Fiber optic cable types and selection guide – specifications, shapes, and length

When installing optical fiber lines or changing equipment connections, there are more and more situations where you have to choose your own "optical fiber cable." However, there are many types, such as "specifications" such as single mode and multimode, "shapes" such as SC and LC, and "lengths," and many people may be confused as to "which one should I choose?"

In this article, we will explain the key points for choosing a fiber optic cable in an easy-to-understand manner, even for beginners. Please use this as a reference for choosing the fiber optic cable that is best suited to your environment.

Different modes of fiber optic cables

Fiber optic cables are broadly divided into two types: "single mode" and "multimode" based on their characteristics.

Each mode has a different way of transmitting optical signals and is suitable for different applications, so it is important to select the correct mode depending on the intended use.

Single Mode

Single-mode fiber optic cables are designed so that optical signals propagate through only one path (mode). The biggest feature of this cable is that the diameter of the central part through which light passes, called the core, is very small.

Specifically, it is about 9 micrometers (μm), thinner than a human hair. Because the light path is limited to one, there is less signal dispersion, which reduces signal attenuation during long-distance transmission.

These characteristics make it suitable for long-distance communications spanning tens or hundreds of kilometers, and for applications requiring high-speed, large-capacity data transmission.

This is a good choice if you want to achieve stable, high-speed communications over very long distances, or if you want to build a high-quality communications environment in anticipation of a possible increase in communication volume in the future.

Multimode

Multimode fiber optic cable is designed to allow multiple paths (modes) of light to propagate simultaneously.

Compared to single mode, it has a thicker core diameter of about 50 or 62.5 micrometers (μm). Because the core is thick, the light can travel while being reflected at various angles, and there are multiple optical paths.

Due to these characteristics, it is relatively easy to connect to a light source, and the price of the cable itself tends to be cheaper than that of single-mode cables. However, there are also aspects in that the signal is more likely to degrade over long transmission distances due to the fact that it travels multiple optical paths, which can cause delays in the arrival time of the signal (modal dispersion).

Therefore, it is mainly used for data communication over relatively short distances. Specific examples include LAN wiring in office buildings, connections between devices in data centers, surveillance camera systems, etc. Its main use is communication over relatively short distances of about several hundred meters, and it is suitable for introducing optical fiber communication while keeping costs down.

Differences in the polished surfaces of connectors

When connecting fiber optic cables, a part called a connector is used.

The tip of this connector (the ferrule end face) is precisely polished to efficiently transmit optical signals. There are several types of connectors available because the way the polished surface is finished can significantly change the light reflection characteristics and affect communication quality.

The two most common surfaces are:

• UPC
• Services

UPC

UPC is a method of polishing the end face of an optical fiber connector so that it is spherical and perpendicular.

This polishing method allows the fibers to be physically attached to each other, which has the effect of reducing light reflection at the connection point. It is an improved version of PC polishing, and achieves even lower return loss (a value that indicates the lack of light reflection).

These connectors are generally identified by the color blue, and because they are relatively inexpensive, they are widely used in many optical communication systems.

Its main applications are in situations where extremely high return loss is not required, such as LAN wiring, general data communications, and telephone lines.

However, it is important to note that repeated insertion and removal can easily cause the polished surface to deteriorate, which may result in a deterioration of the reflective properties.

Services

APC is a method of polishing the end face of an optical fiber connector at an angle (usually 8 degrees).

This angled polished surface is its biggest feature, and is designed so that reflected light generated at the connection point does not return to the fiber core, but instead escapes toward the cladding (the layer that surrounds the core).

This allows for a much lower return loss compared to UPC polishing, minimizing the effects of reflections. These connectors are generally identified by the color green and tend to be more expensive than UPC connectors.

It is primarily used in the transmission of high-quality analog video signals (e.g. CATV) which are highly sensitive to the effects of reflection, long-distance and highly sensitive optical communication systems such as FTTH, and wavelength division multiplexing (WDM) systems.

It is recommended for systems where signal quality is the top priority or where you want to avoid noise and errors caused by reflections as much as possible, especially when handling analog signals.

Differences in the shapes of optical fiber cables

Fiber optic cables are divided into several types based on their appearance and internal structure. These differences in shape have a significant impact on the cable's strength, flexibility, ease of connection, and usage environment.

I will explain this in three parts:

• Connector shape
• Cable Construction
• Cable Type

Connector shape

The connectors that are attached to the end of fiber optic cables come in a variety of shapes to suit the ports (sockets) of the devices to which they are connected.

There are four main types of connectors:

• SC Connector
• LC Connector
• FC Connector
• ST Connector

SC connectors are widely used because they are square in shape and use a push-pull mechanism (push to lock, pull to release) that makes them easy to insert and remove. LC connectors are smaller than SC connectors and are often used in places where high-density wiring is required.

In addition, the FC connector is fixed with a metal screw structure, which makes it resistant to vibration and ensures a reliable connection, while the ST connector is round and uses a bayonet locking system (insert and turn to lock).

The most important thing to consider when choosing a connector is to check which connector shape is compatible with the device you want to connect. You should also consider the frequency of plugging and unplugging, the installation space, and the required reliability of the connection.

Cable Construction

The internal structure of optical fiber cables also varies depending on the usage environment and purpose.

First, depending on the number of optical fiber cores inside, cables are divided into "single-core cables" which contain only one core, and "multi-core cables" which contain multiple cores.

Multi-core cables include "tape core cables" which have multiple overlapping optical fiber ribbons, and "slotted cables" which have multiple optical fibers set into grooves called slots.

They are also divided into "indoor cables" and "outdoor cables" depending on where they are used. Indoor cables are designed to be relatively flexible and easy to handle. On the other hand, outdoor cables are designed to be waterproof, weatherproof, and have enhanced mechanical strength so that they can withstand rain, wind, ultraviolet rays, temperature changes, etc.

When choosing a cable construction, first determine how many optical fiber cores are needed, then consider whether the cable will be installed indoors or outdoors, and how strong and flexible it needs to be.

Cable Type

There are various types of fiber optic cables, each specialized for a different purpose and installation style.

For example, a "drop cable" is an outdoor cable used to pull optical fiber from a utility pole to a house, etc., and is available in self-supporting types and types that include a supporting wire called a messenger wire.

"Indoor cables" are cables suitable for wiring inside buildings; they often use flame-retardant materials and are generally thin and flexible.

A "patch cord" (or optical fiber cord) is a short fiber optic cable with connectors attached to both ends, used to connect devices together or within a distribution panel.

The key point when choosing the type of cable is to first clarify the purpose and where you will be laying it. If you are bringing it into your home, a drop cable is suitable, while if you are connecting equipment within an office, an indoor cable or patch cord is suitable.

It is also important to select the most suitable cable, taking into consideration standards such as the required strength, protective structure, and flame resistance.

Different lengths of fiber optic cables

When choosing a fiber optic cable, its length is a very important factor. If the cable is too short, it will not reach the device you want to connect, and if it is too long, you may have trouble disposing of the excess cable, and in some cases, the quality of communication may be affected.

Here we will explain the differences in the lengths of fiber optic cables.

Differences in length depending on cable type and transmission distance

The length of optical fiber cable is largely determined by whether it is single mode or multimode. Single mode has less optical attenuation and is suitable for long-distance transmission of tens of kilometers or more, and is mainly used in the backbone networks of telecommunications carriers.

On the other hand, multimode fiber is relatively inexpensive but has a short transmission distance, and is used for wiring within building LANs and data centers with distances of a few meters to a few hundred meters. Multimode fiber is further divided into standards such as OM1 to OM5, and is selected according to the transmission speed and distance.

How to choose the length of fiber optic cable

When choosing the length of optical fiber cable, it is important to first determine the minimum length needed, as well as to take into account future needs such as moving or relocating equipment.

Generally, a few meters of extra length is planned, but this is adjusted depending on the installation environment and future plans.

However, if you leave too much slack in the cable, it can make it difficult to manage, and bundling the cables can worsen heat dissipation, and in some cases, it can affect signal quality. It is important to know exactly how long you need and choose a cable that has the appropriate slack but is not too long.

Summary

When choosing a fiber optic cable, be sure to check the points we have explained so far. By keeping these points in mind, you will be able to choose the cable that is best suited to your environment.

If you are unsure of how to choose or have any questions about the specifications, the most reliable method is to contact the manufacturer of the device you are connecting to or the telecommunications company that provides your current line, rather than forcing yourself to make a decision. By choosing the right cable, you can create a comfortable optical communication environment.