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 made for lighting or decoration like Fiber Drawing Machine. Also, they are used on short range communication applications like on vehicles and ships. Due to plastic optical fiber’s high attenuation, they have got 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 mainly created from fused silica (90% a minimum of). Other glass materials like fluorozirconate and fluoroaluminate will also be found in some specialty fibers.
2. Glass optical fiber manufacturing process
Before we start talking how to manufacture glass optical fibers, let’s first check out its cross section structure. Optical fiber cross section is a circular structure composed of three layers inside out.
A. The interior layer is known as the core. This layer guides the light preventing 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 referred to as the cladding. It provides 1% lower refractive index compared to core material. This difference plays an essential part overall internal reflection phenomenon. The cladding’s diameter is generally 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 definitely makes the fiber flexible for handling. Without it coating layer, the fiber can be really fragile as well as simple to break.
Because of optical fiber’s extreme tiny size, it is not practical to create it in a single step. Three steps are required 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 Secondary Coating Line preforms.
This process to create glass preform is known 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) and other chemicals. This precisely mixed gas will then be injected into the hollow tube.
Because the lathe turns, a hydrogen burner torch is moved up and down the outside of 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 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 material evenly. Right after the torch has reached the conclusion in the tube, it is then brought back to the start of the tube as well as the deposited particles are then melted to form a solid layer. This process is repeated until a sufficient level of material has become deposited.
2. Drawing fibers over a drawing tower.
The preform is then mounted towards the top of any 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 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 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. 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: 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.