There are 2 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 often made for lighting or decoration such as SZ Stranding Line. They are also applied to short range communication applications such as on vehicles and ships. Due to plastic optical fiber’s high attenuation, they may have very limited information carrying bandwidth.
When we discuss fiber optic networks and fiber optic telecommunications, we actually mean glass optical fibers. Glass optical fibers are mainly created from fused silica (90% a minimum of). Other glass materials including fluorozirconate and fluoroaluminate can also be found in some specialty fibers.
2. Glass optical fiber manufacturing process
Before we start talking the best way to manufacture glass optical fibers, let’s first check out its cross section structure. Optical fiber cross section is a circular structure made up of three layers inside out.
A. The inner layer is called the core. This layer guides the light and stop light from escaping out with 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 center layer is known as the cladding. It offers 1% lower refractive index than the core material. This difference plays a vital part overall internal reflection phenomenon. The cladding’s diameter is usually 125um.
C. The outer layer is called the coating. It is in reality epoxy cured by ultraviolet light. This layer provides mechanical protection for your fiber and definitely makes the fiber flexible for handling. Without it coating layer, the fiber will be very fragile and simple to break.
As a result of optical fiber’s extreme tiny size, it is really not practical to generate it in a single step. Three steps are essential as we explain below.
1. Preparing the fiber preform
Standard optical fibers are made by first constructing a big-diameter preform, using a carefully controlled refractive index profile. Only several countries including US are able to make large volume, top quality Optical Fiber Proof-Testing Machine preforms.
The process to help make 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) and/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 from the torch approximately 1900 kelvins. This extreme heat causes two chemical reactions to happen.
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 form glass.
The hydrogen burner is then traversed up and down the size of the tube to deposit the material evenly. After the torch has reached the final from 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 quantity of material continues to be deposited.
2. Drawing fibers on a drawing tower.
The preform will then be mounted for the top of the 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 since it drops down.
This starting strand is then 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 the heated preform. The ltxsmu fiber diameter is precisely controlled with a laser micrometer. The running speed of the fiber drawing motor is about 15 meters/second. Up to 20km of continuous fibers can be wound onto a single 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 Sheathing 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 critical for long distance fiber optic links
C. Chromatic dispersion: Becomes increasingly more critical in high-speed fiber optic telecommunication applications.