ISO 20780:2018

Space systems — Fiber optic components — Design and verification requirements

This document specifies requirements for the design and verification of fibre optic components used in space fibre optic sub-systems. In this document, the requirements are established to assure the reliability and environmental adaptability of fibre optic components in space environmental conditions. These are in a range of applications such as ground systems, unmanned applications and manned systems. This document suggests a set of requirements to be applied to the selection of space fibre optic components.

Systèmes spatiaux — Composants à fibres optiques — Exigences de conception et de vérification

General Information

• Status: Published
• Publication Date: 04-Jun-2018
• ICS: 49.140 - Space systems and operations
• Technical Committee: ISO/TC 20/SC 14 - Space systems and operations
• Drafting Committee: ISO/TC 20/SC 14 - Space systems and operations
• Current Stage: 9060 - Close of review
• Start Date: 02-Dec-2028

Relations

• Consolidated By: ISO 18541-4:2021 - Road vehicles — Standardized access to automotive repair and maintenance information (RMI) — Part 4: Conformance test
• Effective Date: 06-Jun-2022

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 20780
First edition
2018-06
Space systems — Fiber optic
components — Design and verification
requirements
Systèmes spatiaux — Composants à fibres optiques — Exigences de
conception et de vérification
Reference number
ISO 20780:2018(E)
©
ISO 2018

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ISO 20780:2018(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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ISO 20780:2018(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, abbreviated terms and symbols . 1
4 General requirements . 4
4.1 Design criterion . 4
4.2 Design input . 4
4.3 Design output . 4
4.4 Design flow . 5
5 Design requirements . 6
5.1 Functional parameter design . 6
5.1.1 Overall design . 6
5.1.2 Optical design . 6
5.1.3 Electrical design . 6
5.1.4 Low power consumption design . 7
5.2 Structural design . 7
5.2.1 External structure design . 7
5.2.2 Internal structure design . 7
5.2.3 Fibre coupling design. 8
5.2.4 Fibre fusing and tapering design . 8
5.2.5 Fibre pigtail design . 9
5.3 Packaging design . 9
5.3.1 Objective . . 9
5.3.2 Packaging requirements . 9
5.3.3 Marking .10
5.4 Thermal design .10
5.5 ESD proof design .11
5.6 Radiation-hardened design .11
5.7 Reliability design .11
5.8 Safety requirements .12
5.9 Manufacturing process requirements .12
6 Verification requirements .13
6.1 Function and parameter verification .13
6.2 Environmental adaptability verification.13
6.3 Reliability verification .14
6.4 MRL verification.15
6.5 Application verification .15
Bibliography .16
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ISO 20780:2018(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/iso/foreword .html
This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles,
Subcommittee SC 14, Space systems and operations.
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ISO 20780:2018(E)

Introduction
Fibre optic sub-systems are finding increasingly wide utilizations in space systems. In these fibre
optic sub-systems, fibre optic components are the significant elements. Hence, the reliability of fibre
optic components is essential to the system lifetime, performance and safety. For space applications
in particular, the environmental adaptability of fibre optic components can be a critical factor in the
mission schedule and success.
This document is a directive document for fibre optic components, which are sorted as a specific
category used in space systems. In this document, the design and verification requirements for
fibre optic components focus on the space environmental adaptability and reliability, the pertinent
procedures and concerns are described in order to provide safe and reliable hardware and operation.
NOTE Each manufacturer could suggest to the customer that tailoring is possible for any part of the standard
that seems difficult to apply because of a manufacturing process that is being used.
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INTERNATIONAL STANDARD ISO 20780:2018(E)
Space systems — Fiber optic components — Design and
verification requirements
1 Scope
This document specifies requirements for the design and verification of fibre optic components used
in space fibre optic sub-systems. In this document, the requirements are established to assure the
reliability and environmental adaptability of fibre optic components in space environmental conditions.
These are in a range of applications such as ground systems, unmanned applications and manned
systems. This document suggests a set of requirements to be applied to the selection of space fibre optic
components.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 14302, Space systems — Electromagnetic compatibility requirements
ISO 14621-1, Space systems — Electrical, electronic, and electromagnetic (EEE) parts — Parts management
ISO 14621-2, Space systems — Electrical, electronic, and electromagnetic (EEE) parts — Control program
requirements
3 Terms, definitions, abbreviated terms and symbols
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http: //www .electropedia .org/
— ISO Online browsing platform: available at https: //www .iso .org/obp
3.1 Terms and definitions
3.1.1
optical fibre
filament shaped optical waveguide made of dielectric materials
[SOURCE: IEC 60050]
3.1.2
optical fibre cable
assembly comprising one or more optical fibres or fibre bundles inside a common covering designed
to protect them against mechanical stresses and other environmental influences while retaining the
transmission quality of the fibres
[SOURCE: IEC 60050]
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3.1.3
optical fibre pigtail
short length of optical fibre, usually permanently attached to a component and intended to facilitate
jointing between that component and another optical fibre or component
Note 1 to entry: "Launching fibre" is synonymous with optical fibre pigtail only when the latter is connected to
an optical source.
[SOURCE: IEC 60050]
3.1.4
fibre optic component
components that are based on optical fibre properties or components that are coupled with optical
fibres that cannot be disassembled, including passive fibre optic components and active fibre optic
components
3.1.5
passive fibre optic component
fibre optic components that could realize certain photoelectric functions with no need for external
energy, including fibre optic connectors, optical fibre couplers, wavelength division multiplexers, fibre
optic attenuators, fibre optic filters, fibre optic isolators, circulators, polarization controllers, fibre
delay lines and fibre optic gratings
3.1.6
active fibre optic component
fibre optic components that require a source of energy for their operation to realize the function of
electro-optical/optical-electro conversion, including semiconductor sources (LD, LED, DFB, QW,
SQW, VCSEL), semiconductor detectors (PD, PIN, APD), fibre lasers, optical amplifiers, wavelength
transducers, optical modulators and optical switches
3.1.7
space fibre optic sub-system
assembly of interconnected basic fibre optic subsystems
Note 1 to entry: The assembly is specified at defined interfaces within the fibre optic system.
[SOURCE: IEC 61281-1:1999, modified]
3.1.8
coupling efficiency
efficiency of optical power transfer between an optical component and its fibre pigtail
3.1.9
fibre alignment dislocation
misalignment between the fibre tip and optic chip (or crystal) facet
3.2 Abbreviated terms
AFOC active fibre optic component
AIT assembly, integration, test
APD avalanche photodiode
COTS commercial off-the-shelf
DFB distributed feedback
DLAT destructive lot acceptance test
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ISO 20780:2018(E)

DPA destructive physical analysis
EEE electrical, electronic, and electromagnetic
ESD electrostatic discharge
FBG fibre Bragg grating
FMEA failure mode and effect analysis
FOC fibre optic component
LAT lot acceptance test
LD laser diode
LED light emitting diode
MRL manufacturing readiness level
MTTF mean time to failure
NA numerical aperture
PD photodiode
PDL polarization dependent loss
PFOC passive fibre optic component
PID process identified document
QW quantum well
RHA radiation hardness assurance
SQW single quantum well
TEC thermal-electric cooler
TRL technology readiness level
VCSEL vertical cavity surface emitting laser
WDM wavelength division multiplexing
3.3 Symbols
V volt
MΩ mega ohm
°C degree Celsius
Hz hertz
2
m/s gravitational acceleration
ms millisecond
μm micrometre
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ISO 20780:2018(E)

N newton
3
cm cubic centimetre
Pa pascal
4 General requirements
4.1 Design criterion
— Design and verification of FOC shall meet related requirements in ISO 14621-1, ISO 14621-2 and
ISO 14302.
— Mature technologies and operating principles, COTS are preferred (TRL 6 (refer to ISO 16290) shall
be demonstrated for any selected technology and associated COTS).
— The design shall satisfy the requirements of environmental adaptability and reliability.
— The design parameters could be optimized by validated software simulations and corrected by
process tests.
— New materials and technologies shall be fully proven before application, verified materials and
technologies for space environment are preferred, TRL 6 (refer to ISO 16290) will be demonstrated
for technology and associated COTS.
— Apply derating design to FOC, the stress exerted on FOC during usage should be lower than the
rated value in order to slow degradation, decrease failure rate and improve reliability of FOC.
— Balance the design of FOC by overall consideration of the function, reliability, risk, and economic
efficiency.
4.2 Design input
— Specific requirements from customer, user and prime contractor.
— Requirements based on the space environment and system application, including mission profile in
order to calculate a consistent MTTF according to dedicated methodology.
— Standards and criteria approved by customer and industry.
— New technology that helps to improve FOC performance in space environment.
— Safety requirements from space systems.
— Safety regarding health regulations.
4.3 Design output
The following output files shall be documented during the design and verification processes, which are
in accordance with the design flow chart shown in Figure 1:
— document for design plans and strategies;
— document for justification (e.g.: design report);
— document for manufacturing process (e.g.: technical document, data record);
— document for verification (e.g.: specifications, reliability report, application verification report);
— document for safety demonstration (e.g.: health, safeguard, operations, transportation, and storage);
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ISO 20780:2018(E)

— document for users (e.g.: operation guides and precautions).
4.4 Design flow
— The design flow chart is shown in Figure 1.
— Conduct failure mode and effect analysis (FMEA) during the design process (IEC 60812:2006) to
identify weak links, safety issues and key items of the design, so as to improve the design iteratively.
— When the design is modified, in principle, verification tests shall be completely conducted again in
accordance with the whole verification process. Conducting effect analysis only on the modified part
with related verification items is allowable. The verification results shall be added to the original
verification report and demonstrate that the modified part does not have unwanted transverse
system effect.
Figure 1 — Design flow chart for fibre optic components
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ISO 20780:2018(E)

5 Design requirements
5.1 Functional parameter design
5.1.1 Overall design
Employ an optimal overall design scheme according to the FOC function and required specifications:
— Operating principles: for the same function, the FOC could be fabricated by different operating
principles. For example, for non-wavelength selective branching components (such as optical fibre
couplers), fibre fused and tapered structure, fibre polished structure or optical waveguide structure
are all usable; for fibre filters, etalon, FBG or thin film filter technologies are both adoptable; and
for semiconductor light sources, different resonant cavities structures could be used. Hence,
the operating principle shall be first determined according to the required specifications and
applications.
— Packaging: determine the packaging type, external structure and fibre bending radius inside the
FOC according to the application environment and dimension requirements; determine the type of
connector and the interface structure of the fibre connectors, such as FC, SC, ST, etc.
— Operating conditions: determine the operating conditions of the FOC according to the application
requirements (e.g.: long life-time application, severe environment application). The FOC shall not be
used out of the range of their qualified characteristics.
— Raw materials and accessories: determine the key parameters of raw materials and accessories
according to the operating conditions. Especially, many kinds of polymeric compounds are used in
FOC, including adhesive, sealant, pouring sealant, etc. Besides the functional requirements, space
environmental adaptabilities shall be considered for polymeric compounds, such as decomposition
under high temperature and irradiation environments, volatilization under vacuum environment.
— TRL 6 (refer to ISO 16290) shall be preferred as a minimum for any choice of technology.
5.1.2 Optical design
The optical parameter design of FOC includes:
— By determining the design of active light-emitting devices, determine the parameters of active light
luminescent devices, such as beam mode field, divergence angle, output power, wavelength, spectral
bandwidth, polarization, side-mode suppression ratio, pulse width and so on.
— By determining the design of active light-receiving devices, determine the parameters of active
optical receivers, such as operating wavelength, responsivity, sensitivity, polarization sensitivity
and so on.
— Design the parameters of passive FOC, such as operating wavelength range, insertion loss, return
loss, PDL, extinction ratio, isolation (e.g. for fibre optic isolators and fibre WDM), split-ratio (optical
fibre coupler, fibre WDM), reflectivity (fibre reflector, fibre grating) and set up the overall optical
loss for the system.
— Analyze compatibility of monitoring optical signal (wavelength, continuous or pulsed signal, power
or energy delivered) with optical detector.
5.1.3 Electrical design
The electrical parameter design of FOC includes:
— Design amplifying circuits for detectors with amplification function, including parameters such as
bias voltage, frequency bandwidth, gain, noise, etc.
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ISO 20780:2018(E)

— Design driving circuits for lasers, including parameters such as operating current range, current
modulation frequency, current modulation duty cycle, etc.
— Design thermal control circuits for components with thermal control function, including parameters
such as heating/cooling current, thermistor, cooling efficiency, etc.
— Design modulation characteristics for waveguide modulation components, including parameters
such as half wave voltage, modulation bandwidth, etc.
— The designer shall provide the electrical parameters such as threshold current, power conversion
ratio, operating current/voltage, and reverse voltage for FOC, such as laser source.
— Operating and responding time (with the required rise time) (minimum/maximum) shall be
expressed for the design and component selection.
5.1.4 Low power consumption design
Meanwhile, low power consumption design shall also be considered for FOC with the aim of reducing
system power consumption, on the premise that the performance and reliability requirements of FOC
could be satisfied, which includes:
— Use low power consumption internal components.
— For light-emitting components, design semiconductor chips with high luminous efficiency to reduce
the required drive current. For example, employ a multi-quantum well structure for the active
region of the chip.
— For thermal control components, choose a high efficiency TEC to reduce the thermal control current
required to maintain the operating temperature range.
5.2 Structural design
5.2.1 External structure design
— The structural design shall satisfy the user’s requirements on the dimension, weight, installation,
interfaces, tightness and decomposition (gas, etc.).
— Appropriate tolerance shall be defined for measured dimensions.
— Besides the seal welding area, the outside surface of the metal shell should be mildew proof with
metal plating (such as gold, nickel, etc.); the outside lead or material shall meet the requirements of
anti-corrosion and solderability with environmental friendly solutions.
— For a tubular passive FOC sealed with sealant or compound (such as a fused and tapered optical
fibre coupler, WDM, isolator, etc.), metal tubes with anti-extrusion, anti-corrosion and anti-
contamination properties shall be applied. The anti-corrosion property, stability and volatility of the
organic sealant applied at the end of fibre-tail shall satisfy the requirements for space application.
No bubbles shall be observed for the sealant under 50X microscopic visual inspection.
— Under the precondition of ensuring the function and installation requirements, the dimension of
FOC shall be as compact as possible.
— Appropriate fixture shall be set up to clamp the optical fibre.
5.2.2 Internal structure design
— According to the function and dimension requirements, choose a suitable size for the internal
elements.
— Design the internal element layout by overall consideration of the specifications of the FOC.
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— The internal conductors and wires shall not be damaged when the maximum allowable operating
current is input.
— Eutectic soldering is the priority for electronic chip bonding of hermetically sealed components.
Organic materials such as conductive sealants could also be used if it is difficult to apply eutectic
soldering because of large chip area or complex structure, but the seal tightness and internal gas
composition should meet the requirements.
— Design internal optical crystals according to the function parameter requirements. Consider
parameters such as the crystal refractive index, overall dimension, crystal orientation, waveguide
structure, surface coating, etc.
— If an organic adhesive is needed for bonding optical crystals, then the adhesive with high hardness
(shore D hardness higher than 70 is recommended), high glass transition temperature (higher than
−6 −1
125 °C is recommended), low expansion coefficient (< 100 × 10 K is recommended), and wide
operating temperature range (−50 °C ~ 125 °C is recommended) shall be applied.
— For a passive FOC with fibre fusing and tapering technology (i.e. optical fibre coupler, WDM, etc.),
the dimension of the fused tapering zone shall be designed (5.2.4) and the packaging size shall be
optimized.
— The optical fibre inside the FOC shall be designed and processed to satisfy the performance
requirements (5.2.5).
— The internal fibre coupling design shall assure the coupling stability (5.2.3) and the packaging
tightness (5.3).
— Thermal design shall be applied for internal structures (5.4).
5.2.3 Fibre coupling design
For FOC, the optical fibre is often coupled with a semiconductor chip or optical crystal. Fibre coupling
design shall be undertaken in order to assure the required beam transmission properties and coupling
efficiency. The coupling structure shall be stable under the appropriate temperature, humidity,
mechanical and shock environmental conditions.
— Design the structure of coupling fibre end according to the light beam properties (5.2.5).
— In order to assure the coupling efficiency, the distance and alignment angle between the fibre end
face and chip (or optical crystal) end face shall be designed precisely.
— After the fibre is aligned with the chip (or crystal), in order to assure the alignment stability, it is
recommended that the fibre is fixed at two points at least.
— Metalized fibre is recommended to use for hermetically sealed components. The metalized fibre is
soldered with the shell with metal, glass or ceramic soldering paste according to different packaging
types; for non-hermetic components, the fibre is bonded with the shell with sealant (5.2.1).
5.2.4 Fibre fusing and tapering design
— For fibre fusing and tapering parameters such as fibre arrangement, heating type, flame type, gas
composition and proportion, gas flow, flame temperature and height, tapering speed and length
shall be designed. The fast and slow axes of polarization maintaining fibre need to be aligned first
before tapering.
— In order to assure the performance and reliability of t
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