The two main 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 like FTTH Cable Production Line. They are also utilized on short range communication applications such as on vehicles and ships. Due to plastic optical fiber’s high attenuation, they 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 mostly produced from fused silica (90% a minimum of). 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 have a look at its cross section structure. Optical fiber cross section is actually a circular structure made from three layers inside out.
A. The inner layer is known as 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 provides 1% lower refractive index compared to 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 referred to as the coating. It really is epoxy cured by ultraviolet light. This layer provides mechanical protection for that fiber and helps make the fiber flexible for handling. Without it coating layer, the fiber will be very fragile and simple to break.
Because of optical fiber’s extreme tiny size, it is really not practical to generate it in a single step. Three steps are required since we explain below.
1. Preparing the fiber preform
Standard optical fibers are created 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, top quality Sheathing Line preforms.
This process to 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 over a special lathe. Oxygen is bubbled through solutions of silicon chloride (SiCl4), germanium chloride (GeCl4) or other chemicals. This precisely mixed gas will be injected into 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 up to 1900 kelvins. This extreme heat causes two chemical reactions to take place.
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 duration of the tube to deposit the content evenly. Right after the torch has reached the final from the tube, this will make it brought back to the beginning of the tube as well as the deposited particles are then melted to make a solid layer. This process is repeated until a sufficient level of material has been deposited.
2. Drawing fibers on a drawing tower.
The preform will be mounted for the top of any vertical fiber drawing tower. The preforms is first lowered in to 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 the heated preform. The ltxsmu fiber diameter is precisely controlled by a laser micrometer. The running speed in 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: 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 increasingly more critical in high-speed fiber optic telecommunication applications.