An optical fibre is a very thin strand of glass or plastic surrounded by several layers of protective coating. It is capable of transmitting light signals over long distances without significant attenuation (loss) or interference from outside sources. The light signals travel along the core of the fibre at speeds close to that of light itself, allowing for extremely high data rates.
Optical fibres are made up of three components: an inner core, a cladding layer and a protective coating. The inner core is where most of the light travels through; it is typically composed of either glass or plastic and has an extremely small diameter (less than 1/10th that of a human hair).
The cladding layer surrounds the core and reflects any stray light back into it so that none escapes outwards; this allows for efficient transmission over long distances without significant losses due to scattering or absorption by external objects.
Finally, there is a protective outer coating which protects against environmental factors such as temperature fluctuations and moisture buildup.
Impact Of Optical Fibers On the Telecommunications Industry
The history of optical fibre dates back to the mid-19th century when Daniel Colladon and Jacques Babinet first proposed that light could be guided through a curved stream of water.
In 1880, John Tyndall demonstrated that light could be directed through a flexible tube filled with water, which was an early precursor to modern fibre optics.
In 1954, Harold Hopkins and Narinder Kapany developed the concept of fibre optics as we know it today, where light is transmitted through cylindrical strands of glass or plastic. To achieve this, Hopkins used a high-power microscope to accurately measure the refractive index of different materials in order to find one that would best guide light along its length. By 1960, Kapany had developed the system further by using bundles of glass fibres as waveguides for transmitting light signals.
By 1970, optical fibres had become commercially viable, but their use was limited due to their high cost and fragility. In order to make them more reliable and cost-effective, scientists developed new techniques such as clad coatings and improved splicing techniques that allowed for stronger connections between fibres. The introduction of these innovations helped to reduce manufacturing costs and improve performance, making fibre optics increasingly popular in communication networks around the world.
In 1977, Corning Glass Works introduced low-loss silica glass fibre cables that were capable of carrying telephone conversations over long distances without significant signal loss or distortion. This marked an important milestone in optical fibre technology as it allowed telephone companies to replace copper wires with optical fibres for long distance calls. By 1979, commercial applications such as fibre optic cables were being laid across Europe and North America for almost all types of telecommunications services including television broadcasting and telephony services.
In 1983, Bell Laboratories developed single-mode optical fibre which could carry higher frequency signals over longer distances without any signal degradation or impairment due to dispersion effects. This innovation made it possible for communication operators to send digital data signals over long distances at much higher speeds than ever before possible with traditional copper wires or coaxial cables.
By 1987, fibre optic cables had become increasingly popular for use in large public networks such as cable TV systems and international telecommunications links between countries. The introduction of dense wavelength division multiplexing (DWDM) technology further increased the capacity of optical fibre systems by allowing multiple channels to be transmitted through a single strand simultaneously while still maintaining signal quality over long distances.
The late 1990s saw major advances in fibre optics technology with the development of multi-mode fibre networks that could support faster data rates over larger distances than previously achievable with single mode fibres. These networks allowed users access to faster internet speeds at lower costs than ever before possible with traditional copper wires or coaxial cables used in broadband access technologies such as cable modems or DSL lines.
Today, optical fibres are used in almost every industry imaginable from telecommunications companies providing phone service and internet access to medical professionals using them for medical imaging purposes like endoscopy procedures in hospitals around the world. Fibre optics has revolutionized global communications by providing us with lightning-fast transmission speeds across vast distances at low prices compared to traditional wiring solutions used in past decades.
How Optical Fibres Are Manufactured
The Quest for Purity
At the heart of every optical fibre lies the pursuit of purity. The manufacturing process begins with the careful selection of high-quality silica, the primary material used in optical fibres. Silica, also known as silicon dioxide (SiO2), is chosen for its exceptional optical properties and low signal loss. To ensure the highest level of purity, the raw silica undergoes a rigorous purification process. The journey starts with the removal of impurities through techniques such as acid leaching or chemical vapor deposition (CVD). These methods effectively eliminate contaminants, such as metallic and organic compounds, that could interfere with the transmission of light signals.
Next, the purified silica is transformed into a glassy form suitable for optical fibre production. The silica is typically melted and then solidified to create cylindrical rods known as boules. These boules act as the foundation for the subsequent manufacturing steps.
Throughout the purification and preparation processes, meticulous attention is paid to maintaining the highest level of purity. Even the slightest impurity can introduce signal loss or distortion, compromising the optical performance of the fibre. Manufacturers employ advanced analytical techniques, such as spectroscopy and microscopy, to verify the material’s quality and purity at each stage.
The quest for purity in optical fibre manufacturing is driven by the need to minimize signal attenuation and maximize transmission efficiency. By starting with the purest silica possible, manufacturers lay the groundwork for the exceptional performance and reliability that optical fibres offer in various applications, from telecommunications to medical imaging and beyond.
Making the Preform
Once the purified silica is ready, the intricate process of building the preform begins. The preform serves as the foundation for the optical fibre, determining its core structure and guiding the transmission of light signals. The construction of the preform involves the precise deposition of silica layers onto a carefully prepared rod. One commonly used method is vapor deposition, where the purified silica is heated in a furnace, causing it to vaporize. The vaporized silica then condenses onto the rod, layer by layer, gradually building up the preform.
Another technique utilized is the Modified Chemical Vapor Deposition (MCVD) process. In MCVD, a reaction between a silicon-containing gas and oxygen creates silica particles. These particles are deposited onto the rod’s surface, forming the desired structure. The deposition process is meticulously controlled to ensure uniformity and accuracy. Factors such as temperature, gas flow rates, and deposition time are carefully calibrated to achieve the desired dimensions and refractive index profile within the preform.
The refractive index profile determines how light propagates through the optical fibre, allowing for efficient transmission and minimal signal loss. Throughout the deposition process, manufacturers employ advanced techniques like plasma-enhanced chemical vapor deposition (PECVD) to enhance the quality and precision of the deposited layers. These techniques enable the fine-tuning of the preform’s properties, optimizing its performance for specific applications.
The artistry lies in striking a delicate balance between precision and control. Each layer deposition is a meticulous step, ensuring that the preform’s composition, refractive index, and geometrical parameters align with the desired optical characteristics. The craftsmanship involved in achieving a uniform and well-controlled preform is crucial for the subsequent stages of optical fibre production.
Drawing the Fibre
With the preform as the starting point, the process of transforming it into a slender fibre begins through a method called fibre drawing. This crucial step involves controlled heating and stretching, where the preform is gradually elongated, reducing its diameter to the desired size and creating the ultra-thin optical fibre.
The preform is loaded into a draw tower, a specialized machine designed for the fibre drawing process. The preform is heated at a specific temperature, typically above its softening point but below its melting point. As the preform softens, a fibre-sized molten region is formed.
Using precise tension and speed controls, the draw tower gradually pulls the molten region downwards. The softened material elongates, causing the fibre to become thinner and thinner as it is drawn through a series of precision dies. The dies play a crucial role in controlling the fibre’s diameter and maintaining its uniformity.
During the drawing process, the fibre’s characteristics, such as its core and cladding dimensions, are carefully monitored to ensure consistency and adherence to the desired specifications. Any irregularities or deviations could impact the fibre’s optical performance and transmission capabilities. Once the fibre has been drawn to the desired diameter, it is rapidly cooled to solidify the material and lock in its structure. The resulting optical fibre is a slender strand, typically only a fraction of a millimetre in diameter, yet capable of transmitting light signals over long distances with minimal loss.
The fibre drawing process requires precision and expertise, as even slight variations in temperature, tension, or speed can affect the fibre’s quality and performance. Manufacturers employ advanced monitoring systems to ensure precise control and real-time feedback, guaranteeing the production of high-quality fibers.
Applying Coatings
To enhance the durability and performance of the drawn fibre, a protective coating is applied to safeguard it from external influences and mechanical stress. This coating provides insulation, mechanical strength, and protection against moisture, chemicals, and other environmental factors.
The coating process involves carefully applying a thin layer of polymer material around the surface of the fibre. This polymer layer acts as a buffer, preventing physical damage and minimizing signal loss caused by microbending or macrobending. The coating also improves the fibre’s flexibility, allowing for easier handling and installation.
The most commonly used coating technique is called the “wet-on-dry” method. In this process, a liquid polymer solution is applied to the fibre surface, which then solidifies to form a protective layer. The thickness of the coating is precisely controlled to ensure uniformity and adherence to industry standards.
The polymer materials used for coating are selected for their mechanical properties, resistance to environmental factors, and compatibility with optical fibres.
Some common coating materials include acrylates, polyimides, and UV-curable materials. Each material offers specific benefits and characteristics, allowing manufacturers to tailor the coating properties to meet different application requirements. Once the coating is applied, the fibre goes through a curing process to solidify the polymer. Curing can involve exposure to ultraviolet (UV) light or thermal treatment, depending on the specific coating material used. This step ensures the coating’s integrity and creates a robust protective layer around the fibre.
After the curing process, the coated fibre undergoes rigorous testing and quality assurance procedures. This includes examining the coating’s thickness, adhesion, flexibility, and resistance to mechanical stress. Only fibres that meet strict quality standards proceed to the final stages of production. The addition of the protective coating enables the optical fibre to withstand the challenges of real-world applications. It ensures the longevity and reliability of the fibre, allowing it to deliver consistent and high-performance optical transmission over extended periods.
Testing
After the manufacturing process is complete, rigorous testing is conducted on each batch of optical fibres to verify their compliance with quality standards and ensure their optimal performance. These comprehensive tests play a crucial role in guaranteeing the reliability and functionality of the fibres before they are deployed in various applications.
One of the primary tests conducted is the measurement of transmission loss, also known as attenuation. This test assesses the amount of signal loss that occurs as light travels through the fibre. Manufacturers utilize sophisticated equipment to accurately measure the attenuation at different wavelengths, ensuring that the fibres meet the specified performance requirements.
In addition to transmission loss testing, manufacturers also inspect the fibres for any defects or irregularities along their length. This involves carefully examining the fibre strands for factors such as core and cladding uniformity, diameter consistency, and surface imperfections. Any deviations from the prescribed standards are meticulously recorded and addressed to maintain the quality and integrity of the fibres. To ensure adherence to industry standards, such as those set by the International Telecommunication Union (ITU), manufacturers validate that their optical fibres meet the recommended specifications. Compliance with ITU standards ensures compatibility and interoperability with the existing telecommunication infrastructure, enabling seamless integration into global communication networks.
Once all the required tests have been successfully completed and the fibres pass stringent quality checks, manufacturers can confidently ship their products for use in various industries. Optical fibres find applications in telecommunications systems, where they enable high-speed data transmission over long distances, as well as in medical imaging systems, where their exceptional clarity and reliability support accurate diagnoses and treatments.
The testing phase is a critical part of the manufacturing process, as it ensures that only fibres meeting the highest quality standards are delivered to customers. Through meticulous testing and compliance with industry regulations, manufacturers uphold their commitment to delivering reliable, high-performance optical fibres that empower advancements in communication and technology.
Fibre Optics at CERN
The large volume of data generated every day at CERN has requested the development of a very large optical fibre network. CERN counts with over 45’000 kilometres of installed optical fibres and more than 200’000 optical terminations. Thousands of laser light sources, each capable of transmitting data at a rate of up to 100 gigabits per second with 2/3 of the light speed (200’000 km/s) play a decisive role in real-time data transmission for many purposes: measurements of the beam and the machine status, transfer of the massive quantities of data produced by the experiments, synchronisation of the accelerators, etc.
The laser power used at the transmitter rarely exceeds 1 mW (less than a thousandth of the power of a normal light bulb) and optical connections must, therefore, have a high-quality standard to keep attenuation within acceptable limits. Over the last years, fibre optics have been used more and more at CERN also as sensor elements. They are currently used in accelerators and experiments to monitor radiation dose as well as humidity and temperature.
