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 an 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 Alignment

Passive 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 Alignment

Active 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:


Local Injection and Detection (LID) System

The 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.


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.


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.


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. 


Fiber Splicer Considerations

When 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 systems.
    • Value — 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 allows 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.


Combination vs. Standard Style Arc Fiber Splicer UCL Swift

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