Methods of Removing Golden Coating on Fibers in Polarization Controllers

Luna uses a special coating on single-mode fibers to enhance the performance and increase the reliability of its fiber squeezer-based polarization controllers. This coating cannot be removed with mechanical fiber stripping tools. The following methods are recommended for removing the coating for connectorization or fusion splicing purposes:

1. Thermal Methods

1.1. Open Flame

Materials Required:
- Naphtha lighter or oxy/hydrogen flame
- Nonabrasive wipes (e.g., Kimwipes)
- Solvent (isopropyl alcohol or acetone)

Procedure:
1. Ignite the lighter or torch and pass the fiber through the center of the flame at a rate of about 1 inch per second. Be careful not to dwell too long, as a burned fiber becomes very brittle.
2. Inspect to ensure the coating has been completely carbonized.
3. Carefully wipe off the soot from the fiber using a solvent-soaked Kimwipe by pulling the fiber in a straight manner with moderate pressure. Repeat until clean.

1.2. Electric Coil Heater

Materials Required:
- Coil heater
- Nonabrasive wipes (e.g., Kimwipes)
- Solvent (isopropyl alcohol or acetone)

Resistive wires wrapped around an insulating tube can create a coil heater capable of rapidly burning off the coating. However, be cautious not to touch the glass, as this may damage the surface and make the fiber brittle.

1.3. Electric Arc

Materials Required:
- Fusion splicer or another electric arc source
- Nonabrasive wipes (e.g., Kimwipes)
- Solvent (isopropyl alcohol or acetone)

Procedure:
1. Mount the fiber in the fusion splicer.
2. Determine the splicer setting by varying the time, power level, and fiber position. The setting should remove the golden coating without melting the glass.
3. Carefully wipe the fiber using a solvent-soaked Kimwipe by pulling the fiber in a straight manner with moderate pressure. Repeat until clean.

Note: There may be redeposition elsewhere on the fusion splicer. Fusion splicers using optics for alignment and positioning are not recommended, as redeposition may contaminate the optics.

2. Chemical Method

Materials Required:
- Concentrated reagent-grade sulfuric acid
- Deionized water

Procedure:
1. Place a small amount of sulfuric acid into a test tube or other small container and heat the acid to 125–135°C.
2. Dip the fiber into the hot sulfuric acid for about 1 minute until the coating is removed.
3. Rinse the fiber with deionized water. Inspect for any residual coating and repeat steps 2 and 3 if necessary.

Note: Compared to thermal methods, the chemical method has the advantage of not embrittling the fiber.