as the light passes through intermediateconnections. This is ideal for encircled flux compliance.​
OptoTest can supply reference cords built from non-bimmf reference grade
50µm fiber. This fiber has a controlled core of +/-1µm. The controlled corehelps to maintain the encircled flux compliance launch through connections.
When testing with encircled compliance launch OptoTest believes non-bend
insensitive fiber is a must to maintain compliance.​ ​As the source travels through fiber optic connections, the launch conditions
can be altered. To maintain the launch, such as an encircled flux compliant
launch, high quality connectors should be used on the equipment cords,
and launch cord matings.

non-BIMMF Reference Cable

non-BIMMF Reference Cable
Figure 20 - Non-BIMMF fiber helps to maintain launch
conditions when testing MM fiber.







Cords should be non bend insensitive hroughout: equipment cord,launch cord, etc.
IEC allows for using both BIMMF and non-BIMMF launch cords
OptoTest believes non-BIMMF launch cords are necessary to obtainaccurate EF compliant measurements and OptoTest can supply suchlaunch cords
Encircled Flux must be maintained through connections
21 of 48

REFERENCE PROCESS
Insertion Loss Reference Method
An insertion loss reference records the powers of each port in the launchcord. These powers will be used to calculate insertion loss during themeasurement process.
1310

1550

1

-2.15

-2.35

2

-2.01

-2.35

3

-2.00

-2.07

4

-1.95

-2.17

5

-2.05

-2.09

6

-1.99

-2.10

7

-2.20

-2.25

8

-2.11

-2.18

9

-2.07

-2.12

10

-1.99

-2.04

11

-1.90

-1.99

12

-2.02

-2.13

Figure 21 - Sample IL reference values for a single mode system.



A reference is taking a baseline optical power measurement for eachchannel and each source wavelength• For a 12f dual wavelength test there will be 24 optical power 		measurements stored for the reference• These will be used to calculate insertion loss

22 of 48

REFERENCE PROCESS
Return Loss Reference Method
An RL reference with OptoTest equipment is done using the pulse-based
method to find the location where the RL will be measured. This is usuallyat the position of the reference connector.
A pulse is sent out to find the open connector of the launch cord and lightreflects back towards the source from this open connector. Based on
the magnitude of the returned pulse and the time it takes to return, thelocation and the reflection size are determined. In the example below,
the reflection is at 3.0m as measured from the front panel. Because this isa flat connector, the reflection is about 14.7dB.
Single mode MPO connectors are typically angled and as such have asmall, undefined reflection value. Angled open connectors can have arange of values from the mid 50dBs to high 70dBs depending on thepolishing process. The undefined nature of this reflection presents
challenges when referencing RL. One way to address this is to use a short
APC to open PC reflector stub to introduce a defined reflection during thereferencing process. This stub would only be used for RL referencing on
angled assemblies and would be removed for IL referencing and whenmeasuring DUTs.

3.0m
14.7 dB

Figure 22 - Pulse-based method for Return Loss referencing and Measurement.

23 of 48

REFERENCE PROCESS
General Rules for Referencing
For IL referencing always re-reference when the cabling setup changes• If the launch cord is exchanged• Equipment cord needs to be replaced

Develop a schedule for referencing• Sources drift slightly with temperature and time
• This may affect the insertion loss reference• It is common to re-reference a setup once every hour or two evenwhen the setup has not changedThe same rules apply for RL referencing• When the length of the reference setup changes re-reference RL• Need to find the new position

If nothing changes with the cabling setup, it isn’t necessary to re-reference
return loss at the same frequency as an insertion loss referenceSM MPO connectors are typically angled and have a low, undefinedreflection value.
• Suggest a short APC to PC MPO cable for a well-defined reflection



System needs to zero out insertion loss along the length of cable up to
the point where the return loss will be measured

24 of 48

CLEANING AND INSPECTION
Cleaning and Inspection Guidance
There should be clear guidance for cleaning and inspection fortechnicians working on an MPO assembly line. Due to MPO assemblies
possibly having male pins, it is necessary to use dedicated MTP®/MPO
cleaning tools. These help to protect the various features of the MPO
endface.
When it is difficult to remove debris, using some alcohol can loosen thedebris so that it can be wiped away.
The guide pins and guide pin holes are essential to a properly mated
MPO connection. These should be routinely cleaned on the reference
connector. This can be done with compressed air or a dental brush.

Figure 23 - Cleaning tools help ensure the performanceand longevity of optical connectors.

25 of 48

CLEANING AND INSPECTION
Cleaning and Inspection Guidance
Cleaning an end face does not guarantee that all the contaminants are
removed, so connectors should be inspected before and after cleaning
to prevent damage when mating. Contaminants on one connector cantransfer to another, so both the reference cord connector and DUT
connector should be inspected, cleaned, and inspected again prior tomating.
Since cleaning and inspection is a pain point for many technicians,
choose tools that make the process simple and smooth. Some inspection
scopes require the user to iterate through each fiber on the MPO
connector. This is time consuming and painful. Instead, use tools that
can inspect all fibers at once. The manta W+ system from Sumix can see
all fibers at once, up to 96. It has a wide field of view allowing the user to
see all 16f of a single row of a 16f ferrule.


Develop clear guidance for cleaning and inspection for your technicians• Inspect the DUT every time it is connected to the reference
connector• Always inspect the reference connector to reduce damage• Assume that if a connector has dust and contamination 		
then the connector it was mated to, also has contamination

Make the inspection process simple and smooth for your technician• Inspect all fibers at once
• Manta W+ system• Can see up to 96 fibers• All 16f in a row

26 of 48

POLARITY
How Fibers are Routed
Polarity describes how fibers are routed from one side of the DUT to the
opposite side. For MPO assemblies there are 3 main types:
1. Type A
Near /

Fiber sequence(viewing the array connector plug end-face with key up)

Far End
Near

1

2

3

4

5

6

7

8

9

10

11

12

Far

1

2

3

4

5

6

7

8

9

10

11

12

2. Type B
Near /

Fiber sequence(viewing the array connector plug end-face with key up)

Far End
Near

1

2

3

4

5

6

7

8

9

10

11

12

Far

12

11

10

9

8

7

6

5

4

3

2

1

3. Type C
Near /

Fiber sequence(viewing the array connector plug end-face with key up)

Far End
Near

1

2

3

4

5

6

7

8

9

10

11

12

Far

2

1

4

3

6

5

8

7

10

9

12

11

When testing MPO assemblies, one must be cognizant of the polarity
types being mated. One of the most common errors is a type A to typeB mating error. This is a simple mistake to make by inserting the ferrule
into the housing upside down.
27 of 48

MEASUREMENT PROCESS– POLARITY VERIFICATION
Prior to testing an MPO assembly for IL and RL, it is advisable to verify
polarity first• A standard large area detector or integrating sphere cannot
differentiate polarity• This should be a quick scan of the assembly• The OP415 can scan 24 fibers within one second• Most common polarities are Type A (key up-key down),
Type B (key up – key up)• TIA TSB-5069 gives guidance on polarity and various
components that affect polarity in a system

Figure 24 - OP415 Polarity Analyzer.

Type B:24

PASS

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Test

Figure 25 - Passing and Failing Polarity Verification on the OP415.

28 of 48

MEASUREMENT PROCESS– INSERTION & RETURN LOSS

Basic Measurement process for MPO to MPO assemblies(standard one-sided method TIA-455-171B, Method D or Method C2 of
IEC 61300-3-4)
To reference connect launch cord to OPM• References powers for all ports

Launch Cord

Connect side A of DUT to launch cord and side B to OPM• Measures IL and RL on side A connector

A
Launch Cord



B
DUT

Connect side B of DUT to launch cord and side A to OPM• Measures IL and RL on side B connector

B
Launch Cord

29 of 48A
DUT

MEASUREMENT PROCESS– INSERTION & RETURN LOSS

Dealing with Gender
Gender on MPO cables can be difficult to manage. Mating connectors of
the same gender can damage connectors (male to male mating) or may
result in poor alignment (female to female mating)When testing assemblies with “like” gender on each side: male-male orfemale-female, a single gendered launch cord can be used.

Female-Female

Male-Male

Example: Testing male-male MPO assemblies
To reference: Connect the launch cord to the OPM (female
connector)

To measure: Connect side A to the launch cord and side B to theOPM. This measures IL and RL on Side A. To measure side B for IL
and RL, flip the cable and connect side B to the launch cord and side
A to the OPM.

A

B

Figure 26 - IL & RL for Side A.

B
Figure 27 - IL & RL for Side B.
30 of 48

A

MEASUREMENT PROCESS– INSERTION & RETURN LOSSWhen an assembly has unlike genders, male-female, there are a few
options:• If twice the channels are available, have two breakouts setup, onewith a male connector and the second with a female connector• All male connectors of the DUT will be tested against the female
breakout and all female connectors will be tested against the malebreakout

The referencing process occurs in two steps:
First, launch cord 1 is connected to the OPM and a reference isperformed.
Male

FemaleFigure 28 - Reference male launch cord.

Second, launch cord 2 is connected to the OPM and a reference isperformed
Male

FemaleFigure 29 - Reference female launch cord.

31 of 48

MEASUREMENT PROCESS– INSERTION & RETURN LOSS

Measuring the DUT
To measure IL and RL on each connector, the proper gendered connector of the
DUT needs to mate to the corresponding launch cord.
The measurement process occurs in two steps:
Side A of the DUT is connected to launch cord 1 with corresponding genderA

B

Figure 30 - Side A is tested against the correctly gendered launch cord.

Side B of the DUT is connected to launch cord 2 with the corresponding gender

B

A

Figure 31 - Side B is tested on the second breakout cable corresponding to its gender.

32 of 48

MEASUREMENT PROCESS– INSERTION & RETURN LOSS

Dealing with GenderWhen an assembly has unlike genders, male-female, but the
instrument set does not have enough ports to accommodate multiple
launch cords, there are a few options:• Test all sides of DUTs that have same gender, then exchange thelaunch cord, swap genders, etc. and test the other side of the
DUTs

To reference: Connect the launch cord to the OPM.

Figure 32 - Male-gender launch cord mated to OPM for reference.

To measure: Connect the DUT side with appropriate gender, forexample female, to the launch cord, which in this example would be amale connector, and the opposite side to the OPM. In this case, after
testing side A do not flip the cable and test side B. The side B gender(male) can not mate to the launch cord. It is best to continue testing the“side A’s” of the DUTs until all have been tested. These are the sides thatmatch the appropriate gender of the launch cable.
DUT 1

DUT 2

DUT N

Figure 33 - Female-gender connector of the DUTs (side A)
is mated to the launch cord and tested first.
33 of 48

MEASUREMENT PROCESS– INSERTION & RETURN LOSS

Dealing with Gender
Once, all “side A’s” have been tested, replace the launch cord with alaunch cord of the appropriate gender to interface with side B, which,since side B is male in this example, the cord would need to have afemale interface. (Note: When exchanging this cord, it is a good practice
to verify a “quality” connection between the equipment cord and newlaunch cord.)MalefemaleFigure 34 - The male-launch cord is swapped out for afemale-launch cord. This allows us to test side B.

When the female launch cord is connected, the system needs to be rereferenced.
Once re-referenced, test all side B’s of the DUTs. At this point both endsof all the DUTs have been tested.
DUT 1

DUT 2

DUT N

Figure 35 - The male-gender connector of the DUTs (sideB) are tested using the female launch cord.
34 of 48

MEASUREMENT PROCESS– INSERTION & RETURN LOSS

Unidirectional Method
The previous methods show one standard way for testing fiber optic
patchcords. Another method is typically referred to as the unidirectional
method.
Measuring insertion loss and return loss in a unidirectional manner

The unidirectional method• This is referred to as “unidirectional” because the IL and RL aremeasured from one side
• There is no flipping the DUT• Performs an IL measurement across the entire assembly• Gives return loss measurements for each connector

RL A		

ILtotal		

RLB

Figure 36 - The unidirectional test method produces
total IL and connector-level RL results.

35 of 48

MEASUREMENT PROCESS– INSERTION & RETURN LOSS

Unidirectional Method- Cable Setup and Process

The cable setup for the unidirectional method is fairly simple. The
reference process is similar to the standard one-side test method. The
power is referenced across all fibers and the position of the launch cord’sreference connector is found. This only gives the position of the front
connector of the DUT. In this method we also want to measure RL on thesecond connector, so this position needs to be known as well.
The measurement is performed by connecting the DUT to the launchcord and then connecting a receive cord on the back end of the DUT. The
receive cord is then connected to the OPM. The IL is measured throughthe entire link, the return loss is measured on the front side of the DUT. To
measure RL on the back side of the DUT, the DUT length either needs to be
known, or the RL instrument needs to perform a scan to find the back endof the DUT.
In this method the DUT has two connections, one to the launch cord and
one to the receive cord. Both of these connections have insertion loss.
Launch Cord

Launch Cord

DUT

Receive Cord

Figure 37 - The use of both a launch cord and a receive cord
make the unidirectional test method possible.

Pros:


Gives all measurements without needing to flip the cable

Cons:


IL measurements of each connector aren’t independent of each other

If an assembly fails for IL, it is not directly known which connector is failing

Need further single sided testing for troubleshooting
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Unidirectional Method- vs Standard One-sided Method
Each test method yields a different set of results
Comparing results:Standard method yields 4 results per fiber optic link
• IL A• ILB• RL A
• RLB

IL A
RL A

ILB
RLB

Figure 38 - The standard method yields connector-level results for IL and RL.

Unidirectional yields 3 results per link
• ILtotal (This is a combination of IL A and ILB)
• RL A• RLB

RL A

ILtotalRLB

Figure 39 - The unidirectional method yields connector-level RL
and throughput IL results.

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Fanouts
Fanout cables require a more complicated test process, similar to
testing hybrid simplex cables. This process usually requires a lot of cable
movement and OPM adapter changes due to the different connector types.

Figure 40 - 12-channel fanout cable with an APC polish MPO
connector fanning out to 12 simplex LC-PC connectors.



Fanouts require a difficult testing process similar to simplex hybrid DUTs
An MPO launch cord and simplex launch cord are necessary

Figure 41 - Recommended launch cable setup for
testing the fanout shown in Figure 40.

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Fanouts– Reference Process
The referencing process requires two steps:
First, connect the MPO to the OPM port and reference the MPO
channels. Second, connect the simplex launch cord to the OPM port
and reference the simplex port. (Note: one needs to change the OPM
adapter from an MPO adapter to a simplex LC adapter for this step)

Figure 42 - The MPO and simplex reference steps for fanout testing.

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Fanouts

Measurement MPO SideThe measurement process requires the user to manually step througheach channel.
First, to test the MPO side of the DUT, connect the launch cord to the
MPO connector of the DUT and then connect Ch1 of the fanout to theOPM. Continue this process for all channels.

Ch. 1

DUT

Ch. 2
DUT

DUT
Ch. 12
Figure 43 - Step through the simplex connectors to test
each port of the MPO side of the fanout DUT.

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Fanouts– Measurement Simplex Side
Second, to test the simplex connectors of the DUT, connect the simplex
launch cord to Ch1 on the fanout side of the DUT and then connect the
MPO connector of the DUT to the OPM. (Note: This requires changing
the OPM adapter.) Continue this process for all simplex channels.

Figure 44 - Connect the simplex connectors to the launch cord
one by one to test each simplex connector of the DUT.

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Fanouts
The unidirectional method can also be used to test fanout DUTs. The
result is a simpler test setup with less moving parts.
Reference setup

Figure 45 - The launch cord is mated to the OPM for the reference step.

Measurement setup

LaunchCord
DUT

Receive
Cord

Figure 46 - Another fanout cable is used as a receive
cable for the unidirectional test method.

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Troubleshooting
Help! My RL is always reporting at less than 20dB for my multimode MPO
cables.
MPO cables that have been used frequently can buildup contamination.
This contamination can be stuck in the guide pin holes or at the baseof guide pins of the reference connector on the launch cord. This
contamination may be outside the field of view of the inspection scope.
If MPO measurements are consistently measuring below 20dB for MM,
this might be a cause. Clean the base of the guide pins and guide pinholes of the reference connector and DUT. Contact your connector orcable vendor for the best methods to do this.
Note: For SM assemblies, return loss values in the mid 50dBs to low
60dBs might be a result of poor fiber contact from contamination on theferrule or guide pin area. Cleaning the guide pins and/or guide pin holes
may fix this issue.

Figure 47 - Dirt can impede proper mating of connectors.

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MEASUREMENT PROCESS– INSERTION & RETURN LOSS

Troubleshooting
Help! My RL is always reporting at less than 20dB for my multimode MPO
cables.
Another potential cause of this issue is core dips. Core dips can cause
an air gap between the two cores when mating and large core dips cancause lower RL. For the reference cord, it is best to keep core dips low.
OptoTest suggests core dips <30nm.

Figure 48 - Core dips prevent the cores from physically matingwhen two connectors are mated to each other.

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General Rules


When failures occur during MPO assembly testing, it is best to retest
the entire connector after rework is done. If fibers that previously
tested well suddenly fail, this could indicate a mating or cleanlinessissue in the setup.



Mating adapters can get dirty too. The dust and debris in mating
adapters can dislodge and land on the end face of connectors. If thetechnician cleans both connectors being mated but dirt continues tobe present, this may be the cause.
• Routinely clean mating adapters. This can be done withcompressed air or placing the mating adapters in an ultrasonic
bath.



OPM adapters can also get dirty. This dirt can transfer onto the DUT or
the launch cord connector. Dirt on the OPM adapter can also impede
light exiting the mated fiber from reaching the detector properly,causing unreliable power measurements that affect IL results. Contact
your equipment vendor for best methods to clean OPM adapters.

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Notes46 of 48

For Application Notes, more detailed Testing
Instructions, and the most up-to-date OptoTest
News go to www.optobuzz.com
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www.optotest.com
1.805.987.1700