Materials For Optical Fibers
There’s two major kinds of optical fibers: plastic optical fiber (POF) and glass optical fiber.
POF fiber is usually designed for lighting or decoration such as fiber optic christmas trees. It is also used on short range communication applications for example on vehicles and ships. Because of plastic optical fiber’s high attenuation, they’ve limited information carrying bandwidth.
Whenever 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% a minimum of). Other glass materials such as fluorozirconate and fluoroaluminate are also utilized in some specialty fibers.
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 called the main. This layer guides the sunshine 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 center layer is called the cladding. It has 1% lower refractive index than the core material. This difference plays part in total internal reflection phenomenon. The cladding’s diameter is usually 125um.
- C. The outer layer is called the coating. It is actually epoxy cured by ultraviolet light. This layer provides mechanical protection for the fiber and helps make the fiber flexible to handle. Without it coating layer, the fiber will be very fragile and simple to interrupt.
Due to optical fiber’s extreme tiny size, it’s not practical to produce it in one step. Three steps are required once we explain below.
1. Preparing The Fiber Preform
Standard optical fibers are created beginning with constructing a large-diameter preform, with a carefully controlled refractive index profile. Only several countries including US be capable of make large volume, high quality fiber preforms. The 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 on the special lathe. Oxygen is bubbled through solutions of silicon chloride (SiCl4), germanium chloride (GeCl4) and/or other chemicals. This precisely mixed gas is then injected in to the hollow tube. Because the lathe turns, a hydrogen burner torch is moved up and down the outside of the tube. The gases are heated 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 be traversed up and down the length of the tube to deposit the fabric evenly. After the torch has reached no more the tube, it is then brought back to the beginning of the tube and the deposited particles are then melted to create a solid layer. This method is repeated until an adequate amount of material has been deposited.
2. Drawing Fibers On The Drawing Tower
The preform will be mounted to the peak 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 because it drops down. This starting strand will be pulled via a number of buffer coating cups and UV light curing ovens, finally onto an electric motor controlled cylindrical fiber spool. The motor slowly draws the fiber from the heated preform. The formed fiber diameter is strictly controlled by a laser micrometer. The running speed of the fiber drawing motor is about 15 meters/second. Up to 20km of continuous fibers could be wound onto a single spool.
3. Testing Finished Optical Fibers
Telecommunication applications require very high quality glass optical fibers. The fiber’s mechanical and optical properties will be checked.
- A. Tensile strength: Fiber must withstand 100,000 (lb/square inch) tension
- B. Fiber geometry: Checks fiber’s 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
After the testing are finished, the optical fiber can be made as fiber optic cable for sale. Whatever kinds of common cables, including single-mode and multimode, or other special ones like figure of 8 cable, are made of glass optical fiber. FiberStore supplies bulk fiber cables which are all strictly manufactured.