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Transcript of Optical Fiber Connector Handbook - Senko Fiber Connector Handbook - ver… · 4 1White PaiprJP...


    Optical Fiber Connector Handbook

    Bernard LeeTom Mamiya




    Optical Fiber Connector Handbook

























    Introduction to SENKO

    Basic of Optical Fiber

    Introduction to Optical Fiber

    Optical Fiber Connectivity

    Fiber Optic Connectors

    Basics of Fiber Optic Connectors

    Fiber Optic Connector Assembly

    Connector Assurance (GR-326-CORE)

    Service Life Test

    Extended Service Life Test

    Random Mating Loss Performance

    Connector Testing

    Insertion Loss

    Return Loss

    Introduction to Test Equipment

    Power Meter & Light Source


    Optical Time Domain-based Measurement (OTDR)


    Backscatter Coefficient Settings

    Index of Refraction (IOR)

    Mode Field Diameter (MFD) Mismatch

    Dead Zone

    Helix Factor



    Optical Fiber Connector Handbook

    Optical Continuous Wave Reflectometer (OCWR)


    Testing Procedure

    Insertion Loss Measurement with Power Meter & Light Source

    Cut-back Method

    Substitution Method

    Insertion Method

    Insertion Loss Measurement with OTDR

    Return Loss Measurement with OTDR

    Return Loss Measurement with OCWR

    Connector Hygiene


    Optical Connector Ferrule & Contamination

    Inspection Standards

    Inspection Tools

    Inspection Tools for MPO Connectors

    Cleaning Tools

    Cleaning Challenges for MPO Connectors

    IEC Connector Type

    IEC 61754-2 BOFC Connector

    IEC 61754-3 LSA Connector

    IEC 61754-4 SC Connector

    IEC 61754-5 MT Connector

    IEC 61754-6 MU Connector

    IEC 61754-7 MPO Connector




























    Optical Fiber Connector Handbook

    IEC 61754-8 CF08 Connector

    IEC 61754-9 DS Connector

    IEC 61754-10 Mini MPO Connector

    IEC 61754-12 FS Connector

    IEC 61754-13 FC Connector

    IEC 61754-15 LSH Connector

    IEC 61754-16 PN Connector

    IEC 61754-18 MT-RJ Connector

    IEC 61754-19 SG Connector

    IEC 61754-20 LC Connector

    IEC 61754-21 SMI Connector

    IEC 61754-22 F-SMA Connector

    IEC 61754-23 LX.5 Connector

    IEC 61754-24 SC-RJ Connector

    IEC 61754-25 RAO Connector

    IEC 61754-26 SF Connector

    IEC 61754-27 M12 Connector

    IEC 61754-28 LF3 Connector

    IEC 61754-29 BLINK Connector

    IEC 61754-30 CLIK! Connector

    IEC 61754-31 N-FO Connector

    IEC 61754-32 DiaLINK Connector

    IEC 61754-34 URM Connector



























    Introduction to SENKO

    SENKO Advanced Components is a wholly owned

    subsidiary of the SENKO Group, which is headquartered

    in Yokkaichi, Japan. From its humble beginnings in 1946, the SENKO

    Group currently has an estimated annual revenue of $1.4 billion

    globally. SENKO Advanced Components itself has 14 offices and

    dozens of design and manufacturing facilities providing local support

    to customers all around the globe.

    SENKO Advanced Components develops, manufactures, markets and

    distributes over 1000 fiber optic products for the telecom & datacom

    industries worldwide.

    SENKO Advanced Components was incorporated in the United States

    in the early nineties and has since being recognized as one of the

    industrys specialists in passive fiber optics interconnect and optical


    An ISO-9001 approved company, SENKO is able to provide

    multinational corporations with the technical expertise to liaise

    with engineers, and the manufacturing flexibility to develop custom

    products for the ever growing high tech industry.

    Many of our products were created to resolve a specific design

    challenge faced by our customers. We offer one of the industrys

    largest product portfolios, and our quality is second to none.

    Our mission is to be the best global provider of passive fiber optic

    components. We strive to provide an extensive portfolio of high

    quality products and services, available on a global scale, with

    excellent delivery time. We will stand by products, providing our

    customers with superior post-sales support.

    Our customers, suppliers and partners are essential to our success, and

    shall be treated with respect and integrity. Our team is committed to

    understanding the technical requirements and service expectations

    of our customers, and share the goal of resolving the specific

    challenges these clients face in their own business.


    Introduction to Optical Fiber

    Optical Fiber Connectivity

    The use and demand for optical fiber networks has experienced

    exponential grown over the past years. Optical fiber networks

    are widely deployed for various applications ranging from global

    telecommunications, signaling to desktop computers. These includes

    the transmission of voice, data and video over short distances of

    meters to hundreds of kilometers across continents.

    Optical fiber is also used in systems for reliable and secure

    transmission of data and financial information between computer

    terminals, companies and countries around the world. Cable television

    companies also use optical fiber to deliver data services and digital

    video content to consumers. With the introduction of online video

    streaming and higher definition video such as the 4K format and

    the upcoming 8K format, optical fiber is required to deliver higher

    bandwidth connectivity.

    Optical fiber also enables new technology, application and services

    such as remote learning and tele-medicine through transmission

    of digital content and low latency control of remote devices. Other

    applications for optical fiber includes automation, automotive,

    industrial, space and military.

    In order to build an optical fiber network, optical connectivity is required to extend, branch or split an optical fiber. There are mainly three

    methods to terminate an optical fiber, which are fusion splicing, mechanical splicing and optical connectors.

    Fusion splicing is the process of welding two optical fibers together. This is usually done by using and electrical arc in a fusion splicer. The ends

    of the two optical fibers are melted and forms a continuous bond. This method results in the lowest attenuation and reflectance. It also provides

    the strongest and most reliable joint between two fibers.

    Mechanical splicing is the process of jointing two optical fibers through a mechanical splice unit. The mechanical splice is a self-contained unit

    that has a V-groove which aligns the optical fiber within the unit. The two fibers are butted against each other with some index matching gel

    to improve the optical transmission. Mechanical splicing is a non-permanent connection.

    An optical connector is a termination at the end of an optical fiber that enables a quick and flexible fiber mating and demating compared

    to splicing. The connectors are mechanically coupled to align the fiber cores. Fiber optic connectors are usually used in situations that require

    quick fiber termination or increased flexibility such as in cross connection panels and customer premises termination.

    Basics of Optical Fiber



    Silicon Photonics/ On-Board Optics

    Data Centers


    Medical Fiber Optic


    Fiber Optic Connectors

    There are many types of optical connectors. Different types of

    connectors are used depending on the equipment and application.

    Optical connectors have been designed throughout the years either

    for specific application, improving on existing connector quality or

    to increase connection density. Optical connection are available for

    different types of fiber such as glass optical fiber, polymer optical fiber

    and plastic optical fiber. In addition, connectors are also available for

    both single mode and multimode networks.

    A good connector design is determined by factors such as low

    coupling loss, interchangeability, ease of assembly, environmental

    resilience, high reliability, ease of connection, repeatability and low

    cost of manufacture and operation. There are many different types

    of connectors which use a variety of techniques for coupling such as

    bayonet, screw-on, latched and push/pull.

    Fiber optic connectors are mostly butt joint type connection where

    the optical fiber is secured in a precision alignment sleeve called a

    ferrule. Two connector ferrules are aligned and butted against each

    other within an adapter to complete the fiber optic connection. There

    are two commonly used butt-joint alignment designs which are the

    straight sleeve and tapered sleeve.

    Basics of Fiber Optic Connectors

    Straight Sleeve


    Alignment Sleeve


    Fiber Optic Connector Assembly

    The connector boot and crimp eyelet is slotted through the fiber cord

    The cord is then stripped to expose the Kevlar and fiber buffer within the cord

    The fiber buffer is then stripped to a certain measurement to expose the optical fiber and cleaned

    A mixture of epoxy is prepared to be used as adhesive for the optical fiber in the ferrule

    The connector ferrule is connected to a pump which sucks the epoxy into the connector ferrule

    The prepared optical fiber is then inserted into the connector ferrule

    The connector ferrule with the optical fiber is then placed in an oven for curing

    After the connector ferrule is cured, excess fiber protruding out of the ferrule is carefully cut

    The connector ferrule is now ready for polishing.


    There are generally 3 steps in the optical fiber connector assembly which are adhesion, polishing and assembly. In this example, the general

    method of connectorizing an optical cord is outlined.

    boot, bare buffer

    boot, short

    crimp eyelet

    connector sub-assembly

    connector housing

    dust cap

    fiber ferrule


    The prepared connector ferrule is then affixed onto a ferrule holder jig

    The jig is then secured onto a polishing machine above a polishing pad

    Depending on the connector ferrule type and connector polishing requirements, suitable polishing films and

    polishing program are chosen

    A piece of polishing film is placed onto the polishing pad. The initial polishing uses a coarse film

    The polishing machine is started. Distilled water is added to help smoothen the polishing

    The polished connector ferrule is then rinsed by using an ultrasonic washer

    The connector ferrule is then polished again by using a finer polishing film and rinsed after finishing

    This step is repeated as many times as required with the suitable polishing film until it is ready for assembly

    After polishing, the ferrule endface is examined by using an interferometer to ensure the prepared ferrule is within

    the acceptable tolerances

    If the connector endface ferrule is not within the acceptable limits, the endface ferrule can be re-polished but this

    can only be done for a limited number of times before the ferrule is rendered unusable.


    After rough polishing

    After fine polishing

    After medium polishing


    After the connector ferrule passes the interferometer testing, connector assembly can begin

    The connector ferrule is slotted into the subassembly then few drops of epoxy can be added to the end of the

    subassembly where it is to be crimped

    The connector Kevlar is then spread around the end of the subassembly

    The crimp eyelet is then slotted over the Kevlar and subassembly then crimped to secure the cord Kevlar

    The boot is then slotted over the crimp eyelet and pushed toward the subassembly

    The connector housing is then slotted over the subassembly according to the connector orientation

    The connector ferrule is then cleaned and the dust cap is slotted over the connector ferrule to complete the connector




    As demand for optical connectors increases globally, so does the

    supply. When one visits trade shows, one will find numerous suppliers

    offering from basic components to finished cable assembly products.

    One key fact that end users have discovered in recent years is not

    all connectors are equal. The quality, reliability, and performance of

    optical components and cable assembly products such as patch cords

    are assured by selecting the best components and by terminating and

    polishing with the best equipment and procedures. These components

    and procedures must assure that the jumper assemblies meet or

    exceed the requirements of all pertinent industry specifications such

    as the internationally recognized GR-326 standards.

    This paper describes the relevance of the criteria in the applicable

    industry specifications, as well as the importance of the physical

    parameters and how they relate to the performance of the jumper


    GR-326-CORE (Generic Requirements for Singlemode Optical

    Connectors and Jumper assemblies) was initially created by Bellcore

    and continues to evolve as one of the more popular standards in

    the telecommunications industry. Bell Communications Research,

    Inc. or Bellcore was established in the early 1980s by the Regional

    Bell Operating Companies (RBOCS) upon their separation from

    AT&T. Bellcore served as the research and development, training

    and standard setting arm for the RBOCs. Following a divestiture

    of the company in 1996, Bellcore was officially renamed Telcordia

    Technologies in 1999. In 2012 Telcordia was acquired by Ericsson.

    GR-326-CORE was written as part of Telcordias General Requirement

    series to be consistent with the Telecommunications Act of 1996 and

    it is intended to be the industrial specifications for long haul high-

    speed applications such as telecommunications and cable TV.

    There has been a total of four issues of GR-326, initial release, Issue

    2 December 1996, Issue 3 September 1999 and the current Issue 4

    February 2010. The Telcordia views in any particular release are

    developed from the expressed needs of the Telcordia Technical Forum

    (TTF), the TTF is made up from the companies who participated in the

    development of each new issue.

    As networks evolve and new products are offered the standards are

    typically reviewed to see if there are changes that need to be made

    or criteria added. A good example of this was the addition of four

    wavelength testing (1310nm, 1490nm, 1550nm, 1625nm) in GR-326

    issue 4, this was added because of the heavy use of connectors and

    cable assemblies in FTTH networks. Field data is also a very important

    part of the process when determining the need for reissues of the

    standard. As some of the current networks have been in service for

    many years, review of FIT (failure in time) rates along with post mortem

    investigations provide invaluable data about the components

    long term reliability. When the standards are developed, there are

    many other industry standards that are referenced. Standards from

    IEC, TIA/EIA, ASTM, ISO, ITU, UL as well as other Telcordia General

    Requirement standards are referenced for test procedures, test

    criteria, intermatebility criteria etc. When these standards are updated,

    they need to be reviewed to determine if a GR-326 reissue is needed

    to bring them in line.

    The purpose for GR-326 is to determine a connector or connector

    assemblys ability to perform in various operating conditions, and to

    determine long term reliability.

    Connector Assurance (gR-326-CORE)

    GR 326CORE


    The GR-326-CORE test is one of the most comprehensive testing methodologies which will not only test the products material and

    manufacturing precision but also the quality of workmanship. A full test will take a minimum of 2000hrs with multiple tests running in parallel.

    As mentioned earlier, the GR-326-CORE test is divided into two main tests (i.e. Service Life Tests & Extended Service Life Tests). In the majority

    of cases, when a sample is requested, a golden sample will be provided which will most definitely pass all tests with flying colors. Hence, one

    should always ask for a GR-326-CORE compliance certificate which is issued to manufacturers whom has passed the GR-326 compliance test at

    any accredited 3rd party test laboratory in the world.

    List of Main Test Categories

    general Requirements These General requirements cover documentation, packaging, design features, intermateability, product markings and safety

    Service Life TestingA sequence of environmental and mechanical tests that simulate possible conditions the connectors or connector assemblies may be under while in service

    Extended Service Life Testing

    Various tests intended to determine long term reliability of the connector or connector assemblies. Usually a simulated 25 year lifetime

    Reliability Assurance Program

    The program focuses on requirements for the manufacturing process that relate to long term reliability and performance of the finish product. Also includes additional testing to ensure the stability of the manufacturing process

    The standard is broken down into 4 main categories as shown in table below:


    Service Life Test

    GR-326-CORE Environmental Service Life Test

    Thermal AgingThe Thermal Age Test is considered the least extreme of the environmental tests in terms of stress applied, and is intended to simulate and accelerate the processes that may occur during shipping and storage of the product. Connectors are subjected to a temperate of 85 degrees Celsius with uncontrolled humidity for duration of 7 days, with measurements taken before and after testing.

    Thermal Cycle During thermal cycling, the temperature fluctuates over an expansive range, subjecting the product to extreme heat and cold. Thermal cycling involves changing the ambient temperature of the connector by 115 degrees Celsius (75 to -40) over the course of three hours. Heavy stresses and strains will be applied to each of the materials in the product. This test will also expose any weaknesses in the termination. If the design and procedures are not optimal, this can lead fiber cracks or breakage.

    Humidity AgingHumidity aging is designed to introduce moisture into the connector and to determine the effect that the moisture has on the samples. This test is performed at the elevated temperature of 75 degrees Celsius for 7 days, while the connectors are exposed to 95% RH (relative humidity)

    Humidity/ Condensation Cycle Humidity/Condensation cycling is performed in order to determine the effect that water has on the connector when a rapid transition in moisture occurs. This can cause water molecules to freeze or evaporate within the connector assemblies, potentially exposing gaps in the physical contact between connectors within an adapter. This phenomenon may have previously been masked by the water acting as an optical intermediary. The purpose is to achieve heavy condensation, so as to simulate a worse-case condition that may occur in outside plant applications.

    dry-out StepThe product is exposed to a drying step at 75 degrees Celsius for 24 hours before the Post-Condensation Thermal Cycle is performed. The purpose is to remove any moisture that may remain from the previously performed Humidity/Condensation Cycling.

    Post Condensation Thermal CycleThis is identical to the Thermal Cycle that was previously performed. The changes that may occur in the connector during Humidity/Condensation cycling are often revealed once the condensation is removed (as is the purpose of the Dry-Out step), and these changes can potentially affect the loss and/or reflectance of the connector.

    The function of the Service Life test is to simulate the stresses a connector may experience during its lifetime. The test is divided into two

    sections namely the Environmental Test & Mechanical Tests. The Environmental Tests are NOT ONLY performed to ensure the jumper assemblies

    will be able to withstand prolonged exposure to 85C or temperature fluctuations of up to 125C but also to accelerate the effects of aging on

    jumper assemblies. Details of each of the test are explained in the following table.


    TaBLE 3 GR-326-CORE Mechanical Service Life Test

    Vibration Test In a vibration test, the products being tested are mounted to a shaker. By stressing the connectors in this fashion, the test will reveal whether high frequencies of vibration induce performance change in the connectors being tested. The test is conducted on three axis for two hours per axis at an amplitude of 1.52mm with the frequency sweeping continuously from 10 and 55 Hz at a rate of 45Hz per minute.

    Flex Test The purpose of performing the flex test is to simulate stresses on the terminated cable and mated connector that could be incurred over the life of the connector. The boot, in particular, is important in this test, as it serves as one of the main points of strain relief. Thus, if the materials in the boot are inadequate, the boot may not function as intended. In addition, this will confirm that the fiber will not become uncoupled from the connector under such circumstances.

    Twist TestThe twist test puts a rotational strain on the fiber, which tests the strength by which it is coupled with the connector. In addition, the adequacy of the crimp will also be tested. This, like the flex test, will help to identify weaknesses in the termination process.

    Proof Test Proof Testing ensures the strength of the latching mechanism of the connector, as well as the crimp during the termination process. Should the jumper assembly receive a sudden tug after installation, this test ensures that the jumper assembly will neither break nor pull out of the adapter.

    TWAL (Transmission With Applied Load) TWAL testing will stress the samples by applying different weights at multiple angles. The series of weights used depends on the media type of the cordage, as well as the form factor. Small Form Factor connectors are subject to a more extensive range of measurements.

    *Note: Live measurements are made while the samples are under stress; this is done to reflect any degradation in transmission that might have incurred while the product is stressed in the field.

    Impact TestImpact Testing is performed to verify that the connectors are not damaged when they are dropped. A cinderblock is mounted to the bottom of the fixture, approximately 1.5m from the horizontal plane that the connector will be dropped from. The connector contacts the cinderblock, and the process is repeated 8 times.

    durability Test Durability testing is designed to simulate the repeated use of a connector. This test involves repetitively inserting (200 times) the connector into an adapter; this is done at different heights (3 ft., 4.5 ft., and 6ft) so as to simulate what a user in the field might encounter when standing in front of a telecom rack. The test can potentially reveal any problems with the design and/or material flaws in the connector, such as any part of the latching mechanism that may be heavily strained or flawed by frequent use

    There are several mechanical tests (Figure 6) required to be performed once the aging is complete. These include: Flex Testing, Twist Testing,

    Proof Testing, Impact Testing, Vibration Testing, Durability, and Transmission with an Applied Load. Again, details of each of the test are

    explained in Table 3.


    dust can seriously impair optical performance. Particles that contaminate endface can block optical signals and induce loss. Whether or not the dust particles find an exposed path to a ferrule endface is

    largely a matter of probability. Over time, dust particles will find their way to the optical connection if it is

    possible. While the dust particles are not difficult to remove, the cleaning process involves disconnecting

    the connector, which not only stops the transmission, but also exposes the endface to additional risk of

    contamination. This test involves intense exposure to a dust of specified size particles in order to determine

    if there is a risk of any particle finding its way to the ferrule endfaces.

    Salt Fog (referred to as Salt Spray) is performed to guarantee the performance of the jumper assembly in free breathing enclosures near the ocean. This test involves exposing the connector to a high concentration

    of Sodium Chloride (NaCl) over an extended period. After the test, optical testing is performed, followed by

    a visual inspection to confirm that there is no evidence of corrosion on the materials.

    The Airborne Contaminants test is designed to guarantee the performance and material stability of connectors in outdoor applications with high concentrations of pollution. The test repeatedly exposes

    mated and unmated connectors to various gases and inspects the connector not only optically, but also

    performing the same visual examination as in the Salt Fog test. An assortment of volatile gases is used in a

    small chamber for 20 days to simulate prolonged exposure to these elements.

    The materials are also verified in the Immersion/Corrosion test. This test has no optical requirements, but instead involves a prolonged submersion in uncontaminated water. This test, like Dust, Salt Fog, and

    Airborne Contaminants, involves both mated and unmated connectors. Mated connectors are checked for

    ferrule deformation by measuring the Radius of Curvature before and after the test, and comparing the

    values. If the ferrule is not geometrically stable during this test, it could be an indication of a flaw in the

    zirconia material used in the ferrule. Unmated connectors are checked for Fiber Dissolution, which involves

    checking to see if the fiber core has not recessed too far into the fiber cladding.

    The final exposure test is groundwater Immersion.This test verifies the ability of the product to withstand underground applications. The Immersion/Corrosion test is strictly to verify the materials involved, and

    uses de-ionized or distilled water. Connectors deployed in underground environments are much more

    likely to be exposed to contaminated mediums if their enclosures fail. During this test, the connector is

    exposed to a variety of chemicals found in sewage treatment and agricultural fertilization, among other

    applications, as well as biological mediums. These chemicals include ammonia, detergent, chlorine, and

    fuel. Presence of these chemicals can have a detrimental effect on the materials comprising the connector

    and adapter, reducing optical performance.

    The criteria for connector and jumper assembly extended service life testing are exclusive to GR-326-CORE. The testing includes

    exposure to a variety of environments, including additional Environmental Testing and Exposure Testing. The additional Environmental

    Tests include extended versions of the Thermal Life, Humidity, and Thermal Cycle. These tests, which run for at least 2000 hours each (83 days),

    are further studies in the life of the connector across a range of service environments. Testing is non-sequential, so there is no cumulative effect.

    The Exposure Tests include Dust, Salt Fog, Airborne Contaminants, Ground Water Immersion, and Immersion/Corrosion. During the extended

    Environmental Testing, many of the extruded compounds used in jacketing and buffering will shrink after exposure to elevated temperatures,

    which can cause micro bending in the glass fibers and induce excessive loss..

    Extended Service Life Test

    GR-326-CORE Extended Service Life Test


    The most common optical performance measurement

    for an optical connector is the Insertion Loss and Return Loss.

    Jumper measurement is usually done at the 1310nm and 1550nm

    wavelength by using a master jumper and a master adapter. This is

    to guarantee the performance measurement consistency. A master

    jumper and master adapter are rare products which have near perfect

    geometric and loss performance. A master jumper and adapter is

    usually used for factory assurance measurement to maintain product

    performance consistency. As such, the connector and adapter loss

    performance report from the factory is based on a measurement

    with a master jumper and adapter. They are usually not used in actual

    network deployment due to its high cost and rarity in production. It

    is commonly misunderstood that the Insertion Loss and Return Loss

    you see tested with a master jumper is what you will be getting in the

    actual usage of the product such as in racks, on devices and any other

    finished product. The IEC 61753-1 standard was introduced to outline

    the Insertion Loss and Return Loss specification based on randomly

    mated connectors. The compliance to this standard guarantees the

    loss performance of random mated connectors and categorizes it into

    4 grades for Insertion Loss and 4 grades for Return Loss. The difference

    of a good connector and a bad connector can clearly be differentiated

    be measuring the Insertion Loss of a randomly mated connector. It is

    known that a connector that has a guaranteed IL of 0.5dB against a

    master can increase to as high as 1.00dB or higher in random mating.

    The tables below outlines the Insertion Loss and Return Loss grades.

    Random Mating Loss Performance

    Insertion Loss data against Master








    Points where Max IL is reached for each connector brand

    GR 326Max IL(0.4dB)

    IECMax IL(0.5dB)

    Attenuation grade Random Mated Return Loss

    Grade 1 60 dB (mated) with 55 dB (unmated)

    Grade 2 45 dB

    Grade 3 35 dB

    Grade 4 28 dB

    Attenuation grade Random Mated Insertion Loss

    Grade A Not Defined Yet

    Grade B 0.12 dB mean 0.25 dB max for > 97%

    of samples

    Grade C 0.25 dB mean 0.5 dB max for > 97%

    of samples

    Grade D 0.5 dB mean 1.0 dB max for > 97%

    of samples

    Random mating Insertion Loss








    Points where Max IL is reached for each connector brand

    IECGrade A(0.15dB)

    IECGrade B(0.25dB)

    IECGrade C(0.50dB)

    IECGrade D(1.0dB)

    SENKO Low Loss

    SENKO Premium

    SENKO Standard

    High quality Competitor

    Low quality Competitor


    Insertion Loss One of the main advantages of fiber optic networks is the efficient

    operational wavelength light transmission suited for long distance

    telecommunications. Optical attenuation occurs when the light

    intensity reduces as light propagates through an optical network.

    Optical attenuation which is also known as Insertion Loss (IL) reduces

    the potential transmission distance of an optical network.

    Although this can be compensated by the use of higher power

    optics, this will introduce a higher deployment cost. In addition, the

    use of high power optics can introduce new set of problems such as

    increased thermal stress on the optical network, thermal lensing, non-

    linear attenuation, and increased requirement for optical hygiene.

    Insertion Loss is defined as the ratio of the optical input power over

    the optical input power. A representation of IL in decibels (dB) is

    shown below:

    The largest contributor of attenuation in an optical network are

    interconnect components such as connectors and splitters. The

    degradation of light intensity is managed through the precise

    engineering, manufacturing, quality control and long term reliability

    of optical fibers and the interconnect components. The IEC 61300-

    3 family of standards outline the basic test and measurement

    procedures for fiber optic interconnecting devices and passive


    Optical connectors is one of the largest contributors of attenuation.

    Fiber optic connectors are an integral part of an optical network to

    enable a point of flexibility to alter the network connectivity such

    as a cross-connect rack in an exchange. A fiber optic connection is

    made up of two connectors which are plugged into an adapter which

    aligns the connector ferrules within its sleeves. Attenuation from

    connectors arise from multiple factors such as connector cleanliness,

    connection gap, core centricity error, angular misalignment and

    lateral misalignment.

    Connector Testing

    Insertion Loss (IL) =

    -10 log10 (Po/Pin)where: Po = Output Power Pin = Input Power


    Example of a perfect connector termination

    Clean connector endface Straight joint with good lateral and angular alignment Fiber core is aligned and in contac

    Example of contaminated connector endface

    Contamination on the fiber core can cause high attenuation and even permanent damage if the contamination is burnt by high optical power

    Contamination in between two connectors can cause a gap

    An air gap between the connectors can result in a lower return loss.

    Example of connector with angular misalignment

    Angular misalignment can be caused by:

    Low quality barrel in the bulkhead adapter or connector ferrule

    Contamination on the side of the ferrule

    Example of connector with lateral misalignment

    Lateral misalignment can be caused by:

    Low quality barrel in the bulkhead adapter or connector ferrule

    Contamination on the side of the ferrule

    Example of core concentricity error

    Position of the fiber core is offset from the actual center of the connector ferrule

    Note: Image is an exaggeration of a core off-set


    connector gap

    Actual position of fiber coreCentral position of fiber core

    Core Concentricity Error


    Optical Continuous Wave Reflectometer (OCWR)

    Optical Time Domain Reflectometer (OTDR)

    Optical Low Coherence Reflectometry (OLCR)

    Optical Frequency Domain Reflectometry (OFDR)

    To ensure the proper performance of an optical transmission system,

    various parameters such as attenuation and Optical Return Loss (ORL)

    must be within the acceptable tolerance level of the transmission and

    receiving equipment. ORL is measured based on components such as

    cables, patch cords, pigtails and connectors as well as an end-to-end

    network ORL level.

    With increasing data speeds and the use of WDM technology, the

    measurement of ORL is becoming more important in characterizing

    optical networks. ORL is defined as the ratio of light reflected back

    from an element in a device, to the light launched into that element.

    This is usually represented as a negative number in decibels (dB). The

    mathematical formula representing ORL is as shown below:

    In addition to the increase in network attenuation, high levels of

    reflected optical power can cause light-source signal interference,

    higher Bit-Error Rate (BER) in digital systems, lower Signal to Noise

    Ratio (SNR), laser output power fluctuations and in more severe

    situations, permanent damage to the laser source. ORL and reflectance

    must be measured on a component level, such as connector and cable

    assembly, and an end-to-end network level.

    Higher transmission bandwidth networks requires higher ORL

    performance. For example, an OC-48 2.5Gbps transmission network

    has a minimum ORL level of 24dB while an OC-768 40Gbps has

    a minimum ORL level of 30dB. An FTTx network delivering video

    content with a low BER tolerance has a minimum ORL level of 32dB.

    As outlined in the IEC 61300-3-6 standard, there are mainly 4 methods

    to measure return loss which are:

    Return Loss

    Return Loss (RL) =

    -10 log10 (Pr /Pin)

    where: Pr = Reflected Power Pin = Input Power


    Rayleigh backscattering is an intrinsic property of optical fiber which

    causes light to scatter. This is usually caused by defects and impurities

    introduced into the fiber core during the manufacturing process, or

    regions of mechanical stress such as microbending. A fraction of the

    scattered light which is directed back to the source is detected as ORL

    while the majority of scattered light will be lost. Rayleigh scattering

    occurs along the total length of fiber.

    light Rayleigh scattering

    reflected light

    light attenuated light

    reflected light

    air gap

    Fresnel backreflection is caused by different network elements

    where a transition through different mediums occur. Optical

    connectors are usually the highest contributors of reflections due

    to air gaps, impurities, geometry misalignments, and manufacturing

    imperfections. Common sources of Fresnel backreflection are optical

    connectors, mechanical splices, open fiber ends and cracks in the

    optical fiber. Significant light is backreflected to the source when

    light travels from the fiber core to air. In ORL sensitive networks,

    Angle-Polished Connectors (APC) are usually deployed to reduce

    backreflection to the source.

    The measurement methods are applied depending on the Device under Test (DUT) condition, level of return loss, measurement distance and

    the measurement resolution. This paper will focus on the return loss measurement using the OCWR and OTDR methods. Back reflectance is

    described as the ratio of reflected optical power to the incident optical power at the input of the device. The term ORL is used to describe the

    ratio of relative magnitude of the cumulated back reflectance or multiple Fresnel events and backscattered signal power to the optical power

    at the input of the device. There are mainly two factors that cause ORL which are Fresnel backreflection and Rayleigh backscattering.

    Causes of Optical Return Loss


    Power Meter & Light Source


    The Power Meter and Light Source works as a pair of devices. As the name suggests, the Light Source is a device that injects a certain amount of

    light into the DUT while the Power Meter detects the light power level that comes out of the other end of the DUT. The difference in the power

    level provides an accurate representation of the DUT insertion loss.

    Unlike the OTDR, the Power Meter & Light Source testing method is unable to discern the individual elements within the DUT. This testing

    method can only give the total insertion loss of the DUT.

    Depending on the connector quality, the act of mating and demating a connector can result in a different insertion loss level. When measuring

    a low attenuation DUT, the connector loss variable can significantly distort the actual insertion loss reading. This limitation can be overcome by

    using a method called the cut-back method which maintains the connector termination to the Light Source and Power Meter but it introduces

    a fusion splicing which is a new loss element, which has a very low attenuation level if done properly, that is not part of the DUT.

    Introduction to Test Equipment

    Optical Time domainBased Measurement (OTdR)

    Optical time domainbased measurement spatially evaluates backreflection characteristics both in individual components and along the length

    of a fiber. One main instrument that uses this measurement method is the optical time-domain reflectometer (OTDR). An OTDR measures the

    backscatter level of the fiber medium itself and the peak reflection level of Fresnel events along an optical link. The backscatter measurement

    level is a function of the fiber backscatter coefficientan intrinsic factor of the fiber under testand the pulse width used for measurement.

    As its name suggests, an OTDR operates in the time domain and measures the backscatter optical-power level from the fiber itself. It enables

    users to measure Fresnel backreflection at any point along the fiber under test without de-mating optical interconnections. A light pulse

    is introduced into an optical link and will experience both backreflection and Fresnel events along the pathway. The power level of light

    reflected back to the source is measured with reference to the time it takes for the light to return to the source. In this way, the OTDR estimates

    the distance of an event from the source according to the elapsed time versus the speed of light. This makes the OTDR a very useful tool in

    evaluating the distance of the optical network under test as well as the location of components in the network, thus enabling the tester to

    evaluate the network for commissioning purposes and locate network faults for maintenance.

    There are two types of OTDRs: the photon-counting OTDR (PC-OTDR) and the network OTDR. Although both types of OTDR use the same

    principles to measure ORL, the PC-OTDR applies a much shorter optical pulse width, enabling a much higher spatial resolution and reflection

    sensitivity. However, this reduced dynamic range lowers the maximum useful DUT length of a PC-ODTR. Due to these differences, the two types

    are applied for different purposes: network OTDRs are typically portable and usually deployed in outside plant networks for commissioning

    and troubleshooting, while PC-OTDRs are usually used for qualification and troubleshooting of individual components, modules, or subsystems

    in which reflections are often closely spaced.

    Max Spatial Resolution

    Reflection Sensitivity

    Reflectance Measurement


    Optical Pulse Length

    Max Length of dUT


    > 1 m 60 dB 50 dB 10 ns < 100 km

    PC-OTdR 10 mm < 120 dB 60 dB 10 ns < 200 m


    Backscatter Coefficient SettingsAs OTDRs measure backreflection power levels, the reflectance of a given element in the DUT depends on the fiber backscatter coefficient,

    optical pulse width, and the measured reflectance amplitude with reference to the backscatter level. An inaccurate backscatter coefficient value

    setting can lead to an error in measuring reflection level. The percentage of measurement uncertainty increases with a lower reflectance value.

    The backscatter coefficient is usually one of the parameters that is set when performing an OTDR measurement. In a fiber-access network,

    especially one that has legacy fibers, there may be a combination of various fiber standards for example from early G652.A fiber to G657.A2

    fiber as well as fiber from different suppliers manufactured with different methods, such as the plasma chemical vapor deposition (PCVD)

    method or the modified chemical vapor deposition (MCVD) process. The OTDRs backscatter coefficient setting cannot be adjusted to match

    the varying fiber characteristics in the network under test.

    Index of Refraction (IOR)IOR is a way to measure the speed of light in a medium with reference to the speed of light in a vacuum, where light moves fastest. Light travels

    at approximately 3 x 108 ms1 in a vacuum. The IOR of a medium such as an optical fiber core is calculated by dividing the speed of light in a

    vacuum by the speed of light in the medium. By definition, the IOR of light in a vacuum is denoted by 1. A typical single-mode fiber has a silica-

    doped core with an IOR of approximately 1.447. The larger a mediums IOR value, the more slowly light travels in that medium.

    An inaccurate IOR setting in an OTDR will cause the total distance of the network measured to be skewed. If the IOR is set too high, the OTDR

    will calculate the network distance to be shorter than it actually is; likewise, if the IOR is set too low, the OTDR will measure too long a distance.

    A difference in IOR setting of just 0.01 can cause a reading difference of 70 m over a 10 km fiber span. When an OTDR is used to locate a specific

    fault in a network, an incorrect IOR setting can cause the fault location shown in the OTDR to be far off from the actual location.


    Mode Field diameter (MFd) Mismatch The MFD of an optical fiber is the area where light propagates. This

    area is usually slightly larger than the fiber core as a portion of

    light propagates through the cladding as well. When two optical

    fibers with different fiber core size and MFD size are spliced, the

    attenuation measurement by using an OTDR can result in a gainer or

    an exaggerated loss. This is due to the propagation of light through

    mediums with different Index of Reflection.

    The attenuation reading from the OTDR depends on the difference

    in fiber MFD and the measurement direction of the OTDR. If the

    OTDR measurement is made from a fiber with a larger MFD to a fiber

    with a smaller MFD, the reading will result in a gainer. However, if the

    measurement is made from a fiber with a smaller MFD to a fiber with

    a larger MFD, the reading will result in an exaggerated loss.







    OTDR measurement results in an exaggerated loss

    OTDR measurement results in a gainer

    Backreflection reduced after splice point due to MFd mismatch

    Backreflection increased at splice point due to MFd mismatch




    dead ZoneA dead zone is the location of a section of network beyond a reflective event, where

    subsequent network characteristics cannot be measured. There are two types of dead

    zones: attenuation dead zones (ADZs) and event dead zones (EDZs).

    An ADZ is the minimum distance required to make an attenuation measurement for

    an event. This value is usually defined as the distance between the rising edge of a

    reflective event to the 0.5 dB deviation from a straight line fit to the optical backscatter

    level. The optical backscatter level is the sloping line that indicates the fiber attenuation

    over distance.

    An EDZ is the minimum distance required for the OTDR to detect two separate events.

    This is usually defined as the distance between two cursor points set at 1.5 dB below a

    reflective peak, where the peak is non-saturating.

    Dead zone measurement depends on the pulse width and the network element

    reflectance level. A shorter pulse width will result in a shorter dead zone, while a

    connector with a high return loss will result in a longer dead zone. When testing a long-

    distance network, testers will use a higher pulse width, thus increasing the length of the

    dead zone. This can cause multiple nearby events to be identified as a single merged

    event. Examples include the connector and splice of a pigtail as well as both connector

    ends of a patch cord.

    Most OTDR manufacturers specify the OTDR dead zone for the shortest pulse width

    and optimal connector reflectance. However, this specification cannot be taken at face

    value. The suitable pulse width to be used for network measurement usually depends

    on the total length of the network, while individual components within the network

    have variable reflectance performance due to manufacturing quality and hygiene.

    Helix FactorOTDRs are widely deployed in testing and measurement of outside-plant optical fiber

    networks. In an outside-plant environment, optical fibers are deployed in cables. The

    most common cable types deployed are loose-tube cables and slotted-core cables.

    Optical fibers within these cables are not strung in a straight line but spiral around a

    central strength member in an SZ fashion within loose tubes.

    As light from an OTDR travels through the optical fiber, OTDRs measure the optical fiber

    distance rather than the cable distance. Depending on the helix factor of a cable

    which can range from 0.3% to 42%, depending on the cable designa cable 700 m

    long may comprise 1,000 m of fiber distance. Without an accurate measurement of the

    helix factor, fault locating by using an OTDR may result in considerable discrepancy.

    Most modern OTDRs have a helix setting to adjust the distance measurement.

    attenuation deadzone definition

    Event deadzone definition

    attenuation deadzones of two concatenated connectors

    attenuation deadzones of two concatenated connectors

    Applies to non-saturating peak (good UPC connector)

    0.5 dB deviation from straight line backscatter


    Applies to non-saturating peak (good UPC connector)


    1.5 dB below peak

    Cant measure OkayADZ-1 ADZ-1

    Cant measure OkayADZ-1 ADZ-1


    Optical Continuous Wave-Based Measurement (OCWR)

    OCWR relies on a basic power-meter measurement of the launch power (assuming no DUT) as a base reference and compares this to the optical

    power reflected back to the source. For a backreflection meter, this method is usually used to measure the ORL of patch cords. For an Optical

    Line Test Set (OLTS), this method can be used to measure the total ORL and attenuation of a network.

    The OCWR method cannot differentiate between Rayleigh backscatter and Fresnel backreflection. If a patch cord tested with a backreflection

    meter yields a low ORL result, it is highly likely that the connector is faultyalthough there is a possibility that the cord itself has been

    manufactured with microbends. When using test instruments that employ the OCWR method, the network or component under test must be

    isolated from the rest of the optical network to prevent any backscatter or reflection from events further down the link. This means that the

    OCWR method cannot be deployed on a live network.

    To isolate the DUT from unwanted reflections, the optical fiber must be terminated at two different points. The two commonly used termination

    methods are the mandrel wrap and the index-matching gel or block. Each of these methods have limitations, as shown in the table below. The

    difference in backreflection between the two termination points is calculated to give the DUT backreflection level.

    Multimode fiber cannot be terminated effectively using mandrel wraps, as the wraps can introduce bend loss but not totally terminate the fiber.

    In most cases, the use of an index-matching gel or block is the only solution. An index-matching gel or block matches the IOR of fiber, which

    causes light to diffuse out of the fiber core rather than experience Fresnel backreflection. However, index-matching gels are not as effective

    as mandrel wraps, and they can never fully prevent backreflection. Multiple measurements are usually required, with the highest return loss

    measurement result taken as an approximation of the potential result if a mandrel wrap is used.


    Mandrel Wrap Index-Matching Gel Index Matching Block

    Not applicable to non-bendable structures such as hardened cables or cords

    Matching gel might leave a residue on the polished connector end face

    Not suitable for connectors with guide pins, such as MPOs, or where the connector end-

    face is not accessible, such as E2000.

    Bend-insensitive fiber does not exhibitbend loss

    Backscatter of the fiber length between the reflective eventand the far end of the cable might amplify reflections

    Cannot optically isolate far endthrough bending.

    Limited effectiveness in terminating reflections

    Manual process to isolate far end and highly depends on the technicians skill level


    Testing Procedure

    OCWR relies on a basic power-meter measurement of the launch power (assuming no DUT) as a base reference and compares this to the optical

    power reflected back to the source. For a backreflection meter, this method is usually used to measure the ORL of patch cords. For an Optical

    Line Test Set (OLTS), this method can be used to measure the total ORL and attenuation of a network.

    In the cut-back method is the most accurate insertion loss measurement for a Device under Test (DUT). This method is usually used for

    component testing in a lab situation. The DUT is connected to a light source with a temporary joint which is usually an optical splice. The output

    of the DUT is then connected to a power meter. The power level measurement is noted as P1.

    The temporary joint is cut and then spliced to the fiber connected to the power meter. The power level measurement is noted as P0. The optical

    attenuation of the DUT can then be calculated as P0 P1.

    The substitution method is usually used for component testing where the input and output of the DUT are connectorised. The DUT is connected

    to a light source by terminating the DUT input connector to a reference adapter. Similarly, the output of the DUT terminated to a power meter

    by using a reference adapter. The power level measurement is noted as P1.

    The input and output connectors of the DUT are disconnected and substituted by a patch cord. To achieve a higher DUT attenuation

    measurement accuracy, a master patch cord with low loss connectors can be used. The power level measurement is noted as P0. The optical

    attenuation of the DUT can then be calculated as P0 P1.

    Cut-back Method

    Substitution Method

    Insertion Loss Measurement with Power Meter & Light Source

    Power Meter

    Temporary joint

    Temporary joint



    Light Source

    Temporary joint

    Temporary joint

    Power MeterLight Source


    The insertion method is usually used to measure a connection attenuation performance such as a splice point, or a field-mountable connector.

    The light source and power meter is directly connected and the power level measurement is noted as P0.

    The connection between the light source and the power meter is then cut. The cut fiber is then spliced to re-establish the optical network with

    a higher attenuation which is measured and noted as P1. The optical attenuation of the DUT, which in this scenario is a splice point, can then

    be calculated as P0 P1.

    An OTDR is not an ideal equipment to measure optical attenuation as it only detects back reflection level at different locations in the optical

    network instead of measuring the actual optical output power with respect to the input power. As outlined in a previous section, if two fibers

    with different specification are spliced, the MFD mismatch may cause a skewed attenuation reading called a gainer and exaggerated loss. The

    gainer and exaggerated loss reading can be corrected by performing a bidirectional OTDR test and getting the average attenuation reading

    of the splice event.

    Insertion Method

    Insertion Loss Measurement with OTdR

    Power Meter

    Temporary joint

    Temporary joint

    Light Source


    Insertion Loss =

    a + b


    IL Excessive Loss





    5.4.2. Return Loss Measurement with OTdR Return Loss Measurement with OTdR

    A launch lead, which is a standard patch cord with suitable connectors

    on both ends, must be used to connect the OTDR to the DUT. This

    ensures that the first event in the DUT can be quantified. If a launch

    lead is not used, the high reflection from the OTDR internal connector

    masks the actual reflectance and attenuation of the DUT.

    The correct parameters suitable for the measurement of the DUT is

    set in the OTDR. These parameters include the IOR, backscatter, helix

    factor, pulse width, measurement distance, and acquisition time. The

    importance of an accurate IOR, backscatter and helix factor settings

    is outlined in the previous section. Other important settings are::

    Pulse width: Smaller pulse width has a higher measurement

    resolution but has limited distance and vice versa.

    Measurement distance: To be set as closest to the actual network

    distance. If set to be lower, the far end of the network is not tested.

    If set to be too high, the resolution of the network under test will

    be low.

    Acquisition time: Test result with low acquisition time will result

    in higher noise level. However, longer acquisition time will require

    longer man hours for testing purposes

    If the optical network parameters are not know, most modern OTDR

    have auto settings. The OTDR tests the network starting with a short

    pulse width and incrementally increases the pulse width until it

    detects an end-of-fiber reading. The OTDR automatically adjusts the

    pulse width and measurement distance setting which best suits the

    DUT conditions.

    An OTDR trace will be produced to indicate the detected events in the

    DUT. There may be discrepancies between the OTDR trace result and

    the actual components in the DUT, this may be due to:

    High quality connectors with low reflectance is recognized as a

    splice rather than a connector.

    Undetected events such as low attenuation splices.

    In PON systems where splitters are installed in the OSP, the use of a

    short pulse width, such as a 5ns pulse width, will not be able produce

    a readable result after the splitter due to the high loss. A 1:16 splitter

    will cause about a 14dB attenuation. This will usually cause the OTDR

    trace to drop below the OTDR noise floor. However, using a larger pulse

    width such as 275ns will cause result in a lower resolution reading

    before the splitter, thus potentially missing events or merging closely

    spaced events.

    One possible method to test such a network is by using a short pulse

    width, such as 5ns to 10ns, to identify all event locations up to the

    splitter. A second test is performed by using a medium pulse width,

    such as 50ns to 100ns, for increased dynamic range to measure splitter

    loss while maintaining good resolution. The third test is performed

    by a longer pulse width, such as 275ns or higher, to test past the

    splitter to the end of the network. Further tests may be required if the

    dynamic range is insufficient to get a noise-floor margin of at least

    6dB. Information from the multiple OTDR traces must be analyzed

    and tabulated into a report. Such testing requires skill and time. In

    addition, tests are usually performed using the 1310nm and 1550nm

    wavelength to detect macrobends, which results in longer test times.

    OTdR dUTLaunch Lead


    Launch LeadConnector

    SpliceReceive End


    Return Loss Measurement with OCWR

    A reference patch cord is terminated to the light source of the OCWR.

    The end of the reference patch cord is coiled around a mandrel to

    increase attenuation and prevent Fresnel backreflection from the

    open end connector from being detected. The mandrel is applied as

    close to the end connector as possible. The detected ORL is set as a

    base reference.

    A DUT is then connected to the reference patch cord. The DUT is

    then coiled around a mandrel as close to the connection point as

    possible. This reduces the optical fiber backscatter from affecting the

    connector reflectance reading. The OCWR displays the ORL of the DUT

    with respect to the base reference value.

    A master patch cord is usually used as the reference patch cord. A

    master patch cord is manufactured with very strict quality standards

    to ensure repeatability of measurement result regardless of the test

    equipment type, manufacturer, the operator or the period of test.

    The connector interface of the master patch cord has near perfect

    specification on the end face radius of curvature, apex offset and fiber

    protrusion/undercut. ORL of Patch Cord under test = ORL B - ORL A


    Reference Patch Cord

    ORL B

    Patch Cord under test


    ORL B


    ORL A


    Reference Patch Cord

    ORL A


    BR = -58.0db

    Backreflection Meter




    Termination Point

    for BRTOTAL

    Termination Point

    for BR0

    Measurement Jumper










    OverviewOne of the drivers of many network operators to deploy optical

    fiber has been, of course, its performance & reliability. Although

    the general maintenance requirement is greatly reduced, many

    network operators around the world is finding one main component

    in an optical fiber network to be the cause of network failures.

    That component is the optical connector, the weakest link of your

    network. Based on a study conducted by NTT Advanced Technology,

    4 of the top 5 causes of network faults are connector related and the

    No.1 cause is contaminated connector end faces. The same problem

    is reported by major optical fiber network operators in Asia with the

    lack of appreciation for fiber cleanliness accounting for 90% of all

    reported faults.

    In the past, connector contamination in optical transport networks

    or data center fiber interconnect networks were less prevalent due to

    the controlled environment of exchanges or data centers. However,

    with the increasing deployment of optical fiber outside plant

    networks, optical connectors are widely used in outdoor enclosures

    such as roadside cabinets and pedestals as well as in customer

    premise termination points that do not have filters to reduce dust

    contamination or environment control systems to reduce humidity.

    Although connector contamination is common, it can be easily

    rectified. The main area of an optical connector that must be cleaned

    is the ferrule endface.

    Connector Hygiene

    Contamination of the connector End Face

    Poor polishing of the ferrule

    Mistakes attaching lables to the cable

    Damage of the optical connector

    Damage of the ferrule End Face

    Connector End Face contamination is the N1 cause of network faults








    The ferrule is the most essential part of the connector which holds

    and centers the optical fiber for connection with another section of

    a fiber network. As defined in IEC 61300-3-35, an optical connector

    end face is separated into three zones which are the Core (Zone A)

    where light travels, Cladding (Zone B) which is the outer section of the

    Core which reflects light back into the Core, and the Buffer Coating

    (Zone C) which protects the optical fiber from moisture or damage

    from external forces.

    The core of a single mode connector is only 9m. A piece of dirt,

    speck of dust or oil smudge in the right position may cause high

    reflection, insertion loss and fiber damage. Connector cleanliness is

    critical in high power transmission systems such as DWDM systems

    or long haul transmission where Raman amplifiers are used, the

    optical signal transmission power may be up 1W to 5W. In a single

    mode fiber transmission, such high power transmission may burn the

    contaminant and fuse the dirt with the silica material of the optical

    fiber, thus requiring the replacement of the connector.

    The source of contamination is usually due to connector mishandling

    and a lack of understanding for optical hygiene. Some of the most

    common mistake for contaminating optical connectors are:

    Image above: example of bad practice

    Leaving a connector uncapped for even a short period of time where it will be prone to dust contamination.

    Touching the connector end face with fingers thus leaving skin oil or passing on dirt

    Using unsuitable cleaning methods or products such as toilet paper, water or even shirt sleeves

    Assuming that connectors which are protected by dust caps are clean or factory guarantee cleaned

    Not cleaning both connector end faces before making a connection.

    Optical Connector Ferrule & Contamination

    Clean connection

    Dirty connection


    The IEC-61300-3-35: Fiber optic interconnecting devices and passive

    components - Basic test and measurement procedures - Part 3-35:

    Examinations and measurements - Visual inspection of fiber optic

    connectors and fiber-stub transceivers sets the standards on

    measurement methods, procedure to assess the connector end face

    and determines the threshold for allowable surface defects such

    as scratches, pits and debris which may affect optical performance

    and it is the de facto standard for the fiber optics industry globally.

    According to the standards document, there are three inspection

    methods which are the:

    direct view optical microscopy

    Video microscopy

    Automated analysis microscopy

    The Direct view optical microscopy is essentially a microscope

    designed to view optical connector end faces. Although most of

    such microscopes have an optical filter to prevent eye damage

    from exposure to transmission lasers, many network operators

    do not approve its use due to health and safety reasons. Another

    disadvantage of this method is different microscopes need to be

    used for inspecting a connector or a connector terminated onto a

    bulkhead adapter.

    Video microscopy uses an optical microscope which projects an

    image onto a display screen thus preventing any direct exposure

    to transmitting lasers. An example of a video microscopy is a

    Fiber Inspection Probe (FIP) with a display unit. Most FIPs available

    in the market have interchangeable tips to inspect bare connectors

    or when it is terminated onto a bulkhead adapter. There are also tips

    available for different connector types.

    The Automated analysis microscopy is similar to the video

    microscopy but with an added feature which uses an algorithmic

    process to automatically analyze the connector hygiene based on a

    set criteria. This analysis provides a Pass or Fail result, thus removing

    any human assessment ambiguity.

    Inspection Standards

    Fiber microscope

    Fiber Inspection Probe (FIP)

    Automated analysis microscopy


    There are two assessment procedures outlined in IEC-61300-3-35 for a single fiber ferrule such as an SC or LC connector and for a multi-fiber rectangular ferrule such as the MPO connector. The end face of the connectors are divided into measurement regions starting from the center of the core and moving outwards.The tables below outline the measurement regions:

    Zone Diameter for single mode Diameter for multimode

    A: Core 0 m to 25 m 0 m to 65 m

    B: Cladding 25 m to 120 m 65 m to 120 m

    C: Adhesive 120 m to 130 m 120 m to 130 m

    D: Contact 130 m to 250 m 130 m to 250 m

    Note 1: All data above assumes a 125 m cladding diameter.Note 2: Multimode core zone diameter is set at 65 m to accommodate all common core sizes in a practical manner.Note 3: A defect is defined as existing entirely within the inner-most zone which it touches.

    Measurement regions forsingle fiber connector

    Zone Diameter for single mode Diameter for multimode

    A: Core 0 m to 25 m 0 m to 65 m

    B: Cladding 25 m to 115 m 65 m to 115 m

    Note 1: All data above assumes a 125 m cladding diameter.Note 2: Multimode core zone diameter is set at 65 m to accommodate all common core sizes in a practical manner.Note 3: A defect is defined as existing entirely within the inner-most zone which it touches.Note 4: Criteria should be applied to all fibers in the array for functionality of any fibers in the array.

    Measurement region formulti-fiber rectangular connector

    The IEC-61300-3-35 standard outlines the Pass/Fail threshold level for the visual requirements for the different connector types. These criteria are designed to guarantee a common level of connector condition for connector performance level measurement. Based on the zones of a connector, the standard outlines the allowable number of scratches as well as the size and number of defects. There are four main requirements outlined which are:

    Visual requirements for PC polished connectors, single mode fiber, RL 45dB

    Visual requirements for angle polished connectors (APC), single mode fiber

    Visual requirements for PC polished connectors, single mode fiber, RL 26dB

    Visual requirements for PC polished connectors, multimode fibers


    Zone Scratches Defects

    A: Core 4 None

    B: Cladding No limit No limit < 2 m / 5 from 2 m to 5 m / None > 5 m

    C: Adhesive No limit No limit

    D: Contact No limit None 10 m

    The table below outlines the visual requirements for a single mode angle polished connector:


    The race to deploy broadband FTTx networks is resulting in a global

    fiber technician skill shortage. It is easy to train a technician to perform

    a connector hygiene test but experience in operating and maintaining

    a fiber network is required to be able to make correct assessments.

    The use of automated techniques de-skill and reduce the risk of poor

    installation. An automatic Pass/Fail analysis function based on the

    IEC-61300-3-35. In addition, Geo tagging features together with cloud

    storage allow centralized review by fewer highly skilled technicians

    and confirmation that procedures were correctly carried out:

    Prevent any error with a standardized and impartial assessment

    Increase productivity by speeding up the assessment process through set algorithm

    Avoid replacement of connectors with slight defects that do not adversely affect performance

    Ensuring excellent long term connectivity performance

    Confidence correct process has been carried out

    To cater for the massive adoption of FTTH services, the cost of

    setting up all the field technician is highly expensive especially with

    the various tools and equipment required to perform their tasks

    effectively. The common connector hygiene inspection tool consists

    of an FIP and a monitor to view the connector end face. The monitor

    may be a standalone unit for the FIP, a different test equipment with

    a monitor such as an Optical Time Domain Reflectometer (OTDR) or a

    laptop. The high cost of these equipment becomes a barrier to entry

    for many fiber technicians or contracting companies and in many

    cases, proper inspection is not conducted. Hence, a low cost and high

    performance alternative is needed to cater for the market.

    The cost effective SENKO Smart Probe is one of these cost effective

    alternative which allows relatively low skilled technicians to inspect

    the fiber end faces and stream the images to any laptop, tablet or

    smartphone. Many technicians already carry smartphones or tablets

    as part of their daily operations hence no additional display device is

    required and the SENKO Smart Probe connect to the smart devices via

    conventional Wi-Fi.

    In order to keep a record of connector inspection, all test results can be

    uploaded into a cloud repository for future references or for reporting

    purposes. These uploaded records with their associated location

    data give skilled technicians the opportunity to review the hygiene

    of individual connectors and provide network operators with the

    confidence that proper procedures have been correctly carried out.

    Inspection Tools


    Inspection Tools for MPO Connectors

    For SM & MM MPO (up to 24F)

    High precision alignment

    Available in APC and PC version

    Visualization of MT 12 fiber connector end face(two fibers of MT 12 fiber connector)

    The race to deploy Connector inspection for MPO is much more

    complicated. With current standard Fiber Inspection Probe (FIP) for

    MPO connectors, the inspection of a single ferrule with multiple

    connectors requires the operator to focus on one single fiber at a

    time. The FIP fiber tip comes with a dial which moves the focus from

    fiber to fiber.

    The inspection is tedious and time consuming. In addition, multi-

    fiber inspection probes the boundaries between Zone C and Zone

    D is usually not visible to enable proper connector evaluation. Due

    to the limited magnification, automated qualification for the MPO

    connector inspection is not available.

    The SENKO MPO FIP can inspect all fiber endface at once. The entire

    connector endface needs to be cleaned even if only one fibre is


    MPO Tip Up to 24F Available


    Optical cleaning tools are specialized tools which are used to remove contaminants from optical connectors and bulk heads. There are two types of cleaning methods namely the dry cleaning and wet cleaning. The standard document, IEC 62627-01: Fibre optic interconnecting devices and passive components - Technical Report - Part 01: Fibre optic connector cleaning methods describes a comprehensive cleaning methodology and is usually adopted as the industrys best practice.Dry cleaning is the most common and fastest cleaning method which is used in connector manufacturing plants and in the field. The drawback of the dry method is the risk of potentially scratching the end face if there are any hard particles on the connector surface. In addition, some dry cleaners cause electro static charges on the

    connector end face which attracts dust particles. The dry method usually cleans the majority of connectors, however, in more severe cases of contamination, the wet method is more effective. The main advantage of the wet cleaning method is the active solvent used in the cleaner which acts as a solvent for oils, raises particles to prevent connector end face damage, removes moisture and is fast drying. The most common solvent used in the market is 99.9% isopropyl alcohol (IPA). The presence of a solvent prevents the buildup of electrostatic charge on the connector end face. However, the excessive use of solvents may cause the contaminants to be pushed to a side of the ferrule and slowly creep back into center after the connector has been inspected and terminated. To prevent such an occurrence, a final dry cleaning is performed after a wet clean.

    Cleaning Tools

    Lint Free Swabs

    Lint free swabs can be used to clean the internal barrel of a bulkhead adapter or the connector end face which is terminated in a bulkhead adapter.

    If sufficiently large, contaminant on the side of the internal barrel may cause misalignment of two connectors thus increasing the connector insertion loss.

    Lint Free Wipes

    Lint free wipes are not usually used to clean connector end face. The operation of wiping the connector end face with a lint free wipe requires delicate skill to avoid damaging the connector end face.

    Cartridge Cleaners

    A small window is opened to expose the cleaning cloth when the lever is pressed. This will also turn the cleaning cloth so that a clean cloth section is used for every clean. The connector end face is pressed and wiped against the cloth. For a more effective clean, specially treated cleaning cloth that prevents electrostatic charge buildup can be used.

    Pen Cleaner

    Pen cleaners have a reel of cleaning cloth that rotates at the tip of the cleaner when it is pressed against a connector in a bulk head adapter or directly onto a connector if a fitting is placed onto the tip. This instrument with a push and click mechanism cleans the ferrule end faces removing dust, oil and other debris without nicking or scratching the end face. There are mainly three types of pen cleaners suitable for 2.5mm, 1.25mm and MPO connectors.

    Adhesive BackedCleaner

    Adhesive backed cleaners have a sticky tip with a soft backing at the top of the cleaner. This cleaner is pressed onto the end face of a bare connector or when terminated in a bulkhead adapter. The soft adhesive removed dust and other particles.

    Compressed Air

    Compressed air or air duster is used to blow air through the nozzle to get rid of dust on the connector end face. To maintain purity and pressure in the canned air, special material such as difluoroethane or trifluoroethane is used. It is advisable to select a material which has a lower Global Warming Potential (GWP) index.

    The following table outlines the most common dry cleaning tools and the area of use:


    Wet cleaning is usually done by applying 99.9% isopropyl

    alcohol to any of the dry cleaner type in situations when

    contamination on connectors is unable to be cleared from dry cleaning

    alone. This usually occurs when contaminant on a connector end face

    is left uncleaned for a long period of time. Multiple wet cleaning may

    be required to fully clean a connector end face and must always be

    followed by a final dry clean to remove isopropyl alcohol residue.

    There is currently no industry standard on the number of iterations

    one should attempt to clean the connector end face before disposing

    it but the common practice is generally 3 times. Nevertheless, an

    internal guideline should be set in order to avoid wasting time and

    resources trying to clean a contaminated/damaged connector. The

    diagram below summarizes the recommended cleaning procedure.

    Inspect endface with fibre scope

    Dry Clean

    Dry Clean

    Inspect endface with fibre scope

    Wet clean immediately

    followed by Dry clean

    Inspect endface with fibre scope

    Inspect endface with fibre scope

    Plug into clean mating connector

    Plug into clean mating connector

    Plug into clean mating connector

    Plug into clean mating connector

    is endface clean?

    is endface clean?

    is endface clean?

    is endface clean?











    Cleaning Challenges for MPO Connectors

    Unlike single fiber connectors, the cleanliness of the total surface of

    a multi-fiber connector such as the MPO connector is also critical to

    making a proper connection. The array of fibers is presented on a flat

    surface which comes into contact when terminated. Any contaminant

    around the optical fibers and alignment pin prevents full contact

    of the two connectors. This creates an air space which reduces the

    connector loss performance. Conventional MPO cleaning tools such

    as the pen cleaner clears contaminants around the optical fiber array.

    However the space around the alignment pins remains contaminated.

    A new type of MPO cleaning tool such as the SENKO Smart Cleaner

    Stick is able to effectively remove oil, dust and dirt particulate from

    pin to pin on the connector endface. An MPO connector is pushed

    onto the cleaner which sticks onto any contaminant, thus removing

    any particulate when the connector is removed.

    Step 2:PUSH MT Ferrule against the stick surface for cleaner

    Step 3:Remove the MT Ferrule, dirt and oil will be transferred from the ferrule to the cleaner

    2 3Step 1:Sticker cleaner contains 10 Stick cleaning area


    Conventional cleaner cleaning area

    Particles around the pin area can remain which could cause air gap.

    Full surface will be cleaned

    NEW Stick Cleaner Cleaning Zone will clean the full end face


    IEC Connector type

    There are many types of connectors specified under the IEC 61754 family of standards. Such standardization enables a more widespread use of

    the connectors through a more diverse manufacturers, connector interoperability and connector quality assurance. The list of connectors that

    are currently specified under the IEC standard is as follows:

    1 IEC 61754-2 BOFC Connector

    2 IEC 61754-3 LSA Connector

    3 IEC 61754-4 SC Connector

    4 IEC 61754-5 MT Connector

    5 IEC 61754-6 MU Connector

    6 IEC 61754-7 MPO Connector

    7 IEC 61754-8 CF08 Connector

    8 IEC 61754-9 dS Connector

    9 IEC 61754-10 Mini MPO Connector

    10 IEC 61754-12 FS Connector

    11 IEC 61754-13 FC-PC Connector

    12 IEC 61754-15 LSH Connector

    13 IEC 61754-16 PN Connector

    14 IEC 61754-18 MT-RJ Connector

    15 IEC 61754-19 Sg Connector

    16 IEC 61754-20 LC Connector

    17 IEC 61754-21 SMI Connector

    18 IEC 61754-22 F-SMA Connector

    19 IEC 61754-23 LX.5 Connector

    20 IEC 61754-24 SC-RJ Connector

    21 IEC 61754-25 RAO Connector

    22 IEC 61754-26 SF Connector

    23 IEC 61754-27 M12 Connector

    24 IEC 61754-28 LF3 Connector

    25 IEC 61754-29 BLINK Connector

    26 IEC 61754-30 CLIK! Connector

    27 IEC 61754-31 N-FO Connector

    28 IEC 61754-32 diaLink Connector

    29 IEC 61754-34 URM Connector


    IEC 61754-2 BOFC Connector

    IEC 61754-3LSA Connector

    The Bayonet Optical Fiber Connector (BOFC) is also more commonly

    known as the Straight Tip (ST) Connector. The ST Connector was

    developed by AT&T as a connector which deploys a plug and socket

    design. This was the first defector standard for fiber optic cabling and

    was widely deployed for networking applications in the late 80s and

    early 90s.

    The connector has a cylindrical shape connector with a 2.5mm

    keyed ferrule. The connector and matching adapter has a latch

    which requires a half-twist bayonet to lock and unlock the connector

    termination. The ST connector is spring loaded to enable an effortless

    mating and demating operation.

    The main application for the ST connector are in CATV networks, LAN

    and measurement equipment. The popularity of the ST connector is

    soon overtaken by the FC connector which uses the same twist lock

    mechanism but with a more compact design.

    The DIN connector was originally standardized by the Deutsches

    Institut fr Normung (DIN), a German national standards organization.

    The term DIN connector usually refers to a family of round connectors

    that is usually used for electrical connectivity such as computing data,

    video and audio. Due to the wide range, the document number of the

    DIN connector standard is also mentioned to discern specific types of

    connectors. The optical fiber connector based on the DIN standard is

    DIN 47256 or also known as the LSA connector.

    The connector body is similar to the more known FC connector with

    a screw on connector body. However, the ferrule is much larger. This

    causes the connector to be much more expensive.


    Proven reliability Expensive ferrule design

    Compact connector design

    ST Connector

    DIN Connectors


    Easy mating and dematingdue to spring loaded design

    Locking mechanism can be misaligned and result in amisaligned ferrule terminationwhich results in high loss




    IEC 61754-4SC Connector

    The Subscriber Connector or more commonly known as the SC

    connector is designed by NTT, a Japanese telecommunications

    company, as an improvement over the FC connector. The SC connector

    is a push/pull type connector which enables a more compact patch

    panel where traditional FC connectors require additional operation

    space to screw and unscrew the connector locking mechanism. In

    addition, the SC connector push/pull mechanism reduces the time to

    terminate connectors.

    The SC connector has a fully plastic body which is cheaper to

    manufacture with a moulding compared to machining metallic

    connectors. The ferrule size of the SC remains the same as the FC

    connector with a 2.5mm ferrule.

    With increasing deployment of SC connectors in the fiber access

    network such as FTTH saw the introduction of field installable

    connectors. There are multiple types of SC connectors where the

    most common types are designed to be compatible with 250m fiber,

    900m fiber, fiber cords as well as direct termination to the ends of

    cables such as the hardened SENKO IP Connector.

    With increasing deployment in netw