preprocessing stage
Fiber insertion and fixation:
Insert the cut fiber bundle into the MPO core hole to ensure that the length of the fiber is consistent (grinding allowance should be reserved).
Fill the tail of the ferrule with epoxy resin (such as UV glue or hot glue), and fix the optical fiber by curing equipment (UV curing furnace or oven) to avoid loosening during grinding.
Plug cutting:
Use a high precision fiber cutting knife (such as a special MPO cutting knife) to cut the excess fiber at the front end of the plug core flat to form the initial end face.
Coarse grinding stage (removal of allowance)
Purpose: to quickly remove most of the allowance on the end face of the plug, and initially form a flat or curved profile.
Grinding pad: silicon carbide (SiC) material, the grain size is usually 800#~1200# (coarse grinding).
Grinders: Specialized MPO grinders (supporting simultaneous grinding at multiple stations, equipped with an Angle adjustment device).
Operation points:
a circular or 8-shaped trajectory for about 3 to 5 minutes until the fiber end face is flush with the core.
Test: Use a microscope to observe the end face to confirm that there is no obvious notch or resin exposure.
Finishing stage (optimizing surface roughness)
Purpose: To reduce the end face roughness, refine the surface texture, and prepare for polishing.
Grinding pad: diamond (Diamond) coated sandpaper, the grain size is usually 3000#~5000# (fine grinding).
Replace the fine grinding pad, keep the fixture pressure moderate (slightly less than rough grinding), and grind for about 5~8 minutes.
Wipe the grinding pad regularly with alcohol to remove debris and avoid scratches caused by particle residue.
Test: Use an interferometer to measure the end face roughness (Ra value should be <0.2μm), or observe whether there are fine scratches through a 400x microscope.
Polishing stage (formation of final curvature)
Purpose: To form a specific curvature (PC/UPC/APC) at the end face to further reduce the reflection loss.
Polishing pad: polyurethane (PU) or non-woven fabric material, combined with polishing liquid (such as alumina suspension).
Curved tooling: grinding machine should be equipped with curvature control module (such as spherical grinding mold).
PC/UPC grinding: the end face is formed into an arc (the radius of curvature is usually 7~15mm) through the elastic deformation of the polishing pad, and the polishing time is about 10~15 minutes.
APC grinding: polishing is required at an Angle of 8 to form a curved surface, which further reduces the return loss (usually <-60dB).
Testing: Use an interferometer to measure the radius of curvature and vertex offset to ensure compliance with industry standards (e.g. IEC 61754-7).
Cleaning and testing stage
cleaning ：
Rinse the end face with anhydrous ethanol or a special cleaner, and remove small particles with ultrasonic cleaning.
Use a dust cloth or air gun to dry to avoid water residue.
Optical performance test:
Insertion loss (IL): Use an optical power meter or insertion loss tester to test the signal attenuation of the optical fiber link (usually less than or equal to 0.5dB).
Return loss (RL): Measure the intensity of reflected light (PC type is greater than-50dB, APC type is greater than-60dB).
End face microinspection: observe whether there are cracks, dents or contaminants on the end face through a microscope of more than 500 times. Unqualified products should be reworked or scrapped.