SIST EN 4533-002:2018

Aerospace series - Fibre optic systems - Handbook - Part 002: Test and measurement

This handbook examines the requirements to enable accurate measurement of fibre optic links from start of life and during the life cycle of the system from installation and through-service. Part 2 will explain the issues associated with optical link measurement and provide techniques to address these issues. This document discusses the measurement of key parameters associated with the passive layer (i.e. transmission of light through an optical harness). It does not discuss systems tests e.g. bit error rates.

Luft- und Raumfahrt - Faseroptische Systemtechnik - Handbuch - Teil 002: Tests und Messungen

Série aérospatiale - Systèmes des fibres optiques - Manuel d'utilisation - Partie 002: Essais et mesures

Aeronavtika - Sistemi iz optičnih vlaken - Priročnik - 002. del: Preskušanje in merjenje

General Information

• Status: Published
• Publication Date: 07-Jan-2018
• ICS: 33.180.01 - Fibre optic systems in general
• ICS: 49.060 - Aerospace electric equipment and systems
• Technical Committee: I13 - Imaginarni 13
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 03-Jan-2018
• Due Date: 10-Mar-2018
• Completion Date: 08-Jan-2018
• Ref Project: EN 4533-002:2017 - Aerospace series - Fibre optic systems - Handbook - Part 002: Test and measurement

Relations

• Replaces: SIST EN 4533-002:2009 - Aerospace series - Fibre optic systems - Handbook - Part 002: Test and measurement
• Effective Date: 27-Dec-2017
• Revised: kSIST FprEN 4533-002:2025 - Aerospace series - Fibre optic systems - Handbook - Part 002: Test and measurement
• Effective Date: 11-Oct-2023
• Revised: SIST EN 4533-002:2009 - Aerospace series - Fibre optic systems - Handbook - Part 002: Test and measurement
• Effective Date: 12-Mar-2014

Overview

EN 4533-002:2017 - "Aerospace series - Fibre optic systems - Handbook - Part 002: Test and measurement" is a CEN handbook that provides guidance for accurate measurement of fibre‑optic links across the lifecycle of aerospace optical harnesses. It focuses on testing the passive layer (transmission of light through an optical harness) from installation through in‑service support. The standard addresses measurement issues specific to aerospace environments (short link lengths, multiple connectors, harsh conditions) and explains techniques to obtain consistent, repeatable results. It does not cover system‑level tests such as bit error rate (BER).

Key Topics

• Scope and purpose: Measurement requirements for start‑of‑life and through‑service verification of passive optical links in aircraft.
• Fibre types: Guidance on multimode (OM1–OM4, 50/62.5 µm) and singlemode (OS1/OS2/A2) fibres, including implications for test methods and launch conditions.
• Key parameters:
  • Insertion loss (I.L.) - importance to system power budget, common measurement methods and sensitivity to launch conditions and connector contamination.
  • Return (reflection) loss (R.L.) - measurement and impact on source/receiver performance.
• Measurement techniques: Use of light‑source + power‑meter, OTDR and OFBR; practical considerations for multimode vs singlemode testing and the need to control launch conditions in multimode systems.
• Reflectometry and footprinting: Techniques for locating events along network paths and identifying connector/splice performance.
• Practical testing considerations: Contamination control, connector repeatability, ageing margins (typical guidance), and reporting arrangements.
• Lifecycle focus: Test regimes for installation, acceptance and in‑service monitoring.

Applications and Users

Who uses EN 4533-002:2017:

• Avionics designers and fibre‑optic system engineers defining power budgets and qualification criteria
• Installation and test technicians performing acceptance and commissioning tests
• Maintenance and repair teams implementing in‑service verification and troubleshooting
• Suppliers and manufacturers of harnesses, connectors and passive components
• Certification and quality teams documenting test evidence for procurement and airworthiness

Typical applications:

• Acceptance testing of new optical harnesses
• Through‑life monitoring and preventive maintenance
• Fault location and repair using OTDR/OFBR techniques
• Establishing consistent test methods for multimode launch conditions and connector cleanliness

Related Standards

• EN 4533-001: Termination methods and tools (handbook Part 001)
• EN 4533-003 / EN 4533-004: Looming/installation and repair/maintenance (Parts 003–004)
• EN 2591-601: Test methods - Optical elements - Insertion loss

Keywords: EN 4533-002:2017, aerospace fibre optic test, insertion loss, return loss, OTDR, multimode launch, optical harness testing, aircraft fibre optic measurement.

Standards Content (Sample)

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.PHUMHQMHLuft- und Raumfahrt - Faseroptische Systemtechnik - Handbuch - Teil 002: Tests und MessungenSérie aérospatiale - Systèmes des fibres optiques - Manuel d'utilisation - Partie 002: Essais et mesuresAerospace series - Fibre optic systems - Handbook - Part 002: Test and measurement49.060Aerospace electric equipment and systems33.180.01VSORãQRFibre optic systems in generalICS:Ta slovenski standard je istoveten z:EN 4533-002:2017SIST EN 4533-002:2018en,fr,de01-marec-2018SIST EN 4533-002:2018SLOVENSKI
STANDARDSIST EN 4533-002:20091DGRPHãþD

EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 4533-002
December
t r s y ICS
v {ä r x r Supersedes EN
v w u uæ r r tã t r r xEnglish Version
Aerospace series æ Fibre optic systems æ Handbook æ Part
r r tã Test and measurement Série aérospatiale æ Systèmes des fibres optiques æ Manuel d 5utilisation æ Partie
r r tã Essais et mesures
Luftæ und Raumfahrt æ Faseroptische Systemtechnik æ Handbuch æ Teil
r r tã Tests und Messungen This European Standard was approved by CEN on
t u July
t r s yä
egulations which stipulate the conditions for giving this European Standard the status of a national standard without any alterationä Upætoædate lists and bibliographical references concerning such national standards may be obtained on application to the CENæCENELEC Management Centre or to any CEN memberä
translation under the responsibility of a CEN member into its own language and notified to the CENæCENELEC Management Centre has the same status as the official versionsä
CEN members are the national standards bodies of Austriaá Belgiumá Bulgariaá Croatiaá Cyprusá Czech Republicá Denmarká Estoniaá Finlandá Former Yugoslav Republic of Macedoniaá Franceá Germanyá Greeceá Hungaryá Icelandá Irelandá Italyá Latviaá Lithuaniaá Luxembourgá Maltaá Netherlandsá Norwayá Polandá Portugalá Romaniaá Serbiaá Slovakiaá Sloveniaá Spainá Swedená Switzerlandá Turkey and United Kingdomä
EUROPEAN COMMITTEE FOR STANDARDIZATION COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre:
Avenue Marnix 17,
B-1000 Brussels
t r s y CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Membersä Refä Noä EN
v w u uæ r r tã t r s y ESIST EN 4533-002:2018

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 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 aerostructures. However, future avionic 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, vibration, 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 lead 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 use airframers. SIST EN 4533-002:2018

EN 2591-601, Aerospace series — Elements of electrical and optical connection — Test methods — Part 601: Optical elements — Insertion loss EN 4533-001, Aerospace series — Fibre optic systems — Handbook — Part 001: Termination methods and tools EN 4533-003, Aerospace series — Fibre optic systems — Handbook — Part 003: Looming and installation practices EN 4533-004, Aerospace series — Fibre optic systems — Handbook — Part 004: Repair, maintenance, cleaning and inspection 3 Fibre types This section gives a brief summary of some of the different fibre types in use within the aerospace industry. Historically, large core, step index multimode fibres were the first to be used on aircraft. At the time of design, these fibres enabled sufficient data bandwidth and the large core enabled ease of coupling (of light) into the fibre as well as ease of fibre alignment in connectors (also termed interconnects). Therefore in some current and legacy systems, fibre optic harnesses based on large core fibres can be found. Common larger core fibres include 200/280 µm, 200/300 µm and 100/140 µm (where the notation indicates the core/cladding size). Improvements in bandwidth (mainly from reduced temporal dispersion), for multimode fibres is possible by using graded index fibres. In simple terms, the graded refractive index profile allows equalisation of different optical paths through a multimode fibre to reduce any pulse spreading in time (dispersion). These results in higher bandwidths compared to step index refractive index profiles. Early graded index fibres for aerospace included 100/140 µm sized fibres. More recently, fibre sizes commonly used in the telecoms and datacomms fields have been utilised for aerospace. Multimode fibres of size 62,5/125 µm and 50/125 µm and with graded index profile are now being deployed for data transmission on both civil and military aircraft, fixed wind and rotary craft. Fibres are available with different bandwidths. Multimode fibres 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. Using these sizes of fibre (particularly with a 125 µm outer diameter enables the use of volume production parts (e.g. ceramic alignment ferrules) from the telecoms industry. SIST EN 4533-002:2018

Figure 1 — Benchtop and portable optical power meters Power meters may be used in conjunction with couplers to measure return loss. Return loss meters are available that integrate the coupler and power meter components (and sometimes an optical source). 4.3.2 Photodectors requirements Power meters will have an active detection area. This should be large enough to collect all the light emerging from the fibre under test (linked to the NA of the fibre). Thus the distance to the active detector element should not be too small so that some of the power is not captured (see Figure 2). This may only be a problem in very large NA fibres or possibly in large core POF fibre. This problem can be managed if the power meter uses an integrating sphere. In some cases it may be important to only collect light within a given distribution or angular spread. An example might be where a data receiver has a smaller area or is fibre coupled (having a short section of fibre from a detector to the active receiver element). In these cases a test lead at the receiver end can be useful in restricting the detected power. Measuring the power with a large area detector may over-estimate the useable system power at the receiver. Another other important aspect of power measurement is the accuracy of reading. Power meters should be calibrated regularly to ensure that the power displayed is correct (traceable to national standards). Most instruments will also have the facility to select a measurement wavelength (this will commonly be one of the main glass fibre transmission wavelengths (e.g. 850 nm, 1 300 nm, 1 550 nm) although some power meters (using different detector materials) can measure at other wavelengths (an example might be 650 nm used for POF systems). SIST EN 4533-002:2018

Key 1 Area of projected beam from the fibre 2 Detector area 3 End of fibre Figure 2 — To prevent the detector in the power meter from filtering the power distribution, the detector has to be larger than the projected beam of light coming from the fibre of the test lead SIST EN 4533-002:2018

6.1 Launch conditions The input launch condition into a multimode fibre system is especially important. In simple terms, different light sources can have different launch conditions and this can lead to different measured values e.g. of insertion loss. Clearly this is undesirable. Further, the insertion loss of a particular component can also depend on its position within the link if launch conditions are not controlled. SIST EN 4533-002:2018

Key 1 Light launch system 2 Optical power mater 3 Insertion loss (dB) 4 Test equipment Figure 3 — Variation in insertion loss measurements made on the same harness (round robin test) using different test sources. This figure emphasises the need to carefully control light launch conditions in multimode aerospace links. The effect of launch conditions on the loss of fibre links is especially dramatic in short haul multi-mode avionic systems that may feature short lengths of fibre as well as many connector breaks and possibly other optical components. The light in such systems does not settle to an equilibrium modal distribution as might happen in say a longer haul link. It is possible to obtain a very large range of loss figures for a system by using different test sources. For example, a source that injects most of its power into a very narrow angle inside the component will measure a much smaller loss compared to a source that injects power over a larger range of angles. This is because light at the higher angles is more likely to be attenuated by imperfections in the construction of the component than light at smaller angles. SIST EN 4533-002:2018

Key 1 Optical Figure 4 — Variation in insertion loss measurements made on an aircraft same harness with and without modal conditioning. This figure emphasises the value of carefully controlling light launch conditions in multimode aerospace links SIST EN 4533-002:2018

The ideal launch condition distribution would lie somewhere between an overfilled launch condition (that would give an unduly pessimistic value for the insertion loss) and a grossly underfilled launch condition (that would give an optimistic value). In general, the optimum launch condition slightly underfills both the core of the fibre and the numerical aperture. This removes that part of the source’s light distribution that is most likely to be attenuated by the harness components due to manufacturing imperfections. Studies have shown that the correct launch condition lies somewhere between an 80:80 and 90:90 launch. Another consequence of using an ideal launch condition to make insertion loss measurements is that the difference between the loss of a complete harness and the sum of the losses of the individual harness components is minimised. It should be mentioned that the launch distribution of a source used to transmit data down the fibre in a real system will also have a given power distribution. This may well be different to the source used to characterise the fibre system although if the two are similar, then the performance of the real system link can be anticipated from the loss data of the system components. In summary, well defined launch conditions are required to:  Ensure reliable measurement of component loss (and therefore allow system loss to be calculated).  Enable reliable and repeatable characterisation of an aerospace multi-mode fibre optic link, in particular to be sensitive to extreme and undesirable effects such as tight bends or incorrect installation practices.  Ensure manufacturers and operators make the ‘same’ standardised measurement. SIST EN 4533-002:2018

Key 1 0,26 NA graded-index fibre with a led source near field 2 0,26 NA graded-index fibre with a led source far field 3 Power (nW) 4 Position(µm) 5 Angle of exit (degrees) 6 0,2 NA step index fibre with white light source near field 7 0,2 NA step index fibre with white light source far field 8 Position (microns) 9 Angle (degrees) Figure 5 — a) and b) are the near and far-field power distributions from a graded-index fibre illuminated by an LED source. The LED source provides a nearly fully-filled launch condition. c) and d) are the near and far-field power distributions of a step-index fibre that is illuminated by a white light source. The source provides an overfilled launch condition SIST EN 4533-002:2018

Key 1 Mode conditioner 2 Conditioned launch 3 System under test Figure 6 — Mode conditioners for generating suitable launch conditions for testing avionic fibre systems. The mode conditioner can be used with existing light sources to generate a suitable and consistent test launch The avionics launch conditions for 50 µm and 62,5 µm core fibres are specified in EN 2591-100 as cross sectional templates of the near and far field power distributions. These are prescribed at 3 intensity levels. It is noted that the telecommunication industry may specify launch conditions in terms of encircled flux (e.g. ISO/IEC 61280-4-1). This is an integrated measure of the power within regions/bands of the fibre cross section. It is useful for measuring coherent sources where speckle interference may be observed between modes. An example is shown in Figure 7. The reader should be aware of these different approaches but generally the aerospace industry has adopted a % fill ratio approach for specifying the launch condition. It is also noted that other test techniques for example using an OTDR may produce different results because the instrument uses a laser source and not an LED. Special launch leads may be required when testing multimode systems with this type of instrument. Some OTDRs also use internal mode conditioning systems according to the recommended standards. SIST EN 4533-002:2018
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