FiberOptics_03_Workmanship

Preparation for Cable Termination

The optical fiber outer jacket, strength member, inner jacket and fiber coating components are prepared for the bonding process by stripping and cleaning.

Cut the required length of cable off the spool. In order for the finished length to be correct, an additional 6 inches should be added to the required length to accommodate a bend that must be put in the end of the cable to hold the optical fiber in place during the first termination process.

Removal of Outer Jacket:

  1. Using a felt tip pin, make a mark on the outer jacket in accordance with the strip dimensions for the termination being performed.
  2. Using an outer jacket stripper, position the cable between the tools jaws until the tool’s blade is on the measured mark.
  3. Allow the tool to close gently (DO NOT FORCE) around the outer jacket.
  4. Rotate the tool 360 degrees around the cable. DO NOT ROTATE THE CABLE.
  5. Open the tool and remove the cable without stripping away the outer jacket.
  6. Pinch the outer jacket with your fingertips, on opposite sides of the scored area, using both hands, as close as possible to the score.
  7. Bend the cable slightly at the scored area to break the outer jacket free.
  8. Remove the cut portion of the outer jacket.
  9. Using ceramic scissors, trim the strength members’ flush to the outer jacket. This will insure a uniform length necessary for achieving a proper fit on the connector.
  10. Using a felt tip pin, make a mark on the outer jacket in accordance with the length of the strength members for the termination being performed.
  11. Using the outer jacket stripper, position the cable between the tools jaw until the tool’s blade is on the measured mark.
  12. Repeat steps 2 through 7.
  13. Straighten and comb out the braid of the exposed strength member by hand.
  14. Slide a pre-cut scrap piece of 1/8” diameter heat shrink tubing, down over the inner jacket so that all of the strength member filaments are on the outside of the tubing. Continue sliding the tube down, folding back the strength member filaments against the outer jacket to approximately 1/10-inch past cut edge. This keeps the strength member filaments pulled tightly back out of the way for the next operation.

Removal of Inner Jacket:

  1. Open the stripping tool and insert the cable’s inner jacket between the triangular portion of the tool’s jaws until the first triangular piece contacts the cable’s folded strength member.
  2. To cut the inner jacket, apply a slow light steady pressure to the tool handle until the tool stop is felt and a slight click is detected. This click is produced by the tool itself. Do not over-squeeze the handle as damage to the tool and cable can result.
  3. Do not rotate the tool or cable.
  4. Open the inner jacket stripper tool without stripping away the inner jacket.
  5. Using both hands, pinch the inner jacket with your fingertips as close to the cut as possible.
  6. A quick pull in opposite directions will separate the inner jacket at the scored area. If the inner jacket does not separate at the scored or cut area and tends to stretch, the stripper tool blades may be dull or damaged.
  7. Inspect the fiber coating for any nicks or cuts. Because of the extremely small dimensions between the inner jacket and the fiber coating, the inner jacket stripper tool compresses the fiber coating slightly during the stripping operation. This slight compression should not be confused with a fiber coating nick. The compression in the fiber coating relaxes back to the original fiber coating diameter after a short period of time.

Fiber Coating:

  1. Determine the length of stripped fiber required for the type of termination being performed. Place a mark on the fiber coating with a felt tip pen.
  2. The chemical strip must be shaken thoroughly before each and every use to ensure proper chemical action and stripping times. Shake the chemical strip in a securely capped container for about 1 minute prior to use.
  3. Insert the fiber into the chemical stripper (a small beaker of methylene chloride) up to the mark. Make sure not to insert past the mark or insert the strength member filaments into the chemical stripper.
  4. Hold the fiber in the stripper for a minimum of two minutes.
  5. Remove the fiber after the appropriate time has elapsed and proceed immediately to the next step so that the softened fiber coating does not dry out which will make it difficult to remove.
  6. Hold the fiber coating firmly with one hand and with the other holding a shop wipe moistened with cleaning solvent, grasp the softened end and pull gently in opposite directions.
  7. If the fiber coating does not come completely off easily, place back in stripper for an additional one-minute.
    • Note: The strength of the chemical strip will vary over time, particularly after it has been used for many stripping operations and after it has been exposed frequently to air. If the coating is not easily and completely removed after two immersions in the chemical strip, the chemical strip is weak and must be discarded.
  8. Using Shop wipes and IPA solvent, remove all residue stripper from the fiber.
  9. Inspect with a microscope at 50x minimum to insure all fiber coating has been removed and that there are no nicks on the outside of the fiber and no wicking of the stripping solution has occurred.
  10. Slide a pre-cut piece of heat shrinkable tubing over the cable’s stripped strength members.
  11. Rinse the cable’s fiber coating using a beaker of cleaning solvent. Immerse approximately 0.25 inch of the fiber coating into the cleaning solvent for 1 minute.
    • Be careful not to let the inner jacket touch the solvent as solvent may wick up the cable and not dry out in time for the bonding operation.
  12. Remove the coating from the solvent and wipe with a dry shop wipe.
    • This step flushes the fiber coating of chemical strip residue which may be present at the very end of the cable’s fiber coating after stripping.
  13. Remove the scrap piece of heat shrinkable tubing from the stripped cable end.
  14. Using a temperature controlled oven, bake out the fiber coating for 15 minutes at 85 º C. Insert at least 1 inch of the cable’s fiber coating into a middle oven cell.
    • This step ensures that any chemical strip residue in the very end of the fiber coating is baked out thus preventing mixing of the chemical strip and the epoxy.
    • Be careful not to break off the glass fiber by contacting the sides or bottom of the oven.

Inspect the stripped cable end for defects.

Cleaning
Take the following steps to ensure proper cleaning:
  1. All beakers shall be wiped down with clean solvent prior to use.
  2. Using a wipe moistened with cleaning solvent from the solvent dispenser wipe all tweezer surfaces.
    • This eliminates any possible contamination due to dirt or oil.
    • Place the tweezers on a large, clean dry wipe until needed later.
  3. Fill two labeled beakers with solvent as follows: 100ml to beaker #1 and #2.
  4. Place epoxy dispensers (syringes) in beaker #1.
  5. Place in ultrasonic cleaner and operate for five minutes.
  6. Set epoxy dispensers aside on clean shop wipe to dry until used.
  7. When instructed to open the package of the terminus, place all parts in beaker #2.
  8. Place in ultrasonic cleaner and operate for five minutes.
  9. Set all terminus parts aside on clean shop wipe to dry until used.
  10. Cut and pre-clean several pieces of heat shrinkable tubing. Cut several pieces of heat shrinkable tubing to 1.0 inch. Place tubing in ultrasonic cleaner for 5 minutes.
  11. IMPORTANT: Ensure that all cleaned items are completely dry both inside and out by checking them visually before assembly. If there is any doubt whether an item is dry, sniff the item as the cleaning solvent can also be detected by smell (do not touch the item to the nose).
Mix Epoxy

Epoxy Tools

  • Roller & Pad, MXR-1001 (Tracon)
  • Epoxy Bi Pak, BAF-253
  • Pre-Cleaned Syringe & Tip

To mix epoxy, take the following steps:
  1. Lay the pad out on top of the desk (red side up).
  2. Record the following information in the shop log:
    • Epoxy Part No.
    • Epoxy Lot No.
    • Manufacturer’s Expiration Date
    • Date of Entry
    • Operator’s Name
  3. Open the epoxy package.
  4. Remove the plastic clip from the middle and discard the clip. A plastic clip separates the resin from the hardener.
  5. Squeeze the package to start the mixing.
  6. Place the package on the pad and using the roller, roll the package 50 times (forcing resin into binder).
  7. Turn the package over and using the roller again, roll the package 50 times (forcing binder into resin).
  8. By this time the epoxy should be a uniform light green color.
  9. Record the time and operators initials on the epoxy-mixing log.
  10. Set the timer for 1 hour and 15 minutes. This is the pot life for the epoxy.
  11. Place the unopened epoxy package in the centrifuge and turn on for 3 minutes.
  12. Cut the package open and pour the epoxy into a pre-cleaned syringe.
  13. Insert the (epoxy) dispenser piston and plunger assembly into the barrel reservoir containing the mixed epoxy.
  14. Push on the dispenser plunger so that the piston completely compresses the epoxy and expels all trapped air in the barrel reservoir. Continue to push the plunger until all trapped air is expelled, including any bubbles that may have been produced, so that only epoxy is discharged from the tip.
  15. The epoxy is now ready for use. Place the assembled dispenser filled with epoxy on a clean, dry wipe. The color will change to dark green as it stands.
Connector Assembly
  1. Once cured, scribe the fiber with a carbide wedge scribe to remove the excess fiber.
  2. Place the scribe’s tip so that it is resting flat on the face of the terminus ferrule.
  3. Hold the scribe at an angle of approximately 30 degrees up from the terminus so that the scribe’s chisel edge is close to the ceramic face, but not flush with the face.
  4. Let the scribe’s chisel edge contact the glass fiber while continuing to hold the scribe in position.
  5. Score the glass fiber by gently drawing the scribe’s chisel edge lightly, once, across the fiber. Do not attempt to break off the glass fiber during this step.
    • NOTE: This is a very important step in the procedure. If the fiber is inadvertently broken off during this step, it may crack below the required polishing surface (creating a hackle) making the terminus scrap.
  6. Cleave the glass fiber. Grasp the glass fiber between the thumb and forefinger and gently pull the fiber straight away from the terminus until the fiber is detached at the scored area.
Polishing and Inspection

Polishing

  1. Start with the 3-micron grit paper. Wipe paper with a shop wipe soaked in alcohol.
  2. Using the appropriate puck, insert the connector to be polished into the puck.
  3. Holding the puck and supporting the connector, start polishing with a figure 8 pattern.
  4. Repeat the polishing pattern, checking often, until there is just a thin coating of epoxy left.
  5. Remove 3-micron grit and switch to 1-micron grit paper.
  6. Clean the end of the connector with shop wipe and alcohol.
  7. Wipe the paper with a clean shop wipe and alcohol.
  8. Holding the puck and supporting the connector start polishing with a figure 8 pattern.
  9. Repeat polishing pattern approximately 20 times.
  10. Remove 1-micron grit and switch to 0.3-micron grit paper.
  11. Repeat steps 6 through 9.
  12. Clean the end of the connector with a shop wipe and Alcohol.
  13. Inspect at 200x with a Fiberscope.

Inspection

  1. Ensure that the hand-held microscope, lens, and terminus adapter are clean before use.
  2. Attach the terminus adapter to the hand-held microscope.
  3. Clean the polished ferrule/terminus face at least two times using a wipe moistened with cleaning solvent.
  4. Insert the polished connector/terminus into the microscope’s adapter.
  5. Turn the knob on the side of the microscope until a sharp image of the face is achieved.
  6. Acceptance Criteria: An acceptable termination will be free from cracks, scratches, edge chips, hackles, pits and other anomalies with the core clearly discerned.
Testing and Assembly Completion

Note: The optical fiber cable must be terminated on both ends and have passed all acceptance criteria up to this point before beginning this section of the procedure.

Performance verification of a completely terminated optical fiber cable is performed in two steps: (1) Measurement verification of the test setup optical power level, and (2) Optical power loss testing of the completely terminated optical fiber cable assembly referred to as the Unit Under Test (UUT). :
  • The test setup includes an optical light source (850nm), an optical power meter (850nm), reference cables, and the UUT.
  • Optical loss measurements of UUT’s used in spaceflight applications must be made at the same wavelength used under spaceflight conditions.

Reference Measurement

The test setup reference measurement is performed to insure that the UUT optical power loss measurements are repeatable. The reference measurement also ensures that there has been no degradation in the optical transmission properties of the reference cables themselves.
  • Ensure that the optical light source and optical power meter are calibrated.
  • Ensure that the reference cables are labeled. Launch Reference Cable, Receive Reference Cable.
  • Ensure that the 200X hand-held microscope, lens, connector, and launch and receive reference cables are all clean.
  • Inspect the connector/terminus for dirt or debris with the 200X hand-held microscope. Clean with wipe and solvent if necessary.
  • Connect the two reference cables together.
  • Turn on the optical light source, and let the light source stabilize for 1 minute.
  • Read the measured reference power level value from the optical power meter.
  • Record the measured reference power level in the certification log supplement. The power level on the optical power meter should be greater than –18.0 dBm (typically within the range of –17.9dBm to –15.5 dBm). If the reference power level is less than –18.0 dBm, most likely there is a problem in the test setup.
  • Turn off the optical light source and the optical power meter.

Power Loss Measurement

The power loss measurement is performed to verify and determine the optical performance of the UUT.
  • Disconnect the launch reference cable from the receive reference cable.
  • Connect the UUT to the launch reference cable and the receive reference cable.
  • Turn on the optical power meter, and let the power meter stabilize for 1 minute. Verify that the power meter wavelength switch is set to 850nm.
  • Turn on the optical light source, and let the light source stabilize for 1 minute.
  • Read the measured UUT power level value from the optical power meter.
  • Record the measured UUT power level value in the certification log supplement.
  • Turn off the optical light source and the optical power meter.
  • Determine the UUT power loss. Algebraically subtract the measured reference power level value recorded in the certification log supplement from the measured UUT power level value recorded in the certification log supplement. Example:
    • Measured UUT Power Level = -18.5 dBm
    • Measured Reference Power Level = -17.1 dBm
    • -18.5 dBm – (-17.1 dBm) = -1.4 dBm Loss ( Record the UUT power loss in the certification log supplement).
  • Determine the length loss acceptance value.
    • Use the cable length value recorded in the certification log supplement.
    • Round the cable length value to the next highest whole number.
    • If the rounded cable length value is less than 34 feet, use –0.1 dB as the length loss acceptance value: otherwise, calculate the length loss acceptance value by multiplying the rounded cable length value by –0.003dB/foot.