Complete Guide for Testing MTP/MPO Fiber Optic Cables

Testing MTP/MPO Fiber Optic Cable Assemblies

A complete guide to testing multifiber push on fiber optic cable assemblies with MPO and MTP Connectors.  Learn various test setups, troubleshooting methods and tips, plus, what to expect in the process.

Introduction:
Testing MTP/MPO Fiber Optic Cables

MTP®/MPO connectors and patch cords are prevalent in fiber networks and their quantities continue to grow as demand for greater capacity and efficiency increases.

These multifiber connectors present unique challenges when it comes to assessing their quality and performance. OptoTest is proud to present 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 maintenance practices to ensure that you have the best testing experience.

Methods for Measuring Optical Return Loss
on MPO MTP Fiber Optic Cables

Comparing two main methods for measuring optical return loss on MPO cables

 

The two main methods to measure optical return loss (ORL) on fiber optic cable assemblies are the continuous wave (CW) method and the OTDR pulse-based method.

Difference between CWRL and OTDR Pulsed-based ORL methods for MPO/MTP cables :

Continuous Wave Return Loss (CWRL)

  • Not recommended for MPO / MTP cables
  • Less expensive equipment purchase
  • More time consuming to setup & requires more steps for testing
  • Requires Mandrel Wrapping and the use of a Matching Block
  • Cannot use this method for Bend-insensitive MultiMode Fiber
  • IL & ORL must be measured in two different steps.
  • Not optimal for production environments

OTDR Pulsed Based Optical Return Loss

  • Ideal for MPO/MTP cables
  • Saves considerable amounts of time in setup
  • Faster, simpler testing process
  • Can measure each reflection independently
  • No terminations needed for RL Tests
  • Works well with higher channel count cables
  • Mandrel wrapping and matching blocks are not needed
  • Can measure both IL and ORL in one pass, saving more time.

Why the Pulse-Based Return Loss measurement method is better

While the CWRL Return Loss test equipment is less expensive than its pulse based counterpart, it is more time consuming and requires more steps for testing MPO assemblies. With the CW method, to properly measure RL, it is necessary to reduce stray reflections caused by 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 to reduce the stray reflections. Using a matching block is also not an ideal solution, especially for MTP®/MPO connectors. Matching blocks can collect debris if left exposed in a production environment, which can then 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.

MTP /MPO Cables Should not be mandrel wrapped or use matching gel

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

The pulse-based (OTDR) method of measuring optical return loss 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 the back connector.

Optical Return Loss Pulse-based (OTDR) Method diagram

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

Test Instrument Selection: 

Automated Solutions

The MPO test process involves many different steps and generates a lot of 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 and stores data to ensure there are no errors and to generate reports.

For multifiber connectors such as MPO assemblies, it is beneficial to include 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 connection of 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 the measurement.

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.

CLX Main Gray
OPLLOG logo image

     

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

Optical Return Loss Testing using OptoTest's OPL-CLX software

 

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

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 for use during the upgrade. In addition, some equipment cannot be upgraded or the cost to do so is comparable to a new system. For instance, not every power meter capable of testing 12 fiber MPO connectors can do the job for 16 fiber connectors. When preparing a production floor to meet current and future needs, it is important to weigh the pros and cons of making a higher initial investment and the hidden costs of failing to do so.

Illustrations of MTP/MPO 12, 16, 24 and 32 fiber connector end faces

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

  • Prior to purchasing equipment, first, understand the immediate and future needs
  • Expandability?  If current requirement calls for 12f, is there a future need for 24, 16, 32, etc.?

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).

Illustration detector spacing on MTP MPO connectors - side view

 

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

Illustration detector spacing on MTP MPO connectors - side view

 

Figure 7

Given the wide pitch of fibers in MPO assemblies, an integrating sphere with 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.

OPM Form Factor

Remote Head Vs. Panel Mount Detector

There are two housings that a detector can come in.  They come as either a remote head or a panel mount detector.

Panel mount detectors are mounted on the front panel of the optical return loss instrument

  • Requires the user to connect the back end of their test assembly to the panel of the instrument every time
  • Sometimes this can be very cumbersome especially with rigid cabling
OP940-SW Multi-Channel ORL Tester Connected with MTP/MPO fiber cables

Figure 8 – Panel Mount Detector.

A remote head detector has the detector in a small semi-portable housing.

  • Tethered to the instrument
  • Allows for a wide range of movement
  • For stiff assemblies or hard-to-route assemblies, the detector can be brought to the DUT
OP940-SW using Sphere for MPO Testing of Optical Return Loss

Figure 9 – Remote Head Detector.

Creating a Multichannel Insertion Loss / Return Loss System

– Method 1:  Simplex ILRL System and External optical switch

There are three options to achieve a multichannel insertion loss and return 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 lead to 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 the switch for MPO testing.

Cons:

  • Complicated setup
  • Possibly affects calibration due to additional external losses in the switch
MPO Testing 2 Fiber Optic Cables with OP940+OP720 for ORL

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

ORL MPO Testing of (4) 12-fiber MPO/MTP Fiber Optic Cables

Figure 11 – 48 Channel test setup using a 1×2 switch cascaded through two 1×24 switches.

– Method 2:   ILRL System with Internal Switch

The second method is a multichannel ILRL meter, combining the elements of the first method in one machine. The all-in-one system allows for a 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.

OP940 Multichannel Insertion Loss return loss power meter

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

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 the front panel makes cable management minimal by eliminating the need for fanout cables. However, expandability is difficult since an external switch cannot be cascaded. This system is also the least flexible with no single fiber connectors for more varied applications.

Dedicated MPO Tester for Insertion Loss and Return Loss OP940-CSW

Typical System Reference Setups

REFERENCE CORD SETUPS: Equipment cord

When setting up an MPO testing station, pay careful attention to the reference 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 and route into a single MTP®
  • Expensive assembly and difficult to replace
  • Stays attached to equipment
Optical Return Loss MPO Testing Setup for 2 12-fiber MPO Fiber Optic Cables using OP940-SW + Sphere

 

Figure 14 – 12f fanout cords connected to a 24 channel ILRL test set.

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 connector of the launch cord will be mated to the DUT.  This open connector is considered the reference connector and as such should be maintained and cleaned 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 adapters should 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 a type 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.  When connecting the launch cord to the equipment cord, the IL and RL should be verified.  Not verifying this connection could result in inaccurate measurements.

OP940SW Testing ORL using launch cords for 2 12-fiber MPO cable testing

 

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

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.

Two 12-fiber equipment cord connected to a 24 channel OP940-sw Illustration

 

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

  • Use two 12f fanout cords to allow for easy transitions between 12 and 24f testing.
Two 12-fiber equipment cords connected to a 24 channel OP940-sw Illustration

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 the equipment cord.

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 cable enables the ability to test dual row cable assemblies.  Figure 18 shows an example of a 24f setup employing 2 12f MPOs to 1 24f MPO.

A dual 12-fiber fanout to single 24f MPO / MTP cable is connected to the equipment cords.

 

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.

Launch/Reference Cords

When setting up the testing space, use reference cords that match your requirements.  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.

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

A jacketed cord is rugged and durable, but does not allow for easy gender changing.   A bare ribbon cord allows for easy gender swapping, but it is fragile 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 is rugged and able to withstand rough handling.

Jacketed cord

  • Rugged and durable
  • Gender not changeable

Bare ribbon cord

  • Easily change gender
  • Ribbon fiber fragile so needs to be handled accordingly

MTP® Pro cord

  • Rugged and durable
  • Gender swappable
  • Best of both worlds

Multimode 50µm Reference Cables

Multimode 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 intermediate connections.  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 core helps 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.

Multimode 50µm MTP/MPO non-BIMMF Fiber Cable Testing

 

Figure 20 – Non-BIMMF fiber helps to maintain launch conditions when testing MM fiber.

  • Cords should be non bend insensitive throughout: 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 obtain accurate EF compliant measurements and OptoTest can supply such launch cords
  • Encircled Flux must be maintained through connections

Reference Process

Insertion Loss Reference Method

An insertion loss reference records the powers of each port in the launch cord.  These powers will be used to calculate insertion loss during the measurement process.

Sample Insertion Loss reference values for a single mode system.

 

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

  • A reference is taking a baseline optical power measurement for each channel 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

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 usually at the position of the reference connector.

A pulse is sent out to find the open connector of the launch cord and light reflects back towards the source from this open connector. Based on the magnitude of the returned pulse and the time it takes to return, the location and the reflection size are determined.  In the example below, the reflection is at 3.0m as measured from the front panel. Because this is a flat connector, the reflection is about 14.7dB.

Single mode MPO connectors are typically angled and as such have a small, undefined reflection value. Angled open connectors can have a range of values from the mid 50dBs to high 70dBs depending on the polishing 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 the referencing process. This stub would only be used for RL referencing on angled assemblies and would be removed for IL referencing and when measuring DUTs.

Pulse-based method for Return Loss referencing and Measurement

 

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

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 even when 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, undefined reflection 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

Cleaning and Inspection Guidance

There should be clear guidance for cleaning and inspection for technicians 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 the debris 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.

Photos of MTP / MPO Fiber Cable cleaning products

Figure 23 – Cleaning tools help ensure the performance and longevity of optical connectors.

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 can transfer to another, so both the reference cord connector and DUT connector should be inspected, cleaned, and inspected again prior to mating.

SMX Manta W+ portable microscope

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

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

Type A Fiber Sequence of MTP Connector
Type A MTP Cable showing left key up - right key down position

2.  Type B

Type B MTP Cable Fiber Sequence
Type B MTP Cable left key up - right key up position

3.  Type C

Type C MTP Cable Fiber Sequence
Type C MTP Cable left key up - right key down position

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 type B mating error. This is a simple mistake to make by inserting the ferrule into the housing upside down.

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
Photo of OP415 MTP/MPO Polarity Testing Benchtop Tester

Figure 24 –  OP415 Polarity Analyzer.

OP415 Polarity Test Pass ScreenOP415 MPO/MTP Polarity Tester "Fail" Screen
Figure 25 – Passing and Failing Polarity Verification on the OP415.

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
MTP Launch Cord Illustration
  • Connect side A of DUT to launch cord and side B to OPM
    • Measures IL and RL on side A connector
MTP Launch cord and Fiber Cable under test
  • Connect side B of DUT to launch cord and side A to OPM
    • Measures IL and RL on side B connector
MTP Launch cord and Fiber Cable under test - Cable Swapped

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 or female-female, a single gendered launch cord can be used.
Male to Male MTP Cable

Male – Male 

Female to Female MTP Cable

Female – Female

Example: Testing male-male MPO assemblies

To reference: Connect the launch cord to the OPM (female connector)

Connecting the launch cord to the OPM (female connector)

To measure: Connect side A to the launch cord and side B to the OPM. 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.

Connecting MTP Cable side A to the launch cord and side B to the OPM

Figure 26 – IL & RL for Side A.

Connecting MTP Cable side B to the launch cord and side A to the OPM

Figure 27- IL & RL for Side B.

  • When an assembly has unlike genders, male-female, there are a few options:

• If twice the channels are available, have two breakouts setup, one with 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 male breakout

The referencing process occurs in two steps:

First, launch cord 1 is connected to the OPM and a reference is performed.

First Reference male launch cord

Figure 28 – Reference male launch cord.

Reference Female launch cord

Figure 29 – Reference female launch cord.

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 gender

Side A is tested against the correctly gendered launch cord

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

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

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

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 the launch cord, swap genders, etc. and test the other side of the DUTs

To reference: Connect the launch cord to the OPM.

Side A is tested against the correctly gendered launch cord.

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

To measure: Connect the DUT side with appropriate gender, for example female, to the launch cord, which in this example would be a male 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 that match the appropriate gender of the launch cable.

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

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

Once, all “side A’s” have been tested, replace the launch cord with a launch 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 a female interface. (Note: When exchanging this cord, it is a good practice to verify a “quality” connection between the equipment cord and new launch cord.)

Example of male-launch cord swapped out for a female-launch cord

Figure 34 – The male-launch cord is swapped out for a female-launch cord. This allows us to test side B.

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

3 Fiber Optic Cables and 3 different test configurations

Figure 35 – The male-gender connector of the DUTs (side B) are tested using the female launch cord.

Unidirectional Method

The previous methods show one standard way for testing fiber optic patch cords. 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 are measured from one side

• There is no flipping the DUT

• Performs an IL measurement across the entire assembly

• Gives return loss measurements for each connector

Uni-Directional Return Loss Configuration with Insertion Loss

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

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’s reference 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 the second connector, so this position needs to be known as well.  The measurement is performed by connecting the DUT to the launch cord 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 through the 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 end of 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.

Fiber Optic Cable Test with Launch and with both launch and receive cords

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

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

  •  ILA
  •  ILB
  •  RLA
  •  RLB
MPO Fiber Cable Test illustration of Side A, Side B

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

Unidirectional yields 3 results per link

  • IL total (This is a combination of ILA and ILB)
  •  RLA
  •  RLB
MPO Fiber Cable Test Illustration of Side A & B for Return Loss and Insertion Loss total

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

Fanout Cables

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.

Fanout Fiber Cable MTP Male to 12 LC connectors

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

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

Fanout Cables

– 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)

MPO Fiber Cable Referencing Step #1
MPO Fiber Cable Referencing Step #2

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

Fanout Cables

Measurement MPO Side

The measurement process requires the user to manually step through each 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 the OPM. Continue this process for all channels.

Step through the simplex connectors to test each port of the MPO side of the fanout DUT illustration

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

– 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.

Illustrations showing how to connect the simplex connectors to the launch cord

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

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

Reference Setup

Illustration showing launch cord mated to the Optical Power Meter for the Reference Step

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

Measurement Setup

Another variation of the Fanout MTP Cable use as receive cable.

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

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 base of 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 pin holes of the reference connector and DUT.  Contact your connector or cable 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 the ferrule or guide pin area.  Cleaning the guide pins and/or guide pin holes may fix this issue.

Illustrations showing how dirt can impede proper mating of fiber optic connectors.

Figure 47 – Dirt can impede proper mating of connectors.

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 can cause lower RL. For the reference cord, it is best to keep core dips low. OptoTest suggests core dips <30nm.

Illustration showing how core dips prevent the fiber cores from physically mating when two connectors are mated

Figure 48 – Core dips prevent the cores from physically mating when two connectors are mated to each other.

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 cleanliness issue 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 the technician cleans both connectors being mated but dirt continues to be present, this may be the cause.
    •   Routinely clean mating adapters.  This can be done with compressed 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.

The Harsh Realities of Testing Ruggedized Fiber Assemblies

Share This...

This content in this post applies to testing military grade connector systems such as MIL-PRF-28876 and MIL-DTL-38999 series connectors, as well as commercial graded connector systems like the Senko™ series IP Plus and IP-9 hardened assemblies.

The content in this post was presented by OptoTest in an Optica Sponsored Webinar “The Harsh Realities of Testing Ruggedized Fiber Assemblies.”  For further clarification of topics that may lack context or not be clear in this post, please Watch the Webinar Here.

OptoTest Webinar October2021 2

favicon  Overview

  • What is a ruggedized assembly?

  • Equipment options for IL and RL testing of ruggedized assemblies
  • Complexities associated with ruggedized assemblies
  • Cabling setups for testing ruggedized assemblies
  • Multimode launch condition concerns
  • Vibration and shock testing

favicon  What is a Ruggedized Assembly?

For the purpose of this presentation, ruggedized assemblies are:

  • Hardened assemblies that, many times, will have rigid cabling.
  • Assemblies terminated where at least one end of the cable is connectorized with a large weather-proof, or vibration/shock proof connector.
  • Typically, assemblies with no available optical power meter adapter for one or all of the connectors.
  • Connectors use 2.5mm, 1.6mm, 1.25mm and MPO ferrules

Rugged webinar pg4a Rugged webinar pg4b

 

favicon Equipment Selection

Insertion Loss and Return Loss Meter

Different configurations:

Simplex system:  Good for Simplex assemblies, hybrid cables, some duplex cables.

Illustration for Simplex assemblies, hybrid cables, some duplex cables.

Multichannel:  Integrated switch for multifiber assemblies, small footprint

Rugged webinar pg5b

 

Optical Power Meter
  • Multichannel Power Meter is good for testing DUTs with multiple connector types
    • Allows for discerning polarity in certain cases.

OP710 Optical Power Meter Benchtop/Rackmount Multichannel

  • Integrating Sphere / Large Area Detector
    • Allows for large wide aperture connectors in most cases.
    • Cannot discern polarity.

OPSPHR integrating sphere

favicon Workstation Organization

  • Ruggedized assemblies can have many fibers and cables within an assembly.
  • Assemblies are typically rigid or difficult to bend.
  • Ruggedized cabling typically has “memory” and when bent might return to their previous form.
  • Handling the reference cords, DUTs, receive cords, etc. can get “clunky” when in constrained spaces.
  • Keeping the workstation organized can help to minimize technician error.

Rugged webinar pg7

 

favicon Selecting a Test Method

  • Understanding what needs to be measured helps to define how to measure.
      • Does each connector need to be measured?
        • Connector Loss measurements.
      • Does the full assembly need to be measured?
        • Link loss measurements.

     

  • The DUT structure and available equipment are factors as well.
    • Simplex or Multichannel source.
    • Simplex or Multichannel optical power meter set.
  • Cable assemblies typically have three components that contribute to insertion loss and return loss.
    • Front connector (Side A).
    • Back connector (Side B).
    • Fiber (Link(s) from A to B).

Rugged webinar pg8

 

Connector Insertion Loss and Return Loss

To accomplish this:

  • Power must be measured directly out of the reference connector during the reference step.
  • Power must be measured directly out of the Side B connector for measurement of side A.

Rugged webinar pg9a 1Rugged webinar pg9b

ILCon (dB) = Pref (dBm) – Pmeas (dBm)

 

Selecting a Test Method (Connector Loss)

For ruggedized assemblies this can become very challenging to measure power out of the reference connector or the DUT connector.

  • OPM adapters are not designed for many of these types of connectors.
  • Measuring power out of each ferrule of a ruggedized assembly could be inaccurate and potentially leave the connector open to dirt and damage during the measurement process.

Rugged webinar pg10a      Rugged webinar pg10b

 

 

favicon What is a “Bucket” Cable?

To properly measure the optical power at the launch reference connector we need to get creative.

  • Large core “bucket” fiber assemblies.
    • Provides a zero-loss connection to route the light to the OPM.
    • Effectively it is an extension of the optical power meter.
    • Fiber has loss, so receive cable should stay rather short.
      • This loss is referenced out.

Rugged webinar pg11a

Rugged webinar pg11b

 

Large Core Bucket Cable Requirements

Large core fiber, must be significantly larger than test fiber. The larger core allows for all light to be transmitted through the connection even if there are slight offsets.

Rugged webinar pg12a

Fiber used should also have a larger NA than the DUT.

  • If the fiber has a larger core size, but lower NA, then high NA light will still escape through the cladding, leading to excess loss at the connection.

Rugged webinar pg12b 1

If possible, use a bucket cable constructed of graded index fiber.

  • This helps to control the modal distribution in the receive cord.
  • Light remains constrained to the center of the fiber.

Rugged webinar pg13

What to Consider When Using a Bucket Cable

This is typically a physical contact mating.

  • Any time two connectors mate there is a possibility of damage to either or both of the connectors.
    • These are typically large channel count connectors and maintaining, inspecting and cleaning can get time consuming.
    • A standard OPM does not present this problem.
      • This is a non-contact solution.
  • Dirt or a poor connection at the mating will reduce the power level measured.
    • If this occurs during the reference, low losses will be measured -> sometimes getting gainers.

Rugged webinar pg14

Typical Connector Loss Measurement With Bucket Cable

Reference and Measure as normal, except treat the bucket cable connector as the OPM connection.

Rugged webinar pg15

Because the mating to the bucket cable is essentially zero loss, it is like connecting directly to the optical power meter.

favicon Testing Connector Loss With a Bucket Cable

The structure of the DUT defines the types of source and receive cords necessary for the test.

  • For a DUT where both ends can mate to each other, such as a receptacle to a plug, the same bucket cable can be used for reference and measurement.
  • Using a multichannel power meter assures proper polarity of the DUT.
  • The system will step through each port and reference insertion loss.
Rugged webinar pg16a
DUT
Reference Setup

Rugged webinar pg19

Referencing return loss, for a pulse-based system, consists of the system finding the position where return loss is to be measured.

  • It is also possible with many systems to specifically tell what position to measure return loss at.
  • For a standard return loss reference leave the bucket cable disconnected from the reference connector.

Rugged webinar pg17b

To measure the DUT it is connected between the reference connector and the bucket cable.

  • Because the loss is negligible at the DUT to Bucket cable mating, the loss measured is effectively due only to the reference connector and DUT mating.
  • Any routing issues will be reported as dark measurements.
Measurement Setup

Rugged webinar pg18

A DUT where both ends cannot mate to each other and there is no hybrid adapter could require two types of bucket cables for the test.

  • The reference setup cable needs to be able to mate to the reference connector.
DUT ruggedized
DUT
Reference Setup

Reference Setup diagram

  • For the measurement setup, the receive cable needs to be able to mate to the DUT.
  • This requires removing the reference receive cable and replacing with another.
    • Potentially introduces error into the test (misrouting receive cable, adding contaminants, etc.)
Measurement Setup

Rugged webinar pg20

To limit the amount of connecting and disconnecting between the reference setup and measurement setup a “zero loss” conversion cable can be used.

  • This should be a large core fiber assembly of similar type to the receive fanout cable.
  • This cable should be similar in structure (same connectors on both ends) and polarity as the DUT.
DUT ruggedized
DUT

Rugged webinar pg21a

 

 

Rugged webinar pg21b

If polarity isn’t a concern, then a different type of receive cable can be used.

  • In this case the receive cable has an MPO connector that can be routed to the OPM.
    • Up to 32 ports in one connector.
Reference Setup

Rugged webinar pg22

In some cases, using a simplex system is easier and cleaner to manage.

Benefits

  • Less expensive than multichannel setup.

Drawbacks

  • Slower than multichannel test setup.
    • Requires one to manually iterate through each port.
  • Less accurate than a multichannel setup. Typically yields higher loss due to the additional connector during the measurement.

Referencing is simple because there is no need for a bucket cable.

  • Connect source/launch cable directly to OPM.
Reference Setup

Rugged webinar pg24

 

Testing Connector Loss With a Bucket Cable (Return Loss Considerations)

  • To reference return loss on this setup, the simplex launch cord needs to be connected to the launch fanout cord.
  • Return loss is then referenced to find the position at the end of the launch fanout reference cord.
  • Return loss will be measured at this position.

Rugged webinar pg25

  • Use a bucket receive cable for zero loss connection on back of DUT.
  • Introduce a fanout cable to the measurement setup
  • For the measurement, the technician needs to iterate through each connector.
    • Inspect and connect to source side
    • Inspect and connect to the OPM.
  • What’s being measured?
    • Insertion loss is being over estimated
    • Insertion loss of the launch cable isn’t being referenced out and is included in the measurement.
    • May not matter, due to quality of connectors and restricted launch conditions.

favicon Concerns When Testing With Simplex System

Identifying port to measure.  In this graphic the cables look nice and organized.  It is almost never like this.Rugged webinar pg27

It usually looks something like this…

Rugged webinar pg27a

Or even worse, after testing/retesting for a few DUTs, it ends up looking like this…

Rugged webinar pg27b

The result is that the technician doing the measurement needs to search for the specific port to test or retest.  This leads to lost time and potentially incorrect measurements.

Identifying port to measure

  • Take a little extra time to organize the launch and receive cables into bundles.
  • These bundles reduce the amount of tangled fibers.
  • Allow for a technician to quickly identify the bundle of the port to be tested.
    • Easily identify the port within the bundle.
  • Bundles can be numbered or color coded.

Rugged webinar pg27c

 

favicon Testing Connector Loss With a Test Probe

  • A test probe can be used to mate a simplex port to a multiport DUT without the need for a fanout launch cable.
  • A test probe mimics a real interconnection.
  • These probes many times have a quick release system to easily insert and remove from the mating adapter.
  • If using a test probe, simply connect the test probe to the OPM using a suitable adapter to reference the test.
    • These are usually: 1.25mm, 1.6mm or 2.5mm universal adapters.
Reference Setup

Rugged webinar pg29

 
Testing Connector Loss With a Test Probe (Alternative)

To test each port:

  • Insert the probe into each port on the adapter.
  • Connect the corresponding receive bucket cable leg to the OPM port to measure IL.
  • The use of an adapter ensures that the mating properly mimics an actual full mating.
  • The loss measured here does not include an additional connection as it did when using the launch fanout cable with a simplex equipment cord.
    • Losses will be more accurate.

Other types of probes are available with standard ferrule sizes that don’t properly mimic a true connection.

  • Don’t latch in properly
  • Probe RL is susceptible to pressure applied.

Rugged webinar pg30

 

favicon Considerations When Testing Bend Insensitive Multimode Fiber

It is recommended to use non-bend insensitive fiber for launch cords.

  • Non-BIMMF maintains launch conditions better.
  • BIMMF can be used but launch conditions shall be conserved.

Short BIMMF DUTs, will hold on to cladding modes for longer lengths of fiber.

  • Under-represent insertion loss because a short BIMMF DUT looks like a large core fiber with low loss.

Rugged webinar pg31

favicon Testing Link Loss of an Assembly

When testing link loss the entire loss of the assembly is to be measured.

Rugged webinar pg32This includes:

  • The front connection
  • The fiber contribution
  • The rear connection

 

Unlike with the connector loss setup, a receive cable of the same fiber type should be used to capture the rear connectors insertion loss.

  • If the DUT is 50μm then the receive cable should be 50μm.

 

favicon  Example Link Loss Test

For a total assembly loss test the source side setup stays the same.

The reference can be performed with a bucket cable to capture the power at the reference connector.

  • For a link loss test try to not use a receive cable of the same fiber type as the DUT.
  • Creates additional losses during the reference setup and leads to loss measurements that are too low.

Return loss is still reference to the end of the reference connector which will be connected to the front end of the connector.

Reference Setup

Reference Setup OP940-SW and OP740 Example Link Loss Test

 

 

For a total assembly loss test the source side setup stays the same.

To measure a DUT, it is possible to replace the receive bucket cable with a receive cable of like fiber type as the DUT.

  • Yields loss across connection A, fiber, and connection B.
  • Cumbersome.

Use “conversion” cables.

Measurement Setup

Rugged webinar pg34a

Example Link Loss Test with OP940sw and OP710

Measuring return loss on the front end is straightforward.

  • The position was found during the referencing process.

To get the second reflection, at the back side of the DUT, the system must scan out and find the second reflection position while the DUT is connected.

Measurement Setup

Rugged webinar pg37

favicon Considerations When Testing Bend Insensitive Multimode Fiber

  • For receive cords, care should be taken when choosing a length of receive cable
  • Too short and losses will be measured too low.
  • BIMMF holds on to lossy modes that standard MMF would have lost dissipated
  • For short lengths this is effectively a bucket cable.
  • Might need to discuss with fiber manufacturer, but usually 10m of fiber is sufficient to remove the lossy modes.

length receive cable

 

 

favicon Launch Conditions for Multimode Assemblies

  • Multimode insertion loss is highly dependent on the launch condition of the reference cord.
  • Military standards call out many different launches.
    • 70/70 (70% spot size, 70% NA).
    • AS50, AS62, AS100.
    • Overfilled (loosely defined)underfilled - overfilled launch
  • Underfilled -> lower measured insertion loss -> less affected by core offsets.
  •  

Underfilled -> lower measured insertion loss -> less affected by core offsets

  • Encircled Flux -> Slightly underfilled launch -> more affected by core offsets.

Encircled Flux -> Slightly underfilled launch -> more affected by core offsets.

 

favicon Summary for Insertion Loss and Return Loss measurements

  • Always keep the work station organized
    • Rack mount test equipment to free up space and go vertical.
  • For connector loss tests
    • Use bucket cables to measure power out of launch cord
    • User large core golden (zero-loss) cables when launch and receive cords can’t mate to each other.
    • When testing with a simplex setup and a simplex (non-test probe) cable organize the fan in and fanout cords to reduce testing time
    • When using a test probe, use a test probe that properly mimics a real connection.
  • For link loss tests
    • Use a bucket cable to still capture all the power from the launch cable.
    • Use a receive cable of the same fiber type as the DUT to connect between the DUT and the large core bucket cable.
  • For multimode cabling tests
    • Always remain conscious of the launch conditions.

 

favicon Shock and Transient Monitoring of Ruggedized Connections

  • Ruggedized connectors and assemblies are intended to be used in harsh environments.
    • Exposed to constant vibrations and quick shocks.
  • Assemblies should be qualified to ensure that connectivity is sustained through the vibrations and shocks.
  • For these tests, a high-speed detector system is necessary.
  • OP740 High Speed Multichannel Optical Power MeterThe OP740 has:
    • Wide dynamic range (+10dBm to -70dBm).
    • IEC 61300-3-28 Transient Loss monitoring.
      • 250µs Sampling.
    • MIL STD-1678-2A.
      • 25us Sampling.
    • Virtually unlimited buffering.

To monitor transients a continuous optical source is needed.OIDA Rugged_750sw-740 illustration

  • For SM a laser source is suggested.
  • For MM an LED source is suggested.
    • With appropriate launch conditions
  • An optical switch cannot be used.

In this case the DUT is inserted during the reference process and a zero level is taken with the DUT connected.

  • All transient measurements will be taken relative to this zero level.Many times, it is only a connection that is being monitored and affected.
  • Shock and Transient Monitoring of Ruggedized Connections illustrationOnce the system is referenced the high-speed power logging can start.
    • For vibration testing the vibration apparatus can start.
      • Typically, vibration testing is done for multiple axes.
      • Requires long logging (deep buffer)
      • Tests typically last for 15 minutes to 1 hour.
    • For shock testing the shock can be induced on the connection.
      • A shock can be induced on multiple axes as well.
  • After the mechanical stress has stopped, the system should still be allowed to relax.
    • This allows for one to monitor residual loss, which is that signal fluctuation as the system returns to steady state.
    • The optical monitoring should continue while the system reaches steady state.

Analyzing Data

  • Typically, one looks for events of data where optical power either increase or decreases by a certain level.
  • AN 147 Figure 4 Shock graph 1There are 3 characteristics
    • The depth is the largest level the signal changes.
    • Width is the length of time the signal drops below the defined threshold.
      • (0.5dB to 3.0dB)
    • Residual loss is the steady state loss of the connection.
      • Once the transient has occurred, where does the signal level out at?
      • This can sometimes be a positive value.

 

favicon Transient Loss Summary

  • Use continuous sources and not a switched source.
  • System needs to be able to log long buffers
    • Vibration typically requires 15 minutes to 1 hour for testing
    • Allows for monitoring residual loss long after the event has occurred.
  • Events have a depth, width and a residual loss.

 

ChrisChris Heisler,
Chief Technology Officer

 

Visit our Resource Library

What is Insertion Loss?

Share This...

Insertion Loss:  What is insertion loss?  Where does it come from?  Single mode and multimode fibers.

Insertion Loss: What is it? 

Continue reading

Graded Index Fiber vs. Step Index Fiber

Share This...

Why use Graded Index Multimode Fiber?

 wedge icon Multimode Fiber Profiles: Step Index vs. Graded Index

  • There are mainly two types of multimode fibers: Step Index and Graded Index fibers
  • The core on a step index fiber has the same refractive index throughout.
  • The refractive index on a graded index fiber gradually changes from the center of the core, to where the core meets the cladding.
Step index vs. Graded index profiles compared

wedge icon Step Index Fiber vs Graded Index Fiber

Step Index Fiber

Shows a clear distinction between the core and cladding.

Step Index fiber microscope view

Graded Index Fiber

Shows a gradual change from the core and cladding.

Graded Index Fiber Shows a gradual change from the core to the cladding

wedge icon Issue with Step Index Fiber

light rays traveling diagram
  • Light rays travel somewhat uncontrolled inside a step index fiber.
  • The blue ray travels directly down the center of the fiber, meaning it travels a shorter distance than the red, green or black ray.
  • Rays that travel a longer distance will take more time to get to the end of the fiber than rays that travel a shorter distance.
  • The result is that some of the signal arrives before the rest of the signal. The signal becomes smeared.
  • This is bad for communication.

wedge icon Advantage of Graded Index Fiber

  • Light rays are controlled well within a graded index fiber.
  • Just as with the step index fiber, certain rays will travel shorter distances than other rays.
  • However, in a graded index profile fiber the rays will reach the end of the fiber at the same time…
  • How does this happen?
graded index light rays travel diagram

wedge icon Optics of Step and Graded Index Fiber

The speed of light depends on the refractive index of whatever the light is traveling in.

  • When traveling in space (air, refractive index is 1.0) light travels at 300,000km/s
  • When traveling in glass, where the refractive index is 1.5, it travels at 200,000km/s
  • Changing the refractive index changes the speed of light!!!
Step index vs. Graded index profiles compared

Since the refractive index of the core in a step index fiber is the same, the light rays will all travel the same speed. (Rays that travel a shorter distance will arrive sooner than rays that travel a longer distance.) However, the refractive index of the core in a graded index fiber changes, which means light rays inside the core will travel a different speeds.

wedge icon Graded Index Fiber

  • In a graded index fiber, the refractive index at the center of the fiber is the highest. This means that the light traveling at the center of the fiber travels slower.
  • Rays that don’t travel in the center will travel faster. As the rays move farther from center, they will travel faster.
  • The result is that all of the rays in the core will arrive at the end of the fiber at the same time. This is ideal for communication.
Graded index profiles graph
graded index light rays travel diagram

wedge icon Step Fiber vs Graded Fiber in the Industry

Step Fiber

  • Short distance applications
  • Lower cost
  • More prone to attenuation
  • Over shorter distances, the disadvantages of step fiber are outweighed by the lower cost of deployment

Graded Fiber

  • Long distance applications
  • Higher Cost
  • Less prone to attenuation
  • Over longer distances, the benefits of the graded fiber are worth the added cost

The Importance of Calibration

Share This...

With any measurement instrument or tool used to qualify product, it is mandatory that the tool or instrument be 100% functional and measure per the appropriate specifications when used.  A manufacturer’s calibration can perform both functions.  A system inspection and calibration verify that the instrument is functional and that the instrument was and is measuring accurately, while routine maintenance helps to ensure the instrument will continue to function going forward.

While an instrument’s self-calibration or internal calibration is convenient for routine spot checking and verification, it should never replace a full calibration performed by an unbiased and trained professional.

Continue reading

How You Accurately Test Performance of Hybrid Cables Tutorial

Share This...
Hybrid Cable diagram

 

Hybrid Cable – Simplex

 

Hybrid Cable Solution Sheet  SOL-001Rev.A

Fiber patch cables, also known as patch cord or jumper cables, are fiber optic cables that are terminated with connectors on both ends. When the connector types on each end are different, the cable is aptly dubbed a HYBRID CABLE. These hybrid cables can serve to link otherwise incompatible infrastructure in existing fiber systems, such as those found in networks or data centers. They can be used to connect newer racks to legacy hardware, in distribution hubs to branch lines from high density panels to the nodes they serve, or to connect between devices from different manufacturers.
Continue reading

Switches, Lossy Components, and the Need for External Reflectance Standards

Share This...

This article focuses on RL measurement setups that are prone to introducing testing errors. Ways to mitigate these errors are discussed. Some errors are unavoidable; therefore, steps for correcting them out or reducing them are also described here. Continue reading

Industry Update – Visual Inspection Standard

Share This...

A recent update to IEC 61300-3-35 (Fiber optic connector endface visual and automated inspection) is moving forward with the intention to modernize inspection practices and provide more uniform results industrywide.

The updates aim to accomplish three things:

  1. Link visual inspection results to optical performance
  2. Make results more uniform between manual (visual) and automated (software) platforms
  3. Make results more uniform between different automated platforms

Continue reading

Ensuring Accurate Return Loss Measurements

Share This...

OptoTest equipment provides the most accurate Return Loss measurements in the industry. In this presentation you will learn more about the elements that make that possible and things to keep in mind to ensure optimal performance.

Ensuring Accurate Return Loss Measurements

Continue reading