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- An optical fiber that has been connectorized using an FC connector is shown in Figure 2 for reference.
Step 1: Clean Fiber Optic Connectors
Place the fiber optic connectors in a beaker or large container and fill with enough reagen-grade isopropyl alcohol to completely cover the connectors. Let
the connectors soak for a few minutes. After soaking, remove the connectors and place on a clean, dry surface. Shake any excess solvent off of the connectors, and place them aside to let the remaining solvent evaporate.
After the connectors have completely dried, inspect the ferrule to verify the capillary, which holds the optical fiber, is clear and free of debris. A light source may be used to facilitate inspection of the ferrule. Light should be clearly visible at the front of the ferrule when the light source is placed at the backside of the connector. Any debris should be removed either by resoaking the fiber or using clean, compressed air to gently flush out the ferrule. This holds true for both single and multimode connectors. Debris in the ferrule may interfere with the insertion of the optic fiber into the connector.
Step 2: Add Strain Relief Boots and Crimp Sleeves
Slip a strain relief boot and crimp sleeve included with the fiber optic connector onto the end of the furcation tubing as shown in Figure 3. The boot and sleeve may be secured using some tape.
Note: Furcation tubing should be selected based on the diameter of the fiber being connectorized and the application. Visit www.thorlabs.com for a wide selection of furcation tube sizes and colors. The most common furcation tubing sizes are Ø900 μm, Ø3 mm, and Ø3.8 mm.
Step 3: Cut Furcation Tubing
The furcation tubing forms the outer jacket of the completed cable, which protects the optical fiber. Figure 3 shows furcation tubing that is comprised of a PVC outer jacket, Kevlar protective threading, an
inner tube, and a nylon pull string. The furcation tubing should be cut so that it is approximately 26 mm longer than the desired length, allowing 13 mm per end to be stripped prior to insertion into each connector. Kevlar Scissors (FS-107) can be used to easily cut through the protective Kevlar threads.
Step 4: Prepare Furcation Tubing
Strip one end of the furcation tubing using a stripping tool, exposing approximately 13mm of Kevlar threads and inner tubing as shown in Figure 4a. Take care not to damage the inner tube or remove too much of the Kevlar threads.
At this point, the Kevlar threads and inner tube should extend approximately 13 mm from the end of the furcation tubing. Trim the inner tube back so that it is the same length as the outer tubing, as shown in
Figure 4b. Repeat this step for the opposite end of the furcation tubing.
Note: The exact length of the Kevlar threading that should be exposed depends on the connector type
being used. Please refer to the length dimensions in Figure 5 for other connector styles.
Step 5: Inserting the Optical Fiber into the Furcation Tubing
The standard Ø3 mm and Ø3.8 mm furcation tubing (Item # FT030 series or FT038, respectively) have nylon pull strings, which aid in inserting small-diameter (usually SM) optical fibers into the inner
tubing. Rigid or larger fibers generally do not require the pull string for insertion into the inner tube. If the pull string will be utilized, the optical fiber should be trimmed so that it is at least 13 cm longer
than the furcation tube length. Prepare the pull string and fiber by cleaning both ends with isopropyl alcohol. Using a quick cure adhesive or epoxy, secure the fiber and pull string together and allow
enough time to dry or cure. Make sure the adhesive is completely dry and the bond between the fiber and pull-string is strong before trying to pull the fiber through the inner tubing. Talcum powder will help
dry the adhesive if it remains tacky.
With the furcation tubing pulled straight, gently pull the pull string and fiber through the inner tube. As the fiber is drawn into the inner tube, make sure the fiber does not get caught or knot up inside the
tubing. Be careful not to pull too quickly or too hard as the fiber or fiber/pull string bond may break. Inaddition, take care not to pull too much fiber through the inner tube leaving no fiber at the other end.
Optical fibers with larger diameters are usually rigid enough to push through the inner tube and do not require the pull string. If the pull string will not be used, it may be removed. The fiber should be
trimmed so that it is 80 mm longer than the furcation tubing. It may then be inserted into the furcation tubing so that 40 mm of fiber protrudes from each end.
Step 6: Trim and Strip Fiber to Length
The optical fiber needs to be trimmed and stripped so that approximately 10 mm of stripped fiber protrudes from both fiber optic connectors. The total length of the optical fiber must also be controlled
to allow proper assembly at both ends of the cable. Using Figure 5 as a guide, trim and strip the fiber so that specified amount of stripped fiber protrudes out of each end of the furcation tubing.
A sample FC-connectorized optical fiber is shown in Figure 6. Note the length of the exposed fiber, cladded fiber, Kevlar threading, and inner tube.
Please note that the values in Figure 5 are approximate and assume crimp style connectors are used to attach the connectors to the furcation tubing. The actual fiber length may vary depending on the
individual connector manufacturer.
Choose a fiber stripping tool whose cladding and coating ranges are compatible with the fiber being connectorized. Adjust the amount of coating to be stripped by setting the stripper slider
bar; the scale on the right handle allows a prescribed length of fiber to be stripped. For best results, remove the fiber optic jacket in a series of 3 mm to 7 mm pieces. See Appendix A for a full description
of the fiber stripping tools offered by Thorlabs. Also, see the Note in Appendix A for specialty fibers.
Hint: Acetone may be used on silica/silica fibers to soften the acrylate jacket prior to stripping. Only the length of fiber to be stripped should be placed in acetone for a few minutes. If stripping is difficult,
repeat the soaking process.
Warning
Acetone should only be used on glass fibers. Many of the special coatings on multimode fibers are damaged by acetone.
Step 7: Clean Optical Fiber
Some of the fiber cladding and/or buffer will remain on the fiber after the fiber is stripped. Remove this material by gently wiping the fiber with a Kimwipe moistened with reagent-grade isopropyl alcohol.
Any debris left on the optical fiber will prevent proper insertion of the fiber into the ferrule.
Step 8: Test Fit the Optical Fiber and Connector
At this point, the optical fiber and connector should be tested (without any epoxy) to ensure that the fiber fits into the connector and the length of exposed fiber is sufficient for connectorization.
After the solvent has evaporated from the fiber, slip the stripped fiber into the back end of the connector, as shown in Figure 7a. Slowly rotate the connector as the fiber is gently pushed through the ferrule. See
Appendix B, troubleshooting, if the fiber does not easily pass through the connector. About 10 mm of stripped fiber should protrude from the tip of the ferrule.
Figure
Slip the furcation tubing into the back end of the first connector. The Kevlar threads should fan around the connector as shown in Figure 7b. Press the connector fully against the furcation tubing, and slide the
crimp sleeve over the connector and Kevlar threads as shown in Figure 7c. Repeat this step for the other end of the cable.
If the fiber does not protrude 10 mm from both ends, after both connectors are seated against the furcation tubing, remove the connector from one end and adjust the length of the stripped section of the fiber and/or adjust the length of the furcation tubing. Remove the connectors and set all the pieces aside.
Special Note: Many large-core-diameter fibers will not fit inside the furcation tubing’s inner tube. When connectorizing large-core-diameter fibers, remove the inner tube and Kevlar threads and slide the
optical fiber into the outer jacket of the furcation tubing. Figure 8 shows a large-core optical fiber (Item# SPCH1000) with SMA connection (Item # 11040A). The black rubber boot was trimmed so that it fits
around the furcation tubing.
Step 9: Prepare the Epoxy
For general purpose use on silica fibers, the F112, 2-gram epoxy BI-PAX is recommended. If you are using a TEQ-coated fiber or any other fibers that are not made exclusively of glass, we recommend the
F123 Epoxy. Call Thorlabs for details. The F112 Epoxy has a working life of about 30 minutes and does not require a curing oven.
Remove the separator bar on the epoxy BI-PAX, and mix the two parts by rubbing the package on the edge of your work table for one minute as shown in Figure 9. Take special care not to burst the epoxy
package while mixing.
After thoroughly mixing the epoxy, cut off the corner of the BI-PAX in preparation for loading the syringe (Item # MS403-10). With the syringe tip firmly threaded onto the syringe body, add the mixed epoxy to the syringe. Once the epoxy has been loaded, insert the syringe plunger and invert the syringe. Leave the plunger positioned in the vertical position until the epoxy settles on the rubber piston; then slowly press the plunger into the syringe body expelling the trapped air through the needle. Continue pressing the plunger into the syringe until only epoxy is expelled. Wipe off any excess epoxy from the tip.
The epoxy in the syringe will now have a useful working time of about 30 minutes for large-core multimode fiber and about 15 minutes for single mode fiber, since single mode fiber is generally not as rigid as multimode fiber.
Step 10: Add Epoxy to the Connector
Insert the syringe into the back of the connector until it bottoms out within the connector. While pressing the syringe plunger, maintain pressure between the syringe tip and the connector body. This pressure will ensure the epoxy injected into the connector flows mainly into the ferrule hole, rather than filling the rear area of the connector (see Figure 10). Continue injecting epoxy through the connector ferrule until a small bead appears on the outside face of the connector ferrule.
Step 11: Insert Fiber into Epoxied Connector
Slide the fiber out of the furcation tube about 50 mm. Push the connector onto the fiber while slowly rotating the connector. This helps to both funnel the fiber into the connector and evenly distribute the
epoxy between the fiber and the connector ferrule. Check for fiber breakage by sliding the connector back and forth, ensuring that the protruding fiber moves in and out of the connector. If the fiber breaks,
clean the connector with a wire cleaner (Item # WC100).
Step 12: Fully Seat Connector
With the back end of the connector seated against the furcation tube, slide the crimp ring over the back end of the connector and the Kevlar threads as shown in Figure 11.
Step 13: Secure Crimp Sleeve
With the connector seated against the PVC jacket and Kevlar, use the 0.178" hex section of the crimp tool die (Item # CT042) to crimp the sleeve in two locations as shown in Figure 12.
Step 14: Examine Epoxy Bead
The end of the connector must have a sufficient bead of epoxy to support the end of the fiber during polishing. Visually compare the connector end to Figure 13. If there does not appear to be sufficient
epoxy dab on a small amount.
A short section of scrap fiber is ideal for applying epoxy since it is rigid enough and large enough to pick up a small bead of epoxy; at the same time, it is flexible enough to minimize the danger of breaking
the fiber that protrudes through the connector.
Step 15: Secure the Strain Relief Boot
Add a small amount of epoxy where the crimp sleeve meets the furcation tubing, as shown in Figure 14. Slide the boot up onto the connector, leaving a small gap between the connector shell and the relief boot
Note: Be careful not to apply too much epoxy in the sleeve/relief boot area, as excess epoxy on the boot can cause the boot to inadvertently adhere to the connector shell. The connector shell must move freely for the cable to operate properly.
Step 16: Check the Fit of the Second Connector
Test the connector on the second end of the fiber. The stripped section should protrude about 10 mm from the tip of the connector. If the fiber is too long, it may break during installation of the final connector. Trim the fiber to size, and strip enough of the fiber so 10 mm of stripped fiber protrudes from the ferrule.
Step 17: Connectorize Second Connector
Repeat Steps 10 – 15 for the second connector.
Step 18: Epoxy Curing
If the F112 epoxy was used, allow the cable assembly to cure overnight. The curing process can be accelerated by heating the connectorized ends of the cable. Refer to Appendix C for a list of commonly used epoxies, their pot lives, and respective curing times.
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