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 made for lighting or decoration such as Optical Fiber Proof-Testing Machine. Also, they are utilized on short range communication applications such as on vehicles and ships. Due to plastic optical fiber’s high attenuation, they have got very limited information carrying bandwidth.
When 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 will also be utilized in some specialty fibers.
2. Glass optical fiber manufacturing process
Before we start talking how you can manufacture glass optical fibers, let’s first take a look at its cross section structure. Optical fiber cross section is actually 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 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 known as the cladding. It provides 1% lower refractive index compared to the core material. This difference plays an essential part overall internal reflection phenomenon. The cladding’s diameter is normally 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 that fiber and helps make the fiber flexible for handling. Without this coating layer, the fiber will be very fragile and easy to break.
Due to optical fiber’s extreme tiny size, it is really not practical to produce it in a single step. Three steps are needed while we explain below.
1. Preparing the fiber preform
Standard optical fibers are produced by first constructing a sizable-diameter preform, with a carefully controlled refractive index profile. Only several countries including US have the capacity to make large volume, high quality SZ Stranding Line preforms.
The procedure to make glass preform is referred to as 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 is then injected in to 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 of the tube and fuse together to make glass.
The hydrogen burner is then traversed up and down the length of the tube to deposit the material evenly. After the torch has reached the conclusion from the tube, this will make it brought back to the starting of the tube as well as the deposited particles are then melted to form a solid layer. This process is repeated until a sufficient quantity of material has become deposited.
2. Drawing fibers on the drawing tower.
The preform will be mounted for the top of any vertical fiber drawing tower. The preforms is first lowered in to 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 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 a laser micrometer. The running speed of the fiber drawing motor is approximately 15 meters/second. As much as 20km of continuous fibers can be wound onto just one 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 Optical Fiber Proof-Testing 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 a lot more critical in high-speed fiber optic telecommunication applications.