EN 4533-001:2020
(Main)Aerospace series - Fibre optic systems - Handbook - Part 001: Termination methods and tools
Aerospace series - Fibre optic systems - Handbook - Part 001: Termination methods and tools
1.1 General
Part 001 of EN 4533 examines the termination of optical fibre cables used in aerospace applications. Termination is the act of installing an optical terminus onto the end of a buffered fibre or fibre optic cable. It encompasses several sequential procedures or practices. Although termini will have specific termination procedures, many share common elements and these are discussed in this document. Termination is required to form an optical link between any two network or system components or to join fibre optic links together.
The fibre optic terminus features a precision ferrule with a tight tolerance central bore hole to accommodate the optical fibre (suitably bonded in place and highly polished). Accurate alignment with another (mating) terminus will be provided within the interconnect (or connector) alignment mechanism. As well as single fibre ferrules, it is noted that multi-fibre ferrules exist (e.g. the MT ferrule) and these will also be discussed in this part of the handbook.
Another technology used to connect 2 fibres is the expanded beam. 2 ball lenses are used to expand, collimate and then refocus the light from and to fibres. Contacts are not mated together. It helps reducing the wear between 2 contacts and allows more mating cycles. This technology is less sensitive to misalignments and dust. Losses are remaining more stable than butt joint contact even if the nominal loss is higher.
A Note on Terminology
Current terminology in the aerospace fibre optics community refers to an optical terminus or termini. The term optical contact may be seen in some documents and has a similar meaning. However, the term contact is now generally reserved for electrical interconnection pins. The optical terminus (or termini) is housed within an interconnect (connector is an equivalent term). Interconnects can be single-way or multi-way. The interconnect or connector will generally house the alignment mechanism for the optical termini (usually a precision split-C sleeve made of ceramic or metal). The reader should be aware of these different terms.
An optical link can be classified as a length of fibre optic cable terminated at both ends with fibre optic termini. The optical link provides the transmission line between any two components via the optical termini which are typically housed within an interconnecting device (typically a connector) with tight tolerancing within the alignment mechanisms to ensure a low loss light transmission.
Part 001 will explain the need for high integrity terminations, provide an insight into component selection issues and suggests best practice when terminating fibres into termini for high integrity applications. A detailed review of the termination process can be found in section 4 of this part and is organised in line with the sequence of a typical termination procedure.
The vast number of cable constructions and connectors available make defining a single termination instruction that is applicable to all combinations very difficult. Therefore, this handbook concentrates on the common features of most termination practices and defining best practice for current to near future applications of fibre optics on aircraft. This has limited the studies within this part to currently available ‘avionic’ silica fibre cables and adhesive filled butt-coupled type connectors. Many of the principles described however would still be applicable for other termination techniques. Other types of termination are considered further in the repair part of this handbook.
It is noted that the adhesive based pot-and-polish process is applicable to the majority of single-way fibre optic interconnects connectors and termini for multi-way interconnects and connectors. They share this commonality.
1.2 Need to high integrity terminations
(...)
Luft- und Raumfahrt - Faseroptische Systemtechnik - Handbuch - Teil 001: Anschlussverfahren und Werkzeuge
Teil 001 der EN 4533 untersucht die Anschlussaspekte von Lichtwellenleiterkabeln für Anwendungen in der Luft und Raumfahrt. Anschließen bezieht sich hierbei auf die Installation einer optischen Endstelle am Ende einer gepolsterten Faser oder eines Lichtwellenleiterkabels. Der Prozess umfasst mehrere Verfahren oder Praktiken, die nacheinander ausgeführt werden. Obgleich verschiedene Anschlüsse spezifische Anschluss¬verfahren aufweisen, teilen viele gemeinsame Elemente und diese werden in diesem Dokument besprochen. Ein Anschluss ist notwendig, um eine optische Verbindung zwischen zwei Netzwerk- oder Systemkompo¬nenten herzustellen oder Lichtwellenleiter zusammenzuführen.
Série aérospatiale - Systèmes des fibres optiques - Manuel d'utilisation - Partie 001 : Méthodes des terminaisons et des outils
La Partie 001 de l’EN 4533 examine la terminaison des câbles de fibres optiques utilisés dans les applications aérospatiales. La terminaison est l'action qui consiste à installer un contact optique à l'extrémité d'une fibre gainée ou d’un câble de fibre optique. Cette action comporte plusieurs modes opératoires ou méthodes séquentielles. Les contacts sont régis par des procédures de terminaison spécifiques ; cependant, nombre d'entre eux partagent des éléments communs qui sont exposés dans ce document. Une terminaison a pour obligation de former une liaison optique entre deux composants d'un réseau ou d'un système, ou d'accoupler des liaisons optiques.
Un contact de fibre optique comporte une ferrule de précision avec un trou central alésé à une tolérance rigoureuse pour recevoir la fibre optique (adéquatement collée en position et hautement polie). Un mécanisme d'alignement dans l’interconnexion (ou le connecteur) permet un alignement précis avec un autre contact (d'accouplement). De même que les ferrules monofibre, il est à noter l'existence de ferrules multifibres (par exemple : ferrules MT à transfert mécanique) qui sont également exposées dans cette partie du manuel d’installation.
La technologie à faisceau élargi est une autre technique d'accouplement de 2 fibres. Elle met en œuvre deux lentilles sphériques pour élargir, collimater et enfin, rétablir le centre optique du rayon lumineux en entrée et en sortie des fibres. Les contacts ne sont pas contraints ensemble, ce qui contribue à diminuer l'usure entre deux contacts tout en permettant d'augmenter les cycles de montage/démontage. Cette technologie est moins sensible aux défauts d'alignement et à la poussière. Les pertes optiques demeurent plus stables que les contacts à accouplement direct même si la perte nominale est plus élevée.
[...]
Aeronavtika - Sistemi iz optičnih vlaken - Priročnik - 001. del: Metode določanja in orodja
General Information
Relations
Overview
EN 4533-001:2020 - Aerospace series: Fibre optic systems - Handbook - Part 001: Termination methods and tools is a practical handbook that describes best-practice methods for terminating optical fibres and fibre‑optic cables used in aerospace applications. Part 001 explains why high‑integrity terminations are required on aircraft, clarifies current aerospace terminology (optical terminus/termini, interconnect/connector), and focuses on common termination elements for avionic silica fibre cables and adhesive-filled, butt‑coupled connectors.
Key topics and technical coverage
This part of the EN 4533 handbook concentrates on the common features of termination practice and tools, including:
- Component selection
- Fibre types and cladding choices, primary buffer materials (acrylate, polyimide, silicone), strength members and outer jackets
- Single‑way and multi‑way interconnects (including multi‑fibre ferrules such as MT ferrules)
- Termination technologies
- Adhesive-based pot‑and‑polish process (typical for single‑way and multi‑way termini)
- Expanded beam connectors (ball‑lens systems that expand/collimate/refocus light; more tolerant of misalignment and contamination, with stable loss over many mating cycles)
- Detailed termination process (sectioned stepwise)
- Cable preparation, jacket and coating removal, handling and trimming strength members
- Primary coating stripping methods, adhesive selection (epoxies, cure schedules and glass transition considerations), and connector preparation
- Fibre insertion, adhesive cure orientation and equipment, excess fibre removal (cleaving) and polishing stages
- Performance control and inspection
- Visual/optical inspection and interferometric inspection methods and pass/fail criteria for beginning‑of‑life assessment
- Health & safety
- Chemical handling, sharps safety and safe tooling practices
Practical applications and users
EN 4533-001:2020 is intended for professionals involved in the design, manufacture, installation and through‑life support of aerospace fibre‑optic harnesses and systems, including:
- Aircraft and avionics designers specifying fibre termination requirements
- Harness manufacturers and installers performing terminations and polishing
- Maintenance, repair and overhaul (MRO) engineers and technicians
- Test laboratories, quality and procurement teams evaluating connectors, adhesives and tooling
- Systems integrators selecting interconnect technologies (butt‑coupled vs expanded beam)
Adopting these best practices reduces optical loss, improves mechanical reliability and supports predictable performance across mating cycles and environmental conditions.
Related standards
Part 001 is one of four handbook parts in EN 4533:
- Part 002: Test and measurement
- Part 003: Looming and installation practices
- Part 004: Repair, maintenance, cleaning and inspection
Keywords: EN 4533-001:2020, fibre optic termination, aerospace fibre optics, termination methods and tools, optical terminus, expanded beam, MT ferrule, pot-and-polish, polishing, cleaving, adhesive cure, interconnects.
Frequently Asked Questions
EN 4533-001:2020 is a standard published by the European Committee for Standardization (CEN). Its full title is "Aerospace series - Fibre optic systems - Handbook - Part 001: Termination methods and tools". This standard covers: 1.1 General Part 001 of EN 4533 examines the termination of optical fibre cables used in aerospace applications. Termination is the act of installing an optical terminus onto the end of a buffered fibre or fibre optic cable. It encompasses several sequential procedures or practices. Although termini will have specific termination procedures, many share common elements and these are discussed in this document. Termination is required to form an optical link between any two network or system components or to join fibre optic links together. The fibre optic terminus features a precision ferrule with a tight tolerance central bore hole to accommodate the optical fibre (suitably bonded in place and highly polished). Accurate alignment with another (mating) terminus will be provided within the interconnect (or connector) alignment mechanism. As well as single fibre ferrules, it is noted that multi-fibre ferrules exist (e.g. the MT ferrule) and these will also be discussed in this part of the handbook. Another technology used to connect 2 fibres is the expanded beam. 2 ball lenses are used to expand, collimate and then refocus the light from and to fibres. Contacts are not mated together. It helps reducing the wear between 2 contacts and allows more mating cycles. This technology is less sensitive to misalignments and dust. Losses are remaining more stable than butt joint contact even if the nominal loss is higher. A Note on Terminology Current terminology in the aerospace fibre optics community refers to an optical terminus or termini. The term optical contact may be seen in some documents and has a similar meaning. However, the term contact is now generally reserved for electrical interconnection pins. The optical terminus (or termini) is housed within an interconnect (connector is an equivalent term). Interconnects can be single-way or multi-way. The interconnect or connector will generally house the alignment mechanism for the optical termini (usually a precision split-C sleeve made of ceramic or metal). The reader should be aware of these different terms. An optical link can be classified as a length of fibre optic cable terminated at both ends with fibre optic termini. The optical link provides the transmission line between any two components via the optical termini which are typically housed within an interconnecting device (typically a connector) with tight tolerancing within the alignment mechanisms to ensure a low loss light transmission. Part 001 will explain the need for high integrity terminations, provide an insight into component selection issues and suggests best practice when terminating fibres into termini for high integrity applications. A detailed review of the termination process can be found in section 4 of this part and is organised in line with the sequence of a typical termination procedure. The vast number of cable constructions and connectors available make defining a single termination instruction that is applicable to all combinations very difficult. Therefore, this handbook concentrates on the common features of most termination practices and defining best practice for current to near future applications of fibre optics on aircraft. This has limited the studies within this part to currently available ‘avionic’ silica fibre cables and adhesive filled butt-coupled type connectors. Many of the principles described however would still be applicable for other termination techniques. Other types of termination are considered further in the repair part of this handbook. It is noted that the adhesive based pot-and-polish process is applicable to the majority of single-way fibre optic interconnects connectors and termini for multi-way interconnects and connectors. They share this commonality. 1.2 Need to high integrity terminations (...)
1.1 General Part 001 of EN 4533 examines the termination of optical fibre cables used in aerospace applications. Termination is the act of installing an optical terminus onto the end of a buffered fibre or fibre optic cable. It encompasses several sequential procedures or practices. Although termini will have specific termination procedures, many share common elements and these are discussed in this document. Termination is required to form an optical link between any two network or system components or to join fibre optic links together. The fibre optic terminus features a precision ferrule with a tight tolerance central bore hole to accommodate the optical fibre (suitably bonded in place and highly polished). Accurate alignment with another (mating) terminus will be provided within the interconnect (or connector) alignment mechanism. As well as single fibre ferrules, it is noted that multi-fibre ferrules exist (e.g. the MT ferrule) and these will also be discussed in this part of the handbook. Another technology used to connect 2 fibres is the expanded beam. 2 ball lenses are used to expand, collimate and then refocus the light from and to fibres. Contacts are not mated together. It helps reducing the wear between 2 contacts and allows more mating cycles. This technology is less sensitive to misalignments and dust. Losses are remaining more stable than butt joint contact even if the nominal loss is higher. A Note on Terminology Current terminology in the aerospace fibre optics community refers to an optical terminus or termini. The term optical contact may be seen in some documents and has a similar meaning. However, the term contact is now generally reserved for electrical interconnection pins. The optical terminus (or termini) is housed within an interconnect (connector is an equivalent term). Interconnects can be single-way or multi-way. The interconnect or connector will generally house the alignment mechanism for the optical termini (usually a precision split-C sleeve made of ceramic or metal). The reader should be aware of these different terms. An optical link can be classified as a length of fibre optic cable terminated at both ends with fibre optic termini. The optical link provides the transmission line between any two components via the optical termini which are typically housed within an interconnecting device (typically a connector) with tight tolerancing within the alignment mechanisms to ensure a low loss light transmission. Part 001 will explain the need for high integrity terminations, provide an insight into component selection issues and suggests best practice when terminating fibres into termini for high integrity applications. A detailed review of the termination process can be found in section 4 of this part and is organised in line with the sequence of a typical termination procedure. The vast number of cable constructions and connectors available make defining a single termination instruction that is applicable to all combinations very difficult. Therefore, this handbook concentrates on the common features of most termination practices and defining best practice for current to near future applications of fibre optics on aircraft. This has limited the studies within this part to currently available ‘avionic’ silica fibre cables and adhesive filled butt-coupled type connectors. Many of the principles described however would still be applicable for other termination techniques. Other types of termination are considered further in the repair part of this handbook. It is noted that the adhesive based pot-and-polish process is applicable to the majority of single-way fibre optic interconnects connectors and termini for multi-way interconnects and connectors. They share this commonality. 1.2 Need to high integrity terminations (...)
EN 4533-001:2020 is classified under the following ICS (International Classification for Standards) categories: 49.060 - Aerospace electric equipment and systems; 49.090 - On-board equipment and instruments. The ICS classification helps identify the subject area and facilitates finding related standards.
EN 4533-001:2020 has the following relationships with other standards: It is inter standard links to EN 4533-001:2006, FprEN 4533-001. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.
You can purchase EN 4533-001:2020 directly from iTeh Standards. The document is available in PDF format and is delivered instantly after payment. Add the standard to your cart and complete the secure checkout process. iTeh Standards is an authorized distributor of CEN standards.
Standards Content (Sample)
SLOVENSKI STANDARD
01-maj-2020
Nadomešča:
SIST EN 4533-001:2009
Aeronavtika - Sistemi iz optičnih vlaken - Priročnik - 001. del: Metode določanja in
orodja
Aerospace series - Fibre optic systems - Handbook - Part 001: Termination methods and
tools
Luft- und Raumfahrt - Faseroptische Systemtechnik - Handbuch - Teil 001:
Verarbeitungsmethoden und Werkzeuge
Série aérospatiale - Systèmes des fibres optiques - Manuel d'utilisation - Partie 001 :
Méthodes des terminaisons et des outils
Ta slovenski standard je istoveten z: EN 4533-001:2020
ICS:
33.180.10 (Optična) vlakna in kabli Fibres and cables
49.060 Letalska in vesoljska Aerospace electric
električna oprema in sistemi equipment and systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN 4533-001
EUROPEAN STANDARD
NORME EUROPÉENNE
February 2020
EUROPÄISCHE NORM
ICS 49.090 Supersedes EN 4533-001:2006
English Version
Aerospace series - Fibre optic systems - Handbook - Part
001: Termination methods and tools
Série aérospatiale - Systèmes des fibres optiques - Luft- und Raumfahrt - Faseroptische Systemtechnik -
Manuel d'utilisation - Partie 001 : Méthodes des Handbuch - Teil 001: Verarbeitungsmethoden und
terminaisons et des outils Werkzeuge
This European Standard was approved by CEN on 2 March 2018.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 4533-001:2020 E
worldwide for CEN national Members.
Contents Page
European foreword . 5
Introduction . 6
a) The Handbook . 6
b) Background . 6
1 Scope . 7
1.1 General . 7
1.2 Need to high integrity terminations . 8
2 Normative references . 8
3 Component Selection . 8
3.1 Elements . 8
3.2 Fibre optic cables . 9
3.2.1 General . 9
3.2.2 Cable construction . 9
3.2.3 Fibre choice . 10
3.2.4 Cladding materials . 12
3.3 Primary buffer materials. 13
3.3.1 Function . 13
3.3.2 Acrylate . 13
3.3.3 Polyimide . 13
3.3.4 Silicone . 14
3.3.5 Strength Members . 14
3.4 Outer jacket . 14
3.5 Fibre optic interconnects (connectors) . 15
3.5.1 Introduction . 15
3.5.2 The Optical interface . 15
3.5.3 Single-way Interconnects/Connectors . 23
3.5.4 Multi-way Interconnects/Connectors . 23
3.5.5 Choice of tooling . 24
4 Health and safety aspects . 25
4.1 General . 25
4.2 Chemicals . 25
4.3 Sharps . 26
5 Termination process . 26
5.1 Objective . 26
5.2 Cable preparation . 26
5.2.1 General . 26
5.2.2 Cutting to length . 26
5.2.3 Removal of outer jacket . 28
5.2.4 Cable Handling tools (gripping the cable) . 33
5.2.5 Strength member trimming/ removal . 34
5.3 Removal of secondary coating(s) . 35
5.4 Removal of primary coatings . 36
5.4.1 General . 36
5.4.2 Mechanical techniques for primary coating removal . 36
5.4.3 Alternative techniques . 42
5.4.4 Troublesome coatings – Polyimide and Silicone . 43
5.4.5 Evidence of strength reduction when stripping primary buffer coatings . 45
5.4.6 To clean or not to clean . 46
5.5 Adhesives . 47
5.5.1 General . 47
5.5.2 Adhesive types . 47
5.5.3 The importance of glass transition temperature (T ) . 49
g
5.5.4 Epoxy cure schedule . 51
5.5.5 Usability. 53
5.5.6 Qualification . 57
5.6 Connector preparation . 57
5.6.1 Dry fitting . 57
5.7 Attachment of fibre to the terminus . 59
5.7.1 Application of adhesive . 59
5.7.2 Inserting Fibre ‘Best-Practice’ . 62
5.8 Adhesive cure . 66
5.8.1 General . 66
5.8.2 Orientation . 66
5.8.3 Curing equipment . 67
5.9 Excess Fibre removal . 71
5.9.1 General . 71
5.9.2 Post-cure rough cleaving . 71
5.9.3 Pre-cleave . 73
5.9.4 Safety . 73
5.9.5 Cleaving tools . 73
5.9.6 Sprung blade hand tools . 74
5.9.7 Cleaving fibres in Multi-fibre Ferrules . 75
5.10 Polishing . 75
5.10.1 Rationale . 75
5.10.2 Performance metrics . 75
5.10.3 End face geometries . 75
5.10.4 End-face geometry parameters . 76
5.10.5 Polishing stages . 86
5.10.6 Methods for controlling end-face geometry . 100
6 Beginning of life Inspection . 106
6.1 Optical or Visual Inspection . 106
6.2 Interferometric Inspection . 109
6.2.1 Inspection and Pass/Fail Criteria . 110
Bibliography . 113
European foreword
This document (EN 4533-001:2020) has been prepared by the Aerospace and Defence Industries
Association of Europe — Standardization (ASD-STAN).
After enquiries and votes carried out in accordance with the rules of this Association, this document has
received the approval of the National Associations and the Official Services of the member countries of
ASD, prior to its presentation to CEN.
This document shall be given the status of a national standard, either by publication of an identical text
or by endorsement, at the latest by August 2020, and conflicting national standards shall be withdrawn
at the latest by August 2020.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 4533-001:2006.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland,
Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North
Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United
Kingdom.
Introduction
a) The Handbook
The purpose of EN 4533 is to provide information on the use of fibre optic components on aerospace
platforms. The documents also include best practice methods for the through-life support of the
installations. Where appropriate more detailed sources of information are referenced throughout
the text.
The handbook is arranged into 4 parts, which reflect key aspects of an optical harness life cycle, namely:
Part 001: Termination methods and tools.
Part 002: Test and measurement.
Part 003: Looming and installation practices
Part 004: Repair, maintenance, cleaning and inspection.
b) Background
It is widely accepted in the aerospace industry that photonic technology offers significant advantages
over conventional electrical hardware. These include massive signal bandwidth capacity, electrical
safety, and immunity of passive fibre-optic components to the problems associated with electromagnetic
interference (EMI). Significant weight savings can also be realized in comparison to electrical harnesses
which may require heavy screening. To date, the EMI issue has been the critical driver for airborne fibre-
optic communications systems because of the growing use of non-metallic aero structures. However,
future avionics requirements are driving bandwidth specifications from 10’s of Mbits/s into the multi-
Gbits/s regime in some cases, i.e. beyond the limits of electrical interconnect technology. The properties
of photonic technology can potentially be exploited to advantage in many avionic applications, such as
video/sensor multiplexing, flight control signalling, electronic warfare, and entertainment systems, as
well as sensor for monitoring aerostructure.
The basic optical interconnect fabric or `optical harness’ is the key enabler for the successful introduction
of optical technology onto commercial and military aircraft. Compared to the mature
telecommunications applications, an aircraft fibre-optic system needs to operate in a hostile
environment (e.g. temperature extremes, humidity, vibrations, and contamination) and accommodate
additional physical restrictions imposed by the airframe (e.g. harness attachments, tight bend radii
requirements, and bulkhead connections). Until recently, optical harnessing technology and associated
practices were insufficiently developed to be applied without large safety margins. In addition, the
international standards did not adequately cover many aspects of the life cycle. The lack of accepted
standards thus leads to airframe specific hardware and support. These factors collectively carried a
significant cost penalty (procurement and through-life costs) that often made an optical harness less
competitive than an electrical equivalent. This situation is changing with the adoption of more
standardized (telecoms type) fibre types in aerospace cables and the availability of more ruggedized
COTS components. These improved developments have been possible due to significant research
collaboration between component and equipment manufacturers as well as the end users air framers.
1 Scope
1.1 General
Part 001 of EN 4533 examines the termination of optical fibre cables used in aerospace applications.
Termination is the act of installing an optical terminus onto the end of a buffered fibre or fibre optic
cable. It encompasses several sequential procedures or practices. Although termini will have specific
termination procedures, many share common elements and these are discussed in this document.
Termination is required to form an optical link between any two network or system components or to
join fibre optic links together.
The fibre optic terminus features a precision ferrule with a tight tolerance central bore hole to
accommodate the optical fibre (suitably bonded in place and highly polished). Accurate alignment with
another (mating) terminus will be provided within the interconnect (or connector) alignment
mechanism. As well as single fibre ferrules, it is noted that multi-fibre ferrules exist (e.g. the MT ferrule)
and these will also be discussed in this part of the handbook.
Another technology used to connect 2 fibres is the expanded beam. 2 ball lenses are used to expand,
collimate and then refocus the light from and to fibres. Contacts are not mated together. It helps reducing
the wear between 2 contacts and allows more mating cycles. This technology is less sensitive to
misalignments and dust. Losses are remaining more stable than butt joint contact even if the nominal
loss is higher.
NOTE Current terminology in the aerospace fibre optics community refers to an optical terminus or termini.
The term optical contact may be seen in some documents and has a similar meaning. However, the term contact is
now generally reserved for electrical interconnection pins. The optical terminus (or termini) is housed within an
interconnect (connector is an equivalent term). Interconnects can be single-way or multi-way. The interconnect or
connector will generally house the alignment mechanism for the optical termini (usually a precision split-C sleeve
made of ceramic or metal). The reader should be aware of these different terms.
An optical link can be classified as a length of fibre optic cable terminated at both ends with fibre optic
termini. The optical link provides the transmission line between any two components via the optical
termini which are typically housed within an interconnecting device (typically a connector) with tight
tolerancing within the alignment mechanisms to ensure a low loss light transmission.
Part 001 will explain the need for high integrity terminations, provide an insight into component
selection issues and suggests best practice when terminating fibres into termini for high integrity
applications. A detailed review of the termination process can be found in section 4 of this part and is
organised in line with the sequence of a typical termination procedure.
The vast number of cable constructions and connectors available make defining a single termination
instruction that is applicable to all combinations very difficult. Therefore, this handbook concentrates on
the common features of most termination practices and defining best practice for current to near future
applications of fibre optics on aircraft. This has limited the studies within this part to currently available
‘avionic’ silica fibre cables and adhesive filled butt-coupled type connectors. Many of the principles
described however would still be applicable for other termination techniques. Other types of termination
are considered further in the repair part of this handbook.
It is noted that the adhesive based pot-and-polish process is applicable to the majority of single-way fibre
optic interconnects connectors and termini for multi-way interconnects and connectors. They share this
commonality.
1.2 Need to high integrity terminations
In order to implement a fibre optic based system on an aircraft it is vital to ensure that all the constituent
elements of the system will continue to operate, to specification, over the life of the system. An important
aspect of this requirement is the need for reliable interconnection components. Interconnects are a key
component in any fibre optic system or network. Digital communications links, sensor systems,
entertainment systems etc. all require interconnects both at equipment interfaces and for linking cables
and harness sections together over the airframe.
Interconnects need to be robust to mating and demating operations, environmental changes and also the
effects of contamination. They need to be amenable to inspection and cleaning for through life support.
The choice of technology used in optical links and connections is mainly dependant of the environment.
In service performance is a pillar in the component selection. Cable to connector interface needs to be
assessed to prove the effectiveness of the solution.
High integrity terminations are required to ensure reliable, low loss light transmission through the
interconnection. High integrity terminations are produced by observing best practice and using the
correct materials, tools and procedures with appropriate controls.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
All interconnection technologies are taken in account in the context of the EN 4533-001.
EN 4533-002, Aerospace series — Fibre optic systems — Handbook — Test and measurement
EN 4533-003, Aerospace series — Fibre optic systems — Handbook — Looming and installation practices
EN 4533-004, Aerospace series — Fibre optic systems — Handbook — Repair, maintenance, cleaning and
inspection
3 Component Selection
3.1 Elements
It is important to recognise that a fibre optic termination, while appearing straightforward, is in fact a
complex interaction of the constituent elements such as: fibre, ferrule, fibre coatings, connector design,
cable strength member anchorage method, adhesive type and cure regime (where used), material
properties and so on. Each of these elements will have an impact on the termination, in terms of reliability,
integrity and process complexity.
The following sections discuss the key elements to the termination.
3.2 Fibre optic cables
3.2.1 General
There are many types of fibre optic cable on the market today. Cables are essentially assemblies that
contain and protect the optical light guide (used to carry the system light signal). The central light guide
is usually made from silica glass although other materials can be used. Glass is inherently strong
although it must be protected from external damage and other factors that could cause weakening
(generally moisture and fluid contamination in the presence of any defects and stress). The cable
provides the protective layers to the glass and generally also incorporates a strength member (this
element is important in the termination for providing strain relief) and a protective outer jacket.
For aerospace applications, most encountered cables will carry a single, central optical fibre (suitably
protected as discussed in the following sections). There can be variation in single fibre cable designs.
Some may be of tight jacket construction, some of loose jacket construction. Cables are also being
developed with many fibres contained within a protective tube construction. It is noted that many of the
cable designs used in terrestrial telecommunications and data communications will not be suitable for
aerospace use. This is generally due to environmental capability limitations often due to environmental
characteristics.
3.2.2 Cable construction
As mentioned in the introduction, the cable construction provides the protection to the central
lightguide(s).
Although the design of fibre optic cable for use on aircraft is fairly similar from one manufacturer to
another there are important differences between cables. The two main areas of difference are fibre
coatings and the cable strength member materials. Each has its own positive and negative attributes in
the context of termination procedures. Avionic fibre optic simplex cables are typically constructed as in
Figure 1.
Another distinction between cable designs is whether all the coatings are “tight” or “semi loose” onto the
underlying layers. This will also impact the operation of the terminated cable, (referring to full pull
proofness achievable with loose structure cables)
A tight cable is a cable which shows no movements between all layers.
A semi-loose cable is a cable which shows limited movements between layers. It could be a movement
between the fibre and the buffer (case of 900 µm cables) or between the buffer and the above layers
(case of simplex 1,8 mm cables)
A tight construction is generally easier to terminate but can be more sensitive to environmental changes if
materials are not well chosen. Some cable designs have a semi-loose construction where the central fibre
has some mobility within one of the cable layers (usually an inner sheath). This design is generally more
difficult to terminate but can have superior environmental performance (because the fibre is isolated from
the other layers).
The behaviour of the connector is different whether the cable is tight or semi loose. Generally on tight
construction fibre contact is interrupted when pulling. The semi loose construction permits a pull safe
termination.
Key
1 Core
2 Cladding
3 Primary buffer
4 Secondary buffer
5 Strength member
6 Outer jacket
Figure 1 — Typical avionic fibre optic cable construction
NOTE The glass fibre lightguide comprises the core and cladding regions.
The figure highlights the key elements of an aerospace fibre optic cable. These elements are now
discussed in more detail.
Figure 2 — Examples of EU standardised cables
3.2.3 Fibre choice
The central lightguide is defined by the core/cladding region. This is the fibre that needs to be suitably
protected by the cable. It is noted that both the core and the cladding are generally formed from glass.
The glass in the core is of higher refractive index than the cladding and this allows light guiding along the
fibre via total internal reflection. Whilst most aerospace fibres are made from glass it is recognised that
other fibre constructions exist including plastic optical fibre (POF), plastic clad silica (PCS). Very novel
fibres such as photonic crystal fibres (PCF) or polarisation maintaining fibre (PM) may also find some
specialised aerospace applications in the future.
One of the primary distinctions between cables is whether the cable carries a singlemode or a multimode
optical fibre lightguide. The choice of lightguide will be dictated by the system or network. Most current
data communication systems on aircraft use multimode based cables. The relatively short lengths
encountered on aircraft mean that multimode fibres can currently provide sufficient bandwidth (up to
~10 Gbps) and their relatively large cores are easier to interconnect (compared to singlemode). Sensor
systems will generally require singlemode based cables. Future bandwidth requirements or the need for
data multiplexing down common fibres may drive the need for more singlemode fibre cables in
aerospace although it must be recognised that singlemode fibres (~ 9 µm core size) are harder to align
and keep free from contamination.
Multimode fibres can be either Step Index (SI) or Graded Index types. Graded index fibres have a graded
profile to the refractive index of the fibre. In essence this increases the bandwidth of the fibre by
equalising the various possible light paths within the core region (thus reducing any dispersion or data
pulse spreading that can occur). Higher data rates are possible with graded index fibres. Step index fibres
may be seen particularly on legacy systems. As its name suggests, the refractive index profile shows a
step change in value defining the change from core to cladding material.
Historically, avionic fibre sizes have tended to be larger than the standard high volume fibres such as
those used in the data communication and telecommunication market and have therefore had an
associated cost and availability penalty (associated components required for termination have also been
non-standard and therefore more expensive). Examples of larger fibre sizes are 200/280 µm,
100/140 µm (where the convention denotes the core/cladding dimension). The data communications
and telecommunications industries typically use fibres of size 62,5/125 µm, 50/125 µm (multimode) and
9/125 µm (singlemode). The last fibres are now being specified for new systems on aircraft with these
fibre sizes, which is becoming the standard configuration.
Importantly for termination, these fibres have a common outer cladding diameter of 125 µm. This means
that the ferrules used in fibre optic termini can be lower cost (these components are mass produced for
the telecommunications market). A number of companies are now packaging these data communication
and telecommunication standard fibres in an aerospace cable meaning that higher bandwidth cables are
now available to the aircraft industry.
Other factors worth mentioning in the choice of fibre are
Bandwidth:
Multimode fibres (within the cable) are designated by the OM identification (meaning ‘optical
multimode’). OM1 describes 62,5/125 µm fibre, OM2, OM3 and OM4 describe 50/125 µm fibres
of increasing bandwidth.
Radiation resistance ( radiation hard):
These may be specified on some military programs.
Bend resistance:
Cables with bend tolerant or bend resistant fibres are now also becoming more widely
manufactured. These cables exhibit lower losses when bent compared to the ones which are
based on bend sensitive fibres. However, as noted elsewhere in EN 4533, fibres should not be
bent beyond their recommended minimum bend radius. They are no stronger than conventional
fibres
The below table is summarising the basics feature of a fibre. Fibres have been categorised according to
ITU rules.
Table 1 — Basics feature of a fibre according to ITU rules
Minimum modal
Bandwidth
Ø core
Mono / multi-mode Category
(µm)
(MHz.km)
850nm / 1 310nm
Mono 9 n/a G652
Mono 9 n/a G657
Multi 62,5 200 / 500 OM1
Multi 50 500 OM2
Multi 50 1500 / 2000 OM3
50 3500 / 4700 OM4
From the perspective of termination there is little difference between small and larger core optical fibres.
The main fibre issues that impact upon the termination process relate to cladding size and primary
coating materials.
The emerging use of multifibre array connectors (e.g. those based on the MT ferrule discussed later) in
some aerospace applications means that cables with multiple fibres are required. A typical construction
is shown below. Early multifibre cables designs were of a flat ‘ribbon’ type. However more recent designs
have been of a round profile cable with loose fibres (suitably protected) within. The cables typically also
include a strength member. This technology is not yet standardised.
Figure 3 — Example of multi-way cable
3.2.4 Cladding materials
3.2.4.1 Coatings and Buffers – A note on terminology
The central lightguide is protected in the cable by various layers of material. The reader should be aware
that different texts will refer to these layers in different ways. Common to most texts however is the
designation of the order of layers. Thus primary layers exist immediately next to the lightguide (usually
applied onto the cladding layer of the fibre). Secondary layers will be applied above the primary layer
and so on.
Where there is sometimes confusion is the inconsistent use of terms such as coatings, buffers and sheaths.
For instance it is common for the terms primary buffer and primary coating to be seen in different texts.
Terms such as secondary coating and secondary buffer would also refer to a coating lying above the first
(primary) layer of protection. Secondary layers can sometimes be hybrid, composed of different materials
(sometimes difficult to separate). Finally a boundary sheath layer may exist in the cable. The term
boundary sheath implies a tube type construction that allows the coated fibre to move within the cable
(semi loose).
3.3 Primary buffer materials
3.3.1 Function
Immediately above the optical fibre is a primary buffer layer. The major function of the primary buffer is
to protect the fibre from abrasive and environmental damage. It also limits micro-bending losses in the
fibre. Generally this coating is applied at the time of fibre manufacture. It provides the first layer of
protection to the glass. It must provide protection but also be easily removable when performing a
termination.
Most fibres use an acrylate type material for the primary buffer, other materials can be encountered
however, such as silicone, polyimide, proprietary polymers and even metal, such as gold or aluminium
(although these are somewhat specialised and will not be considered here). These alternative buffer
materials can extend the operating temperature of the fibre. Carbon is sometimes applied to special
fibres to hermetically seal the fibre surface and prevent moisture reaching the glass surface (typically
used on space applications). For a detailed review of materials see below sections
It should be emphasised that the temperature capability of a glass fibre is not limited over the
operational envelope of an aircraft. Glass will survive (and indeed is used in other applications) at very
high and very low temperatures. It is the temperature range of the protective layers (which are essential
in preventing damage to the fibre) that limit the temperature performance of the cable. In comparison,
other types of fibre (e.g. POF and PCS) may be fundamentally limited by the operating temperature of the
fibre material itself.
In aerospace applications, the most widely used primary coating materials are, acrylate, polyimide and
silicone. A brief description of each material is placed below.
3.3.2 Acrylate
This is perhaps the most common of all the optical fibre primary buffer materials and is relatively easy to
remove with hand tools. The buffer is usually a UV cured acrylate that is translucent and is typically the
same thickness as the fibre. Standard acrylates have a limited temperature performance of up to
approximately 90 °C to 100 °C (above this temperature they can break down and become discoloured
and brittle) however in recent years higher temperature acrylate (HTA) has become a standard buffer
material and is now being packaged in aerospace cables. HTAs extend the operation to the region of
150 °C and up to 180 °C. Low temperature limits are in the region of − 60 °C. Acrylate is subject to
degases when used in unpressurised environments. Some manufacturers have operated these buffers
down to − 65 °C with no degradation.
3.3.3 Polyimide
This buffer has a higher temperature range than UV cured acrylates and can be used in temperatures up
to 300 °C and up to 400 °C short term. Although useful for high temperature applications, polyimide
buffers are difficult to remove using common mechanical tools. Fibres employing this material are
designed to be installed into connector ferrules without the need to remove the primary buffer. This is
only possible because the core/cladding/primary buffer concentricity and outer diameter tolerances are
tightly controlled. This would appear to be an ideal design solution because the fibre surface does not
need to be touched. However the enlarged polyimide diameter is not compatible with standard
connector ferrule bore dimensions, thus non-standard ferrules need to be used with an associated cost
and availability penalty. Removal of polyimide buffers is discussed later in this document (see 5.4.4).
Polyimide is not degasing when used in unpressurised environments.
3.3.4 Silicone
The main benefits of silicone as a primary coating are the reduction of fibre micro-bend effects due to the
“cushioning” effect of the soft primary coating layer, its high temperature capability (up to 200 °C), its
resilience to water penetration and its low flammability. However, as with acrylate, this material needs
to be stripped prior to inserting optical fibres into fibre optic connectors. This is by no means easy (see
later section on removing troublesome primary coatings) and can leave a residue which could
compromise fibre/ferrule bonding. Again removal of silicone is also discussed in 5.4.4 some ‘soft silicone’
coatings may allow lower temperature operation of fibres e.g. down to − 100 °C.
3.3.5 Strength Members
Almost all fibre optic cables employ some form of strength member layer. Its function is to isolate cable
external loads from the fibre within and provide excellent longitudinal strength; it is usually in the form
of stranded fibres running along the fibre axis or woven in a braid. The most common material used for
this purpose is a very tough, strong material known as aramid yarn. However, it is by no means the only
material used for this purpose – fibreglass being one of the main alternatives. New designs of aerospace
fibre optic cable are now implementing a fibreglass / aramid yarn mix to provide a strength member
with lower smoke emissions than that of a pure aramid yarn strength member.
Fibreglass is better matched to the optical fibre’s thermal coefficient of expansion compared to aramid
yarn and has been used where high temperature (> 135 °C) dimensional stability is required of a cable.
This aspect must be considered if a cable is to be subjected to prolonged exposure of rapid thermal
cycling stresses over a wide temperature range. However, aramid yarnappears to meet most current
avionic temperature requirements (− 65 °C to 150 °C).
These two materials need to be treated in quite different ways in order to achieve effective optical fibre
load isolation during the termination process. Aramid yarn and other similar materials can be crimped
directly onto a connector or termini; fibreglass can
...
기사 제목: EN 4533-001:2020 - 항공우주 분야 - 광섬유 시스템 - 핸드북 - 파트 001: 종단 방법과 도구 기사 내용: EN 4533의 파트 001은 항공우주 분야에서 사용되는 광섬유 케이블의 종단에 대해 검토한다. 종단은 버퍼링된 광섬유나 광섬유 케이블의 끝에 광 종단기를 설치하는 것을 의미한다. 종단은 여러 순차적인 절차나 실천 방법을 포함한다. 종단기는 각각 종단 절차가 있지만, 많은 종단기가 공통 요소를 가지고 있으며 이에 대해 이 문서에서 논의된다. 종단은 네트워크 또는 시스템 구성요소 간 광 링크를 형성하거나 광섬유 링크를 연결하기 위해 필요하다. 광섬유 종단기는 광섬유를 수용하기 위한 고정밀한 페룰과 중앙보어 홀이 포함되어 있다(적절하게 접착되고 고도로 광택을 갖춤). 다른 (동맥) 종단기와 정확하게 정렬될 수 있도록 이와 다른 종단기는 interconnect(또는 커넥터) 정렬 메커니즘 내에서 제공된다. 단일 광섬유 페룰 외에도 다중 광섬유 페룰(예: MT 페룰)도 이 핸드북의 이 부분에서 다루어진다. 두 광섬유를 연결하는 또 다른 기술은 확장 빔이다. 2개의 볼 렌즈를 사용하여 광섬유로부터 빛을 확장, 정렬하고 다시 초점을 맞춘다. 연락은 서로 연결되지 않는다. 이 기술은 2개의 연락 사이의 마모를 줄이고 더 많은 연결 주기를 가능하게 한다. 이 기술은 정렬 오차와 먼지에 민감하지 않기 때문에 상대적으로 안정적인 손실을 제공한다. 버틀리 스타일의 연락보다도 안정적이다. 용어에 대한 주의 현재 항공우주 광섬유 커뮤니티에서는 광 종단기 또는 종단기라는 용어를 사용한다. 광 연락이라는 용어는 일부 문서에서 볼 수 있으며 비슷한 의미를 가진다. 그러나 연락은 일반적으로 전기적 상호연결 핀을 위해 사용된다. 광 종단기 또는 종단기는 일반적으로 interconnect(일반적으로 세라믹이나 금속으로 만든 정밀한 분할 C 슬리브) 내에 있으며 광 종단기의 정렬 메커니즘을 포함한다. 독자는 이러한 다른 용어를 알고 있어야 한다. 광 링크는 광섬유 케이블의 양쪽 끝에 광 종단기를 가지고 있는 것으로 분류될 수 있다. 광 링크는 광 종단기(일반적으로 커넥터와 동일한 의미)가 일반적으로 착용되는 연결 장치(일반적으로 커넥터) 내에서 광섬유를 통한 전송 선로를 제공한다. 파트 001은 고성능 종단의 필요성을 설명하고 구성 요소 선택 문제에 대한 통찰력을 제공하며, 고성능 응용 프로그램을 위해 광섬유를 종단기로 종단시킬 때 최상의 실천 방법을 제안한다. 종단 과정에 대한 자세한 검토는 파트 4에서 찾을 수 있으며, 전형적인 종단 절차의 순서에 따라 구성되어 있다. 다양한 케이블 구성과 커넥터의 가용성으로 인해 모든 조합에 적용 가능한 단일 종단 지시사항을 정의하는 것은 매우 어렵다. 그러므로 이 핸드북은 대부분의 종단 실천 방법의 공통 요소에 집중하고 현재부터 가까운 미래의 항공기 광섬유 응용 프로그램에 대한 최상의 실천 방법을 정의한다. 이로 인해 이 부분의 연구는 현재 사용 가능한 "항공전자" 실리카 광섬유 케이블과 접착 제품으로 가득한 버틀리 스타일 커넥터에 한정되었다. 그러나 다른 종단 기술에 대해서는 이 핸드북의 수리 파트에서 자세히 다룬다. 대부분의 단방향 광섬유 커넥터와 다중방향 커넥터를 위한 접착제 기반 pot-and-polish 과정이 공통으로 적용된다는 점을 유의한다. 1.2 고신뢰 종단이 필요한 이유 (...)
The article discusses Part 001 of EN 4533, which focuses on the termination of optical fibre cables in aerospace applications. Termination involves installing an optical terminus onto the end of a fibre optic cable to create an optical link between network or system components. The terminus features a precision ferrule and can be single or multi-fibre. The article also introduces the expanded beam technology, which uses ball lenses to connect two fibres. Terminology related to optical termini and connectors is explained, and the need for high integrity terminations is emphasized. The article provides insight into component selection and best practices for terminating fibres. It also acknowledges the challenges of defining a single termination instruction due to the variety of cable constructions and connectors available. The focus is on currently available silica fibre cables and adhesive-filled butt-coupled connectors. The article concludes by mentioning that the pot-and-polish process with adhesive is commonly used for termination.
記事のタイトル：EN 4533-001：2020 - 航空宇宙シリーズ - 光ファイバシステム - ハンドブック - パート001：終端方法とツール 記事の内容：EN 4533のパート001では、航空宇宙アプリケーションで使用される光ファイバーケーブルの終端について調査しています。終端は、バッファリングされた光ファイバまたは光ファイバケーブルの端に光終端子を取り付ける行為を意味します。終端にはいくつかの順番に従う手順や実施方法が含まれます。終端は、2つのネットワークまたはシステムコンポーネント間の光リンクを形成するために必要であり、また、光ファイバリンクを接続するためにも必要です。 光ファイバ終端子には、光ファイバを収容するための精密なフェルールと、光ファイバが適切に接着されて高品質に研磨された中央の貫通孔が備わっています。他の（マッティング）終端子との正確な整列は、インターコネクト（またはコネクタ）の整列機構内で提供されます。シングルファイバフェルール以外にも、マルチファイバフェルール（例：MTフェルール）も本ハンドブックのこの部分で議論されます。 2本の光ファイバを接続する別の技術として、展開ビームがあります。2つのボールレンズを使用して光を拡大、整列し、再び焦点を合わせます。接点は互いに結合されません。これにより、接点間の摩耗が減少し、より多くの結合サイクルを可能にします。この技術は、傾斜や埃に対しても感度が低く、通常のバット接合コンタクトよりも安定した損失が得られます。 用語に関する注意 現在の航空宇宙の光ファイバコミュニティでは、光終端子または終端子という用語が使用されます。光接点という用語も一部の文書で見られ、似た意味を持ちます。ただし、接点という用語は一般的に電気的な接続ピンに対して使用されます。光終端子は、通常はセラミックや金属製の精密な分割Cスリーブで構成されるインターコネクト（通常はコネクタ）内に収容されます。読者はこれらの異なる用語に注意する必要があります。 光リンクは、光終端子で両端の光ファイバ終端子が接続された光ファイバケーブルのことを指すことができます。光リンクは、光終端子が通常は整合メカニズムを備えたインターコネクトデバイス（通常はコネクタ）内に収められ、低損失の光伝送を確保するためのトランスミッションラインを提供します。 パート001では、高い信頼性の終端の必要性を説明し、コンポーネントの選択問題の洞察を提供し、高い信頼性のアプリケーション向けに光ファイバを終端子に終端する際のベストプラクティスを提案しています。詳細な終端プロセスのレビューは、このパートのセクション4に記載されており、通常の終端手順の順序に従って組織されています。 利用可能なケーブル構造とコネクタの多様性のため、すべての組み合わせに適用可能な単一の終端指示を定義することは非常に困難です。そのため、このハンドブックでは、一般的な終端手法の共通点に焦点を当て、現在から近い将来の航空機のファイバオプティックスアプリケーションのベストプラクティスを定義しています。本部分の研究は、現在利用可能な「航空エレクトロニクス」と呼ばれるケイ酸塩ファイバケーブルと接着剤入りのバットカップル接合型コネクタに限定されています。しかし、他の終端技術については、このハンドブックの修理パートで詳述されています。 粘着性のポットとポリッシュプロセスは、ほとん
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