QPOpticalFiber Quality Control for the CMS-HF Detector at Polymicro

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QPOpticalFiber Quality Control for the CMS-HF Detector at Polymicro Powered By Docstoc
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Available on CMS information server                                              CMS NOTE 2002/000




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                                                                                            28 February 2002




 QP Optical Fiber Quality Control for the CMS-HF
    Detector at Polymicro Technologies, LLC
                                  J.P. Clarkin, G.W. Nelson, R.J. Timmerman
                                       Polymicro Technologies, Phoneix, AZ

                                               J-P. Merlo, Y. Onel
                                         University Of Iowa, Iowa City, IA

                                            N. Akchurin, R. Thomas
                                        Texas Tech University, Lubbock, TX
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                                                 I. Dumanoglu




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                                        Cukurova University, Adana, Turkey



                                                    Abstract


     Production of high performance large core polymer clad silica core optical fibers (QP) requires atten-
     tion to detail throughout the manufacturing process. In-line and off-line process/product quality tests
     help to ensure consistency and uniformity in the final product. This technical note discusses the quality
     control elements of fabricating the CERN QP600 optical fiber at Polymicro Technologies, LLC.
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1 QP Process Review
A good starting point is with a general overview of the quality control process steps. Figure 1 shows the quality
tasks starting with incoming raw materials inspection through final off-line inspection. Following this general
overview a more detailed discussion will be presented. Incoming Inspection Upon receipt, the raw materials




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(consisting of optical fiber rods, uncured hard clad polymer, and uncured acrylate buffer polymer) are subject to
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incoming inspection at which time any flawed or damaged material is isolated, with the rejected material being
returned to the vendor for replacement. Vendor Certifications (CERTs) and analysis results are reviewed with
respect to the material specification. A Polymicro lot number is assigned to each vendor lot, the goods are then held
in a climate controlled inventory storage area. Polymer coatings are maintained in the original vendor containers
to help eliminate possible contamination or exposure to stray light.


1.1 Facility and Equipment Checks
A class 100 clean room is maintained along the fiber path during the draw and coating steps. To ensure the
equipment is maintaining the desired level of cleanliness a particle counter is used to check particle levels before
drawing the fiber. Draw tower systems (coating, laser micrometers, lump detection, concentricity) are setup and
calibrated before the fiber draw.


1.2 Materials Preparation
Manufacturing obtains raw materials on an as needed basis, so only a small quantity of raw material is physically
on the production floor at any one time. This reduces the risk of damage or misplacement of expensive raw
materials. At the rod preparation step, data is recorded concerning the rod’s condition plus the fiber lot number
is assigned. Polymer coatings are handled in original vendor container throughout the draw process helping to
eliminate possible contamination sources and exposure to stray UV light.


1.3 Fiber Draw - In-Line Fiber Checks
The draw process involves a series of related processes that require setup and calibration before drawing the optical
fiber. During the draw, a number of in-line process and/or product checks are conducted to insure process stability
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and product uniformity. Laser micrometer dimensional data is recorded during the draw and stored on the local
PC hard drive and on the network server hard drive. A statistical dimensional data summary for each spool is




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generated. In addition to the dimensional measurements, lump detection (rapid diameter changes), clad/buffer
concentricity and proof strength tests are conducted in-line on 100% of the fiber. After each fiber spool comes
off the take-up equipment, the fiber ends are dimensionally checked on a microscope as a verification of the laser
micrometer data.
Proving the operator with rapid feedback on fiber quality is very important to producing consistent high quality
fiber. Optical loss data is obtained by an insertion loss test right at the draw tower workstation. With this feedback,
many optically related draw problems can be detected by the operator. Real-time SPC charting of the fiber dimen-
sions provides instant feedback on draw stability. In addition to the above checks, during the draw systems checks
are conducted periodically and recorded.
All data obtained from these tests are recorded and stored on the computer database for easy retrieval and sum-
marizing. These in-line quality checks help to insure consistency and uniformity in the fiber. With the large core
fiber, considerably scrap can be created if the processes are not precisely controlled.


1.4 Final QC - Off-Line Fiber Checks
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Once the draw is complete, the fiber is transferred to the fiber inspection area for final testing and packaging. The
off-line tests check two critical fiber characteristics - optical and mechanical. Environmental tests like radiation
resistance are conducted by Texas Tech University with test samples from each cladding lot. The off-line tests
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include: Optical * UV-VIS and VIS-NIR spectral attenuation * Numerical aperture (NA) * OTDR spool length
check Mechanical * 100kpsi proof test - 2-axis bend - 100% of fiber. * Breaking Strength - Two-point bend test
on a random sampling of lots to establish and monitor fiber break strength - Weibull Plots summarize the test
data. * Short-term strength test - 6 cm bend radius for 1minute, approximately a 50kpsi stress level, on every lot
* Long-term strength test - the shipping spool subjects the fiber to a 10 cm bend radius, approximately a 30kpsi


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stress level. If any weak fiber sections exist they may break on the spool or when attempting to remove the fiber
from the spool. The long-term strength test acts to filter out any weak fibers before building fiber assemblies.
Documenting the on-line and off-line tests, a data summary package is sent with each shipment as the product
history record. Included with this data packaged are the complete UV-VIS and VIS-NIR spectral attenuation plots.




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For those interested, a detailed discussion of the QC tests will be covered in the following sections.
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2 Material Control
All raw materials for the QP fiber are under strict lot control with vendor certification (CERT) and analysis data
supplied with each lot. Polymicro incoming inspection ensures that documentation, ordered quantities, dimensions
and general condition of goods all meet the product specifications. Inspecting the raw materials for flaws or
contaminates is generally not very productive. It’s like looking for a needle in a haystack. Since its extremely
difficult or impossible to locate sub-micron flaws or ppm contaminates in bulk material. The preferred method is
to inspect the drawn fiber for flaws. Turning the raw materials into optical fiber brings the problem(s) to the surface
in the form of poor optical characteristics or poor mechanical strength. With the lot tracking system, every lot of
raw material can be tracked from start to finish so bad or poor quality material can be removed from the system.
All polymer coatings are maintained in the original vendor containers to help eliminate possible contamination.


3 Fiber Manufacturing Control
All optic fiber products are under a document control system with an engineering change order (ECO) system.
The QP fiber product is defined by a manufacturing control document (MCD) while the manufacturing process
is controlled by the process control document (PCD). All deviations to the MCD or PCD are documented by the
operator and supervisor.
The draw tower environment is temperature and humidity controlled. Localized particle control (HEPA Filters) is
used on each draw tower to maintain a clean room environment (Class 100) around the fiber path. Particle counts
on each draw tower are conducted using a Lasair Particle Counter model 510-6.
Core, clad and buffer dimensional data are displayed on a monitor during the draw in the form of a real-time SPC
chart. This provides the operator with real-time information on the stability and uniformity of the draw process.
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Operators use this information to monitor and control the draw. Improvements in the lot-to-lot consistency can be
observed with introduction of this real-time information.




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A manufacturing/quality database is utilized to record draw information, provide the operator with the up-to-
date MCDs and PCDs, record dimensional data for future chart preparation and record operator/quality inspector
comments. In addition, to the real-time dimensional SPC charts, SPC charts of the breaks per kilometer and reel
length parameters are maintained. This provides additional information on operator/system performance. All
production equipment is on a preventive maintenance schedule (weekly, monthly and annual). Each draw tower
has an equipment logbook to track equipment changes and problems. Equipment calibration is handled by internal
as well as external technical personal. A quality technician calibrates all measurement microscopes every Monday
morning in order to ensure accurate and repeatable dimensional measurements. Microscope calibration can be
repeated at any time if a problem develops or a special need arises. Other equipment is calibrated on a lower
frequency generally by outside vendors. A detailed equipment calibration logbook is maintained. In addition,
calibration labels are used on equipment throughout the plant. Quality audits include repeatability testing on all
personnel doing dimensional measurements on an annual basis. This ensures everyone is capable of performing
the measurement function to the level of accuracy and repeatability call for in the product specifications. Training
is conducted for those needing improvement. Monthly product audits are performed by the quality department
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to monitor parameters such as break strength, thermal performance and polymer to glass bonding. This helps to
ensure that all processes are functioning within acceptable limits and with minimal process drift.


4 Material Handling and Preparation
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The optical fiber rods are individually cleaned and bagged by the vendor. Polymicro does just-in-time chemical
cleaning and O2/H2 fire polish operations on the core rod to remove any scratches, finger oils, and/or debris. At this
step, a visual inspection of the core rod is done to locate any badly flawed rods that should not be used. A detailed
log is kept on the observations and process cleaning parameters. This data is entered into the production/quality
database.

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Buffer and clad materials are under lot control as well. They are maintained in the original containers to reduce
cross contamination. The coating delivery systems located on the draw tower obtain the clad or buffer material
directly from the vendors’ container for direct application to the fiber. This helps to reduce contamination possibil-
ities and exposure to stray light. No core, clad or buffer materials are reused or recycled. In addition, the cladding




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lots are not mixed. Helping to maintain the material cleanliness the coating system delivery tubing, reservoirs and
dies are inspected and cleaned before the start of each draw.
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4.1 Draw Process
The fiber draw system in figure 2 shows the basic equipment layout. The fiber manufacturing procedure is detailed
in many other books and publications so those details with be skipped in this technical note.


5 Fiber QC
The quality department has the final responsibility to ensure that all fiber specifications are complied with in the
production of QP fiber. Both in-line and off-line tests are audited periodically to ensure the tests are functioning
correctly.
Presented below are detailed discussions of all the in-line and off-line tests.


5.1 In-line Manufacturing Tests
In-line Proof Test 100% of the fiber is proof tested during the draw at a 100kpsi level using a three-axis bend
      type proof tester. Data recorded during the draw are the number of breaks if any and reasons for break(s). A
      breaks per kilometer chart is supplied with each fiber shipment.
Core OD Measurement A TSI Target System Holix 5000 Series Dual Axis Laser Micrometer with TS 5000
     Control and Display, XY 5007 Gauge Head is used to record the fiber core od during the draw process.
     Statistical data is calculated by the computer system using the TSI system data. The core average od,
     standard deviation, minimum, maximum and number of samples is recorded and supplied in the QP fiber
     data package for each draw.
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Clad OD Measurement A TSI Target System Holix 5000 Series Dual Axis Laser Micrometer with TS 5000




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     Control and Display, XY 5007 Gauge Head is used to record the fiber clad od during the draw process.
     Statistical data is calculated by the computer system using the TSI system data. The clad average od, standard
     deviation, minimum, maximum and number of samples is recorded and supplied in the QP fiber data package
     for each draw.

Buffer OD Measurement A TSI Target System Holix 5000 Series Dual Axis Laser Micrometer with TS 5000
     Control and Display, XY 5007 Gauge Head is used to record the fiber buffer od during the draw process.
     Statistical data is calculated by the computer system using the TSI system data. The buffer average od,
     standard deviation, minimum, maximum and number of samples is recorded and supplied in the QP fiber
     data package for each draw.
Lump Detection The detection of lumps or diameter spikes in the glass, cladding or buffer is monitored during
    the draw using the TSI Target Systems listed above.
Clad Concentricity The cladding to core concentricity is monitored throughout the draw using a forward scatter
     laser concentricity monitoring system. This instrument has been designed to be a go/no go gauge. If the
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     concentricity is poor (¿3um), the signal or pattern is very unstable. Good to excellent concentricity yields a
     very stable and symmetrical signal or pattern.
Buffer Concentricity The buffer to clad concentricity will be monitored using a forward scatter laser concentric-
     ity monitoring system. This instrument has been designed to be a go/no go gauge. If the concentricity is
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     poor (¿3um), the signal or pattern is very unstable. Good to excellent concentricity yields a very stable and
     symmetrical signal or pattern.




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5.2 Off-line Manufacturing/QC Tests
Fiber Dimensions End samples from each spool will be measured to cross check the in-line laser micrometer
      values and concentricity monitors. The core od, clad od, buffer od., min/max clad and buffer thickness
      are measured using an Olympus PME3 microscope with Boeckeler Instruments Microcode II digital filar




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      measurement system model 1-MS.
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Spectral Attenuation Using Ocean Optics spectrometers Models USB2000 and SD2000, the attenuation is mea-
     sured in the 300 - 850 nm range in dB/km on every preform (every 2-3km). This wavelength range requires
     two separate spectral attenuation tests (UV-VIS 300 to 450nm and VIS to NIR 400 to 850nm) to get accu-
     rate values over the entire wavelength range. Figures 3 and 4 show typical VIS-NIR and UV-VIS spectral
     attenuation charts for this fiber. The increasing attenuation as wavelength decreases causes a decrease in the
     signal to noise ratio on fiber lengths typically used to test longer wavelengths ( 150m, VIS - NIR). There-
     fore, a shorter fiber length (20m) is used to obtain accurate attenuation values or signal to noise ratios on the
     UV-VIS test.
Numerical Aperture (NA) Using a far field radiation pattern scanning system the NA of each cladding lot is
    measured. NA data is supplied for each fiber lot.
Proof Test In addition to the 100% in-line proof test performed at the draw towers, Polymicro Technologies per-
     forms an off-line two-axis bend proof test (100 kpsi) on 100% of the QP fiber before shipment. Any breaks
     obtained at this proof test step will be added to the draw tower break numbers to calculate the breaks/km
     factor discussed in the fiber draw section above. Breaks per kilometer chart are supplied with each shipment.
Break Strength Test Using a 2-point bend tester, a break strength test will be conducted at every 150th km of
     fiber manufactured. A Weibull plot as shown in Figure 5 is supplied.

Short and Long Term Strength Test Refer to overview section for a discussion of these strength tests.


6 Summary
For critical applications, the customer’s confidence in the optical fiber’s quality and performance must be very high.
Providing a high level of confidence in large volume production of large core step-index polymer clad optical fibers
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requires attention to detail at all process steps. To reach this goal a series of in-line and off-line quality/process
checks are conducted to insure the stability and consistency of the fiber manufacturing process. The in-line quality




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checks insure process and product conformance directly at the point of manufacture, thereby minimizing product
variation while maximizing process efficiency. The off-line quality checks confirm the repeatability and consis-
tency by determining actual performance values for many of the optical and mechanical fiber characteristics. The
level of detail provided raises everyone’s confidence in the product quality and performance.
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