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 usually created for lighting or decoration including Secondary Coating Line. They are also utilized on short range communication applications like on vehicles and ships. Due to plastic optical fiber’s high attenuation, they have got limited information carrying bandwidth.
When we talk about fiber optic networks and fiber optic telecommunications, we actually mean glass optical fibers. Glass optical fibers are mostly made from fused silica (90% at the very least). Other glass materials including fluorozirconate and fluoroaluminate can 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 check out its cross section structure. Optical fiber cross section is a circular structure composed of three layers inside out.
A. The interior layer is known as the core. This layer guides the light and prevent 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 middle layer is referred to as the cladding. It has 1% lower refractive index compared to the core material. This difference plays a crucial part in total 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 that fiber and makes the fiber flexible for handling. Without this 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 far from practical to generate it in a single step. Three steps are essential since we explain below.
1. Preparing the fiber preform
Standard optical fibers are produced by first constructing a sizable-diameter preform, having a carefully controlled refractive index profile. Only several countries including US have the capacity to make large volume, high quality Optical Fiber Ribbon Machine preforms.
This process to create glass preform is known 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 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 from 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 make 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 conclusion from 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 quantity of material continues to be deposited.
2. Drawing fibers on the drawing tower.
The preform will 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 is then 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 with 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 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.