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. While these fiber optic devices are readily available, 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 are often overlooked when laying out fiber optic networks, mainly due to the lack of common sense of the engineers involved. Fiber loss is a term for signal loss that 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 into calculating fiber loss, as well as tips on how to reduce fiber loss in your 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 can contribute to loss. Fiber loss is caused by a series of intrinsic and extrinsic factors. Fiber loss or signal loss, also known as fiber attenuation, is caused by the intrinsic and extrinsic properties of single-mode and multimode fibers. These factors need to be addressed if one wants to know how to calculate fiber loss in a 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 arise from small variations in compositional fluctuations, material density, manufacturing imperfections, and structural inhomogeneities. Often, these changes can be observed on a microscopic level.
• Dispersion Loss : Sometimes, an optical signal can be distorted while traveling through an optical fiber, which causes dispersion loss. There are two types of dispersion loss: intra-modal and inter-modal. Intra-mode dispersion is mainly caused by the spread of pulses in single-mode fibers. This pulse spreading occurs due to a change in the propagation constant or refractive index along the length. In contrast, intermodal dispersion is pulse broadening that occurs due to propagation delays between modes in multimode fiber.
• Absorption Loss : These are considered to be one of the main causes of optical loss in fiber optic cables. Photons interact with different glass components, metal ions or electrons during the transport. Light is absorbed and transformed into other forms of energy during this interaction, such as heat, wavelength impurities, and molecular resonance.

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

• Insertion loss : also known as connector loss, is the loss of optical power that occurs when a device is inserted into an optical fiber or transmission line. Typically, factory-assembled single-mode connectors have losses in the 0.1-0.2dB range, while field-terminated connectors can have losses as high as 0.2-1.0dB. 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. There are three types of laser transmitters, low, medium and high, also known as short-range, medium-range and long-range transmitters. LED Emitters Available in standard and high power LED emitters. The correct choice of transmitter depends on the type of fiber used. When selecting these emitters, the light output 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 loss factors of 2.5 (@850nm) and 0.8 (@1300 nm) dB/km. In contrast, single-mode fiber has loss factors of 0.25 (@1550nm) and 0.35 (@1310nm) dB/km. Singlemode fiber is compatible with laser transmitters and is available in short and long reach types. Multimode fibers are often integrated with LED emitters because their transmission distance will not exceed 1 km due to lack of energy. High power LED transmitters are used with single mode fiber.
• Fiber Loss Factor : The loss factor is usually defined by the manufacturer in dB/km. The calculation of optical fiber loss coefficient can be simply calculated as loss coefficient × distance. This distance is the total length of the fiber optic cable, not just the distance of the network.
• Redundancy: This is a broad term that covers factors such as aging of receiver and transmitter components, fiber optic aging, twists and bends in fiber optic cables, scope for future equipment additions, splices added to repair cable breaks. Generally speaking, the fiber loss budget margin is kept between 3 and 10dB.
• Fiber splicing: Fusion splicing helps to join the two ends of the optical fiber. This is done to ensure that the light passing through the cable is as strong as a single fiber. Mechanical splices and fusible splices are two important types of splices used in fiber optic cable networks. Among them, the mechanical splicing uses a connector set at the end of the fiber, while in the fusion type, the fiber end is directly mated. The loss of a mechanical splice is generally considered to be in the range of 0.1-1.5 dB per connector, while in a fusion splice it is 0.1-0.5 dB per splice. Fusion splices are most preferred due to their low loss coefficient.
• Bending : A small portion of fiber loss is caused by bending. This bend can be caused by improper handling of the cable. There are two types of bending - macrobending and microbending. Macrobends are larger bends in the cable, while microbends are small 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) x 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. Although you have learned how to calculate fiber loss, remember that it is only an estimate. Actual values ​​may be higher or lower depending on different factors, so a balance needs to be maintained.

For example, if considering a 40km long singlemode link with 5 splices and 2 connector pairs at 1310nm, the calculation would be:

• 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 0.4 dB/km + 0.1dB/km x5 + 0.75dBx + 3.0dB

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

Tips for Reducing Fiber Loss in Networks

Sufficient headroom 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 of the receiver. The following changes can be made in fiber link design and installation to minimize fiber loss in the network.

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

Summarize

When designing and setting up fiber optic networks, it is important to account for fiber link loss. However, addressing this loss involves several considerations. This article discusses these considerations in detail along with 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, installing quality equipment and cabling is just as important.