IEC 61280-1-4:2023

IEC 61280-1-4 ®
Edition 3.0 2023-01
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Fibre optic communication subsystem test procedures –
Part 1-4: General communication subsystems – Light source encircled flux
measurement method
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IEC 61280-1-4 ®
Edition 3.0 2023-01
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Fibre optic communication subsystem test procedures –
Part 1-4: General communication subsystems – Light source encircled flux
measurement method
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.180.01 ISBN 978-2-8322-6399-0

– 2 – IEC 61280-1-4:2023 RLV © IEC 2023
CONTENTS
FOREWORD . 4
INTRODUCTION . 2
0.1 General .
0.2 Changes from previous edition .
0.3 Assumptions applicable to the characterization of data sources .
0.4 Assumptions applicable to the characterization of measurement sources .
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Symbols . 9
5 Assumptions . 10
5.1 Assumptions applicable to the characterization of data sources . 10
5.2 Assumptions applicable to the characterization of measurement sources . 10
6 Apparatus . 10
6.1 Common apparatus . 10
6.1.1 General . 10
6.1.2 Computer. 11
6.1.3 Image digitizer . 11
6.1.4 Detector . 11
6.1.5 Magnifying optics . 12
6.1.6 Attenuation Attenuator . 12
6.1.7 Micro positioner (optional) . 13
6.1.8 Input port . 13
6.1.9 Calibration light source . 13
6.2 Transmission source apparatus . 13
6.2.1 General . 13
6.2.2 Test jumper assembly . 14
6.2.3 Fibre shaker . 14
6.3 Measurement source apparatus . 15
7 Sampling and specimens . 15
8 Geometric calibration . 16
9 Measurement procedure . 16
9.1 Safety . 16
9.2 Image acquisition . 16
9.2.1 Raw image acquisition . 16
9.2.2 Dark image acquisition . 17
9.2.3 Corrected image . 17
9.3 Optical centre determination . 17
9.3.1 General . 17
9.3.2 Centroid image . 17
9.3.3 Centroid computation . 18
9.4 Test source image acquisition . 18
10 Computation of encircled flux . 19
10.1 Computation of radial data functions . 19
10.2 Integration limit and baseline determination . 21
10.2.1 Integration limit . 21

10.2.2 Baseline determination . 21
10.2.3 Baseline subtraction . 21
10.3 Computation of encircled flux . 21
11 Results . 22
11.1 Information available with each measurement . 22
11.2 Information available upon request . 22
12 Specification information . 22
Annex A (informative) Measurement sensitivity considerations . 24
A.1 Baseline averaging considerations . 24
A.2 Pixel sensitivity variation calibration . 26
A.3 Correlated double sampling . 26
A.4 Imperfections of practical detectors and optics . 27
Annex B (informative) Theory of geometric calibration using the micropositioner .
Annex C (normative) Procedure for geometric calibration using the micropositioner .
Bibliography . 37

Figure 1 – Apparatus block diagram . 11
Figure 2 – Typical set-up for transmission source measurement . 14
Figure 3 – Fibre shaker example . 15
Figure 4 – Pixel and ring illustration . 19
Figure A.1 – Core images from instrument A and instrument B . 24
Figure A.2 – Compressed core images from instrument A and instrument B . 25
Figure A.3 – Intensity versus radius for instruments A and B. 25

– 4 – IEC 61280-1-4:2023 RLV © IEC 2023
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIBRE OPTIC COMMUNICATION SUBSYSTEM
TEST PROCEDURES –
Part 1-4: General communication subsystems –
Light source encircled flux measurement method

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
This redline version of the official IEC Standard allows the user to identify the changes
made to the previous edition IEC 61280‑1‑4:2009. A vertical bar appears in the margin
wherever a change has been made. Additions are in green text, deletions are in
strikethrough red text.
IEC 61280‑1‑4 has been prepared by subcommittee 86C: Fibre optic systems and active
devices, of IEC technical committee 86: Fibre optics. It is an International Standard.
This third edition cancels and replaces the second edition published in 2009. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) improvement of calibration procedure and calibration traceability;
b) improvement of fibre shaker description and requirements;
c) addition of pulsed light sources;
d) removal of a poorly traceable calibration process using a micro positioner.
The text of this International Standard is based on the following documents:
Draft Report on voting
86C/1806/CDV 86C/1828/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts of the IEC 61280 series can be found, under the general title Fibre optic
communication subsystem test procedures, on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates that it
contains colours which are considered to be useful for the correct understanding of its
contents. Users should therefore print this document using a colour printer.

– 6 – IEC 61280-1-4:2023 RLV © IEC 2023
INTRODUCTION
0.1 General
This part of IEC 61280 is used specifies how to measure the encircled flux of a multimode light
source. Encircled flux is a measure, as a function of radius, of the fraction of the cumulative
output power to the total output power radiating from as a function of radial distance from the
centre of the multimode optical fibre’s core.
The basic approach is to collect two-dimensional (2D) nearfield data, using a calibrated camera,
and to mathematically convert the 2D data into three normalized functions of radial distance
from the fibre’s optical centre. The three functions are intensity, incremental flux, and encircled
flux. Intensity has dimension optical power per area; incremental flux has dimension power per
differential of radius; and encircled flux has dimension total optical power, all three being
functions of radius. The intensity represents optical power per surface area (in watts per square
meter). The incremental flux represents optical power per radius differential (in watts per meter),
and the encircled flux represents a fraction of the cumulative output power to the total output
power.
These three radial functions are intended to characterize fibre optic laser sources either for use
in mathematical models predicting the minimum guaranteed length of a communications link, or
to qualify a light source to measure insertion loss in multimode links.
0.2 Changes from previous edition
This edition of the standard differs from its predecessor in both scope and content. Many of the
content changes improve the measurement precision. Several changes have been made to the
computation procedure:
• the integration methodology of the radial functions was simple summation, and is now
specified to use trapezoidal integration or other higher-order techniques (see 9.3);
• a baseline subtraction step is specified to improve immunity to DC drifts (see 9.2.2 and
9.2.3);
• the ring width parameter is explicitly specified (see 9.2.1);
• the integration limit is specified (see 9.3).
The geometric calibration of the apparatus microscope now specifies either (depending on the
application) the methodology of IEC 61745 or the original technique using the micropositioning
stage (see Clause 7). Pixel sensitivity uniformity correction is now optional.
0.3 Assumptions applicable to the characterization of data sources
The 50-µm or 62,5-µm core near-parabolic graded-index multimode fibre used as the “test
jumper assembly” is treated as if it possessed perfect circular symmetry about its optical centre,
as asymmetries in the launched optical flux distributions will dominate any lopsidedness of the
test jumper assembly. It is further assumed that all cladding modes will be stripped by passage
through the specified ten metres or more of fibre. The modes of a mode group need not carry
equal flux. (In fact, with such short fibres, one thousand metres or less, unequal distribution of
flux in the modes of a group is the norm, not the exception.)
0.4 Assumptions applicable to the characterization of measurement sources
Measurement sources are assumed to be sufficiently broadband and incoherent that speckle is
not a problem, and to have a sufficiently symmetrical nearfield distribution that the truncated
centroid of that nearfield indicates the location of the optical centre of the fibre with sufficient
accuracy for the purposes of this standard.

FIBRE OPTIC COMMUNICATION SUBSYSTEM
TEST PROCEDURES –
Part 1-4: General communication subsystems –
Light source encircled flux measurement method

1 Scope
This part of IEC 61280 is intended to characterize the encircled flux of two types of light
sources: transmission light sources, which are usually coherent and substantially under-excite
the mode volume of a multimode fibre, and measurement light sources, which are incoherent
and excite most of the mode volume of a multimode fibre.
This part of IEC 61280 establishes the characterization process of the encircled flux
measurement method of light sources intended to be used with multimode fibre.
This document sets forth a standard procedure for the collection of two-dimensional fibre optic
nearfield greyscale data and subsequent reduction to one-dimensional data expressed as a set
of three sampled parametric functions of radius from the fibre’s optical centre. This revision of
IEC 61280-1-4 continues to fulfil its original purpose, characterization of transmission light
sources, which enables the accurate mathematical prediction of minimum guaranteed link
length in 1 gigabit per second or greater fibre optic data communication systems. New to this
revision is support for improved measurement precision of insertion loss in multimode fibre optic
links through the characterization of measurement light sources.
Estimation of the fibre core diameter is not an objective of this document.
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.
IEC 60793-2-10, Optical fibres – Part 2-10: Product specifications – Sectional specification for
category A1 multimode fibres
IEC 60825-1, Safety of laser products – Part 1: Equipment classification and requirements
IEC 61745:1988, End-face image analysis procedure for the calibration of optical fibre geometry
test sets
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp

– 8 – IEC 61280-1-4:2023 RLV © IEC 2023
3.1
calibration light source
light source used to find the optical centre of a multimode fibre
3.2
centroid image
image used to determine the optical centre of the multimode fibre core
3.3
corrected image
image which has had a dark image subtracted from it and whose elements have had uniformity
correction applied
3.4
dark image
image taken with the measured light source either turned off or not installed in the input port
Note 1 to entry: Stray light and electrical signals of the detection system will remain in the dark image.
3.5
image
two-dimensional rectangular array of numbers whose elements are pixels and whose pixel
values linearly correspond to the optical power falling on the pixels
3.6
light source
something that emits light that is coupled into a fibre, the output of which can be measured
EXAMPLE Calibration light source, transmission light source, light source used for attenuation measurements.
3.7
measurement light source
light source intended to be used in the measurement of attenuation
3.8
nominal core radius
half the nominal core diameter of the multimode fibre to be measured
3.9
ring smoothing
technique to reduce the two dimensional near field image into a 1-D near field intensity profile
while cancelling the effects of the periodic spacing of imager pixels of finite area
3.10
transmission light source
light source used to transmit digital data over multimode fibre optic links
3.11
uniformity correction
process to correct the sensitivity of a pixel so that it performs substantially like an average pixel
3.12
valid pixel
optical detection element in the detector matrix whose sensitivity, when corrected, is within 5 %
of the mean sensitivity of the average conversion efficiency of the detector

4 Symbols
B baseline intensity
NOTE 1 This value is determined from a region of the computed near field just outside the
core boundary.
D distance from the centre of the centroid image to the nearest boundary of
the image
set of distances from the centre of the centroid image to, respectively, the
D , D , D , D
L R T B
left, right, top and bottom boundaries of the image
NOTE 2 The minimum of this set is used to compute D.
EF(i) encircled flux vector
EF'(i) non-normalized encircled flux vector
i
index parameter used in the parametric result vectors R(i), I(i) and EF(i) and
EF(i)
I matrix of pixel intensities of a dark image as measured by the detector and
dark
digitizer
I matrix of pixel intensities of the light source, before correction, as measured
raw
by the detector and image digitizer
I near-field intensity matrix
r,c
NOTE 3 This is a matrix of pixel intensities, based on I , as measured by the detector and
raw
corrected using U and I .
dark
I(i) ring-smoothed intensity vector, each element being the arithmetic average
of the set of radial coordinates of all the pixels in a given ring
N number of rings used to compute the 1-D near field
R
N number of rows in an image
r
NOTE 4 All columns in an image have the same number of rows.
N number of columns in an image
c
NOTE 5 All rows in an image have the same number of columns.
P most intense valid pixel in the centroid image
Max
P least intense valid pixel in the centroid image
Min
R radial coordinate, in μm, of the centre of any pixel, referenced to the optical
centre X , Y
0 0
R(i) ring-smoothed radial vector, each element being the arithmetic average of
th
the radii of all the pixels in the i ring
R integration limit along the radius
max
S column-weighted summation of all pixel intensities greater than T in the
c
centroid image
S (i) intensity summation vector used in ring smoothing
I
S summation of all pixel intensities greater than T in the centroid image
P
S (i) pixel counting vector used in ring smoothing
N
S (i) radius summation vector used in ring smoothing
R
S row-weighted summation of all pixel intensities greater than T in the centroid
r
image
– 10 – IEC 61280-1-4:2023 RLV © IEC 2023
S horizontal geometric calibration factor (along columns)
x
S vertical geometric calibration factor (along rows)
Y
T threshold used to determine which pixels in the centroid image will be used
to determine the optical centre
NOTE 6 All pixels greater than or equal to T are used to compute the centroid.
U sensitivity correction matrix, applied to a dark-subtracted image to reduce
r,c
non-uniformity of the detector’s pixel-to-pixel conversion efficiency
W half-width, in μm, of the rings used to compute the 1-D near field
X X axis (column) location of the centre of the centroid image
Y Y axis (row) location of the centre of the centroid image
5 Assumptions
5.1 Assumptions applicable to the characterization of data sources
The 50 μm or 62,5 μm core near-parabolic graded-index multimode fibre used as the "test
jumper assembly" is treated as if it possessed perfect circular symmetry about its optical centre,
because asymmetries in the launched optical flux distributions will dominate any distortions
introduced by the test jumper assembly, such as lateral and angular misalignments. It is further
assumed that all cladding modes will be stripped by passage through the specified ten metres
or more of fibre. The modes of a mode group need not carry equal flux. In fact, with such short
fibres, one thousand metres or less, unequal distribution of flux in the modes of a group is the
norm, not the exception.
5.2 Assumptions applicable to the characterization of measurement sources
Measurement sources are assumed to be sufficiently broadband and incoherent, so that speckle
is not a problem, and to have a sufficiently symmetrical nearfield distribution, so that the
truncated centroid of that nearfield indicates the location of the optical centre of the fibre with
sufficient accuracy for the purposes of this document.
6 Apparatus
6.1 Common apparatus
6.1.1 General
Figure 1 below shows an apparatus block diagram.

a
The image digitizer may can be either part of a camera or a computer add-in board.
b
The detector electronics are usually integral to the camera and digitizer.
c
Attenuation is best placed in the collimating region of the optical path, but not all optical designs will have an
accessible collimating region. When this is not possible, the attenuation should be placed on the detector side of
the optics.
d
When a micro positioner (not shown) is employed, the input port will be physically attached to it.
Figure 1 – Apparatus block diagram
6.1.2 Computer
A computer is required, because the acquired image contains many thousands of pixels, and
the reduction of the image to encircled flux requires substantial computation. The computer will
usually be connected to the image digitizer to control the acquisition of an image through
software and may can also control the micro positioner (and the source, if correlated double
sampling is implemented).
6.1.3 Image digitizer
The nearfield of the fibre core is imaged onto the detector and then digitized by the image
digitizer. The image digitizer may can be an integral part of a camera, which also contains the
detector, or may can be an add-in frame-grabber board in the computer.
Automatic circuitry in the digitizer, for example AGC or automatic gain control (ABC) often found
in video cameras, shall be disabled.
6.1.4 Detector
The detector is typically a charge-coupled device (CCD) or complementary metal-oxide
semiconductor (CMOS) camera. Other types of array cameras may can be considered. In any
case, detectors shall be both nominally linear and memoryless; this excludes for instance lead
sulphide vidicon detectors. Absolute radiometric measurement of flux (optical power flow) is not
required.
Automatic circuitry in the detector, for example AGC or automatic gain control often found in
video cameras, shall be disabled.
The difference in conversion sensitivity from pixel to pixel in the detector will affect the
measurement accuracy. The non-uniformity in the corrected conversion efficiency of the
detector shall not exceed ±5 %. It is possible to calibrate and correct a detector, whose
uncorrected uniformity is worse than 5 %, by applying a pixel-by-pixel sensitivity correction
matrix, U, to the raw image. Often, this correction is part of the camera function (and so each
element of U may can be taken as unity). Sometimes, the correction matrix may can be supplied
provided by the detector supplier. In other cases, the correction matrix shall be determined by
the procedure outlined in Clause A.2.

– 12 – IEC 61280-1-4:2023 RLV © IEC 2023
Detectors can have invalid pixels, which are pixels whose corrected conversion efficiency
exceeds ±5 % of the average conversion efficiency of the detector. Invalid pixels will often
produce no signal or, a completely saturated signal, or be stuck at some intermediate value.
Detectors whose invalid pixel count exceeds 0,1 % of the total number of pixels shall be
rejected.
In most cameras and image digitizers, the setting of the "black level" is user adjustable. Since
the detector will be slightly noisy, it is important that the detector and digitizer do not clip random
black signals at zero (in common systems, random noise in a detector will have a standard
deviation less than 0,5 % of the saturation level). To ensure no clipping of the noise, when
settable, set the black level to produce a small positive signal (typically at least five times the
standard deviation of the noise) when no light is impinging on the detector.
6.1.5 Magnifying optics
Suitable optics shall be provided to project the magnified image of the input port onto the
detector, in such a way that the detector can measure the entire nearfield flux distribution. The
numerical aperture of the magnifying optics shall exceed the nominal numerical aperture of the
fibres (as specified in the fibre’s family specification) used in calibration or measurement.
Microscope objectives are often appropriate for this purpose.
NOTE 1 When a microscope objective is used, its actual magnification as used in the present apparatus generally
will not be the same as the nominal magnification factor engraved into the side of the objective, because the present
apparatus differs from the standard microscope for which that nominal magnification factor was computed. The
geometric calibration procedures outlined in Clause 8 determine the actual magnification.
NOTE 2 When characterizing measurement light sources, measurement precision is important, so optical distortion
is kept to a minimum. Care in selection and application of the lenses and other optical components should be
considered. Plan-type microscope objectives are an example of suitable optics. The procedures found in IEC 61745
can be used to assess the optical integrity of the apparatus.
NOTE 3 Reflections from optical surfaces may can seriously degrade the measurement of
encircled flux. Anti-reflection coating at the wavelength of measurement or other forms of
reflection control may can be considered to reduce reflections.
Measurement precision is important when characterizing measurement light sources, so that
optical distortion is kept to a minimum. Careful selection and application of the lenses and other
optical components is recommended. Plan-type microscope objectives are an example of
suitable optics. The procedures found in IEC 61745:2017 can be used to assess the optical
integrity of the apparatus.
It is important that the distance between the detector and all elements of the magnifying optics
be held fixed once calibration is performed. When the relationship between these elements
changes, the magnification is expected to change enough that recalibration will be required.
Focusing shall be accomplished by changing only the distance between input port and the
magnifying optics.
6.1.6 Attenuation Attenuator
Often, the optical flux of the source will saturate the detector and the only effective solution is
to employ optical attenuation. Any attenuation element shall not reduce the numerical aperture
of the optical system and shall not be the source of significant reflections or optical distortions,
which will bias the resulting encircled flux.
NOTE 1 When neutral density filters are used in the optical system, geometric distortions may can be introduced.
NOTE 2 Changing the attenuation between the optical centre image and the image of the measured source may
can cause the location of the optical centre of the measurement source to move away from that determined using
the optical centre image, causing errors in the resulting radial data functions.

6.1.7 Micro positioner (optional)
The micro positioner is an optional part of the apparatus. Depending on the apparatus design,
it is possible to rely on connector ferrule geometry to place the image completely onto the
detector without a micro positioner. In many implementations, only a focus adjustment (Z axis)
is necessary, and in some cases, all three axes may only require alignment during construction
or maintenance of the apparatus. Using the ferrule to place the fibre core image onto the
detector does not relieve the requirement of finding the optical centre as required by 9.3.
When used, the purpose of the micro positioner is to bring the projected image of the fibre face
into focus on the detector and to determine the magnification of the apparatus (see Clause 8).
Mechanical locking mechanisms or their equivalents are required for all three axes to prevent
mechanical drift during measurement. The micro positioner can optionally be driven by motors
and can optionally employ feedback mechanisms to control the actual position of the stage (and
thus the fibre face). When geometric calibration is done using the micropositioner (see Clause
7 and Annex C), the performance requirements are specified in Annex B; otherwise, the only
performance requirement is in the focal axis, which shall have high enough resolution to bring
the fibre end into sufficient focus to achieve the required measurement precision.
6.1.8 Input port
The input port is where the calibration artefacts and measurement samples are connected to
the apparatus. The input port characteristics depend on which type of source is to be
characterized.
When characterizing transmission light sources, the input port is the distal end of the test jumper
assembly. The proximal end of the test jumper assembly will be imaged onto the detector. When
a micro positioner is used, the proximal end will be attached to the micro positioner.
When characterizing measurement light sources, the input port is commonly a connector
bulkhead or its equivalent. When a micro positioner is employed, the bulkhead will be attached
to the micro positioner.
See 6.2 and 6.3 for particular requirements.
6.1.9 Calibration light source
The calibration light source is used when calibrating the apparatus (see Clause 8). When this
source is used to illuminate the test jumper assembly, the calibration source shall overfill the
modes of the jumper. Optionally, a mode scrambler may can be used with the chosen calibration
source to ensure more uniform overfilling of the fibre. See IEC 60793-1-41 for information on
mode scramblers.
Any spectrally broad non-coherent light source, such as a tungsten-halogen lamp, a xenon arc
lamp, or a light-emitting diode (LED), may can be used to overfill the fibre of the test jumper
assembly. When calibrating the apparatus for the characterization of measurement light
sources, the centre wavelength of the calibration source shall be within 30 nm of the nominal
wavelength of the light sources to be qualified, and its spectral width (i.e., full width at half
maximum) shall be no more than 100 nm. When calibrating the apparatus for the
characterization of transmission light sources, the spectral characteristics of the calibration
source are not specified, but it is recommended that its spectrum be similar to the sources to
be characterized. The chosen calibration source shall be stable in intensity over a time period
sufficient to perform the measurements.
6.2 Transmission source apparatus
6.2.1 General
When characterizing transmission light sources, the input port of the apparatus consists of two
elements, the test jumper assembly and the fibre shaker (see Figure 2 below).

– 14 – IEC 61280-1-4:2023 RLV © IEC 2023

Figure 2 – Typical set-up for transmission source measurement
6.2.2 Test jumper assembly
The purpose of the test jumper assembly is to strip cladding modes, and to allow speckle to be
averaged out by mechanical flexing of a portion of the test jumper assembly. The test jumper
assembly is used only when qualifying light sources for multimode transmission.
The test jumper assembly shall be at least 10 m in length, made of germanium-doped near-
parabolic graded-index fused-silica multimode "glass", an IEC 60793‑2‑10 class A1-OM2 to
OM5 fibre with a core diameter of either 50 μm or class A1-OM1 fibre with a core diameter
62,5 μm. The test jumper assembly shall consist of a single, uncut length of fibre with
connectors at each end. The test jumper assembly connectors shall have single-mode
mechanical tolerances, even though the fibre is multimode.
6.2.3 Fibre shaker
The purpose of the fibre shaker is to change the differential path length of the various modes
in the test jumper, ensuring that speckle in the averaged image will be reduced, as the image
is averaged. Speckle reduction can be accomplished in a variety of ways and shall be good
enough to ensure sufficient repeatability in the measurement of encircled flux. Shaking of the
test jumper assembly with a mechanical device is required to reduce speckle.
Part of the test jumper assembly shall be mechanically shaken continuously in each of three
nominally orthogonal directions (using three independent shaker mechanisms) during the
measurement, making at least one hundred shake cycles in each of the three directions during
the measurement period. The shake frequencies in the three directions shall be chosen such
that the three shake cycles synchronize no more often than once every five hundred cycles of
the middle shake frequency.
A fibre shaker mechanism may can be of any design as long as it induces large amplitude
movements and flexing in the optical fibre. Fibre transverse displacements of more than 25 mm
are suggested. The fibre shakers shall include a fibre holding fixture for securely holding the
fibre.
One exemplary mechanism, shown in Figure 3, has three turns of fibre coiled into a 3-ply figure-
eight arrangement, with the loops each being approximately 120 mm in diameter. A motor-
driven eccentric drives a slider back and forth at about one stroke per second, alternately
flattening and stretching one loop of the figure eight with 25-mm amplitude. Three such
mechanisms in series will consume about 3 × 3 × (2 × π × 0,120) = 6,8 m of the test jumper
assembly’s fibre.
NOTE 1 Only one figure-eight loop of the three loops is shown here, for visual clarity. Fibre clips are used to keep
fibre in place, in addition to elastic fibre clamps that prevent transmission of fibre motion. Loose fibre clips not shown.
NOTE 2 Fibre is moved back and forth as shown, with a peak-to-peak amplitude of about 25 mm, distorting one
fibre loop.
Figure 3 – Fibre shaker example
Another exemplary approach is to hang large loose loops of fibre in front of a large fan which
blows these loops about, the turbulence in the stream of the fan randomizing the motion.
NOTE 1 The fibre ends leading into and out of the fibre shakers are mechanically fixed or stabilized to prevent
movement of fibres at connection points. In addition, the fibre shakers are mechanically isolated from the rest of the
test setup so that vibrations are not transmitted to connection points throughout the apparatus, or to the micro
positioner, detector, or magnifying optics. Vibration reduction is easier if the fibre shaker is both statically and
dynamically balanced, and if all moving components are light in weight.
NOTE 2 There is no required relation between the measurement period (containing the one hundred strokes) and
the acquisition time of an image. Typically, in each measurement period, many individual images are taken and later
summed or averaged by the computer; this technique may can help to avoid detector saturation. The detector and
digitizer may be able to can per
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