Products

Fusion Splicing Basics (Part 2): Strippers and Cleavers

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.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 StrippingCoating StrippersRegardless 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.  Mechanical StrippingWith 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 StrippingThermal 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. Mechanical Stripper (left) vs. Thermal Stripper (right) Chemical StrippingChemical 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 StrippingArc 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. CleaversTo 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 CleaversSingle-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.ConsiderationsIt 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: 1. Both the fiber and cleaver must be clean.2. The blade must be kept and maintained in good condition. Many systems now use an auto-rotation blade to extend blade life or onboard monitoring to track lifetime performance and notify the operator that a blade change is necessary.3. The proper operating technique must be followed.  Splice ProtectionAfter 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 before 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. 

Jan 21, 2024

Products

Fusion Splicing Basics (Part 3): Methods, Practices and Testing

This blog is the third and final in a series of blogs that 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. Methods and Practices — Single Fiber SplicingThe preparation process before inserting the fiber into the splicer is very important. Optical fibers must have the coating removed down to the bare glass. The fibers must be cleaned properly and must have a good quality cleave. It is important to be aware of and use the correct cleave length for the particular fusion splicer that is being used.This length varies with splicer manufacturers, so it is recommended to consult the operating manual for the specific unit before beginning the splicing process. The three main steps to preparing the fiber are as follows.  Step 1: StripAll coatings (900 μm, 250 μm, and/or 200 μm) should be removed and bare glass exposed.Step 2: CleanThe bare glass should be cleaned to remove all contaminants. The most common cleaning method is to use a clean lint-free wipe saturated with 99% isopropyl alcohol. This wipe is pulled over the bare glass removing any acrylate coating and other contaminants that may be on the bare glass.It is important to ensure that the glass is not touched with the bare fingers or contaminated with anything after the cleaning step, as this can adversely affect the cleaving, alignment, and fusion process. Non-alcohol low-residue cleaners are increasing in popularity and can also be used.  Step 3: CleaveThe cleaving of optical fibers involves several processes. The fiber is inserted into the cleaver after being cleaned. The cleaving process is achieved through a combined movement of scoring and breaking. Both fiber ends can then be inserted into the splicer and are ready to be spliced together. The fiber’s end face quality affects the final splice result. The better and cleaner the fiber end faces are, the lower the splice loss that can be achieved.Methods and Practices — Multiple Fiber (Mass Splicing)Multiple fibers may be spliced together simultaneously. This is commonly referred to as mass splicing. Mass fusion splicing is the same in principle as single-fiber splicing. There are some differences in the process. Mass fusion splicers use the passive alignment system with a fixed v-groove.The fibers can be in ribbon form, ribbonized by the craftsperson from individual fibers, or loose when used in combination with specialized holding equipment. The multiple fibers are stripped — usually with a thermal stripper — cleaned and then cleaved simultaneously to ensure the fibers are the same length.The fibers are inserted into the fusion splicer and the process is essentially the same as with single-fiber splicing. The splice point can be protected with heat-shrink sleeves.Multiple ribbon types of different spacings (200 / 200 μm, 250/250 μm, 200 / 250 μm, etc.) require the usage of correct ribbonizing methods and equipment holders to correctly position the fibers and reduce splice loss.   Factors That Affect Splice LossCleanliness The fibers and equipment must be clean. Dirt and contaminants can cause (1) misalignment issues, (2) increased loss and (3) degradation of equipment.Fiber Geometry The position of the core relative to the center of the fiber will affect splice loss. If fibers with eccentricity offsets are being spliced, active core alignment units will provide the best splice loss results.Equipment: It is important to use the correct equipment for the specific application and ensure it is used and maintained correctly.Proper maintenance of mechanical and optical systems on fusion splicing equipment is necessary to ensure it functions correctly and provides future use. The use of appropriate holders and/or clamps for the correct fiber type supports lower fiber loss.Training/Skill LevelFusion splicing requires proper training and personnel development to obtain consistent good quality low loss splices. The Importance of TestingA typical loss value is usually less than 0.1 dB (in single-mode fiber). It’s important to test optical fiber systems to: - Verify the system works correctly- Ensure splices are acceptable- Identify problems- Provide a baseline for maintenance and troubleshooting  Testing MethodsAn optical fiber system can be tested using- A power meter/source-An Optical Time Domain Reflectometer (OTDR) The meter/source method tests the entire system. It determines end-to-end loss including any components and fiber in the system. This is a good way to get actual values for the entire system; however, it does not allow individual splices or components to be singled out.  The Swift Test product line from UCL Swift consists of six Fiber Optic Test Equipment Kits, designed to accommodate both your budget and network testing requirements. The OTDR operates on a principle known as Rayleigh backscatter. Light is input into one end of the system. A certain amount of light is reflected from events. Events can be fusion splices, connectors, mechanical splices, etc. The OTDR interprets these events and determines where they are located along the fiber and the attenuation value.This can be used to verify specific splice loss values and where they are located in the system. This information can be saved for documentation proposes and validation of the system.OTDR analysis is limited by the resolution of the device being used. This limitation is exhibited by the minimum measurement distance between events that can be determined. Unfortunately, for most splice-on connectors the distance between the splice and the connector end face does not allow the OTDR to measure both events; rather it will show a single event with represents a combination of the splice joint and the connector end face. As technology advances, new equipment and techniques will be created and utilized in the fiber industry. For example, laser cleaving has become more popular in the connector sector but has not yet entered the splicing field. The innovation is in the early stages in the fiber optic domain. But with a thorough understanding of these splicing basics, you’ll be ready for what’s on the horizon.

Jan 21, 2024