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Fusion Splicing Basics (Part 1): Fiber Alignment

This blog is the first 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 it comes to ensuring that your fiber network can provide superior performance, utilizing fusion splicing offers many distinct advantages over mechanical splicing. Fusion splicing consists of aligning and permanently fusing stripped, cleaned and cleaved optical fibers with a high-temperature arc.Mechanical splicing utilizes an alignment device and index-matching gel with a similar refractive index and covers the possible air gaps, helping light travel from one fiber to another. Because mechanical splicing simply “holds” the spliced fiber ends together, the typical insertion loss can be higher than a fusion splice which provides a continuous connection between two fibers.From splice-on connectors to pigtails or installation and repair for direct cable-to-cable splicing, fusion splicing provides overall better performance and better protection from signal failure. As mentioned, fusion splice losses are typically lower and are not subject to the environmental limitations of mechanical splices. They provide a fast, reliable, low-loss connection with the lowest loss (in the range of 0.01 dB to 0.10 dB for single-mode fibers) and are practically non-reflective. While fusion splicing does offer the most benefits for performance, their ability to provide this performance in a variety of environmental settings is what makes them so versatile and a must-have for fiber network installs.Fusion splicers are typically used in the field or within a Lab/OEM environment. While you may use many splicers in either environment, some splicers are designed for specific performance environments. Two fiber alignment techniques are:- Passive Alignment (Single-axis)- Active Alignment (Multi-axis)  Passive Fiber AlignmentPassive alignment systems do not move the fibers in the x or y axes but move the fibers in the z-axis only (single-axis).You should use this technique in fixed v-groove machines.Fiber alignment is dependent on how the fibers are positioned relative to each other in the precision-cut grooves in the x and y axes. To achieve a good quality splice, you must align the two fiber ends correctly.The cleanliness and good condition of the v-grooves are essential to ensure that the fibers are positioned in the v-groove to allow the proper alignment necessary for a good quality splice. Active Fiber AlignmentActive alignment systems detect and compensate for any fiber misalignment, moving the fibers in the x, y and z axes (multi-axis). Active alignment methods fall within one of the following categories: 1. Local Injection and Detection (LID) SystemThe LID system aligns and monitors the fusion splice with an optical transmitter and receiver. It allows for the cores to be optimally aligned. A source (transmitter) injects a light signal into the fiber through a bending coupler, and a power meter (receiver) measures the received light signal through another coupler. When the transmitted signal is at its maximum level, both fiber cores are perfectly aligned.The transmitted signal from the LID source is present throughout the process, allowing effective control of the splicing process. The LIDTM system provides a splice loss measurement after the splice is complete by comparing the post-splice light level to the pre-splice level.2. Core Detection System (CDS)Another active alignment method, the CDS, uses the luminescence properties of optical glass. The core and the cladding of optical fiber have different optical properties. For example, the fiber core glows brighter than the cladding when an arc is applied to the fiber due to its different doping. To detect the core, a short arc fires, allowing the core-cladding-contrast to be detected.3. Lens-Profile Alignment System (L-PAS)With an L-PAS method, an optical system consisting of cameras, lenses, prisms, and LEDs makes the fiber visible. The fiber image is generated by a backlit arrangement, using LEDs that shine through prisms that project the fiber’s shadow through lenses onto a camera. Analyze the fiber alignment by comparing the positions of the two fibers. The system “sees” mainly the cladding, producing alignment using the relative cladding diameters.4. Profile Alignment System (PAS)The PAS works on the same principle as the L-PAS system, except that in addition to “seeing” an image of the cladding, focus lenses also allow an image of the core to be detected.  5. Fiber Splicer ConsiderationsWhen choosing the right fusion splicer for a particular application, it is crucial to take into consideration some of the following aspects: Loss Requirements : Determine the loss requirement of the application. Active core alignment splicers provide more precise and lower loss results than passive alignment systemsValue : In general active alignment units are more expensive; however, they typically provide lower splice loss and can be used wherever a passive alignment unit can. It is essential to determine what application you will most often use and match those needs to the correct fusion splicer.Features and Ease of Use : These are necessary to consider when choosing your splicer. They increase productivity and allow various skill levels of personnel to use the machine. Combination-style splicers combine multiple tools within a single chassis versus standard splicers grouped with other tools such as strippers and cleavers.Alignment Methods : Splicing 250 um fiber and 200 um fiber leads to challenges of adequately holding and aligning the fiber. Using the correct fiber equipment holders and clamps will allow the fiber to be captured and presented in the V-grooves.

Jan 21, 2024

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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