There are 2 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 usually made for lighting or decoration including Secondary Coating Line. They are also applied to short range communication applications including on vehicles and ships. As a result of plastic optical fiber’s high attenuation, they have got restricted information carrying bandwidth.
Whenever we discuss fiber optic networks and fiber optic telecommunications, we actually mean glass optical fibers. Glass optical fibers are mostly made from fused silica (90% at least). Other glass materials like fluorozirconate and fluoroaluminate are also 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 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 referred to as the core. This layer guides the light and stop 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 normally 125um.
C. The outer layer is called the coating. It really is 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 really fragile and simple to break.
Because of optical fiber’s extreme tiny size, it is really not practical to generate it in a single step. Three steps are needed while we explain below.
1. Preparing the fiber preform
Standard optical fibers are made by first constructing a sizable-diameter preform, having a carefully controlled refractive index profile. Only several countries including US have the ability to make large volume, high quality SZ Stranding Line preforms.
This process to help make 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 be injected into the hollow tube.
Since the lathe turns, a hydrogen burner torch is moved up and down the outside the tube. The gases are heated up by the torch as much as 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 inside of the tube and fuse together to form glass.
The hydrogen burner will then be traversed up and down the length of the tube to deposit the content evenly. Right after the torch has reached the final of the tube, it is then brought back to the start of the tube and the deposited particles are then melted to create a solid layer. This method is repeated until a sufficient amount of material continues to be deposited.
2. Drawing fibers on the drawing tower.
The preform will then be mounted for 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 number 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 from the fiber drawing motor is all about 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 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 critical for long distance fiber optic links
C. Chromatic dispersion: Becomes more and more critical in high speed fiber optic telecommunication applications.