The two main major types of optical fibers: plastic optical fibers (POF) and glass optical fibers – so how are optical fibers made?
1. Materials for optical fibers
Plastic optical fibers are generally designed for lighting or decoration such as Fiber Coloring Machine. They are also utilized on short range communication applications like on vehicles and ships. Due to plastic optical fiber’s high attenuation, they may have very limited information carrying bandwidth.
Once we speak about fiber optic networks and fiber optic telecommunications, we actually mean glass optical fibers. Glass optical fibers are mainly made from fused silica (90% at least). Other glass materials such as fluorozirconate and fluoroaluminate are also found in some specialty fibers.
2. Glass optical fiber manufacturing process
Before we start talking how to manufacture glass optical fibers, let’s first check out its cross section structure. Optical fiber cross section is a circular structure made from three layers inside out.
A. The interior layer is referred to as the core. This layer guides the light and stop light from escaping out by way of a phenomenon called total internal reflection. The core’s diameter is 9um for single mode fibers and 50um or 62.5um for multimode fibers.
B. The middle layer is referred to as the cladding. It provides 1% lower refractive index than the core material. This difference plays an essential part in total internal reflection phenomenon. The cladding’s diameter is normally 125um.
C. The outer layer is called the coating. It is actually epoxy cured by ultraviolet light. This layer provides mechanical protection for the fiber and makes the fiber flexible for handling. Without it coating layer, the fiber can be really fragile and simple to break.
Because of optical fiber’s extreme tiny size, it is really not practical to produce it in a single step. Three steps are essential while we explain below.
1. Preparing the fiber preform
Standard optical fibers are created by first constructing a sizable-diameter preform, having a carefully controlled refractive index profile. Only several countries including US have the capacity to make large volume, high quality Sheathing Line preforms.
The process to create glass preform is referred to as MOCVD (modified chemical vapor deposition).
In MCVD, a 40cm long hollow quartz tube is fixed horizontally and rotated slowly over a special lathe. Oxygen is bubbled through solutions of silicon chloride (SiCl4), germanium chloride (GeCl4) or other chemicals. This precisely mixed gas is then injected to the hollow tube.
Because the lathe turns, a hydrogen burner torch is moved up and down the outside of the tube. The gases are heated up through the torch approximately 1900 kelvins. This extreme heat causes two chemical reactions to occur.
A. The silicon and germanium interact with oxygen, forming silicon dioxide (SiO2) and germanium dioxide (GeO2).
B. The silicon dioxide and germanium dioxide deposit on the inside the tube and fuse together to make glass.
The hydrogen burner is then traversed up and down the size of the tube to deposit the content evenly. After the torch has reached the conclusion of the tube, it is then brought back to the beginning of the tube and the deposited particles are then melted to make a solid layer. This procedure is repeated until a sufficient level of material has become deposited.
2. Drawing fibers over a drawing tower.
The preform is then mounted for the top of any vertical fiber drawing tower. The preforms is first lowered right into a 2000 degrees Celsius furnace. Its tip gets melted until a molten glob falls down by gravity. The glob cools and forms a thread because it drops down.
This starting strand will be pulled through a series of buffer coating cups and UV light curing ovens, finally onto a motor controlled cylindrical fiber spool. The motor slowly draws the fiber through the heated preform. The ltxsmu fiber diameter is precisely controlled by way of a laser micrometer. The running speed from the fiber drawing motor is approximately 15 meters/second. As much as 20km of continuous fibers can be wound onto just one spool.
3. Testing finished optical fibers
Telecommunication applications require very high quality glass optical fibers. The fiber’s mechanical and optical properties are then checked.
A. Tensile strength: Fiber must withstand 100,000 (lb/square inch) tension
B. Fiber geometry: Checks Optical Fiber Coloring Machine core, cladding and coating sizes
A. Refractive index profile: By far the most critical optical spec for fiber’s information carrying bandwidth
B. Attenuation: Very critical for long distance fiber optic links
C. Chromatic dispersion: Becomes more and more critical in high-speed fiber optic telecommunication applications.