There are two 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 usually made for lighting or decoration including SZ Stranding Line. They are also applied to short range communication applications like on vehicles and ships. Because of plastic optical fiber’s high attenuation, they 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 mostly produced from fused silica (90% a minimum of). Other glass materials including fluorozirconate and fluoroaluminate are also 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 check out its cross section structure. Optical fiber cross section is really a circular structure composed of three layers inside out.
A. The inner layer is called 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 middle layer is known as the cladding. It offers 1% lower refractive index compared to the 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 really is epoxy cured by ultraviolet light. This layer provides mechanical protection for your fiber and helps make the fiber flexible for handling. Without this coating layer, the fiber can be really fragile and simple to break.
Due to 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, using a carefully controlled refractive index profile. Only several countries including US are able to make large volume, top quality FTTH Cable Production Line preforms.
The 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) or other chemicals. This precisely mixed gas will then be injected into the hollow tube.
Since the lathe turns, a hydrogen burner torch is moved up and down the away from the tube. The gases are heated up from the torch as much as 1900 kelvins. This extreme heat causes two chemical reactions to occur.
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. After the torch has reached the end of the tube, this will make it brought back to the start of the tube and also the deposited particles are then melted to form a solid layer. This process is repeated until a sufficient amount of material continues to be deposited.
2. Drawing fibers on a drawing tower.
The preform is then mounted to 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 since it drops down.
This starting strand will be pulled through a series 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 about 15 meters/second. Up to 20km of continuous fibers can be wound onto just one spool.
3. Testing finished optical fibers
Telecommunication applications require very good 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: 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.