There are 2 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 including Optical Fiber Ribbon Machine. Also, they are applied to short range communication applications such as on vehicles and ships. Due to plastic optical fiber’s high attenuation, they may have very limited information carrying bandwidth.
Whenever we talk 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 such as fluorozirconate and fluoroaluminate will also be found 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 composed of three layers inside out.
A. The interior layer is referred to as the core. This layer guides the light and prevent 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 middle layer is referred to as the cladding. It provides 1% lower refractive index compared to core material. This difference plays a vital part overall internal reflection phenomenon. The cladding’s diameter is generally 125um.
C. The outer layer is known as the coating. It really is epoxy cured by ultraviolet light. This layer provides mechanical protection for the fiber and makes 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 essential as we explain below.
1. Preparing the fiber preform
Standard optical fibers are made by first constructing a large-diameter preform, using a carefully controlled refractive index profile. Only several countries including US are able to make large volume, good quality Sheathing Line preforms.
The process 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) and/or 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 the tube. The gases are heated up through the torch as much as 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 form glass.
The hydrogen burner will then be traversed up and down the length of the tube to deposit the material evenly. After the torch has reached the conclusion from the tube, it is then brought back to the starting of the tube and the deposited particles are then melted to form a solid layer. This method is repeated until a sufficient amount of material has been deposited.
2. Drawing fibers over a drawing tower.
The preform will be mounted to the top of a 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 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 way of a laser micrometer. The running speed of the fiber drawing motor is all about 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 Sheathing 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 more and more critical in high-speed fiber optic telecommunication applications.