Transcript
Automated Inspection with Large Field of View,
High Dynamic Range, and Occluded Area Metrics Doug Wilson and Jan Endresen FiberQA, LLC AS-3 Meeting 23 September 2014
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Agenda
• Introduction • Large FOV with High Resolution • HDR Imaging • Occluded Area • Bonus Topic:
“Free” Ferrule Height Measurement
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Large Field of View (FOV) Fiber Imaging 3
Background on Current Scopes
• Industry standards (such as IEC 61300-3-35) call for low and high magnification systems.
• Known commonly as “200x” and “400x”,
with resolutions of 0.8 and 0.4 μm/pixel.
• Scrolling is used to move from fiber to fiber on MT ferrules • At high magnification, many scopes and probes have FOV smaller than the IEC contact zone spec for single fiber ferrules.
• Short working distance of 3 mm precludes in shell testing for MIL-38999.
• Probes must be inserted inside the shell, requiring care to avoid damage to ferrules.
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Large FOV and High Resolution
• “High Mag” system uses a telecentric lens with optical magnification of 4X
• Paired with large format camera, system
achieves spatial resolution of 0.42 μm/pixel and FOV of 1.54 x 1.11 mm
• Working distance is 65 mm, allowing
flexibility in Z location, including inspection well outside of connector shells
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Large FOV Imaging
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FastMT-200 images entire fiber region
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FOV: 2.31 x 3.22 mm Resolution: 0.835 um/pixel
FastMT-400 image in
3 images
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FOV: 1.54 x 1.1 mm Resolution: 0.418 um/pixel
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Samples Ferrule Images: MT-12 FastMT-200: One image for all fibers
FastMT-400: Three images for all fibers
Note: Not to scale. Images sized to fit on slide 7
Sample Fiber Images Two fibers from same MT-24
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FastMT-200
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0.835 μm/pixel
FastMT-400
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0.418 μm/pixel
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MT-72 with Processing Overlay
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MT Single Fiber View-Process Results
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Single Fiber View-Process Results
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Large FOV Summary
• New technique for fiber inspection on MT and single fiber ferrules.
• Inspects all (200x) or significant portion (400x) of fibers on MT at one time.
• Single operation focus, capture and process for all fibers • For single fiber ferrules the larger FOV allows high resolution inspection well beyond contact zone.
• Long working distance enables imaging outside the shell for MIL-38999 and other high density connectors.
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HDR Imaging
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Dynamic Range Issue in Fiber Inspection
• Multi-mode fiber cable assemblies have ~2:1 core peak:cladding mean intensity ratios
• Fibers with bright cores and lensed
connectors can have reflectance ratios >10:1.
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Camera Bit Depth
• Allowable reflectance ratio without non-
linear effects limited to about 3:1 without serious reduction in detection capability
• Most fiber scopes, including FastMT, use an 8-bit camera {0:255}
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Highly Reflective Core Example Long Exposure
Short Exposure
Cladding processing works well. Core processing impossible due to clipping.
Poor detection in cladding. Core processing works well.
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The Solution - HDR Imaging
• HDR (High Dynamic Range) imaging is a cost effective solution
• Combines two or more SDR (Standard
Dynamic Range) images to create an HDR
• Commonly employed in digital still cameras including those in modern cell phones
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HDR Line Profiles Short Exposure Normal Core Dark Cladding 250"
250"
200"
200" 150" 100"
100" 50"
0"
0" 0"
100" 200" 300" Posi+on((μm(from(Center)(
2000" 1800" 1600" 1400" 1200" 1000" 800" 600" 400" 200" 0"
150"
50" 400"
Long & Short Exposures Higher Bit Depth Scaled by Gain
Intensity(
300"
Intensity(
Intensity(
Long Exposure Clipped Core Normal Cladding
0"
0"
100" 200" 300" Posi+on((μm(from(Center)(
400"
100" 200" 300" 400" Posi+on((μm(from(Center)( Long"Exposure" Short"Exposure"Scaled"
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FastMT HDR- Good Detection in Clad and Core
HDR Compressed Image No Overlay
Found defects on Core and Cladding. Zones are centered on core.
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HDR Summary
• Compressed HDR method has been implemented in FastMT system.
• Good defect detection in both cladding and bright core in one measurement.
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Occluded Area
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Occluded Area Concept
• Occluded area (OA) is a direct measure of the total blocked area due to defects
• Weighting by optical power function yields single metric for entire surface
• Number/size of particles not relevant • Insertion Loss (IL) worse as OA increases 22
Occluded Area
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OA Investigated in iNEMI Research
• SM fiber contamination study data was used to evaluate Occluded Area (OA)
• Strong correlation between Gaussian Weighted OA and IL
• Individual zone OA can place upper limits in specific zones
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GWpOA Correlates with IL
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High (~82%) Correlation between GWpOA and IL
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Predicts increase in IL as function of OA
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Can set limit on OA based on desired max IL increase
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Bonus Topic: Ferrule Height
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Focus Position
• FiberQA systems (AVIT and FastMT) automatically
focus by setting the working distance of fixed zoom optics at optimally focused position
• Final focus “Z” location can be used to determine the fiber/ferrule height
• Plane fit to 3 or more ferrule height values and then estimate the height difference of all the ferrules
• Reference datum by fixture or measurement to convert to absolute height measurement
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AVIT Fiber Heights on MIL-38999
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AVIT (desktop version) fitted with product specific fixtures
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Prototype MIL-38999 fixture used to obtain ferrule (termini) height relative to proposed “Datum C”
on male connector 28
Ferrule Camera Images
Datum C
Ferrule 29
Fiber Camera Images
Datum C
Fiber 30
Ferrule Height Data from Fiber Focus Positions
• • •
Test repeated with pressure applied to seat termini between runs Each run includes 8 repeats of the measurement StDev is about 0.0002” overall (0.00015” to 0.00035” by ferrule) 31
Fiber Height Summary
• Initial measurements very promising • Standard deviation under 0.0004”, or 1/10th minimum tolerance
• Comparison with independent
measurements required for accuracy estimate
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Contact Info
Doug Wilson
[email protected] (860) 961-8559 (c) www.fiberqa.com
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