There is no doubt that fiber optics have revolutionized the technologies which are now used in almost every industry and consumer application imaginable. However, in order to keep your fiber optic products and connections running properly, they need to be polished. Terminating optical fibers with connectors (that also include an adhesive) and then polishing the ferrules is a very common practice. In fact, it has been in use since the very beginning of fiber optics. Let’s take a closer look at some of the factors involved in this interesting process.
The Fiber Ferrules:
Interestingly enough, the diameter of most optical fibers are really too small to be polished directly. For this reason, it is quite common to have either ceramic, glass, or metal ferrules used as a way to protect the fibers themselves. Most commonly, this will be either metal or ceramic. Having said this, each type of use and coating or polishing method will also determine what type of material will be best. As an example, when optical coating is used after polishing glass ferrules are the best option since this will allow for better adhesion.
When choosing which type of adhesive will be used it is important to consider your options. There are three general types including epoxy, hot melt, and anaerobic adhesives. There are a wide range of epoxies, with some curing quickly in an oven at a temperature of 90-100 degrees Celsius. Others can be cured at room temperature, but will likely require up to 12 hours. The hot melt process uses an oven at a temperature of about 200 degrees Celsius (then the fiber is inserted and allowed to cool in order to set the adhesive). Anaerobic options are very fast-setting adhesives that work almost instantly. Either way, you need to ensure that there is a reliable adhesion between the fiber and the ferrule.
Key Polishing Ingredients:
When polishing optics, you really must keep in mind that this is not like lens polishing. The convex surface of fiber ferrules is actually achieved by pressing them on flexible polishing pads. This domed surface is also ideal for physical contact between two single mode fiber cores, if desired. The radius of curvature is determined by the pressing force, the hardness and thickness of the polishing pad. Physical contact will also normally require a slight undercut of the fiber itself, with the amount of this being determined by factors like the type of polishing film used, force applied, and the polish speed.
Another vital polishing ingredient is the polishing machine. This must be well-designed and properly tuned in order to produce the desired results. Great care should go into properly maintaining such a vital piece of equipment.
There are also several choices for the actual material used in polishing films today. This includes diamonds, silicon carbide, and aluminum oxide. It is also interesting to note that in some cases a mixture of these three ingredients may be needed in order to achieve the best result. You will also need to have de-ionized water for the cooling process, no matter which type of polishing film is chosen.
Of course, these are just a few of the factors that need to be considered when engaging in fiber optic polishing. It is both a science and an art, which means that this is a skill where practice really can make perfect, over time. The actual procedure and training are just as valuable as using the right type of polishing machine and ingredients for the job.
Ray Pierce is dedicated to educational development in the market of fiber optics.