There are two 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 often created for lighting or decoration such as Fiber Drawing Machine. Also, they are used on short range communication applications including on vehicles and ships. Because of plastic optical fiber’s high attenuation, they have very limited information carrying bandwidth.
When we discuss fiber optic networks and fiber optic telecommunications, we actually mean glass optical fibers. Glass optical fibers are mainly made from fused silica (90% at least). Other glass materials including fluorozirconate and fluoroaluminate can also be used 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 known as the core. This layer guides the light and prevent 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 center layer is known as the cladding. It provides 1% lower refractive index compared to the core material. This difference plays a crucial part overall internal reflection phenomenon. The cladding’s diameter is generally 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 the fiber and helps make the fiber flexible for handling. Without it coating layer, the fiber can be really fragile as well as 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 essential while we explain below.
1. Preparing the fiber preform
Standard optical fibers are made 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 create 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 on the special lathe. Oxygen is bubbled through solutions of silicon chloride (SiCl4), germanium chloride (GeCl4) and other chemicals. This precisely mixed gas is then 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 approximately 1900 kelvins. This extreme heat causes two chemical reactions to happen.
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 within the tube and fuse together to create glass.
The hydrogen burner will then be traversed up and down the duration of the tube to deposit the material evenly. Following the torch has reached the final in the tube, it is then 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 has been 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 as 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 a laser micrometer. The running speed in the fiber drawing motor is all 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 Optical Fiber Proof-Testing Machine 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 more and more critical in high speed fiber optic telecommunication applications.