There are 2 major kinds 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 often made for lighting or decoration such as Fiber Coloring Machine. They are also applied to short range communication applications including on vehicles and ships. Because of plastic optical fiber’s high attenuation, they may have limited information carrying bandwidth.
Once we discuss fiber optic networks and fiber optic telecommunications, we actually mean glass optical fibers. Glass optical fibers are mostly produced from fused silica (90% at the very least). Other glass materials such as fluorozirconate and fluoroaluminate will also be found in some specialty fibers.
2. Glass optical fiber manufacturing process
Before we start talking how to manufacture glass optical fibers, let’s first have a look at its cross section structure. Optical fiber cross section is really a circular structure composed of three layers inside out.
A. The interior layer is referred to as the core. This layer guides the light preventing light from escaping out by 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 called the cladding. It provides 1% lower refractive index compared to core material. This difference plays a crucial part in total internal reflection phenomenon. The cladding’s diameter is generally 125um.
C. The outer layer is referred to as the coating. It really is epoxy cured by ultraviolet light. This layer provides mechanical protection for the fiber and helps make the fiber flexible for handling. Without this coating layer, the fiber can be really fragile and easy to break.
As a result of optical fiber’s extreme tiny size, it is not practical to create it in a single step. Three steps are required while we explain below.
1. Preparing the fiber preform
Standard optical fibers are created by first constructing a large-diameter preform, having a carefully controlled refractive index profile. Only several countries including US have the ability to make large volume, top quality FTTH Cable Production Line preforms.
The process to help make glass preform is known as MOCVD (modified chemical vapor deposition).
In MCVD, a 40cm long hollow quartz tube is fixed horizontally and rotated slowly on a special lathe. Oxygen is bubbled through solutions of silicon chloride (SiCl4), germanium chloride (GeCl4) or other chemicals. This precisely mixed gas will then be injected into the hollow tube.
Since the lathe turns, a hydrogen burner torch is moved up and down the away from the tube. The gases are heated up by the torch approximately 1900 kelvins. This extreme heat causes two chemical reactions to occur.
A. The silicon and germanium react with oxygen, forming silicon dioxide (SiO2) and germanium dioxide (GeO2).
B. The silicon dioxide and germanium dioxide deposit on the inside of the tube and fuse together to create glass.
The hydrogen burner will be traversed up and down the duration of the tube to deposit the content evenly. Following the torch has reached the final in the tube, it is then brought back to the starting of the tube as well as the deposited particles are then melted to form a solid layer. This procedure is repeated until a sufficient amount of material continues to be 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 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 as it drops down.
This starting strand will be pulled through a number of buffer coating cups and UV light curing ovens, finally onto a motor controlled cylindrical fiber spool. The motor slowly draws the fiber from your heated preform. The ltxsmu fiber diameter is precisely controlled by way of a laser micrometer. The running speed from the fiber drawing motor is all about 15 meters/second. Approximately 20km of continuous fibers can be wound onto a single spool.
3. Testing finished optical fibers
Telecommunication applications require very good 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 FTTH Cable Production Line 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 crucial for long distance fiber optic links
C. Chromatic dispersion: Becomes more and more critical in high speed fiber optic telecommunication applications.