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 generally made for lighting or decoration like Sheathing Line. They are also applied to short range communication applications like on vehicles and ships. Due to plastic optical fiber’s high attenuation, they have got limited information carrying bandwidth.
Once we discuss fiber optic networks and fiber optic telecommunications, we actually mean glass optical fibers. Glass optical fibers are generally produced from fused silica (90% a minimum of). Other glass materials including fluorozirconate and fluoroaluminate will also be used 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 have a look at its cross section structure. Optical fiber cross section is really a circular structure made up of three layers inside out.
A. The interior layer is referred to as the core. This layer guides the light and stop light from escaping out by way of 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 has 1% lower refractive index than the core material. This difference plays an essential part altogether internal reflection phenomenon. The cladding’s diameter is generally 125um.
C. The outer layer is known as the coating. It is actually epoxy cured by ultraviolet light. This layer provides mechanical protection for your fiber and makes the fiber flexible for handling. Without it coating layer, the fiber will be very fragile and easy to break.
Because of optical fiber’s extreme tiny size, it is not practical to generate it in a single step. Three steps are needed since we explain below.
1. Preparing the fiber preform
Standard optical fibers are made by first constructing a big-diameter preform, having a carefully controlled refractive index profile. Only several countries including US have the ability to make large volume, top quality Sheathing Line 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 on a special lathe. Oxygen is bubbled through solutions of silicon chloride (SiCl4), germanium chloride (GeCl4) and other chemicals. This precisely mixed gas will then be injected into the hollow tube.
As 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 as much as 1900 kelvins. This extreme heat causes two chemical reactions to occur.
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 inside the tube and fuse together to form glass.
The hydrogen burner will be traversed up and down the duration of the tube to deposit the material evenly. Following the torch has reached the conclusion from the tube, this will make it brought back to the start of the tube and the deposited particles are then melted to create a solid layer. This process is repeated until a sufficient quantity of material has been deposited.
2. Drawing fibers over a drawing tower.
The preform will be mounted towards 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 as 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 through the 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. 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 Fiber Drawing Machine core, cladding and coating sizes
A. Refractive index profile: 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.