Components of Optical Fiber
Optical fibers are circular dielectric wave-guides used to transport optical energy and information. Their cores are surrounded by a cladding that has a slightly lower refractive index than the core.
There are several types of fibers, based on their refractive index profile. These include step-index and graded-index fibers.
Core
The core of an optical fiber is a thin glass tube that sits at the center of the cable. It is responsible for transmitting light through the optical cable and providing the highest speed of transmission.
Optical fibers use the principle of total internal reflection, which means that rays of light are guided along the core. The core is then surrounded by a layer of glass with a lower refractive index, known as the cladding. The cladding is used to reflect the light back into the core, allowing the signal to travel to its destination.
There are several different types of cores and claddings, each with its own uses. Some fibers are suited for harsh environments such as those associated with avionics, aerospace, and space. Others are designed for oil and gas drilling.
Single-mode fiber has a core diameter of 8-10 micrometers, while multi-mode fiber has a larger core diameter. The number of modes that can be propagated through the fiber is based on the wavelength of the light and the core and cladding dimensions.
Step-index multi-mode fiber uses the difference in the core and cladding materials’ index of refraction at the boundary to guide light. Using this method, different modes in the core are propagated in curved paths with nearly equal travel times.
Graded-index multi-mode fiber uses variations in the composition of the core to compensate for the varying path lengths of the modes and thus reduces modal dispersion. This type of fiber offers hundreds of times more bandwidth than step-index multi-mode fiber – up to about 4 gigahertz/km.
The most important loss mechanism in modern optical fibers is scattering. This can be due to microscopic-scale variations in the index of refraction or irregularities in the core or cladding components of optical fiber materials. The most common type of scattering is Rayleigh scattering. Irregularities in the core or cladding diameter, or changes in the fiber’s axis direction also contribute to scattering.
Cladding
Cladding is a thin layer that surrounds the core and provides a lower refractive index to make the optical fiber work. This allows light to travel through the entire length of the fiber.
The cladding is typically made from glass or plastic, depending on the desired transmission spectrum. Occasionally, another material is used, such as silicon dioxide.
During transmission, light signals are reflected off the cladding in a series of zig-zag bounces, which is referred to as total internal reflection. This process helps to reduce the data transfer rate by about 30%.
In addition to the cladding, the optical fiber may also have a coating on the outer surface. This is designed to absorb shock, scrapes and moisture that can damage the cladding. It also gives extra protection against excessive cable bends.
Other components of the fiber include a ferrule and connector. These are designed to fit tightly around the core and provide additional protection against crushing forces during installation.
The cladding is usually 125 microns in diameter, but can be a different size to accommodate specific applications. The cladding may be a single flat sheet, or it can be part of a composite or built-up system.
Cladding is usually reinforced with Kevlar(r) or wire strands to help protect the core from excessive tension and crushing during installation. The cladding is also sometimes filled with gel-filled sleeves to absorb any excess air that might leak out of the fiber.
Optical fiber is one of the most powerful tools in data transmission today, due to its ability to transmit data at very high speeds and low attenuation rates. Its primary use is as a data transmission medium, but it also has many other uses. For example, it can be used for * Illumination – Using a bundle of fibers in conjunction with a light source to illuminate areas that are difficult to reach, such as inside the human body or an endoscope.
Coating
Optical fibers consist of a core, cladding and coating. The core is components of optical fiber the glass that contains the light source, and the cladding is the second layer of glass that surrounds the core to reflect the light back to its destination. The coating is applied to the cladding and helps protect the core from mechanical stress or abrasions.
Coatings can be a single layer, a double-layer, or a combination of two layers. They are applied to the cladding before being bonded to the glass, and they may be cured using UV lamps or heat.
The primary coating is typically a urethane acrylate or a polyimide-based material, which has a low refractive index and strips out any unwanted light that would otherwise escape through the cladding. It also has a high Young’s modulus, making it resistant to wear and tear in harsh environments.
In addition to protecting the core from mechanical stress, some coatings are used for thermal protection. This is especially important in the harsh environments where fibers are exposed to high temperatures for long periods of time.
Some of the coatings are a few angstroms thick, providing excellent durability and lifetime. They are commonly used in applications where the fiber will be exposed to high stress, or installed in a tight coil, and/or there will be exposure to high humidity.
The uv-curable acrylate family of resins is the dominant choice for coating glass fibers. The major vendors offer many variants for different draw-tower curing systems, environmental requirements and optical and mechanical performance properties. Increasingly, they are offering resins optimized for the use of UV LEDs to cure optical fibers. This offers fiber manufacturers promising benefits in terms of temperature control and energy savings.
Boot
Boot is a term used to describe the initialization of a computer, a process that loads an operating system (OS) onto the hard drive or other storage device and transfers control to it. This is usually performed by the BIOS and consists of a series of steps that include doing power-on self-tests, searching through all possible storage configurations until it finds the boot sector (or sectors), copying information from it to memory, and performing some core initialization tasks before transferring control to the OS.
The boot may be referred to as the initial program load (IPL) or the reboot, and is typically implemented on larger computers. The boot also includes a POST or pre-operating system test, which performs a power-on self-test to ensure that the computer is functioning properly and can be started.
Optical fibers, which work on the principle of total internal reflection of light, are able to transmit data at long distances without degradation of the quality of the signal. However, this is dependent on the fiber core size (i.e., 50/125 to 62.5/125).
To prevent excessive bending of the cable at the connector end during connection, reinforcing boots are commonly installed. These boots extend out from the connector to encase a length of the cable, and can be secured to the connector during connection.
In one embodiment of the invention, a guide boot 1 is provided for circumferentially twisting or bending (if desired) an optical fiber cable 90 before it exits the boot 1. This angle could be about 45 degrees, for example, though any angle can be used to accomplish this purpose.
The guide boot 1 is a one-piece assembly that includes an angled section 10 and a straight section 20 for receiving the cable 90 and terminating it. The angled section 10 is inserted through a cut-out window 14 that has been formed in the body 15 of the guide boot 1, and is twisted to an amount desired before securing the cable to the termination port 17.
Connector
Connectors are devices that connect fiber optic cable to the equipment that it will be used with. There are a number of different types of connectors available, depending on the type of fiber and the equipment that will be using it.
Optical fiber connectors have several important components that make them function effectively. These include a ferrule, sub-assembly body and a connection device.
The ferrule is the device that holds the end of the fiber, preventing damage from vibration or other mechanical forces. It is also designed to withstand high temperatures.
Another important component of an optical fiber connector is a stress relief boot. This allows the connector to be mounted in a tight space and still maintain its strength.
Strain relief protects the connection from damage by providing a non-conductive layer to transfer forces away from the fragile electrical connections between the wires. In addition, this can help protect the optical cable from breaking if the connector is knocked over or dropped.
Besides these features, connectors must be able to resist insertion and removal cycles from circuit boards. This is especially critical for industrial applications.
The connector must also be able to withstand electromagnetic interference from nearby equipment. This can be a major problem with wire cables, as it can disrupt the transmission of data. However, this is not a concern with fiber cables as they have little or no signal loss caused by the inter-symbol interference (ISI).
