There are 2 major kinds 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 designed for lighting or decoration such as Sheathing Line. Also, they are applied to short range communication applications like on vehicles and ships. As a result of plastic optical fiber’s high attenuation, they have restricted 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 the very least). Other glass materials such as fluorozirconate and fluoroaluminate are also utilized in some specialty fibers.

2. Glass optical fiber manufacturing process

Before we start talking the best way to manufacture glass optical fibers, let’s first have a look at its cross section structure. Optical fiber cross section is actually a circular structure made up of three layers inside out.

A. The interior layer is called 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 referred to as the cladding. It provides 1% lower refractive index than the core material. This difference plays an essential part altogether 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 it 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 really not practical to produce it in a single step. Three steps are essential as we explain below.

1. Preparing the fiber preform

Standard optical fibers are made by first constructing a sizable-diameter preform, with a carefully controlled refractive index profile. Only several countries including US have the capacity to make large volume, good quality FTTH Cable Production Line preforms.

The process to make glass preform is called 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 is then injected into the hollow tube.

As the lathe turns, a hydrogen burner torch is moved up and down the outside of the tube. The gases are heated up by the torch as much as 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 create glass.

The hydrogen burner will be traversed up and down the length of the tube to deposit the material evenly. Right after the torch has reached the final in the tube, this will make it brought back to the beginning of the tube and the deposited particles are then melted to create a solid layer. This procedure is repeated until a sufficient amount of material continues to be deposited.

2. Drawing fibers over a drawing tower.

The preform will then be mounted to the top of any vertical fiber drawing tower. The preforms is first lowered in to 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 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 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 a single 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.

Mechanical Properties:

A. Tensile strength: Fiber must withstand 100,000 (lb/square inch) tension

B. Fiber geometry: Checks Fiber Drawing Machine core, cladding and coating sizes

Optical Properties:

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 a lot more critical in high-speed fiber optic telecommunication applications.

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