The two main 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 made for lighting or decoration including Optical Fiber Proof-Testing Machine. They are also applied to short range communication applications such as on vehicles and ships. As a result of plastic optical fiber’s high attenuation, they may 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 mostly created 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 actually a circular structure composed of three layers inside out.
A. The inner layer is called 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 referred to as the cladding. It has 1% lower refractive index compared to the core material. This difference plays an essential part in total internal reflection phenomenon. The cladding’s diameter is usually 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 makes the fiber flexible for handling. Without this coating layer, the fiber will be very fragile and simple to break.
Due to 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 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 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) and/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 away from the tube. The gases are heated up by the torch up to 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 within the tube and fuse together to form glass.
The hydrogen burner is then traversed up and down the size of the tube to deposit the fabric evenly. After the torch has reached the end 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 level of material has been deposited.
2. Drawing fibers on the drawing tower.
The preform is then mounted for the top of the 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 as it drops down.
This starting strand will 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 the heated preform. The ltxsmu fiber diameter is precisely controlled by a laser micrometer. The running speed from the fiber drawing motor is approximately 15 meters/second. Up to 20km of continuous fibers can be wound onto one particular 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 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 critical for long distance fiber optic links
C. Chromatic dispersion: Becomes increasingly more critical in high speed fiber optic telecommunication applications.