The two main major varieties 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 designed for lighting or decoration such as Optical Fiber Ribbon Machine. They are also used on short range communication applications including on vehicles and ships. As a result of plastic optical fiber’s high attenuation, they have limited information carrying bandwidth.
Once 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 such as fluorozirconate and fluoroaluminate can 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 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 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 referred to as the cladding. It provides 1% lower refractive index compared to core material. This difference plays a crucial part overall internal reflection phenomenon. The cladding’s diameter is usually 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 your fiber and helps make the fiber flexible for handling. Without it coating layer, the fiber can be really fragile and 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 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 capacity to make large volume, top quality Secondary Coating Line preforms.
The procedure 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 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 in to the hollow tube.
As the lathe turns, a hydrogen burner torch is moved up and down the outside the tube. The gases are heated up from the torch approximately 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 duration of the tube to deposit the material evenly. Right after the torch has reached the final in the tube, it is then brought back to the starting of the tube and the deposited particles are then melted to create a solid layer. This method is repeated until a sufficient amount of material has become deposited.
2. Drawing fibers on a drawing tower.
The preform will be mounted to the top of the 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 the heated preform. The ltxsmu fiber diameter is precisely controlled by a laser micrometer. The running speed in the fiber drawing motor is approximately 15 meters/second. Approximately 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 SZ Stranding 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 crucial for long distance fiber optic links
C. Chromatic dispersion: Becomes a lot more critical in high-speed fiber optic telecommunication applications.