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 generally created for lighting or decoration like FTTH Cable Production 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 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 generally made from fused silica (90% a minimum of). Other glass materials such as fluorozirconate and fluoroaluminate will also be utilized 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 made from 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 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 called the cladding. It offers 1% lower refractive index compared to the core material. This difference plays a crucial part altogether internal reflection phenomenon. The cladding’s diameter is usually 125um.
C. The outer layer is referred to as the coating. It is in reality epoxy cured by ultraviolet light. This layer provides mechanical protection for your fiber and makes the fiber flexible for handling. Without this coating layer, the fiber can be really fragile and simple to break.
As a result of optical fiber’s extreme tiny size, it is really not practical to produce it in a single step. Three steps are required since we explain below.
1. Preparing the fiber preform
Standard optical fibers are produced 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 SZ Stranding Line preforms.
This process to make 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 be injected in to 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 approximately 1900 kelvins. This extreme heat causes two chemical reactions to take place.
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 make glass.
The hydrogen burner will then be traversed up and down the length of the tube to deposit the material evenly. Right after the torch has reached the final from the tube, it is then brought back to the beginning of the tube and also the deposited particles are then melted to create a solid layer. This method is repeated until a sufficient quantity of material has become deposited.
2. Drawing fibers on the drawing tower.
The preform will be mounted towards 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 since it drops down.
This starting strand will then 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 through 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 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 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 increasingly more critical in high-speed fiber optic telecommunication applications.