There are two 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 usually made for lighting or decoration including Fiber Drawing Machine. They are also utilized on short range communication applications including on vehicles and ships. Because of plastic optical fiber’s high attenuation, they have got very limited information carrying bandwidth.
Whenever we speak about fiber optic networks and fiber optic telecommunications, we actually mean glass optical fibers. Glass optical fibers are mostly created from fused silica (90% at the very least). Other glass materials like fluorozirconate and fluoroaluminate can also be used in some specialty fibers.
2. Glass optical fiber manufacturing process
Before we start talking how you can manufacture glass optical fibers, let’s first take a look at its cross section structure. Optical fiber cross section is a circular structure made from three layers inside out.
A. The inner layer is called the core. This layer guides the light and prevent 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 referred to as the cladding. It offers 1% lower refractive index compared to the core material. This difference plays a vital part overall internal reflection phenomenon. The cladding’s diameter is generally 125um.
C. The outer layer is known as the coating. It is in reality epoxy cured by ultraviolet light. This layer provides mechanical protection for that fiber and makes the fiber flexible for handling. Without it coating layer, the fiber will be really fragile and easy to break.
As a result of optical fiber’s extreme tiny size, it is really not practical to produce it in a single step. Three steps are required while we explain below.
1. Preparing the fiber preform
Standard optical fibers are made by first constructing a big-diameter preform, with a carefully controlled refractive index profile. Only several countries including US have the ability to make large volume, high quality Optical Fiber Proof-Testing Machine preforms.
The process to create glass preform is called MOCVD (modified chemical vapor deposition).
In MCVD, a 40cm long hollow quartz tube is fixed horizontally and rotated slowly on the special lathe. Oxygen is bubbled through solutions of silicon chloride (SiCl4), germanium chloride (GeCl4) and other chemicals. This precisely mixed gas is then injected to the hollow tube.
As the lathe turns, a hydrogen burner torch is moved up and down the outside of the tube. The gases are heated up by the torch as much as 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 the tube and fuse together to create glass.
The hydrogen burner will be traversed up and down the size of the tube to deposit the content evenly. Right after the torch has reached the final in the tube, this will make it brought back to the beginning of the tube and also the deposited particles are then melted to create a solid layer. This method is repeated until a sufficient amount of material has been deposited.
2. Drawing fibers over a drawing tower.
The preform will then be mounted towards 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 because it drops down.
This starting strand will then be pulled through several 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 a laser micrometer. The running speed in the fiber drawing motor is all about 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 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 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 more and more critical in high-speed fiber optic telecommunication applications.