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 like Optical Fiber Coloring Machine. Also, they are applied to short range communication applications including on vehicles and ships. Because of plastic optical fiber’s high attenuation, they may have very limited information carrying bandwidth.
When we speak about fiber optic networks and fiber optic telecommunications, we actually mean glass optical fibers. Glass optical fibers are generally made from fused silica (90% at the very least). Other glass materials such as fluorozirconate and fluoroaluminate are also utilized 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 take a look at its cross section structure. Optical fiber cross section is really a circular structure made from 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 known as the cladding. It offers 1% lower refractive index compared to the core material. This difference plays an essential part altogether internal reflection phenomenon. The cladding’s diameter is usually 125um.
C. The outer layer is referred to as the coating. It is actually epoxy cured by ultraviolet light. This layer provides mechanical protection for the fiber and helps make the fiber flexible for handling. Without it coating layer, the fiber will be very fragile as well as simple to break.
Because of optical fiber’s extreme tiny size, it is 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 created by first constructing a large-diameter preform, having a carefully controlled refractive index profile. Only several countries including US are able to make large volume, high quality FTTH Cable Production Line preforms.
This 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 on the special lathe. Oxygen is bubbled through solutions of silicon chloride (SiCl4), germanium chloride (GeCl4) or other chemicals. This precisely mixed gas will be injected in to the hollow tube.
Because the lathe turns, a hydrogen burner torch is moved up and down the outside the tube. The gases are heated up through the torch up to 1900 kelvins. This extreme heat causes two chemical reactions to take place.
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 within the tube and fuse together to make glass.
The hydrogen burner will be traversed up and down the duration of the tube to deposit the material evenly. Right after the torch has reached the conclusion of the tube, this will make it brought back to the starting of the tube and also the deposited particles are then melted to make a solid layer. This method is repeated until a sufficient amount of material has been deposited.
2. Drawing fibers on the drawing tower.
The preform is then mounted to the top of a 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 since 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 through the heated preform. The ltxsmu fiber diameter is precisely controlled by a laser micrometer. The running speed from the fiber drawing motor is about 15 meters/second. Up to 20km of continuous fibers can be wound onto one particular 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 Secondary Coating Line core, cladding and coating sizes
A. Refractive index profile: Probably 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 a lot more critical in high speed fiber optic telecommunication applications.