Fiber Optic Mechanical Splices
This article describes the working principle of mechanical splices and different designs. You can get the fiber mechanical splice products here or by clicking on the following picture.
What Is Mechanical Fiber Splice?
Fiber optic mechanical splice performs a similar function to the fusion splice except that the fibers are held together by mechanical means rather than by a welding technique. Mechanical splices somewhat look like fusion splice protection sleeves.
In a mechanical splice, two cleaved fiber tips are mechanically aligned to each other by a special housing. Usually, index matching gel is positioned between the fiber tips to maximize coupling and minimize back reflection.
Advantages of Mechanical Splice
There are some significant advantages of using mechanical fiber splice than fusion splices. Here are a few of them:
- Mechanical splices require no power supplies
- Many mechanical fiber splice designs require no extra tools beyond a fiber stripper and fiber cleaver
- They can be used in situations where fusion splicing is not practical or impossible
- Mechanical splices can be made within a couple of minutes, this makes it ideal for temporary connections
Disadvantages of Mechanical Fiber Splices
Fiber optic mechanical splices have their cons too.
- Higher insertion loss. The typical insertion loss for a mechanical splice is about 0.2dB which is significantly higher than the 0.02dB loss for a typical fusion splice.
- Mechanical splices are typically for multimode fibers. The tough alignment tolerance for single mode fibers makes it hard for mechanical splices to meet
- Mechanical splice is more expensive than fusion splices. But if you take into account the expensive fusion splicing machines that fusion splices need, the average cost is actually much lower for mechanical splice if you just do a few splices.
- Since the refractive index of most index matching compounds varies with temperature, so the optical performance of a mechanical splice can be sensitive to ambient temperature
- Mechanical splices are not thought to be as reliable as fusion splices over long periods of time
- Mechanical splices are used only in relatively benign environments such as inside an office building
Alignment Mechanisms of Mechanical Fiber Optic Splices
The principle of mechanical splice is simple and straightforward. Two fibers are stripped, cleaned and cleaved. They are then aligned and held in position either by epoxy resin or by mechanical clips.
1. V-Groove Type
V-groove has been used widely in aligning optical fibers. The most obvious example is its success in fusion splicing machines. Look at the following illustration.
V-groove is the most commonly used alignment mechanism for mechanical fiber splices. V-groove consists of a base plate in which a precise V-groove is etched.
- Cleaved fibers are placed into the groove and their ends are butt-coupled into contact.
- Index matching gel is used to bridge the gap between the two ends to prevent gap loss and to reduce Fresnel reflection
- A locking mechanism then holds the fibers in position and provides mechanical protection for the fibers
- Index matching epoxy can be used in place of index matching gel. The epoxy is usually cured with ultraviolet light. The epoxy can hold the fibers in place
2. Bent Tube Type
Bent tube design actually uses the same principle as V-groove. A length of fiber is pushed into a tube which is curved, the springiness of the fiber forces itself to follow the outside of the curve. If the tube is of square cross-section, the fiber will follow the far corner. The fiber is now positioned by a V-shaped wall of the tube.
In some designs, the cross-section of the bent tube is circular instead of square.
Index matching gel is added before the fibers are inserted.
3. Precision Tube Type
The precision tube type is very simple and straightforward. A precise hole with a slightly larger diameter than the fiber OD is formed through a piece of ceramic or other material. When a piece of bare fiber is inserted from each end, the two fibers are aligned when they contact.
The disadvantage of this type is that insertion loss is higher than other types. This is caused by the hard to control tolerance of the hole diameter.
