This blog is the second in a series that will overview fusion splicing equipment and methods, particularly those of interest to the cable/broadband industry. Information to support this series was sourced from Fusion Splicing Equipment and Applications for the Cable/Broadband Industry (SCTE 134 2021) — an SCTE Standard authored by UCL Swift Fiber Optic Engineer Rich Case.
Miss the first part? Catch up:
When performing a fusion splice, the optical fiber must be stripped down to the bare glass. Various techniques can remove the coating:
- Mechanical Stripping
- Thermal Stripping
- Chemical Stripping
- Arc Stripping
Regardless of the method used to strip the coating, it is important to use the correct tools and techniques to prevent damage to the bare glass. Ensuring the fiber is not damaged is critical to creating a low loss, strong splice.
With mechanical stripping, the coating is removed using a tool that physically “shaves” the coating off. This may be accomplished by machining the tool with a precise profile to match the fiber itself. Advantages are that it is fast and inexpensive, usually found in various hand tools (typically used for single-fiber applications). Disadvantages include reliance on skilled operator technique and potential for scratching the glass due to physical contact with the tool surfaces.
Thermal stripping uses heat to soften the coating before removal. Heating the coating allows much easier removal and lessens the possibility of physical damage to the glass itself. Thermal stripping can be used with single-fiber splicing but is typically used with multi-fiber splicing since it simultaneously strips up to twelve fibers. Thermal stripping is usually more of an automatic process (the equipment does most of the work) and is more friendly to a novice operator.
Chemical stripping uses the application of a chemical to soften the coating, possibly causing it to blister. This allows the material to be wiped away and removed. Care must be taken so that the chemicals used are not harmful to the glass or the operator applying them.
Arc stripping removes the coating using a high-temperature arc plasma, similar to the arc generated during the splicing operation. Care must be taken to avoid thermal shock to the fiber during the stripping process.
To achieve good splice results, it is vital for the fiber ends to be properly cleaved. Consistent, good-quality end-faces can only be achieved if the cleaver is well maintained. Cleave angle deviations or chips and knicks in the end-face can only be compensated for by using unusually high fiber feed during the fusion process. This can create a splice with an outer cladding that may look good, but the actual loss could be increased due to core bending. For best results, the smaller the core (i.e., single-mode fiber), the lower the tolerance of cleave angle deviation.
Various cleavers are available that operate in different ways, but the general principles for cleaving the fiber are:
- Score – A score is introduced into the glass.
- Bend – The glass is bent to propagate the score.
- Tension – Tension is applied to separate glass.
Types of Cleavers
Single-fiber cleavers are designed to cleave one fiber at a time and provide a high-quality end-face angle that leads to low-loss splices. Most multi-fiber cleavers can cleave multiple or single fibers. In many instances, a different handler or adapter may be necessary to accommodate single fiber cleaving.
It is important to consider several aspects when choosing a cleaver for a particular application as with fusion splicers.
- Performance – A good cleave is essential to obtain good low-loss splices.
- Usability – Ease of use is important for users and in obtaining consistent, high-quality results.
- Quality of Cleave – To obtain quality cleaves from a cleaver, keep these things in mind:
- Both the fiber and cleaver must be clean.
- The blade must be kept and maintained in good condition. Many systems now use an auto-rotation blade to extend blade life or use onboard monitoring to track lifetime performance and notify the operator that a blade change is necessary.
- The proper operating technique must be followed.
After the fibers have been successfully spliced together, it is important to protect the joint. There are various options for splice protection. One of the most common techniques is a heat shrink sleeve. This sleeve is placed over the fiber prior to splicing and placed away from the splice point during preparation and fusing. After the splice is complete, the heat shrink is placed over the splice point. It is then placed in a heat shrink oven, where the material is heated and shrunk down over the fiber, protecting the joint.
Clamshell-type protectors are also available. These protectors commonly have a hinged joint that allows it to be placed on the splice point after completing the splice. Most versions use adhesive to hold the fiber in a groove while the other half of the “clamshell” is closed on the fiber that is holding and protecting the joint.