After dealing with a lot of the physical background of fiber optics, we consider a few practical aspects: some of the tools and accessories that are often required when working with fiber optics.
Fiber Stripping and Cleaving Tools
In Part 5 on fiber optic ends, we have explained that fiber ends typically need to be stripped and cleaved, and mentioned some commonly used tools. Here is a brief overview:
Common fiber stripping tools look like pliers. When using fiber optic cable , we need to use a stripping tool to cut into the polymer jacket and pull one end of the jacket apart. The tool can also be used to strip the polymer buffer in the last few centimeters of the fiber. (Some strippers are designed specifically for sheath removal or for stripping buffer and smaller polymer coatings). This device is designed to cut into the sheath or buffer coating without damaging the fiberglass inside. In order to avoid damaging the fiber and causing a break, we need to handle it carefully. Residue on the coating can cause problems later, we can also use a pad soaked in alcohol to remove.
Fiber cleaving can usually be accomplished using very simple mechanical fiber cleaving tools. In the simplest case, only a sharp diamond, carbide or ceramic blade (scriber) in the shape of a pencil is used to scratch the fiber and break it with a finger kick. Alternatively, the fiber can be placed on a simple support, held with two fingers, scraped between them, and finally snapped by applying more tension. This simple blade and bracket is included in the Simple Fiber Termination Kit (Prep Kit).
More complex fiber cleavers have a fiber holder with a V-groove and some mechanism that clamps, pulls, scribes, and ultimately cleaves the fiber; the user simply inserts the stripped fiber and pushes down on some levers.
There is a special device called a mechanical precision fiber cleaver that cleaves under more controlled conditions, resulting in more consistent results, and works as follows: Typically, a V-groove and two clamps are used first to insert the stripped fiber and fix it, then apply adjustable tension (for example with a screwdriver), then bring the diamond blade close to the fiber to make the desired scratch, the blade can be vibrated with a small electromagnet or piezoelectric, and finally , increasing the tension causes the fiber to break. Some semi-automatic fiber cleavers also allow angle cutting, which is used to prepare fiber end faces at an angle to the fiber axis.
Typically, stripping and cleaving is no problem with standard silica fibers. However, there are problems with non-standard fiber diameters, photonic crystal fibers with large air filling factors, or fragile fluoride fibers.
fiber optic connection equipment
Fiber connection splicing means splicing two fiber ends together so that light can be transmitted from one fiber to the other without excessive coupling loss. We need to distinguish between the following two techniques:
Mechanical splicing uses mechanical components to join the fiber ends.
Fusion splicing means that the fiber ends are fused together by heat treatment.
Mechanical joints can be made from relatively simple consumables and do not require expensive equipment. Simply insert the stripped and cleaved fiber end into the mechanical splice (some versions are transparent so you can see the fiber end inside). Using a lock nut, the fiber can be secured. The fiber needs to be inserted to such an extent that there is essentially no air gap between the fiber ends. Some mechanical splices are reusable, meaning that a fiber can be removed and the splice used on another fiber. Others allow the use of index-matching fluids, which can greatly reduce insertion loss, but require extra cleaning when redoing the joint. In some cases, the fibers are glued together with a UV-curing epoxy, which makes the connectors non-reusable.
For welding, there are sophisticated welding equipment. The stripped and carefully cleaved fiber end must be inserted into the clamp and positioned correctly. With the push of a button, the device tightly joins the ends of the fiber and heats it through an electric arc (or possibly using a CO2 laser ) so that the ends of the fiber are fused together. Fusion splicers are very expensive, but they produce the most reliable and low-loss splices without the need for expensive consumables.
Although fusion splices are quite strong compared to virgin fibers, stripped fibers are less protective. Therefore, people often use splice protectors to protect the splice area.
Check Fiber Ends and Connectors
Visual fault locators can help locate fiber optic faults, especially connector faults. This device contains a visible (usually red) laser source in a small box with a fiber optic connector , where the fiber under test is connected, and then injects some visible light into the fiber, only where there is a fault, a large number of Only light is scattered from the fiber and can be seen. Obviously, the mechanical joint should be transparent so that the inspection method can work properly.
There are also fiber optic microscopes for inspecting fiber ends, these can be less expensive than general purpose microscopes because they work at a fixed (relatively high) magnification. It is useful to regularly check the quality of eg fiber cut and polished surfaces, as this is critical for successful splicing and low loss connections. Microscopic examination requires minimal time – much less than subsequent fault finding and repair.
Special interferometers are available to check the fiber end surface quality and dome radius. Typically, the fiber under test is inserted together with its connector.
Fiber Optic Connectors and Patch Cords
Fiber optic connectors are useful for non-permanent connections, such as fiber optic patch cords. We have discussed fiber optic connectors in Part 6 and in the encyclopedia article. There are many different versions of fiber optic patch cords that have been connected by the manufacturer:
There are many different connector types and sometimes different quality levels.
Different single-mode and multimode fibers are available.
Depending on the use environment, fiber optic jumpers have different moisture-proof, heat-resistant and fire-resistant properties. For indoor applications, fire safety is a very important aspect. Moisture and temperature resistance are essential for outdoor cables, but not usually for patch cords. Mechanical protection is also important, for example to prevent people from walking on the cable, so there will be a particularly strong cable.
Please note that some related equipment is usually required for connection, that is, fiber optic connectors for connection. In addition to stripping and cutting equipment, specialized tools are often included depending on the connector type. However, some fiber optic users can use prefabricated fiber optic connection equipment and patch cords instead of installing the connectors themselves.
fiber optic adapter
There are many types of fiber optic adapters. Many of them allow the connection of two fiber ends already equipped with fiber optic connectors – possibly of different types. Because there are many different kinds of fiber optic connectors, many different adapters are required.
In many situations, it is desirable to convert the light exiting the fiber end into a collimated beam. For this, a fiber collimator can be attached to the fiber end. Typically, collimators are used to connect fiber ends, ie ends with fiber optic connectors, such as FC or SMA types. Essentially, this collimator consists of an anti-reflection coated lens and an adapter for a fiber optic connector, or some kind of mount for bare fiber optics. The beam radius of a collimated beam is approximately the focal length of the lens multiplied by the half angle of beam divergence from the fiber. For single-mode fiber, the beam divergence is approximately the wavelength divided by π times the mode radius. Larger collimated beams require fiber collimators with both long and large diameters.
Fiber collimators can also be used to launch collimated beams into optical fibers.
Fiber Optic Machine Parts
People often use a V-groove with some clips on top to hold the fiber firmly in place. By arranging such V-grooves in an array, it is possible to install a fiber array in which often a few fibers (sometimes even thousands of fibers) are arranged in a line at a constant well-defined pitch. There are also special fiber optic connectors designed for fiber optic arrays.
To launch the laser light into the fiber, there is a complete fiber launch system, including V-grooves and clamps mounted on a precision translation stage, and some focusing lenses. An alternative could be to use a fiber collimator mounted on the translation stage (see above).
If some bulky optics need to be inserted into a fiber optic setup, it may be convenient to use an assembly with two fiber collimators with some space in between. Especially when used with single-mode fibers, high mechanical stability is important.