1. Basic Interferometry For PC Polished Connectors
The purpose of this presentation is to provide an understanding of the importance of performing interferometric inspections of PC polished connectors for quality control and quality assurance.
Neal Wagman
Norland Products Inc

2. Surface quality only critical at center of connector.
PC Polish Concept
Spherical polish
Fiber at apex
ADVANTAGE:
Surface quality only critical at center of connector.
Single fiber connectors are made using the PC polish concept. PC stands for Physical Contact. This entails polishing the ferrule end to a spherical surface with the fiber at the highest point. Instead of trying to make the entire endface smooth and flat, we need only be concerned with a small area in the center of the connector. This slide shows the cross section of a typical ferrule with the fiber in the center of the spherically polished ferrule surface.
Fiber

3. PC Polish Concept On connection:
Fibers meet in intimate optical contact. No air gap.
Fibers compress until ferrules contact.
Ferrules take majority of compressive force.
Because the fibers are at the apex of the polish, on connection, the fibers are the first to contact and this eliminates any possible air gap. Because of the spring pressure, the fibers actually compress slightly and the ferrules come into contact. To prevent further movement, the ferrules take the majority of the spring pressure to keep the connection solid.

4. Importance Of Controlling Undercut And Protrusion
A. Undercut
The amount of fiber which is protruding from the ferrule surface or recessed below the ferrule surface is critical for the long term performance of the connector. If the fiber is undercut below the ferrule surface, on connection, there is an immediate air gap which causes backreflection.
Backreflections
Internal connector reflections can cause spurious modulation and noise in laser light (Feedback Lasers)
   Reflection noise is an important concern in analog video

5. Importance Of Controlling Undercut And Protrusion
B. Protrusion
If a connector has too much fiber protrusion, the pressure of the first fiber against the opposite fiber will push the opposite fiber back over time. If this connector is mated with another connector, an air gap will be present causing backreflection again which will degrade the quality of the light transmission.
High forces concentrated on the fiber –
Causes Fiber Pushback and affects long term performance

6. Interferometry
Submicron measurements of differential height by reflecting monochromatic light off a surface and combining with light reflecting off a standard to form constructive and destructive interference patters.
Interferometry is the method used to identify these tiny differences in the connector surface. Inteferometry provides submicron measurements of differential height by reflecting monochromatic light off a surface, combined with light reflecting off a standard to form constructive and destructive interference patters.

7. Why Use Interferometry?
Problem
Standard QC of connectors
Inspect for scratches
Measure light loss
Backreflection if necessary
Not enough for critical systems
SOLUTION – Interferometry checks 3D polish geometry
Assures consistency
Assures long term performance
Effects to consider:
Temperature cycling
Contact pressure
Vibration
Detailed information = more control over process
Interferometry is needed whenever backreflection is import to the system. Many companies only use a microscope to inspect for dirt and scratches and test for light loss and back reflection. This is not enough for critical systems.
Only interferometric inspection will assure consistency and long term performance. Testing light loss and back reflection in at room temperature after polishing cannot predict how the connector with perform over time, with temperature cycling, immense contact pressure of the ferrules, and any environment vibration. Interferometry allows the manufacturer or user to control the critical endface geometry of the connectors to known standards. The result is that interferometry provides more detailed information on the quality of the polish, giving more control over the process of manufacturing and installation. In other words, it provides unmatched quality control and quality assurance for the long term performance of the system.

8. Typical Interferometric Image
VERTEX OF
APEX OFFSET
CONSTRUCTIVE
INTERFERENCE
DESTRUCTIVE
INTERFERENCE
CENTER OF
FIBER

9. 3D Measurement
The computer analyzes the fringe pattern and assigns a height to every pixel on the surface and displays the resulting image of the ferrule and fiber in three dimensions. The computer can measure any geometrical parameter from this data.

10. Fringes = Steps Down Surface
Circular interferometric fringes can be visualized as plateaus or equal steps down the surface.

11. Measurement Areas
Fitting Area: Centered on the ferrule surface and defined by a circular area having a diameter D with a smaller Extracting Area subtracted from its center. D= 250 microns.
Extracting Area: Includes the fiber endface region and the adhesive region and is defined by a circular area having a diameter E. E= 140 microns.
Averaging Area: This is set on the fiber surface and defined by a circle having a diameter F. F=50 microns
Because the connector surface is not a perfect sphere, measurement areas have been defined to standardize the test procedure for endface geometry measurements.
The measurement areas are:
A Fitting Area: Centered on the ferrule surface and defined by a circular area having a diameter D with a smaller Extracting Area subtracted from its center. D = 250 microns.
An Extracting Area: Includes the fiber endface region and the adhesive region and is defined by a circle having a diameter E. E=140 microns. 
An Averaging Area: This is set on the fiber surface and defined by a circle having a diameter F. F=50 microns.

12. Radius Of Curvature Radius of sphere defined by Fitting Area
Center of Fiber
Radius
The radius of curvature is one of the critical measurements. This is defined as the measurement of the radius of the polished sphere in the fitting area of the ferrule.

13. Distance from center of fiber to highest point of ferrule
Offset Of Polish
Distance from center of fiber to highest point of ferrule
The offset polish is the second critical measurement. This is the linear measurement from the fiber center to the apex of polish. The apex of polish is defined as the high point of polish on the ferrule. If the linear offset is too large, the fibers will not be the first to meet and there will be an air gap that will cause back reflections.

14. Spherical Fiber Height
SPHERICAL FIBER HEIGHT – the ideal connector endface (ferrule & fiber) is considered to be a continuous sphere. It is defined as the difference in height between the center of the fiber and the theoretical height in the center based on the ferrule radius.
SPHERICAL FIBER HEIGHT – Because the ideal connector endface is considered to be a continuous sphere, spherical height is the standard measurement for PC polished connectors. It is defined as the difference in height between the center of the fiber and the theoretical height in the center based on the ferrule radius.
In this diagram, the fiber is below the theoretical radius and therefore is considered to be undercut. If the fiber was above the theoretical radius, then the fiber would be considered protruded.

15. Norland CC-6000 Breakthrough Technology
Low cost automated interferometer for analyzing PC/APC connectors that operates on any PC through USB port.
Base price < $13K.
Norland Products is continuously looking for ways to improve interferometric testing to provide capabilities to everyone who needs it. In keeping with this philosophy, we have developed a novel system unlike anything on the market today. This breakthrough technology provides users with a low cost automated interferometer that operates on any PC through the USB port to quickly analyze the endface geometry of single fiber PC and APC connector and provide pass/fail analysis to industry standards. The new technology allows this equipment to be sold at about half the cost of any competitors system with a base price of under $13,000.

16. CC 6000 - Results Displays: Quantitative measurements
Visual pass or fail
Stores to database
Exports to Excel
Prints individual reports
The clean and simple user interface provides a quick measure button and displays quantitative measurements and a visual pass or fail. The data is stored in a database and can be exported to Excel or printed as individual reports.

17. CC Results
Display 3D color contour map of surface detailing fiber and ferrule endface.
Results can also be display as a 3D color contour map of the surface with details of the fiber and ferrule endface.

18. CC6000 Advantages
Breakthrough technology which makes interferometric testing affordable to everyone.
Easy-to-use software loads quickly and will not crash.
Fast, accurate measurements of PC and APC connectors.
Allows quick pass/fail measurements for production.
Trouble shooting instrument for the field.
Robust system requires no maintenance.
In summary, the CC6000 is the only system in its class because of breakthrough technology which provides an affordable interferometer to everyone. With fast, accurate measurement of all PC and APC connectors, the unit is ideal for quality control of a polishing process or trouble shooting tool in the field. The robust system is simple to use and requires little or no maintenance. Norland Products is the only company that can provide you with this.

19. Ideal Polish Circular fringes around ferrule and across fiber.

20. Protrusion
Circular fringe jogs away from center as it crosses the fiber.
Circular fringe jogs away from center as it crosses the fiber

21. Undercut Circular fringe jogs toward center as it crosses fiber

22. Good Polish With Some Scratches

23. Fiber Shattered on Cleave

24. Underpolished – High Protrusion

25. Overpolished - Fails

26. Ideal Polish
Circular fringes around ferrule and across fiber

27. CC6000 for Quality Control
Fast measurements provide instant feedback on polish quality in a production process and provide indication if corrective action is required.

28. Pass/Fail Measurements
Quality control with pass/fail measurements.

29. Smooth Polish – High Offset

30. Undercut with Dirt on Fiber

31. Fail

32. Quality Assurance Pass/Fail assures Long Term Performance PC APC
Telecordia8
ROC
7-25 mm
5 to 12 mm
Apex Offset
<50μm
Fiber Protrusion
0.05μm
0.1μm
Fiber Undercut
(ROC 7-10mm) μm
(ROC 10-12mm) 0.1 μm
(ROC 13-17mm) 0.075μm
(ROC 18-25mm) 0.05μm

33. Summary Importance of Interferometry Used as a training tool
Used for QC of hand or machined polishing
Used for Quality Assurance w/Pass/Fail Specs.
Used for Trouble Shooting Systems
Gives immediate feedback on connector
Guarantees Long Term Performance of System
In summary, interferometric testing is critical for high performance fiber optic connectors. It can be used in the factory or in the field for quality control, quality assurance. The immediate feedback on connector endface geometry is ideal for trouble shooting problems in a system. The use of interferometry guarantees long term performance of the fiber optic network by meeting the recognized standards in the industry.

34. For the Best Connectors
Connect-Chek 6000
From Norland Products Inc.