IEC TR 62627-05:2013

IEC/TR 62627-05 ®
Edition 1.0 2013-10
TECHNICAL
REPORT
colour
inside
Fibre optic interconnecting devices and passive components –
Part 05: Investigation on impact of contamination and scratches on optical
performance of single-mode (SM) and multimode (MM) connectors

IEC/TR 62627-05:2013(E)
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IEC/TR 62627-05 ®
Edition 1.0 2013-10
TECHNICAL
REPORT
colour
inside
Fibre optic interconnecting devices and passive components –

Part 05: Investigation on impact of contamination and scratches on optical

performance of single-mode (SM) and multimode (MM) connectors

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
V
ICS 33.180.20 ISBN 978-2-8322-1159-5

– 2 – TR 62627-05 © IEC:2013(E)
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Abbreviations . 7
4 Experimental methodology. 8
5 The impact of scratches on A and RL of single-mode connectors. 9
6 Effects of scratches on RL of MM connectors . 10
7 Investigation of impact of contamination on optical performance of 2,5 mm and
1,25 mm connectors . 11
7.1 General . 11
7.2 Zone definitions . 11
7.3 Experimental data for 2,5 mm ferrule connectors . 12
7.4 Experimental data for 1,25 mm ferrule connectors (LC, MU) . 13
7.5 Image analysis . 16
7.6 Gaussian weighted per cent occluded area . 16
7.7 Inspection criteria matrix . 17
8 Correlation study between contamination and signal degradation in single-mode
APC connectors . 18
8.1 General . 18
8.2 Experimental data and analysis for SM APC connectors . 18
8.3 Inspection criteria matrix . 20
9 Development of cleanliness specifications for single-mode, angled physical
contact MPO connectors . 21
9.1 General . 21
9.2 Core zone analysis . 21
9.3 Cladding zone analysis . 21
9.4 MT APC scratch analysis . 23
10 Conclusion . 24
Annex A (informative) The nature of particle redistribution during series of
matings/dematings . 26
A.1 General . 26
A.2 Accumulation of particles near the core during repetitive fibre matings
and de-matings for 2,5 mm ferrule connectors . 26
A.3 Redistribution of particles during series of repetitive matings/de-matings
for MPO connectors . 28
A.4 Attenuation changes and separation factor . 29
Bibliography . 30

Figure 1 – Block diagram of design of experiment . 8
Figure 2 – Connector endface with the scratches outside the MFD area . 9
Figure 3 – Connector endface with scratches passing through the core . 10
Figure 4 – Examples of characterized endfaces using confocal microscope [7] . 10
Figure 5 – RL random mated connectors, λ=1 300 nm [7] . 11
Figure 6 – Influence of the particle location on performance . 12

TR 62627-05 © IEC:2013(E) – 3 –
Figure 7 – FC01 images of DUT and reference fibre after contamination and fifth
mating . 13
Figure 8 – FC04 images of DUT and reference fibre after contamination and second
mating . 13
Figure 9 – LC07 images of the DUT and the T07 reference fibre after contamination
and first mating . 14
Figure 10 – LC07 images of the DUT and the T07 reference fibre after contamination
and third mating . 15
Figure 11 – LC07 images of the DUT (Figure 11a) and the T07 reference fibre (Figure
11b) after contamination and fifth mating . 15
Figure 12 – Labelled detected particles with 5 µm annular rings and fibrescope image
for LC07-WD-5M . 16
Figure 13 – Delta attenuation versus GWPOA . 17
Figure 14 – Left to right: Group A, Group B and average return loss decrease by group . 18
Figure 15 – Behaviour of relatively large particles versus small particles . 19
Figure 16 – Test connector in pristine condition (RL= 67,5 dB) and after scratches
applied (RL= 68,5 dB) . 20
Figure 17 – Impact of contamination in core zone for SM APC MPO connectors . 21
Figure 18 – Contamination failures due to loss of physical contact by fibre position for
connections of angled MT ferrules . 22
Figure 19 – Endface images of DUT and reference connector showing no impact to
signal performance . 22
Figure 20 – Minimal MT/APC contamination on limit sample #1 with signal degradation . 23
Figure 21 – Typical lack of impact on signal performance of light scratches on
MT/APC connections . 24
Figure A.1 – Experimental methodology block diagram . 26
Figure A.2 – Relationship between the particle centre moving speed and the charge . 27
Figure A.3 – Particle migration and the A signal degradation of MPO connector
(channel 2) after series of matings/de-matings . 28
Figure A.4 – Evolution of particle centre position for channel 1-11 of an MPO connector
pair . 28
Figure A.5 – Measured and calculated delta attenuation as functions of GWPOA . 29

Table 1 – Summary of the result . 7
Table 2 – A and RL statistics for representative samples . 14
Table 3 – Inspection criteria for SMF pigtail and patch cord connectors, RL >45 dB . 18
Table 4 – Inspection criteria for single-mode APC pigtail and patch cord connectors . 20

– 4 – TR 62627-05 © IEC:2013(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIBRE OPTIC INTERCONNECTING DEVICES
AND PASSIVE COMPONENTS –
Part 05: Investigation on impact of contamination and
scratches on optical performance of single-mode (SM)
and multimode (MM) connectors
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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The main task of IEC technical committees is to prepare International Standards. However, a
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data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC/TR 62627-05, which is a technical report, has been prepared by subcommittee 86B: Fibre
optic interconnecting devices and passive components, of IEC technical committee 86: Fibre
optics.
TR 62627-05 © IEC:2013(E) – 5 –
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
86B/3442/DTR 86B/3489A/RVC
Full information on the voting for the approval of this technical report can be found in the
report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the IEC 62627 series, published under the general title Fibre optic
interconnecting devices and passive components can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication 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 – TR 62627-05 © IEC:2013(E)
INTRODUCTION
Contaminated optical connectors result in degradation of optical performance, which can be
quantified by return loss (RL) and attenuation (A), functional failures and increased
deployment costs. Fibre optic connector endface cleaning is recognized as a necessity for
optimal signal performance. It is known that contamination impacts signal performance by
blocking the core and impeding light transmission, as well as by preventing direct physical
contact creating an air gap between the two connector enfaces [1, 2] . If an air gap exists,
optical performance will be impacted due to the change in transmission medium. As
contaminated connectors are mated and demated, contamination can be redistributed around
the connectors’ endface and block the fibre core. This presents a risk of signal performance
degradation during the service life.
Since 2002, the iNEMI (International Electronics Manufacturing Initiative) working group has
done substantial work, both theoretical and experimental, on impact of scratches and
contamination on connector optical performance (A and RL). The following connector types
have been used for this research: single-mode (SM) physical contact (PC) connectors, SM
angle polished connectors (APC) and SM APC MPO connector. The impact of polishing
scratches has been investigated for SM and multimode (MM) connectors. The work presented
in this technical report was used as a base work for the development of IPC-8497-1 [3] and
IEC 61300-3-35 [4].
_____________
Figures in square brackets refer to the Bibliography.

TR 62627-05 © IEC:2013(E) – 7 –
FIBRE OPTIC INTERCONNECTING DEVICES
AND PASSIVE COMPONENTS –
Part 05: Investigation on impact of contamination and
scratches on optical performance of single-mode (SM)
and multimode (MM) connectors
1 Scope
This part of IEC 62627, which is a technical report, summarizes the extensive industry
research on development of cleanliness specifications for single-mode (SM) and multimode
(MM) connectors.
The summary of the result shows Table 1.
Table 1 – Summary of the result
Samples A/RL Clause Reference
Scratch/Contamination/Defect
SM/MM Single-fibre/
multi-fibre
SM PC Single-fibre Scratch RL 3 [1], [5], [6]
MM PC Single-fibre Scratch RL 4 [7]
SM PC Single-fibre Contamination A and RL 5 [2], [6]. [8]
SM APC Single-fibre Contamination A 7 [11]
SM APC Single-fibre Scratch RL 7.2 [11]
SM APC Multi-fibre Contamination A and RL 8 [12]

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.
IEC 61300-3-6, Fibre optic interconnecting devices and passive components – Basic test and
measurement procedures – Part 3-6: Examinations and measurements – Return loss
IEC 61755-3-1, Fibre optic connector optical interfaces – Part 3-1: Optical interface, 2,5 mm
and 1,25 mm diameter cylindrical full zirconia PC ferrule, single mode fibre
3 Abbreviations
A attenuation
APC connector angle polished connector
DUT device under the test
GWPOA gaussian weighted per cent occluded area
MFD mode field diameter
MM connector multimode connector

– 8 – TR 62627-05 © IEC:2013(E)
OTDR optical time-domain reflectometer
OCWR optical continuous-wave reflectometry
PC physical contact
RL return loss
SM connector single-mode connector
4 Experimental methodology
In order to collect the data required to enable correlation between changes in optical
performance (A and RL) with fibre optic images of the corresponding connectors, the
experiment followed a multi-step process that involved
a) initially inspecting, cleaning and imaging connectors being tested (DUTs) and reference
connectors; making multiple matings and dematings of each DUT with a reference
connector, and recording A and RL data after each cycle,
b) manually applying dust to the cleaned endfaces of the DUTs, then
c) mating contaminated DUTs with clean reference connectors at least five times, taking A
and RL measurements after each mating and saving fibre endface images for both
connectors. The block diagram of the experiment is shown in Figure 1.
All DUTs and reference connectors were initially inspected and cleaned using a cleaning
cassette. Endface images were saved using fibrescope and image analysis software. This
software was used to accurately measure the number of particles, their size and their location
at the connector endfaces. More than 80 cables with SC simplex connectors (the DUTs) were
used for the experiment. A small group of DUTs (five cables) with FC connectors, ten DUTs
with LC connectors, and five DUTs with MU connectors were added.

Figure 1 – Block diagram of design of experiment
After clean measurements and images were recorded, Airzona test dust was manually applied
to the cleaned endface of the DUT. The two grades of Airzona test dust used for the
experiment were ultra-fine (1-5 µm) and fine (6-25 µm). The contaminated DUT was mated
with a clean reference connector. A and RL data were recorded. Each DUT and reference
connector pair was mated and demated five times. After each mating, A and RL
measurements were taken. After demating, the images of the DUT and reference connector
endfaces were saved.
If the change in A or RL exceeded three times the standard deviation of A or RL for clean
connector, the connector was judged a failure due to contamination. The pass criteria were
achieved when both delta A and delta RL were within three standard deviations of A and RL.
The experimental methodology for SM APC connectors and for SM, APC MPO connectors
was also based on design of the experiment shown in Figure 1. The details of the
experimental procedure for these connector types are described in Clauses 8 and 9. The
details of the experimental methodology for MM connectors are provided in Clause 6.

TR 62627-05 © IEC:2013(E) – 9 –
5 The impact of scratches on A and RL of single-mode connectors
A quantitative description of surface defects such as scratches and digs on optical
performance was developed based on theory of surface scattering [5]. Further development
led to a complete model for analysis of scratches impact on RL performance [6]. The model
was based on the Gaussian distribution of incident power and included the effects from
scratch location, size and number of the scratches. Based on the model it was predicted that
the scratches through the fibre core cause some severe degradation, the scratches outside
but near the core have some impact on RL, while scratches beyond 25 µm diameter centre
area show little impact on RL performance [6]. These predictions were supported by
experimental data [1]. To properly characterize the impact of scratches on performance
parameters of mated optical connectors, first the optical performance parameters of pristine
optical connectors were measured. Then, after applying scratches at different locations on the
fibre endface, the optical performance parameters were measured again.
A sample set of 24 optical cable assemblies and launch cables were polished to PC
performance using standard polishing process. The samples were divided into two groups.
Scratches were induced only within the cladding region of the first group of connector
endfaces, while for second group of optical cable assemblies the scratches were applied to
the fibre mode field diameter (MFD).
The results of this study indicated that
a) polishing scratches and scratches made during connector cleaning, outside the fibre MFD,
have no impact on A and RL of the mated optical connectors,
b) scratches 2 µm wide or less within the mode field diameter have no impact on A; the A
change observed is within the measurement uncertainty of the test equipment,
c) scratches, within the fibre MFD, can degrade the RL of the mated connectors. The level of
degradation depends on the size (width and depth), and the number of scratches crossing
the fibre MFD. Figure 2 and Figure 3 provide the images of the connector endface with the
scratches outside the MFD area and scratches through the fibre core correspondingly.

Key A =  0,14 dB; RL = 54,7 dB     Key   A = 0,11 dB; RL = 54,8 dB
Figure 2a – Pristine connector Figure 2b – Scratched connector
Figure 2 – Connector endface with the scratches outside the MFD area

– 10 – TR 62627-05 © IEC:2013(E)

Key A =  0,10 dB: RL = 52,7 dB    Key   A = 0,10 dB; RL = 40,7 dB
Figure 3a – Pristine connector Figure 3b – Scratched connector
Figure 3 – Connector endface with scratches passing through the core
6 Effects of scratches on RL of MM connectors
The effects of scratches on return loss of 50 µm core diameter MM connectors have been
experimentally investigated. The results were presented at IEC SC86B, WG4 and WG6
meetings, Charlotte, in 2005. All samples had initial endface geometry according to
IEC 61755-3-1. The samples were polished using 3 µm polishing paper. The RL
measurements have been performed per IEC 61300-3-6 (Method 1, OCWR or Method 2,
OTDR) at λ = 1 300 nm. The connector endface was characterized using a confocal
microscope as shown in Figure 4. The data for scratch width, depth, and length were
analysed and found to correlate with connector RL performance.
Figure 4 – Examples of characterized endfaces using confocal microscope [7]

TR 62627-05 © IEC:2013(E) – 11 –
It was found that all tested multimode samples exceed 20 dB RL as shown in Figure 5.

Figure 5 – RL random mated connectors, λ=1 300 nm [7]
Based on the study, the visual criteria for polished connectors, 20 dB RL, 50 µm was
proposed [7].
7 Investigation of impact of contamination on optical performance of 2,5 mm
and 1,25 mm connectors
7.1 General
This clause summarizes research performed by the iNEMI (International Manufacturing
Electronics Initiative). The fibre optic signal performance project was focused on the
development of a cleanliness specification for single- mode connectors. The influence of two
grades of Airzona test dust on optical performance of single-mode fibres was investigated [2,
8].
7.2 Zone definitions
The impact of particle location on SC connector optical performance was studied in [2].
The iNEMI used image analysis software to measure the distance from the core centre to the
closest edge of the particle. The dependence of delta attenuation, which is equal to A of the
contaminated case minus A of the clean case, is shown in Figure 6a.

– 12 – TR 62627-05 © IEC:2013(E)

Figure 6a – Attenuation performance Figure 6b – RL performance
Figure 6 – Influence of the particle location on performance
Particles located in the core area may result in catastrophic degradation of A. The delta A was
from 0,2 dB to 1,8 dB. The graph of delta RL as a function of the distance from the centre of
the core to the edge of the closest particle is shown in Figure 6b. The presence of particles in
the core zone as well as the presence of clusters of particles in the cladding and ferrule areas
may result in the catastrophic degradation of the RL with delta RL from 10 dB to 40 dB. Based
on this study the core zone with a diameter of 25 µm was recognized as the most critical in
terms of the connector performance.
The following zone system was applied to both 1,25 mm and 2,5 mm ferrules: Zone A, with a
diameter of 25 µm; Zone B within the cladding area, (25 µm to 120 µm); the epoxy ring, zone
C (120 to 130 µm) and Zone D within the contact area (130 µm to 250 µm diameter). The
zones are shown on all connector images.
7.3 Experimental data for 2,5 mm ferrule connectors
Two examples of contaminated FC connectors are shown in Figure 7 and Figure 8 for
samples FC01 and FC04, respectively. In Figure 7, FC01 after the fifth mating is an example
of negligible contamination within Zone A. In Figure 8, FC04 after second mating, is an
example of significant contamination in Zone A.
The A and RL mean and standard deviations for clean samples and the individual A, RL, delta
A and delta RL data are shown in Table 2.
The pass/fail, based on the first method of testing delta against a three standard deviation
limit, is also shown in Table 2. As seen in this table, FC01 (after all mating) passed, as the
contamination did not cause a significant increase in either A or RL.
After five matings/dematings the 25 µm zone remained clean. The A did not change. The RL
change was within 3 standard deviations for the clean fibre. FC04 (second mating), Figure 8,
failed, as it had a large particle blocking a significant portion of Zone A, resulting in a
significant increase in A and decrease in RL (degraded performance). These changes were, in
fact, much larger than the three standard deviation limit. The core stayed contaminated during
the next matings/dematings. After five matings/dematings the optical performance was
approximately the same as after the second mating/demating. The presented data are in good
correlation with the previous data for SC connectors. The contamination of 25 µm zone
resulted in a significant increase of the A and a reduction of RL. In many cases, the reduction
of the RL was observed when a 25 µm zone was blocked and large clusters (>30 µm) of the
particles were located in a cladding layer. The contamination of cladding and ferrule zone
didn’t result in any significant changes in optical performance if the 25 µm zone was clean.

TR 62627-05 © IEC:2013(E) – 13 –

Figure 7a – DUT Figure 7b – Reference fibre
Figure 7 – FC01 images of DUT and reference fibre
after contamination and fifth mating

Figure 8a – DUT Figure 8b – Reference fibre
Figure 8 – FC04 images of DUT and reference fibre
after contamination and second mating
7.4 Experimental data for 1,25 mm ferrule connectors (LC, MU)
The fibrescope image of LC07, a 1,25 mm connector, after the first mating, Figure 9, revealed
one small particle located in Zone A. However the contamination distribution (at the first
mating) had no impact on optical performance as shown in Table 2.
After the third mating/demating the particle distribution had been significantly changed. The
particles moved from the ferrule and cladding areas towards the core of connector L07 and
reference cable T07 as shown in Figure 10 and Figure 11. The DUT failed the pass/fail criteria
for both A and RL.
The contamination level in Zone A area was further increased after fourth and fifth
matings/dematings as shown in Figure 11. As expected, the A and RL both were degraded, as
shown in Table 2.
– 14 – TR 62627-05 © IEC:2013(E)
Table 2 – A and RL statistics for representative samples

a a
A mean A 3σ RL mean RL 3σ Delta A Delta RL
Sample ID Pass/fail
dB dB dB dB dB dB
FC01 (clean) 0,04 0,02 54 3,0 -– – –
FC01 (1st mate) 0,05 – 55 – 0,01 1 Pass
FC01 (5th mate) 0,04 – 55 – 0,00 1 Pass
FC04 (clean) 0,13 0,03 54 1,4 – – –
FC04 (2nd mate) 0,26 – 34 – 0,13 20 Fail
LC07 (clean) 0,11 0,02 53 1,0 – – –-
LC07 (1st mate) 0,12 – 53 – 0,01 0,0 Pass
LC07 (3rd mate) 0,23 – 28 – 0,12 25,0 Fail
LC07 (5th mate) 0,57 – 19 – 0,46 34,0 Fail
a
σ means standard deviation.
Figure 9a – DUT Figure 9b – T07 reference fibre
Figure 9 – LC07 images of the DUT and the T07 reference
fibre after contamination and first mating

TR 62627-05 © IEC:2013(E) – 15 –

Figure 10a – DUT Figure 10b – T07 reference fibre
Figure 10 – LC07 images of the DUT and the
T07 reference fibre after contamination and third mating

Figure 11a – DUT Figure 11b – T07 reference fibre
Figure 11 – LC07 images of the DUT (Figure 11a) and the
T07 reference fibre (Figure 11b) after contamination and fifth mating
Approximately 60 % of all investigated LC and MU connectors demonstrated the particle
movement during the series of matings/dematings operations, with a corresponding increase
of A of 0,5 dB to 1,1 dB. The physical mechanism of the particle movement has to be further
investigated. SC and FC connectors appear to be more resistant to particle movement during
repeated mating/demating operations.
Contamination can also prevent direct physical contact creating an air gap between two
connector endfaces. An air gap of less than 200 nm for SC connectors was calculated based
on the RL of clean and contaminated connectors, as well as on geometric parameters (apex
offset, radius of curvature and fibre undercut) of the DUT and reference connector [2].
Overall, the contamination has similar impact on the optical performance of 2,5 mm and
1,25 mm connectors.
– 16 – TR 62627-05 © IEC:2013(E)
7.5 Image analysis
A correlation between A and RL and the distance from the core to the edge of the nearest
particle was reported in [2]. It was a much more complex and difficult task to investigate the
potential correlation between A and RL and multiple particles distribution. The three main
characteristics of interest are the particle’s area, diameter and location relative to the fibre
centre. The occluded area feature of the image software computes the occluded area for
annular regions centred on the cladding [8]. The occluded area is the total particle area, for all
particles, within that annular region. An example of the occluded particle area binary image is
shown in Figure 12a for the fibrescope image shown in Figure 12b. The image has the particle
binary data colour-coded to identify within which annular ring a portion of each particle is
contained. The black background is the ferrule region, the light grey background is the fibre
cladding and core, and the white background is the epoxy zone. The width of the each ring,
shown in Figure 12a, was 5 µm, although the ring width used in the analysis was finer at
2,5 µm.
Figure 12a – 5 µm annular rings Figure 12b – Fibrescope image
Figure 12 – Labelled detected particles with 5 µm
annular rings and fibrescope image for LC07-WD-5M
7.6 Gaussian weighted per cent occluded area
Normalizing by both area and a Gaussian weighting function, based on a model of the
intensity distribution of the fundamental fibre mode, yields the Gaussian weighted per cent
occluded area (GWPOA). The GWPOA is a single valued figure of merit representing the
overall cleanliness of the endface.
The intensity distribution of fundamental fibre mode [9] is expressed as
2 2
I exp(-2r /ω ),
O f
where
I is the peak intensity;
O
r is the radial position;
ω is the mode-field radius of single-mode fibre.

f
TR 62627-05 © IEC:2013(E) – 17 –
To account for the effect of this intensity profile on the attenuation, the Gaussian weighting
2 2
factor, Γ = exp(-2r /ω ) was introduced. This weighting factor can be applied to the occluded
f
particle areas to weight the particle’s blocking effect based on the intensity profile. The
GWPOA is defined as
N
aΓ
∑ i i
GWPOA= ×100 % (1)
N
AΓ
i i
∑
where
a is the size of particle;
i
Γ is the Gaussian weighting factor;
i
th
A is the area of the i ring.
i
For i = 0, the ring is a circle centred on the fibre centre.
The mode field diameter of SMF-28 is 10,4 µm at 1 550 nm. The GWPOA was calculated for
96 images. The graph of delta attenuation versus GWPOA is presented in Figure 13. The
analysis does not include the particle effect of the mating reference connector. The
correlation between the data points and the fitted curve is 0,82. The theoretical relationship
between A and the GWPOA is of great interest for further investigation.

Figure 13 – Delta attenuation versus GWPOA
7.7 Inspection criteria matrix
Based on our previous research for scratches and contamination, as well as, on the
experimental data described in this paper, the inspection criteria matrix, Table 3, is proposed
for 2,5 mm and 1,25 mm ferrule PC connectors, SM fibre. The area with a diameter of less
than 25 µm, Zone A, is considered the most critical in terms of optical performance. No
contamination and scratches are allowed in Zone A. The pass/fail criteria for the cladding
zone (Zone B), the adhesive zone (Zone C), contact zone (Zone D), are based on
experimental results for A and RL as well as on cosmetic requirements. The maximum size of
the contact zone of 250 µm is defined on the conservative approach of the contact diameter
calculation for SC connectors [2].

– 18 – TR 62627-05 © IEC:2013(E)
Table 3 – Inspection criteria for SMF pigtail and patch cord connectors, RL >45 dB
Allowable defects and scratches
Diameter
Zone/description
µm
Defects Scratches
Zone A: Core zone 0 to 25 None None
No limit <2 µm
No limit ≤3 µm
5 from 2 µm to 5 µm
Zone B: Cladding zone 25 to 120
None >3 µm
None >5 µm
Zone C: Adhesive 120 to 130 No limit No limit
Zone D: Contact 130 to 250 None =>10 µm No limit

8 Correlation study between contamination and signal degradation in single-
mode APC connectors
8.1 General
This clause summarizes the correlation study between contamination and scratches on single-
mode APC connectors and signal degradation leading to an acceptance criteria matrix. The
research has been published by Photonics North 2009 conference, Quebec City, Quebec,
Canada, May 2009 [10].
A group of 25, high quality, patch cords with SC/APC connectors on each end was tested in a
pristine state for baseline performance (both the average and standard deviation of RL).
Starting with pristine connectors and introducing only a small amount of loose particulate, it
was studied how particles are redistributed during successive matings. Next, the effect of
scratches on SC APC connectors using a similar design of experiment was studied.
8.2 Experimental data and analysis for SM APC connectors
From previous study on SM PC connectors, it was predicted that the core zone would be
highly sensitive to contamination. For this reason, a sample set was divided into two groups.
Group A contained samples where dust touched or overlaid the 9 µm core. Group B contained
samples with dust on the cladding, but not touching the core. Typical pictures of the connector
endfaces from Group A and B are shown in Figure 14.

Figure 14 – Left to right: Group A, Group B and average return loss decrease by group
As predicted, connectors in Group A demonstrated a dramatic decrease in average return loss
of 14,2 dB. In comparison, Group B, where dust was present on the cladding but the core was
clear, demonstrated a negligible change in return loss of 0,15 dB. It was concluded that strict
limitations on contamination in the core zone are required. Analysing Group B and
establishing failure thresholds for the cladding then became the focus of the study. While
contamination on the cladding does not always create signal degradation, it does in some
instances. Further, it has long been postulated that contamination on the cladding can
relocate during successive matings. To understand this problem, the behaviour of relatively

TR 62627-05 © IEC:2013(E) – 19 –
large particles (~10 µm diameter) versus small particles (<5 µm diameter), was investigated
as shown in Figure 15. Loose particles were deposited on pristine connectors and mated
successively.
NOTE 1 Four images at left are relatively large particles (~10 µm) “exploding” and spreading across fibre.
NOTE 2 Four images at right are small particles (< 5 µm) that do not demonstrate significant movement under
successive matings.
Figure 15 – Behaviour of relatively large particles versus small particles
Further investigation established that particle migration during successive matings also
occurs on the ferrule within the contact zone (approximately <250 µm), but does not seem to
be an issue beyond that zone.
In parallel, the effect of scratches on APC connectors was investigated, It was found, as
shown in Figure 16, that even large numbers of scratches, including scratches across the
core, do not measurably degrade back reflection (return loss). This was contrary to the results
for PC connectors and was consistent with the design theory that underlies APC connectors.

– 20 – TR 62627-05 © IEC:2013(E)

Figure 16 – Test connector in pristine condition (RL= 67,5 dB)
and after scratches applied (RL= 68,5 dB)
8.3 Inspection criteria matrix
Based on the experimental data described in a previous paper [10], an inspection criteria
matrix is proposed for SM APC connectors as shown in Table 4. For practicality,
contamination and all other defects are grouped under the single heading of “defects”.
Scratches are controlled separately. Zone A is tightly controlled for defects and a limit of four
scratches is placed as a demonstration of workmanship and process control. Zone B is
governed partly by the experimental results for signal degradation (RL) and partly by the
threat that particles in this zone are highly likely to redistribute to Zone A during successive
matings. As particles below 5 µm in diameter are unlikely to move during mating cycles, it is
practical to allow a small number of particles between 2 µm and 5 µm in a cladding zone.
Zone C is prone to minor edge chipping, epoxy spread and other defects that are nearly
impossible to discern from fixed particulate matter. Further, as this zone is relatively far from
the core, there are no defined failure conditions. Zone D is unlikely to contribute to signal
degradation but some level of control is needed to address the threat of particle migration
during mating cycles. It is technically reasonable to establish no limit on scratch count for
these outer three zones.
Table 4 – Inspection criteria for single-mode APC pigtail and patch cord connectors
Allowable defects and scratches
Diameter
Zone/description
Defects
µm
Scratches
Number & width
Zone A: core 0 to 25 None ≤ 4 scratches
No limit ≤ 2 µm
Zone B: cladding 25 to 120 5 from 2 to 5 µm No limit
None > 5 µm
Zone C: adhesive 120 to 130 No limit No limit
Zone D: contact 130 to 250 None =>10 µm No limit

Clause 8 focused on the impact of contamination and scratches on signal performance of SM
APC optical connectors. Contamination led to clear proof that contam
...