How to Reduce Optical Power Losses in Optical Fiber?

In the realm of contemporary communication, optical fiber assumes a pivotal role. However, the ensuing challenge of addressing optical power loss in fiber optic transmission remains a pressing concern. These fiber losses combination impacts network transmission efficiency while greatly escalating network management costs.This article offers a comprehensive exploration of diverse fiber optic losses and proffers pragmatic remedies to ensure a seamless and efficient network transmission solution.

What is Power Loss in Optical Fiber?

Fiber optic power loss refers to the attenuation or reduction of signal strength of the optical signal transmission, measured in dB/km, which means the signal fiber loss per km of fiber optic link. As a result of resistance, scattering, absorption, and other factors encountered by the optical signal during transmission, fiber optic power loss may lead to degradation of signal quality, limit transmission distance, increase signal noise and interference, and affect the performance and reliability of the communication system. Therefore, fiber power loss is one of the key factors to measure the quality of fiber optic communication.

 Introduction to Common Attenuation in Optical Fiber

Absorption loss  in Optical Fiber

Absorption loss denotes the phenomenon wherein physical materials hinder the transmission of optical signals (electromagnetic waves) by absorbing a portion of the optical power. Within optical fibers, the principal constituent is quartz, which exhibits electronic resonance absorption within the 8 ~ 12 μm infrared range, resulting in power absorption. Additionally, certain materials possess inherent absorption bands in the ultraviolet spectrum,  thus extending into the 0.7 ~ 1.1 μm wavelength range. 

 

Impurity absorption depletion refers to the impact of detrimental impurities, primarily transition metals (e.g., iron, cobalt, nickel, copper, manganese, chromium), as well as hydroxyl groups (OH), on the absorption of light within optical fibers, leading to subsequent depletion.

Bending Losses  in Optical Fiber

Optical fiber bending loss occurs when an optical fiber cable is bent or flexed beyond a specific threshold, leading to a reduction in signal strength. This phenomenon stem from the interaction between the optical signal and the fiber's core and cladding structure. During light transmission in an optical fiber, excessive bending can cause the optical signal to escape the core and be absorbed by the cladding or surrounding materials.

 

The impact of fiber bending loss is more pronounced in fibers with smaller core diameters and higher refractive index disparities between the core and cladding. Additionally, the wavelength of the transmitted light contributes to bending loss susceptibility, with certain wavelengths being more affected than others.

Scattering Losses in Optical Fiber

Scattering loss arises from small variations in the density of the fiber material and uneven distribution of the refractive index within the fiber due to different concentrations of components such as silica, GeO2 and P2O5. These refractive index differences cause localized irregularities that result in light scattering. As a result, some of the optical power is scattered outside the fiber, and the power loss due to this inherent scattering is known as Rayleigh scattering loss. 

 

On the other hand, we are familiar with the waveguide scattering loss, in the optical fiber manufacturing process, due to process, technical problems and some random factors, may cause structural defects in the optical fiber, such as incomplete core and cladding interface of the fiber, core diameter changes, uneven roundness, residual bubbles and cracks in the fiber and so on. The size of these structural imperfections is much larger than the wavelength of the light wave, causing wavelength-independent scattering loss.

Insertion Loss in Optical Fiber

Insertion loss is the reduction in transmitted power within a transmission system upon the incorporation of a component or device. It is shown as the ratio between the power received at the load before the insertion of the component/device and the power received at the uniform load after the insertion. It covers a variety of factors including absorption, scattering and reflection losses due to the presence of connectors, splices or other optical components.The lower the insertion loss, the better, such as OM4 insertion loss of 0.3dB, while the OS2 fiber optical cable insertion loss of about 0.25dB.

 

Calculation Formula: IL = -10 * log10 (power output / power input)

Fiber Attenuation Coefficient

Tips on How to Calculate Transmission Losses in Optical Fiber

Accurately calculating fiber optic loss is an essential skill in optimizing optic fiber cable links. It's imperative to begin by grasping the fundamental calculation formulas.

Recognized formula: Total Link Loss = Cable Attenuation + Connector Loss + Opticle Loint Attenuation + Safety Margin

Below we demonstrate the calculation process with a practical example.

 

 

Wavelength: 1310nm   9μm

Cable Attenuation: 30Km x 0.4dB/Km=12dB

Connector Loss: 2 x 0.3dB=0.6dB

Opticle Splice Attenuation: 4x 0.01dB=0.04dB

Safety Margin: 3dB

Total Link Loss：10.5dB+1.2dB+0.4dB+3dB=15.64dB

 Impact of Fiber Optic Losses in Transmission Line

Transmission Losses Cause Signal Degradation

Fiber optic losses significantly influence the signal quality within optical communication systems directly. As optical signals traverse through fiber optic cables, they unavoidably interact with internal and external factors like scattering, absorption, and dispersion. Scattering scatters light in various directions, consequently diminishing the signal's strength. The process of absorption absorbs a portion of the light energy, ultimately leading to an overall signal attenuation. Additionally, dispersion causes distinct signal components to reach their destinations at disparate times, causing distortion and signal overlap.

 

In practical scenarios, these various forms of losses synergize, culminating in diminished signal coverage, reduced data transmission rates, and compromised data integrity.

Fiber Attenuation Exacerbate Distance Limitations

Similarly, signal attenuation over distance exacerbates the limitations on effective transmission. This has a particularly pronounced effect on long-distance communications. As the transmission distance increases, the sensitivity to external factors, such as signal noise and interference, increases, resulting in a degradation of signal quality and potentially introducing data errors, and therefore failing to ensure effective transmission over long distances.

Fiber Loss Bring Higher Network Cost

Increased signal loss means increased network costs. To offset the impact of fiber loss, network users have to strategically deploy signal amplification equipment and signal regeneration points at regular intervals. These additions not only increase the upfront investment in infrastructure, but also increase ongoing operational costs in terms of maintenance and energy consumption. As a result, the challenge of fiber optic loss places an economic burden on the establishment and maintenance of efficient and reliable communication networks.

How to Reduce Losses in Optical Fiber？

In the previous section, we learned about some of the negative effects of fiber optic attenuation on data transmission, so let's discuss what can be done to reduce or eliminate these attenuations?

 

High-Quality Fiber Selection: Start by using optical fibers with low attenuation coefficients. Single-mode fibers are typically preferred for long-distance communication due to their lower dispersion and attenuation properties compared to multi-mode fibers.

 

Optimized Fiber Design: Choose fibers with optimized design features, such as larger core diameters and reduced cladding thickness, to minimize scattering and absorption losses.

 

Effective Signal Amplification: Incorporate optical amplifiers, such as erbium-doped fiber amplifiers (EDFAs), along the fiber route. These amplifiers selectively amplify optical signals without introducing excessive noise, compensating for signal loss over longer distances.

 

Precise Splicing and Connectorization: Ensure high-quality splicing and connectivity to minimize signal losses at connection points. Properly aligned and well-maintained connectors reduce signal reflections and enhance signal integrity.

 

Optical Isolators: Use optical isolators to prevent back reflections that can degrade signal quality. These devices allow signals to flow in one direction while attenuating reflections.

 

Low-Loss Fiber Couplers and Splitters: Utilize low-loss fiber couplers and splitters to split or combine signals without significant loss. These components are crucial for efficient network architectures.

 

Mode Conditioning Patches: Employ mode conditioning patches in multi-mode fibers to improve the launch conditions of signals, minimizing modal dispersion and loss.

 

Proper Cable Routing: Ensure that optical cables are properly routed and protected from environmental factors like bending, crushing, and temperature fluctuations. Improper cable handling can cause microbending and macrobending losses.

 

Avoid Bending Losses: Minimize excessive bending of fiber cables, as tight bends can lead to bending losses. Use appropriate cable management techniques to maintain minimum bend radii.

 

Polarization-Maintaining Fibers: In applications sensitive to polarization, such as coherent communication systems, use polarization-maintaining fibers to preserve signal polarization and minimize polarization-dependent losses.

 

Regular Maintenance: Implement optical monitoring systems to continuously assess the health and performance of the optical network. Regularly inspect and clean connectors, splices, and other optical components to prevent dust and contaminants from causing additional losses.

At QT, we uphold strict production standards and processes for fiber optic cables, including OS2, OM3, OM4 fiber patch cable for option, which ensures our customers receive cost-effective products with minimal fiber optic loss. If you have any need, feel free to contact QSFPTEK's CCIE/HCIE engineers at [email protected].

Conclusion

Power Losses in optical fiber mainly include absorption loss, bending loss, and scattering loss. By understanding the origins of these three forms of loss, we can optimize connection components, establish usage norms, and implement effective management practices, thereby reducing optical loss. Moreover, a fundamental understanding of the link loss calculation formula is the key to optimizing our optical fiber transmission.