You will need:
In addition to the equipment already specified:
Rubber polishing pad
5 micron diamond polishing film
1 micron diamond polishing film
Polishing slurry or alcohol
Optional: nylon polishing pucks - one for each grade of diamond polishing film
Background
Because the core diameter
of singlemode fiber is only 9 microns compared to the 62.5 micron
diameter of multimode fiber, minute scratches and alignment become
more critical in singlemode connectors. In some singlemode applications,
e.g. low speed data, there is little concern over return loss
or back reflection. In these situations using multimode polishing
techniques on the singlemode connector is acceptable. When return
loss is a concern, the polishing technique must be changed from
that used with multimode connectors.
A rubber pad is always used on the polishing surface to present
a soft surface to the connector. This helps give the ferrule
a convex-shape and provide a physical contact (PC) connection
when mated with another connector.
The connector is "wet" polished on a diamond grit lapping
films. Alcohol or a polishing "slurry" acts as a coolant,
lubricant and also helps keep the lapping film clean. Diamond
grit used instead of aluminum oxide lapping film. When using
the aluminum oxide paper the fiber is polished away at a faster
rate than the ferrule. This can actually leave the fiber recessed
in the ferrule. The diamond grit will polish away ferrule material
along with the glass fiber to leave a clean, convex, physical-contact
connector.
The same deburring method is used as in multimode polishing,
air polish with 12 micron aluminum oxide polishing film. After
deburring, the connector is placed in a plastic/nylon polishing
puck or a stainless steel puck. The diamond grit will grind stainless
steel away shortening the life of the polishing film. For highest
surface finish, it is sometimes recommended that a nylon puck
be dedicated to each grade of polishing film. The connector is
polished in a "figure O" pattern. The "figure
O" will give a more thorough polish and help give the connector
the proper convex shape.
Cable Preparation and Connector
Attachment
Follow the directions for the connectors and adhesive (epoxy
or anaerobic) being used for the termination. These processes
are exactly the same as multimode fiber.
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- Polishing For Low Loss and Back Reflection
Singlemode polishing is normally done with an "air polish" to remove the fiber left after cleaving, a first polish on 5 micron diamond film and a final polish on 1 micron diamond film. This should yield -30 dB back reflection (30 dB return loss. If better back reflection performance is needed, a final polish with 0.3 micron diamond film is used.
To achieve the scratch-free polished needed for a low return loss and low insertion loss singlemode connector, follow these directions.
Cleave the fiber
Air polish the fiber
Place soft rubber pad on the polishing plate.
Place the diamond polishing film on the rubber pad and wash the film with alcohol.
Wash the polishing puck with alcohol
Gently place the connector in the puck and carefully lay it on the polishing film.
Use a few drops of alcohol or polishing slurry as a polishing lubricant and sweep the fixture across the film in a "figure O motion. Place only moderate pressure on the connector as you polish.
When changing to a finer grit polishing film; remove the connector from the puck, wash it with alcohol and/or insert it into the other cleaned puck reserved for the finer grit.
After every 5-10 connectors wash the polishing puck with a small brush and alcohol and replace the film.
Inspect the connector with a microscope for end finish
Test with power meter and source per FOTP-171 for loss and FOTP-107 for back reflection if required.- Inspection of SM Connectors
- Besides high power microscopes (200-400X), interferometers are used to profile the end of the fiber.
- The rings on the image to the left show the centering of the polished dome of the connector and the shape. The 3D image shows the undercutting of the fiber below the ferrule.
- Polishing For Low Loss and Back Reflection
