How to calculate and reduce fiber losses in your network?

Fiber optic networks have become popular over the years. These networks use fiber optic equipment and offer advantages such as low electromagnetic noise, high data transfer rates, and enhanced security. Today, traditional copper networks are slowly being replaced by fiber optic networks in various industrial applications. Despite the easy availability of these fiber optic equipment, designing a network may not be easy. Several key factors must be addressed to ensure the overall integrity and performance of the network.

Fiber loss in the network is one of the factors that is often overlooked when laying fiber optic networks, which is mainly caused by the lack of common sense of the relevant engineers. Fiber loss is a term for signal loss, which affects the reliability of transmission. Therefore, it is very important to calculate the fiber loss and take appropriate measures. Next, we briefly share some insights on calculating fiber loss, as well as tips on how to reduce fiber loss in the network.

Important factors to consider when calculating fiber loss

Fiber optic system design is not an easy task, but a balancing act that should address all system factors that may cause losses. Fiber optic losses are caused by a range of intrinsic and extrinsic factors. Fiber optic loss or signal loss, also known as fiber optic attenuation, is caused by the intrinsic and extrinsic characteristics of single-mode and multimode optical fibers. These factors must be addressed if you want to know how to calculate fiber optic losses in your network.

Here are some factors to consider when calculating your fiber loss budget:

• Intrinsic attenuation loss: This term refers to three types of losses - absorption loss, scattering loss and dispersion loss.

• Scattering losses : They are caused by small variations in composition fluctuations, material density, manufacturing defects and structural inhomogeneities. Often, these variations can be observed at a microscopic level.
• Dispersion Loss : Sometimes, the optical signal may get distorted while transmitting through the optical fiber, which results in dispersion loss. There are two types of dispersion loss: intramodal and intermodal. Intramodal dispersion is mainly caused by the spreading of the pulse in a single-mode fiber. This pulse spreading occurs due to the variation in the propagation constant or refractive index along the length. In contrast, intermodal dispersion is the broadening of the pulse that occurs due to the propagation delay between the modes in a multimode fiber.
• Absorption losses : These are considered one of the main causes of light loss in fiber optic cables. Photons interact with different glass components, metal ions or electrons during transmission. Light is absorbed during this interaction and converted into other forms of energy such as heat, wavelength impurities and molecular resonances.

The intrinsic attenuation of 50/125 µm and 6.25/125 µm multimode fibers is 3.5 dB/km@850nm, and the intrinsic attenuation of 9 µm single-mode fibers is 0.4 dB/Km @1310nm and 0.3 dB/Km@1550nm.

• Insertion loss : Also known as connector loss, it is the loss of optical power that occurs when a device is inserted into a fiber or transmission line. Generally speaking, factory-assembled single-mode connectors have a loss in the 0.1-0.2 dB range, while field-terminated connectors may have a loss as high as 0.2-1.0 dB. Multimode connectors have a loss of 0.2-0.5 dB.
• Transmitters : Laser transmitters and LED transmitters are two important types of transmitters used in most fiber optic networks. Laser transmitters are available in low, medium, and high types, also known as short-range, medium-range, and long-range transmitters. LED transmitters are available in standard and high-power LED transmitters. The right choice of transmitter depends on the type of fiber used. When selecting these transmitters, the light output factor at the connector needs to be considered. For example, -5dB is the most common light output.
• Type of Fiber Used : Most networks use single-mode or multimode fiber or a combination of both. Most multimode fibers have a loss factor of 2.5 (@850nm) and 0.8 (@1300 nm) dB/km. In contrast, single-mode fibers have a loss factor of 0.25 (@1550nm) and 0.35 (@1310nm) dB/km. Single-mode fibers are compatible with laser transmitters and are available in short- and long-distance types. Multimode fibers are often integrated with LED transmitters because they do not travel more than 1 km due to lack of energy. High-power LED transmitters are used with single-mode fibers.
• Fiber loss factor : The loss factor is usually defined by the manufacturer in dB/km. The calculation of the fiber loss factor can be simply calculated as loss factor × distance. The distance is the total length of the optical cable, not just the distance of the network.
• Redundancy: This is a broad term that covers multiple factors, such as the aging of receiver and transmitter components, fiber aging, twists and bends in the cable, scope for future equipment additions, and splices added to repair cable breaks. Generally speaking, fiber loss budget margin is maintained between 3 and 10 dB.
• Fiber Splicing: Fusion splicing helps to connect the two ends of an optical fiber. This is done to ensure that the light passing through the cable is as strong as it would be if it were a single fiber. Mechanical splices and fusion splices are two important types of splices used in fiber optic cable networks. Among them, mechanical splices use a connector set at the ends of the optical fibers, while in the fusion type, the ends of the optical fibers are directly plugged. The loss of mechanical splices is generally considered to be in the range of 0.1-1.5 dB per connector, while in fusion splices, the loss per splice is 0.1-0.5dB. Fusion splices are most preferred due to their low loss factor.
• Bends : A small portion of fiber loss is caused by bends. This bend can be caused by improper cable handling. There are two types of bends – macrobends and microbends. Macrobends are larger bends in the cable, while microbends are smaller bends in the cable.

How to Calculate Fiber Loss

To calculate fiber loss, you need to know these formulas:

Total link loss = splice loss + cable attenuation + connector loss + safety redundancy splice loss (dB) = splice loss tolerance (dB) x number of splices Cable attenuation (dB) = maximum cable attenuation factor (dB/km) × length (km)
Connector loss (dB) = Connector loss tolerance (dB) x number of connector pairs

Total loss is the sum of several variables in a fiber segment. Now that you know how to calculate fiber loss, remember that it is only an estimate. The actual value may be higher or lower depending on different factors, so a balance needs to be maintained.

For example, if we consider a 40 km single mode link with 5 splices and 2 connector pairs at 1310nm, the calculations are:

• Cable attenuation (dB) = 40km x 0.4 dB/km
• Splice loss = 0.1dB/km x 5
• Connector loss = 0.75dB x2
• Safety margin = 3.0dB

Link loss: 40km x 0.4dB/km + 0.1dB/km x5 + 0.75dBx + 3.0dB

Calculations show that at least 21dB of power is required to be transmitted over a fiber link. Once the network is set up, the actual link loss needs to be measured and verified. This will help identify performance issues).

Tips for Reducing Fiber Losses in Your Network

Sufficient margin needs to be left to accommodate performance degradation over time. This consideration will help ensure that the power output of the light is within the sensitivity range of the receiver. Some of the following changes can be made in the fiber link design and installation to minimize fiber losses in the network.

• Make sure you use high-quality cables throughout your network. The cables must have similar characteristics.
• Try to use qualified connectors whenever possible. Always ensure that the insertion loss is less than 0.3dB and any additional loss is less than 0.2dB.
• Try to follow the environmental and splicing requirements when welding.
• Make sure to use clean connectors.
• Choose the best method when laying fiber optic cables.
• Make sure to use the entire disc for your configuration. A single disc can be up to 500m or more. This will help minimize the number of joints.
• It is necessary to install protection against environmental factors such as electrical, lightning, mechanical and corrosion.
• Try to use high quality for all components including cables, connectors, transmitters, media converters, switches. This will help ensure high performance and minimize fiber losses in the network.

Summarize

When designing and setting up a fiber optic network, it is important to account for fiber link loss. However, there are several considerations involved in addressing this loss. This article discusses these considerations in detail as well as how to calculate fiber loss and tips for minimizing fiber loss in your network. While these calculations will help take all necessary steps to prevent fiber loss in your network, it is equally important to install quality equipment and cabling.