Optical Fibre Technology

Introduction to fibre optic technology in networking

Optical fibre technology is a cornerstone of modern networking, offering high-speed and reliable data transmission over long distances. It uses light to transmit data instead of the electrical signals used in traditional copper cables. 

The best place to start about fibre optic cables is talk about their benefits

In networking, optical fibres offer several key benefits that make them almost essential for modern data transmission. 

High bandwidth

Optical fibre cables provide significantly higher bandwidth compared to traditional copper cables. This high bandwidth enables the transmission of large volumes of data at extremely fast speeds, making it ideal for networking applications where high data throughput is essential.

Long-distance transmission

Another significant benefit is that the optical fibre experiences minimal signal loss over long distances, allowing for data transmission over hundreds of kilometres without the need for signal amplification. This makes them well-suited for long-haul networking applications, such as underwater cables and backbone networks.

Low latency

Light travels through optical fibre cable at near the speed of light, resulting in low latency transmission. Low latency is critical for real-time applications such as online gaming, video conferencing, and financial trading, where even small delays can have significant consequences.

Security

Optical fibre cables are difficult to tap into without detection, providing a high level of security for sensitive data transmission. Unlike copper cables, which emit electromagnetic signals that can be intercepted, optical fibres transmit data using light signals that are not easily intercepted or monitored.

Immunity to Electromagnetic Interference (EMI)

Optical fibre cables are immune to electromagnetic interference, making them ideal for networking applications in environments with high levels of electromagnetic noise, such as industrial settings or areas near power lines.

Scalability

Optical fibre networks are highly scalable and can easily accommodate increasing bandwidth demands by adding more fibre or implementing advanced multiplexing techniques such as wavelength division multiplexing (WDM) or dense wavelength division multiplexing (DWDM).

Reliability

Optical fibre cables are less susceptible to environmental factors such as moisture, temperature fluctuations, and corrosion compared to copper cables. This results in higher reliability and uptime for networking infrastructure deployed in diverse environments.

Cost-Effectiveness

While the initial installation cost of optical fiber networks may be higher than copper-based networks, they offer lower long-term operational costs due to reduced maintenance requirements, higher reliability, and lower energy consumption.

Flexibility

Optical fibre cables can be easily routed and installed in various configurations, allowing for flexible network designs to meet specific requirements. They can also be deployed in challenging environments, such as underwater or underground installations.

Data transmission using fibre optic cables

Fibre optic cables are capable of transmitting light signals over long distances with minimal attenuation (signal loss). The exact distance light can travel through a fibre optic cable without significant degradation depends on several factors, including the type of fibre, the quality of the cable, the wavelength of the light, and the presence of any signal amplification or regeneration.

Single-mode fibre is designed for long-distance transmission and can carry light signals over distances of tens to hundreds of kilometres without the need for signal regeneration. The precise distance depends on factors such as the purity of the fibre, the wavelength of the light (commonly 1310 nm or 1550 nm), and the quality of the optical components used.

For example, it can transmit light up to 7,000 km (Berlin to Washington).

Multimode fibre is typically used for shorter-distance transmission within buildings or campuses. While it can support transmission distances of several kilometres, the maximum distance is generally limited compared to single-mode fibre due to modal dispersion (where different light modes travel at different speeds through the fibre, causing signal degradation over longer distances).

The quality of the fibre optic cable itself, as well as the installation method and environmental conditions, will impact transmission distances. Properly installed and maintained fibre optic cables can achieve longer transmission distances with minimal signal loss.

Interesting facts about fibre optic cables

The fibre optic core thickness of human hair (one fibre) has the capacity to carry out 37 million telephone calls or transfer the content of a city library 4000 km in 1 second. 

The highest speed so far is 255 terabits per second (250 000 000 000 bits per second) on a 7-core fibre. 

There are over 2 billion kilometres of fibre installed on the earth. They would reach from the earth to the sun 13 times 😀.

Fibres for telecoms

The wave theory of light

The wave theory of light, also known as the wave model of light, proposes that light is a wave that propagates through space in a periodic, oscillating pattern. The wavelength of light is a fundamental property of this wave, and it is defined as the distance between two consecutive points on the wave that are in phase with each other, meaning they have the same oscillation pattern.

In other words, the wavelength is the distance a wave travels in the time it takes to complete one full cycle of oscillation. This cycle is also known as a period. The wavelength is typically denoted by the symbol λ (lambda) and is measured in units of distance, such as meters or nanometres.

The wavelength of light is an important characteristic because it determines the colour of the light. Different wavelengths of light correspond to different colours, with shorter wavelengths appearing as violet or blue and longer wavelengths appearing as red or orange.

The wavelength (λ) and frequency (f) of light are related by the speed of light (c). This relationship is expressed by the following equation:

c = λf

Where:

* c is the speed of light (approximately 3 x 10^8 meters per second)

* λ is the wavelength of light (in meters)

* f is the frequency of light (in hertz, or Hz

This equation shows that the speed of light is equal to the product of the wavelength and frequency. In other words, if you know the wavelength of light, you can calculate its frequency, and vice versa.

Here's a key insight:

* As the wavelength of light decreases, its frequency increases.

* As the wavelength of light increases, its frequency decreases.

This means that light with shorter wavelengths (like violet or blue) has higher frequencies, while light with longer wavelengths (like red or orange) has lower frequencies.

This relationship is a fundamental aspect of wave theory, and it has important implications for our understanding of light and its behaviour.

The principal fiber wavelengths refer to the primary wavelengths of light that are commonly used in fiber optics for communication purposes. These wavelengths are typically in the infrared range and are crucial for transmitting data over long distances with minimal signal loss. Here are some of the principal fiber wavelengths used in fiber optics:

850 nm**: Often used for short-range multimode fibre optic communication.

1310 nm**: Commonly used for both single-mode and multimode fibre optic communication over medium distances.

1550 nm**: Frequently used for long-distance single-mode fibre optic communication due to its low attenuation characteristics.

1260 nm: Used in dense wavelength division multiplexing (DWDM) systems to increase the data-carrying capacity of optical fibres.

1490 nm: Another wavelength commonly used in DWDM systems for transmitting data alongside other wavelengths.

1625 nm: This wavelength is sometimes used in combination with other wavelengths in DWDM systems to maximise the capacity of fiber optic networks.

These wavelengths are key to the operation of fiber optic networks and play a vital role in enabling high-speed data transmission over long distances.

Total internal reflection

Total internal reflection of light is a phenomenon that occurs when a light ray traveling from a medium with a higher refractive index to a medium with a lower refractive index strikes the interface between the two mediums at an angle greater than the critical angle. Instead of refracting out of the medium, the light ray is reflected back into the higher refractive index medium.

Key points about the total internal reflection of light:

Critical Angle: The critical angle is the minimum angle of incidence at which total internal reflection can occur. It is determined by the refractive indices of the two mediums.  

Conditions for Total Internal Reflection:

  - Light must travel from a medium with a higher refractive index to a medium with a lower refractive index.

  - The angle of incidence must be greater than the critical angle.

Applications:

  - Fiber Optics: Total internal reflection is utilized in fiber optic cables to guide light signals along the fiber by ensuring that the light remains trapped within the core through multiple reflections.

  - Mirage Formation: Total internal reflection is responsible for the formation of mirages, especially in hot environments where there is a gradient in air density near the ground.

Total internal reflection is a fundamental principle in optics and plays a crucial role in various technologies that rely on the controlled transmission of light.

Making fibre cable 

The fibre has a central core region with a high refractive index, surrounded by a cladding region with a lower refractive index.These regions form a waveguide for light. Light travelling down the fibre is bound into the core by the core cladding interface.This is known as Total Internal Reflection

The finished primary coated fibre will be used in the manufacture of a variety of optical cables. The coating is essential for protection and gives the fibre flexibility. Without it, the fibre is easily broken. A secondary nylon coating of 900 microns in diameter may be added to give the fibre greater protection. Fibre coated in this way is used to make patchcords and internal cables. This fibre is called “tight buffered, secondary coated,” or “ruggedized fibre.”

Modes

It is easy to visualise modes by representing them as ray paths, as shown above. Each mode takes a slightly different path, and some take longer paths than others. The result of this is that a pulse of light carried on several modes will begin to spread as it travels down the fibre; this is known as Didispersion. . If dispersion is severe or the length of fibre is long enough, dispersion will lead to pulses merging together and the optical signal will be corrupted.

Number of Modes = 0.5 x (Core diameter X NA X )2

For a 62.5/125 multimode fibre at 850nm, this would give 1945 modes and at 1300nm, 831 modes

Graded Index multimode fibre slows light passing down the centre of the fibre relative to light passing to the outer part of the core. Single mode has a very small core, which restricts light to one mode only, which eliminates modal problems but means that it is very difficult to launch light into single mode fibre.

Summary

Optical fibre technology is a cornerstone of modern networking, offering high-speed and reliable data transmission over long distances. It uses light to transmit data instead of the electrical signals used in traditional copper cables. Optical fibre technology has revolutionised the way data is transmitted, providing faster speeds and more reliable connections than ever before. While producing fibre optic cables involves sophisticated technology and skilled workers, the challenges lie in maintaining high precision in each step of the process. However, with advanced machinery and quality control systems, it's possible to produce high-quality fibre optic cables at scale.

Fibre optic cables offer several significant benefits in networking, making them the preferred choice for modern infrastructure. Additionally, there are solid trends in fibre optic technology that are shaping the future of networking.