Components of Optical Fiber

Optical fibers are one of the most powerful tools in data transmission. They consist of three concentric elements: Core, Cladding and Coating.

The core of the optical fiber is a solid di-electric cylinder with radius a and refractive index n1. A material surrounding the core, called cladding, has a lower refractive index than the core. This causes total internal reflection to occur along the core-cladding boundary.

Core

Optical fiber consists of three major components: the core, cladding and coating. These components enable light to travel through the core, enabling data to be sent down the cable.

The core of an optical fiber is made from high-purity silica glass, so pure that the contaminant level is measured in parts per billion. This purity is important to ensure that the signal is carried without degrading it.

In the core, a difference in refractive index (the number of refractions required to break a wave into a series of discrete individual rays) between the core and the cladding material allows rays to be guided along the fiber by total internal reflection. Specifically, when a ray meets the boundary of the core-cladding interface at an angle greater than the critical angle for this interface (a line drawn at a normal distance from the boundary), it is completely reflected by the cladding.

This process of total internal reflection occurs continuously as the rays strike the core-cladding interface and travel along the length of the fiber, guiding them until they reach their final destination. As they pass through the cladding, a small portion of the energy in each ray is absorbed and quickly dissipated, while a larger fraction of the energy is converted into a wave of evanescent light.

There are several causes of loss in optical fiber: * Fabrication — Various manufacturing methods can cause minute bending of the fiber geometry, producing very slight losses due to stress from the bending forces on the core/cladding interface. This can lead to dB/km loss, and can be very significant for multi-mode fibers used in longer distance applications.

Fortunately, there are several ways to reduce these losses. One method is to add a low-index layer of glass to the cladding to guide or reflect lost light back into the core. This is known as an optical trench, and can be used with both multimode and single-mode fibers. Another way is to use bend-insensitive fibers, which are manufactured with a smaller core diameter. These are usually used in patchcords, small-diameter high-fiber count cables called micro cables and specialty cables.

Cladding

The cladding of an optical fiber is a thin layer extruded over the core. This cladding serves as a boundary for light waves and allows data to travel through the cable. The cladding is typically made from a material that has a lower index of refraction than the core.

Optical fiber is comprised of three concentric elements: the core, cladding and coating (Figure 1). The cladding is designed to absorb any moisture that can penetrate the core, and also provides cushioning for the optical fiber when it is bent or stretched.

There are different types of claddings, depending on the performance and environment requirements. Commonly used cladding materials include acrylate, carbon, silicon and polyimide.

Most claddings have a soft surface to provide cushioning for the optical fiber. This is important to prevent breakage during drawing and helps protect the cladding from scrapes, nicks and other damage.

Some claddings have a hard surface, such as a nitrided phosphate, to improve heat and abrasion resistance. These claddings are typically used in harsh environments, such as components of optical fiber avionics and aerospace, or for applications like mining and oil and gas drilling.

Total internal reflection, the principle that causes rays of light to bounce off the boundary between the core and cladding, is one of the most important properties of optical fiber. The angle at which a ray of light hits the core-cladding boundary is measured to define the “numerical aperture” or NA of the fiber.

Coating

The coating of an optical fiber is a plastic layer that protects the core and cladding within it. It helps to absorb shocks, help prevent excessive cable bends, and protects the core against crushing forces.

The outer coating may be colored to distinguish strands in bundled cables. It also helps protect glass optical fiber from environmental conditions that can affect its performance and long-term durability.

There are three main components of the coating on an optical fiber: a primary coating, an outer secondary coating, and a tight buffer coating. The primary coating acts as a shock absorber, minimizing attenuation due to microbending; the outer secondary coating is used as a barrier against mechanical damage and acts as a barrier for lateral force; and the tight buffer coating is used in applications that require higher crush or impact forces.

During the process of making an optical fiber, it is first shaped into a large diameter pre-form, then consolidated and drawn to form the strand. This process can be done using one of three chemical vapor deposition methods: inside vapor deposition, outside vapor deposition, and vapor axial deposition.

Each of these processes is designed to create a fiber with a specific refractive index profile and to ensure that the end product is smooth and without striations, cracks, or other defects. During this process, the silica is usually suspended in an ultra-clean and climate-controlled environment.

The total internal reflection of light that occurs at the interface of a fiber’s core and cladding determines how efficiently that light travels. This effect is called the acceptance cone of a fiber. The maximum range of angles between the core and cladding that a beam of light can penetrate without leaking out is known as the numerical aperture (NA). This is the most important factor in splicing and working with an optical fiber because it can reduce bit errors.

Boot

The boot of optical fiber protects the optical cable as it exits the connector, preventing breakage, kinks, and general strain on the cable. The boot also supports the connector as it plugs into equipment, reducing the chance of damage to the wires and the connector itself.

Optical cables have multiple components, but the boot is the most important. It acts as a support, allowing the cable to be twisted and rotated without damaging the fiber itself or degrading signal quality.

A guide boot is a one-piece body that defines an inner passageway and has a first end for receiving the fiber and a termination port through which the fiber extends. The boot may be angled in a desired manner, such as about 45 degrees or 90 degrees.

An angled section 10 of the body 15 defines the passageway and is used for guiding, bending, or twisting (if desired) the cable 90 before exiting the boot. The angled section 10 may be tapered to prevent the cable 90 from twisting or rotating too much before exiting the boot.

This type of angled boot is useful in situations where there aren’t enough spaces for a standard connector, such as in a panel of connectors. It allows for a smaller, less bulky connector, which can be easier to handle and more efficient in the data center.

AMS Technologies carries a wide variety of angled boots for various fiber cable sizes. These include a 3.0mm black OM2 ST boot with factory-cleaved 900um tight buffered fiber and a crimp and stress relief boot for O 3.0 mm tubing. These parts are available from stock and are compatible with our fiber optic connector kits that allow single mode (SM), multi mode (MM) or polarization maintaining (PM) fibers to connect.

Connector

The connector is the part of an optical fiber that plugs into a port or interface to connect one device to another. It components of optical fiber can be either male (containing one or more exposed pins) or female (containing holes in which the male connector can be inserted).

Connectors can be made from a variety of materials, including plastic, metal, glass and ceramic. A key component of the connector is the ferrule, which holds the optic fiber in place and helps ensure that it aligns during mating.

Ferrules are often made from hardened materials like stainless steel or tungsten carbide. They can also be molded from plastic or ceramic. The end of the ferrule is usually polished into a convex dome shape that makes it easier for fibers to make contact.

This process eliminates some of the reflection that can occur when using a flat ferrule. It also improves insertion repeatability by up to 0.2 dB.

When choosing a connector, consider the performance parameters and intermateability standards that apply to the type of fiber you want to use. This information will help you choose the best fiber connector for your needs.

FC, or fixed connection, connectors are a good choice for high-speed communication links. They use a ceramic ferrule and stainless steel screw mechanism for attachment, which provides an improved connection to the fiber that’s much more resistant to accidental removal.

LC, or Lucent Connectors, are small form factor fiber optic connectors with 1.25 mm diameter ferrules. They are ideal for data centers and high-density mounting cabinets where many connections must fit into a limited space.

These are some of the most popular connector types on the market, but there are several other options as well. They all offer different advantages and disadvantages, so it’s important to know what you need before deciding on a connector for your fiber optic cable assembly.