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 generally created for lighting or decoration such as Sheathing Line. They are also utilized on short range communication applications including on vehicles and ships. Due to plastic optical fiber’s high attenuation, they have very limited information carrying bandwidth.
Once we discuss fiber optic networks and fiber optic telecommunications, we actually mean glass optical fibers. Glass optical fibers are mainly produced from fused silica (90% at the very 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 have 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 known as the core. This layer guides the light preventing light from escaping out by 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 called 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 referred to as the coating. It is actually 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 can be really fragile as well as simple to break.
Because of optical fiber’s extreme tiny size, it is really not practical to create it in a single step. Three steps are required since we explain below.
1. Preparing the fiber preform
Standard optical fibers are made by first constructing a large-diameter preform, having a carefully controlled refractive index profile. Only several countries including US have the ability to make large volume, top quality Optical Fiber Ribbon Machine preforms.
The process to help 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) or other chemicals. This precisely mixed gas will then be injected into the hollow tube.
As the lathe turns, a hydrogen burner torch is moved up and down the outside the tube. The gases are heated up by the torch up to 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 within the tube and fuse together to make glass.
The hydrogen burner is then traversed up and down the duration of the tube to deposit the fabric evenly. After the torch has reached the final of the tube, this will make it brought back to the beginning of the tube as well as the deposited particles are then melted to create a solid layer. This process is repeated until a sufficient level of material continues to be deposited.
2. Drawing fibers on the drawing tower.
The preform will be mounted to the top of any 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 then be pulled through several buffer coating cups and UV light curing ovens, finally onto a motor controlled cylindrical fiber spool. The motor slowly draws the fiber from your heated preform. The ltxsmu fiber diameter is precisely controlled with a laser micrometer. The running speed of the fiber drawing motor is about 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 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 Secondary Coating 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 increasingly more critical in high-speed fiber optic telecommunication applications.