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Cleaning Technology |
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The results of a recent NEMI study range from
predictable to surprising.
Anomalies that commonly occur in manufacturing
processes can affect signal performance in an
optical connector. Scratches and/or contamination
in the form of particles and even oil from fingerprints
often negatively impact insertion loss (IL), return
loss (RL), and bit-error rate (BER).
The National Electronics Manufacturing Initiative
(NEMI) Fiber Optic Signal Performance project
is working to quantify the severity of optical-signal
loss due to common hazards in manufacturing. The
goal of the project is to develop industry-standard
criteria and specifications for fiber-connector
end-face inspection. The project also plans to
develop guidelines for cleaning procedures and
contamination prevention.
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FIGURE 1. Common
defects seen at the optical connector end
face include scratches (left), particles (center),
and oil (right). |
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The NEMI team tested three groups of cables
with SC singlemode simplex connectors featuring
2.5-mm ceramic ferrules. Scratches were introduced
to the first group of cables, the second group
was contaminated with carbon particles, and
the third group was contaminated with oil.
Each device under test consisted of 20 to
24 cables and launch cables, polished to UPC
performance. Each cable connector was visually
inspected before and after defects were introduced
to its end face, using a 200× or 400× fiberscope.
Measurements of IL, RL, and BER were taken
for the clean (defect-free) and defected connectors. |
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| The scratch experiment
involved two sample groups. In one group,
scratches were induced within the cladding
region?outside the fiber mode field
diameter (MFD)?while, in the second
group, scratches were applied to the
fiber MFD. The results indicate that
scratches made during connector cleaning
or polishing outside the fiber MFD have
no impact on IL and RL of the mated
optical connectors (see Fig. 2). |
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FIGURE
2. The two scratch groups in the
experiment revealed that scratches
within the fiber MFD degrade the
return loss of mated connectors
(wavelength is 1550 nm). |
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Similarly, scratches 2 μm wide or less
within the MFD have no impact on IL;
the change observed is within the measurement
uncertainty of the test equipment. However,
scratches within the fiber MFD can degrade
the RL of the mated connectors, with
the level of degradation depending on
the width, depth, and number of scratches
crossing the fiber MFD. In the NEMI
investigation, the average difference
in RL due to scratches within the fiber
MFD was 4 dB. |
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| In the particle contamination
analysis, carbon particles were used
to contaminate connector end faces.
Particles can be trapped on any of three
basic areas of the connector end face:
the core, cladding, and ferrule. Seven
possible anomaly conditions may exist,
with contaminants found on the core
only, cladding only, ferrule only, core/cladding,
cladding/ferrule, core/ferrule, or core/cladding/ferrule. |
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FIGURE 3. Insertion
loss measurements (left) and return
loss measurements (right) varied depending
on the percentage of the fiber core
and connector end faces blocked by particles.
In the JSC1 case, more than 90% of the
core region was blocked. In JSC2, approximately
5% to 10% of the core was blocked. In
JSC4, 60% to 70% of the core was blocked,
and in TSC138, 20% to 40% of the core
was blocked. |
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| The study showed that
mating caused loose contaminants to
spread. Through connection, a significant
amount of the particles were transferred
from the contaminated connector to the
clean reference connector in a pattern
similar to that seen on the contaminated
connector.
The study also showed that particles
on the core of the fiber resulted
in catastrophic failures (tremendous
increase in IL and decrease in RL),
while the presence of particles on
the ferrule did not degrade performance
(see Fig. 3). The team is planning
further study of the proportion of
increase in IL and decrease in RL
and the percentage of blocked core
area.
Particles on both the ferrule and
the cladding area created mixed results.
In many cases, measurements of IL
and RL showed no significant difference
between the clean and contaminated
connectors. However, a few exceptions
showed that the presence of particles
on the cladding very near the core
can increase the IL and/or RL. In
one case, the particles spread out
during mating and blocked a small
portion of the core and, as a result,
both the IL and RL of this connector
increased significantly. In another
connector, there was no evidence of
particles blocking the core, but the
IL increased from 0.25 to 1.07 dB,
while its RL didn't change significantly.
More research is needed in this area. |
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| To test the effects of
oil contamination, the team introduced
finger oil to the connector end face
before mating with the reference connector.
The location of the oil contamination
has a two-dimensional random distribution.
Small oil drops of 2 to 60 μm provided
coverage of the core, cladding layer,
and ferrule. The oil distribution changed
during mating with a clean test connector,
transferring partially from the test
connector to the reference connector
(see Fig. 4). |
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FIGURE 4. Measurements
of clean and oil-contaminated samples
at λ = 1550 nm and 1310 nm show that
insertion loss is not greatly affected
by oil contamination (left). Return
loss, however, is significantly reduced
by the contamination at both wavelengths
(right). |
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| Test results indicate
that oil contamination does not affect
the IL of the connector; however, it
causes significant decrease in RL. The
average RL decreased from 56.37 to 43.64
dB at λ = 1310 nm and from 57.18 to
45.15 dB at λ = 1550 nm.
The small difference between the
refractive indices of fingerprints
(1.4602) and fiber (1.467) indicates
that the behavior of oil contamination
is similar to the behavior of refractive-index
matching material.* (Index matching
material is applied to fill the gap
between the two fiber end faces to
reduce the Fresnel reflection resulting
from the discontinuity in propagation
medium.) This similarity can explain
why IL did not change after oil contamination.
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| Testing done to
date by the NEMI project shows that
the effect of contamination/scratches
on connector optical performance is
dependent on the type of contamination
(fingerprints, carbon, metallic particles,
and so on), size of the contaminated
area, and location on the connector
end face. The influence of the contamination/scratches
becomes more evident if they are located
in the core/cladding areas. Particle
contamination may cause a significant
increase in IL (up to ten times), decrease
in RL (up to three times) and increase
in BER test results (two to ten times)
if they are located near the core. Scratches
applied to the fiber MFD decreased RL
by up to 25%, while scratches located
in the cladding layer showed little
effect on IL, RL, or BER test results.
Multiple heavy scratches passing through
the core caused severe performance degradation
in IL and RL and catastrophic BER test
failures. The
project team is planning further research
to develop mathematical modeling for
scratches, particles, and oil contamination.
Future studies will also investigate
the effects of particles located at
the cladding (and close to the core)
area and focus on particle size, quantity,
and different particle types.
Typically, OEMs and
electronics manufacturing services
(EMS) providers have their own inspection
criteria. However, these specifications
differ from company to company, and
the differences can cause materials
to be "nonconforming" at
user/customer sites. If a supplier
has ten customers and must meet ten
different sets of specifications,
product costs will increase. Defining
industry-wide standards for inspection
criteria will help ensure quality
while keeping costs under control.
Data from the NEMI investigations
will be used to help define industry-standard
specifications for cleanliness of
fiberoptic connectors. NEMI is already
collaborating with the International
Electrotechnical Committee (IEC),
Telecommunications Industry Association,
and IPC-Association Connecting Electronics
Industries. The standard being developed
will be jointly submitted to IEC Working
Group 6 (interconnecting devices)
and to IPC for incorporation into
the existing IPC-0040 standard (Optoelectronic
Assembly and Packaging Technology).
Initial results were presented to
the IEC WG6 last October. |
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Contributing team members include
Nick Albeanu (Celestica International),
Les Aseere (Sanmina-SCI), Yves Pradieu
(Iphotonics/Solectron), David Silmser
(Alcatel Canada), and Eloise Tse (Celestica).
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*.N. Albeanu, et al., "Optical Connector
Contamination/Scratches and its Influence
on Optical Signal Performance," Journal
of SMT, Volume 16, Issue 3, 2003.
TATIANA BERDINSKIKH
is engineering advisor for Celestica International
(Toronto) and chair of the NEMI Fiber Optic
Signal Performance Project. She can be reached
at (416) 448-5579 or tberdins@celestica.com.
HEATHER TKALEC is test
engineer for Alcatel Canada (Ottawa, Ontario)
and co-chair of the project. JENNIFER
NGUYEN is advisory engineer for
Solectron Corp. (Milpitas, CA).
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The National Electronics Manufacturing Initiative
is an industry-led consortium of approximately 70
electronics manufacturers, suppliers, and related
organizations whose mission is to assure leadership
of the global electronics manufacturing supply chain. 오후 3:38 2016-03-09
For additional information, visit www.nemi.org |
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